Tissue Oxygenation Assessment in Critical Care

Effective management of critically ill patients requires not only optimisation of systemic haemodynamics but also assurance of adequate oxygen delivery at the tissue level. Traditional monitoring of macrocirculatory variables such as blood pressure and cardiac output may fail to detect regional perfusion deficits that contribute to organ dysfunction. Over the past decade, non-invasive optical techniques have emerged to assess tissue oxygen saturation (StO2) and microvascular function at the bedside. Among these, near-infrared spectroscopy (NIRS) enables continuous measurement of the balance between oxygen supply and demand within superficial muscle beds. When coupled with a vascular occlusion test (VOT), NIRS provides dynamic indices of oxygen extraction and reperfusion, thereby offering insight into endothelial integrity and capillary recruitment. The clinical utility of these measurements spans early detection of hypoperfusion, guidance of fluid or vasoactive therapy, and prognostication in sepsis, shock and major surgery. Recent advances in sensor design, data processing algorithms and integration with other monitoring modalities promise to enhance signal fidelity and facilitate personalised resuscitation strategies. Standardisation of measurement sites, probe configurations and challenge protocols remains a priority to ensure comparability across centres and patient populations. As optical monitoring technologies mature, they hold potential to bridge the gap between global haemodynamic targets and regional tissue oxygenation, ultimately improving outcomes in the most vulnerable patients.

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Tissue Oxygenation Assessment in Critical Care publication trend

The graph below shows the total number of articles in tissue oxygenation assessment in critical care across all publications each year (not limited to Nature Index journals).

Technical terms

Near-infrared spectroscopy (NIRS): A non-invasive technique that uses light in the near-infrared spectrum to measure concentrations of oxy- and deoxyhaemoglobin in superficial tissues, providing an index of regional oxygenation.

Tissue oxygen saturation (StO2): The percentage of haemoglobin in a given tissue bed that is oxygen-bound, reflecting the balance between oxygen delivery and extraction at the microcirculatory level.

Vascular occlusion test (VOT): A controlled procedure in which arterial inflow to a limb is temporarily halted, allowing quantification of oxygen consumption during ischaemia (downslope) and reperfusion capacity (upslope).

Microvascular reactivity: The ability of small arterioles and capillaries to dilate or recruit in response to metabolic or occlusive challenges, indicative of endothelial health and tissue perfusion reserve.

References

1. Microvascular reactivity and clinical outcomes in cardiac surgery. Critical Care (2015).
2. Journal of Clinical Monitoring and Computing 2017/2018 end of year summary: monitoring—and provocation—of the microcirculation and tissue oxygenation. Journal of Clinical Monitoring and Computing (2019).
3. Microvascular reactivity is altered early in patients with acute respiratory distress syndrome. Respiratory Research (2016).
4. Characterization of tissue oxygen saturation and the vascular occlusion test: influence of measurement sites, probe sizes and deflation thresholds. Critical Care (2009).