[Effect of morphine on circulatory control in acute progressive hemorrhage]

The effects of acute, progressive haemorrhage, 1 ml/s were examined in the same mongrel dogs on separate days, unanaesthetized and anaesthetized with morphine (2 mg/kg i.v.) and with administration of nasal oxygen to maintain arterial blood gases at physiological levels. In normal, unanaesthetized dogs mean arterial pressure was well maintained through 30 ml/kg of blood loss. Cardiac output fell with haemorrhage (70 +/- 2%; mean +/- S.E.M.) but heart rate and total peripheral resistance rose by 72 +/- 11% and by 124 +/- 11%, respectively. Morphine induced slight but significant changes in heart rate and mean arterial pressure but did not affect the ability to withstand hemorrhage. Thus, in contrast to barbiturates and volatile anaesthetics, morphine does not seem to comprise the efficacy of the rapidly acting pressure control system in response to progressive hemorrhage. The results of the present investigation are not consistent with the hypothesis that opioids are hypotensive factors in hypovolaemic shock.