Effects of decreasing inspiratory flow rate during simulated basic life support ventilation of a cardiac arrest patient on lung and stomach tidal volumes

Abstract

If the airway of a cardiac arrest patient is unprotected, basic life support with low rather than high inspiratory flow rates may reduce stomach inflation. Further, if the inspiratory flow rate is fixed such as with a resuscitator performance may improve; especially when used by less experienced rescuers. The purpose of the present study was to assess the effect of limited flow ventilation on respiratory variables, and lung and stomach volumes, when compared with a bag valve device. After institutional review board approval, and written informed consent was obtained, 20 critical care unit registered nurses volunteered to ventilate a bench model simulating a cardiac arrest patient with an unprotected airway consisting of a face mask, manikin head, training lung [with lung compliance, 50 ml/0.098 kPa (50 ml/cmH2O); airway resistance, 0.39 kPa/l/s (4 cmH2O/l/s)] oesophagus [lower oesophageal sphincter pressure, 0.49 kPa (5 cmH2O)] and simulated stomach. Each volunteer ventilated the model with a self-inflating bag (Ambu, Glostrup, Denmark; max. volume, 1500 ml), and a resuscitator providing limited fixed flow (Oxylator EM 100, CPR Medical devices Inc., Toronto, Canada) for 2 min; study endpoints were measured with 2 pneumotachometers. The self-inflating bag vs. resuscitator resulted in comparable mean±SD mask tidal volumes (945±104 vs. 921±250 ml), significantly (P<0.05) higher peak inspiratory flow rates (111±27 vs. 45±21 l/min), and peak inspiratory pressure (1.2±0.47 vs. 78±0.07 kPa), but significantly shorter inspiratory times (1.1±0.29 vs. 1.6±0.35 s). Lung tidal volumes were comparable (337±120 vs. 309±61 ml), but stomach tidal volumes were significantly (P<0.05) higher (200±95 vs. 140±51 ml) with the self-inflating bag. In conclusion, simulated ventilation of an unintubated cardiac arrest patient using a resuscitator resulted in decreased peak flow rates and therefore, in decreased peak airway pressures when compared with a self-inflating bag. Limited flow ventilation using the resuscitator decreased stomach inflation, although lung tidal volumes were comparable between groups.