Four ways to ventilate during cardiopulmonary resuscitation in a porcine model: a randomized study

BACKGROUND The optimal method for out-of-hospital ventilation during cardiopulmonary rescue (CPR) is controversial. The aim of this study was to test different modes of ventilation during CPR for a prolonged period of 60 min. METHODS Pigs were randomized to four groups after the induction of ventricular fibrillation, which was followed by one hour of mechanical cardiac compressions. The study comprised five pigs treated with free airways, five pigs treated with ventilators, six pigs treated with a constant oxygen flow into the tube, and six pigs treated with apnoeic oxygenation. RESULTS The free airway group was tested for 1 h, but in the first 15 min, the median PaO2 had already dropped to 5.1 kPa. The ventilator group was tested for 1 h and still had an acceptable median PaO2 of 10.3 kPa in the last 15 min. The group was slightly hyperventilated, with PaCO2 at 3.8 kPa, even though the ventilator volumes were unchanged from those before induction of cardiac arrest. In the group with constant oxygen flowing into the tube, one pig was excluded after 47 min due to blood pressure below 25 mmHg. For the remaining 5 pigs, the median PaO2 in the last 15 min was still 14.3 kPa, and the median PaCO2 was 6.2 kPa. The group with apnoeic oxygenation for 1 h had a resulting median PaO2 of 10.2 kPa and a median PaCO2 of 12.3 kPa in the last 15 min. DISCUSSION Except for the free airway group, the other methods resulted in PaO2 above 10 kPa and PaCO2 between 3.8 and 12.3 kPa after one hour. CONCLUSION Constant oxgen flow and apnoeic oxygenation seemed to be useable alternatives to ventilator treatment.