The arteriovenous vascular area, dominated by the direct fistula, is used in preference to central venous catheters, including in children.
Arteriovenous fistulas:
Distal radial arteriovenous fistula:
Distal cephalic arteriovenous fistula (FAV) was described by Brescia and Cimino in 1966. It remains the best vascular approach. Communication between the superficial radial vein (distal cephalic) and the radial artery is created on the wrist.
The preoperative state of these two vessels must be specified:
• the clinical examination verifies the radial pulse, appreciates the state of the superficial radial vein under tourniquet if the subcutaneous adipose panniculus is not too important;
• radiography without forearm preparation detects arterial calcification, particularly in diabetic patients;
• iodine venography is the gold standard examination. She appreciates the caliber and distensibility of the vein all the way to the forearm, but also its proximal drainage to the right atrium. This examination is contraindicated in cases of allergy to iodine. It is also not recommended for patients with pre-term chronic renal failure who have not yet started dialysis. In this case, the renal toxicity of iodine can decompensate the kidney situation and precipitate the need for an extrarenal cleansing method.
In these cases, the injection of iodine can be replaced by the injection of CO 2 (A. Raynaud);
• the ultrasound scan provides a precise map of the superficial and deep venous network. It also indicates the state of the arteries.
However, he is uncomfortable with the proximal and central venous stenosis that is common in patients with a history of central venous catheterization.
The anastomosis is most often lateral on the artery and terminal on the vein. She is gladly performed under regional anesthesia. Prophylactic haemostasis by Esmarch tape and pneumatic tourniquet is recommended, as well as the use of magnifying glasses and especially the operating microscope which is indispensable in children. Instruments and microsurgical sutures are used.
The development of the fistula will be done during the 3 or 4 weeks postoperative in the adult. The artery and vein dilate. The venous side will thus become easily punctured, without risk of transfixing punctures which would be source of hematomas and venous stenoses. Its flow will increase in considerable proportions. hemodialysis, by double puncture of the vein, will be made with a flow rate of the order of 350 ml / min. This blood flow conditions the efficiency of the extracorporeal treatment session. For sessions of 3 to 4 hours, the total volume of treated blood is of the order of 50 to 100 liters. For low flow rate fistula (<300 ml / min), the actual extracorporeal blood flow efficiency loss may be in the range of 20 to 30%. This loss of blood flow results in reduced clearance of solutes and a risk of insufficient dialysis. In children, the maturation of the vein can be much slower and it is recommended to create the fistula 3 to 6 months before the presumed start of hemodialysis.
Sometimes the development of fistula is slow, but additional delay may be sufficient. The creation of a new anastomosis above the first may be necessary in case of stenosis of the anastomosis, as well as the correction by percutaneous endoluminal angioplasty of a stenosis of the trunk of the vein or the artery, passed unnoticed until there.There are cases where we will have to change site, that is to say create a fistula on the opposite wrist, or even a more proximal fistula.
Other fistulas:
The ulnar fistula on the wrist, between the superficial cubital vein (distal basilica) and the ulnar artery on the wrist;these vessels are smaller in size than the radial vessels so that the operating microscope is particularly useful.
Cephalic fistula proximal to the elbow, between the cephalic vein and the brachial artery.
The basilic fistula proximal to the elbow, between the basilic vein and the brachial artery, which always requires a surgical superficialization of this deep vein, often done in a second stage operation.
Fistulas in the thigh: rare saphenous fistula, femoral fistula with superficialization of the femoral vein.
Evolution. Complications:
The evolution of fistulas over the years of dialysis is quite variable. If a radial wrist fistula, created sufficiently early before the onset of hemodialysis, in a patient whose superficial and deep venous capital has hitherto been respected, can be used for several decades, it happens quite often that there are complications that are dominated by stenosis.Some stenoses are due to a poor previous state of the vein, others are due to clumsy and traumatic venous punctures sometimes explained by an imperfect functioning of the fistula.
Infection:
Infection is a rare complication of simple arteriovenous fistulas (without prosthesis interposition); intraoperative prophylactic antibiotic therapy resulted in the disappearance of infections from the surgical site; infections on puncture sites are generally benign (except associated skin necrosis) and accessible to antibiotic treatment; Oslerian grafts at the level of direct fistulas are exceptional.
Stenosis:
Stenosis of the arteriovenous anastomosis:
It is usually the result of intimal hypertrophy that occurs in the first few millimeters of the vein. This hypertrophy is caused by the size and swirling nature of the flow. The stenosis is slowly formed and can be suspected in the presence of insufficient flow dialysis or puncture difficulties.
In fistulas located in the forearm, the treatment of choice for this stenosis is the surgical repair of an anastomosis above the previous one. This is usually a simple gesture because of the previous increase of the caliber of the two vessels.
It allows of course the immediate resumption of dialysis. The recurrence of the stenosis will not occur before long.
