Introduction :
Efficacy and quality of extrarenal replacement therapy by hemodialysis condition the survival of patients with chronic renal failure at the end stage. The term “hemodialysis” describes the set of extrarenal treatment methods (ERA) with extracorporeal blood circulation connecting the “internal environment” of the patient and the “external environment” with an electrolyte exchange solution produced by a generator of dialysate. This method effectively corrects the metabolic abnormalities of uremia and periodically restores the homeostasis of the chronic renal failure patient. The intermittent nature of locum therapy, however, provides only partial and periodic correction of these disorders and causes cyclic changes in the internal environment of the uremic tract. This is why the term “adequate”, which characterizes the effectiveness of hemodialysis, must always be considered relative.
The adequacy of hemodialysis is based on a series of sometimes delicate assessment objectives. The dialysis program must be able to meet the patient’s vital metabolic needs while ensuring a good quality of life and preventing the occurrence of complications. The treatment is based on periodic cleansing sessions (usually three per week), the overall effectiveness of which increases with time. Optimizing the program requires personalized treatment regimens and permanent quality control.
In all cases, the adequacy of dialysis involves a quantitative concept that reflects the solute mass transfers achieved during dialysis sessions. and a qualitative notion that includes clinical tolerance, quality of life and prevention of any specific morbidity. The complexity of the metabolic disorders of uremia is such that it does not allow the use of a single and universal marker to judge the effectiveness of the locum program.
This is why nephrologists established a series of therapeutic goals in the 1970s that brought together the vital needs of dialysis patients. These therapeutic targets serve as a framework for “adequate dialysis” and represent “quality” indicators in dialysis patients. The use of these criteria has allowed the development of contemporary dialysis and has ensured the survival of thousands of patients with chronic renal failure. The complications of “long-term” dialysis, reported over the last two decades, are there nevertheless to remind us of the limits of effectiveness of the methods of substitution. The occurrence of this specific pathology of dialysis suggests that adequate initial dialysis criteria are no longer sufficient. Although the initial criteria remain necessary for the survival of dialysis patients, they are no longer sufficient to confirm the optimal nature of renal replacement therapy.
Prescribing a hemodialysis program therefore requires a perfect knowledge of the performance of the extrarenal treatment system and the metabolic characteristics of the treated patient. The choice of the therapeutic modality depends on:
• individual characteristics (comorbidity, vascular access, lifestyle, psychological impact, degree of autonomy) or family environment;
• habits and know-how of the health care team;
• local logistical and technical constraints (development of therapeutic structures, reception capacity, distance).
The prescription of a dialysis session is part of a global strategic perspective and should not remain an isolated therapeutic act. From a general point of view, the prescription of a dialysis program has two stages:
• a first step, which consists in making an empirical prescription based on the anthropometric and metabolic characteristics of the patient;
• a second step, which consists of adjusting the program according to the clinical and biological results and whether or not the “targets” are set.
Objectives of renal replacement therapy by dialysis:
The prescription of the dialysis therapeutic program must meet a series of objectives: 1) to guarantee the effectiveness of the locum program by administering the appropriate “dialysis dose”; 2) prevent poor clinical tolerance of dialysis sessions; 3) correct biological abnormalities; 4) prevent the complications of long-term dialysis.
Administer the correct “dialysis dose”:
The concept of “dialysis dose” was introduced in the 1980s by F. Gotch to quantify the effectiveness of the session and the dialysis program. It is based on modeled kinetic analysis of urea during a dialysis cycle.
Although objectionable, this approach had the merit of demonstrating that the morbidity and mortality of hemodialysis patients depended on the “dialysis dose” administered. The US National Cooperative Dialysis Study (NCDS) was the first prospective randomized study showing that “dialysis dose” conditioned the degree of nitrogen retention and protein catabolism and influenced the morbidity and mortality of dialysis patients. Many subsequent studies have confirmed that the morbidity and mortality of dialysis patients is inversely correlated with the “dialysis dose,” suggesting that urea could be considered a “substitute” for uremic toxins. Note however that in all these studies, the impact of the “dialysis dose” on the morbidity and mortality of patients has always appeared much more deleterious in its low values than in its high values. The limits of this approach have recently been demonstrated by the HEMO-Study study which showed that beyond a minimum threshold value, the increase in the “dialysis dose” did not bring any significant reduction. of morbidity and mortality in dialysis patients. Despite these limitations, urea remains an interesting, simple, universal, inexpensive marker that verifies the effectiveness of dialysis sessions and assesses the protein intake of patients. International Good Clinical Practice Guidelines recommend regular use of this indicator as part of a quality control of the effectiveness of the dialysis program. Various efficacy indices derived from urea have been developed as part of the follow-up of dialysis patients. They are reported in the box below.
The oldest and simplest is represented by the percentage reduction of blood urea (PRU) per dialysis session. This index reflects the percentage of urea mass subtracted from the patient during a session. It includes error factors (volume variation, compartmentalization, postdialytic rebound) and should no longer be used without corrective factors as an indicator of efficacy. Standardized body clearance, also known as fractional clearance, more commonly referred to as Kt / Vurea, remains the most relevant efficacy indicator and is recommended by the best practice guidelines for hemodialysis. The Kt / V index represents the product of the total body clearance of urea (product of the instantaneous clearance of the dialyzer [K] by the duration of the session [t]) relative to the total volume of water of the patient (V ).His calculation uses simple parameters, blood urea concentrations in pre- and postdialysis, duration of the session, dry weight and weight loss of the patient. The precision of the result imposes a rigorous methodology for the end-of-session blood sampling and the use of calculation formulas taking into account the postdialytic rebound. Daugirdas’ second-generation formula is currently the reference for good practice guides. Note that it is now possible to obtain, on some dialysis monitor generators, a direct online measurement of the clearance (or dialysis) of urea (or a substitute) and to deduce from it the Kt / V index. These measurements are made from the effluent dialysate (or ultrafiltrate): in one case, the direct determination of urea makes it possible to calculate its clearance; in the other case, the dialysate conductivity variation allows a calculation of the ionic dialysance (substitute of the clearance of the urea).
At present, this concept of “dialysis dose” tends to be broadened and applied to all solutes that are exchanged during a dialysis session. The calculation of the mass transfer of these different solutes thus offers a quantifiable approach to the efficiency of the session. This approach also makes it possible to affirm the good adequacy of the efficiency of the dialysis with respect to the needs of the patient. Subtraction of high molecular weight uremic toxins is becoming increasingly necessary in the context of effective dialysis of the future.
This is why it is essential that the notion of “molecular spectrum” of purified toxins be associated with that of “dialysis dose”. So that to the old quantitative concept, based exclusively on the purification of solutes of low molecular weight, must be associated that qualitative, privileging the purification of substances of high molecular weight. Within uremic toxins, b -2-microglobulin refers to:
• it has a high molecular weight (11.8 kDa);
• it is produced continuously by the body; it accumulates gradually in chronic renal failure;
• it is a major component of amylose- b -2-microglobulin in elderly dialysis patients;
• it is a biological marker and an indicator of morbidity and mortality in dialysis patients.
The subtraction of b -2-microglobulin thus appears highly desirable in long-term dialysis patients. The current challenge is to answer a number of questions: what optimal level of circulating b -2-microglobulin should be targeted?Which mass of b -2-microglobulin should be subtracted per session? What are the factors that affect the level of b -2-microglobulin outside the purification?
Maintain a satisfactory nutritional status:
Maintaining a satisfactory nutritional status should remain an essential goal for dialysis patients. Caloricoprotidic undernutrition is a major morbidity and mortality factor in uremic patients. This undernutrition occurs early in the course of renal failure and only partially improves in dialysis patients. Prevalence studies among dialysis patients consistently indicate that nearly one-third of patients show signs of relatively severe caloricoprotid malnutrition. Nutritional management is therefore essential in this population, especially in older patients who are more exposed to these disorders.
It includes a monitoring of food intake (dietary surveys and counseling), a global subjective assessment (ESG) and anthropometric assessment of nutritional status (clinical or lean / fat mass) and regular monitoring of nutritional parameters (albumin, prealbumin, cholesterol total, creatinine production rate).
Correct excess extracellular volume and control blood pressure:
The correction of sodium overload and the control of blood pressure are two essential objectives in the hemodialysis patient. This is a major cardiovascular protective factor in uremic disease. Sodium depletion is obtained by ultrafiltration and reduction of the sodium content of the dialysate.
This water-soluble depletion responds to an empirically established goal set by the clinician and established around the “dry weight”. Personalized dietary management and the restriction of sodium intake are likely to facilitate this goal.The tension control will be all the more easily obtained that the sodium depletion will be regularly obtained.
Prevent hemodynamic and clinical maltolerance of dialysis sessions:
The hemodynamic tolerance of the sessions is conditioned by two major factors: the instantaneous ultrafiltration rate and the hemodynamic adaptation of the patient to volume depletion.
Ultrafiltration represents the net loss of weight (expressed in kilograms or liters per session) imposed on the patient to reduce it to “dry weight” and restore the equilibrium of its extracellular volume. The instantaneous ultrafiltration rate (in ml / min) represents the ratio of weight loss over session duration. The volume of ultrafiltration required per session is closely related to the dietary compliance of the subject and its residual diuresis.
The hemodynamic response to volume depletion is an individual characteristic. It involves several elements:
• vascular filling rate;
• increased peripheral vascular resistance and venous tone;
• the increase in the cardiac ejection fraction.
In all cases, longer session times reduce the flow of ultrafiltration and significantly improve session tolerance. Similarly, an increased frequency of sessions (daily sessions for example) considerably reduces the interdialytic weightings and bleeding rate of ultrafiltration. Other options in the prescription of hemodialysis are proposed to improve tolerance:
• generalization of the bicarbonate buffer;
• use of custom ultrafiltration and conductivity profiles;
• dialysate temperature reduction (36 ° C) or isoneutral thermal balance;
• use of high permeability synthetic membranes;
• high convective methods (haemofiltration [HF] and haemodiafiltration [HDF]). The correction of anemia by erythropoiesis stimulating agent also appeared to be an essential factor in improving session tolerance.
Correct electrolyte and phosphocalcic abnormalities:
The electrolyte abnormalities are constant in the hemodialysis patient at the beginning of the session. They usually associate with hyponatremia, hyperkalemia, and metabolic acidosis.
The magnitude of these abnormalities depends on the food intake and residual renal function of the subject. This helps to remind the importance of dietary advice and compliance. Hyponatremia (hypo-osmolality) is a faithful reflection of fluid intake and the state of cellular hyperhydration. Hyperkalaemia is a reflection of the intake of fruits, vegetables and other foods particularly rich in potassium (chocolate, dried fruits, etc.). Metabolic acidosis is a reflection of proton production and dietary protein intake.
