Anesthetic regimen effects on a pediatric porcine model of asphyxial arrest

Abstract

The effects of three anesthetic regimens on an established model of pediatric porcine hypoxic-hypercarbic arrest were examined. Twenty-four preadolescent miniature piglets were paralyzed, mechanically ventilated and anesthetized with one of three regimens: IM+IV pentobarbital ( n=8); IM+IV ketamine ( n=8); or IM ketamine+inhaled isoflurane ( n=8). Asphyxial cardiopulmonary arrest was induced and, after an 8 min cardiac arrest nonintervention interval, a standardized protocol of manual CPR with mechanical ventilation was performed. Outcome variables included incidence of ventricular fibrillation, time to cardiac arrest, endogenous plasma epinephrine levels and arteriovenous epinephrine gradients. IV Ketamine anesthesia produced the highest incidence of ventricular fibrillation ( P<0.01 vs. pentobarbital and isoflurane). Time to asphyxia induced cardiac arrest was greatest for the pentobarbital group ( P<0.05 vs. ketamine and isoflurane). During induction of asphyxial cardiac arrest (low cardiac flow), endogenous venous epinephrine accumulation was highest in the pentobarbital anesthetized group ( P<0.05). After 8 min of untreated cardiac arrest and 1 min of CPR (low flow), arterial epinephrine levels were highest in the ketamine group ( P<0.05). Endogenous epinephrine gradients were venous>arterial in all groups at the end of the 8 min cardiac arrest non-intervention interval (no flow). After 1 min of CPR, the gradients had either equalized or reversed to arterial>venous in all groups except for pentobarbital. As designed and expected, return of spontaneous circulation did not occur in any animal. We conclude that, in developing models of porcine asphyxial cardiopulmonary arrest and resuscitation to simulate pediatric human arrest, variations in anesthetic regimen produce significant differences in parameters that are important to consider: time to asphyxia induced cardiac arrest, fibrillation threshold, plasma epinephrine level and arteriovenous epinephrine gradient. Anesthetic effects need to be carefully considered and clearly explained to facilitate the interpretation of studies of interventions in cardiopulmonary arrest and resuscitation.