Near-infrared spectroscopy of the thenar eminence : comparison of dynamic testing protocols

• Background: Near-infrared spectroscopy of the thenar eminence (NIRSth) is a non-invasive bedside method for assessing tissue oxygenation. The vascular occlusion test (VOT) with a pressure cuff can be used to provide a dynamic assessment of the tissue oxygenation response to ischaemia. VOT has been applied to assess the microcirculation by NIRSth in critically ill patients. The optimal mode of performing such VOT, however, remains controversial. Design, participants and setting: Prospective observational study among a cohort of 11 healthy volunteers in a tertiary intensive care department. Intervention: Measurement of NIRS-derived parameters using 1-, 2- and 3-minute VOTs or VOT to 40% tissue oxygen saturation (StO(2)). Main outcome measure: Changes in StO(2) and tissue haemoglobin index (THI) over time, and relative change from baseline for StO(2) and THI. Results: Mean baseline StO(2) was 80% (SD, 5%) and mean THI was 13.7 (SD, 1.9). The lowest StO(2) at the end of the VOT was 39% (SD, 13%) and 39% (SD, 2%) in the 3-minute and the 40% StO(2) VOTs, respectively. The duration of the 40% StO(2) VOT ranged from 1:35 to 8:21 minutes (median, 3:29 min). There was a difference between the StO(2) curves for the 3-minute and 40% StO(2) VOT (P = 0.005) but not the THI curves. Reported pain score was a median of 3.5 (IQR, 2.5-5.5) and 4 (IQR 2-4) for the 3-minute and 40% StO(2) VOTs, respectively. Conclusions: The 3-minute VOT and the 40% StO(2) appear equivalent. However, the 3-minute VOT carries a degree of decreased patient discomfort and shorter overall duration of execution.

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