Use of assumed versus measured oxygen consumption for the determination of cardiac output using the Fick principle

✍ Scribed by Wolf, Andreas ;Pollman, Matthew J. ;Trindade, Pedro T. ;Fowler, Michael B. ;Alderman, Edwin L.

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 176 KB
• Volume: 43
• Category: Article
• ISSN: 0098-6569
• DOI: 10.1002/(sici)1097-0304(199804)43:4<372::aid-ccd3>3.0.co;2-5

✦ Synopsis

Assumed oxygen consumption (VO 2 ) is increasingly used as a convenient surrogate for measured VO 2 for calculation of cardiac output. This substitution is often based on empirical formulae, previously validated only in relatively young patients. To assess the inaccuracy introduced by extrapolating these formulae to older patients, we compared measured VO 2 with assumed VO 2 in 57 patients. VO 2 was measured using an open circuit analyzer. Assumed VO 2 was calculated according to the LaFarge or Bergstra formulae. Agreement between both methods was assessed according to the method of Bland and Altman. The mean difference of measured VO 2 minus assumed VO 2 was 7.9 ml/min/m 2 (P F 0.02) using the LaFarge formula, and ؊15.6 ml/min/m 2 (P F 0.0002) using the Bergstra formula across a range of measured VO 2 from 70 to 176 ml/min/m 2 . A systematic error was introduced by assumed VO 2 from both formulae of underestimating higher and overestimating lower values of VO 2 , resulting in poor overall agreement with measured VO 2 . The same error and poor agreement was found when analyzing subgroups of patients H60 or F70 years of age.

In summary, use of assumed VO 2 introduces large, unpredictable errors in adult patients, suggesting requirement for measurement of VO 2 when calculating cardiac output.