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

The strength of the rationale for incorporating total body oxygen consumption (VO(2)) and delivery (DO(2)) 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 DO(2) and VO(2), 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 VO(2)-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 VO(2) and VO(2)/DO(2) analysis might be recommended. Although studies that support such recommendations are limited they are based on a widely accepted physiological model. VO(2) and DO(2) analysis is also limited by theoretical and technical difficulties. In this article, we discuss the validity of these limitations in the bedside assessment of VO(2) and DO(2), and review data supporting the use of VO(2)/DO(2) analysis in the clinical evaluation of complex cases.