The oxygen supply-demand balance: a monitoring challenge.

The principal task of acute critical care is to avoid or correct oxygen debt by increasing oxygen delivery (DO2) and/or decreasing oxygen consumption (VO2). The most commonly used methods to assess the relationship of adequate delivery and consumption are mixed venous oxygen saturation and its surrogate, central venous oxygen saturation (ScvO2). The purpose of this article is to review the values and limitations of the two parameters and evaluate the clinical use of ScvO2 in certain clinical scenarios, such as anaemia and transfusion, hypovolaemia, major surgery, septic shock, and in difficult-to-wean patients.