Elevation of the arteriovenous oxygen difference as a prognostic marker in critically ill patients: a systematic review

The assessment of tissue oxygenation in critically ill patients represents a constant challenge in clinical practice, particularly in intensive care units (ICUs), where the balance between oxygen delivery and consumption is essential for maintaining cellular function and preventing organ dysfunction. The literature highlights that critically ill patients are at increased risk of tissue hypoperfusion, which is directly associated with cellular injury and multiple organ failure, reinforcing the importance of systemic perfusion monitoring in clinical practice (Réa-Neto et al., 2006). In this context, arterial and venous blood gas analysis are important tools for evaluating oxygenation and tissue perfusion in critically ill patients. While arterial blood gas analysis provides information on pulmonary oxygenation and acid–base status, venous blood gas analysis—particularly through central venous oxygen saturation (ScvO₂)—allows inference of the relationship between oxygen delivery and consumption (Vincent & De Backer, 2004; Mallat et al., 2016). Thus, the integrated analysis of these parameters may provide relevant information regarding the hemodynamic status and prognosis of patients. Furthermore, parameters derived from the relationship between arterial and venous values, such as the arteriovenous oxygen difference, allow a more direct assessment of tissue oxygen extraction. An increase in this difference may reflect enhanced oxygen extraction by tissues, often associated with hypoperfusion states, reduced cardiac output, or increased metabolic demand, suggesting potential clinical relevance for the early identification of physiological dysfunctions in critically ill patients (Guyton & Hall, 2016). Observational studies conducted in ICUs have shown that venous oxygenation parameters, such as ScvO₂, correlate with other indicators of tissue perfusion; however, they are not fully equivalent and should be interpreted in a complementary manner within the clinical context (Rivers et al., 2001). Additionally, the literature demonstrates that these parameters are associated with relevant clinical outcomes, including mortality, length of hospital stay, and the need for ventilatory support (Ospina-Tascón et al., 2013). Despite the clinical potential of the arteriovenous oxygen difference, there are still gaps in the literature regarding the definition of values considered elevated, as well as its applicability as a prognostic marker across different clinical settings. Moreover, the equivalence between parameters obtained from arterial and venous blood gas analysis in assessing tissue oxygenation remains limited, as different methods reflect distinct aspects of perfusion and cellular metabolism (Cecconi et al., 2014; Rivers et al., 2001). Therefore, conducting a systematic review is relevant to synthesize the available evidence on the elevation of the arteriovenous oxygen difference as a prognostic marker in critically ill patients, contributing to a better understanding of its clinical applicability and supporting decision-making in intensive care.