To the Editor:—
Dr. Arnberger et al. 1are to be commended for their study showing the efficacy of P6 stimulation in reducing the incidence of nausea and vomiting in female patients undergoing laparoscopic surgery. They stimulated the P6 acupuncture site by altering the technique that most anesthesiologists use to monitor neuromuscular blockade. Instead of placing the electrodes over the ulnar nerve, as is commonly done, they placed them over the median nerve. The median nerve innervates almost all of the muscles in the thenar eminence, including muscles responsible for abduction, flexion, and opposition of the thumb. Stimulating this variety of muscles of the thumb and its effect on interpretation and significance of accelerography data has not been extensively studied.
All patients were reversed identically with 0.4 mg of glycopyrrolate and 2.5 mg of neostigmine until 100% of twitch height was reached, but were extubated based on clinical signs of full recovery. Recovery detected clinically occurs earlier than electromyographic or accelerographic evidence of “full recovery.” If the patients were extubated on the basis of clinical data, many awake patients would have to be stimulated with 50 ma of current for varying degrees of time until their twitch height returned to 100%. If the patients were kept intubated until a return to baseline of twitch height was seen, then the patients would have been anesthetized for varying lengths of time after their surgery and clinical recovery of neuromuscular blockade was observed. No mention is made of what happened to patients who never returned to baseline, had problems with the accelerography measurement, or had significant protocol violations such as conversion to an open procedure or missing data points.
The authors recognized that a single-twitch method of monitoring neuromuscular blockade is not often used. This is because double-burst stimulation and train-of-four stimulation are more sensitive when qualitative methods of assessing residual neuromuscular blockade are employed. It is for these reasons that I must take issue with one of the concluding statements of the authors, that “… electrical stimulation of the P6 acupuncture point with monitoring neuromuscular blockade is simple and easy to perform, without any danger to the patient (emphasis added).” Changing standard neuromuscular monitoring techniques to reduce nausea and vomiting is laudable, as long as it does not diminish the clinician’s ability to detect inadequate reversal. It is well established that incomplete reversal can be a cause of patient morbidity and mortality. Until well done studies are performed to show that this variation of monitoring is as effective in detecting inadequate reversal of neuromuscular blockade, labeling it as completely safe is premature.
Albany Medical Center, Albany New York. groudis@mail.amc.edu
