Introduction: The need for rescue breaths in bystander CPR has been questioned after several studies have shown that omitting ventilation does not worsen outcome. Chest compression may produce passive tidal volumes large enough to provide adequate ventilation in animal studies, but no recent clinical studies have examined this phenomenon. We measured passive ventilation during optimal chest compression to determine whether compression-only CPR provides adequate gas exchange during cardiac arrest.
Methods: Adult cardiac arrest patients were treated according to European Resuscitation Council guidelines. Chest compressions were performed using a mechanical chest compression device (LUCAS) with active decompression disabled to mimic manual compression. Respiratory variables were measured during periods of compression-only CPR.
Results: Emergency Department data were collected during compression-only CPR from 17 patients (11 male) aged 47-82 years who had suffered an out-of-hospital cardiac arrest. Median tidal volume per compression was 41.5 ml (range 33.0-62.1 ml), being considerably less than measured deadspace in all patients. Maximum end-tidal CO2 was 0.93 kPa (range 0.0-4.6 kPa). Minute volume CO2 was 19.5 ml (range 15.9-33.8; normal range 150-180 ml).
Conclusions: At an advanced stage of cardiac arrest, passive ventilation during compression-only CPR is limited in its ability to maintain adequate gas exchange, with gas transport mechanisms associated with high frequency ventilation perhaps generating a very limited gas exchange. The effectiveness of passive ventilation during the early stages of CPR, when chest and lung compliance is greater, remains to be investigated.