Non-invasive blood haemoglobin and plethysmographic variability index during brachial plexus block

Abstract

Background: Plethysmographic measurement of haemoglobin concentration (SpHb), pleth variability index (PVI), and perfusion index (PI) with the Radical-7 apparatus is growing in popularity. Previous studies have indicated that SpHb has poor precision, particularly when PI is low. We wanted to study the effects of a sympathetic block on these measurements. Methods: Twenty patients underwent hand surgery under brachial plexus block with one Radical-7 applied to each arm. Measurements were taken up to 20 min after the block had been initiated. Venous blood samples were also drawn from the non-blocked arm. Results: During the last 10 min of the study, SpHb had increased by 8.6%. The PVI decreased by 54%, and PI increased by 188% in the blocked arm (median values). All these changes were statistically significant. In the non-blocked arm, these parameters did not change significantly. Conclusions: Brachial plexus block significantly altered SpHb, PVI, and PI, which indicates that regional nervous control of the arm greatly affects plethysmographic measurements obtained by the Radical-7. After the brachial plexus block, SpHb increased and PVI decreased.