Effect of Oxymorphone Hydrochloride on Ovine Fetal Heart Rate Variability

Abstract

In order to determine the effect of the narcotic analgesic oxymorphone hydrochloride (Numorphan, DuPont) on fetal heart rate (FHR) variability, mathematical indices of short-term and long-term FHR variability were determined continuously from R–R intervals of the electrocardiogram in eight chronically instrumented ovine fetuses for 60 min before and after a maternal intravenous bolus of 0.04 mg/kg oxymorphone. The index of short-term variability decreased from 12.7 ± 2.0 during control to 9.7 ± 1.7 during the period from 10 to 30 min after oxymorphone administration during periods of low-voltage, high-frequency electrocortical activity (LVHF ECoG) (P < 0.05). Mean FHR was decreased from 169 ± 8 beats per minute (bpm) during control to 155 ± 7 bpm 30 to 50 min after oxymorphone (P < 0.05). Fetal electrocortical activity was also determined and the decrease in FHR short-term variability occurred despite an increase in the percent time spent in LVHF electrocortical activity from 53 ± 4% during the control period to 74 ± 5% after the oxymorphone injection (P < 0.05). Long-term FHR variability was unaffected by the oxymorphone administration. This study indicates that maternal administration of oxymorphone hydrochloride causes decreased short-term fetal heart rate variability in sheep.

Key Words:

• Fetal heart rate variability
• Narcotic
• Oxymorphone hydrochloride
• Electrocorticographic activity