Adaptability of muscle tissue oxygenation to repeated vascular occlusion

Introduction

Dynamic testing of muscle tissue oxygenation (StO₂) with near-infrared spectroscopy and vascular occlusion (VOT) is a developing area of research in critical care. VOT is often performed multiple times during analysis. We report the impact of repeated VOT on StO₂ parameters.

Methods

Twenty-five healthy subjects were studied with the InSpectra 650 monitor and a 15 mm probe. VOT was set at systolic blood pressure + 50 mmHg for 3 minutes in triplicate. Each VOT was separated by a 5-minute rest period. StO₂ data are reported for baseline%, downslope (DS) and upslope (US)%/min, overshoot%, area over the ischaemic curve (AOC Isch) and area under the recovery curve (AUC Rec)%/min and recovery time (Rec Time) in minutes. Data were compared by ANOVA.

Results

See Table 1.

Table 1 Population StO₂ means (± SD) for consecutive VOT and significance

Conclusion

It is important to understand the impact of serial VOT. We have observed sequential change in rates of StO₂ decline during ischaemia (reduced DS gradients, total drop and AOC Isch). Although the overshoot was unchanged, the AUC Rec and Rec time demonstrated increases approaching significance. These patterns imply a preconditioned adaptation to repeated VOT and an exaggerated hyperaemic response. Further studies are required to determine acceptable rest periods between VOTs to ameliorate these changes.