Sign of complete sympathetic blockade: Sweat test or sympathogalvanic response?

The sensitivity, specificity, and accuracy of the cobalt blue and ninhydrin sweat tests were compared with the sympathogalvanic response (SGR) in assessment of complete sympathetic blockade. Patients were randomly assigned to receive epidural administration of either preservative-free physiologic saline solution and 80 mg methylprednisolone (group I, control group, 9 patients) or 1.5% lidocaine with 80 mg methylprednisolone (group II, sympathetic blocked group, 10 patients). In group I, there was one false positive SGR (absence of SGR) before the block and there were four false positive SGRs after the block. In comparison, there were no false positive sweat tests (absence of sweating) before and after injection in group I. In group II, there were three false positive SGRs and no false positive sweat test before injection. After injection, one patient with an upper level of sensory blockade at T5 had persistent SGRs and positive sweat tests (false negative results). The study showed the sensitivity of the SGR and the sweat tests to be 90%. The specificity of the SGR was 56% compared to 100% for the sweat tests. The accuracy of the SGR was 74% compared to 95% for the sweat tests.