To determine the strength of evidence for each research article, we used the Johns Hopkins Nursing Evidence-based Practice: Levels of Evidence and Quality Guide.[31] We found 24 studies deemed level I evidence by the evidence and quality guide. Level I is an experiment-based study such as an RCT, experimental study, or systematic review of RCTs with or without a meta-analysis. [31] Of the 24 studies, 12 were given grade B, and 12 were given grade A.
 

          Eighteen studies concluded that the preemptive use of ondansetron may help to mitigate hypotension after SABs or significantly reduce its severity.[3, 4, 6–20, 25, 32] For participants in many of the studies, fewer vasoactive drugs were required to treat episodes of hypotension occurring after SAB.[6, 8–13, 15–18, 20, 23, 25, 29] However, gaps and weaknesses exist in current evidence, which limits any definitive conclusions that may be drawn. More studies, including larger RCTs targeting specific patient populations (ie, elderly and parturients), could significantly strengthen current evidence.