Cardiovascular effects of morphine during hypothermia.

The cardiovascular effects of morphine were determined in anesthetized dogs at 37 and 30 degrees C. Intravenous (i.v., 1 mg/kg) but not intracisternal (i.c., 0.1 mg/kg) morphine produced a significant cardiovascular depression only at 30 degrees C. These effects were antagonized by i.v. naloxone (1 mg/kg) suggesting a peripherally mediated opiate mechanism. Moreover, hypothermia significantly increased plasma and cerebrospinal fluid morphine levels and enhanced the morphine-induced histamine release. The results suggest that opiates could have detrimental effects in patients with poor cardiovascular reserve in which high doses of opiates and hypothermia may be used concomitantly.