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 cmH₂O) 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.