ABSTRACT
In theory, intermittent mechanical ventilation might have two beneficial effects in patients with severe, stable COPD. First, ventilatory assistance might reduce fatigue and increase the strength and endurance of the respiratory muscles, thereby reducing chronic hypercap nia and dyspnea and improving exercise tolerance. Second, since sleep-induced hypoventi lation and hypoxemia are common in patients with severe COPD, positive-pressure venti lation might improve sleep quality and help to maintain adequate nocturnal oxygenation. Despite these potential benefits, the results of studies examining the elective use of both positive-and negative-pressure ventilation in patients with COPD have been largely disap pointing. Most long-term, randomized trials of intermittent negative-pressure ventilation using a poncho or cuirass-type device have failed to show improvements in baseline respi ratory muscle function, blood gases, dyspnea, or exercise tolerance. In addition, this form of ventilatory assistance can worsen upper airway obstruction during sleep and has a low level of patient compliance owing to the uncomfortable and cumbersome nature of the equipment. A number of studies have examined the effectiveness of noninvasive positivepressure ventilation (NIPPV) using the BiPAP system. Although beneficial effects-such as decreased dyspnea, improved exercise tolerance, reduction of chronic hypercapnia, and improved sleep efficiency-have occasionally been documented, most studies have shown no improvement in any of these parameters. Furthermore, in the absence of obstructive sleep apnea, NIPPV, when combined with supplemental oxygen, is no more effective than oxygen alone in eliminating sleep-induced hypoxemia. Based on these findings, intermit tent ventilatory assistance cannot be recommended in the routine management of patients with stable COPD.
