Antiemetic Prophylaxis for Office-based Surgery: Methodologic Concerns

To the Editor:—

We read with great interest the article by Tang et al.  1regarding the efficacy of adding 5-HT³antagonists to a combination of droperidol and dexamethasone in the prevention of postoperative nausea and vomiting (PONV) following office-based surgery. It would seem, however, that the validity of the conclusion should be viewed with some caution because of the following methodologic concerns.

First, the occurrence of PONV after discharge was assessed by a telephone interview 24 h after patient discharge from the private office-based surgical center. This would certainly introduce the potential for recall bias , particularly with regard to the number of episodes of nausea at home. It is also conceivable that the observed average age of the study patients would make this type of bias more likely to occur than not. The risk of recall bias would have been avoided had patients been instructed to keep a diary of their postoperative adverse events.

Second, despite the above-mentioned limitation, the authors reported an overall incidence of PONV of 18% in the control group, 11% in the dolasetron group, and 13% in the ondansetron group (see table 3 of the article). 1Given the number of study participants, an α of 0.05, and the observed results, the study had a power of 15%, at best, to detect differences in the incidence of PONV among the study groups. Although one could argue that the observed 39% reduction in PONV in patients who received dolasetron (compared with those who received saline) was clinically relevant, 396 patients would have had to be recruited per group to make this difference statistically significant, which is clearly neither feasible nor practical.

Finally, although we acknowledge the current contribution of Tang et al.  to the literature on the role of prophylactic antiemetic therapy in office-based anesthesia, we believe that the posed question of whether the addition of a 5-HT³receptor antagonist to a droperidol-dexamethasone combination reduces the occurrence of PONV after office-based surgery remains to be answered.