Impact of sleep in respiratory failure.

Sleep has a physiological influence on respiration, which can have major adverse effects on gas exchange in patients with respiratory insufficiency. These effects relate largely to a reduction in various stimulant inputs to the brainstem respiratory centre. Conditions that may be associated with sleep-related respiratory insufficiency range from pulmonary disorders (such as chronic obstructive pulmonary disease (COPD)), to central respiratory insufficiency (such as central alveolar hypoventilation), neurological and neuromuscular disorders (such as polio and muscular dystrophy), and thoracic cage disorders (such as kyphoscoliosis). All these conditions have in common the finding of hypoxaemia and hypercapnia, which become more pronounced during sleep. The relative hypoventilation, which is common to each condition, is due to varying combinations of an inadequate respiratory drive and an increase in the work of breathing. Management of respiratory insufficiency during sleep should be directed first at optimizing the underlying disorder, then at correcting hypoxaemia with controlled low-flow supplemental oxygen. Pharmacological therapy may be effective in some instances, but the choice of agent varies with the underlying disorder. Assisted ventilation is an important part of the management of advanced cases, and the recent development of intermittent positive pressure ventilation by nasal mask (NIPPV) has been an important advance in this area. Use of NIPPV during the night is associated with beneficial effects during the day, particularly improved awake gas exchange and respiratory muscle strength, in addition to less dyspnoea and improved quality of life. Electrophrenic pacing of the diaphragm is helpful in highly selected cases, particularly patients with central respiratory insufficiency and high quadriplegia, but is frequently complicated by the development of obstructive sleep apnoea.