A safety evaluation of profound hypothermia-induced suspended animation for delayed resuscitation at 90 or 120min

Background: The successful treatment of military combat casualties with penetrating injuries is significantly dependent on the time needed to get the patient to an adequate treatment facility. Profound hypothermia induced suspended animation for delayed resuscitation(SADR) is a novel approach for inducing cardiac arrest and buying additional time for such injuries. However, the time used to safely administer circulatory arrest(CA) is controversial. The goal of this study was to evaluate the safety of hypothermia-induced SADR over 90 and 120 min time intervals.Methods: Sixteen male BAMA minipigs were randomized into two groups: CA90 group(90 min, n =8) and CA120 group(120 min, n =8). Cannulation of the right common carotid arteries and internal jugular veins was performed to establish cardiopulmonary bypass for each animal. Through the perfusion of cold organ preservation solution(OPS), cardioplegia and profound hypothermia(15℃) were induced. After CA, cardiopumonary bypass(CPB) was restarted, and the animals were gradually re-warmed and resuscitated. The animals were assisted with ventilators until spontaneous breathing was achieved. The index of hemodynamic perioperative serum chemistry values [alanine transaminase(ALT), aspartate aminotransferase(AST), creatinine(CR), lactic dehydrogenase(LDH) and troponin T(TnT)] and survival were observed from pre-operation to 7 days post-operation.Results: Fifteen animals were enrolled in the experiment, while 1 animal in CA120 group died from surgical error. All 8 animals in CA90 group recovered, with only 1 animal displaying mild disability. However, in CA120 group, only 2 animals survived with severe disability, and the other 5 animals died after 2 days post-operation. In CA90 group, the perioperative serum chemistry values increased at 1 day post-operation(ALT 84.43±18.65 U/L; AST 88.99±23.19 U/L; Cr 87.90±24.49μmol/L; LDH 1894.13±322.26 U/L; TnT 0.849±0.135 ng/ml) but decreased to normal or almost normal levels at 7 days post-operation(ALT 52.48±9.04 U/L; AST 75.23±21.46 U/L; Cr 82.69±18.41μmol/L; LDH 944.67±834.32 U/L; TnT 0.336±0.076 ng/ml).Conclusion: Profound hypothermia-induced SADR is an effective method for inducing cardiac arrest. Our results indicate that inducing CA for 90 min(at 15℃) is safer than doing so for 120 min. Our results indicate that 120 min of CA at 15℃ is dangerous and can result in high mortality and severe neurological complications. Further experimentation is needed to determine whether 120 min of CA at temperatures lower than 15℃ can lead to safe recovery.