The maternal and fetal cardiovascular effects of epidural morphine in the sheep model

Abstract

Interest in the use of epidural narcotics for analgesia has been widespread since the demonstration of opiate receptors in the spinal cord in the mid nineteen-seventies. Recently, several studies have attempted to evaluate the effectiveness of epidural narcotics for the relief of pain in labor and after cesarean section. Using the chronically catheterized maternal-fetal sheep model, we injected 5 mg of preservative-free morphine into the epidural space. No statistically significant changes were observed, neither in maternal or fetal arterial pressure and acid-base status, nor in maternal central venous pressure, systemic and pulmonary vascular resistance, cardiac output, or intrauterine pressure (p greater than 0.05). There was a significant, although small, decrease in maternal heart rate (8%) and uterine blood flow (9%) at 120 minutes (p less than 0.05), and then a return to control values. The maternal levels of morphine peaked at 15 minutes (29 ng/ml) and the fetal levels of morphine peaked at 90 minutes (3 to 4 ng/ml). We conclude that the injection of 5 mg of morphine into the maternal epidural space has no adverse effect on mother or fetus in the sheep model.