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YAutonomic dysreflexia
Autonomic dysreflexia, "AD" also known as "autonomic hyperreflexia or Hyperreflexia, is a potentially life
threatening condition which can be considered amedical emergency requiring immediate attention. AD
occurs most often in spinal cord-injured individuals with spinal lesions above the (T6) spinal cord level.
Acute AD is a reaction of the autonomic (involuntary) nervous system to overstimulation. It is characterised
by severe paroxysmal hypertension (episodic high blood pressure) associated with throbbing headaches,
profuse sweating, nasal stuffiness, flushing of the skin above the level of the lesion, bradycardia,
apprehension and anxiety, which is sometimes accompanied by cognitive
impairment.[1]
The sympathetic discharge that occurs is usually in association with spinal cord injury (SCI)
or disease (e.g. multiple sclerosis). AD is believed to be triggered by afferent stimuli (nerve signals that
send messages back to the spinal cord and brain) which originate below the level of the spinal cord lesion.
It is believed that these afferent stimuli trigger and maintain an increase in blood pressure via a
sympathetically mediated vasoconstriction in muscle, skin and splanchnic (gut) vascular beds (Karlsson,
1999).
Causes
The most common causes of autonomic hyperreflexia in patients with spinal cord injury are loss of bowel
and bladder function, resulting in impaction in the case of the bowels and distention in case of the bladder.
These are generally found in patients with a spinal cord injury above the T6 (6th Thoracic Vertebral) level,
but can occur in patients with a transection as low as T10 (10th Thoracic Vertebral) level. When a painful
stimulus occurs, as when voiding is interrupted or a bowel obstruction occurs, nerve impulses are sent to
the brain via the spinal cord.[2]
However, in spinal cord transection, these impulses are unable to travel past
the injury. This results in a spinal cord reflex to the autonomic nervous system in response to pain. In
patients with spinal cord transection, types of stimulation that are tolerated by healthy people create an
excessive response from the person's nervous system.
Other causes include medication side effects and various disease processes. The use of stimulants such
as cocaine and amphetamines which can result in urinary retention, and the use of CNS depressants and
other psychotropic and psychoactive drugs can also lead to urinary retention and constipation thus leading
to autonomic dysreflexia when in use over an extended period of time.Guillain-Barre syndrome a
demyelinating disease that can result in peripheral paralysis can progress to encompass autonomic
functions leading to a loss of normal respiratory, bladder and bowel function, thus resulting in autonomic
dysreflexia. Severe head trauma, and other brain injuries[3]
can instigate autonomic dysreflexia at
the Central Nervous System by interfering with the reception of the signal that brings the urge to void the
bladder and bowels and with the volutary abiliity to micturate and defecate. Other causal theories for
Autonomic Dysreflexia include Noxious Stimuli or painful stimuli arising from the peripheral sensory
neurons. These stimuli are interrupted in their journey to the brain due to a transection of the spine result in
a paradoxical stimulation of autonomic pathways of the Autonomic Nervous System.
Controversy Over Peripherally Noxious Causes of Autonomic Dysreflexia
Current scientific literature suggests that noxious (painful) stimuli are the primary initiators of AD. However,
different studies have found that activation of pain receptors in muscle and skin below the lesion in spinal
cord injured individuals did not trigger AD.[4][5]
These studies suggests that not all noxious stimuli are
reliable triggers of AD, and because non-noxious stimuli can also trigger AD, attribution of an episode of
AD to noxious stimuli may cause clinicians to overlook underlying non-noxious triggers. As a result, non-
noxious trigger factors remain undetected, prolonging an episode of AD. They concluded that when
deducing the potential causes of AD it is important to consider non-noxious sources of stimulation in
addition to noxious triggers. Current Assessment of Autonomic Dysreflexia in patients with known causitive
factors include palpation of the bladder and bowel and can also include bladder scan.
