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OBSTETRIC ANESTHESIA

Combined Spinal-Epidural Anesthesia for Cesarean Delivery: Dose-Dependent Effects of Hyperbaric Bupivacaine on Maternal Hemodynamics

From the Department of Anesthesiology and of Obstetrics and Gynaecology, University Hospitals Gasthuisberg, Katholieke Universiteit Leuven, Leuven, Belgium.

Address correspondence and reprint requests to Marc Van de Velde, MD, PhD., Director Obstetric Anesthesia and Extra Muros Anesthesia, Department of Anesthesiology, University Hospitals Gasthuisberg, Herestraat 49, B - 3000 Leuven, Belgium. Address e-mail to marc.vandevelde{at}uz.kuleuven.ac.be.

	Abstract

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Hypotension remains an important side effect of spinal anesthesia for cesarean delivery. There is limited evidence that reducing the spinal dose has a favorable effect on maternal hemodynamic stability. We designed the present randomized trial to test the hypothesis that reducing the spinal dose of local anesthetics results in equally effective anesthesia and less maternal hypotension. Fifty term pregnant patients were randomly assigned to two study groups. In the HIGH-group combined spinal-epidural anesthesia was performed using 9.5 mg hyperbaric bupivacaine combined with 2.5 µg sufentanil. In the LOW-group combined spinal-epidural anesthesia was performed using 6.5 mg hyperbaric bupivacaine combined with 2.5 µg sufentanil. Demographic data, obstetrical data, visual analog scale score for pain, number of medical interventions for pain, maternal hemodynamics, and neonatal outcome were recorded. Patients in the HIGH-group experienced more pronounced and longer hypotensive periods as compared with the LOW-group. The mean lowest recorded systolic blood pressure was higher in the LOW-group (102 ± 16 versus 88 ± 16 in the HIGH-group; P < 0.05). More patients in the HIGH-group experienced hypotension compared with the LOW-group (68% versus 16%; P < 0.05). In the HIGH-group 15 patients required pharmacological treatment for hypotension compared with 5 in the LOW-group. Duration of effective anesthesia (block to cold sensation above or at T3) was longer in the HIGH-group as compared with the LOW-group (95 ± 25 versus 68 ± 18 min, respectively, P < 0.05). We conclude that small-dose spinal anesthesia (6.5 mg hyperbaric bupivacaine combined with sufentanil) better preserves maternal hemodynamic stability with equally effective anesthesia that is of shorter duration.

	Introduction

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Despite prophylactic measures, hypotension remains a common side effect of spinal anesthesia for cesarean delivery, causing nausea, vomiting, and even fetal acidemia (1–13). Limitation of the spinal dose may reduce maternal hypotension but at a price. Fan et al. (14) demonstrated a dose-dependent effect of intrathecal bupivacaine on maternal arterial blood pressure. Unfortunately decreasing the dose of bupivacaine can result in pain during surgery. Adding opioids to small dose spinal bupivacaine may improve anesthetic quality without causing hypotension.

The present randomized, double-blind trial was designed to compare the hemodynamic effects and anesthetic efficacy of 2 intrathecal mixtures combining 2 doses of bupivacaine, each with 2.5 µg sufentanil.

	METHODS

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After ethical committee approval and written informed consent, 50 healthy patients, carrying a singleton pregnancy, scheduled for elective cesarean delivery were randomized. After IV intravascular fluid administration with 10 mL/kg crystalloid, the epidural space was identified at the L3-4 interspace with an 18-gauge Tuohy needle using the loss-of-resistance to saline technique. A 27-gauge pencil-point was advanced via the epidural needle and when cerebrospinal fluid was obtained, the study solution was injected. A 20-gauge epidural catheter was positioned 4 cm into the epidural space. The patient was positioned supine with 15° left lateral tilt. A 15° Trendelenburg position was assumed to optimize cephalic spread of the anesthetic. Epidural volume extension was performed to improve local anesthetic spread using 10 mL saline 5 min after initiation of anesthesia (15).

Patients were randomized to two groups, using sealed envelopes. Twenty-five patients received 9.5 mg hyperbaric bupivacaine (HIGH-group) and 25 patients received 6.5 mg hyperbaric bupivacaine (LOW-group). In both groups 2.5 µg sufentanil was added to the bupivacaine. Preparation of study solutions was performed by an anesthesiologist not involved in data recording. Maternal arterial blood pressure was recorded using noninvasive measurements. Baseline arterial blood pressure was measured at admission to the labor ward, and hypotension was defined as a decrease in systolic arterial blood pressure (SAP) of >20% below baseline. Blood pressure measurements were performed every 1 min for 10 min and every 2.5 min thereafter. If SAP decreased more than 10%, 5 mg ephedrine was administered IV, followed by another 5 mg if required. If SAP remained decreased by more than 10%, phenylephrine was administered IV in a dose of 100 µg repeated until SAP returned to within 10% of baseline. Spread of anesthesia was recorded every 5 min using ether swabs. Adequate anesthesia was defined as an upper sensory spread (absence of sensation to cold) to a level of T3 and not requiring epidural supplementation. Anesthesia was supplemented using epidural lidocaine 2% when pain occurred or if the T3 dermatome was not reached within 15 min. Time to reach the T3 dermatomal level, incision to delivery interval, duration of cesarean delivery, duration of adequate anesthesia (time from the start of spinal anesthesia to the time breakthrough pain occurred or the upper sensory level decreased to below T3), umbilical artery blood gas analysis, Apgar scores, and neonatal weight were recorded. Before and after combined spinal-epidural (CSE) anesthesia, transabdominal maternal-fetal Doppler examinations were performed.

