α-2 agonists vs. fentanyl as adjuvants for spinal anesthesia in elective cesarean section: a meta-analysis

INTRODUCTION: Elective cesarean section (CS) is usually performed using spinal anesthesia (SA), which requires the use of local anesthetic (LA) agents, commonly combined with adjuvant drugs. We performed a systematic review and meta-analysis aimed at studying the advantages of α-2 agonists as compared to fentanyl during SA for CS. EVIDENCE ACQUISITION: We screened PubMed and EMBASE for randomized controlled trials (RCTs). We calculated the mean difference (MD) for continuous outcomes, and the relative risk for dichotomous outcomes, using a random-effect model with 95% confidence interval (CI). We performed a Trial Sequential Analysis (TSA) assuming an alpha risk of 5%. The primary outcome was the time to first rescue analgesia. EVIDENCE SYNTHESIS: Eight RCTs were included. Time to first rescue analgesia was significantly longer when the α-2 agonists were used (MD 85.9 min [95% CI: 23.8, 147.9]; P=0.007). Duration of sensory block was also longer in the α-2 group (MD 40.5 [95% CI: 20.21,60.7]; P<0.0001), while no differences were found for onset of sensory block and onset and duration of motor block. Rates of shivering and nausea or vomiting were significantly lower in the α-2 agonist group, while risk of hypotension or respiratory depression were not different. The TSA on the primary outcome suggests the need of further research before drawing conclusions. CONCLUSIONS: α2-agonists seem to increase the time to first rescue analgesia and to prolong the duration of sensory block when used as adjuvants to LA in CS patients compared to fentanyl. Also, α2-agonists may reduce the incidence of shivering and nausea or vomiting.