Nausea and vomiting during Caesarean section

We read with interest the article by Abouleish et al. concerning ondansetron vs. placebo for the control of nausea and vomiting during Caesarean section under spinal anaesthesia (Anaesthesia 1999; 54: 479–83). We note that prior to delivery, despite the use of a 1-L crystalloid preload and a prophylactic ephedrine infusion, hypotension occurred in 69% of the population, nausea in 48% and vomiting in 39%. We wish to suggest a more likely explanation for the nausea than those proposed by the authors. In our hospital, prospective data on the incidence of hypotension, nausea and vomiting at Caesarean section are collected on all patients as part of routine audit. In the 12-month period April 1998 − March 1999, 724 Caesarean sections were performed under spinal anaesthesia, 709 receiving intrathecal opioids. Following preloading with 750–1500 ml crystalloid, a prophylactic infusion of 30 mg ephedrine is started. We routinely measure blood pressure every minute and use further boluses of 3–6 mg ephedrine if the blood pressure is diminishing. Our incidence of hypotension (using the same definition as the authors) is 23% (95% CI 20–26%). Intra-operative nausea occurs in 5.4% (95% CI 3.7–7.0%) and vomiting in 1.7%. (95% CI 0.7–2.6%). It is well recognised that nausea and vomiting is closely related to maternal hypotension following spinal anaesthesia [1]. It is our observation that nausea, in the absence of hypotension, is effectively treated by an anticholinergic drug. In our series, nausea was precipitated by hypotension in 59% (95% CI 43–75%). However, only 13% (95% CI 8–18%) of women with hypotension experienced nausea. We find that if hypotension is corrected rapidly enough it is rare for nausea to occur. If the blood pressure does drop, simply increasing the speed of the ephedrine infusion acts too slowly, and we need to use ephedrine boluses from a syringe as well. In the study by Abouleish et al., blood pressure was measured at 5-min intervals. It is likely that measuring the blood pressure at this frequency and relying on the ephedrine infusion alone led to delayed detection and treatment of hypotension. This is a more plausible explanation for the high incidence of nausea and vomiting than that suggested in their study. The authors suggest that the ondansetron might be more effective if given prophylactically before the spinal is performed. Our data do not support the routine use of prophylactic anti-emetics at this time. More emphasis should be placed on the rapid recognition and treatment of intra-operative hypotension. Postoperatively, many women have nausea precipitated by movement and we do use prophylactic cyclizine at the end of surgery in women receiving intrathecal diamorphine. At present, the British National Formulary [2] advises the avoidance of ondansetron in pregnancy and breast feeding women due to a lack of data. No such restriction is placed on cyclizine. Furthermore, if all of our 724 women received prophylactic ondansetron, the cost to our hospital would be £3785 compared with £447 for cyclizine. We feel that before using the more expensive drug it should be proven to be more effective than the alternatives.