IT is highly unlikely that any single agent will ever be 100% effective in preventing postoperative nausea and vomiting (PONV); however, multimodal approaches to the management of this vexing problem have shown excellent results.1The failure of monotherapy is not surprising given the complex nature of PONV with the myriad pathways and receptors involved in this physiologic process.2Clinicians continue to search for other techniques and strategies to add to the currently available therapeutic armamentarium. In this issue of Anesthesiology, Arnberger et al. 3have evaluated a simple but surprisingly effective technique that will likely have widespread clinical applicability. The approach studied by Arnberger et al. uses a standard neuromuscular blockade monitor as a means of stimulating the P6 or Neiguan acupuncture point. Their approach is readily adaptable to virtually any patient undergoing a general anesthetic. There is little doubt that electrostimulation of the P6 acupuncture point is effective in reducing PONV4; however, until now, it has been necessary to use proprietary devices,5–7which add not only to the cost of providing care but also add more complexity to the already dizzying array of equipment used in administering general anesthesia. By placing the electrodes over the median nerve at the wrist (i.e. , the P6 point; see the text of the article for the details) the authors were able not only to assess the degree of neuromuscular blockade throughout the anesthetic, but also to provide stimulation of the P6 point for the duration of the anesthetic.
In their study, the authors have chosen to limit the study population to females undergoing gynecologic or abdominal laparoscopic surgery. Although the exclusion of males might be viewed with concern by some, a more homogeneous study population does have merit, particularly in a proof-of-concept study such as this. By its very nature, this study population does have a higher risk of developing symptoms postoperatively, which increases the likelihood of detecting a difference between groups, if in fact a difference does exist. The best data currently available indicate that interventions to limit PONV likely result in a relative risk reduction rather than an absolute risk reduction.8The authors have evaluated nausea and vomiting as categorical data endpoints. Their endpoint of PONV is defined as any episodes of vomiting or retching, or a patient report of any nausea. Data collection was conducted during 24 h, with the time course subdivided into early (0–6 h), late (6–24 h), and overall (0–24 h). In addition to the PONV endpoint, the authors also evaluated both nausea and vomiting as distinct endpoints. It is the separate endpoint (i.e. , nausea vs. vomiting) by time period evaluation that provides the most meaningful information. P6 stimulation resulted in a reduction in nausea from 51% to 33% during the 0–6 h time period. This translates to a relative risk reduction of 35% and number needed to be treated of 5.6. The reduction in emesis did not reach statistical significance during any of the time periods evaluated. Although it is always suspect to ascribe “significance” to data that are not “statistically different,” in all cases the “trend” was toward less vomiting in the P6 group. Nevertheless, this preponderant effect of P6 stimulation on nausea rather than vomiting is in keeping with the findings of other studies.4Because the PONV endpoint chosen by the authors is actually a composite of both nausea and vomiting, it is not surprising that overall PONV reached statistical significance primarily as a result of the impact of P6 stimulation on nausea during the 0–6 h time period. With this caveat in mind, it is still interesting to compare these findings with data for more conventional pharmacologic approaches to the prevention of PONV. Ondansetron, dexamethasone, and droperidol have all been shown to result in an approximate 25% reduction in PONV (using the same definition as in the current study).8The relative risk reduction for overall PONV, as reported here, is 26%!
There are several aspects of this study that are particularly worth noting. First, the authors’ study design used an active control group, not just a “sham” control as has been occasionally used in the past.5,6The active treatment group had the electrodes placed over the median nerve, whereas the control group had the electrodes placed over the ulnar nerve. Both groups had single twitch stimulation at 1 Hz and a constant current of 50 mA applied throughout the duration of the anesthetic. Because electrical stimulation that was delivered was the same for both groups, the only difference was electrode placement. In fact, the point of application was separated by approximately 2 cm. This study design should provide further assurance to anyone who might still be skeptical about the efficacy of P6 stimulation for preventing PONV.
Second, the authors have again confirmed that P6 stimulation is particularly effective in decreasing the incidence of postoperative nausea,4a finding that is of considerable clinical importance given that the majority of currently available pharmacologic agents seem better at reducing the incidence of vomiting, rather than preventing the extremely unpleasant sensation of nausea. This is particularly true for the 5-hydroxytriptamine type 3 antagonist class of drugs, (e.g. , ondansetron, dolasetron, granisetron, and so forth), which have become the mainstay for the management of PONV, both for prevention and for treatment.
Third, and perhaps of particular note, is the fact that P6 stimulation was applied only during the course of the anesthetic. Despite this, there was substantial carryover of efficacy into the postoperative recovery phase. This phenomenon of carryover of efficacy has been observed previously7and has now been reconfirmed. Although it is possible that there may be added benefits in terms of prolongation of efficacy with continued application of P6 stimulation into the recovery phase after general anesthesia,5this study has demonstrated a benefit even when P6 stimulation is only applied during the course of the anesthetic.
The benefit of P6 stimulation demonstrated by Arnberger et al. may seem modest. The impact is mostly on nausea and occurs almost entirely in the first 6 h after surgery; however, this is also the time period during which patients are most likely to experience symptoms. Furthermore, when compared with other interventions, the relative risk reduction is indistinguishable. And, as noted above, conventional pharmacologic agents seem to be better at reducing vomiting rather than nausea. It is likely that the anti-nausea effect of P6 stimulation is additive to pharmacologic therapy for the prevention of PONV.9Because the technique described by Arnberger et al. can be used during virtually any general anesthetic without the need for additional equipment or supplies, it may prove to be an excellent addition to the currently available strategies for limiting or even eliminating PONV.
Department of Anesthesiology, Wake Forest University School of Medicine, Winston-Salem, North Carolina. pscuderi@wfubmc.edu
