Comparison of invasive and less-invasive techniques of cardiac output measurement under different haemodynamic conditions in a pig model.

Background and Objective: Despite the introduction of various less-invasive concepts of cardiac output measurement, pulmonary arterial thermodilution is still the most common measurement technique.
Methods: This prospective controlled study was designed to compare different methods of cardiac output measurement simultaneously. Pulmonary arterial thermodilution, transpulmonary thermodilution (PiCCO), trans-oesophageal echo-Doppler probe (HemoSonic) and partial carbon dioxide rebreathing technique (NICO monitor) were evaluated against a peri-aortic transit-time flow-probe as reference method in a clinically relevant animal model. After approval from the Local Ethics Committee on Animal Research, the investigations were conducted in nine anesthetized domestic pigs. Systemic haemodynamics were modulated systematically by the application of catecholamines, caval occlusion and exsanguination. Statistical analysis was performed with Bland-Altman and linear regression.
Results: A total of 366 paired cardiac output measurements were carried out at a reference cardiac output between 0.5 and 7 L min(-1). The correlation coefficients for pulmonary arterial and transpulmonary thermodilution against reference were 0.93 and 0.95, for trans-oesophageal Doppler and partial rebreathing technique 0.84 and 0.77. Pulmonary arterial thermodilution and transpulmonary thermodilution showed comparable bias and limits of agreement. Where HemoSonic showed an overestimation of cardiac output at a higher precision, NICO overestimated low and underestimated higher cardiac output values.
Conclusions: Our data suggest that pulmonary arterial thermodilution and PiCCO may be interchangeably used for cardiac output measurement even under acute haemodynamic changes. The method described by Bland and Altman demonstrated an overestimation of cardiac output for both thermodilution methods. HemoSonic and NICO offer non-invasive alternatives and complementary monitoring tools in numerous clinical situations. Trend monitoring and haemodynamic optimizing can be applied sufficiently, when absolute measures are judged critically in a clinical context. The use of the NICO system seems to be limited during acute circulatory changes.