Effects of peripheral vasodilation induced by regional anaesthesia blocks on resting tissue oxygenation values

Introduction

Near-infrared spectroscopy is a technique for continuous, noninvasive, bedside monitoring of tissue oxygenation (StO₂). The nature of the relationship between the kinetics of StO₂ and changes in peripheral circulation has not been investigated. After successful regional anaesthesia blocks, local vasodilation and increased local blood flow occur as a result of blockade of sympathetic nerve fibers. We therefore studied the effects of peripheral vasodilation induced by regional anaesthesia blocks on resting StO₂ values.

Methods

We recruited healthy adult patients (n = 8) scheduled for selective upper limb surgery under axillary sympathetic blocks. StO₂ was continuously monitored over the thenar of the blocked arm using an InSpectra Model 325 probe (Hutchinson Technology Inc., Hutchinson, MN, USA) from the beginning of the local anesthetic (T0) injection until 30 minutes was elapsed (T30). The contralateral arm was used as a control. Differences between group means were tested by Wilcoxon signed test. P < 0.05 was considered statistically significant.

Results

StO₂ values in the blocked arm were significantly higher in all patients after the anaesthesia (Figure 1). T30 versus T0, 94 ± 2 versus 82 ± 3; P = 0.002. StO₂ did not increase in the control arm.

Figure 1

Effect of peripheral blood flow variations in StO ₂ during regional block.

Conclusion

Peripheral vasodilation increases StO₂ in normal conditions.