These abnormalities are corrected by hemodialysis and their level of equilibrium depends on the electrolytic composition of the dialysate.
Phosphocalcic disturbances and bone metabolism are also constant in the hemodialysis patient. They associate hyperphosphoremia, hypocalcemia and hypomagnesemia. These disorders vary according to the dietary regime (phosphorus intake depending on the intake of animal protein), the effectiveness of the dialysis program, the residual renal function and also the bone metabolism (bone remodeling intensity). These disturbances are partly corrected by the hemodialysis which ensures at each session a phosphate subtraction and a calcium and magnesium load. They are also dependent on diet and oral treatment to reduce the digestive absorption of phosphate (digestive fixatives) and to increase the intake of calcium and vitamin D.
Prevent the complications of long-term dialysis:
At present, the concept of effective dialysis can no longer be reduced to a correction of the main biological abnormalities of uremia.
The long-term complications of the dialysis patient (accelerated atherosclerosis, vascular and cardiac calcifications, amylose-2-microglobulin, accelerated aging, undernutrition, osteodystrophy, hepatitis, neuropathy, heart failure …) must be prevented. This requires a more effective, more physiological and more hemocompatible dialysis program which is described later in this chapter.
Prescription of the dialysis program:
Choice of extracorporeal treatment modality:
The choice of extrarenal treatment is based on a medical prescription in which several decision elements intervene: the clinical state of the patient, the age, the comorbidity, the performances of the purification system, the tolerance of the sessions, the availability of the various ERA modalities and the convictions of the nephrologist.
Hemodialysis remains the classic EER modality and is used in approximately 90% of cases. It is indicated initially in any endemic uremic patient. The optimal use of high-performance hemodialysers makes it possible to obtain, in the usual way, effective dialysis in the short term. The choice of the dialyzer remains an important decision of the nephrologist in the prevention of long-term complications. It is to meet these needs that alternatives to conventional hemodialysis have been proposed: high permeability hemodialysis,
high efficiency hemodialysis, high efficiency haemofiltration, high efficiency haemodiafiltration.
Hemodialysis with a high permeability dialyzer can be performed on any generator equipped with an ultrafiltration master.
However, it requires the use of ultrapure bicarbonate dialysate.
Hemofiltration (pre- or post-dilution) uses membranes of high permeability and involves purely convective exchanges.Post-dilution HF is the most effective modality whose clinical interest is reduced due to limited filtration rates and prolonged duration of sessions. The HF remains current in its predilutionnel mode which allows large volumes of exchanges (70-100 l per session) with short treatment times. HF is only viable with “on-line” production of the replacement fluid.
Hemodiafiltration currently offers the best cost-effectiveness-tolerance compromise among extra-renal replacement methods. The simultaneous combination of diffusive and convective transfers provides HDF with high clearances for all solutes, including average molecular weights. Hemodynamic tolerance is good, including in elderly patients or at high cardiovascular risk. The “on-line” production of the substitute liquid guarantees the economic viability of the method. Different forms of HDF exist: postdilutional, predilutional, mixed, midilutional.
The choice of one or the other of these modalities must be established on the basis of the sought performances and the hemorheological problems met.
Choice of duration of sessions and frequency of dialysis sessions:
Duration and frequency of dialysis sessions are two major components of renal replacement therapy. These two elements ensure the efficacy and the tolerance of the treatment. Time has a vital role in the purification capabilities of the system. On the one hand, it conditions the clearance of uremic toxins and the subtracted solute mass. The “dialysis dose” is proportional to the duration of the session regardless of the molecular weight of the solute. This notion also applies to the dialysance of solutes and electrolytes provided by the dialysate. On the other hand, it conditions the body clearance of solutes. The concentration of toxins present in the circulating bloodstream accessible to extracorporeal purification is conditioned by their rate of internal diffusion. The extracorporeal clearance of a solute is indeed limited by its intracorporeal clearance (internal mass transfer coefficient or resistance coefficient). The rate of internal diffusion is itself conditioned by other factors: distribution space, protein and tissue affinity, concentration gradients as a function of regional circulation rates (high-flow surface compartment or low-flow deep compartment).Let’s compare, by way of example, the per- and postdialytic kinetics of two uremic toxins: one of low molecular weight, urea (60 Da); the other of high molecular weight, b -2-microglobulin (11.8 kDA). Intracorporeal clearance of urea is close to 800 ml / min and that of b- microglobulin 80 ml / min.
The intracorporeal clearance of urea is very much higher than that of the dialyser clearance. In theory, this suggests that body scrubbing of urea must be performed without limitations. In practice, the internal body diffusion of urea does not occur homogeneously during the dialysis session, which leads to the formation of a concentration gradient between the superficial and deep compartments (apparent sequestration) and leads to a rebalancing brutal after dialysis in the form of a postdialytic rebound (20 to 30%).
The mass of urea subtracted during the session remains nevertheless very important and little amputated by this sequestration.
The problem is totally different with b -2-microglobulin and phosphates. The kinetics of b -2-microglobulin are complex and the methods are capable of substantially eliminating them (HD high permeability or haemodiafiltration). During the dialysis session, the rapid disappearance of b -2-microglobulin in the accessible area is not compensated for by internal diffusion, and significantly reduces the extracorporeal mass transfer of b -2-microglobulin. At the end of the session, the rebalancing of the compartments results in a very important postdialytic rebound. Inorganic phosphates have a kinetics close to b -2-microglobulin while their molecular weight is about 300 times lower. This reflects the strong resistance to the internal transfer of phosphates due to their cellular and mitochondrial localization and specific characteristics conferring them a strong hydrophilicity and strong electronegativity.
These facts underline the major role of the time and the frequency of the sessions on the transfers of solutes with strong internal resistance. The lengthening of the duration of the sessions and the increased frequency of the sessions significantly increase the mass transfers, all the more as the solute has a high molecular weight and has a weak internal diffusion.
The lengthening of the duration of the sessions also has a very beneficial role on the tolerance of the sessions. This lengthening of the sessions reduces the instantaneous ultrafiltration rate and facilitates volume filling and hemodynamic adaptation. It also helps to preserve blood volume, by facilitating vascular filling by effective liquid recruitment of the deep sector.
The weekly frequency of sessions is also a very important element in the prescription of a treatment regimen. The intermittent nature of the sessions, which is based on three sessions per week, creates a cycle alternating solute concentrations, sometimes high (“peaks”) and sometimes low (“valleys”). This type of conventional three-week program is in contrast to physiological dialysis goals aimed at stabilizing the indoor environment. The current prescription tends to increase the number of weekly sessions. The first approach is to practice alternate day sessions (four sessions per week). The second approach is to perform daily sessions (five to seven sessions per week). This type of treatment scheme poses logistical problems in dialysis centers forced to treat four to six patients per shift. On the other hand, these schemes fit perfectly well to patients treated in autodialysis or home-type structures, with an individual dialysis generator. All of the reported work on increased frequency hemodialysis supports the idea that this is the future path needed to improve the effectiveness and increase the tolerance of dialysis programs.
Different treatment regimens can be proposed by combining the duration and frequency of EER sessions. The minimum conventional scheme recommended by the European Guide to Good Practice (EBPG) is based on three 4-hour sessions, ie 12 hours per week. Different treatment regimens are currently proposed, they all aim to increase the duration (5 to 8 hours) or the frequency (4 to 6 per week). Short (3 hours) or ultra-short (2 hours) tri-weekly regimens should be reserved for special cases of patients with significant residual renal function ( ≥ 5 ml / min) or very low body weight with reduced metabolic requirements.
Choice of the hemodialyzer:
The hemodialyzer is the exchange interface between the patient’s internal environment and the dialysate’s external environment. Its role is twofold: on the one hand, it conditions the exchanges of solutes, it is a bio-exchanger; on the other hand, it puts the patient’s blood in contact with the dialysate, it is a bioreactor.
The choice of a dialyzer is based on different considerations:
• performance (permeability to solutes);
• hemocompatibility (hemoreactivity);
• hemorrheological (design of dialyzer and membrane);
• economic (price of the module).
The choice of a dialyzer must take into account several elements: the nature, the permeability and the surface of the membrane, the geometry of the dialyzer, the mode of sterilization, the specific conditions of use. In recent years, hollow fiber dialysers have emerged as reference dialyzers. The geometry of capillary dialyzers gives them optimal performance for maximum compactness.
Depending on their chemical nature, there are three types of membranes: cellulosic membranes, substituted cellulosic membranes and synthetic membranes. Each membrane is characterized by specific permeability and hemoreactivity.
The permeability makes it possible to distinguish dialyzers from:
• low permeability (low flux [LF]);
• medium permeability (MF);
• high permeability (high flux [HF]);
• very high permeability (super flux [SHF]).
Note that permeability is determined by hydraulic permeability (Kuf), solute permeability (KoA or sieving coefficient) and albumin loss. The performance of the dialyser (solute clearance) is also affected by the effective exchange surface and the thickness of the fiber membrane. The surface of the dialyzers distinguishes small (<1.0 m 2 ), intermediate ( ≥1.0 and <1.5 m 2 ) and large surface ( ≥ 1.5 to 2.1) dialysers. m 2 ).
Hemoreactivity makes it possible to distinguish schematically three types of dialyzers:
• those with high hemoreactivity (bio-incompatible);
• those with low hemoreactivity (biocompatible);
• those with specific biological activity (bioactives).
It should be noted that hemoreactivity is currently defined on a simple and easily measurable criterion, the activation of complement and the induction of early leukopenia. The use of more sensitive markers (cytokine production, free radical production, induction of cell apoptosis) suggests that there are currently no fully biocompatible dialyzers. This criterion is therefore to be used with a great deal of relativity.
It should be noted that the manufacture of hemodialyzers has benefited in recent years from two important innovations:
• on the one hand, the application of nanotechnology, which has made it possible to considerably reduce the mass of material involved in the constitution of a dialyzer (membrane, potting, shell) and to calibrate in a more precise and homogeneous way the porosity of the membranes;
• on the other hand a new design of the internal hydraulics of dialyzers. The latter is intended for:
C increase the internal filtration phenomena by increasing the resistances (increase of the length of the fiber bundle and reduction of their internal diameter) and to increase the convective exchanges (ultrafiltration / retrofiltration); C to reinforce the phenomena of turbulence (fiber separator, fiber and bundle ripple) to reduce the thickness of the liquid film and to minimize the resistance to solute transfer.
It should also be noted that the performance of a hemodialyzer is closely related to its conditions of use. In other words, the optimal performance of a dialyzer is obtained when the conditions of use (real blood flow, dialysate flow, anticoagulation …) are adapted to the physical characteristics of the hemodialyzer and to the manufacturer’s recommendations.
