Noninvasive cardiac output monitoring in a porcine model using the inspired sinewave technique

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

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)


Background: Cardiac output (Q˙) monitoring may 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 non-invasive and fully automated method that uses the inspired sinewave technique to continuously monitor cardiac output (Q˙ IST ). 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). Q˙ IST 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 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 –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). Conclusions: The inspired sinewave technique provides continuous and non-invasive 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.

Original languageEnglish
Pages (from-to)126-134
Number of pages9
JournalBritish Journal of Anaesthesia
Issue number2
Early online date4 Apr 2019
Publication statusPublished - Aug 2019


  • cardiac output
  • haemodynamic
  • mechanical ventilation
  • monitoring
  • nitrous oxide
  • noninvasive
  • respiration
  • thermodilution


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