Comprehensive Assessment of Pain and Physiological Parameters of Sympathetic Blockade to Accurately Determine the Success of High Thoracic Erector Spinae Plane Block

<b>Background/Objectives</b>: High thoracic erector spinae plane block (ESPB) is a novel technique for managing chronic radicular and sympathetically mediated pain. Although physiological changes, such as increased skin temperature, perfusion index (PI), and optic nerve sheath diameter (ONSD), are known to reflect ESPB-induced sympatholysis, their predictive value for analgesic success remains unclear. In this context, the objective of this study is to investigate whether these objective indicators of sympathetic blockade are associated with the clinical success of high thoracic ESPB. <b>Methods</b>: The sample of this prospective, observational study consisted of 35 adult patients with chronic radicular pain undergoing a high thoracic ESPB procedure. Pre- and post-procedure assessments included bilateral skin temperature, PI, ONSD measurements, and administration of a visual analog scale (VAS). Patients with a greater than 50% decrease in VAS score were deemed responders to the procedure. <b>Results</b>: Of the 35 patients, 29 (82.9%) were responders. The patients' post-procedure ipsilateral skin temperature (<i>p</i> < 0.001), PI (<i>p</i> = 0.002), and ONSD (<i>p</i> < 0.001) values were significantly higher than their pre-procedure values. However, none of these parameters differed significantly between responders and non-responders (<i>p</i> > 0.05). There was also no significant correlation between VAS score and changes in PI, ONSD, or skin temperature (<i>p</i> > 0.05). <b>Conclusions</b>: In conclusion, although high thoracic ESPB resulted in measurable physiological changes suggestive of sympathetic blockade, these changes did not predict clinical analgesic success.