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Spirometric versus Fick-derived oxygen consumption: which method is better?
1Department of Anesthesiology, University of South Florida College of Medicine, Tampa, USA.
Critical Care Medicine
|January 1, 1996
Summary
The Fick equation for measuring oxygen consumption (VO2) showed significant bias compared to spirometry in pigs. These findings suggest caution when using Fick-derived VO2 for critical care decisions.
Area of Science:
- Physiology
- Critical Care Medicine
Background:
- Oxygen consumption (VO2) is crucial for assessing critically ill patients.
- The Fick equation is a common method for calculating VO2, relying on cardiac output and arterial-venous oxygen content difference.
Purpose of the Study:
- To compare the accuracy of VO2 measurements using the Fick equation against a spirometric technique.
- To evaluate the interchangeability of these two methods for VO2 determination.
Main Methods:
- A prospective study was conducted in a university laboratory setting using nineteen adult pigs.
- VO2 was calculated via the Fick equation using cardiac output (thermodilution) and oxygen content (galvanic fuel cell).
- A spirometric technique measured VO2 by oxygen disappearance rate; VO2 was pharmacologically varied (dobutamine, labetalol).
Main Results:
- A bias of 58 mL/min and a precision (SD of bias) of 35 mL/min were observed between Fick-derived and spirometrically measured VO2.
- Fick-derived VO2 values were consistently higher than those measured spirometrically.
- A strong correlation (r=0.90) was found, but a significant unexplained difference persisted.
Conclusions:
- Despite efforts to minimize error, a notable discrepancy exists between Fick and spirometric VO2 measurements.
- The Fick method and spirometry are not interchangeable for VO2 determination.
- Caution is advised when utilizing Fick-derived VO2 data for therapeutic decisions in critical care.
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