Level of postoperative analgesia is a critical factor in regulation of myometrial contractility after laparotomy in the pregnant baboon: Implications for human fetal surgery

Abstract

Objectives: We used 2 dosage levels of postoperative opioid administration to determine whether the degree of postoperative analgesia after laparotomy during the last third of baboon pregnancy alters maternal pituitary-adrenal function, androgen secretion, and placental estrogen production. We also determined the relationship of estrogen production to surgery-induced increase in myometrial contraction activity. Study Design: After laparotomy under halothane general anesthesia at 0.75 gestation, 10 pregnant baboons were administered intra-arterially either a normal dose or a double dose of the opioid analgesic buprenorphine for 48 hours. Maternal plasma samples for steroid hormone and oxytocin analyses were obtained at circadian time 1000 hours and at circadian time 1800 hours, 4 hours before and 4 hours after the lights went off, respectively. Myometrial electromyographic contraction activity was quantified for the 6 hours from circadian time 1100 hours to circadian time 1700 hours. Results: Maternal plasma cortisol and dehydroepiandrosterone sulfate concentrations were lower in the dark period (at circadian time 1800 hours) than during daylight (at circadian time 1000 hours) in the double-dose group but not the normal dose group. In contrast, maternal plasma estradiol level was higher at circadian time 1800 hours than at circadian time 1000 hours in the normal dose group but not in the double-dose group. Maternal plasma estrogen level was higher during the hours of darkness in the normal dose group than in the double-dose group. Furthermore the number of myometrial contractions around the onset of darkness was greater in the normal dose group than in the double-dose group. Conclusions: The double dose of analgesia results in lower maternal nighttime plasma estradiol concentrations and significantly less nocturnal contraction activity. These observations further confirm an association between increased maternal plasma estrogen concentrations and increased myometrial contractility in the nonhuman primate. In addition, they suggest that adjustment of the level of postoperative analgesia may be of importance in preventing premature labor after chuman intrauterine fetal surgery. (Am J Obstet Gynecol 1999;180:1196-201.)