Abstract P113: Hypothermia Improves Survival When Added to Extracorporeal Membrane Oxygenation Resuscitation after Asphyxial Cardiac Arrest in Rats
Background The use of emergency ECMO (eECMO) as a resuscitative measure during or after manual cardiopulmonary resuscitation demonstrates promising improvements in survival in preliminary clinical and experimental reports. However, hypothermia is only rarely used clinically with the initiation of eECMO. Because the benefits of hypothermia are uncertain when used with eECMO we sought to evaluate the effect of different temperatures on neurological outcome when used with eECMO resuscitation in an asphyxial cardiac arrest model in rats.
Methods Twenty-one rats were studied in three groups: normothermia group (group 1, n=7), mild hypothermia group (group 2, n=8) and moderate hypothermia group (group 3, n=6). After 8 min of normothermic asphyxial cardiac arrest induced by vecuronium, rats were resuscitated with eECMO at 37°C in group 1, 34°C in group 2 and 30°C in group 3 for one hour. During this initial hour full cardiac output eECMO was run for ~10 min to get ROSC, then flow was decreased gradually to ~½ cardiac output gradually by 40 min, then maintained at ½ cardiac output for 20 min. During the second hour ECMO was discontinued and ventilatory support was provided (37°C for group 1; 34°C for groups 2; from 30°C gradually up to 34°C in 1 h for group 3). After weaning off ventilation, 6 hours temperature control was maintained at 37°C for group 1, 34°C for groups 2 and 3. Survival, Overall Performance Category (OPC, 1=normal, 5=death) and Neurologic Deficit Score (NDS, 0 –10%=normal, 100%=death) were assessed at 72 h post arrest.
Results All rats in three groups achieved ROSC with eECMO. In the normothermic group 1, 0/7 rats survived to 72 h, while 5/8 and 5/6 rats survived in the hypothermia groups 2 and 3 respectively (P<0.05). OPC was best in group 3 (2.2±1.6) compared with group 1 (5±0, P<0.05) and group 2 (3.3±1.7, P=0.051). Likewise NDS was best in group 3 (25±37), intermediate in group 2 (50±43), and poorest in group 1 (100±0) (Group 1 versus Groups 2&3, P<0.05).
Conclusions The addition of hypothermia to eECMO resuscitation significantly improved survival compared with normothermic eECMO which is currently a commonly practiced method. Moderate hypothermia may prove more beneficial than mild hypothermia but the optimal temperature strategy remains to be fully determined.