Assessment of tissue oxygen saturation during a vascular occlusion test using near-infrared spectroscopy: role of the probe spacing and measurement site studied in healthy volunteers

Introduction

To assess potential metabolic and microcirculatory alterations in critically ill patients, near-infrared spectroscopy (NIRS) has been used, in combination with a vascular occlusion test (VOT), for the noninvasive measurement of tissue oxygen saturation (StO₂), oxygen consumption, and microvascular reperfusion and reactivity. However, the methodologies for assessing StO₂ are very inconsistent in the literature and results vary from study to study. In this study we investigated the effects of the probe spacing and measurement site, using both a 15 mm and a 25 mm probe spacing on the thenar and the forearm, in healthy volunteers.

Methods

StO₂ was noninvasively measured in eight healthy volunteers during 3-minute VOTs using two InSpectra Tissue Spectrometers equipped with either a 15 mm or a 25 mm probe. VOT-derived StO₂ traces were analyzed for baseline, ischemic, reperfusion, and hyperemic parameters.

Results

Although not apparent at baseline, the probe spacing and measurement site significantly influenced VOT-derived StO₂ parameters (Figures 1 and 2). StO₂ parameters in the hyperemic phase of the VOT were shown to significantly correlate to the minimum StO₂ value after 3 minutes of ischemia.

Figure 1

Mean ± SD StO ₂ values in the thenar during a 3-minute VOT. BSLN, baseline.

Figure 2

Mean ± SD StO ₂ values in the forearm during a 3-minute VOT. BSLN, baseline.

Conclusion

The present study showed that NIRS measurements in combination with a VOT are measurement site and probe dependent. Additionally, this study indicated that reactive hyperemia depends on the extent of ischemic hit and supports the use of a target StO₂ over the use of a fixed time of occlusion.