Ondansetron and Spinal Anesthesia-Associated Hypotension: Using Risk Difference to Assess Therapeutic Effectiveness
Abstract Number: SA-27
Abstract Type: Original Research
Ondansetron, an agent frequently used for nausea/vomiting prophylaxis and treatment, has been shown to reduce spinal anesthesia-related hypotension, bradycardia, nausea, and vomiting in obstetric and non-obstetric patients(1). However, given the potential adverse effects of antepartum administration of ondansetron, we questioned the clinical relevance of these findings.
We included data from ten randomized controlled trials identified in a recent meta-analysis(1) that evaluated risk ratios in treatment and control groups. Inclusion/exclusion criteria were as described(1). We calculated risk differences with 95% confidence intervals (CIs).
Six of the ten randomized trials compared ondansetron with control in obstetric patients. Five of six trials revealed at least a 20% risk difference between ondansetron and control groups (Figure), such that ondansetron prevented hypotension. The overall risk difference of ondansetron administration vs. placebo was -21.54 (95% CI -21.63 to -21.45).
For non-obstetric and obstetric surgery (10 studies), the overall risk difference for spinal anesthesia-related nausea with ondansetron administration vs. placebo was -21.62 (95% CI -21.7 to -21.54).
Estimates of risk difference provide more clinically relevant information than risk ratio(2). Using risk difference to analyze data from ten randomized controlled trials, we found that patients in the ondansetron group had approximately 22 fewer cases of hypotension or nausea per 100 patients when compared with control group. Thus, ondansetron reduces the incidence of spinal anesthesia-related hypotension in obstetric patients in a clinically significant way. However, practitioners should consider the risks of antenatal administration, including QT prolongation and potential effects on the fetus, when deciding whether to use prophylactic ondansetron.
1. Gao, L., G. Zheng, J Han, Y Wang, and J Zheng. "Effects of Prophylactic Ondansetron on Spinal Anesthesia-induced Hypotension: A Meta-analysis." International Journal of Obstetric Anesthesia 24.4 (2015): 335-43.
2. Naylor C, Chen E, and Strauss B. Measured enthusiasm: does the method of reporting trial results alter perceptions of therapeutic effectiveness? Ann Intern Med. 1992;117(11): 916-921.