Measurement of Dead Space During Anesthesia

Abstract

To the Editor Badal et al.1 were neither precise nor consistent in the terminology and abbreviations used as part of the article describing measurements of dead space during anesthesia. They state that Bohr's equation was used to calculate alveolar dead space when, in fact, Enghoff's modification of Bohr's original equation (VD/VT = PaCO2 − PECO2/PaCO2) measuring physiologic dead space (which contains alveolar dead space and airway-anatomic dead space) was used.2 Because such imprecise terminology (apparatus, anatomic, pulmonary, alveolar, physiologic) and abbreviations (VDS/VT, VDC, VDc, VD) appear throughout the text, figures, and table, it is difficult to judge the results unless one is very familiar with the subject. A second point concerns study design and results. Referencing their previous work,3 the authors acknowledge the inherent limitations of their methods providing “an accurate approximation” of mixed expired PCO2. Therefore, a randomized study with a larger, more uniform population combined with measurement of true alveolar dead space using standard mainstream volumetric capnography would provide more insights into the real clinical value of the proposed method. Third, the method is presented as simple and inexpensive. However, it requires an additional capnograph as well as significant modification of the anesthesia circuit with the potential of leakage at the entrance of the sample line into the ventilator bellows. Yves P. S. Moens, DVM Division of Anaesthesiology and perioperative Intensive Care University of Veterinary Medicine Vienna, Austria [email protected] Gerardo Tusman, MD Department of Anaesthesiology Hospital Privado de Comunidad Mar del Plata, Argentina Martina Mosing, DVM Section of Anaesthesiology Vetsuisse Faculty University of Zürich Zürich, Switzerland Stephan Böhm, MD CSEM Centre Suisse d'Electronique et de Microtechnique SA Research Centre for Nanomedicine Landquart, Switzerland