Does the sympathetic block outlast sensory block: a thermographic evaluation.

Abstract

A study to evaluate the duration of sympathetic and sensory block in the L2 and L5 dermatome distributions using thermography and pinprick was conducted. Twenty patients received epidural block using 2% lidocaine with epinephrine. Onset and duration of the sensory and sympathetic blocks were determined and compared statistically. There was no difference between the duration of sensory and sympathetic block over the L2 dermatome, but sympathetic block was significantly longer than sensory block in the L5 dermatome. This study demonstrates that the duration of sympathetic block can be either longer or shorter than sensory block in L2 and L5 dermatomes. This has important implications for interpretation of results of differential epidural studies in that one cannot predict the duration of sympathetic block based on duration of sensory block.