Phenylephrine Infusion and Nausea-Vomiting under Obstetric Spinal Anesthesia: Around and Beyond Hypotension!

Sir, The randomized controlled trial (RCT) by Bedi et al.[1] is a welcome addition to the existing literature on intraoperative nausea-vomiting (IONV) in obstetrics under spinal anesthesia. Having compared 50 µg/min infusion with 25 µg/min phenylephrine infusion, that is, P50 versus P25, the RCT outlined a significantly lesser number of IONV episodes in the P50 group when compared to the P25 and the control group (0.09 ± 0.29, 0.23 ± 0.42, and 0.55 ± 0.84, respectively, with P < 0.05).[1] Meanwhile, the primary finding was also associated with significant inter-group differences in the rescue mephentermine requirement for treating hypotension; the comparison of the actual number of patients experiencing IONV in the three groups did not achieve statistical significance.[1] Motivated by an interesting set of observations, we wish to present our reflections on the corresponding research. As far as hypotension following spinal anesthesia for cesarean section (CS) is concerned, Klöhr et al.[2] adequately emphasize how the lack of a universally acceptable definition can be counterproductive for research endeavors in the subject. That said, one remains intrigued with the Bedi et al.[1] choice of defining hypotension as a fall in mean arterial pressure of greater than 25%, particularly when the literature search by Klöhr et al.[2] delineates the threshold of decline below 80% of the baseline as a commonly chosen cut-off for connoting hypotension during CS under spinal. More importantly, the simultaneous inclusion of elective and semi-elective CS who happened to be differently fasted in the preoperative period introduces a component of clinical heterogeneity in the index RCT, which again could have been relevant from the purview of intraoperative hypotension.[1,3] Moreover, there can be a multitude of factors (beyond hypotension) contributing to IONV in general and specific to these circumstances. Bedi et al.[1] do acknowledge some of the relevant factors such as the dose of uterotonics, when they discuss a study by George et al.[4] comparing phenylephrine infusion with bolus for IONV prevention in obese parturients undergoing CS. Of note, George et al.[4] additionally catered to the general patient predisposition, in the form of a history of motion sickness or, for that matter, preexisting smoking status. They concurrently highlighted the need to report the indication and the incidence of the use of antiemetics while contemplating a study on IONV.[4] It was IONV unrelated to hypotension (again defined as <80% of the baseline) that was treated with ondansetron 4 mg intravenous (IV) in their study, with the documentation of the requirement for intraoperative rescue antiemetics.[4] Bedi et al.[1] sufficing to declare nausea-vomiting being treated with ondansetron 4 mg IV, is indeed difficult to overlook when attempting to comprehend a research frame dealing with hypotension, IONV, and drug therapies, pretty much all at the same time. Finally, it is believed that amidst a rather intertwined set of investigator-reported and unreported outcomes, quality improvement initiatives in obstetrics would be better served with a patient-centered approach, including outcomes like self-reported maternal satisfaction.[4,5] Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.