Frequency distribution of mixed venous oxygen hemoglobin saturation in two populations of `optimized' patients according to the protocol of Rivers and colleagues []. The left-hand panel represents the population of 1,000 patients as seen in Figure 3 but total body oxygen consumption needs and cardiac output (CO) were set at 120% and 130% of the expected values at basal metabolism for modeling septic conditions. Other variables were distributed as reported by Rivers and colleagues: age =67 ± 17.4 years, 50.8% male sex ratio, temperature =35.9 ± 3.2°C, hemoglobin concentration (Hb) >100 ± 15 g/L and arterial oxygen hemoglobin saturation (SaO2) >0.93. The right-hand panel represents the same real population of post-cardiosurgery patients as shown in Figure 3 but restricted to CO >1.3 basal values, Hb >100 ± 15 g/L and SaO2 > 0.93 (8,067 measurements). SvO2, mixed venous oxygen saturation.