Diagnosis
The diagnosis is usually not subtle, although asymptomatic events have been documented. Autonomic
dysreflexia differs from autonomic instability, a term used to describe the variety of modest cardiac and
neurological changes that accompany a spinal cord injury, including bradycardia, orthostatic hypotension,
and ambient temperature intolerance. In autonomic dysreflexia, patients will experience hypertension,
sweating, and erythema (more likely in upper extremities) and may suffer from headaches and blurred
vision. Mortality is rare with AD, but morbidity such as stroke, retinal hemorrhage and pulmonary edema if
left untreated can be quite severe. Older patients with very incomplete spinal cord injuries and
systolic hypertension without symptoms are usually experiencing essential hypertension, not autonomic
dysreflexia. Aggressive treatment of these elderly patients with rapidly acting antihypertensive medications
can have disastrous results.
Onset
The risk is greatest with cervical spinal cord lesions and is rare with lesions below T6 Thoracic vertebrae. It
has rarely been reported in spinal cord lesions as low as T10. The first episode may occur weeks to years
after spinal cord injury takes place, but most people at risk (80%) develop their first episode within the first
year after injury.
Symptoms
This condition is distinct and usually episodic, with the patient experiencing remarkably high blood pressure
(often with systolic readings over 200 mm. Hg), intense headaches, profuse sweating, facialerythema,
goosebumps, nasal stuffiness, and a "feeling of doom". An elevation of 40 mm. Hg. over baseline systolic
should be suspicious for dysreflexia.
Treatment
Proper treatment of autonomic dysreflexia involves administration of anti-hypertensives along with
immediate determination and removal of the triggering stimuli. Often, sitting the patient up and dangling
legs over the bedside can reduce blood pressures below dangerous levels and provide partial symptom
relief. Tight clothing and stockings should be removed. Catheterization of the bladder, or relief of a blocked
urinary catheter tube may resolve the problem. The rectum should be cleared of stool impaction, using
anaesthetic lubricating jelly. If the noxious precipitating trigger cannot be identified, drug treatment is
needed to decrease elevating intracranial pressure until further studies can identify the cause.
Drug treatment includes the rapidly acting vasodilators, including sublingual nitrates or oral clonidine.
Topical nitropaste is a convenient and safe treatment—an inch or two can be applied to the chest wall, and
wiped off when blood pressures begin to normalize. Autonomic dysreflexia is abolished temporarily
by spinal or general anaesthesia. These treatment are used during obstetric delivery of a woman with
autonomic dysreflexia.
Complications
Autonomic dysreflexia can become chronic and recurrent, often in response to longstanding medical
problems like soft tissue ulcers or hemorrhoids. Long term therapy may include alpha blockers orcalcium
channel blockers.
Complications of severe acute hypertension can include seizures, pulmonary edema, myocardial
infarction or cerebral hemorrhage.
Prognosis
The cause of autonomic dysreflexia itself can be life threatening, and must also be completely investigated
and treated appropriately to prevent unnecessary morbidity and mortality.
The Consortium for Spinal Cord Medicine has developed evidence-based clinical practice guidelines for the
management of autonomic dysreflexia in adults, children, and pregnant women. There is also a consumer
version of this guideline.
Autonomic Dysreflexia in Spinal Cord Injury Introduction
Background
Autonomic dysreflexia (AD) is a syndrome of massive imbalanced reflex sympathetic discharge
occurring in patients with spinal cord injury (SCI) above the splanchnic sympathetic outflow (T5-T6).
Anthony Bowlby first recognized this syndrome in 1890 when he described profuse sweating and
erythematous rash of the head and neck initiated by bladder catheterization in an 18-year-old patient
with SCI. Guttmann and Whitteridge completed a full description of the syndrome in 1947. This
condition represents a medical emergency, so recognizing and treating the earliest signs and
symptoms efficiently can avoid dangerous sequelae of elevated blood pressure. SCI patients,
caregivers, and medical professionals must be knowledgeable about this syndrome and its
management. (See image below and Image 1.)
