Journal: Can J Anesth 54(7):531-537, 2007. 19 References
Reprint: Dept of Anesthesiology, Box 249C, The Ottawa Hospital – Civic Campus, 1053 Carling Avenue, Ottawa, Ontario K1Y 4E9, Canada (GL Bryson, MD, FRCPC, MSc)
Faculty Disclosure: Abstracted by L. Easley, who has nothing to disclose.
Contemporary anesthesia texts advocate the use of 12-mg doses of hyperbaric bupivacaine for subarachnoid block for cesarean section (CS). Maternal hypotension occurs in 60-94% of such anesthetics. The primary objective of this study was to compare maternal vasopressor use during CS in patients receiving spinal bupivacaine 12 mg and 4.5 mg. The secondary objective was to determine if anticipated reductions in hypotension, nausea, and motor blockade were reflected in increased patient satisfaction. The study involved 52 patients, 20-40 years of age, undergoing elective CS of singleton pregnancy at greater than 36 weeks gestation via a lower segment transverse incision. Patients were randomized to one of two study groups; patients in the small dose group received isobaric bupivacaine 4.5 mg, while those in the large dose group received hyperbaric bupivacaine 12 mg. Patients in both groups received fentanyl 50 mcg and morphine 200 mcg.
Automated, non-invasive blood pressure measurements were taken before injection of study medication, every minute for 15 minutes after injection, then every 3 minutes until the end of surgery. The sensory and motor block progression was assessed with a blunt pin-prick and Bromage score, respectively. Apgar scores, neonatal weight, and acid-base data from umbilical artery and vein were recorded. Frequency of hypotension, nausea, vomiting, intraoperative discomfort, and preference for present technique among those undergoing repeat CS were assessed using the Chi-square statistic. There were no differences in any of the hemodynamic variables between dose groups. The depth of motor block and the time required for resolution of the motor block were significantly less in the 4.5 mg group. Satisfaction with intraoperative anesthesia was high in both groups. Correlations between visual analogue scale recovery (VASR) and quality of recovery (QoR) scores at similar times were statistically significant suggesting convergent validity between these measures of recovery.
The primary results of this study suggest that decreasing the bupivacaine dose from 12 mg to 4.5 mg does not lead to reductions in hypotension and vasopressor use during CS. Factors influencing distribution of sensory block during spinal anesthesia include baricity, rate of injection and volume of injection of the solutions employed. Patient and surgeon satisfaction with 4.5 mg bupivacaine anesthesia was comparable to that noted with 12 mg doses. It is important to note that requests for supplemental analgesia were significantly reduced only in those patients receiving 40 mcg doses of fentanyl or greater. The QoR scores reported 6 hours postoperatively were similar to those noted following minor surgery suggesting opioid-related side effects did not significantly impair recovery.
In summary, the results of this study suggest that 4.5 and 12 mg doses of bupivacaine administered with fentanyl 50 mcg and morphine 200 mcg intrathecally provide similar anesthesia for CS. Marked reduction in depth and duration of motor block was apparent in the lower dose group. Further research is required to determine the dose of intrathecal fentanyl required to provide an adequate compromise between intraoperative analgesia and side effects.
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