Noninvasive cardiac output monitoring in a porcine model using the inspired sinewave technique: a proof-of-concept study

Richard M Bruce,Douglas C Crockett,Anna Morgan,Minh Cong Tran,Federico Formenti,Phi Anh Phan,Andrew D Farmery

doi:10.1016/j.bja.2019.02.025

Richard M Bruce, Douglas C Crockett + Show 5 more

Open Access

https://doi.org/10.1016/j.bja.2019.02.025

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Abstract

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.

Highlights

Cardiac output ðQ_ Þ monitoring can support the management of high-risk surgical patients, but the pulmonary artery catheterisation required by the current ‘gold standard’dbolus thermodilution ðQ_ TÞdhas the potential to cause life-threatening complications
BlandeAltman analysis of absolute Q_T and Q_IST values (Fig. 3a) shows a mean bias of 0.79 L minÀ1 (0.51, 1.07) with limits of agreement (LOA) ranging from 5.5 (4.6, 6.4) to e3.9 L minÀ1 (e2.8, e4.7). Despite this wide LOA between data points from all animals, the LOA within each animal is substantially narrower: the LOA for each animal ranged between 0.31 and 0.8 L minÀ1. This is reflected in the BlandeAltman analysis of DQ_IST vs DQ_T (Fig. 3b), where data were normalised to the individual mean baseline value, showing a mean bias of e0.52 (e0.41, e0.63) with LOA ranging from e2.4 (e2, e2.6) to 1.3 (0.9, 2.6), and linear regression analysis reveals an equation of DQ_IST À DQ_T 1⁄4 0:27 Â mean DQ_À 0:56, r1⁄40.48
We showed that a prototype device that utilised the inspired sinewave technique (IST) could be integrated in a breathing circuit of mechanical ventilator, suggesting that it is feasible to use within the perioperative setting

Summary

Introduction

Cardiac output ðQ_ Þ monitoring can support the management of high-risk surgical patients, but the pulmonary artery catheterisation required by the current ‘gold standard’dbolus thermodilution ðQ_ TÞdhas 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 ðQ_ ISTÞ. 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. Results: Before lung lavage, changes in Q_ IST and Q_ T from baseline had a mean bias of e0.52 L minÀ1 (95% confidence interval [CI], e0.41 to e0.63). Concordance was slightly reduced (89.4%), and the mean angular bias widened to 21.8 (e4.2, 47.6). Conclusions: The inspired sinewave technique provides continuous and noninvasive monitoring of cardiac output, with a ‘marginalegood’ trending ability compared with cardiac output based on thermodilution.

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