(A) A strong sensory input (not necessarily noxious) is carried into the spinal cord via
intact peripheral nerves. The most common origins are bladder and bowel. (B) This
strong sensory input travels up the spinal cord and evokes a massive reflex sympathetic
surge from the thoracolumbar sympathetic nerves, causing widespread vasoconstriction,
most significantly in the subdiaphragmatic (or splanchnic) vasculature. Thus, peripheral
arterial hypertension occurs. (C) The brain detects this hypertensive crisis through
intact baroreceptors in the neck delivered to the brain through cranial nerves IX and X
(Vagus). (D) The brain attempts 2 maneuvers to halt the progression of this
hypertensive crisis. First, the brain attempts to shut down the sympathetic surge by
sending descending inhibitory impulses. These impulses do not get to most sympathetic
outflow levels because of the spinal cord injury at T6 or above. Inhibitory impulses are
blocked in the injured spinal cord. In the second maneuver, the brain attempts to bring
down peripheral blood pressure by slowing the heart rate through an intact vagus
(parasympathetic) nerve; however, this compensatory bradycardia is inadequate and
hypertension continues. In summary, the sympathetics prevail below the level of
neurologic injury, and the parasympathetic nerves prevail above the level of injury. Once
the inciting stimulus is removed, reflex hypertension resolves.
Pathophysiology
This phenomenon occurs after the phase of spinal shock in which reflexes return. Individuals with
injury above the major splanchnic outflow may develop autonomic dysreflexia (AD). Below the injury,
intact peripheral sensory nerves transmit impulses that ascend in the spinothalamic and posterior
columns to stimulate sympathetic neurons located in the intermediolateral gray matter of the spinal
cord. The inhibitory outflow above the SCI from cerebral vasomotor centers is increased, but it is
unable to pass below the block of the SCI. This large sympathetic outflow causes release of various
neurotransmitters (norepinephrine, dopamine-b-hydroxylase, dopamine), causing piloerection, skin
pallor, and severe vasoconstriction in arterial vasculature.1 The result is sudden elevation in blood
pressure and vasodilation above the level of injury. Patients commonly have a headache caused by
vasodilation of pain sensitive intracranial vessels.
Vasomotor brainstem reflexes attempt to lower blood pressure by increasing parasympathetic
stimulation to the heart through the vagus nerve to cause compensatory bradycardia. This reflex
action cannot compensate for severe vasoconstriction, explained by the Poiseuille formula, where
pressure in a tube is affected to the fourth power by change in radius (vasoconstriction) and only
linearly by change in flow rate (bradycardia). Parasympathetic nerves prevail above the level of injury,
which may be characterized by profuse sweating and vasodilation with skin flushing.
Cameron and colleagues have found that site-directed genetic manipulation of fiber sprouting in the
spinal dorsal horns in a cord compression rat model could alter the extent of hyperreflexia after bowel
distention, indicating that endogenous spinal cord circuitry/neural sprouting plays a role in the
pathophysiology of AD.2
Frequency
United States
Reported prevalence rates vary, but the generally accepted rate is 48-90% of all individuals who are
injured at T6 and above. Some incidence has been reported in SCI as low as T10. Autonomic
dysreflexia (AD) occurs during labor in approximately two thirds of pregnant women with SCI above
the level of T6. The occurrence of AD increases as the patient evolves out of spinal shock. With the
return of sacral reflexes, the possibility of AD increases.3
Mortality/Morbidity
Morbidity related to autonomic dysreflexia is associated with hypertension, which can cause
retinal/cerebral hemorrhage, myocardial infarction, or seizures. Mortality is rare.
Sex
The male-to-female ratio for sustaining SCI is 4:1; therefore, autonomic dysreflexia is primarily a male
phenomenon.
Age
No specific relationship has been documented between autonomic dysreflexia and age.
Clinical
History
The patient with autonomic dysreflexia generally gives a history of blurry vision, headaches, and a
sense of anxiety. Feelings of apprehension or anxiety over an impending physical problem commonly
are exhibited.
Physical
A patient with autonomic dysreflexia (AD) may have 1 or more of the following findings on physical
examination:
A sudden significant rise in systolic and diastolic blood pressures, usually associated with
bradycardia, can appear. The normal systolic blood pressure for SCI above T6 is 90-110 mm
Hg. Blood pressure 20-40 mm Hg above the reference range for such patients may be a sign
of AD.
Profuse sweating above the level of lesion, especially in the face, neck, and shoulders, may
be noted, but it rarely occurs below the level of the lesion because of sympathetic cholinergic
activity.
