Cerebral oxygen extraction during cardiopulmonary resuscitation (CPR) for ventricular fibrillation (VF) with and without assisted ventilation (AV)

Introduction

Recent studies have challenged the recommendation of assisted ventilation during the first 10 min of CPR for VF. They have shown that AV during initial CPR does not improve outcome and increases the procedural difficulty. The present study evaluated respiratory, cerebral and systemic oxygenation parameters in an animal model of 'bystander CPR' with and without AV.

Methods

Fourteen dogs were randomized to two groups: group 1, VF without AV (n = 7); group 2, VF with bag ventilation (15:2) (n = 7). A 10-min CPR followed 1-min unassisted cardiac arrest. After CPR, animals underwent defibrillation and advanced cardiac life support. Blood samples from the cerebral transverse venous sinus and the pulmonary artery were collected for gas analysis and lactate. Ventilatory parameters were measured by a flow transducer.

Results

There was no significant difference between groups in baseline measurements and successful CPR (three in each group). Systemic and cerebral oxygen extractions were significantly higher in group 2, although there was no difference in lactate between the groups. During CPR, PaO₂ and PaCO₂ were, respectively, higher and lower in group 2. There was no difference in the minute respiratory volume during the first 5 min of CPR. Thereafter, the minute respiratory volume decreased significantly in the group without AV.

Conclusions

In this experimental model of CPR for VF, assisted ventilation (15:2) maintained higher arterial oxygen saturation and higher systemic and cerebral oxygen extraction but did not result in higher return of spontaneous circulation. After the first 5 min of CPR, AV maintained significantly higher ventilation and oxygenation parameters.