The alternative treatment is endoluminal angioplasty, which is accompanied by a higher rate of stenosis recurrence.
In case of localization of the fistula at the elbow, this repair of anastomosis is not easy because of the distance of the two vessels (cephalic fistula) and the difficulties that it would be to mobilize the superficialized vein (basilic fistula) It is therefore endoluminal angioplasty that must be used in these cases.
Stenosis on puncture site:
It is located at a distance from the arteriovenous anastomosis; it is clinically evoked by an increase in pressure upstream of the stenosis, confirmed by Doppler and angiography, and best treated by endoluminal angioplasty.
Downstream stenosis:
If the stenosis is located downstream of the anastomosis, it causes overpressure in the venous segment downstream, contributes to recirculation and may be responsible for aneurysmal dilation downstream.
It varies according to the type of fistula.
In the case of radial fistula, elbow stenosis is quite common if the superficial veins in the elbow have been previously damaged by repeated punctures. Drainage is then generally ensured by the perforating vein of the fold of the elbow which is sometimes of insufficient size. In cases of severe hyperpressure, the radiological recanalization of a superficial vein of the elbow is rarely effective for a long time. It is the same for the surgical cure.
In the case of cephalic fistula, the downstream stenosis is located at the level of the cephalic vein crest. This stenosis can cause a significant dilatation of the vein in the arm.
Such stenosis may be amenable to careful endoluminal angioplasty. Surgical treatment requires the tilting of the end of the cephalic vein on the basilic vein. It should only be considered if the trunk of this basilic vein is no longer accessible to a fistula with superficialization, because of previous lesions caused by a history of humeroaxillary bypass.
In the case of basilic fistula with superficialization, the downstream stenosis usually occurs at the upper limit of superficialization, related to an intimal hypertrophy that respects the transposed venous segment to reach the undissected vein. The treatment of this stenosis, frequent but fortunately rather late, is endoluminal angioplasty.
Proximal venous stenosis:
It concerns the subclavian vein and its downstream drainage. It is particularly common after catheterization of the subclavian vein, currently proscribed in any patient likely to have recourse to hemodialysis. It is still a frequent complication of catheterization of the internal jugular vein. This stenosis must be detected before the fistula is created using phlebography. Otherwise it can be revealed by a “big arm”.
These stenoses are usually accessible to repeated endoluminal angioplasty. In the case of occlusive stenosis, a radiological recanalization should be attempted, sometimes followed by the placement of a stent (endoluminal prosthesis). The severity of these often recurrent proximal venous stenoses can not be overemphasized, especially when they are bilateral.
Thrombosis:
It is in rule the consequence of an unknown stenosis. It often follows a drop in blood flow on dialysis or prolonged low blood pressure. It is much later here than in the bypasses. When it concerns only the arteriovenous anastomosis or the first centimeters of the vein of a fistula sitting on the forearm, an anastomosis repair is indicated. This repair has a better long-term result than radiological recanalization. When this anastomotic thrombosis occurs on a fistula in the elbow, or when the thrombosis extends to the trunk of the vein of a distal fistula, the best treatment is radiological by percutaneous thromboaspiration and endoluminal angioplasty.
Aneurysm:
Two different types of aneurysms can be observed:
• false aneurysms, without vascular wall, which are the result of a transfixing puncture of the vein. The formation of these pseudoaneurysms is seen at the sites of repeated punctures and puncture sites for AEP. They are treated by surgical evacuation and closure of the vascular orifice;
• True aneurysms, limited by a vascular wall, which dilate the vein, in fusiform ruler. They are readily associated with downstream stenosis, high flow and especially weakening of the vein and its cutaneous cover by repeated punctures.
The major risk is that of cracking with haemorrhage and sometimes infection.
Skin necrosis:
When it occurs on microaneurysm on puncture site, it runs the risk of massive bleeding. In the absence of superinfection, a cutaneous plasty makes it possible to preserve the fistula. It is always necessary to look for an associated downstream stenosis which requires a clean treatment, generally by endoluminal angioplasty.
Broadband:
Its frequency is probably underestimated. Doppler flowmetering proves this. Normal flow rates in adults are generally considered to be 600 to 800 ml / min for distal fistula and 900 to 1200 ml / min for proximal fistula. The reduction is indicated in the case of a large number (> 1500 ml / min in an adult) and / or cardiac resonance. The banding is far from proven.
In case of high flow on a distal fistula, the ligation of the proximal artery leaving only the supply by the distal artery against the current can reduce the flow rate by half. In the case of high flow on proximal fistula, closure of the arteriovenous anastomosis at the elbow is followed by refeeding of the vein by a prosthetic bridging connected to the wrist on a small artery. This bridging can advantageously be replaced by a flip-flop of the radial artery, particularly in children.
