Central venous oxygen saturation vs. oxygen extraction ratio in septic shock resuscitation: Which metric is more informative?

Abstract Septic shock is a life-threatening syndrome characterized by profound circulatory dysfunction and disordered cellular metabolism, necessitating precise physiologic monitoring to guide resuscitation. In this context, sepsis-induced hemodynamic derangements range from early vasoplegia and hyperdynamic circulation to later-stage myocardial depression and microcirculatory failure. These dynamic changes create a heterogeneous perfusion landscape that challenges traditional approaches to oxygen transport assessment. Central venous oxygen saturation (ScvO 2 ) has long been used as a surrogate marker of cardiac output and global tissue oxygenation; however, in sepsis, impaired cellular oxygen utilization may result in paradoxically normal or elevated ScvO 2 despite ongoing tissue hypoxia. In contrast, the oxygen extraction ratio (O 2 ER) offers a more integrative assessment of oxygen transport by reflecting the balance between oxygen delivery and consumption. Unlike ScvO 2 , O 2 ER may remain informative in the presence of microcirculatory and mitochondrial dysfunction and may demonstrate greater sensitivity to changes in oxygen delivery, based on physiological reasoning and observational data. Accordingly, O 2 ER may provide complementary physiological insight in complex shock states, although this approach has not been validated in randomized interventional trials. This narrative review synthesizes foundational and contemporary evidence to propose a physiologically grounded framework for oxygen transport monitoring, delineating the strengths, limitations, and clinical utility of ScvO 2 , O 2 ER, and metabolic markers in guiding resuscitation strategies for patients with septic shock.