Reducing tissue hypoxia is the ultimate goal of severe sepsis and septic shock therapy.Venoarterial PCO2 difference /arteriovenous O2 content difference ratio (△PCO2/Ca-vO2) is considered to be a good indicator of global anaerobic metabolism.The purpose of this study was to compare the efficacy of △PCO2/Ca-vO2 and central venous oxygen saturation (ScvO2) in the treatment of severe sepsis and septic shock.