Choice of “dry weight”:
The “dry weight” (synonym of “base weight”) represents the weight of the patient reached at the end of the session after normalization of its extracellular volume. In other words, it is the weight obtained after restoration of the equilibrium of the hydrosodée balance.
In practice, it is the weight of end of dialysis session which makes it possible to correct the arterial pressure without recourse to antihypertensive medications. The “dry weight” is an eminently variable parameter, individual and very subjective. Defining the “dry weight” of a dialysis patient is not an easy task. It is a parameter that varies considerably over time and requires periodic readjustments taking into account the nutritional status and clinical situation of the patient. The slow changes in dry weight observed over time reflect, in fact, more changes in nutritional status than changes in extracellular volume.
Empirically, “dry weight” is achieved when the following three conditions are met: no peripheral edema, no sign of cardiopulmonary overload and normalization of pre-dialytic arterial pressure.
More objectively, physical measures are sometimes used. A chest x-ray can be used to assess the cardiac figure, to measure the cardiothoracic ratio and to look for signs of pulmonary overload. Echocardiography is used to evaluate cardiac function (heart cavity diameter, shortening and ejection fraction, ventricular mass) and to look for signs of hypervolemia.
The measurement of the diameter of the inferior vena cava is also an element of evaluation of the volemia. More recently,
it has been proposed to use the kinetics of body impedance (total or segmental) to evaluate the volume status and to investigate the isovolemic situation of dialysis patients.
In clinical practice, the search for “dry weight” is an essential and permanent goal for any dialysis patient. The restoration of the sodium balance and the control of the blood pressure by the hemodialysis are major criteria of adequate dialysis.
Choice of blood flow:
Extracorporeal blood flow conditions the effectiveness of the extracorporeal treatment session. Solute clearance is an exponential function of blood flow for a constant dialysate flow rate. The maximum clearance is obtained for blood flow rates of between 300 and 400 ml / min for a dialysate flow rate of 500 ml / min. The body clearance of a solute varies according to the volume of blood treated per session. For sessions of 3 to 4 hours, the total volume of blood treated is of the order of 50 to 100 l per session.
The actual extracorporeal blood flow is usually less than the rate displayed by the hemodialysis monitor. For arteriovenous fistulas or arteriovenous bypass grafts (> 600 ml / min) the loss of efficacy is low, usually less than 5%.For arteriovenous fistulas or arteriovenous bypass grafts (<300 ml / min) and for venous catheters, the loss of efficacy is much greater and can reach 20 to 30%. This loss of blood flow results in a reduction in clearance of solutes with the risk of insufficient dialysis. Extracorporeal blood flow is limited by the flow of vascular access, in the case of arteriovenous fistulas or bypass grafts, and by the low venous pressure in the case of venous catheters. Blood flow monitoring of vascular access is part of the monitoring parameters of a hemodialysis patient.
Actual extracorporeal blood flow conditions the overall effectiveness of the session. The actual blood flow is calculated on some dialysis generators taking into account the pressure drop (pressure) upstream and downstream of the blood pump. Blood flow can also be measured accurately on the extracorporeal circuit using an ultrasonic method based on the Transonics ™ monitor. Other non-invasive external devices for measuring actual blood flow are being evaluated.
In practice, the prescription of blood flow must meet the requirements imposed by the treatment modality and the type of hemodialyzer and must be compatible with the rate of vascular access. Evaluation of the actual blood flow must be part of the surveillance parameters imposed for good practice of dialysis. Noninvasive periodic monitoring (ultrasonography, ultrasonic flow meter, Transonics ™) of arteriovenous fistula (or bypass) flow is necessary to optimize the prescribing of blood flow. Similarly, measuring the recirculation rate of vascular access is necessary to detect any dysfunction that is detrimental to the effectiveness of the session.
Choice of anticoagulation:
The introduction of extracorporeal blood circulation induces the activation of coagulation and requires the use of an antithrombotic agent.
Standard non-fragmented heparin is usually used to provide systemic anticoagulation of the patient.
Anticoagulation involves the intravenous administration of a loading dose (50 to 100 international units [IU] kg- 1 ) immediately relayed by continuous intravenous injection (iv). to the electric syringe pump with doses between 500 and 1500 IU h -1 .
In case of haemorrhagic risk, it is recommended to use low molecular weight heparins (LMWH). The prolonged half-life of these substances makes it possible to obtain a sufficient antithrombotic effect for 3 to 4 hours with a single injection at the beginning of the session. Other antithrombotic methods are proposed in case of haemorrhagic risks. We will only mention here hemodialysis without anticoagulant with iterative rinses of the circuit with saline serum, the regional anticoagulation based on the use of sodium citrate and the prevention of thrombosis by antiplatelet agents with short half-life (prostacyclin by example).
Choice of dialysate composition:
The dialysate is the electrolytic solution produced by the hemodialysis generator and intended to allow exchanges with the patient. The dialysate results from a mixture of electrolytes (liquid or powder concentrates to dissolve) and treated water.
The final electrolytic composition of the dialysate is close to that of the plasma water of a normal subject. It’s sort of the “third sector” of the organization. Its electrolytic content is intended to correct the abnormalities of the uremic patient.
The sodium content of the dialysate which defines the osmolality of the dialysate is close to that of the plasma, ie approximately 280 mosm / kg H 2 O. The sodium concentration of the dialysate varies within reasonable limits of 135 to 145 mmol / l. The sodium content is established according to the needs and the tolerance of the patients. Most dialysis generators have an option to vary the sodium concentration of the dialysate according to profiles (predefined and customized) coupled to the ultrafiltration rate. This option aims to promote vascular filling and improve the hemodynamic tolerance of the sessions. On certain hemodialysis generators, it is already possible to preserve the constant volume by means of a feedback control regulating the ultrafiltration and the sodium concentration of the dialysate.
The potassium content of the dialysate is usually 2 mmol / l. This eliminates a sufficient amount of potassium in chronic anuric patients. In some cases (elderly, cardiopathy, arrhythmia, digitalis treatment) the concentration of potassium in the dialysate should be increased to 3 or 4 mmol / l.
The calcium content of the dialysate is between 1.25 and 1.75 mmol / l. The choice of calcium content is defined by the calcium load sought by dialysis session. The calcium concentration of the dialysate which provides a neutral calcium balance is 1.5 mmol / l. The calcium content of the dialysate should also take into account oral calcium intake, control of blood calcium balance, parathyroid hormone (PTH), and vascular calcification status. The goal is to maintain serum calcium at an optimal target level to prevent hyperparathyroidism while preventing hypercalcemia and increased phosphocalcium production. The magnesium level is usually between 0.50 and 0.75 mmol / l.
Sodium bicarbonate is the universal tampon used in hemodialysis. The conventional concentration of the dialysate which provides a sufficient bicarbonate feed is 35 mmol / l. The formation of insoluble precipitates of calcium carbonate and magnesium is prevented by acidification (pH dialysate 7.1 to 7.2) by addition of acetic acid (or hydrochloric acid) at a concentration of 4 mmol / l. This means that, finally, the final bicarbonate concentration is 31 mmol / l.
The addition of glucose to the dialysate is indicated to prevent the loss of glucose. It is desirable in elderly and fragile subjects. The glucose content is usually between 5.5 and 11 mmol / l. In the absence of glucose in the dialysate, the perdialytic loss of glucose is of the order of 40 to 50 g / session. This supplementation is essential for diabetics, malnourished patients and very old people.
Choice of flow rate and dialysate temperature:
The dialysate flow rate is set by default on the hemodialysis generator at 500 ml / min. This flow rate makes it possible to optimize the clearances of solutes for blood flow rates of 300 ml / min.
Most contemporary generators give the possibility of increasing the dialysate flow rate from 500 to 800 ml / min. This option increases the clearance of solutes and produces a replacement fluid for online hemodiafiltration methods. The impact of this measure on solute clearance remains modest on small molecules. Doubling the dialysate flow rate (1000 vs 500 ml / min) only increases the clearance of urea by 15 to 20% even though this measure doubles the consumption of electrolyte concentrates.
The dialysate temperature is set by default on the generators at 37 ° C. This is the temperature considered thermoneutral for the patient. Thermal balance studies showed that at 37 ° C, the dialysis patient accumulates thermals and is in a positive thermal balance. This thermal load causes vasodilatation (arterial and venous) responsible for a decrease in peripheral vascular resistance, which is a source of poor hemodynamic tolerance. The reduction of dialysate temperature to 36 ° C or better the use of a temperature monitor ensuring isothermal balance improves the hemodynamic tolerance sessions and remove annoying symptoms such as pruritus and cramps.
Choice of the microbiological quality of the dialysate:
The microbiological purity of dialysate has emerged in recent years as a new standard of contemporary dialysis recommended by the hemodialysis guidelines of good practice. The ultrapure water and dialysate is an essential component for the hemocompatibility of the dialysis system. The dialysate is considered a pharmaceutical product.The regular production of ultrapure dialysate is based on an adequate water treatment system, a well-designed distribution network and particularly thorough hygiene and disinfection procedures.
The use of ultrapure dialysate is strongly recommended with HD methods using high permeability membranes but also with low permeability dialyzers.
The use of ultrapure dialysate is essential with high efficiency convective purification methods (HDF or HF) involving intravenous line injection of the replacement fluid. In the latter case, the utrapur character of the dialysate and the infusate can only be guaranteed by interposing a sterilizing filtration (ultrafilter or microfilter) on these circuits.
Prescription of the dialysis program in special cases:
Some patients have a specific risk profile and need personalized treatment.
Three categories of patients are particularly concerned.
Diabetic patients:
Diabetics (type I or II) represent a category of patients called “high risk” vital. The creation of vascular access is often difficult because of small and calcified arteries. Proximal high-flow fistulas expose them to distal flight syndrome and gangrene of extremities due to diabetic arterial disease. Ocular complications (microaneurysmal retinopathy) involve a hemorrhagic risk that must be prevented by appropriate anticoagulation. Autonomic neuropathy and frequent heart disease in these patients make sodium depletion difficult. Glycemic balance is also disrupted by EER sessions. For this reason, it is advisable in these cases to use prolonged sessions, using convective methods, high permeability membranes, glucose-enriched dialysate, control of thermal balance and blood volume. line.
Elderly
The prevalence of elderly patients on hemodialysis is important, affecting more than two thirds of dialysis patients over 65 years of age. Cardiovascular comorbidity is very common at this age. It complicates dialysis sessions by increasing hemodynamic instability. Caloricoprotein malnutrition is a major problem in elderly people. Management of the elderly uremic subject should be comprehensive, ensuring renal replacement and nutritional support. In this case, the dialysis program should prioritize measures to improve hemodynamic tolerance (duration, convection, thermal balance, volume control) and to correct nutritional deficiencies.
