Effect of hyperoxia and vascular occlusion on tissue oxygenation measured by near infra-red spectroscopy (InSpectra™): a volunteer study.

Standard cardiorespiratory monitoring may fail to detect occult tissue ischaemia. This study assessed whether a near infra-red spectroscopy tissue oxygen saturation monitor (InSpectra™) could detect progressive peripheral tissue ischaemia and whether hyperoxia may confound tissue oxygen saturation measurement. Tissue oxygen and arterial oxygen saturations were measured continuously in 30 healthy volunteers, first during a period of progressive increase in inspired oxygen concentration and subsequently during two periods of low- and high-pressure limb ischaemia. Increasing inspired oxygen concentration was associated with a small increase in mean (SD) tissue oxygen saturation of 5.3 (7.1) %, reaching a plateau between 30% and 40% inspired oxygen. The rate and magnitude of decreases in tissue oxygen saturations were greater during high- than low-pressure ischaemia with a mean (SD) desaturation rate of 3.3 (0.9) vs 1.8 (0.8) %.min(-1) (p<0.01). The dose-related association and lack of confounding by hyperoxia suggest that tissue oxygen saturation monitoring may be a useful adjunct to detect occult ischaemia.