The primary outcome variable was the incidence of hypotension and the lowest recorded arterial blood pressure. Power analysis based on previous literature (15,16) and institutional experience showed that 21 patients would be required per group to demonstrate a reduction in the incidence of hypotension from 60% in the HIGH-group to 10% in the LOW-group. Continuous variables were analyzed statistically using analysis of variance and Scheffé’s post hoc test or unpaired Student’s t-testing whenever appropriate. Categorical data were analyzed using the Fisher’s exact test and ² analysis. A P value < 0.05 was considered statistically significant.

	RESULTS

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Demographic data, duration of surgery and incision to delivery interval were comparable between the groups (Tables 1 and 2). Time required to achieve adequate anesthesia was 8.0 ± 2.1 min in the LOW-group versus 5.5 ± 2.2 min in the HIGH-group (Table 2) (P < 0.05). The duration of adequate surgical anesthesia was significantly shorter in the LOW-group (68 ± 18 versus 95 ± 25 min respectively, P < 0.05) (Table 2).

The mean lowest recorded SAP was higher in the LOW-group (102 ± 16 versus 88 ± 16 in the HIGH-group; P < 0.05) (Table 3, Figs. 1 and 2). SAP, mean arterial blood pressure, and diastolic arterial blood pressure decreased by a larger percentage in the HIGH-group. More patients in the HIGH-group experienced hypotension (68% versus 16% in the LOW-group; P < 0.05). Total duration of hypotension was longer in the HIGH group (7.4 ± 2.2 versus 1.5 ± 0.4 min, respectively; P < 0.05). More phenylephrine was required to maintain arterial blood pressure in the HIGH-group. More patients in the HIGH-group experienced nausea and vomiting (15 versus 3 patients; P < 0.05).

View larger version (18K): [in this window] [in a new window]   Figure 1. Mean arterial blood pressure (MAP) in patients undergoing cesarean delivery using combined spinal-epidural anesthesia using 9.5 mg (HIGH-group) or 6.5 mg (LOW-group) hyperbaric, intrathecal bupivacaine combined with 2.5 µg sufentanil. BL, baseline measurement. *P < 0.05 versus HIGH-group.

View larger version (14K): [in this window] [in a new window]   Figure 2. Maximal decrease (%) in arterial blood pressure in patients undergoing cesarean delivery with combined spinal-epidural anesthesia using 9.5 mg (HIGH-group) or 6.5 mg (LOW-group) hyperbaric, intrathecal bupivacaine combined with 2.5 µg sufentanil. SAP, systolic arterial blood pressure; MAP, mean arterial blood pressure; DAP, diastolic arterial blood pressure. *P < 0.05 versus HIGH-group.

	DISCUSSION

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This is the first randomized, double-blind trial investigating the hemodynamic effects of different doses of spinal bupivacaine combined with opioids during cesarean delivery under CSE, using identical methods in both groups and avoiding prophylactic use of ephedrine or colloids. Under the conditions of the present trial, 6.5 mg spinal bupivacaine was associated with less hypotension than 9.5 mg bupivacaine. This may result in improved maternal comfort as demonstrated by the reduced incidence of nausea and vomiting.

Several trials have reported an infrequent incidence of hypotension when small doses of bupivacaine were used (16,18,19). However, these trials were flawed because of the lack of a control group. Lew et al. (20) did compare different doses and failed to demonstrate a beneficial effect of reducing the spinal dose. However, they only measured blood pressure every 2.5 minutes and may have missed differences. Furthermore, they used different anesthetic techniques in both groups. Only Fan et al. (14) directly compared different bupivacaine doses and came to similar conclusion as in the present trial.

Unfortunately, the trial by Fan et al. (14) did not add opioids to the anesthetic mixture, resulting in a frequent incidence of inadequate anesthesia. The addition of opioids improves anesthetic quality without affecting hemodynamics (16,18,19–24). The small dose bupivacaine combined with sufentanil in the present trial produced adequate anesthesia, although of limited duration. Small dose spinal anesthesia is therefore only feasible if epidural catheter backup is possible, as with a CSE technique. This was also demonstrated by Ranasinghe et al. (25). What is relevant is its frequent overall success as compared with single-shot spinal or epidural anesthesia alone (25).

The dose used in our HIGH-group (9.5 mg) is at the lower end of recommended spinal doses of bupivacaine for anesthesia during cesarean delivery (26,27). However, this dose was based on the trial by Sarvela et al. (17), who used 9 mg intrathecal bupivacaine (combined with fentanyl) and observed a 60% incidence of hypotension. If we had used larger doses the difference between our HIGH- and LOW-group would have been more pronounced.

It remains unclear whether smaller spinal doses are beneficial for the fetus. Low umbilical artery pH values (<7.2) were noted in 4% of patients in the LOW-group compared with 16% in the HIGH-group. To establish a statistically significant difference with a power of 0.95 or 0.80, respectively, approximately 180 or 113 patients would be required per group. Our trial is therefore significantly under-powered to draw any conclusions regarding the effects of small intrathecal bupivacaine doses on the fetus and neonate. The observed Doppler ultrasound effects of anesthesia were limited and no significant effects on the arterial and venous fetal perfusion could be identified.

We conclude that small dose spinal anesthesia with bupivacaine and sufentanil better preserves maternal hemodynamic stability while resulting in equally effective anesthesia. However, duration of adequate surgical block is limited, suggesting that these small doses only be used when the block can be reinforced with a catheter (28).

	ACKNOWLEDGMENTS

 
The authors wish to express their thanks to the midwifery staff of the University Hospitals Gasthuisberg for their expertise and excellent help throughout this trial.

	Footnotes

 
Accepted for publication February 27, 2006.

	REFERENCES

Top Abstract Introduction METHODS RESULTS DISCUSSION REFERENCES

 

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