SaO2t

SaO2t is a term used in some medical and research contexts to denote the arterial oxygen saturation within tissue microvasculature. It is intended to represent the oxygen saturation of arterial blood as it exists in the tissue microcirculation, and it is distinct from systemic arterial oxygen saturation measured by blood gas analysis (SaO2) or from peripheral oxygen saturation obtained by pulse oximetry (SpO2). In practice, SaO2t is not a universally standardized measure and its definition can vary between studies and devices.

Measurement of SaO2t is not routinely performed with standard clinical technologies. It may be inferred from tissue oximetry approaches such as near-infrared spectroscopy (NIRS) or diffuse optical spectroscopy, sometimes using models to separate arterial and venous contributions, or it may be estimated indirectly from arterial blood gas data combined with microcirculatory assumptions. Because tissue blood contains a mix of arterial, capillary, and venous blood, SaO2t can be sensitive to changes in perfusion, microvascular flow, and local metabolism, which can complicate interpretation.

Physiological relevance centers on tissue oxygen delivery and consumption. SaO2t, when defined and measured, aims to provide a microenvironmental view of oxygenation that complements systemic measures (SpO2, SaO2) and tissue saturation indices (StO2). It has potential utility in research on shock, sepsis, anesthesia, and critical care, where microcirculatory dysfunction may predominate.

Limitations include lack of standardization, dependence on device algorithms, and confounding factors such as hemoglobin concentration, edema, and skin or tissue optics. Consequently, SaO2t is not routinely used in clinical practice and is primarily a research or specialized measurement concept.