To the Editor:—

We wish to comment about the article by Greif et al.  1The authors correctly identify the many anesthetic and nonanesthetic factors that affect the incidence of postoperative nausea and vomiting (PONV). The possible beneficial effect of supplemental oxygen in preventing PONV would be of great value because antiemetic therapy, as noted by the authors, is costly and is associated with complications. However, the interpretation of the results is confused by lack of attention to specific details.

Studies of PONV demand the use of a standardized antiemetic regime 2(a variety of antiemetic agents was used in this study). This is an obvious source of bias between the groups. We know that there is a difference in PONV outcome among individual anesthetists, 3and antiemetic choice is a possible factor in this difference. If rescue therapy were at physician discretion, then the study should have ended when rescue therapy was necessary.

Pain is known to be an influence on PONV. 4Postoperative pain is significant after laparotomy. In this study, we were provided with information regarding postoperative opiate requirement, which was similar between the groups. Opiate requirement is too crude a means of assessing postoperative pain between the groups, without pain scores or information regarding other analgesics received.

Grief R, Laciny S, Rapf B, Hickle R, Sessler D: Supplemental oxygen reduces the incidence of postoperative nausea and vomiting. A nesthesiology 1999; 91:1246–52
Korttila K: The study of postoperative nausea and vomiting. Br J Anaesth 1992; 69(suppl 1):20—3
Hovorka J, Korttila K, Erkola O: Nitrous oxide does not increase nausea and vomiting following gynaecological laparoscopy. Can J Anaesth 1989; 36:145–8
Andersen R, Krohg K: Pain as a major cause of postoperative nausea. Can Anesthetists Soc J 1976; 23:366–9