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LETTERS TO THE EDITOR

Arterial Hypotension During Induction of Anesthesia May Not Be a Risk Factor for Postoperative Nausea and Vomiting

Department of Anesthesiology, University of Würzburg, Würzburg, Germany Department of Anesthesiology, University of Kiel, Kiel, Germany Department of Anesthesiology, Klinikum Ludwigshafen, Ludwigshafen, Germany

To the Editor:

In the recently published report by Pusch et al. (1), the investigators concluded that a marked systolic blood pressure decrease >35% from preanesthetic baseline occurring during induction of anesthesia is associated with an increased incidence of postoperative nausea and vomiting (PONV). However, the association may be far weaker than the presented analysis suggests. Table 1 demonstrates that there is consistent bias with respect to proven risk factors for PONV between the hypotensive group (n = 54) and the cohort of patients classified as being normotensive (n = 246), namely the duration of anesthesia (114 min vs 97 min), nonsmokers (74% vs 60%), postoperative opioid administration (72% vs 58%), history of motion sickness (33% vs 26%) and PONV (44% vs 25%), the latter even being significantly different. Unfortunately the authors did not correct for these risk factors in their analysis. A logistic regression analysis that adjusts for the different "risk profiles" considering established risk scores (2) or potential confounding factors would have either provided a more convincing message or confirmed that we can rely on the already established risk factors for PONV that should be reported as minimal standard in trials on PONV (3).

References

1. Pusch F, Berger A, Wildling E, et al. The effects of systolic arterial blood pressure variations on postoperative nausea and vomiting. Anesth Analg 2002; 94: 1652–5.[Abstract/Free Full Text]
2. Apfel CC, Kranke P, Eberhart LH, et al. Comparison of predictive models for postoperative nausea and vomiting. Br J Anaesth 2002; 88: 234–40.[Abstract/Free Full Text]
3. Apfel CC, Eberhart LHJ, Kranke P, Rüsch D. Recommendations for randomized controlled trials to prevent or treat postoperative nausea and vomiting. Anaesthesiol Intensivmed 2002; 43: 69–74.

Response

Department of Anesthesiology and General Intensive Care, University of Vienna, Vienna, Austria Department of Anesthesiology and General Intensive Care, Hospital of Korneuburg, Korneuburg, Austria

In Response:

Unfortunately, Kranke et al. misinterpreted the aim of our study and stated erroneously in consequence that "Table 1 demonstrates that there is consistent bias with respect to proven risk factors for PONV between the "hypotensive group" and "non-hypotensive" patients". . . and "unfortunately the authors did not correct for these risk factors in their analysis." Our research group is not interested in the detection of independent risk factors or the construction of some risk models. We try to find pathophysiological interactions between the occurrence of PONV, hemodynamic variables, the vestibular, and the autonomic nervous system. Results of our study should help to improve our daily anesthesia practice. Proven independent risk factors like female gender or historical PONV does not influence us by changing our anesthesiologic approach in gynecological surgery. Between group differences in our Table 1 should demonstrate that a systolic blood pressure decrease of >35% is not an independent risk factor. Furthermore, in our introduction, we reported that the aim of our study was to determine the association between a marked decrease in systolic blood pressure from the preanesthetic baseline during the introduction as well as during the maintenance of general anesthesia and the incidence of risk factors of PONV. We concluded: "Whether the blood pressure decrease triggers PONV or PONV symptoms influence hemodynamic variables is not clear." We never suggested that a systolic blood pressure decrease during any phase of anesthesia is a proven independent risk factor for PONV. We agree with Kranke et al. that between the occurrence of PONV and a systolic blood pressure decrease of >35% during anesthesia induction only a weak association was found by us.

I hope that a rereading of our publication will clear up misunderstandings.

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