Cardiopathic and arteriopathic patients:
The prevalence of heart disease and vasculopathy is also important. It concerns nearly 60% of patients treated in hemodialysis beyond 65 years. Heart failure makes rapid volume depletion difficult and is frequently accompanied by episodes of low blood pressure.
Vascular disease is easily complicated by ischemic phenomena during falls in blood pressure and variable expression (thoracic or splanchnic angina, rhythmic disorders, cerebral accidents …). This is why, in this case, the dialysis sessions must be prolonged in order to reduce the instantaneous ultrafiltration flow rate, and they must favor the convective methods and the neutral thermal balance, but also a laryamic volume control. .
Monitoring of the hemodialysis session:
Each dialysis session carries risks. They must be well known and prevented by using proven equipment and following detailed procedures.
Connection and boot phase:
The establishment of a dialysis session requires a vascular access of quality to establish a high-speed extracorporeal blood circulation. The measurement and recording of the main vital parameters (weight, blood pressure, heart rate, temperature) are performed before any connection. These settings are recorded on a specific monitoring sheet.Usually, the priming of the blood circuit is obtained after puncture of fistula or arteriovenous bypass. More rarely, it is obtained from a direct connection on deep venous catheters. A bipartite system (or bicathet) with an artery (exit) and a vein (return) is most often used. The priming of the blood circuit may be empty circuit or full circuit.
In the case of the empty circuit, priming is performed slowly (50 to 100 ml / min) after connection of the arterial line to the arterial needle of the patient and emptying of the saline serum contained in the circuit in a flexible plastic bag. In this case, the patient’s blood pushes saline saline from the circuit into an empty pouch.
In contrast, the boot can be full circuit. In this case, the arterial and venous circuits are connected simultaneously to the arterial and venous needles of the patient. Once the blood circuit is closed, the blood flow is gradually increased and adjusted to reach the optimal blood flow (300 to 400 ml / min). Systemic anticoagulation is obtained by intravenous injection of a standard heparin embolus and then relayed by a continuous infusion. The prevention of thrombosis of the extracorporeal circuit is furthermore achieved by the single intravenous injection of a low molecular weight heparin embolus (LMWH) 3 to 4 minutes before the extracorporeal circuit is connected. The air detection system and generator safety clamp are turned on as soon as the blood reaches the blood pump. The session schedule and the settings of the various generator parameters with their alarm ranges are then saved.
Dialysis phase proper:
The dialysis session begins when the blood circulation has been established stably. The air detection device and its safety clamp must be activated at the beginning of the session. In the dialysis center, the dialysis patient is supervised by a specialized nursing staff.
Monitoring involves periodic recording of blood pressure and heart rate. The use of external monitors (blood pressure, heart rate) is a valuable aid that undoubtedly facilitates clinical monitoring.
The occurrence of intercurrent events during the session is recorded on the dialysis monitoring sheet. The frequency of occurrence of these events is used to judge the clinical tolerance of the sessions (hypotension, nausea, vomiting, cramps, headache …). Recording of technical parameters provided by the dialysis monitor (blood flow, venous and arterial pressure, blood leakage, conductivity, dialysate temperature, hourly weight loss) is required. It can be done manually during nurse surveillance or automatically from preprogrammed monitors. The monitoring of dialysis parameters is useful for assuring the smooth running of the dialysis session.
Note that this task can be automated on some generators. It allows an immediate analysis of the data and a storage where a remote transmission of the selected constants (telemonitoring).
Disconnection phase and restitution:
At the end of the session, the blood contained in the extracorporeal circuit is returned. This involves stopping the blood pump, disconnecting the arterial line, and fitting it to a flexible plastic bag filled with isotonic saline (0.5 to 1.0 l) or fitting it to a specific generator comprising an infusion of sterile and pyrogen-free liquid. The return of the blood to the patient and the flushing of the extracorporeal blood circuit usually require 200 to 500 ml of saline. It should be noted that in the event of blood collection at the end of the session, it must be performed in good conditions, ie before release and after an equilibration phase obtained after reduction of the blood flow (50 ml / min) for 2 minutes.
The removal of the needles or the disconnection of the catheters are carried out immediately after restitution. The control of the vital parameters (blood pressure, heart rate, weight, temperature) is then achieved. All these parameters are recorded on the dialysis sheet.
Effective hemodialysis. Hemodialysis adequate. Optimal hemodialysis:
Prescribing a dialysis program does not bode well for its effectiveness. The efficiency check that is required has two purposes:
• first, ensure that the prescribed prescription has been achieved;
• On the other hand, ensure that the program effectively covers the metabolic needs of the patient.
This is a quality approach necessary to ensure the long-term effectiveness of the program.
The complexity of the metabolic abnormalities of the uremic makes it difficult to choose efficiency criteria. This is why in clinical practice it is necessary to use a series of therapeutic targets and targets that cover the vital metabolic needs of the uremic patient. The criteria and values used in this chapter are those established by the expert groups and are included in the professional recommendations.
For convenience, adequate dialysis criteria have been grouped into two categories:
• short and medium term criteria;
• long-term criteria.
Adequate dialysis in the short and medium term:
The short- and medium-term criteria mainly concern vital metabolic needs. They are of two types: subjective and objective.
Subjective criteria:
Correction of uremic syndrome:
The disappearance of the uremic symptomatology is obtained within 1 to 2 weeks (three to six dialysis sessions) after instituting the substitution treatment. The reappearance of even minimal uremic functional symptomatology should suggest a loss of dialysis efficiency and an inadequate dialysis program.
Tolerance of dialysis sessions:
Reducing the incidence of laryngeal morbidity (hypotension, cramps, nausea, vomiting, headache, angina, loss of consciousness …) is an essential objective of contemporary dialysis. The hemodynamic tolerance of the dialysis sessions was very much improved by the use of the bicarbonate buffer and by the generalization of the ultrafiltration masters. Other measures are likely to further improve this tolerance: haemocompatible hemodialysers, individualized profiles of ultrafiltration and conductivity, heat balance neutrality, volume control.
Quality of life :
The goal of extra-renal replacement therapy is not simply to prolong the life of the uremic. It must also restore a quality of life as close as possible to normal. The assessment of rehabilitation is not easy. Grids and simplified evaluation scores are currently proposed (SF36). Several factors contribute to improving the quality of life of dialysis patients:
• a vascular connection that is easy to use;
• well-tolerated dialysis sessions;
• an adequate dialysis program;
• the absence of uremic complications;
• a dialysis program integrated into the patient’s lifestyle, facilitating his reintegration into daily life.
Objective criteria:
“Dialysis dose” administered:
As discussed above, the concept of “dialysis dose” was introduced in the 1980s by F. Gotch to evaluate the effectiveness of dialysis and personalize the dialysis program. Urea quickly appeared in this context as the marker of choice. The pharmacokinetics of urea in hemodialysis is relatively simple because of its low molecular weight (60 Da), its aqueous body diffusion and its simple dosage. In addition, urea is correlated with protein catabolism, its production rate can be likened to protein catabolism and that of dietary protein intake. Finally, its accumulation in the body is close to that of other uremic toxins. The modeled kinetic analysis of urea in dialysis patients quantifies the purifying capacity of the system and assesses protein catabolism of the patient. This approach had many advantages, for the first time it provided a quantified assessment of the quality of the treatment and the protein nutrition of the patient.
The indicators used to quantify the effectiveness of dialysis from urea are of four types:
• urea reduction percentage (PRU) per session;
• the fractional clearance of urea better known as the Kt / V index;
• the mass index of urea subtracted;
• equivalent renal clearance.
The decay of blood urea during dialysis is of the biexponential type. The kinetics of urea represented on a semi-logarithmic scale thus describes a line whose slope is equivalent to the body clearance (K). During a dialysis cycle (dialysis and interdialysis), the kinetics of urea is characterized by two alternating phases: during the session, urea decreases on a double slope, reflecting the purification of two distinct compartments ( shallow and deep) at different speeds; at the end of the session, urea increases abruptly and exponentially in the hour following the session (“rebound” phenomenon) and then rises gradually and linearly until the next session. The decay rate of urea is proportional to the elevation of the dialyser clearance (K), the duration of the session (tHD) and inversely proportional to the volume of distribution of the patient (V). The urinary ascending rate of urea is proportional to protein catabolism (urea generation rate) and inversely proportional to residual renal function and volume of distribution. The amplitude of the postdialytic rebound is proportional to the slope of perdialytic decay.
This kinetics of urea emphasizes the major importance of the end-of-session blood test. This sampling remains very sensitive because it is carried out in full phase of imbalance. It must therefore be performed according to a standardized protocol so that the derived calculations are valid.
Urea Reduction Percent (PRU) is a relative estimate of urea mass subtracted per session. It is a crude indicator of effectiveness that is affected by the terms of the end-of-session sampling and the volume contraction.
The blood sample should therefore be taken appropriately and an appropriate calculation formula should be used.
The Kt / V urea index is the indicator of choice for evaluating the effectiveness of dialysis sessions. The product Kt represents the total body clearance obtained per session. Kt / V represents the normalized body clearance and is related to the volume of distribution of the patient. This index depends on the postdialytic sampling conditions and volume contraction during dialysis. It is therefore appropriate to use an appropriate calculation formula. Only Kt / V formulas, using either a postdialysis equilibrium blood sample, or a calculation formula that corrects for this imbalance (equivalent double-pool), are recommended for this calculation. The use of on-line monitors measuring the effective clearance of urea, either by direct measurement of urea in the dialysate (or ultrafiltrate), or by measurement of ionic dialysance (substitute for urea clearance) ), allows for continuous monitoring of the effectiveness of dialysis sessions.
The urea mass transfer index (solute removal index [SRI]) has been proposed. This index appeared very attractive in that it accurately and directly evaluated the effectiveness of the dialysis session. The SRI represented the ratio urea mass subtracted from patient urea mass. In fact, its clinical use was not as easy as expected in that it required a direct evaluation of the urea mass subtracted in the effluent dialysate measured by an in-line urea monitor. It should be noted that SRI and PRU are very similar dialysis efficiency indicators when dialysis sessions have a low volume variation and that postdialysis sampling is done in good conditions.
The concept of equivalent renal clearance (KReq, ml / min) has been proposed to incorporate biological fluctuations due to intermittent treatment and provide clinicians with an indicator closer to the concept of renal physiology.
This value actually represents the integrated value of urea clearance per dialysis session relative to the period of time considered (48 h to 1 week). Equivalent renal clearance can be calculated for patients performing three sessions per week from the mean Kt / V urea value using the following linear relationship KReq = 1 – 10 Å ~ Kt / V. The value of the average urea integrated on the dialysis cycle can also be calculated by knowing the concentration values of urea before, after the session and before the next session. These last two parameters in turn make it possible to calculate the rate of generation of urea and to estimate the rate of protein catabolism and protein intakes.
