Use of hyperbaric versus isobaric bupivacaine for spinal anaesthesia for caesarean section

Bupivacaine is an amide local anaesthetic used in hyperbaric and isobaric forms. These are administered intrathecally into the spine to provide regional anaesthesia for caesarean section. Several trials have compared hyperbaric and isobaric bupivacaine but none have conclusively shown benefit of either.

This systematic review aimed to summarize the effectiveness and safety of hyperbaric versus isobaric bupivacaine in providing anaesthesia for caesarean section. We considered the adequacy of anaesthesia for completion of caesarean section and the need for interventions to treat complications.

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 4), MEDLINE (January 1966 to May 2011) and EMBASE (January 1980 to May 2011). We handsearched journals. We imposed no language restriction. We reran our search in the above databases from January 2011 to January 2013; the studies are awaiting assessment and will be dealt with when we update the review.

We included all randomized controlled trials involving parturients undergoing spinal anaesthesia for elective caesarean section that compared the use of hyperbaric with isobaric bupivacaine.

Two authors independently extracted the data. The data that were extracted included the number of events and the sample sizes in both the intervention and control groups. For continuous outcomes, we extracted mean and standard deviation.We reported odds ratios and risk ratios (RR) for binary outcomes and mean differences (MD) for continuous outcomes.

We included six studies with a total of 394 patients in this review. Anaesthesia performed with hyperbaric bupivacaine appeared to be less likely to need conversion to general anaesthesia (two studies, 158 patients included in meta-analysis; RR 0.17, 95% confidence interval (CI) 0.03 to 0.94). There was no difference in the need for supplemental analgesics. The time till sensory block to the T4 level was also shorter with hyperbaric bupivacaine (two studies, 126 patients; MD -1.06 minutes, 95% CI -1.80 to -0.31). There were no other significant differences between the two anaesthetics.

The criteria for conversion to general anaesthesia should be clearly defined in future research. This review found that intrathecal hyperbaric bupivacaine had a more rapid onset of sensory blockade at the T4 level than isobaric bupivacaine. It may also result in less need for conversion to general anaesthesia and supplemental analgesia. However, due to the rarity of this outcome, variability in the dose, use of adjuvant drugs and differences in the technique used for regional anaesthesia the evidence is weak. Any apparent advantage of hyperbaric bupivacaine needs to be confirmed in larger randomized trials. There were no differences in the adverse effects studied.