For many years, mechanical ventilation has been employed in patients with chronic obstructive pulmonary disease (COPD) but the recent development of noninvasive techniques, particularly nasal and face mask ventilation, have considerably increased its use. The enthusiasm for these methods, however, has not been matched by the results from well-constructed studies, and the role of ventilatory support both in acute and chronic respiratory failure is still not settled.
Acute respiratory failureThe steadily increasing number of publications on the use of noninvasive ventilation in acute infective exacerbations of COPD are hard to evaluate for several reasons. Firstly, most of the studies are uncontrolled or use historical or other unsatisfactory control groups. The definition of an infective exacerbation and its severity also varies considerably between the studies. Some studies compare the results of ventilation against "standard" medical treatment but this is frequently unspecified and, where details are given, oxygen appears to have been provided in flow rates sufficiently high to risk precipitating hypercapnia. Lastly, the criteria for the success or failure of noninvasive ventilation, such as the need for intubation, differ between studies.Series published before the use of noninvasive ventilation indicated that the intubation rate was around 25% for hospitalized COPD patients with an acute infective exacerbation [1,2]. Their survival to discharge from hospital was around 60-75%, and at 1 year was around 50% and 2 years around 35% [3-6]. The major areas of interest with noninvasive techniques have been to show whether they can adequately ventilate these patients, reduce the intubation rate and improve survival. Approximately 60-80% of patients tolerate both positive pressure ventilation by face or nasal mask [7,8] and negative pressure ventilation [9]. With mask ventilation, the arterial blood gases can usually be improved within 1-2 h, especially if the initial arterial carbon dioxide tension (Pa,CO 2 ) is raised [10][11][12][13][14][15][16], although in a controlled study there was no difference in the blood gases between the ventilated and nonventilated patients [17]. Early studies with negative pressure ventilation also showed that ventilation could be adequately supported [18][19][20][21][22], and these findings have been confirmed in subsequent uncontrolled studies [9,[23][24][25]. The mechanisms by which noninvasive ventilation achieves these effects have not been established.It can reduce respiratory muscle activity [26] and increase maximum inspiratory pressures [9, 24], but whether these or any changes in respiratory drive or mechanics are clinically significant is still uncertain.There are few data regarding the ability of negative pressure systems to avoid or delay intubation, but this question has been addressed in several reports of mask ventilation. Three series using historical controls suggested that the intubation rate could be reduced [27][28][29]. The results of a fourth are published in this ...
