CPAP or not CPAP?

In the past 5 years there has been a considerable increase in the survival rate of infants suffering from the idiopathic respiratory distress syndrome (RDS) (Roberton and Tizard, 1975). Though considerable changes in treatment have occurred during this period, many workers attribute a large part of the fall in mortality to the technique of continuous positive airways pressure (CPAP, or continuous distending pressure-CDP, or continuous inflating pressure-CIP) first described in 1971 (Gregory et al., 1971). The effects of CPAP on lung function are complex (Bancalari, Garcia, and Jesse, 1973), but in animals it minimizes surfactant consumption (Wyszogrodski et al., 1975), and from a practical point of view there can be no doubt that it improves the pattern and regularity of respiration (Spiedel and Dunn, 1975) and virtually always improves arterial oxygenation in infants with RDS (Baum and Roberton, 1974). However, the technique is not without its hazards. The incidence of pneumothorax may be at least three times higher in infants receiving CPAP and thus undoubtedly worsens their prognosis (Yu, Liew, and Roberton, 1975). Sudden deterioration of the infant may occur during the manipulation required to initiate CPAP (Roberton and Tizard, 1975). Other complications described are intraventricular haemorrhage (Vert, Andre, and Sibout, 1973), excoriation of the neck by the seal of a CPAP headbox (Krauss and Marshall, 1975), and brachial plexus palsy from the same apparatus (Turner, Evans, and Brown, 1975). There are also the hazards specifically associated with endotracheal tubes when these are used to apply CPAP. If CPAP is applied by face mask (Rhodes and Hall, 1973) or nasal prongs (Kattwinkel et al., 1973), which can be set up with minimal disturbance to the infant, many of these complications can be avoided. Despite these problems, only two controlled trials of CPAP have been reported in full. Rhodes and Hall (1973) showed a small but significant improvement in mortality only in infants weighing more than 1500 g at birth. Fanaroff et al. (1973), though showing improved oxygenation and shorter duration of oxygen therapy, showed no improvement in mortality in their treated group. Both this study and two other controlled studies reported in abstract only (Krouskop, Brown and Sweet, 1974; Mockrin and Bancalari, 1974), showed that CPAP, particularly if started early, considerably shortened the course of the illness and the duration of oxygen therapy, and minimized the need for intermittent positive pressure ventilation (IPPV). It is intuitively obvious that any technique which shortens the illness in infants with RDS, and minimizes their exposure to high inspired oxygen concentration and to IPPV, must improve their chances of survival, and many workers attribute the improvement in mortality from RDS in their units to CPAP (Dunn, 1974). Chernick (1973) felt able to write, 'one or two controlled trials in the use of constant distending pressure in severe hyaline membrane disease, although daring, are welcome; many more would be foolish'. On page 163, Durbin and his co-authors (1976) from University College Hospital, having ignored Chernick's advice, come up with what now seems to be the standard answer from controlled trials of CPAP-that it makes no difference to mortality, but does shorten the duration of exposure to high oxygen concentration, though in their study it did not reduce the number of infants requiring IPPV. Why do the controlled studies of CPAP fail to show an improvement in mortality from RDS when there is such a body of opinion that it has saved the lives of many infants with this condition? In the UCH study it could in part be due to their starting CPAP late in the course of the illness. This was no doubt forced on them by the large number of infants in their nursery referred from outside hospitals. If a major benefit of CPAP is to minimize surfactant destruction early in the course of RDS (Farrell and Avery, 1975), the later it is started, the less likely it is to be of great benefit to the infant. However, as Durbin et al. point out, even starting CPAP much earlier in their study would at best have resulted in a 5% decrease in the mortality from RDS. Yet looked at the other way this means approximately halving the mortality! (88% survival to 93% survival = 12% mortality to 7% mortality.) The major reason for the failure of controlled trials of CPAP to show a significant fall in the RDS mortality must be that they have been carried out in intensive care units whose staff not only are experienced with CPAP, but who are very com-