The “dialysis dose” administered has a direct influence on the mortality and morbidity of dialysis patients. All of the recent work reported tends to show that the higher the “dialysis dose”, the better the survival of patients.
The HEMO-study suggests that there is no clinical benefit from administering a high dialysis dose (Kt / V urea greater than 1.5) in patients receiving a tri-weekly program. The European recommendations (EBPG) suggest that the “minimum dialysis dose” estimated by the Kt / V urea indicator could be 1.4 with single-pool [sp] models and 1.2 with models. bicompartmental (double-pool [dp]). In other words, the minimum weekly dialysis dose (Kt / Vhebd) should be close to 4.2 with a monocompartmental model and 3.6 with a two-compartment model. In this calculation, the residual renal function of the patient, whose contribution to the overall effectiveness of the program can be significant, is not taken into account (for example, 1.2 ml / min of residual clearance contributes 0.1 to Kt / V).
It should also be noted that it is the weekly “cumulative dose” that determines the effectiveness of the therapeutic program.
This is why periodic and regular monitoring of dialysis efficacy indices should be performed in dialysis patients. This approach is part of a permanent quality control and meets current requirements for good medical practice. Any drift or loss of effectiveness of the program leads to investigate the cause, to correct it quickly and readjust the therapeutic program if necessary.
The “dialysis dose” also has a major impact on the nutritional status of dialysis patients. Protein catabolism, a reflection of protein intake in dialysis patients with nitrogen balance, is also a very important evaluation element provided by the kinetic analysis of urea. The rate of protein catabolism (PCR) is correlated linearly with the urea generation rate (GU) according to the following equation: GU = 0.154 PCR – 1.7. The application of the law of mass conservation to the patient couple / dialysis system over a period of 1 week makes it possible to write that the mass of urea subtracted per session is equivalent to the mass of urea produced between two sessions. The amount of urea subtracted (MU) per session can be calculated in several ways: integration of the area under the curve of the kinetics of blood decay (or dialysate) of urea; direct measurement by mass transfer analysis obtained by collection (total or partial) of the dialysate (and ultrafiltrate) or by on-line monitoring of urea in the dialysate (or ultrafiltrate). The urea generation rate (GU) can thus be calculated as the ratio of the subtracted urea mass (MU) divided by the duration of the interval (t).
The rate of normalized protein catabolism for the dry weight (kg) of the patient (nPCR, g / kg / 24 h) can then be deduced from the rate of urea generation (GU, μmol / min) according to the following relation: nPCR = 0.262 (GU + 54) / dry weight.
More recently, formulas for estimating the rate of protein catabolism (nPCR) have been proposed. These formulas only use simple parameters such as the concentration of blood urea at the beginning of dialysis, the value of Kt / V and the duration of the session. Note that these formulas do not include the residual renal clearance of the patient and that the value of protein catabolism (nPCR) is a reflection of protein intake in stable subjects.
Other markers are of particular interest.
Carbamylated hemoglobin has been proposed to assess the degree and duration of uremic intoxication.
Creatinine allows, by kinetic model analysis, to estimate the lean muscle mass of dialysis patients.
Recent studies indicate that the instantaneous production of creatinine (creatinine index) and its evolution over time are nutritional markers with a high prognostic value.
Inorganic phosphates are directly involved in the determinism of bone disease and vascular calcification. Despite their low molecular weight, inorganic phosphates are difficult to purify with conventional hemodialysis regimens. They possess biphasic kinetics due to high internal resistances which limit their accessibility and extracorporeal purification.Phosphate depletion is therefore much more conditioned by the duration and frequency of the sessions than by that of the permeability of dialyzers and the use of convective transfers.
B -2-microglobulin has emerged in recent years as a reference uremic toxin. In addition to its involvement in the amylose- b -2-microglobulin “old dialysis”, b -2-microglobulin appears as a direct risk factor in the morbidity and mortality of hemodialysis patients.
This role is emphasized by the HEMO study. The complexity of its body kinetics and the strong resistance to internal transfers make it possible to understand the relative inability of conventional extra-renal replacement methods to maintain its circulating levels in optimal targets in the long term.
Other uremic toxins, recently identified protein glycosylation (AGE) or oxidized protein (AOPP) products are also difficult to purify by conventional hemodialysis methods. In these cases, the removal of these substances requires the use of purification methods with a strong convective component and with more frequent and prolonged sessions.
The residual renal function of the patient contributes to increasing the overall effectiveness of the therapeutic program.It broadens the molecular spectrum of purified toxins and facilitates the management of patients’ water balance. The residual clearance of the patient must be taken into account in evaluating the effectiveness of the therapeutic program.It should be evaluated regularly in patients whose daily diuresis is more than 300 ml. Residual clearance is measured over a prolonged interdialytic period of 48 or 72 hours and requires the total collection of urine over this period.Residual renal function is in fact the average of the creatinine and urea clearance. The calculation is based on blood samples taken (urea and creatinine) at the end of one session and the beginning of the next. Schematically, a residual clearance of 1.2 ml min -1 in a 70 kg patient equals 0.1 Kt / V value point.
The recommended therapeutic targets are to administer an optimal dose of dialysis. Current recommendations have established that the minimum value of acceptable Kt / Vdp urea is greater than 1.2 with a protein intake higher than 1.2 g kg -1 d -1 and a urea level before dialysis less than 30 mmol / l. For other solutes (inorganic phosphates, b -2-microglobulin, AOPP …) it is more difficult to establish optimal target values. It is nevertheless recommended to keep the circulating levels of these substances in the ranges as close as possible to normality: for inorganic phosphates, the maximum concentration before dialysis is fixed at 1.75 mmol / l; for b -2-microglobulin, a recent study suggests that the rate before dialysis should be less than 27 mg / l.
Maintenance of nutritional status:
Correction of nutritional status is an essential criterion of effective dialysis. This can only be achieved after correcting the clinical and biological disorders of chronic renal insufficiency, allowing restoration of dietary intakes required to maintain the caloric balance. The assessment of nutritional status is based on:
• anthropometric elements (changes in dry weight, body mass index, muscle mass and fat mass by measuring skin folds and muscle perimeters);
• calculated biological indices (from urea, protein catabolism and creatinine, muscle mass);
• nutritional surveys, visceral proteins (albumin, prealbumin or transthyretin);
• tissue indicators assessing lean and fat mass (bio-impedancemetry, tissue density).
The recommended optimal nutritional targets are to maintain an albumin level greater than or equal to 40 g / l with a prealbumin level greater than or equal to 300 mg / l and to ensure that dietary protein intake is greater than or equal to 1 , 2 g / kg / day and calorie intake greater than 35 kcal / kg / day. The rate of protein catabolism (PCR) established from the rate of urea generation is a precise way to estimate the protein intake of a stable subject. Monitoring of nutritional status is essential for any dialysis patient. It is an essential criterion of quality control and follow-up of the dialysis patient.
Control of extracellular volume, water balance and blood pressure:
Regular recovery and at each dialysis session of the hydro-sodium balance is a primary goal of adequate dialysis. This is the only way to achieve satisfactory blood pressure control in a dialysis patient by limiting the use of antihypertensives. The voluntarily dependent part of hypertension is important. It is found in almost 80% of dialysis patients. Obtaining “dry weight” is an essential goal of the dialysis program that must be achieved by a regular adjustment of dry weight (ultrafiltration) and a simultaneous stop of antihypertensives. Control of extracellular volume is all the easier as dietary sodium restriction is effective (reduction of interdialytic weightings) and dialysis sessions are long and frequent (reduction of ultrafiltration hourly). The recommended therapeutic targets are to maintain a blood pressure (pre-dialysis) on average less than or equal to 140/80 mmHg without antihypertensive (value to be modulated according to the age and co-morbidity of the patient) and to limit the hourly weight loss ( hourly ultrafiltration rate) less than or equal to 700 ml (value adaptable according to the individual tolerance).
Control of acidosis:
The correction of metabolic acidosis is a priority objective of adequate dialysis. The deleterious metabolic effects of chronic acidosis are manifold:
• increased protein catabolism by the ubiquitin and proteasome pathways;
• aggravation of bone lesions by consumption of bone carbonate pads;
• reduced sensitivity of cellular hormone receptors, especially those of insulin;
• reduction of protein anabolism.
Acidosis of the dialysis patient is largely dependent on protein catabolism and protein intake. Hemodialysis ensures the subtraction of fixed acids and the intake of bicarbonate buffer. The bicarbonate feed is proportional to the instantaneous dialysance of the bicarbonate, the bicarbonate rate in the dialysate and the duration of the sessions.The bicarbonate feedstock is between 100 and 150 mmol / l for a bicarbonate dialysate close to 35 mmol / l. In this case, the target therapeutic target is the maintenance of a pre-dialysis bicarbonate level greater than or equal to 20 mmol / l.
Control of the serum potassium:
The maintenance of serum potassium in an optimal zone is an essential criterion for the effectiveness of the dialysis program. Potassium depletion is rapid, but quantitatively limited in hemodialysis and is between 40 and 60 mmol / session. This is often insufficient to maintain a correct serum potassium between two dialysis sessions. This is why the combination of a restrictive potassium diet and taking ion exchange resins (sodium, kayexalate, calcium, calcium sorbitsterit) is often necessary. The objective is to maintain the predialysis serum potassium less than or equal to 6.0 mmol / l and that of postdialysis greater than or equal to 3.0 mmol / l. The potassium content of the dialysate is usually between 2 and 3 mmol / l.
Control of phosphocalcic balance, magnesium and intact parathyroid hormone level 1-84:
The control of the phosphocalcic balance is fundamental to prevent the progression of the dialysis bone disease and the occurrence of vascular and tissue calcifications. Hemodialysis allows phosphate depletion and provides a calcium load that must be adapted to the needs of the patient.
Phosphate depletion varies according to the instantaneous clearance of the dialyzer and the duration of the session.Phosphate body depletion is nevertheless limited because of very high internal resistances. Phosphorus control usually requires the use of digestive phosphorus fixatives to reduce digestive absorption. Digestive digestive agents of phosphorus fall into four categories:
• alumina salts (gastric bandages);
• calcium salts (calcium carbonate, calcium acetate);
• ion exchange resins (sevelamer);
• lanthanum carbonate salts (being recorded).
These digestive fixing salts must be taken at the time of the main meals of the day so that their effectiveness is maximum. The required dose is groped by progressive week titration against the results and the phosphoremic target.The recommended target phosphorus concentration for predialysis should be 1.75 mmol / l and postdialysis should be 0.75 to 1.00 mmol / l.
