Effects of morphine anesthesia on myocardial contractility, blood flow, and metabolism

Abstract

Morphine sulfate is an anesthetic that is frequently used in cardiac operations. Because the knowledge regarding the effects of this drug on the hemodynamic status and myocardium is yet to be defined, we undertook a study in which the effects of morphine sulfate and saline (control group) were compared. Fifteen dogs were anesthetized with chloralose and underwent median sternotomy. A 2 mg/kg dose of morphine sulfate was administered intravenously three times—each time at a 30-min interval (morphine group, eight dogs). In the remaining seven dogs, an equal amount of saline was administered intravenously. The following parameters were measured 10 min after each injection: arterial, central venous, left atrial, and left ventricular pressures, arterial and coronary sinus blood gases and lactates, cardiac output, myocardial blood flow (microsphere technique), and myocardial ATP, glycogen and lactate. Cardiac output, mean arterial pressure, left ventricular dp/dt, myocardial blood flow, myocardial lactate, and lactate extraction did not change significantly in the control group. However, in the morphine group, cardiac output decreased from 103 ± 11 ml/kg/min to 43 ± 6 ( P < 0.005), mean arterial blood pressure decreased from 121 ± 7 mm Hg to 76 ± 10 ( P < 0.05), left ventricular dp/dt decreased from 3134 ± 439 mm Hg/sec to 1548 ± 305 ( P < 0.05), and myocardial blood flow fell from 63 ± 5 ml/min/100 g to 47 ± 4 ( P < 0.05), in spite of a reduction in coronary vascular resistance from 1.66 ± 0.14 mm Hg/ml/100 g/min to 0.74 ± 0.17 ( P < 0.01). Myocardial lactate increased in the morphine sulfate group from 3.04 ± 0.50 μmoles/g to 4.80 ± 0.71 ( P < 0.05), and lactate extraction decreased from 0.23 ± 0.06 μmoles/ml to -0.07 ± 0.13 ( P < 0.05). In chloralose-anesthetized animals, anesthetic doses of morphine sulfate decreased left ventricular contractility, cardiac output, and myocardial blood flow, and increased production of lactate by the myocardium. Our study indicates that morphine sulfate is not as safe a cardiac anesthetic as commonly thought.