Head helmet versus face mask for non-invasive continuous positive airway pressure: a physiological study

Objective. To assess selected physiological effects of non-invasive continuous positive airway pressure delivered by head helmet (CPAP(H)), a special interface device designed to completely contain the head of the patient, compared to face mask (CPAP(M)). Design. Randomized physiological study. Setting. University research laboratory. Patients. Eight healthy volunteers. Intervention. Continuous positive airway pressure delivered by face mask and CPAP(H) in random order. Three gas flow rates (20-30-40 l/min and 30-45-60 l/min, respectively, for CPAP(M) and CPAP(H)) and four CPAP levels (0-5-10-15 cmH(2)O) were employed in a randomized sequence. Measurements and results. In each patient we monitored airway pressure, esophageal pressure, expiratory flow, and inspiratory and expiratory CO2 concentration. End-expiratory lung volume changes from CPAP 0 were measured by inductance plethysmography. The application of increased levels of CPAP resulted in a significant increase in end-expiratory lung volume, similar for CPAP(H) and CPAP(M). Inspiratory changes of airway pressure were comparable for the two CPAP modes. Inspiratory CO2 concentration was higher during CPAP(H) (significantly decreased at increased gas flow rates), compared to CPAP(M). Conclusions. Continuous positive airway pressure delivered by head helmet is as effective as CPAP(M) in increasing end-expiratory lung volume and in compensating for airway pressure changes without the need of a reservoir bag. Higher gas flow rates are necessary to maintain a relatively low inspiratory CO2 concentration.