Prehydration and combined spinal epidural labor analgesia

INTRODUCTION: Intravenous prehydration fails to prevent hypotension after spinal anesthesia in parturients. Its role during labor analgesia is unknown. METHODS: With approval of our Human Studies Committee, 40 women with singleton pregnancies gave written informed consent and participated in this randomized, prospective, blinded study. Women were randomly allocated to receive either 500 mL of intravenous lactated Ringer's solution or maintenance fluids before induction of combined spinal epidural labor analgesia (intrathecal bupivacaine 2.5 mg + sufentanil 1.2 μg). Blood Pressure was measured before and every 3 minutes for 30 minutes after drug injection. Fetal Heart Rate (FHR) tracings from 20 minutes before to 40 minutes after the CSE were analyzed by a blinded obstetrician. RESULTS: There were no differences between the no prehydration (n=20) and the prehydration (n=20) groups in age, height, weight, gravidity/parity, gestational age, or cm dilation at time of CSE. Blood pressure decreased significantly in both groups (p < 0.001). The incidence of hypotension (>20% decrease in systolic blood pressure) was similar in the two groups (40% vs. 45%, p > 0.9). Only two women, both in the prehydration group, received intravenous ephedrine. Thirty-two fetal heart rate traces were examined, 16 from each group. Before induction, 25% of patients had some FHR abnormality (early, variable, late or prolonged decelerations). After the CSE, 62.5% of the no prehydration group and 43.8% of the prehydration group had abnormalities (p=0.47). More babies in the no prehydreation group had early decelerations (4/16 vs. 0/16, p = 0.1) or prolonged decelerations (3/16 vs. 0/16, p = 0.22). The incidence of late decelerations was similar (3/16, prehydration vs. 4/16, no prehydration, p > 0.9). Labor outcome was similar in the two groups. DISCUSSION: These data suggest that prehydration with 500 mL crystalloid lacks effect on the hemodynamic consequences of intrathecal bupivacaine/sufentanil in laboring women. The frequency of hypotension, the need for ephedrine and the incidence of perfusion-related FHR changes (late decelerations) were not affected by prehydration. Prolonged decelerations after induction of labor analgesia are often related to increased uterine activity. Prehydration transiently decreases uterine activity. Greater uterine activity in the no prehydration group may explain the more frequent incidence of prolonged decelerations in these fetuses. Alternatively, this difference could have arisen by chance alone.