Morphine sparing with droperidol in patient-controlled analgesia

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To the Editor: We read with interest the study by Lo et al [1] showing a morphine-sparing effect of droperidol when used in combination with patient-controlled analgesia. This analgesic property of droperidol is relatively unknown and its mechanism unclear, although it has already been observed in patients undergoing rotator-cuff repair surgery [2]. The results of both studies suggest that droperidol might be administered systematically to any patient undergoing general anesthesia and requesting patient-controlled analgesia with morphine not only to lower the incidence of postoperative nausea and vomiting, but also to diminish the incidence of other side effects of morphine, such as respiratory depression. However, we have some concerns regarding this study. Although, as stated by the authors, no other opioids or nonsteroidal anti-inflammatory drugs were permitted for three days after the operation, were any other analgesic agents administered, such as paracetamol or nefopam? If so, these agents, which are frequently used in balanced postoperative analgesia, might have greatly influenced the authors’ study results. Besides, a study comparing the morphine-sparing effect of droperidol, when all common analgesic agents are used in combination, would be of great interest to evaluate its actual clinical impact in multimodal postoperative analgesia. Moreover, since no information about the normality of the data distribution is given, why did the authors use a combination of parametric (one-way analysis of variance) and nonparametric tests to compare their data? The use of an inadequate test, if any, might have introduced bias into the study. Another bias in this study might have occurred from the statistical tests used: because different measurements were performed during time, the data should have been compared by two-way analysis of variance, or, although less appropriate, the P value should have been corrected according to the Bonferroni method [3]. This method is to be used when making multiple comparisons because the tests are not independent, as they are all performed on the same subject. Therefore, the likelihood of accepting false-positive conclusions (type 1 error) increases, which might have occurred in the Lo et al study. In conclusion, although the assessment of morphinesparing effects of droperidol would be of great interest in clinical practice, the results of the Lo et al study might be interpreted with caution, and further studies are needed before recommending the use of droperidol as an analgesic agent. Emmanuel Boselli MD (Anesthesiologist and Intensivist) Bernard Allaouchiche MD, PhD (Anesthesiologist and Intensivist) Department of Anesthesiology and Intensive Care Edouard Herriot Hospital Lyon 69003, France