Chronic Respiratory Failure

Chronic respiratory failure is defined by the inability of the lungs normally ensure oxygenation of the arterial blood. The result is an arterial hypoxia. The finding of a PaO 2 ≤ 60 mmHg sign a basic IRC.

IRC A- A STEADY STATE:

1- COPD:

– Basic hypoxemia (by shunting)

– Hypercapnia (by alveolar hypoventilation present in advanced disease)

– PH maintained normal renal adaptation (respiratory acidosis compensated): increased tubular reabsorption of bicarbonates (chronic hypercapnia).

– Increasing labor respiratory muscles

– Desensitization of bulbar respiratory centers to hypercapnia stimulus

– Hypoxia becomes the main stimulus

– Hypoxic pulmonary vasoconstriction with PAH more or less fixed, precapillary (elevation precapillary pulmonary pressures without increasing the occlusion pressure)

– Polycythemia secondary to hypoxia

2- IRC RESTRICTION:

– Infringement of the interstitium: abnormal diffusion with hypoxemia effort initially and basic hypoxemia (advanced disease)

– Infringement of the chest wall: especially alveolar hypoventilation

B- etiologies of IRC:

1- obstructive IRC:

These obstructive pulmonary obstructive chronic bronchitis; Asthma continuous dyspnea; emphysema;
Aside: bronchiectasis (DDB) and cystic fibrosis

2- restrictive IRC:

– Infiltrative diseases of the lung (chronic interstitial disease: pulmonary fibrosis …)

– Violations of the chest: chest deformities; pleural disease; neuromuscular disease.

3- IRC pulmonary vascular disease:

– Chronic pulmonary heart (CPC) post embolic

– Primary pulmonary hypertension.

C- LONG-TERM OXYGEN:

1- Indications:

– PaO2 ≤ 55 mmHg at baseline (verified at least 2 months away from acute decompensation)

– PaO2 ≤ 60 mmHg if there are signs of right heart failure, polycythemia, nocturnal desaturation.

– Essential Fact: chronic no-shows hypercapnia against the long-term oxygen therapy.

2- ways:

– This is a priori lifelong treatment

– The duration must always be at least 15 hours a day

– The O2 flow must be adapted to obtain a PaO2 ≥ 70 mmHg without increase PaCO2 (one starts with a flow rate of 1L / min)

D- DECOMPENSATION ACUTE COPD:

– In case of aggravation of the burden on the respiratory muscles, decompensation means: the exhaustion of the diaphragm, the use of inspiratory accessory muscles (SCM external intercostals); active expiration with the contraction of the abdominals.

– Consequence on gas exchange

* The dramatically worsening alveolar hypoventilation

* Hypercapnia is most aggravated compared to baseline

* Hypoxaemia also worsened relative to baseline

* Respiratory acidosis is decompensated with a decreased pH (kidney adaptation possibilities are exceeded) despite bicarbonates ++.

– Hemodynamic failure by increasing PAH (IVD); the importance of hypoxia may be responsible for neuropsychiatric signs.

– Sweats associated with hypercapnia

– HTA or rarely collapse; it does not (generally) shock sign.

– Disorders of consciousness: drowsiness, coma or agitation and asterixis -> intubation and mechanical ventilation in emergency.

– It is the clinical tolerance that determines the therapeutic approach in emergency

– Mechanical ventilation is the best treatment for the rest of the respiratory muscles, a proper oxygenation with hemodynamic improvement, frequent bronchial aspirations, freeing the airway.

– Non-invasive ventilation by face mask avoiding endotracheal intubation for mechanical ventilation in the absence of impaired consciousness and exhaustion.

– Low-flow nasal O2 (0.5 to 1 L / min) to avoid worsening hypercapnia (risk of oxygen at high flow rate) in chronic hypercapnia.

Indications of mechanical ventilation:

* Respiratory Exhaustion (weak chest expansion, paradoxical breathing, ineffective cough)

* Impaired consciousness, asterixis

* Hypotension or shock

* Respiratory acidosis not quickly improved medical treatment (pH <7.30 persistent)