Predictive value of muscle tone loss and perfusion index in the success of supraclavicular brachial plexus block: A pilot study

Abstract

Background

Currently, no standardized tool accurately predicts the success of supraclavicular brachial plexus block (SBPB) in the shortest time possible. This study aimed to evaluate the early predictive value of muscle tone loss and perfusion index in predicting SBPB success. This is the first study to report the use of this device for objective assessment of nerve block success.

Methods

A prospective observational pilot study was conducted at "Dr. Ignacio Morones Prieto" Central Hospital, Mexico, involving 33 patients (ASA 1, 2, 3) requiring surgery on the distal third of the upper limb with ultrasound-guided SBPB. Exclusion criteria included infections at the puncture site, local anaesthetic allergies, coagulopathies, restrictive pulmonary pathologies, oxygen dependency, brachial plexus radiculopathy, and uncontrolled diabetes. The motor block was assessed with a conductive ink flexion sensor (FS), and the sympathetic block was evaluated with perfusion index via pulse oximeter at 3, 5, 10, and 15 min. Block success was defined as a Numerical Rating Scale (NRS) for pain <2 during surgical stimulation. Statistical comparisons were made between successful and unsuccessful blocks, with ROC curve analysis identifying optimal cutoff points for predictive variables.

Results

Of the 33 patients, 24 had a successful block, and 9 did not. At 5 min, a PI > 196.07 showed 100% sensitivity, 87.5% specificity, and AUC 92% (p < 0.001). A 27.38% loss in muscle strength showed 100% sensitivity, 87.5% specificity, and AUC 95% (p < 0.001). Combined, these parameters had a 100% predictive value (p < 0.005).

Conclusion

PI and muscle strength loss are reliable early predictors of SBPB success, offering a valuable tool for optimizing anaesthetic strategies.