Mixed vs central venous oxygen saturation may be not numerically equal, but both are still clinically useful.

and related disciplines; and to provide interesting and valuable content to members of the American College of Chest Physicians and to CHEST readers and subscribers. A new " face " of CHEST heralds a new era. M ixed venous oxygen saturation (Sv ៮o 2) in sepsis is commonly referred to as an end point of low impact on clinical decisions in sepsis patients because of the following common refrain: " Sv ៮o 2 is always increased in septic ICU patients. " However, there are fundamental principles that render this modality clinically useful when applying it to the supply-dependent phase of sepsis (ie, global tissue hypoxia). The presence of global tissue hypoxia not only has pathologic significance in vitro, 1 but there is a pathologic link among the clinical presence of global tissue hypoxia (ie, low Sv ៮o 2 and cardiac index), the generation of inflammatory mediators, and mi-tochondrial impairment of oxygen utilization that is seen in septic ICU patients. 2 Furthermore, identifying sudden episodes of supply dependency in septic ICU patients (ie, sudden decreases in Sv ៮o 2) has diagnostic and prognostic significance. 3 With this background, the rationale for using central venous oxygen (Scvo 2) saturation as a surrogate for Sv ៮o 2 to detect and treat global tissue hypoxia in the most proximal phase of sepsis management (supply dependency) was the basis for its use in the Early Goal Directed Therapy in Severe Sepsis and Septic Shock Study (EGDT). 4 Early hemodynamic assessment using physical examination , vital signs, 5 central venous pressure, 6 and urinary output 7 fails to detect supply dependency or persistent global tissue hypoxia. Shock patients who are resuscitated to having normal vital signs continue to exhibit evidence of global tissue hypoxia (Scvo 2 Ͻ 70% and increased lactate levels) and require additional resuscitation, as shown by Rady et al. 6 Similar findings were confirmed in the EGDT study as 39.8% of the control group vs 5% of the EGDT group continued to have global tissue hypoxia after 6 h of resuscitation despite the fact that all patients attained the same vital sign goals (ie, MAP, Ͼ 65 mm Hg; CVP, Ͼ 8 mm Hg; urine output, 0.5 mL/kg/h). These findings of global tissue hypoxia, or " cryptic shock, " in patients 8 have prognostic significance as this state was associated with a 56.5% in-hospital mortality rate. The therapeutic significance was realized as the …