Ratios of central venous-to-arterial carbon dioxide content or tension to arteriovenous oxygen content are better markers of global anaerobic metabolism than lactate in septic shock patients

Background To evaluate the ability of the central venous-to-arterial CO 2 content and tension differences to arteriovenous oxygen content difference ratios (∆ContCO 2 /∆ContO 2 and ∆PCO 2 /∆ContO 2 , respectively), blood lactate concentration, and central venous oxygen saturation (ScvO 2 ) to detect the presence of global anaerobic metabolism through the increase in oxygen consumption (VO 2 ) after an acute increase in oxygen supply (DO 2 ) induced by volume expansion (VO 2 /DO 2 dependence). Methods We prospectively studied 98 critically ill mechanically ventilated patients in whom a fluid challenge was decided due to acute circulatory failure related to septic shock. Before and after volume expansion (500 mL of colloid solution), we measured cardiac index, VO 2 , DO 2 , ∆ContCO 2 /∆ContO 2 and ∆PCO 2 /∆ContO 2 ratios, lactate, and ScvO 2 . Fluid-responders were defined as a ≥15 % increase in cardiac index. Areas under the receiver operating characteristic curves (AUC) were determined for these variables. Results Fifty-one patients were fluid-responders (52 %). DO 2 increased significantly (31 ± 12 %) in these patients. An increase in VO 2 ≥ 15 % (“VO 2 -responders”) concurrently occurred in 57 % of the .