Goose bumps above, or possibly below, the level of the lesion may be observed.
Flushing of the skin above the level of the lesion, especially in the face, neck, and shoulders,
frequently is noted.
The patient may report blurred vision.
Spots may appear in the patient's visual fields.
Nasal congestion is common.
No symptoms may be observed, despite elevated blood pressure.
Causes
Episodes of autonomic dysreflexia (AD) can be triggered by many potential causes.4 Essentially any
painful, irritating, or even strong stimulus below the level of the injury can cause an episode of AD.
Although the list is not comprehensive, the following events or conditions all can cause episodes of
AD:
Bladder distension
Urinary tract infection
Cystoscopy
Urodynamics
Detrusor-sphincter dyssynergia5
Epididymitis or scrotal compression
Bowel distension
Bowel impaction
Gallstones
Gastric ulcers or gastritis
Invasive testing
Hemorrhoids
Gastrocolic irritation
Appendicitis or other abdominal pathology trauma
Menstruation
Pregnancy, especially labor and delivery
Vaginitis
Sexual intercourse
Ejaculation
Deep vein thrombosis
Pulmonary emboli
Pressure ulcers
Ingrown toenail
Burns or sunburn
Blisters
Insect bites
Contact with hard or sharp objects
Temperature fluctuations
Constrictive clothing, shoes, or appliances
Heterotopic bone
Fractures or other trauma
Surgical or diagnostic procedures
Pain
More on Autonomic Dysreflexia in Spinal Cord Injury
Overview: Autonomic Dysreflexia in Spinal Cord Injury
Differential Diagnoses & Workup: Autonomic Dysreflexia in Spinal Cord Injury
Treatment & Medication: Autonomic Dysreflexia in Spinal Cord Injury
Follow-up: Autonomic Dysreflexia in Spinal Cord Injury
Multimedia: Autonomic Dysreflexia in Spinal Cord Injury
References
Further Reading
Differential Diagnoses
Other Problems to Be Considered
Essential hypertension
Pheochromocytoma
Treatment
Rehabilitation Program
Physical Therapy
Physical therapists who treat SCI patients need to have a good understanding of autonomic
dysreflexia (AD) and be familiar with the signs and symptoms of this potentially life-threatening
condition.3When completing physical therapy sessions, the therapist needs to monitor the urinary
catheter for any blockage or twisting. If the patient becomes hypertensive during therapy, he/she
should be placed in an upright position immediately, rather than remain in a supine or reclining
position. The therapist needs to complete careful inspection to identify the source of painful stimuli
(eg, catheter, restrictive clothing, leg bag straps, abdominal supports, orthoses).4
A less common cause of AD during physical therapy sessions may originate with muscle stretching,
either from range of motion or passive stretching. If the patient develops AD, the physical therapist
needs to treat it as a medical emergency and be familiar with established protocols for medical
management within his/her particular setting. The individual therapy session then must be
discontinued to allow the patient to stabilize and recover.
Occupational Therapy
Occupational therapy is another discipline involved extensively in the rehabilitation of individuals with
SCI. The occupational therapist also must be familiar with the signs and symptoms of autonomic
dysreflexia (AD) and be able to respond quickly if the condition develops during a therapy
session.3 The occupational therapist performs extensive training in the performance of activities of
daily living with patients who have sustained SCI. Activities of daily living include proper bowel and
bladder management, which can help prevent the occurrence of AD. The occupational therapist may
be involved in establishing a regular bowel program and also may complete patient and
family/caregiver education on this aspect of care. The occupational and physical therapists should
educate the patient and family members about AD and ensure that they are familiar with prevention
strategies, signs and symptoms, and proper management of the condition.
Speech Therapy
Generally, the treatment provided by the speech therapist is not associated with any painful stimuli
below the lesion that may precipitate an autonomic dysreflexia response; however, as health care
providers involved in the care of individuals with SCI, the speech therapist must be familiar with the
manifestations of this potential life-threatening complication.3
Recreational Therapy
Recreational therapists also are important members of the rehabilitation team, as they help patients
with SCI to become involved in recreational and social activities. As members of the SCI team, they
also must be knowledgeable about autonomic dysreflexia and know how to respond appropriately if
the patient develops symptoms during a recreational therapy session.3
Medical Issues/Complications
Complications associated with autonomic dysreflexia result directly from sustained, severe peripheral
hypertension and include retinal/cerebral hemorrhage, myocardial infarction, and seizures.
