Mask ventilation is a procedure routinely used in emergency medicine. Potential hazards are inadequate alveolar ventilation and inflation of the stomach with air, leading to subsequent regurgitation and aspiration. The aim of this study was to measure lung function and gastric inflation pressures during mask ventilation.

For this purpose, 31 patients scheduled for routine urological procedures were studied during induction of anesthesia. Lung function was assessed by recording respiratory flow and pressure directly at the face mask. Gastric inflation was observed with a microphone taped to the epigastric area.

Gastric inflation occurred in 22 of the 31 patients. Mean gastric inflation pressure was 27.5 ±6.55 cm H2O, mean compliance was 67 ±24.1 ml/cm H2O, mean resistance was 17.4 ±6.41 cm H2O/L/sec, and the mean respiratory time constant was 1.1 ±0.26 seconds.

These data suggest that inspiratory pressure be limited to 20 cm H2O, and that an inspiratory time of at least four times the respiratory time constant be allowed. Monitoring airway pressure and gastric inflation is a simple technique that may improve the safe-ty of patients during mask ventilation.