Autonomic Hyperreflexia

Question 1

What is autonomic hyperreflexia?

Answer 1

A syndrome of widespread reflex sympathetic discharge in patient with chronic spinal cord lesions (usually at or above the T7 level) in response to stimuli below the lesion.

Question 2

Describe the physiology of autonomic hyperreflexia.

Answer 2

Descending inhibitory signals from supraspinal centers are unable to modulate afferent input from below the level of the cord lesion. As a result, sympathetic stimulation below the level of the lesion causes a reflex arc leading to massive sympathetic efferent discharge below the level of the lesion. The ensuing hypertension initiates corrective reflexes such as bradycardia and vasodilation.

Question 3

What are the clinical features of autonomic hyperreflexia?

Answer 3

1. Below the lesion:
  pallor
  pilomotor erection
  intense somatic and visceral muscle contraction
  increased spasticity

2. Above the lesion:
  flushing of face and neck
  mucous membrane and conjunctival congestion
  intense sweating
  mydriasis

3. bradycardia, AV block, PACs, PVCs
4. severe HA, szs, SAH, LOC
5. dyspnea, LV failure/pulm edema
6. blurred vision
7. anxiety, agitation
8. chest pain/MI
9. nausea

Question 4

What is the differential diagnosis when suspecting autonomic hyperreflexia?

Answer 4

chronic hypertension
hypertensive crisis of other etiology
pheochromocytoma
drug toxicity (e.g. cocaine)
thyrotoxicosis
CNS herniation

Question 5

What is the management of autonomic hyperreflexia?

Answer 5

communicate with surgeon and remove preciptating stimulus (e.g. empty the bladder)
consider deepening anesthesia if under GA
if under neuraxial analgesia, consider raising level of block
treat severe hypertension with fast acting easily titratable agents
look for evidence of end-organ involvement of hypertension and treat accordingly

Question 6

What agents would be useful to treat the severe hypertension of autonomic hyperreflexia?

Answer 6

alpha-blocking agents like phentolamine 5mg IV PRN
direct vasodilators (hydralazine 10 - 20 mg IV)
sodium nitroprusside start 1mcg/kg/min up to 3 - 4 mcg/kg/min
calcium channel blockers (e.g. nicardipine 5mg/hr titrating up to 15mg/hr max)

Question 7

What are the physical findings of autonomic hyperreflexia above the lesion?

Answer 7

flushing of the face and neck
mucous membrane and conjunctival congestion
intense sweating
mydriasis

Question 8

What are the physical findings of autonomic hyperreflexia below the lesion?

Answer 8

pallor
pilomotor efection
intense somatic and visceral muscle contraction
increased spasticity