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

Abstract

Background Cardiac output monitoring can support the management of high-risk surgical patients, but the pulmonary artery catheterisation required by the current ‘gold standard’—bolus thermodilution —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 . Methods Over successive breaths the inspired nitrous oxide (N 2 O) concentration was forced to oscillate sinusoidally with a fixed mean (4%), amplitude (3%), and period (60 s). was determined in a single-compartment tidal ventilation lung model that used the resulting amplitude/phase of the expired N 2 O sinewave. The agreement and trending ability of were compared with during pharmacologically induced haemodynamic changes, before and after repeated lung lavages, in eight anaesthetised pigs. Results Before lung lavage, changes in and from baseline had a mean bias of –0.52 L min −1 (95% confidence interval [CI], –0.41 to –0.63). The concordance between and 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). Conclusions The 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.

Lung simulation to support non-invasive pulmonary blood flow measurement in Acute Respiratory Distress Syndrome in animals

“…In another research, a proof-of-concept study in eight different pigs concluded that IST and thermodilution have good agreement in capturing the trend when the cardiac output changed [7]. Our study fitted into the gap of the absolute value comparison.…”

Simulation-based optimisation to quantify heterogeneity of specific ventilation and perfusion in the lung by the Inspired Sinewave Test

“…In this work, we demonstrated the ability of the IST, a relatively simple to implement lung function test, as a diagnostic tool. The IST results are reliable and clinically meaningful 17 , 18 . Previous studies indicated that, in ventilated subjects, the IST could measure the effective lung volume (“baby lung”) and capture the pulmonary blood flow trend 17 , 18 .…”

“…The IST results are reliable and clinically meaningful 17 , 18 . Previous studies indicated that, in ventilated subjects, the IST could measure the effective lung volume (“baby lung”) and capture the pulmonary blood flow trend 17 , 18 . The IST does not require special, forced manoeuvres, which patients often find challenging and uncomfortable.…”

Lung heterogeneity and deadspace volume in animals with acute respiratory distress syndrome using the inspired sinewave test

“…Theory dictates that in the completely homogeneously ventilated and perfused lung, the values of ELV and Qp recovered from the IST are independent of the tracer gas period used. The IST accuracies of ELV and Qp values are published elsewhere A c c e p t e d M a n u s c r i p t [14,15]. However, as the degree of heterogeneity increases, the ELV and Qp values (based on the assumption of perfect homogeneity) begin to diverge from true values, and moreover, those values recovered from periods of 60 and 180s also diverge from each other.…”