Despite a duration of only 2 week, repeated IVRS (intravenous regional sympathetic block) efferent blocks are an attractive alternative to the higher-risk techniques of thoracic sympathetic block and thoracic surgical or thoracoscopic sympathectomy. (p. 848)
Table 42-1
Classification of percutaneous neural destructive procedures:Anatomy
1. Peripheral neurotomy (such as destruction of intercostal, ilioinguinal nerves)
2. Rhizotomy (spinal dorsal root rhizotomy, trigeminal rhizotomy)
3. Destruction of sensory pathways in the spinal cord (midline punctuate myelotomy, cordotomy)
4. destruction of brain sensory centers (hypophysectomy)
5. Sympathectomy(p.992)
The authors found that the incidence of hypotension was a function of the level of sympathetic denervation, occurring in 60% of patients with a T7 sympathectomy, and in 100% of patient with a T4 or higher level of sympathectomy.
(p 226)
After thoracoscopic sympathectomy for hyperhidrosis, very severe discomfort and hyperhidrosis in the neighboring non-sympathectomized regions occurred with alarming frequency and intensity.
(p.879)
Cardiovascular effects of epidural blockade
"Central" Sympathetic block (T1-T4) - Blockade of
Cardiac sympathetic outflow from vasomotor center
Cardiac sympathetic reflexes at segmental level
Vasoconstrictor fibers to head, neck, and arms
Effect:
HR ↓ CO ↓
Vasodilation in upper limbs
"Inappropriate bradycardia"; "sudden bradycardia"; vagal arrest (p. 247)
↓↓Venous return may result in sudden parasympathetic tone ("faint response")
↓ ↓ HR → cardiac arrest
"Inappropriate" bradycardia (i.e. "normal" HR in face of ↓MAP with sensory level T3-T4)
Peripheral vasodilation should evoke an ↑ HR. But ↓ venous return → ↑vagal tone, so HR remains at preblock rate but is "inappropriately" slow.
↓HR with visceral traction in presence of blockade to T1.
Total sympathetic block
Unopposed vagus
Changes in vagal tone → profound changes in HR; may → transient asystole (p. 248)
Thermoregulation and Shivering
Hypothermia (a decrease in core temperature) is common in patients undergoing surgery with epidural anesthesia and is thought to result from heat loss to the cold environment due to sympathectomy-induced vasodilation. The normal process by which thermoregulation usually minimizes intraoperative core temperature is prevented, since epidural anesthesia directly inhibits vasoconstriction in the analgesic dermatomes. (p.253)
Central neuraxial anesthesia-induced sympathectomy leads to peripheral vasodilation, reduced preload, and subsequently decreased cardiac output. The incidence and extent of hypotension depends on the height of the block, the patient's position, and whether appropriate measures were instituted prophylactically to minimize hypotension.
Wolters Kluwer HealthEdition: 4 - 2008
