• Jennifer Jouwena, Delphine Verbeke, Andre M De Wolf, Arne Neyrinck, and HendrickxJan F AJFA0000-0002-1360-9662Department of Basic and Applied Medical Sciences, Ghent University, Ghent, Belgium; Department of Anesthesiology, UZLeuven, Leuven, Belgium; Department of Cardiovascular Sciences, KULeuven, Leuven, Belgium; Department.
• Department of Anesthesiology, Onze Lieve Vrouw Hospital, Aalst, Belgium; Department of Anesthesiology, UZLeuven, Leuven, Belgium; Department of Cardiovascular Sciences, KULeuven, Leuven, Belgium.
• Anesthesiology. 2024 Mar 1; 140 (3): 450462450-462.

BackgroundCarbon dioxide absorbers allow the use of fresh gas flow below minute ventilation (V˙E). Models are developed and tested in vitro to quantify their performance with variable carbon dioxide load (V˙CO2), fresh gas flow, V˙E, end-tidal carbon dioxide (ETco2) fraction, and the type of workstation used.MethodsFirst principles are used to derive a linear relationship between fresh gas flow and fractional canister usage or FCU0.5 (the reciprocal of the time for the inspiratory carbon dioxide fraction to reach 0.5%). This forms the basis for two basic models in which V˙E was measured by spirometry or calculated. These models were extended by multiplying V˙E with an empirical workstation factor. To validate the four models, two hypotheses were tested. To test whether the FCU0.5 intercept varied proportionally with V˙CO2 and was independent of V˙E, FCU was measured for 10 canisters tested with a fixed 0.3 l/min fresh gas flow and a range of V˙CO2 while V˙E was either constant or adjusted to maintain ETco2 fraction. A t test was used to compare the two groups. To confirm whether a change in V˙CO2 accompanied by a change in V˙E to maintain ETco2 fraction would shift the linear fresh gas flow-FCU0.5 relationship in a parallel manner, 19 canisters were tested with different combinations of V˙CO2 and fresh gas flow. These measured FCU values were compared to those predicted by the four models using Varvel's performance criteria.ResultsWith 0.3 l/min fresh gas flow, FCU0.5 was proportional with V˙CO2 and independent of whether V˙E was adjusted to maintain ETco2 fraction or not (P = 0.962). The hypothesized parallel shift of the fresh gas flow-FCU0.5 relationship was confirmed. Both extended models are good candidate models.ConclusionsThe models predict prepacked canister performance in vitro over the range of V˙E, fresh gas flow, and V˙CO2 likely to be encountered in routine clinical practice. In vivo validation is still needed.Copyright © 2023 American Society of Anesthesiologists. All Rights Reserved.

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