Consultations
If the cause of the autonomic dysreflexia episode is not found and blood pressure remains elevated,
recommend that the patient go to the nearest emergency department for close monitoring and further
investigation of the possible cause. Consult an intensive care specialist for ICU monitoring and
treatment of the hypertension.
Medication
Check the patient's blood pressure. If blood pressure is elevated and the person is supine, have the
person sit up immediately and loosen any clothing or constrictive devices. Sitting leads to pooling of
blood in the lower extremities and may reduce blood pressure. Monitor blood pressure and pulse
every 2-5 minutes until they have stabilized; blood pressures can fluctuate quickly during an AD
episode from impaired autonomic regulation. Survey the person for instigating causes, beginning with
the urinary system, the most common cause of autonomic dysreflexia (AD).6
If an indwelling urinary catheter is not in place, catheterize the patient.
If the individual has an indwelling urinary catheter, check the system along its entire length for
kinks, folds, constrictions, or obstructions and for correct placement of the indwelling catheter.
If the catheter appears to be blocked, gently irrigate the bladder with a small amount of fluid,
such as normal saline at body temperature. Avoid manually compressing or tapping on the
bladder.
If the catheter is draining and blood pressure remains elevated, suspect fecal impaction, the
second most common cause of AD, and check the rectum for stool using lidocaine jelly as
lubricant.
Use an antihypertensive agent with rapid onset and short duration while the causes of AD are
being investigated.
The most commonly used agents are nifedipine and nitrates (eg, nitroglycerine paste).
Nifedipine should be in the immediate release form; bite-and-swallow is the preferred method
of administration, not sublingual. Other agents used are mecamylamine, diazoxide, and
phenoxybenzamine.
Use antihypertensives with extreme caution in older persons or people with coronary artery
disease.
Monitor the individual's symptoms and blood pressure for at least 2 hours after resolution of
the AD episode to ensure that elevation of blood pressure does not recur. AD may resolve
because of medication, not because of resolution of the underlying cause.
If there is poor response to treatment and/or if the cause of the AD has not been identified,
send the patient to ER for monitoring, maintenance of pharmacologic control of blood
pressure, and investigation of other possible causes of the AD.
Document the episode.
A Taiwanese study indicated that in patients with SCI who have detrusor sphincter dyssynergia, using
a combination of fluoroscopy and electromyography to localize the external urethral sphincter, with a
Foley catheter employed to visualize vesicourethral anatomy, makes transperineal injection of
botulinum toxin type A into the external urethral sphincter safe, accurate, and easy to perform.5 Such
injections have been shown to reduce the occurrence and degree of autonomic dysreflexia, as well as
of vesicoureteral reflux, hydronephrosis, and urinary tract infection.
Antihypertensives
Antihypertensive agents with rapid onset and short duration are administered while the causes of
autonomic dysreflexia (AD) are investigated if BP is at or above 150 mm Hg systolic. Patients who
have experienced episodes of AD are treated with antihypertensives prior to procedures known to
cause their AD episodes.
Nifedipine (Procardia)
Calcium ion influx inhibitor (slow-channel blocker or calcium ion antagonist); inhibits transmembrane
influx of calcium ions into cardiac and smooth muscle. Reduces arterial pressure at rest and at a
given level of exercise by dilating peripheral arterioles and reducing the total peripheral resistance
(afterload).
Dosing
Interactions
Contraindications
Precautions
Adult
10 mg cap PO initially; bite and swallow
Pediatric
Not recommended
Nitroglycerine (Depo-Nit, Nitrostat, Nitrol, Nitro-Bid)
Principal pharmacologic action of nitroglycerin is relaxation of vascular smooth muscle, producing
vasodilator effect on both peripheral arteries and veins with more prominent effects on the latter.
