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To the Editor,
We read Drs Barak and Yussim’s comments with great interest.1 They raise the hypothesis that the end-tidal CO2 (ETCO2) variation observed following passive leg raising (PLR) is caused by a variation in alveolar dead space instead of an increase in cardiac output. Even if this hypothesis and argument are based on sound physiological principles, we cannot agree with their conclusions.
When alveolar ventilation is kept constant (assuming stable carbon dioxide production), simultaneous ETCO2 and cardiac output variations have been well described in the literature in multiple clinical situations.2,3 Also, in our study, cardiac output and ETCO2 measurements were performed simultaneously. Fluid responders had a significant change in their cardiac output and ETCO2 following the PLR maneuver, which is a well-recognized method to assess fluid responsiveness.4,5 Therefore, in our study, we think that the ETCO2 variation represents real cardiac output variation.
References
Barak M, Yussim E. Assessment of fluid responsiveness with end-tidal carbon dioxide using a simplified passive leg-raising maneuver: a prospective observational study. Can J Anesth 2017; 64. DOI: 10.1007/s12630-017-0847-7.
Maslow A, Stearns G, Bert A, et al. Monitoring end-tidal carbon dioxide during weaning from cardiopulmonary bypass in patients without significant lung disease. Anesth Analg 2001; 92: 306-13.
Jin X, Weil MH, Tang W, et al. End-tidal carbon dioxide as a noninvasive indicator of cardiac index during circulatory shock. Crit Care Med 2000; 28: 2415-9.
Monnet X, Rienzo M, Osman D, et al. Passive leg raising predicts fluid responsiveness in the critically ill. Crit Care Med 2006; 34: 1402-7.
Monnet X, Teboul JL. Passive leg raising. Intensive Care Med 2008; 34: 659-63.
Conflict of interest
Dr. Denault is a Speaker for Covidien and CAE Healthcare and receives royalties from Taylor and Francis.
Editorial responsibility
This submission was handled by Dr. Philip M. Jones, Associate Editor, Canadian Journal of Anesthesia.
Funding
Montreal Heart Institute Foundation and the Richard I. Kaufman Endowment Fund.
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Toupin, F., Denault, A.Y. In reply: Assessment of fluid responsiveness with end-tidal carbon dioxide using a simplified passive leg-raising maneuver: a prospective observational study. Can J Anesth/J Can Anesth 64, 547 (2017). https://doi.org/10.1007/s12630-017-0848-6
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DOI: https://doi.org/10.1007/s12630-017-0848-6