Background and objective: The aim of this study was to compare cardiac output (CO) measurements by arterial trans-cardiopulmonary thermodilution (ATD) and pulmonary arterial thermodilution (PATD) with CO estimated on the basis of the Fick calculation via a metabolic monitor in septic shock.
Methods: In a prospective animal study 20 anaesthetized, ventilated pigs (20.9 ± 1.9 kg) were investigated. Septic shock was induced with faecal peritonitis. A pulmonary artery catheter was used for conventional measurement of CO. Simultaneously ATD was measured with a thermistor tipped catheter inserted into right carotid artery. Whole body oxygen consumption was measured by indirect calorimetry. Eighty data pairs of simultaneous CO measurements were analysed.
Results: CO measured with Fick and that measured with PATD were significantly correlated (r = 0.94, r2 = 0.87, P < 0.001). Mean CO measured by PATD was 94.3 ± 40.1 mL min−1 kg−1. Bias was 10.1 mL min−1 kg−1 (95% confidence interval (CI): 6.0–14.2 mL min−1 kg−1) with limits of agreement of −26.8 to 47.0 mL min−1 kg−1 . Correlation between Fick derived CO estimation and ATD CO was similar (r = 0.91, r2 = 0.83, P < 0.001). Mean CO measured by trans-cardiopulmonary thermodilution was 104.3 ± 43.2 mL min−1 kg−1 . Bias was 0.75 mL min−1 kg−1 (95% CI: −3.8 to 5.3 mL min−1 kg−1) with limits of agreement of −39.7 to 41.2 mL min−1 kg−1.
Conclusions: Even during haemodynamic instability in septic shock the correlation of arterial trans-cardiopulmonary thermodilution and PATD derived CO with direct Fick was good. As arterial trans-cardiopulmonary thermodilution is less invasive than PATD, the former may offer practical advantages.