Fifteen RCTs were included in the review (1,004 patients, range 32 to 239) and 12 of these were included in the meta-analysis (693 patients). Three trials scored the maximum of 5 on the Jadad scale, five scored 4, five scored 3 and two scored 2.
Primary outcomes: Compared with conventional dose bupivacaine, low dose bupivacaine was associated with a significantly higher risk of analgesic supplementation during caesarean delivery (RR 3.76, 95% CI 2.38 to 5.92; Ι²=0%; 10 RCTs). The evidence was graded as high quality. The number needed to harm was four patients. There was no evidence of publication bias.
Sensitivity analysis using odds ratios and a fixed-effect model did not alter results. Subgroup analyses and meta-regression that assessed possible confounding variables did not reveal interaction or effect modification. Conversion to general anaesthesia occurred in only one trial that reported two events from 21 patients in the low dose group and none in the conventional dose group.
Secondary outcomes: Compared with conventional dose bupivacaine, low dose bupivacaine was associated with a statistically significantly lower risk of hypotension (RR 0.78, 95% CI 0.65 to 0.93; Ι²=29%; nine RCTs), lower risk of nausea and vomiting (RR 0.71, 95% CI 0.55 to 0.93; Ι²=6%; 11 RCTs). The evidence was graded as moderate quality. Other secondary outcomes could not be calculated.