A modified breathing pattern improves the performance of a continuous capnodynamic method for estimation of effective pulmonary blood flow |
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Authors: | Caroline Hällsjö Sander Thorir Sigmundsson Magnus Hallbäck Fernando Suarez Sipmann Mats Wallin Anders Oldner Håkan Björne |
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Affiliation: | 1.Department of Anaesthesiology, Surgical Services and Intensive Care Medicine,Karolinska University Hospital,Solna,Sweden;2.Department of Physiology and Pharmacology,Karolinska Institutet,Stockholm,Sweden;3.Maquet Critical Care AB,Solna,Sweden;4.Hedenstierna’s Laboratory, Department of Surgical Sciences, Section of Anaesthesiology and Critical Care,Uppsala University,Uppsala,Sweden;5.CIBER de enfermedades respiratorias (CIBERES), Instituto Carlos III,Madrid,Spain |
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Abstract: | In a previous study a new capnodynamic method for estimation of effective pulmonary blood flow (COEPBF) presented a good trending ability but a poor agreement with a reference cardiac output (CO) measurement at high levels of PEEP. In this study we aimed at evaluating the agreement and trending ability of a modified COEPBF algorithm that uses expiratory instead of inspiratory holds during CO and ventilatory manipulations. COEPBF was evaluated in a porcine model at different PEEP levels, tidal volumes and CO manipulations (N = 8). An ultrasonic flow probe placed around the pulmonary trunk was used for CO measurement. We tested the COEPBF algorithm using a modified breathing pattern that introduces cyclic end-expiratory time pauses. The subsequent changes in mean alveolar fraction of carbon dioxide were integrated into a capnodynamic equation and effective pulmonary blood flow, i.e. non-shunted CO, was calculated continuously breath by breath. The overall agreement between COEPBF and the reference method during all interventions was good with bias (limits of agreement) 0.05 (?1.1 to 1.2) L/min and percentage error of 36 %. The overall trending ability as assessed by the four-quadrant and the polar plot methodology was high with a concordance rate of 93 and 94 % respectively. The mean polar angle was 0.4 (95 % CI ?3.7 to 4.5)°. A ventilatory pattern recurrently introducing end-expiratory pauses maintains a good agreement between COEPBF and the reference CO method while preserving its trending ability during CO and ventilatory alterations. |
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