Ventilation/perfusion indices do not correlate with the difference between oxygen consumption measured by the Fick principle and metabolic monitoring systems in critically ill patients.
OBJECTIVE
To determine whether the difference between oxygen consumption (VO2) measured by metabolic gas monitoring systems and by the Fick principle is related to venous admixture, deadspace/tidal volume ratio, or alveolar-arterial oxygen tension gradient in critically ill patients.


METHODS
A prospective study.


METHODS
An 11-bed general ICU in a 900-bed teaching hospital.


METHODS
Twenty critically ill patients admitted to the ICU who required mechanical ventilation, right heart catheterization, and arterial and mixed venous gas measurements for normal clinical management.


RESULTS
Thirty-three recordings were analyzed. The mean VO2 measured by the metabolic gas monitoring system was 308 +/- 63.9 (SD) mL/min and was significantly greater than the mean VO2 measured by the Fick principle of 284 +/- 72.0 mL/min. The difference between the two measurements of 24.3 +/- 47.6 mL/min correlated poorly with venous admixture (r2 = .0009), dead-space/tidal volume ratio (r2 = .0064) and alveolar-arterial oxygen tension gradient (r2 = .017).


CONCLUSIONS
If the difference in VO2 measured by metabolic gas monitoring systems and the Fick principle is due to intrapulmonary VO2 then in critically ill patients the ventilation/perfusion indices of venous admixture, deadspace/tidal volume ratio and alveolar-arterial oxygen tension gradient correlate poorly with intrapulmonary VO2.
Myburgh
J A
JA
Intensive Care Unit, Royal Adelaide Hospital, South Australia.
Webb
R K
RK
Worthley
L I
LI
D000328:Adult; D000368:Aged; D001784:Blood Gas Analysis; D001944:Breath Tests / Q000379:methods; D016638:Critical Illness; D005260:Female; D006801:Humans; D016018:Least-Squares Analysis; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology*; D011446:Prospective Studies; D011652:Pulmonary Circulation / Q000502:physiology; D013990:Tidal Volume; D014692:Ventilation-Perfusion Ratio / Q000502:physiology*
D010100:Oxygen