High Thoracic Epidural Anesthesia Does Not Inhibit Sympathetic Nerve Activity in the Lower Extremities |
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Authors: | Magnú sd ttir, Helga M.D. Kirn , Klaus M.D., Ph.D. Ricksten, Sven-Erik M.D., Ph.D. Elam, Mikael M.D., Ph.D.
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Affiliation: | Magnúsdóttir, Helga M.D.*; Kirnö, Klaus M.D., Ph.D.†; Ricksten, Sven-Erik M.D., Ph.D.‡; Elam, Mikael M.D., Ph.D.§ |
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Abstract: | Background: Sympathetic nerve activity was recorded in the leg during high thoracic epidural anesthesia with a segmental sensory blockade of the upper thoracic dermatomes to test the hypothesis that the sympathetic blockade accompanying thoracic epidural anesthesia includes caudal parts of the sympathetic nervous system. Methods: Experiments were performed on 10 patients scheduled for thoracotomy. An epidural catheter was inserted at the T3-T4 or T4-T5 interspace. In the main protocol (seven patients), blood pressure, heart rate, and skin temperature (big toe, thumb) were continuously monitored, and multiunit postganglionic sympathetic nerve activity was recorded with a tungsten microelectrode in a muscle-innervating fascicle of the peroneal nerve. After baseline data collection, muscle sympathetic nerve activity was recorded for an additional 45-min period after epidural injection of 4-6 ml bupivacaine, 5 mg/ml. In an additional three patients, the effects of thoracic epidural anesthesia on skin-innervating sympathetic nerve activity were qualitatively assessed. Results: Activation of thoracic epidural anesthesia caused no significant changes in peroneal muscle sympathetic nerve activity (n = 7), blood pressure, or heart rate. Skin temperature increased significantly in the hand 15 min after activation of the blockade, from 32.7 +/- 2.4[degrees]C to 34.4 +/- 1.5[degrees]C (mean +/- SD), whereas no changes were observed in foot temperature. The sensory blockade extended from T1 (C4-T2) to T8 (T6-T11). |
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