The calcium load provided by dialysis depends on the calcium dialysance of the dialyzer, the calcium concentration of the dialysate and the duration of the session. The calcium intake achieved during a dialysis session is between 20 and 40 mmol. This charge is obtained with a dialysate whose calcium content is 1.75 mmol / l. It is nearly 50% lower with a dialysate at 1.50 mmol / l and becomes negative with a dialysate at 1.25 mmol / l. The combination of digestive fixing digestive calcium salts of phosphorus and active vitamin D (1,2 [OH] 2 cholecalcidiol) with a dialysate comprising a calcium at 1.75 mmol / l exposes to a major hypercalcemic risk. This is why, in this context, a dialysate at 1.5 mmol / l is indicated in the majority of cases to maintain a positive calcium balance without major risk of hypercalcemia. The bath indication with low calcium content (1.25 mmol / l) must be reserved for particular clinical situations (hypercalcemia malignant for example) and used for short periods. Indeed, with this calcium content, the calcium balance is negative and stimulation of parathyroid secretion is observed. The target target calcium level is between 2.20 and 2.40 mmol / l in predialysis. This is total calcium which must be corrected according to the albumin level.
The control of hyperparathyroidism is an essential element in the management of the dialysis patient. The primary goal is to slow the secretion of PTH to prevent the occurrence or aggravation of bone lesions. The effectiveness of dialysis is a determining factor insofar as it aims to periodically correct the phosphocalcic abnormalities involved in the stimulation of parathyroid secretion. Dialysis, however, is not enough on its own to curb this secretion. It requires a therapeutic supplement in the form of a combination of active vitamin D and calcium salts. Calcimetics (cinacalcet) represent a new therapeutic class that can significantly curb the secretion of PTH by mimicking the action of calcium on parathyroid receptors.
Their clinical use is, however, too recent to define precisely their place in the early braking of hyperparathyroidism. The braking of parathyroid secretion must however remain cautious and limited in order to prevent the occurrence of hypoparathyroidism and adynamic osteopathy, which, in addition to its bone risk (fracture risk), exposes the accelerated development of vascular calcifications. The optimal target recommended for 1-84 intact PTH is between 150 and 300 μg / ml. The assay of the bioactive PTH hormone (7-84) is currently proposed in addition to the determination of intact PTH. It would make it possible to determine more precisely the risk of adynamic osteopathy.
The control of magnesium is also important. It relies on the use of a dialysate whose magnesium concentration is usually 0.5 mmol / l. Lower concentrations of magnesium (0.35 mmol / l) are sometimes necessary if the patient uses magnesium salts (magnesium carbonate) to control his phosphoremia.
Correction of anemia:
Anemia is little or not corrected by hemodialysis.
This is not surprising since it results from a relative deficiency of erythropoietin. The severity of renal anemia, however, varies, depending on sex, age, underlying pathology and dialysis conditions.
The use of an erythropoiesis stimulating agent (ESA) is most often required to correct anemia in these patients. This treatment usually starts in the conservative phase of kidney failure and continues naturally in dialysis. The optimal management of anemia also requires that the aggravating factors are removed and that the resistance factors are corrected. For the record, we will only mention the main factors: iron deficiency, inadequate dialysis, severe undernutrition, hemolysis, regular blood spoliation, inflammatory state, aluminum intoxication or severe hyperparathyroidism.
The recommended targets for anemia and martial status are to maintain a hemoglobin level greater than or equal to 11g / dl (hematocrit ≥ 33%), transferrin saturation greater than or equal to 30% and ferritinemia between 150 and 300 ng / ml.
Prevention of neuropathy and pericarditis:
Neuropathy of the lower limbs and pericarditis are two complications that have become rare during extra-renal replacement therapy. The occurrence of either of these two events should be a strong warning sign, reflecting a serious dialysis deficiency. In all cases, the search for its cause is necessary and a complete revision of dialysis conditions must result. Improving the effectiveness of the dialysis program usually involves lengthening the duration and frequency of dialysis sessions, exploring vascular access (fistula flow, recirculation) and changing the therapeutic strategy (modality purification, type of dialyzer, revision of anticoagulation, revision of the dry weight).
Optimum long-term dialysis:
The criteria for adequate long-term dialysis defined in this chapter are intended to recall the fact that dialysis patients have a life expectancy close to that of a non-uremic age matched population and comorbidity. So that the criteria of effectiveness, called adequate dialysis, which ensure the survival of the patient in the short or medium term are no longer sufficient to qualify the long-term results (more than 10 years). This is why it is necessary to consider optimal dialysis. The associated pathology present in incident patients is a determinant of prognosis in these patients. An accurate analysis of comorbidity (diabetes mellitus, coronary artery disease, cardiac disease, arterial disease, smoking), present in dialysis care, is necessary to evaluate the results of renal replacement therapy in uremic patients.
Prevention of cardiovascular diseases:
The incidence of cardiovascular disease (angina, myocardial infarction, stroke) is high in patients with renal insufficiency who are hemodialysis patients. It is the leading cause of death in uremic disease, occurring 10 to 100 times higher than in an age-matched non-uremic population.
Atherosclerosis:
Atherosclerosis is obviously accelerated in the uremic.
This pathological process starts early in kidney disease, is not really improved by locum therapy, and does not respond to conventional risk factors. The cardiovascular risk factors identified in dialyzed urethra are readily grouped into two categories, traditional factors and non-traditional factors. Among the traditional factors are high blood pressure, lipid disorders, family history, smoking, physical inactivity. Non-traditional factors include markers of protein and cell activation, oxidative stress, chronic inflammation, hyperparathyroidism and the presence of hyperhomocysteinemia.The control of blood pressure, which plays a major role in the progression of vascular lesions, must be obtained on a regular basis. Smoking and sedentary lifestyle that contribute to the progression of vascular lesions must be effectively combated. Improving the quality of dialysis (biocompatibility of the circuit, ultrapure dialysate) and its effectiveness (high permeability, increased convection, more frequent or longer sessions) is likely to reduce this risk and must be promoted.
Vascular and valvular calcifications:
Vascular and valvular calcifications are complications that are more and more frequently observed in dialysis patients.They represent a specific risk factor and independent of atherosclerosis. These calcifications are the result of two main anomalies:
• phosphocalcic disorders (hyperphosphoremia, hypercalcemia, increase in phosphocalcic product, hyperparathyroidism) favorable to passive tissue deposits of microcrystals;
• the intrinsic vascular and valvular disorders of the uremic induce an active “ossification” phenomenon of the tissues (inflammation, lipid oxidation, transdifferentiation of the smooth muscle cells).
Tight calcified aortic stenosis is part of these late and serious complications of dialysis. Other calcific valvulopathies are less frequent and less severe in terms of cardiac functional repercussions. The control of phosphocalcic balance, the cautious braking of hyperparathyroidism and the correction of proatherogenic metabolic abnormalities are among the key therapeutic objectives.
Hypertrophic heart disease:
Hypertrophic heart disease is present in almost 80% of patients in dialysis care. Its screening and identification have benefited greatly from echocardiography. It is a specific risk factor, especially in its form of hypertrophic and dilated cardiopathy. Its causes are multifactorial: arterial hypertension, chronic anemia, chronic sodium overload, arteriovenous fistula, uremic toxins. The correction of ventricular hypertrophy is partly possible thanks to a very strict control of the blood pressure, thanks to an early and adequate correction of the anemia by ASE but also by an improvement of the quality and the effectiveness of the program dialysis.
Hypertension:
Arterial hypertension is present in 80 to 90% of uremic patients at the stage of treatment in dialysis.
It is a major cardiovascular risk factor in uremic disease.
The volodependency of hypertension is found in 70 to 80% of dialysis patients. This means that in 20 to 30% of dialysis patients, arterial hypertension persists despite correction of extracellular volume and adequate decrease in dry weight. The prescription of antihypertensives should therefore be considered only after repeated failure of blood pressure control despite an adaptation of the dialysis conditions (lengthening of sessions, sodium content of the dialysate, isolated ultrafiltration). The different antihypertensive therapeutic classes can be used. Prescription antihypertensive always be careful, using initially low doses and gradually increasing. The choice of antihypertensive is based on its effectiveness and tolerance.
Certain classes of antihypertensives (conversion enzyme inhibitors) that have been the subject of past reactions of severe anaphylactoid reactions with synthetic reactive membranes (AN69) should be used with caution.
Prevention of amylose-b-2-microglobulin:
The amylose- b -2-microglobulin of uremic dialysis is a late complication and long asymptomatic dialysis. It is characterized by the presence of fibrillar amyloid deposits mainly in the articular and paraarticular tissues (synovial and tendons, ligaments) and in the bones (cysts). Note that these deposits can be found in all tissues of the body but mainly in the heart, the digestive tract and microvessels. This amyloid substance is composed mainly of carbamylation-modified b -2-microglobulin associated with smaller quantities of globin chains (14 kD), light chains j or k (20 kD) and α -2 microglobulin (150 kD). These microfibrillary deposits are characteristic of amyloidosis and are easily identified by ultramicroscopy, by specific staining and immunostaining.
The formation of these deposits is clinically manifested by the appearance of articular and periarticular pain syndromes and ductal syndromes. Carpal tunnel syndrome and scapular pain are usually the first manifestations of amylose-2-microglobulin. In historical studies, the incidence of carpal tunnel syndrome reaches 50% at 10 years and 100% after 20 years of dialysis. These pain syndromes involve more or less marked functional impotence. Bone amyloid deposits result in geodes located near the joints (carpal bones, humerus neck, pelvis, femoral necks and condyles, tibial plateau) which weaken the bone and can be complicated by pathological fractures. Erosive spondyloarthropathy is a particularly severe form that is characterized by erosive lesions of the cervical or lumbar vertebral plateaus and infiltration of the medullary canal. The progressive destruction of the intervertebral disc (pseudospondylodiscitis) and vertebral bodies can be complicated by fracture-compression and spinal cord compression (lumbar canal or cervical canal).
The pathogenesis of this amylose-2-microglobulin has been largely elucidated by recent scientific work.
The increase in circulating levels of b -2-microglobulin in uremic patients results in fact from a dual mechanism: on the one hand, the relative ineffectiveness of conventional dialysis programs in purifying this substance; on the other hand, the increased release of b -2-microglobulin linked to the bioincompatibility (inflammation, oxidative stress) of the dialysis system. Tissue deposition and amylose-2-microglobulin formation nevertheless require biochemical modifications of circulating b -2-microglobulin (carbamylation and oxidation) and favorable tissue conditions (local inflammation, presence of tissue cytokines, enzymatic defect, phagocytic disorders).
