Effects of Ketamine Analgesia on Cardiorespiratory Responses and Survival to Trauma and Hemorrhage in Rats

Abstract

Ketamine is the recommended analgesic on the battlefield for Soldiers with hemorrhage, despite a lack of supportive evidence from laboratory or clinical studies. Hence, this study determined the effects of ketamine analgesia on cardiorespiratory responses and survival to moderate (37% blood volume; n=8/group) or severe hemorrhage (50% blood volume; n=10/group) after trauma in rats. We used a conscious hemorrhage model with extremity trauma (fibular fracture + soft tissue injury) while measuring mean arterial pressure (MAP), heart rate (HR), and body temperature (Tb) by telemetry, and respiration rate (RR), minute volume (MV), and tidal volume (TV) via whole body plethysmography . Male rats received saline (S) or 5.0 mg/kg ketamine (K) (100 µl/100 gram body weight) intra-arterially after trauma and hemorrhage. All rats survived 37% hemorrhage. For 50% hemorrhage, neither survival times (180 min (SD 78) vs 209 min (SD 66) nor percent survival (60% vs 80%) differed between S and K-treated rats. After 37% hemorrhage, K (compared with S) increased MAP, and decreased Tb and MV. After 50% hemorrhage, K (compared with S) increased MAP but decreased HR and MV. K effects on cardiorespiratory function were time-dependent, significant but modest, and transient at the analgesic dose given. K effects on Tb were also significant but modest, and more prolonged. Using this rat model, our data support the use of K as an analgesic in injured, hypovolemic patients.