Despite its invasiveness and inherent risks, the pulmonary artery catheter (PAC) is still regarded as the clinical standard for cardiac output (CO) determination. Arterial trans-cardiopulmonary thermodilution is a less invasive method (PAC not necessary) for CO monitoring. The aim of this study was to compare arterial trans-cardiopulmonary thermodilution to conventional pulmonary arterial thermodilution for CO determination during substantial hemodynamic variations in a sepsis model.

In a prospective study 24 anaesthetized, mechanically ventilated pigs (19.7 ± 1.6 kg) with peritonitis-induced septic shock were investigated. Cardiac output was determined using a 7.5F thermodilution catheter placed in the pulmonary artery and a 4F thermistor tipped catheter (Pulsion Medical Systems, Germany) inserted into the right carotid. Nine sets of corresponding CO determinations were obtained during a period of 8 h in each animal, all measurements were performed in triplicate. Data were analyzed using Bland-Altman analyses, linear regression and correlation.

During the period from induction of peritonitis to profound septic shock, major variations in heart rate (range: 48-310 beats/min) and systemic vascular resistance (range: 7400–1340 dyne×sec×cm^-5) were observed. 196 sets of CO determinations were yielded with a mean CO measured by pulmonary arterial thermodilution (PATD) of 2.0 ± 0.7 L/min (range: 0.7–5.2 L/min). Mean CO measured by arterial trans-cardiopulmonary thermodilution (ATPTD) was 2.17 ± 0.6 L/min (range: 1.0–4.4 L/min). Linear regression equation was: ATPTD=0.711×PATD +0.82; r²=0.68. The mean bias was 0.17 L/min (95% confidence interval: 0.125-0.215 L/min), with limits of agreement of -0.61 to 0.95 L/min and a precision of 0.34 L/min.

Arterial trans-cardiopulmonary thermodilution CO correlates acceptably with pulmonary arterial thermodilution CO even during pronounced hemodynamic instability.