• J A Myburgh, R K Webb, and L I Worthley.
• Intensive Care Unit, Royal Adelaide Hospital, South Australia.
• Crit. Care Med. 1992 Apr 1; 20 (4): 479-82.

ObjectiveTo 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.DesignA prospective study.SettingAn 11-bed general ICU in a 900-bed teaching hospital.PatientsTwenty 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.ResultsThirty-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).ConclusionsIf 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.

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