Effects of epidural anesthesia on sympathetic nerve discharge to the skin

Abstract

Direct intraneural recordings of skin sympathetic activity (SSA) were performed to determine the magnitude of blockade of sympathetic fibers to the lower extremities during epidural anesthesia. Lumbar epidural catheters were inserted in nine volunteers. Multiunit postganglionic sympathetic activity was recorded in a skin fascicle of the peroneal nerve before and after injection of 4 ml of mepivacaine 2% epidurally, followed by an additional 12-16 ml after 5 min. Arousal stimuli such as sudden loud noises and noxious electrical skin stimulation were used to elicit transient sympathetic activation. Epidural anesthesia with upper level of sensory blockade at T4-T8 (n = 7) completely blocked spontaneous SSA and no detectable skin sympathetic activity could be provoked by arousal stimuli later than 14 min after the test dose. Sympathetic blockade was accompanied by marked increases in foot skin blood flow and loss of skin resistance responses to arousal. Epidural anesthesia with sensory blockade up to T10-11 (n = 2) only produced a partial sympathetic blockade. The result shows that epidural anesthesia with sensory blockade at T8 or above is equally as effective as injections of local anesthetics directly at postganglionic nerve fibers or ganglionic blockade in producing a complete sympathetic blockade of intraneurally recorded SSA. This neural blockade was paralleled by skin vasodilatation and a loss of sudomotor responses in the foot.

Skin vasomotor reflex responses in two contrasting groups of autonomic failure

“…Although BLE has previously been demonstrated as a means to elicit SkVR in MSA (Asahina et al 2003), mild motor impairment in our MSA subjects (although none required antiparkinsonian treatment), may have contributed to the greater variability of response seen with this test. A relationship between laser Doppler recordings of SkVR responses and direct intraneural recordings of skin sympathetic activity has been reported (Lundin et al 1990). SkVR responses require intact peripheral sympathetic nerves as shown by studies in surgically sympathectomised subjects (Bolton et al 1936;Rex et al 1998) and temporary nerve blocks (Netten et al 1995;Lehtipalo et al 2000).…”

Local metabolic changes in subcutaneous adipose tissue during intravenous and epidural analgesia

“…This has been demonstrated by Lundin et al . in humans, where a total blockade of sympathetic nerve activity in the skin and muscle of the leg could be obtained during lumbar epidural anesthesia (14, 15). Postoperative analgesia with a thoracic epidural technique aims at a low dose of local anesthetics epidurally to avoid systemic effects, e.g.…”

“…Previous investigations have shown that interstitial glycerol concentration in the subcutaneous adipose tissue may serve as a marker for the intracellular lipolytic rate (10). Subcutaneous lipolysis is activated by the sympathetic nervous system (11–13), and the activity in the sympathetic nerve fibers could be blocked within the area covered by epidural anesthesia (14, 15). Therefore, we hypothesized that epidural analgesia would attenuate the regional lipolysis within the area covered by the epidural analgesia, reflected as decreased glycerol concentrations as measured using the microdialysis technique.…”

Effects of intrathecal morphine and spinal anaesthesia on sympathetic nerve activity in humans

“…Using indirect methods such as measurements of blood flow, skin resistance and skin temperature (1-3), contradictory results have been obtained concerning the magnitude and extent of the sympathetic blockade accompanying epidural and spinal anaesthesia. I n two studies direct intraneural recordings of muscle (MSA) and skin (SSA) sympathetic activity in the peroneal nerve were performed during epidural blockade (4, 5) and it was demonstrated that a sensory block above T,,-T, inhibited all spontaneous efferent sympathetic activity and blocked the sympathetic activation elicited by apnoea or arousal stimuli (ix. sudden unexpected sounds or touches, mental arithmetic), Based on the lack of changes in heart rate and blood pressure (6)(7)(8)(9), the administration of morphine epidurally or intrathecally is not believed to have any effect on sympathetic nerve fibres.…”