The thermodilution (TD) method is routinely used for the estimation of cardiac output (Q̇C). However, its accuracy, compared with the gold-standard Fick method, where systemic oxygen uptake (V̇O2) is directly measured, and Q̇C calculated from V̇O2 and the arterio-venous oxygen difference (“direct” Fick), has not been well validated. The present study determined the agreement between TD and Fick methods in consecutive patients who underwent pulmonary artery catheterization for a broad range of clinical conditions. This is a subanalysis of a previous study comparing the indirect versus Fick method based on a prospective, consecutive patient registry of 253 patients who underwent pulmonary artery catheterization for clinical indications at a single center between 1999 and 2005. We included patients that had an estimation of Q̇C both by the Fick method using measured V̇O2 by exhaled gas analyses from timed Douglas bag collections and by TD. Cardiac index was classified as low when ≤2.2 L/min/m2 or normal when >2.2 L/min/m2. The median (25th, 75th percentile) age of the cohort was 59 (50,67) years, and 50% were female. A total of 43.5% had normal left ventricular function by ventriculography, and 25.7% had ischemic heart disease. Median overall Fick and TD Q̇C were 4.4 (3.5, 5.5) and 4.3 (3.7, 5.2) L/min, respectively (p = 0.04). The median absolute percent error between Fick and TD Q̇C was 17.5 (7.7, 28.4)%, with a typical error of 0.88 L/min (95% confidence interval [CI] 0.82 to 0.95). Median absolute percent error was comparable in the low (n = 118) and normal Q̇CI (n = 135) groups (16.9% vs 18.9%, respectively, p = 0.88). typical error was 0.3 (95% CI 0.27 to 0.33) and 0.49 (95% CI 0.45 to 0.55) L/min/m2 in that comparison. Percent error >25% between Fick and TD Q̇C was observed in over 30% of patients. Overall, Fick and TD Q̇C modestly correlated (Rs = 0.64, p <0.001), with a nondirectional error introduced by TD Q̇C [mean bias of 0.21 (−2.2, 2.7) L/min]. There was poor agreement between TD and the gold-standard Fick method, highlighting the limitations of making clinical decisions based on TD.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine