title: Assumed oxygen consumption frequently results in large errors in the determination of cardiac output.
abstract: 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.
  
  
  CONCLUSIONS
  The use of assumed instead of measured oxygen consumption values introduces large errors in the determination of cardiac output.
authors.affiliation: Department of Pediatric Cardiology and Congenital Heart Disease, Technische Universität München, Germany. fakler@dhm.mhn.de
authors.forename: Ullrich
authors.initials: U
authors.lastname: Fakler
authors.forename: Christian
authors.initials: C
authors.lastname: Pauli
authors.forename: Michael
authors.initials: M
authors.lastname: Hennig
authors.forename: Walter
authors.initials: W
authors.lastname: Sebening
authors.forename: John
authors.initials: J
authors.lastname: Hess
mesh_terms: D000293:Adolescent; D000328:Adult; D006328:Cardiac Catheterization; D002302:Cardiac Output / Q000502:physiology; D002648:Child; D002675:Child, Preschool; D005260:Female; D006330:Heart Defects, Congenital / Q000503:physiopathology* / Q000601:surgery; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D019300:Medical Errors; D016343:Monitoring, Intraoperative; D010101:Oxygen Consumption / Q000502:physiology*