Evaluation of the Change in Vascular Tone Following Brachial Plexus Nerve Block Using Amplification of Video From a Mobile Device

Abstract

Purpose: To evaluate the efficacy of using an iPhone as a pulse plethysmograph in detecting changes in cutaneous perfusion and vascular tone caused by regional anesthesia in the form of clinically established brachial plexus block techniques. Methods: 50 patients scheduled to undergo brachial plexus blocks as part of their planned surgeries were enrolled in this study. Bilateral iPhone contact photoplethysmography recordings and Radical 7 pulse co-oximeter measurements were made shortly prior to and for 20 minutes after the placement of the brachial plexus block. Shorter recordings were made after the completion of surgery and again once per hour for 4 hours or until the patient was discharged home. Admitted patients were further monitored at 24-hour post-block. Results: Skin temperature changed significantly, however measurements made by the Radical 7 and iPhone did not show significant changes after brachial plexus block. Conclusions: Although there was likely increased blood flow to the periphery as evidenced by the significant change in skin temperature, neither the Radical 7 nor the iPhone was able to detect significant changes in the plethysmograph signal. Further study is necessary to determine whether this is truly due to a failure of the iPhone or whether differences in the study protocol resulted in the blunted effect size that was also seen in the Radical 7 data.