High thoracic segmental epidural anesthesia diminishes sympathetic outflow to the legs, despite restriction of sensory blockade to the upper thorax.

To evaluate whether, after high thoracic segmental epidural anesthesia, sympathetic blockade spreads caudally beyond sensory blockade, we assessed regional skin temperatures by infrared telethermometry in 53 nonpremedicated patients at constant ambient temperature. Either bupivacaine (4.2 ml, 0.75%, n = 10) or an equal volume of saline (placebo, n = 10) was injected at the C7-T2 epidural space in a randomized double-blinded fashion. Results were contrasted to those observed after midthoracic (T6-T9, n = 13) and lumbar (L2-T12, n = 10) epidural injection of an identical dose of bupivacaine or saline (n = 10). Despite restriction of sensory block to the upper thorax with high thoracic epidural anesthesia, skin temperatures increased significantly (P less than 0.05 vs. saline) on the foot (great toe: +1.2 degrees C +/- 2.9 SD; little toe: +0.9 degrees C +/- 2.6) and hand (thumb: +2.0 degrees C +/- 4.0, digit 5: +2.9 degrees C +/- 4.2) but decreased after saline. Midthoracic injection also increased significantly skin temperature on the foot (great toe: +4.0 degrees C +/- 4.9; little toe: +3.6 degrees C +/- 4.8) but not on the hand. In contrast, with lumbar epidural anesthesia, skin temperature increased significantly on the foot (great toe: +8.5 degrees C +/- 2.5; little toe: +8.6 degrees C +/- 2.8) but decreased significantly on the hand (thumb: -3.1 degrees C +/- 2.1; digit 5: -2.8 degrees C +/- 2.5).(ABSTRACT TRUNCATED AT 250 WORDS)