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A common problem arising when cardiopulmonary resuscitation (CPR) is performed by conventional mouth-to-mouth ventilation is accidental gas inflation into the stomach. During ventilation of the unprotected airway by mouth-to-mask techniques, distribution of the inflated gas to the lungs or to the stomach depends on the compliance of the respiratory system 1 and possible obstruction of the upper airway. 2
Accidental stomach inflation is a significant issue due to the danger of regurgitation of gastric content and subsequent aspiration 3 and damage to the respiratory epithelium and due to a reduction of pulmonary compliance 4 resulting in reduced oxygen delivery to the tissues.
Decreasing compliance requires a higher pressure to achieve the desired tidal volume, and thereby a further increased risk of gastric inflation results. 5
The aim of this study was to evaluate the effects of artificial ventilation as a part of cardiopulmonary reanimation (CPR) training by non-physician healthcare professionals and dentists as subgroups of informed and pretrained basic life support providers. The devices tested were commercially available masks in connection with a prototype pressure relief valve designed to avoid excess airway pressure and thereby reduce gastric inflation volume and, on the other hand, to control adequate ventilation by a sound generating part of the valve indicating correct expiration of the manikin.
The hypothesis was that gastric inflation can be markedly reduced or even avoided by adding the pressure relief valve with the acoustic control device connected to the expiration part of the valve to the mask, whereas tidal volume is not reduced.
Methods
Ventilation devices
Conventional ventilation masks, either the Ambu mask Size III or a soft seal mask manufactured by VBM Medical (Sulz a.N., Germany) of the same size, were connected to a safety pressure relief valve. This valve is depicted in figure 1 .
The safety valve was assembled using commercially available spare parts for artificial ventilation. The main part was an Ambu Mark III valve. Additionally, a whistle taken from a toy was integrated to give an acoustic alarm.
The valve combination was designed to avoid excess pressure applied to a patient's airway during CPR. The non-rebreathing valve is designed for ventilation avoiding excess pressure and thereby gastric inflation. As a control of correctly performed pulmonary gas inflation a sound generating...