Impact of tidal volume during cardiopulmonary resuscitation: an experimental pilot porcine study

The optimal tidal volume (V_T) during Cardio-Pulmonary Resuscitation (CPR) remains unknown. Capnogram could permit to detect ventilation induced harmful effect.

The objectives of the present study were to describe the impact of different V_T on hemodynamics during CPR; and to evaluate whether capnogram analysis can assess the influence of ventilation on circulation.

Eighteen pigs had five minutes of untreated ventricular fibrillation followed by CPR with automated continuous chest compressions and ventilation settings randomly combining V_T 6, 10 or 14 ml/kg. Capnograms were recorded to determine thoracic distension patterns. After return of spontaneous circulation (ROSC), all surviving animals were ventilated 2 h and lungs were withdrawn for histological analysis.

V_T was associated with differences in the hemodynamic parameters studied. V_T at 6 or 14 ml/kg graphically showed poorer cerebral and coronary perfusion pressures and mean arterial pressure than a V_T at 10 ml/kg. The capnogram could distinguish three levels of thoracic distension. Thoracic distension was associated with differences in the hemodynamic parameters studied. Animals with either low or high distension showed poorer cerebral and coronary perfusion pressures and mean arterial pressure than those with moderate distension. ROSC was obtained in 13 (72%) animals. Histology showed that both low and high V_T was associated with a trend towards higher lung damage.

In this animal study, a U-shaped relationship observed with V_T suggests that both small and large V_T may impair circulation. Capnogram analysis could contribute to identify ventilation settings associated with hemodynamic compromise.