Caffeine for the prevention of postoperative nausea and vomiting - Reply.

Sir,

I read with pleasure the letter to the editor regarding our paper entitled “Caffeine for the prevention of postoperative nausea and vomiting (PONV),[1]” which was published in your journal. While our paper represents a first ever prospective, randomized, double-blind, placebo-controlled study examining the effects of intravenous caffeine on PONV rates and other side-effects of general anesthesia, more studies are needed to potentially uncover any positive effects of caffeine on postoperative recovery. In our study, we attempted to account for as many PONV risk factors as possible, and control for them appropriately. For example, we controlled for four major risk factors such as female gender, smoking status, prior history of PONV, and perioperative opioid use.[2] In addition, we controlled for baseline caffeine consumption, duration of anesthesia, and type of surgery all known to potentially influence study results.[3] In addition, we made every attempt to standardize induction and maintenance of anesthesia among different practitioners. All patients received intravenous induction with propofol, and anesthesia was maintained with an inhalational agent. Overall, this was a well-controlled study. In fact, the most recent PONV guidelines from the Society for Ambulatory Anesthesia published a list of overall positive risk factors, which were all acknowledged and controlled for in our study.[4] As far as intravenous fluid administration is concerned, we agree that there is some evidence that high amount of intravenous fluid administration can reduce postoperative emesis.[56] Our ambulatory anesthesia practitioners follow internally developed ambulatory anesthetic protocols that allow little room for variation. In our study, most patients would have received similar amounts of fluid as these cases were generally short and similar in duration; similarly, although we did not report the intraoperative dose of the inhalational agent(s), we believe it would have had a minor effect on the reported outcomes. In summary, our pilot study explores the possibility of using a different drug modality (intravenous caffeine) for the prevention of PONV and other anesthetic side-effects. Larger prospective studies are warranted to further explore this drug's potential.