Near infrared spectroscopy (NIRS) is a technique for continuous, non-invasive, bedside monitoring of tissue oxygen saturation (StO2). Like pulse oximetry, NIRS uses the principles of light transmission and absorption to non-invasively measure the concentrations of oxygenated hemoglobin and reduced hemoglobin in tissue. NIRS offers greater tissue penetration and does not discriminate between compartments. Therefore it provides a global assessment of oxygenation in all vascular compartments (arterial, venous and capillary) in sample volume of underlining tissue. We have previously shown that thenar muscle tissue oxygen saturation during stagnant ischemia decreases slower in septic shock patients compared to patients with severe sepsis, localized infection and healthy volunteers. This may be due to microcirculatory or metabolic changes, and probably correlates to muscle tissue oxygen consumption. The rate of StO2 decrease correlated with SOFA score, norepinephrine requirement, and plasma lactate concentration. As recently described, StO2 in sample volume of underlining tissue depends in vivo on 3 major determinants: the concentration in oxy-hemoglobin, capillary recruitment and the vascular size (vasodilatation or constriction). The StO2 during stagnant ischemia has then to be viewed in light of these determinants. The gradual decrease (slope) of StO2 after cuff inflation-induced vascular occlusion depends mainly on the augmentation of the concentration of deoxy-hemoglobin and estimates tissue oxygen consumption and to a lesser degree on vessel de-recruitment. The StO2 upslope during reperfusion (cuff deflation) can be analyzed in light of flow papers during ischemia/reperfusion test. Vasodilatation after ischemia leads to recruitment of more vessels and increase in the local blood flow, which in turn results in a StO2 increase. It remains unclear which of the described changes is more influential, however this StO2 increase mirrors the maximal local DO2 at the time of measurement. The development on NIRS signal processing might be able to provide a clinical important tissue hemoglobin concentration index and local oxygen consumption as shown by De Blasi et al., such an index may help to clarify the mechanism(s) by which StO2 signal varies.