Postpartum uterine pressures under halothane or enflurance anesthesia.

Postpartum uterine pressures were measured in healthy women with an intrauterine microballoon before, during, and after administration of different concentrations of halothane or enflurane. Arterial blood samples for anesthetic levels were obtained at intervals. Frequency and intensity of contractions diminished markedly when blood levels exceeded the equivalent of 1/2 MAC (minimum alveolar anesthetic concentration which produces immobility in one-half of subjects exposed to a noxious stimulus) of nonpregnant adults, but normal patterns returned promptly on lightening of anesthesia. Response to 10 mU of oxytocin was suppressed at blood levels corresponding to between 3/4 and 1 MAC of the agents. Halothane and enflurane exert equipotent dose-related reversible effects on the activity of the full-term pregnant human uterus.