Tissue Oxygenation

Oxygen that is required for aerobic metabolism is transported to the cell with a series of convective-diffusive processes. 97% of oxygen in arterial blood is carried in combination with hemoglobin, the remaining 3% being dissolved in the plasma. The interaction between hemoglobin and partial oxygen pressure results in oxyhemoglobin dissociation curve which shifts rightward in the presence of acidosis, anemia, hypercapnia, hyperthermia, increased level of 2,3 diphosphoglycerate. The amount of oxygen delivered to the tissue (DO2) is the product of cardiac output and arterial O-2 content, and is about 1020 ml/min when hemoglobin is fully saturated. Oxygen consumption is the rate of 02 uptake from circulation. VO2 is the the product of cardiac output and the chtference between the arterial and venous oxygen content, and is about 251 ml/min. Oxygen consumption depends on the requirement. However, when oxygen. delivery decreases beyond a certain point (critical DO2), VO2 becomes supply dependent. Oxygen extraction(2) (O2ER) is the ratio of oxygen consumption to oxygen supply (O2ER=VO2/DO2=0.25). Mixed venous oxygen saturation (SvO(2)) may represent useful interpretations about DO2 and VO2. Continuous central venous oxygen saturation measurement is suggested to use for early detection of major derangements in oxygen balance. It is aimed in this review to represent the details and clinical interpretations of tissue oxygenation.