[Effect of high dosages of morphine and meperidine on haemodynamics, coronary blood flow and myocardial oxygen consumption in comparison to fentanyl and piritramide (author's transl)].

Although morphine is one of the oldest drugs known to man, it has only recently been used in large doses as an anesthetic agent. The main advantage is the cardiovascular stability. The purpose of this investigation was to study the circulatory response to high equianalgesic doses of morphine and meperidine. In 10 closed chest dogs during normoventilation and light background-anaesthesia (0.5 Vol. % halthane; N2O:O2 = 2:1) 2.0 mg/kg morphine and 15.0 mg/kg meperidine were given at random. Morphine produced a decrease in mean arterial blood pressure by 28%, which was paralleled by an identical fall in total peripheral resistance. No negative inotropic effects were found. In contrast to this, the severe hypotension developing with meperidine (decrease in blood pressure by 54%) was the result of peripheral vasodilatation (46%) and of myocardial depression indicated by a sharp drop in dp/dtmax (59%), dp/dtmax/IP (14%) and in left ventricular ejection fraction (33%). Utilizing the thermodilution technique, the cardiac output remained largely unaffected with both narcotic analgesics, as the increase in heart rate (morphine 27%; meperidine 101%) compensated for the fall in stroke volume (morphine 19%; meperidine 55%). In spite of the altered haemodynamics there was no change in the myocardial energy demand, which was adequately met by the coronary blood flow measured with the pressure-difference technique. Both, morphine and meperidine, produced initially an increase in coronary blood flow and coronary venous oxygen saturation indicating coronary vasodilation. While the mechanism for the change in cardiovascular status with high doses of morphine is vasodilatation probably due to histamine release, the results of this study suggest a peripheral as well as a central (myocardial depression) site of action with meperidine. The results obtained from this study were compared with the data from a previous investigation on equianalgesic doses of fentanyl and piritramide and their clinical implications were discussed.