Distal ischemia:
This is a formidable complication that is particularly observed in cases of proximal fistula in diabetic and elderly patients. The minor postoperative manifestations of tingling at the fingertips will often give way to a very active mobilization of the hand. In case of trophic or neurological manifestations, a Doppler and angiographic assessment is urgently needed. The latter is looking for multiple fistula that must be closed, an arterial stenosis upstream or downstream that must be treated. Ischemia can also be secondary to a high flow whose reduction is not always sufficient, and finally to a distal arteriolitis before which one remains disarmed. If the technique of the DRIL described by Schanzer (ligation of the artery downstream of the fistula to suppress the retrograde flow and arteriarterial bypass to re-energize the distal arteries) must sometimes be tried, it must be remembered that the emergency closure of the fistula is sometimes necessary.
Arteriovenous bypasses:
In the absence of a superficial vein or deep vein that can be superficialized, it is necessary to resort to a vascular prosthesis, interposed as a rule on the arm between an artery and a vein. Its very superficial subcutaneous route will allow punctures. The material used may be a modified human vein, a modified bovine vein, a thin-walled or reinforced polytetrafluoroethylene (PTFE) prosthesis, or a polyurethane prosthesis. Punctures are usually allowed between the tenth and twentieth postoperative day.
Evolution. Complications:
The infection is of sufficient concern (risk of valvular grafting) that excision of the prosthesis is frequently necessary.
The seroma is a serum filtration around the first juxta-arterial centimeters of the PTFE prosthesis which has lost its tightness sometimes due to intraoperative maneuvers (hyperpressure, betadine); the diagnosis can be difficult to do because inflammatory swelling is a good sign of an infectious process; segmental replacement of the porous segment is indicated.
The stenosis of the venous anastomosis, by intimal hypertrophy at the level of the receiving vein, is the most frequent, the earliest and most serious complication of these bypasses. It must, absolutely, prefer simple arteriovenous fistula to the use of these prostheses. This stenosis is detected on the existence of a palpable hyperpressure in the assembly, poor dialysis results, a rise in the return pressures or a decrease in the flow rate of the bypass.
Doppler can help to quantify it. The treatment of choice is percutaneous endoluminal angioplasty, which will often have to be repeated a few months later. Stent placement can also help reduce the frequency of these angioplasties.Surgical correction by proximal extension of the bypass may become necessary. The establishment of a new bypass at the same site is indicated in case of associated abnormalities reaching the prosthesis or its cutaneous cover.
Bridging thrombosis is usually a consequence of this stenosis of the venous anastomosis. The treatment is radiological, associating the thromboaspiration and the angioplasty of the stenosis. The immediate success rate exceeds 95%. In the absence of such radiological possibilities, the surgical removal should be done by skin incision next to the venous anastomosis so as to associate the Fogarthy tube disobstruction and the correction of the stenosis of the venous anastomosis.
Central venous catheters:
They are in double standing: two lights contiguous in rifle barrel (Permcath ® type catheter) or independent (Dual-Cath ® type catheter). They are introduced by puncture of the internal jugular vein under ultrasound guidance. Their ends are placed in the right atrium under image intensifier. Subcutaneous tunneling allows a pre-thoracic emergence point.
These are “temporary” approaches that make it possible to start dialysis immediately in a patient whose arteriovenous fistula has not been created early enough or whose approach has ceased to work. More rarely, these are “definitive” catheters, that is, the cardiac state does not allow the creation of an arteriovenous approach, or the vascular capital has been exhausted.
They have the enormous defect of being the object of frequent abnormalities of functioning, of being the source of sometimes dramatic infectious complications, and of provoking proximal or central venous stenoses very prejudicial to the future arteriovenous fistulas. The devices of the “punctureable injection chamber” type make it possible to avoid the transcutaneous exit of the catheters. They run the same risk of central venous stenosis and it does not seem that the risks of infection are significantly lower. The increase in the frequency of catheter use currently seen in most countries is “daunting,” according to Rayner and Besarab.
To learn more about the complications of this type of access, please refer to the corresponding chapter.
Infection is the most common complication of catheters.
It is in the form of a local infection of the exit orifice, subcutaneous route (tunnellite), fever, isolated bacteremia, infected thrombosis, even sepsis or even right endocarditis. They most often follow contamination of the catheter by septic manipulation or skin carriage.
Thrombosis of the host vein is a serious complication. It may be secondary to venous microtrauma repeated by the catheter, stimulation of prothrombotic factors of infectious or inflammatory origin or coagulation pathways.
Conclusion:
Permanent approach to extrarenal treatment is a lifesaving intervention. The realization of a good approach is the guarantee of quality purification and the absence of complications in the long term. If the techniques evolve, it is for many the improvement of imaging techniques (ultrasound, CO 2 venography) and interventional radiology that have profoundly modified the management of arteriovenous approaches.