Oxygen transport in the critically ill

Abstract Adequate oxygen delivery is crucial for organ survival. The main determinants of oxygen delivery are cardiac output, haemoglobin concentration, and arterial oxygen saturation. The adequacy of oxygen delivery also depends on oxygen consumption, which may vary widely. Mixed venous oxygen saturation reflects the amount of oxygen not extracted by the tissues, and therefore provides useful information on the relationship between oxygen delivery and oxygen needs. If not in balance, tissue hypoxia may ensue and arterial lactate concentration increases. This occurs at higher oxygen delivery rates in acute compared with chronic diseases where metabolic adaptions often occur. Arterial and mixed venous oxygen saturation are related to each other. The influence of mixed venous saturation on arterial saturation increases with an increasing intrapulmonary shunt. This chapter discusses interactions between the components of oxygen transport and how they can be evaluated. Various methods for measuring tissue oxygenation and oxygen consumption are also presented, together with their limitations.