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 PaO(2) had already dropped to 5.1 kPa. The ventilator group was tested for 1 h and still had an acceptable median PaO(2) of 10.3 kPa in the last 15 min. The group was slightly hyperventilated, with PaCO(2) 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 PaO(2) 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 PaO(2) of 10.2 kPa and a median PaCO(2) of 12.3 kPa in the last 15 min. DISCUSSION: Except for the free airway group, the other methods resulted in PaO(2) above 10 kPa and PaCO(2) 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.