Figure 2
From: Central venous oxygenation: when physiology explains apparent discrepancies
Mixed venous oxygen hemoglobin saturation adaptation to fluctuations of related variables. Mixed venous oxygen saturation (SvO2) changes were modeled in 1,000 patients using JMP (SAS Institute, Cary, North Carolina, USA). In both panels, we used a random uniform distribution of age (range 20 to 90 years) and temperature (range 34 to 41°C) and the normative tables as modeled by the Hemodyn software® [7],[26]-[29]. This generates a wide range of total body oxygen consumption (VO2) needs (70 to 290 ml/minute.m2) and their corresponding cardiac output values (2.28 to 4.22 L/minute.m2) from which individual values of needed SvO2 can be inferred from Equation 2 according to different values of hemoglobin concentration and arterial oxygen hemoglobin saturation. In the left-hand panel, only old and hyperthermic patients have an expected physiological SvO2 < 0.65. In the right-hand panel, most patients have an expected SvO2 < 0.65 in response to a combined mild decrease in SaO2 and hemoglobin concentration. These examples have been created assuming no VO2 gap. In case of hypoxia, SvO2 values exceed the modeled value, proportionally to the VO2 gap following Equation 6.