Abstract P107: The Effect of Type of Anesthesia and Technique of Cardiac Arrest Induction on Outcomes in Rats
Animal models of outcome after cardiac arrest may be affected by anesthesia or by the technique used to induce arrest. In rats, asphyxial cardiac arrest (ACA) results in bardycardia and pulselessness over several minutes, which may mimic respiratory crises in humans, whereas cardioplegic cardiac arrest (CCA) results in immediate cessation of blood flow, which may mimic sudden cardiac death in humans. This study tested whether survival and response to therapeutic hypothermia differed between ACA under two anesthetics, and then compared ACA to CCA.
Methods: We examined archival experimental data from rats (N=199) subjected to 8 min ACA (paralysis with cessation of ventilation) under halothane anesthesia. Separate rats were subjected to 8 min ACA (N=11) or 8 min CCA (iv bolus of 8 mg esmolol) (N=26) under ketamine/xylazine anesthesia. A single, experienced surgeon performed all preparations and resuscitations during this time. Each ACA or CCA rat was maintained at either normothermia (NORM, 37°C for 24 hours) or hypothermia (HYPO, 33°C from 1–24 hours) by continuous computer monitoring and control. We excluded rats with other manipulations that affected outcome. Neurological scores were determined daily. Survival was compared using Kaplan-Meier survival curves with alpha level=0.05.
Results: ACA and CCA result in coma with a characteristic pattern of neurological recovery over a period of days. Rats with slow neurological recovery and persistent coma did not survive. Survival after ACA is superior under halothane anesthesia than under ketamine/xylazine (p=0.006). Under ketamine/xylazine, survival did not differ between ACA and CCA (p=0.68). Neurological recovery and survival were superior with HYPO treatment compared to NORM for both ACA (p<0.001) and CCA (p=0.01).
Conclusion: These results indicate that neurological injury affecting survival is reduced by halothane anesthetic, perhaps due to the neuroprotective effects of inhalational anesthesia. Injury is similar between ACA and CCA under a single anesthetic. Finally, HYPO improves outcomes independently of anesthetic or method of arrest (ACA or CCA). Notably, HYPO is beneficial even when brain injury is very severe and survival over the first few days is low (CCA with ketamine/xylazine).