Oxygen Delivery and Perfusion

Vertebrates have evolved a respiratory pigment (hemoglobin) in red blood cells to carry oxygen in the blood because of the poor solubility of oxygen in plasma. The cardiovascular system delivers the hemoglobin-bound oxygen to the tissues. The bulk transport of oxygen or ‘convective’ oxygen delivery is determined by cardiac output and blood oxygen content. At the circulatory level, convective oxygen delivery is distributed via regional regulation of arterial tone, but oxygen is delivered by diffusion at the cellular level. Tissue hypoperfusion is the central defining feature of circulatory shock, and is characterized by inadequate oxygen delivery (supply dependence) that may be compounded by microcirculatory abnormalities and cellular dysoxia. This chapter will discuss these concepts of convective oxygen delivery and microcirculatory blood flow, the assessment of hypoperfusion, with a combination of clinical, arterial and venous oxygen and carbon dioxide parameters and blood lactate levels guides therapeutic interventions and discuss the experience with early goal-directed therapy.