A 2017 meta-analysis by Tubog et al [7] examining 13 RCTs, did not report on the variations in vasopressor administration. Mohamed et al [27] found no statistically significant difference in the amount of phenylephrine administered to control and experimental groups (p>0.05). This is consistent with Oofuvong et al [28], who reported no difference in amounts of ephedrine administered to control groups or to two experimental groups that received weight-based doses of ondansetron before SAB. Terkawi et al [26] did not treat hypotension with ephedrine, instead opting only to use phenylephrine. The group that received ondansetron had a mean requirement of 350 mcg of phenylephrine compared to the control group that required a mean dose of 450 mcg of phenylephrine.[26] While the mean dose is reduced, Terkawi et al [26] did not provide the results of statistical analysis for doses of vasopressors, so the statistical significance is unavailable. 

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         Owczuk et al [8] examined geriatric patients receiving SAB and reported that twelve patients in the control group received ephedrine compared to 5 patients in the experimental group who received ondansetron (p=0.049). [8] Similarly, Tatikonda et al [23] showed that 52 patients required ephedrine in a randomized controlled trial. Nineteen patients who received ondansetron before SAB required ephedrine compared to thirty-three patients who did not receive ondansetron. Statistical analysis results in a p-value equal to 0.029.[23]

 
          Marashi et al [9] compared ondansetron 6 mg and 12 mg to placebo in parturients undergoing SAB and reported that only twelve patients in the control group required administration of ephedrine (p=0.04), but did not comment on total doses of ephedrine. Neither of the experimental groups demonstrated significant hypotension or bradycardia, but the published p-value is 0.06.[9]

          More recently, in 2022, Hou et al [6] published a systematic review and meta-analysis titled “Ondansetron reduces the risk of hypotension after spinal anesthesia: a systematic review and meta-analysis,” which is the most exhaustive review of evidence to date. Hou and colleagues [6] found fifteen studies that reported using vasopressors to treat hypotension and, with a 95% confidence interval, found that ondansetron reduces the number of patients requiring vasopressor administration (p < 0.01). These results are consistent with a 2015 meta-analysis by Gao et al [25], which included 10 RCTs and 863 patients. Gao et al [25] reported that the mean difference in ephedrine consumption is -2.35mg (95% CI, p<0.05), and the mean difference in phenylephrine consumption is -31.15mcg (95% CI, p < 0.05).