[Pathophysiology and clinical aspects of global respiratory insufficiency]

Patients in hypercapnic respiratory failure have got a poor prognosis. The recognition of pathophysiological mechanisms is required in order to choose adequate therapy. During the past years it has been shown that pathological respiratory events during sleep occur early in the disease process and that blood gas changes are usually most pronounced during sleep. Minute ventilation and functional residual capacity (FRC) decrease during sleep even in normal subjects and upper airway resistance increases markedly. PO2 slightly decreases and paCO2 increases. In most patients with hypercapnic respiratory failure episodes of marked hypoxemia and hypercapnia occur, mainly during REM sleep. Suggested pathomechanisms are worsening ventilation-/perfusion mismatching, impaired respiratory muscle function and a reduction in ventilatory drive, the latter two being of major importance. The relation between load and capacity is shifted towards an increased load and ventilatory drive is decreased at the same time. Therapeutic strategies that reduce the load of the respiratory pump, increase minute ventilation and prevent sleep related hypoventilation, thus noninvasive ventilation should be used. Symptoms of hypercapnic respiratory failure are often unspecific. Dyspnea, headache and awakening from sleep with dyspnea are often reported. Signs of right heart failure will be present in advanced disease stages. Early diagnosis and treatment provided, noninvasive ventilation achieves excellent improvement of both quality of life and life expectancy, especially if the primary disease progress is not rapidly progressive.