Lumbar sympathetic block for sympathetically maintained pain: Changes in cutaneous temperatures and pain perception

Lumbar sympathetic block (LSB) is used in the management of sympathetically maintained pain states. We characterized cutaneous temperature changes ove r the lower extremities after LSB. Additionally, we examined the effects of iohexol, a radio-opaque contrast medium, on temperature changes and pain r elief. After institutional review board approval and written, informed cons ent, 28 LSBs were studied in 17 patients. Iohexol or normal saline was inje cted in a randomized, double-blinded fashion before bupivacaine. Lower extr emity cutaneous temperatures were measured. Pain, allodynia, interference w ith daily function, and perceived pain relief were reported in a subset of 15 LSBs for 1 wk after the block. The distal lower extremity ipsilateral to the LSB had the greatest magnitude (8.7 degrees +/- 0.8 degrees C) and rat e (1.1 degrees +/- 0.2 degrees C/min) of temperature change. The great toe temperature was within 3 degrees C of core temperature within 35 min after LSB. There were no differences in temperature change between the groups. Th e iohexol group had greater relief of pain until the morning of the first p ostblock day (P = 0.002) and longer perceived relief of pain (P = 0.01). Th e maximum temperature of the great toe correlated with allodynia relief (P = 0.0007). Thus clinicians should expect ipsilateral toe temperatures to in crease to within similar to 3 degrees C of core temperature. Iohexol does n ot alter the efficacy of LSB and may improve relief of symptoms. The magnit ude of temperature change may predict relief of allodynia.