Minimal Effective Weight-based Dosing of Ondansetron to Reduce Hypotension in Cesarean Section Under Spinal Anesthesia

A Randomized Controlled Superiority Trial

Maliwan Oofuvong; Thitikan Kunapaisal; Orarat Karnjanawanichkul; Nussara Dilokrattanaphijit; Jaranya Leeratiwong


BMC Anesthesiol. 2018;18(105) 

In This Article


Spinal anesthesia is now the technique of choice for women undergoing cesarean section. However, hypotension is a common problem after surgery with reported incidences varying from 53 to 85% worldwide.[1,2] The Bezold–Jarisch reflex, which occurs after spinal anesthesia, induces vasodilatation and decreases venous return which results in bradycardia and hypotension.[3] A systematic review reported that neither intravenous fluid preload nor vasoconstriction given before spinal anesthesia is effective in preventing hypotension.[4] One factor known to influence the Bezold–Jarisch reflex is serotonin. Ondansetron is a serotonin receptor blocker. It decreases serotonin induced by the Bezold–Jarisch reflex by suppressing venodilatation.[5] Two studies found that ondansetron given at a dose of 8 mg before spinal anesthesia could reduce hypotension by 86% in general surgery[6] and by 33% in cesarean section.[7] However, another study showed that the same dose of ondansetron could not significantly reduce hypotension in pregnant women.[8] Fattahi et al.[9] showed that the mean arterial pressure after spinal anesthesia in patients who had a cesarean section was significantly higher in women given ondansetron 0.15 mg/kg compared to the control group. Sahoo et al.[10] reported the lower dose of ondansetron (4 mg) compared to control group could reduce hypotension in parturients in cesarean section. In terms of safety, Pasternak et al.[11] and Einarson et al.[12] showed that ondansetron administered in over 600,000 pregnant women had no significant effect on the newborn.

All of these studies used a fixed dose of ondansetron. To our knowledge, the optimal dose based on the patient's weight has never been investigated. Using a weight-based dose of ondansetron might maximize its effect and prevent suboptimal dose or overdose in some parturients since they have a larger volume of distribution compared to normal patients. Hence, this study aims to determine the minimal weight-based dose of ondansetron required to reduce hypotension after spinal anesthesia in women undergoing cesarean section.