The Effect of Neuromuscular Blockade on Human Fetal Heart Rate and Its Variation

Objective To determine the effect of neuromuscular blockade on fetal heart rate and its variation. Design Case control study. Setting Tertiary referral fetal medicine unit in a London teaching hospital. Subject Forty women with rhesus iso-immunisation requiring an intravascular fetal blood transfusion between 28 and 34 weeks gestation. Intervention Intravascular injection of pancuronium to the fetus prior to fetal blood transfusion in 20 cases. Main outcome measures Comparison between the group receiving pancuronium and the control group with regard to differences in perceived fetal activity and computer derived numerical indices of fetal heart rate and fetal heart rate variation after fetal blood transfusion. Results After transfusion in the control group, there were fewer perceived fetal movements, a small reduction in fetal heart rate but no differences in number of fetal heart rate accelerations or measures of fetal heart rate variation. In the study group, pancuronium produced no change in fetal heart rate despite a virtual abolition of perceived fetal movements and fetal heart rate accelerations. Measures of fetal heart rate variation were reduced by 60%. Comparison of the pre- to post-transfusion changes between the two groups showed significant differences for all fetal heart rate indices. Conclusion Fetal activity accounts for more than half the measured variation of the human fetal heart rate.