Background Gastric inflation is a significant issue when ventilation of the unprotected airway is performed. The purpose of this study was to evaluate a prototype pressure relief valve with an acoustic expiration control mechanism connected to two different masks.

Methods 12 non-physician healthcare professionals (group 1) and 10 newly certified dentists (group 2) performed 10 cycles of cardiopulmonary resuscitation on a manikin using this device compared with mouth-to-mouth technique. Dentists also employed a mask without the valve. Lower oesophageal sphincter pressures had been adjusted to 1.5 kPa (group 1) and 0.3 kPa (group 2); the valve relief pressure to 1.5 kPa (group 1) and 2.0 kPa (group 2).

Results In group 1 tidal volumes by valve mask techniques (medians 350 and 400 ml) differed minimally from mouth-to-mouth ventilation (medians 475 and 600 ml). Almost no gastric inflation was observed. Gastric inflation only occurred using the safety valve connected to the mask (median 122 ml) and the mask alone (median 260 ml) (p=0.004). Only in group 1 the acoustic device delivered adequate signals.

Conclusion Gastric inflation occurred less frequently and to a lesser extent when the valve was connected, going ahead with a trend towards lower tidal volumes. The protective effect of the safety valve may be of benefit even if it leads to smaller tidal volumes.