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J Thorac Cardiovasc Surg 2005;130:272-276
© 2005 The American Association for Thoracic Surgery

Surgery for Congenital Heart Disease

Assumed oxygen consumption frequently results in large errors in the determination of cardiac output

^a Department of Pediatric Cardiology and Congenital Heart Disease, German Heart Center, Technische Universität München, Munich, Germany
^b Institute of Medical Statistics and Epidemiology, Technische Universität München, Klinikum r.d. Isar, Munich, Germany

Received for publication November 20, 2004; revisions received January 15, 2005; accepted for publication February 8, 2005.

^_* Address for reprints: Ullrich Fakler, MD, German Heart Center, Department of Pediatric Cardiology and Congenital Heart Disease, Technische Universität München, Lazarettstraße 36, D-80636 Munich, Germany (Email: fakler{at}dhm.mhn.de).

OBJECTIVE: We sought to investigate the differences in assumed and measured oxygen consumption values for the determination of cardiac output by using the Fick principle in a pediatric population with congenital heart disease.

METHODS: The patient population consisted of 143 patients with a mean age of 11.3 years (age range, 2 days to 23.8 years) undergoing cardiac catheterization during general anesthesia and with mechanical ventilation. Oxygen consumption was measured with a standard commercial analyzing system (Deltatrac II; Datex, Engström, Helsinki, Finland). Assumed oxygen consumption values were calculated according to the formulas of Krovetz and Goldbloom and LaFarge and Miettinen. Comparisons between measurements and assumptions were performed by Bland-Altman plots. Two-sided paired t tests were used to assess a difference of the assumed and measured values.

RESULTS: The range of measured oxygen consumption values was between 55.2 and 249 mL·min^–1 ·m^–2. The Krovetz-Goldbloom formula led to systematically larger values compared with the measured values (P = .0001; mean difference of –53.3 mL·min^–1 ·m^–2; 95% confidence interval, –56.7 to –49.8 mL·min^–1 ·m^–2). The use of the LaFarge-Miettinen formula tends to overestimate oxygen consumption (P = .0037; mean difference of –15.9 mL·min^–1 ·m^–2; 95% confidence interval, –26.5 to –5.4 mL·min^–1 ·m^–2). A similarly poor agreement was found when analyzing a subgroup of 25 patients with Fontan-type circulation.

CONCLUSION: The use of assumed instead of measured oxygen consumption values introduces large errors in the determination of cardiac output.

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