Note that only the prevention of this amylose- b -2-microglobulin is possible, since these deposits are made, no therapy including kidney transplant is able to make them disappear. The most recent work indicates that improved dialysis quality, including the use of high-permeability synthetic membrane dialyzers, increased convective clearance, and regular use of ultrapure dialysate, is able to prevent effectively the occurrence of amylose- b -2-microglobulin. The European Guide to Good Hemodialysis Practice (EBPG) recommends the regular use of high permeability synthetic membranes, enhanced convective clearance and the use of ultrapure dialysate to prevent this complication.
Prevention of bone disease:
Disruption of divalent ion metabolism (Ca, PO4, Mg) and vitamin D activation occur early in chronic renal failure (CKD) (stage 3). These abnormalities induce hyperparathyroidism and vitamin D deficiency that cause bone lesions. Dialysis only imperfectly corrects these abnormalities and additional oral medical treatment is necessary.
Bone disease of dialysis associates to varying degrees several types of lesions: hyperparathyroidism (increased bone resorption), osteomalacia (relative vitamin D deficiency), osteopenia (lack of mineralization), adynamic osteopathy (lack of bone turnover), aluminum osteopathy ( in case of aluminum poisoning). For more information on this dialysis bone disease, refer the interested reader to reference works. It should be noted that vascular disease, and in particular the occurrence of vascular and valvular calcifications, tends to be closely related to bone disease. Indeed, there is a parallelism between bone demineralization on one side and vascular calcification on the other.
The recommendations of good practice reported by the K / DOQI emphasize the need to optimally control the phosphocalcic balance, to limit calcium intake (1.5-2 g / day), to limit the braking of hyperparathyroidism ( vitamin D, parathyroidectomy) to prevent bone and vascular injury.
Prevention of viral contamination (HBS, hepatitis C virus, human immunodeficiency virus, human T-cell lymphoma virus):
The viral risk remains very high in hemodialysis patients, especially since they are treated in a center and share generators and monitoring equipment with other patients. Viral prevention must remain a daily concern in hemodialysis patients. This mainly concerns the risks of viral transmission interpatients whose vector is caregivers or shared equipment. Hepatitis B has virtually disappeared from dialysis centers thanks to the early vaccination of chronic renal failure patients and the isolation measures of the patients with contaminants. The current problem is in fact mainly represented by hepatitis C, the prevalence of which varies between 7 and 20% in the centers. The risk of nosocomial interhuman transmission has been fully demonstrated. Most of the time, it results from mistakes made in the layout of the centers and in the practice of care. This is why the standard rules of hygiene, disinfection of equipment and universal precautions must be applied very strictly in dialysis units. The viral serological profile (presence of antibodies, viral replication rate) of patients treated in a dialysis unit should be known and monitored regularly. The geographic or temporal isolation of replicating HVC-positive patients (HVC-PCR positive) is recommended. The serotyping of the HVC virus is advisable to evaluate the pathogenic risk. With regard to the other hepatotropic viruses (delta, G …) the safety instructions are the same as those concerning the HVC virus. As for other viruses (human immunodeficiency virus [HIV], human T-cell lymphoma virus [HTLV]), the risk of human-to-human transmission by surface or generator is low. The proposed measures are those universally applied to other viruses. In all cases, the universal rules of asepsis and isolation are imposed vis-à-vis the risk of blood contamination to patients and caregivers.
Complications of dialysis:
The complications of dialysis fall into two categories: acute complications occurring during the dialysis session or short-term in the interdialytic period; chronic or long-term complications, occurring after a few months or years of treatment. Only acute complications of importance in daily practice are discussed in this section.
The prevention of these preventions implies, on the part of the caregivers, a perfect mastery of the dialysis technique and, on the part of the patients, a good understanding and an adherence to the constraints of the treatment and the dietetics.
Acute complications of hemodialysis:
Common and benign manifestations occurring during the dialysis session:
Cardiovascular instability and access to arterial hypotension:
Hypertensive access to the liver is the most common complication of hemodialysis patients. It concerns 5 to 20% of the sessions. Many factors are involved in the occurrence of these episodes: the patient and his comorbidity, ongoing treatments, dialysis conditions and especially the weight loss hour.
The drop in blood pressure is usually completely asymptomatic.
Sometimes it is accompanied by suggestive symptoms, nausea, vomiting, yawning, feeling tired.
Rarement, l’hypotension est sévère et comporte perte de connaissance, convulsion, angor ou troubles du rythme.
L’hypotension répond habituellement à l’arrêt de l’ultrafiltration, à la mise en position déclive et à une recharge volémique veineuse (sérum salé isotonique ou hypertonique).
Crampes musculaires :
Les crampes musculaires des membres inférieurs traduisent souvent une déplétion volémique brutale ou excessive. Les crampes cèdent à l’administration de solutions hypertoniques (sodium 10 %, glucose 50 %) et à l’arrêt de l’ultrafiltration.
Nausées. Vomissements :
Les nausées et les vomissements qui surviennent en dialyse sont habituellement contemporains de chute tensionnelle et traduisent une hypovolémie. Plus rarement, ils accompagnent un accès hypertensif, des céphalées, des manifestations neurologiques centrales (obnubilation, troubles visuels) et font évoquer un syndrome de déséquilibre ou une hypercalcémie (syndrome de l’eau dure).
Syndrome de déséquilibre :
Ce syndrome est caractérisé par l’apparition, dans la seconde partie de la séance, de céphalées avec photophobies et nausées.
Dans les formes sévères, ces troubles peuvent survenir dans les heures qui suivent la fin de la séance de dialyse. Ce tableau complique volontiers les premières séances de dialyse. Ce syndrome correspond à un oedème cérébral dont la physiopathologie est complexe. Schématiquement, il répond à l’établissement d’un gradient osmolaire entre le plasma et le milieu cellulaire cérébral par baisse rapide de l’osmolalité plasmatique, souffrance cellulaire, génération cellulaire d’osmoles idiogéniques et formation d’un oedème cérébral lésionnel. La correction rapide des désordres acidobasiques a été également invoquée dans sa genèse. La prévention de cet accident impose des séances initiales de dialyse de faible efficacité. L’injection intraveineuse répétée de solutés hypertoniques (mannitol 10 %, glucose 50 %) est un facteur de protection.
Fatigue postdialytique :
L’asthénie persistante plusieurs heures après la fin de la dialyse est assez fréquente. Cette fatigue s’observe plus volontiers avec des séances de très grande efficacité, avec parfois ultrafiltration importante et souvent hypovolémie postdialytique.
L’utilisation de dialysat enrichi en glucose (11 mmol/l) permet d’améliorer cette symptomatologie.
Céphalées :
Les céphalées de fin de séance sont fréquentes au cours des premières séances ou au décours de séances à très haute efficacité. Ces céphalées font suspecter un oedème cérébral induit par des modifications électrolytiques et osmolaires trop rapides. Elles sont parfois contemporaines d’accès hypertensifs et de malaise. Elles doivent faire rechercher un syndrome de déséquilibre, une hypercalcémie, une alcalose métabolique ou une lésion cérébrale sous-jacente.
Manifestations rares et graves survenant pendant la séance de dialyse :
Réactions au dialyseur et au circuit :
Les premières minutes d’une séance de dialyse peuvent être troublées par des manifestations associant, à des degrés divers, une gêne respiratoire, un bronchospasme, une toux quinteuse, un écoulement nasal, une conjonctivite, un érythème cutané prurigineux et parfois une chute de tension artérielle. Ces manifestations évoquent une réaction allergique. Plus rarement, le tableau est extrêmement brutal prenant la forme d’un choc anaphylactique.
Les causes sont multiples et doivent faire rechercher :
• une allergie à un agent de stérilisation (oxyde d’éthylène), au désinfectant du matériel de dialyse (formaldéhyde, acide peracétique), au matériel de dialyse (polyuréthanne) à un médicament injecté, une réaction endotoxinique ;
• une interaction de la membrane de dialyse (particulièrement avec l’acrylonitrile, AN69) avec un inhibiteur de l’enzyme de conversion.
En cas de réaction d’intolérance aiguë, la circulation sanguine extracorporelle doit être interrompue immédiatement et le circuit non restitué au patient. En fonction de la gravité du tableau, il est nécessaire de recourir à l’utilisation d’adrénaline et de corticoïdes. L’allergène devra être identifié et éradiqué afin de prévenir toute réaction plus grave et en particulier celle d’un choc anaphylactique.
Troubles du rythme cardiaque :
La survenue d’extrasystoles ventriculaires ou de troubles rythmiques supraventriculaires (accès de fibrillation ou de flutter), n’est pas rare, en particulier chez les sujets cardiopathes. Ces troubles rythmiques sont accrus par l’hypovolémie, l’hypokaliémie et l’hypoxémie en cas de chute de tension.
Angor. Infarctus du myocarde :
Angina attacks or myocardial infarction can occur during hemodialysis in patients at risk. They are generally indicative of latent coronary artery disease and occur readily in the event of a drop in blood pressure or a rhythmic disorder.Restitution of the blood circuit is essential in these cases with cardiological monitoring including the dosage of creatine phosphokinases (CPK), lactodehydrogenases (LDH) and troponin Ic. The coronarography will then be performed secondarily.
Convulsions:
The onset of a dialysis crisis in dialysis is rare. It must first evoke severe hypotension in a vascular subject. In this case, the restoration of the blood circuit, the correction of the hypovolemia and the cessation of the dialysis are enough to remedy the problem. The occurrence of seizures in dialysis treatment should lead to suspicion of severe hypocalcemia. The repetition of these seizures suggests a cerebral cause and requires specific exploration by imaging (CT, nuclear magnetic resonance).
Febrile reactions and pyrogenic shocks:
The occurrence of febrile reactions during the dialysis session is extremely rare at present. It must be suspected of bacteremia of exogenous origin (catheter or fistula infection), a pyrogenic reaction (endotoxin or other) by contamination of the dialysate (or infusate) or the revelation of a deep infectious focus. An infectious investigation should be performed including blood cultures, blood count (CBC), C-reactive protein (CRP) and procalcitonin, and screening for dialysate contamination.
Gas embolism:
Any extracorporeal mechanical blood circulation carries a risk of air embolism. Despite the apparent safety afforded by monitors on the dialysis machine, this risk persists throughout the dialysis session. The occurrence of an air embolism must be prevented by the respect of the basic rules of safety concerning all extracorporeal blood circulation. Increased vigilance of the nursing staff must be provided in the delicate phases of connection and return of blood to the patient.Immediate and permanent start-up of air detection systems and safety clamps is imperative once the blood circuit is primed. No exception should justify the transgression of these rules during a dialysis session.
Intravascular haemolysis:
The occurrence of intravascular hemolysis is exceptional, but extremely dangerous in dialysis. In severe forms, the clinical picture begins with violent lumbar pains in “bar” quickly associated with general discomfort with shock. The venous blood tubing changes color, giving the blood a lacquered appearance. The causes of hemolysis are of several types:
• osmotic, induced by an anomaly of the electrolytic composition of the dialysate (severe hypoosmolality);
• chemical, related to a disinfection residue of the dialysis generator;
• mechanical, by excessive depression occurring on the plicated blood circuit;
• thermal, by malfunction of the dialysate heating system;
• toxic, in relation to a substance carried by dialysate and water (chloramines for example).
In all cases, the blood circulation must be stopped immediately and the blood not returned. The patient must be transferred to the intensive care unit.
Incidents and accidents occurring during the interdialytic period:
Malignant hyperkalemia:
This is the most common and most serious accident to the extent that it can lead to sudden cardiac arrest. Easy to diagnose, hyperkalemia must be recognized and treated very quickly. Hyperkalaemia is more frequently observed at the end of the weekend and after the longest interdialytic intervals. This accident reflects an excessive consumption of foods rich in potassium (fruits, vegetables, chocolate …) and sometimes insufficiently effective dialysis. He must be dreaded and warned. The prevention of hyperkalemia is based on a dietary education of the patient, the use of ion exchange resins (kayexalate, calcium sorbitsteril) in interdialysis and the use of dialysis bath with low potassium content (2 mmol / l).
Extracellular volume overload:
The extracellular volume overload (sodium inflation) is part of a context of excessive sodium food intake and insufficient ultrafiltration. Sometimes it takes the form of acute pulmonary edema requiring the rapid introduction of a dialysis or ultrafiltration session, sometimes, on the contrary, it is of insidious installation, resulting in peripheral edema, hypertension difficult to control arterial dyspnoea of increasing effort and deterioration of the general state. In all cases, sodium overload is the consequence of either a loss of weight of the patient without adaptation of the “dry weight” or an excessive interdialytic weight gain and insufficient ultrafiltration. The therapeutic sanction must be a rapid downward revision of the “dry weight”.
Infections:
The risk of infection is greater in uremic patients than in normal subjects. This particular sensitivity actually reflects two phenomena, a persistent decrease in immune defenses in uremic dialysis and increased exposure to pathogens through extracorporeal therapy. Infectious, bacterial or viral complications are the second leading cause of hospitalization and mortality of dialysis patients. The application of strict hygienic and aseptic measures during dialysis connections and disconnections is the only measure capable of guaranteeing the prevention of these complications.
Ischemic colitis:
Digestive ischemic complications are relatively rare with bicarbonate buffer and ultrafiltration control. This risk nevertheless persists in vascular patients. It is most often mucosal ischemia and not mesenteric infarction by thrombosis of large trunks. Mucous ischemia (colic or small bowel) is usually triggered by an episode of severe or prolonged hypotension occurring during a dialysis session. The table is revealed in the hours following a dialysis session, by a painful abdominal syndrome preceded by diarrhea and quickly followed by ileus with fever. Abdominal computed tomography allows us to visualize a thickening of the right colic wall and the last ileal loops. Colonoscopy can be useful when it targets ischemic areas of the colonic mucosa. The digestive rest, under cover of anti-anaerobic antibiotic therapy and parenteral nutrition, provides a medical cure. That said, it is often necessary to resort to a surgical procedure involving digestive resection.
Haemorrhages. Hematoma:
The haemorrhagic risk exists because of the anticoagulation performed during the dialysis sessions. This risk persists in the hours following the dialysis session. Among the hemorrhagic complications, let us consider:
• hematomas and hemorrhages of vascular access;
• muscular haematomas (grand rights, psoas) and mesenteric hematomas of pseudosurgical abdomen type;
• digestive haemorrhages;
• haemorrhages on renal cysts;
• cerebral hematomas (meningeal hemorrhage, subdural hematoma).
Chronic complications of hemodialysis:
Inadequate or insufficient dialysis:
Inadequate dialysis corresponds to the reappearance of uremic symptoms in a dialysis patient. This complication is synonymous with an insufficiently effective purification program.
Most often, this results in a rough picture associating an alteration of the general state with loss of appetite and rare nausea, impatience of the lower limbs with insomnia and finally poorly controlled hypertension. Sometimes the revelation is noisier, resulting in pericarditis or pulmonary edema. The quality of the treatment is poor (Kt / V <1,2 or PRU <60%), the nitrogen retention is increased and other biological abnormalities are evocative such as acidosis, hyperkalemia, hyperphosphoremia, anemia and hypoalbuminemia.
The causes of this relative inefficiency are multiple. We will only mention the main ones:
• therapeutic program unsuited to the metabolic needs of the patient (operational conditions not respected or sessions too short);
• low blood flow from vascular access; recirculation of vascular access;
• insufficiently efficient dialyzer.
More rarely, this is concomitant with a loss of residual renal function of the patient.
The correction of these abnormalities requires a complete revision of the dialysis program and an improvement of its efficiency. As a first step, this can be achieved through a daily dialysis program, and secondarily, by a more appropriate prescription for the dialyzer, blood flow and duration of sessions.
Pericarditis:
Pericarditis is rare in CKD. It is a major and serious sign of poorly controlled urine. Several pathogenic factors have been invoked:
• accumulation of uremic toxins of medium or high molecular weight;
• excess of extracellular volume;
• formation of urate, oxalate or pyrophosphate crystals;
• undernutrition;
• virosis.
It should be noted that the intensification of the dialysis program is usually enough to dry up and correct this pericarditis.
Disorders of the martial reserves
The prescription of recombinant erythropoietin indicated in the treatment of anemia of the dialysis patient has considerably modified the iron requirements. Data from recent studies show that 10% to 30% of dialysis patients treated with ESA have true or functional iron deficiency. In contrast, 20 to 30% of dialysis patients have a tissue iron overload. This is often the result of martial supplementation performed by venous leaky pathway.
Complications of vascular connections:
The quality of the vascular connection largely determines the efficiency and morbidity of dialysis. Vascular access for hemodialysis can be divided into two categories:
• permanent access, arteriovenous fistulas and bypasses;
• temporary access, short or long term catheters, implantable ports.
Complications of vascular connections are the leading cause of morbidity in dialysis patients. We will only mention them here and refer the interested reader to the corresponding chapters of the Medical and Surgical Encyclopedia.
Complications of fistulas and arteriovenous bypasses:
A stenosis may develop on one of the arterial and venous branches of the fistula. If the stenosis is located on the tributary artery or the arteriovenous anastomosis, it reduces the flow of blood access and disrupts the course of the session. If the stenosis is located downstream of the anastomosis, it causes an overpressure in the venous segment downstream and contributes to recirculation and prolonged postdialysis bleeding. In all cases, the dysfunction of vascular access reduces the cleaning performance of the dialysis session.
Aneurysmal dilatation may develop on the fistula-irrigated anterior venous network. The formation of “false aneurysms” is more readily seen on the drainage network (vein or bypass) of the fistula or bypass and at the places of repeated punctures. The risk of fissuring with haemorrhage and sometimes infection usually requires ligation or excision of access.
Acute thrombosis of the arteriovenous fistula or bypass often results from a drop in blood flow on dialysis or prolonged hypotension. It should be emphasized that this is a precipitating phenomenon, usually occurring on a fistula or bypass already presenting a stenosis.
The “flight syndrome” reflects a subacute ischemia of the hand. It is due to the decrease in perfusion of the palmar arches due to a high rate of arteriovenous (AVF) fistula (more readily proximal – eg, humerobasilic FAV) than distal) created on a limb bearing a distal arterial disease.
Superinfection is the most feared complication of arteriovenous fistulas and bypasses. It is facilitated by repeated punctures at the same site and reflects a lack of asepsis.
Superinfection is marked by local signs, sometimes minor (indurated venous segment, red and painful), sometimes worrying (mycotic aneurysm at the seat of the anastomosis) and by general signs (high fever, severe sepsis).Staphylococcal aureus or epidermidis sepsis should be suspected and treated immediately. It carries a major risk of acute mutilating endocarditis often fatal.
More rarely, deep vein thrombosis (Pirogoff venous confluence, stenosis or superior vena cava thrombosis) is revealed by the creation of an arteriovenous fistula that is complicated by the appearance of a “big arm”.
Complications of permanent catheters:
Infection is the most common complication of catheters. It comes in different forms: local dermal exit infection, subcutaneous route infection, isolated fever and / or bacteremia, infected thrombosis, sepsis with secondary septic location, right endocarditis. It follows a contamination of the catheter by septic manipulation or cutaneous carriage of germs in the region of emergence of the catheter. The germs can then progress into the subcutaneous tissue or pass endoluminally and create a biofilm. These are, in all cases, formidable infections that require extreme vigilance and must discuss the removal of catheters and the implementation of targeted antibiotic therapy.
Thrombosis or stenosis of the host vein are also serious complications. They result from different causes:
• venous microtrauma repeated by the catheter;
• stimulation of prothrombotic factors of inflammatory or infectious origin;
• stimulation of the coagulation cascade.
The revelation is rarely noisy except when creating an arteriovenous fistula and the appearance of a “big arm”. Most often, the anomaly remains latent; its discovery is the result of radiographic exploration (phlebography, catheterography, angiotodensitometry) for catheter dysfunction.
Other complications can be observed with catheters. We will only mention catheter dysfunctions (insufficient flow, venous or arterial pressure) resulting from endo- or extraluminal thrombosis, partial or total, catheter rupture with risk of endovascular embolization and air embolism.
Conclusion:
Extra-renal replacement methods are now part of the therapeutic arsenal of chronic end stage renal failure. Despite their obvious limitations, extra-renal cleansing methods ensure the survival of more than one million patients around the world. While mastery of dialysis techniques has virtually eliminated fatal accidents occurring during the session, progress is needed to maximize efficiency and ensure better prevention of long-term complications.
Greater efficacy of the methods and a better understanding of the physiopathological mechanisms, atherogenesis and amyloidogenesis in particular, already make it possible to provide partial answers to these problems. The wider use of high permeability membranes and low hemoreactivity, the generalization of sterile and pyrogen-free bicarbonate dialysate, the increase of convective and adsorptive transfers, allow to glimpse therapeutic programs of increased effectiveness and hemo-incompatibility. In addition, a new approach to dialysis, including more frequent (alternating days or daily) and shorter sessions allows to develop a more physiological dialysis.
Improving the quality of the results obtained in long-term patients requires regular quality control and continuous improvement of practices that are part of a quality assurance procedure.
Adequate hemodialysis, an old concept that reflected the effectiveness of the extra-renal plan, must now be replaced by a broader and more restrictive concept called optimal hemodialysis.
