Predicting successful lumbar plexus block using blood flow index measured by laser speckle contrast imaging

Abstract

Background: Laser speckle contrast imaging (LSCI) is a powerful optical imaging technique for real-time and dynamic measurement of regional blood flow. The objective of this prospective observational study was to investigate blood flow after changes blockade of lumbar plexus or its three major branches respectively, with LSCI technique.Methods: This study included 47 adult patients scheduled for elective lower limb surgery. For the selective blockade of lumbar plexus, femoral nerve, obturator nerve, and lateral femoral cutaneous nerve, blood flow images and pinprick sensory scores of the blocked lower limb were recorded 5 min pre block and every 5 min for 30 min post block. Blood flow index (BFI) values of toes were calculated by LSCI software.Results: In this study, we have 21 cases of successful lumbar plexus blocks, 2 cases of failed lumbar plexus block, 8 cases of successful femoral nerve blocks, 8 cases of successful obturator nerve blocks, and 8 cases of successful lateral femoral cutaneous nerve blocks. The BFI values of all five toes were significantly increased as early as 5 min after successful lumbar plexus block, whereas no significant difference was found in BFI values after failed lumbar plexus block. BFI changes after successful selective blockade of femoral nerve, obturator nerve, or lateral femoral cutaneous nerve were negligible. BFI value of the big toe at 5 min after the successful lumbar plexus block was increased by 2.57 fold compared with the baseline value, which represented the highest increase among five tested toes. BFI value of the big toe at 10 min after lumbar plexus block showed great power to predict block outcome with a sensitivity of 100% and a specificity of 100%. The optimal cut-off value given by ROC analysis was 22.11 PU.Conclusions: Increased blood flow index measured by laser speckle contrast imaging is a reliable indicator of successful lumbar plexus block, but cannot indicate successful selective blocks of three major branches of the lumbar plexus. BFI value of the big toe at 10 min after lumbar plexus block could well predict block outcome with the cut-off value of 22.11 PU.Trial registration: NCT03169517 (Date of registration: May 25, 2017).