Twitter: @Dr_H_Collier; @ChrisDarwen3; @ProfAndyS Postoperative nausea and vomiting (PONV) is a common complaint of patients following a general anaesthetic.Without appropriate prophylaxis, around 30% of all patients will report such symptoms, but this can rise to nearly 80% in the presence of certain patient characteristics [1]. Apfel et al.suggested that the four key risk-factors of female sex, nonsmoker status, history of motion sickness and previous PONV were highly predictive [2]. Anaesthetic technique can also influence the rate of PONV. Avoiding general anaesthesia, by using regional techniques [3] can make PONV less likely, but this is not always possible. Further, inhalational agents are more likely to cause PONV than intravenous anaesthesia [4] and depth of anaesthesia also seems to play a role [5]. Avoiding opioids may also help [6], but pain in itself can also cause nausea [7] and the use of opioids may be necessary. We frequently fast patients before surgery, yet hydration status can also be a factor [8]. Most anaesthetists would have reviewed the physiology of nausea and vomiting during their training; the complexity of the systems involved cannot be understated. While the prevention and treatment of PONV are a routine part of anaesthetic practice, local variations in treatment persist; the drugs used, and doses employed, are variable. It is unsurprising that the prevention of PONV is a continuing area of research. There are hundreds of studies investigating PONV and its prevention, making the dissemination and interpretation of evidence challenging. In this issue of Anaesthesia, Weibel et al. publish an abridged version [9] of their recent Cochrane systematic review and network meta-analysis of drugs for preventing postoperative nausea and vomiting [10]. The review tries to bring some clarity to the abundance of published articles and studies on this topic by presenting the first network meta-analysis to compare all available anti-emetic drugs. The scope and scale of the work are truly impressive, with data being drawn from 585 randomised controlled trials (RCT) involving over 97,500 participants to allow comparison of efficacy and safety for single and multiple drug treatments. Frequently used, and widely studied, agents such as dexamethasone, ondansetron and droperidol, are included, as well as a wide range of less commonly given drugs. Six pharmacological classes feature: 5-hydroxytryptamine-3 antagonists; dopamine-2 antagonists; neurokinin-1 receptor antagonists; corticosteroids; antihistamines; and anticholinergics. Forty-four single agents and 51 combinations were assessed. Seventy-two per cent of the included studies investigated one drug and 66% included a placebo control for comparison. There was good quality evidence, expressed as relative risk (95%CI) of

mographic Batch Service (DBS) and Trust clinical databases. Patients who did not proceed to surgery were excluded from the analysis.There were 41 (4.5%) deaths at 90 dy and 133 (14.5%) at 1 yr. For the V E /VCO 2 slope at a cut-off > 42 the risk of 90 dy and 1 yr mortality was OR (95% CI) 4.8 (2.2,10.7), p < 0.0005 and 2.5 (1.3,4.5), p¼0.004 respectively whilst VE/VCO2 AT > 42 was non-significant for mortality at both 90dy and 1yr. For a cut-off > 34 the OR was significant for both V E /VCO 2 AT and V E /VCO 2 slope at both 90dy and 1yr but V E /VCO 2 slope demonstrated a higher OR. At 90dy this was OR (95% CI) 2.8 (1.4,5.4), p¼.002 for V E /VCO 2 AT and OR (95% CI) 4.1 (2.1,7.7) p<0.0005 for V E /VCO 2 slope. V E /VCO 2 slope potentially offers advantages over V E /VCO 2 AT in identifying patients at increased mortality risk following major abdominal surgery. V E /VCO 2 slope over the whole exercise should be measured alongside V E /VCO 2 AT in patients undergoing preoperative CPET.