Duration of cardiac arrest requires different ventilation volumes during cardiopulmonary resuscitation in a pig model.

Abstract

There are few studies examining the ventilation strategies recommended by current CPR guidelines. We investigated the influence of different minute volume applying to untreated cardiac arrest with different duration, on resuscitation effects in a pig model. 32 Landrace pigs with 4 or 8min (16 pigs each) ventricular fibrillation (VF) randomly received two ventilation strategies during CPR. "Guideline" groups received mechanical ventilation with a tidal volume of 7ml/kg and a frequency of 10/min, while "Baseline" groups received a tidal volume (10ml/kg) and a frequency used at baseline to maintain an end-tidal PCO2 (PETCO2) between 35 and 40mmHg before VF. Mean airway pressures and intrathoracic pressures (PIT) in the Baseline-4min group were significantly higher than those in the Guideline-4min group (all P < 0.05). Similar results were observed in the 8min pigs, except for no significant difference in minimal PIT and PETCO2 during 10min of CPR. Venous pH and venous oxygen saturation were significantly higher in the Baseline-8min group compared to the Guideline-8min group (all P < 0.05). Aortic pressure in the Baseline-8min group was higher than in the Guideline-8min group. Seven pigs in each subgroup of 4min VF models achieved the return of spontaneous circulation (ROSC). Higher ROSC was observed in the Baseline-8min group than in the Guideline-8min group (87.5% vs. 37.5%, P = 0.039). For 4min VF but not 8min VF, a guideline-recommended ventilation strategy had satisfactory results during CPR. A higher minute ventilation resulted in better outcomes for subjects with 8min of untreated VF through thoracic pump.