Effect of mild hypercapnia on outcome and histological injury in a porcine post cardiac arrest model

Aim of the study. To evaluate in an established porcine post cardiac arrest model the effect of a mild hypercapnic ventilatory strategy on outcome. Methods. The left anterior descending coronary artery was occluded in 14 pigs and ventricular fibrillation induced and left untreated for 12 min. Cardiopulmonary resuscitation was performed for 5 min prior to defibrillation. After resuscitation, pigs were assigned to either normocapnic (end-tidal carbon dioxide (EtCO2) target: 35-40 mmHg) or hypercapnic ventilation (EtCO2 45-50 mmHg). Hemodynamics was invasively measured and EtCO2 was monitored with an infrared capnometer. Blood gas analysis, serum neuron-specific enolase (NSE) and high sensitive cardiac troponin T (hs- cTnT) were assessed. Survival and functional recovery were evaluated up to 96 h. Results. Twelve pigs were successfully resuscitated and eight survived up to 96 h, with animals in the hypercapnic group showing trend towards a longer survival. EtCO2 and arterial partial pressure of CO2 were higher in the hypercapnic group compared to the normocapnic one (p<0.01), during the 4-hour intervention. Hypercapnia was associated with higher mean arterial pressure compared to normocapnia (p<0.05). No significant differences were observed in hs-cTnT and in NSE between groups, although the values tended to be lower in the hypercapnic one. Neuronal degeneration was lesser in the frontal cortex of hypercapnic animals compared to the normocapnic ones (p<0.05). Neurological recovery was equivalent in the two groups. Conclusion. Mild hypercapnia after resuscitation was associated with better arterial pressure and lesser neuronal degeneration in this model. Nevertheless, no corresponding improvements in neurological recovery were observed.