• Richard M Bruce, Douglas C Crockett, Anna Morgan, Minh Cong Tran, Federico Formenti, Phi Anh Phan, and Andrew D Farmery.
• Centre for Human and Applied Physiological Sciences, School of Basic and Medical Sciences, King's College London, London, UK; Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK. Electronic address: richard.bruce@kcl.ac.uk.
• Br J Anaesth. 2019 Aug 1; 123 (2): 126-134.

BackgroundCardiac output (Q˙) monitoring can support the management of high-risk surgical patients, but the pulmonary artery catheterisation required by the current 'gold standard'-bolus thermodilution (Q˙T)-has the potential to cause life-threatening complications. We present a novel noninvasive and fully automated method that uses the inspired sinewave technique to continuously monitor cardiac output (Q˙IST).MethodsOver successive breaths the inspired nitrous oxide (N2O) concentration was forced to oscillate sinusoidally with a fixed mean (4%), amplitude (3%), and period (60 s). Q˙IST was determined in a single-compartment tidal ventilation lung model that used the resulting amplitude/phase of the expired N2O sinewave. The agreement and trending ability of Q˙IST were compared with Q˙T during pharmacologically induced haemodynamic changes, before and after repeated lung lavages, in eight anaesthetised pigs.ResultsBefore lung lavage, changes in Q˙IST and Q˙T from baseline had a mean bias of -0.52 L min-1 (95% confidence interval [CI], -0.41 to -0.63). The concordance between Q˙IST and Q˙T was 92.5% as assessed by four-quadrant analysis, and polar plot analysis revealed a mean angular bias of 5.98° (95% CI, -24.4°-36.3°). After lung lavage, concordance was slightly reduced (89.4%), and the mean angular bias widened to 21.8° (-4.2°, 47.6°). Impaired trending ability correlated with shunt fraction (r=0.79, P<0.05).ConclusionsThe inspired sinewave technique provides continuous and noninvasive monitoring of cardiac output, with a 'marginal-good' trending ability compared with cardiac output based on thermodilution. However, the trending ability can be reduced with increasing shunt fraction, such as in acute lung injury.Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved.

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