Dilation of postcapillary vessels, including large veins, promotes peripheral pooling of blood and
decreases venous return to the heart, thereby reducing left ventricular end-diastolic pressure
(preload). Arteriolar relaxation reduces systemic vascular resistance and arterial pressure (after-load).
Dosing
Interactions
Contraindications
Precautions
Adult
0.4 mg per metered spray for SL use or 2% nitroglycerine ointment
Start with 0.5-in strip to chest wall and titrate as necessary; alternatively, 0.15-0.6 mg tab SL or 5
mcg/min IV
Pediatric
Not established
Phenoxybenzamine hydrochloride (Dibenzyline)
Long-acting, adrenergic, alpha-receptor blocking agent that can produce and maintain chemical
sympathectomy by oral administration; increases blood flow to skin, mucosae, and abdominal viscera
and lowers supine and erect blood pressures.
No effect on parasympathetic system.
Dosing
Interactions
Contraindications
Precautions
Adult
Adjust dose to fit needs of each patient
Slowly increase dose until desired effect obtained or side effects from blockade problematic
Observe patient on each level before instituting increase
Dosage should provide symptomatic relief and/or objective improvement, but not to where side effects
from blockage are troublesome
Initially, administer 10 mg of Dibenzyline (phenoxybenzamine hydrochloride) PO bid; increase dose
qod, usually to 20-40 mg 2 or 3 times/d, until an optimal dosage is obtained, as judged by blood
pressure control
Pediatric
Not established
Mecamylamine (Inversine)
Potent oral secondary amine, antihypertensive agent, and ganglion blocker.
Produces smooth and predictable reduction of blood pressure with small oral dose.
Antihypertensive effect predominantly orthostatic, but supine blood pressure also significantly
reduced.
Used for management of moderately severe-to-severe essential hypertension and in uncomplicated
cases of malignant hypertension.
Dosing
Interactions
Contraindications
Precautions
Adult
2.5 mg PO prn
Pediatric
Not established
Diazoxide (Hyperstat)
Nondiuretic benzothiadiazine antihypertensive agent; achieves prompt reduction of blood pressure by
relaxing smooth muscle in peripheral arterioles; cardiac output increases as blood pressure is
reduced.
Dosing
Interactions
Contraindications
Precautions
Adult
1-3 mg/kg IV to maximum dose of 150 mg in single injection; repeat at 5-15 min intervals until
reduction of BP is satisfactory (eg, diastolic pressure <100 mm Hg)
Pediatric
Administer as in adults
Follow-up
Deterrence
Good bladder and bowel care (ie, preventing fecal impaction, bladder distention) are mainstays in
preventing episodes of autonomic dysreflexia.
Patient Education
All medical professionals should educate the patient and family members or caregivers about this
potentially life-threatening complication of SCI.3
Miscellaneous
Medicolegal Pitfalls
Failure to have a high index of suspicion and recognize autonomic dysreflexia quickly could present
medical and legal problems for the physician. For example, a physician who assumes that headache
and anxiety in a person with complete C6 tetraplegia is a manifestation of depression, without
checking vital signs, is at medical/legal risk.
Media file 1: (A) A strong sensory input (not necessarily noxious) is carried into the spinal cord via
intact peripheral nerves. The most common origins are bladder and bowel. (B) This strong sensory
input travels up the spinal cord and evokes a massive reflex sympathetic surge from the
thoracolumbar sympathetic nerves, causing widespread vasoconstriction, most significantly in the
subdiaphragmatic (or splanchnic) vasculature. Thus, peripheral arterial hypertension occurs. (C) The
brain detects this hypertensive crisis through intact baroreceptors in the neck delivered to the brain
through cranial nerves IX and X (Vagus). (D) The brain attempts 2 maneuvers to halt the progression
of this hypertensive crisis. First, the brain attempts to shut down the sympathetic surge by sending
descending inhibitory impulses. These impulses do not get to most sympathetic outflow levels
because of the spinal cord injury at T6 or above. Inhibitory impulses are blocked in the injured spinal
cord. In the second maneuver, the brain attempts to bring down peripheral blood pressure by slowing
the heart rate through an intact vagus (parasympathetic) nerve; however, this compensatory