[Risk factors for nausea and vomiting after general anesthesia: fictions and facts]

Numerous factors have been claimed to influence postoperative nausea and vomiting (PONV). A critical review of the literature reveals, that strong evidence based on original double-blind, randomized, controlled trials or their meta-analyses is only available for very few risk factors. For most other factors, although mentioned in narrative reviews, there is insufficient evidence. Sufficient evidence on original data or meta-analyses is present for female gender, a history of PONV or motion sickness, non-smoking-status, young age, volatile anaesthetics, nitrous oxide and postoperative opioids. Factors with conflicting results are the menstrual cycle, hypnotics for induction, mask ventilation and nasogastric tube, the experience of the anaesthetist, muscle relaxants and their antagonists and laparoscopic procedures. Insufficient evidence is present for the other types of operation, psychological factors including anxiety and pain. No evidence due to lack of data applies to postoperative movement, hemodynamic stability, hypercarbia and acid-base-shifts. For adipositas++ there is not only a lack of evidence for an effect but evidence for a lack of effect based on several multivariate analyses. In conclusion, we have developed the following simplified view: PONV is mainly caused by opioids and volatile anaesthetics when applied to susceptible patients (females, non-smoker, positive history of previous sickness).