Matching total body oxygen consumption and delivery: a crucial objective?

The strength of the rationale for incorporating total body oxygen consumption (VO₂) and delivery (DO₂) into our decision making strategies contrasts with the absence of demonstrated benefits of bedside calculations in clinical practice. This situation mandates a careful reappraisal of the theoretical limitations of bedside calculations of DO₂ and VO₂, including a re-evaluation of the clinical situations in which these calculations are valid. Three levels of complexity can be distinguished when analysing a patient’s hemodynamic status: 1) simple cases where investigations can be limited to clinical monitoring, including lactate changes over time; 2) intermediate situations requiring invasive investigations in which continuous monitoring of VO₂-related variables such as cardiac output and mixed venous oxygen saturation often provide enough information to guide clinical decision; and 3) complex situations where assessment of VO₂ and VO₂/DO₂ analysis might be recommended. Although studies that support such recommendations are limited they are based on a widely accepted physiological model. VO₂ and DO₂ analysis is also limited by theoretical and technical difficulties. In this article, we discuss the validity of these limitations in the bedside assessment of VO₂ and DO₂, and review data supporting the use of VO₂/DO₂ analysis in the clinical evaluation of complex cases.