Tissue oxygenation index reflects changes in forearm blood flow after brief ischemia

Whether the near-infrared spectroscopy (NIRS) technology correctly detects the changes in oxygenation related to ischemia and reperfusion of organs and tissues other than brain remains unclear. The present study examined how different tissue oxygenation parameters derived from NIRS reflect the changes in the forearm blood flow (FBF) according to the brief ischemia and the subsequent reperfusion, and whether values of these parameters move in parallel with the medial and lateral sides of FBF. Thirteen volunteers underwent the prospective observational study. The tissue oxygenation index (TOI), regional saturation of oxygen (rSO₂), skin tissue oxygenation (StO₂), and FBF values were evaluated in the forearm. Medial rSO₂ values at 1 to 3 minutes after the termination of brief ischemia were higher than lateral rSO₂ and respective TOI values. FBF and StO₂ values quickly increased according to the cessation of brief ischemia, whereas the medial and lateral values did not differ during and after the brief ischemia. TOI and StO₂, but not rSO₂, reflected changes in FBF of both medial and lateral sides simultaneously in response to the reperfusion after brief ischemia. The muscle tissue oxygenation during reperfusion favors the use of TOI and StO₂, but not rSO₂, as the surrogate parameter.