We thank Drs. Neustein, Groudine, and Awad for their interest in our work on the effect of transcutaneous electrical stimulation of the P6 acupuncture point while neuromuscular blockade monitoring,1and would like to respond to their major comments about neuromuscular reversal and the use of stimulation modes as well as the potential confounder of nonsmoking as a trigger for postoperative nausea and vomiting (PONV).

Dr. Neustein notices a relatively high incidence of PONV in our study. We did a study in women using volatile anesthetics, which are well known PONV triggers.2We strongly agree that the reduction in nausea by the P6 stimulation plays an important role in a prophylactic multimodal antiemetic approach as proposed by Scuderi et al.  3,4 

All patients were reversed and extubated based on clinical signs of full recovery as is daily clinical practice at the hospital. No problems were found in any of the studied patients after extubation. The intention of the study was to reduce PONV by continuous monitoring of neuromuscular blockade over the P6 acupuncture point using single-twitch response during surgery. We thank Dr. Groudine for the comment that accelerography stimulated over the median nerve has not been extensively studied, and for noting that double-burst and train-of-four stimulation are more reliable in detecting residual blockade. For patient safety reasons, we also recommend changing from the single-twitch mode to one of the modes mentioned above, which is easy to do without harming the patient during recovery from neuromuscular blockade.

Conversion to open procedure occurred in five patients of the control group and in seven patients of the P6-stimulation group (P = 0.77, chi-square). We had only two problems with the accelerograph, and both were in the control group (ulnar nerve stimulation). The battery had to be replaced in both cases to continue the electrical stimulation.

Because we were concerned about trigger factors for PONV, we recorded risk factors that were evenly distributed between both groups; only smoking showed a higher difference of 11%. Dr. Awad is right that stratification would have omitted that, but stratifying for all of the major risk factors (PONV history, motion sickness, and smoking) would have complicated a rather simple study design. We assumed that our relatively large sample size would distribute all confounders equally in both groups. To assure that smoking was not a potential confounder affecting the outcome, we performed a multiple logistic regression analysis (including PONV history, motion sickness, postoperative opioid therapy, and smoking),5which revealed only the different stimulation side as a significant factor (P =0.028). Because no significant difference was found for the demographic and PONV-related data, we did not include that analysis in the original manuscript.

In summary, we would like to see further studies in this area using a multimodal prophylactic approach including acupuncture to reduce PONV. At the emergence from anesthesia, meticulous attention should be applied to avoid residuals of neuromuscular blockade using our approach. Smoking was evenly distributed between the ulnar nerve stimulation group and the P6-acupuncture stimulation group.

*University Hospital Bern, Bern, Switzerland, and Donauspital/SMZO, Vienna, Austria. robert.greif@insel.ch

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Apfel CC, Roewer N, Korttila K: How to study postoperative nausea and vomiting. Acta Anaesthesiol Scand 2002; 46:921–8