(119) - Effects of ketamine on cardiovascular and respiratory responses to traumatic hemorrhage in rats

Abstract

Ketamine is recommended for analgesia on the battlefield for soldiers with hemorrhage. However, there are no studies of ketamine used as an analgesic in hypovolemic patients. This study determined the effects of an analgesic dose of ketamine on cardiovascular and respiratory compensatory responses and survival time after trauma and hemorrhage in rats. Rats (male; ~ 330 grams) were instrumented with telemetry transmitters for continuous measurement of mean arterial pressure (MAP) and heart rate (HR). Trauma was induced by soft tissue injury and fibula fracture. Hemorrhage (~55% of blood volume via carotid catheter) was conducted after rats were placed in a whole-body plethysmography chamber to measure respiratory rate (RR) and tidal volume (TV). After hemorrhage, rats received either .9% saline (S; n = 6) or 5.0 mg/kg ketamine (K; n = 6) intravenously. MAP, HR, RR, and TV were monitored for up to 4 hours after hemorrhage. Survival times did not differ (P = .53) between S (194 ± 30 min; Mean ± SEM) and K rats (220 ± 20 min). No differences in HR and MAP were detected between treatment groups. TV at 10 min (2.4 ± .4 vs 1.6 ± .1 ml; P = .01) and 45 min (2.3 ± .3 vs 1.6 ± .1 ml; P = .03) post injection was greater in S vs K rats. RR at 10 min post injection was less in S vs K rats (134 ± 12 vs 187 ± 11 breaths/min; P = .04). Differences were transient and were not observed after these time points. These results show that at the time administered, and at the analgesic dose given, ketamine had minimal effects on cardiovascular and respiratory function for up to ~3.5 hours after injection in an animal model of trauma and hemorrhage. Funding provided by the US Army CRMRP, JPC8, Applied Pain Research Programs.