Fetal heart rate responses to meperidine alone and in combination with propiomazine

A study was performed to evaluate the effects of three regimens of intrapartum analgesia upon fetal heart rate characteristics. Either meperidine 50 mg (M50), meperidine 50 mg plus propiomazine 20 mg (M50/P20), or meperidine 25 mg plus propiomazine 10 mg (M25/P10) was given intravenously for intrapartum analgesia to 204 patients in the first stage of labor, and the effects were evaluated upon fetal heart rate variability (FHRV) and fetal heart rate reactivity (FHRR). M25/P10 was found to cause a decrease in FHRV in fewer patients than M50/P20 (13.6% vs 36.5%, P less than .005), while still providing adequate analgesia for most patients. Although M50 also caused a decrease in FHRV in fewer patients than M50/P20 (19.1% vs 36.5%, P less than .05), it produced emesis in 20% of patients. When FHRV was minimal or moderate before the analgesic was given, FHRV became absent in only eight of 222 doses (3.6%). FHRR was lost in fewer patients given M50 than in those given M50/P20 (45% vs 71%, P less than .01); there was no significant difference between M50 and M25/P10. We conclude that the effects of meperidine upon fetal heart rate characteristics are both potentiated by propiomazine, and, when meperidine is given with propiomazine, dose-related. We also conclude that absent FHRV is rarely caused by meperidine; when FHRV becomes absent after meperidine administration, the patient should be fully evaluated for the possibility of fetal distress before the absence of variability is attributed to analgesia.