The maxim ‘primum nihil nocere’ has been a cornerstone of medical tradition ever since Hippocrates' Oath bade us ‘to abstain from doing harm’. This tenet remains central to the practice of medicine and serves as the foundation for all our therapeutic interventions, including peri-operative management of post-operative nausea and vomiting (PONV), once called ‘the big little problem’,1 which is as old as anaesthesia itself. In the absence of prophylaxis, it constitutes an important burden of disease for at least one fifth of all patients undergoing surgery with general anaesthesia, and patients are willing to pay considerable amounts of money from their own pockets for a remedy that works.2,3 The publication each month of clinical trials4–8 underlines the unmet need for an effective cure. Although for a majority of patients, with appropriate combined treatment options, the misery of PONV can be prevented,9,10 a single ‘magic bullet’ has not yet been found. Interest in this problem has made the current pharmacological regimens for the management of PONV among the best tested interventions in the peri-operative setting, with an extremely low potential for side effects. Most clinicians prescribe in the belief that the benefits outweigh the risk and costs, but side effects may occur and may even be life-threatening.11–16
Given these circumstances, with patient welfare foremost, anaesthesiologists may look favourably upon remedies that offer simple and relatively problem free treatment of PONV,17 without adding further to the risk of adverse drug reactions. If acupuncture techniques, which are non-pharmacological, are considered to be an important component in a multimodal approach to pain,18 why should they not be considered in the management of PONV? At the very least, acupuncture could be incorporated within existing regimens to boost the effectiveness of traditional antiemetics.
This approach has been considerably strengthened by a recent Cochrane review of P6 stimulation for the prevention of PONV that included more than 30 trials conducted between 1986 and 2008. It concluded that ‘There was no evidence of difference between P6 acupoint stimulation and antiemetic drugs in the risk of nausea [relative risk (RR) 0.82, 95% confidence interval (CI) 0.60 to 1.13], vomiting (RR 1.01, 95% CI 0.77 to 1.31), or the need for rescue antiemetics (RR 0.82, 95% CI 0.59 to 1.13)’.19 Why has P6 stimulation failed to achieve equal popularity with pharmacological methods, especially in patients at increased risk for PONV?20,21 There might be a number of reasons:
- Many anaesthesiologists are unfamiliar with acupuncture compared to the ease of an intravenous push
- Clear recommendations as to when and how to stimulate at P6, and for how long, have yet to emerge
- Drugs are easier to administer (anaesthesiologists like the intravenous route because they have visual evidence that the drug has been given and the effect is immediate)
- The evidence for acupoint stimulation still fails to convince
Despite the fact that the metaanalysis within the Cochrane review also showed a significant overall reduction of nausea and vomiting compared to a sham control there is still controversy about the efficacy of P6 stimulation.22. Critics of the meta-analysis question the quality of the methodology with regard to blinding, randomisation and number of participants of many included studies. There are also concerns regarding their heterogeneity, given the different methods of stimulation (invasive or non-invasive, electrical versus manual stimulation), varying primary outcomes (nausea, vomiting, rescue medication, short-term or long-term effect), different control groups (invasive or non-invasive sham, medication), different patient groups (high and low risk for PONV, paediatric versus adult patients), different surgical procedures and techniques of anaesthesia (volatile or intravenous). And, last but not least, some high quality studies failed to show an effect like that reported in the study of Majholm and Moller22 published in this issue of the European Journal of Anaesthesiology.
Of all methods of stimulation, acupressure seems to be the easiest to apply and the least invasive. However, Majholm et al.22 do not give support to earlier encouraging acupressure studies, not only because efficacy is lacking, but also because of the surprising number of side effects. However, we must be careful not to generalise and overinterpret the trial results. In the context of the existing evidence, we have to consider that in the Cochrane review, the trials with invasive stimulation seemed to be more successful than those with non-invasive stimulation. The few experimental studies that provide a physiological basis for acupuncture, revealing effects on neurotransmitters, vagal modulation and gastric relaxation, were all performed with invasive acupuncture and not acupressure.23
The high incidence of side effects reported by Majholm et al.22 may be attributed to the special kind of device that was used in this study. Their recommendation that this kind of device should not be used for routine care should receive support. However, their findings should not be generally applied to all acupuncture techniques.
Additional evidence from three recently published studies also deserves to be taken into account. They showed a significant reduction of PONV with electrostimulation of the P6 point.24–26 Arnberger et al.17 in an earlier study showed that a simple nerve stimulator placed at P6 had a significant effect on nausea. Therefore, it would be reasonable to propose that electrostimulation might be more effective than acupressure.
Despite the negative results of the trial published in this issue, an overview of the complete body of work does support some antiemetic effect for acupoint stimulation of P6, though this is subject to qualification. Further reviews should try to evaluate which kind of stimulation is the most effective, has fewest side effects and is easy to apply within routine care. This method should then be compared and/or combined with standard prophylaxis to evaluate its position in the clinical arena. As with every intervention implementation into a busy clinical environment represents a critical hurdle,27,28 trials with a stronger focus on implementation in routine practice may also be needed prior to any further recommendation.
In presenting their well conducted study, Majholm et al.22 have reminded us that although the body of evidence favours the clinical efficacy of acupuncture in the peri-operative period, it seems too early to assume that it is equal to well proven pharmacological agents. While the jury is out, anaesthesiologists should reflect on the recent quotation: ‘What matters more in a doctor than knowledge, is knowledge of one's own limits’.29 Recognising the limit here means that the provision of devices that stimulate acupuncture points like P6 is not a valid argument to withhold routine pharmacological prevention from those suffering with, or at increased risk of, PONV. However, they may complement the PONV armamentarium, perhaps in a multimodal approach, or as an alternative to drugs in patients requiring therapy, but in whom exposure is undesirable, e.g. pregnant or breastfeeding women, and those with contraindications that prevent sufficient pharmacological prevention.
This article was checked and accepted by the Editors, but was not sent for external peer-review.
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