Autonomic dysreflexia (AD) is a potential medical emergency classically characterized by uncontrolled hypertension and bradycardia, although tachycardia is known to occur commonly.
AD occurs most often in individuals with spinal cord injuries with lesions at or above the T6 spinal cord level, although it has been reported in patients with lesions as low as T10. Guillain–Barré syndrome may also cause autonomic dysreflexia.
Uncontrolled hypertension in AD may result in mild symptoms, such as sweating above the lesion level, goosebumps, blurred vision, or headache; However, severe hypertension may result in potentially life-threatening complications, including seizure, intracranial bleeding, or retinal detachment.
AD is triggered by either noxious or non-noxious (harmful) stimuli, resulting in sympathetic stimulation and hyperactivity. The most common causes include bladder or bowel over-distension from urinary retention and fecal compaction. The resulting sympathetic surge transmits through intact peripheral nerves, resulting in systemic vasoconstriction below the level of the spinal cord lesion.
The peripheral arterial vasoconstriction and hypertension activate the baroreceptors, resulting in a parasympathetic surge originating in the central nervous system to inhibit the sympathetic outflow; however, the parasympathetic signal cannot transmit below the level of the spinal cord lesion. This results in bradycardia, vasodilation, flushing, pupillary constriction and nasal stuffiness above the spinal lesion. At the same time, there is piloerection and pale and cool skin below the lesion due to the prevailing sympathetic outflow.
Initial treatment involves sitting the patient upright, removing any constrictive clothing (including abdominal binders and support stockings), rechecking blood pressure frequently, and then checking for and removing the inciting issue, which may require urinary catheterization or bowel disimpaction. Suppose systolic blood pressure remains elevated (over 150 mm Hg) after the initial steps. In that case, fast-acting short-duration antihypertensives are considered, while other inciting causes must be investigated for the symptoms to resolve. See the TREATMENT section below for more information.
Prevention of AD involves educating the patient, family and caregivers about the precipitating cause, if known, and how to avoid it and other triggers. Since bladder and bowel are common causes, prevention involves routine bladder and bowel programs and urological follow-up for cystoscopy/urodynamic studies.
Signs and symptoms This condition is distinct and usually episodic, with the people potentially experiencing remarkably high blood pressure, intense headaches, profuse sweating, facial erythema, goosebumps, nasal stuffiness, a "feeling of doom" or apprehension, and blurred vision.
An elevation of 20 mm Hg over baseline systolic blood pressure, with a potential source below the neurological level of injury, meets the current definition of dysreflexia.
Complications Autonomic dysreflexia can become chronic and recurrent, often in response to longstanding medical problems like soft tissue pressure injuries or hemorrhoids. Long-term therapy may include alpha blockers or calcium channel blockers.
Complications of severe acute hypertension can include seizures, pulmonary edema, myocardial infarction, or cerebral hemorrhage. Additional organs that may be affected include the kidneys and retinas of the eyes.
Causes The first episode of autonomic dysreflexia may occur weeks to years after spinal cord injury, but most people at risk (80%) develop their first episode within the first year after injury. Early AD tends to be associated with less severe increases in blood pressure.
One common causative factor may be an undetected urinary tract infection. The difficulty in assessing this may be complicated by using indwelling or suprapubic catheters. 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 psychoactive drugs can also lead to urinary retention and constipation, thus leading to autonomic dysreflexia when in use over an extended period.
Pain Current scientific literature suggests that noxious (painful) stimuli are the primary initiators of AD. (Note: Not all noxious stimuli will cause AD. Some otherwise severe noxious stimuli in unaffected people, e.g. broken bones, may not result in AD and may even go unnoticed.) 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.
These studies suggest that not all noxious stimuli are reliable triggers of AD. 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 AD episode.
They concluded that when deducing the potential causes of AD, it is important to consider non-noxious sources of stimulation and noxious triggers. Current assessment of autonomic dysreflexia in patients with known causative factors includes palpation of the bladder and bowel and can also include a bladder scan.
Mechanism Supraspinal vasomotor neurons send projections to the intermediolateral cell column, composed of sympathetic preganglionic neurons (SPN) through the T1-L2 segments. The supraspinal neurons act on the SPN and its tonic firing, modulating its action on the peripheral sympathetic chain ganglia and the adrenal medulla.
The sympathetic ganglia act directly on the blood vessels they innervate throughout the body, controlling vessel diameter and resistance. In contrast, the adrenal medulla indirectly controls the same action by releasing epinephrine and norepinephrine. The descending autonomic pathways, which are responsible for the supraspinal communication with the SPN, are interrupted, resulting in decreased sympathetic outflow below the level of the injury. In this circumstance, the SPN is controlled only by spinal influences.
The decreased sympathetic outflow causes reduced blood pressure and sympathetic reflex in the first couple of weeks after a spinal injury. Eventually, synaptic reorganization and plasticity of SPN develop into an overly sensitive state, which results in abnormal reflex activation of SPN due to afferent stimuli, such as bowel or bladder distension. Reflex activation results in systemic vasoconstriction below the spinal cord disruption.
The peripheral arterial vasoconstriction and hypertension activate the baroreceptors, resulting in a parasympathetic surge originating in the central nervous system, which inhibits the sympathetic outflow; however, the parasympathetic signal is unable to transmit below the level of the spinal cord lesion. This results in vasodilation, flushing, pupillary constriction and nasal stuffiness above the spinal lesion, while piloerection, pale and cool skin below the lesion due to the prevailing sympathetic outflow.
This issue is much more prominent for lesions at or above the T6 level because the Splanchnic nerves emerge from the T5 level and below. Loss of the brain's control over T6 and below causes splanchnic arteries to reflexively vasoconstrict. Since the Splanchnic arteries are the body's largest reservoir for circulating blood, their vasoconstriction dramatically affects blood pressure.
Diagnosis The symptoms are usually not subtle, although asymptomatic events have been documented. Autonomic dysreflexia differs from autonomic instability, the various modest cardiac and neurological changes accompanying a spinal cord injury, including bradycardia, orthostatic hypotension, and ambient temperature intolerance. In autonomic dysreflexia, patients will experience hypertension, sweating, spasms (sometimes severe spasms) and erythema (more likely in the upper extremities) and may experience 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 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.
Treatment Proper treatment of autonomic dysreflexia involves the administration of anti-hypertensives along with immediate determination and removal of the triggering stimuli. Sitting the patient up and dangling the legs over the bedside can reduce blood pressures below dangerous levels and provide partial symptom relief. Tight clothing and stockings should be removed. Straight 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 rapidly acting vasodilators, sublingual or topical nitrates, oral hydralazine, or clonidine. Ganglionic blockers are also used to control sympathetic nervous system outflow. Topical nitroglycerin ointment is a convenient and safe treatment—an inch or two can be applied to the chest wall or forehead and wiped off when blood pressures begin normalising. Autonomic dysreflexia is abolished temporarily by spinal or general anaesthesia. These treatments are used during obstetric delivery of women with autonomic dysreflexia.
Pharmacological Treatment BEFORE ADMINISTERING PHARMACOLOGICAL TREATMENT, ALWAYS CHECK FOR INTERCURRENT AND/OR RECENT USE OF MEDICATION FOR ERECTILE DYSFUNCTION
Oral agents Glyceryl Trinitrate (GTN) DO NOT USE GTN SPRAY, TABLETS OR PATCH IF A MEDICATION FOR ERECTILE DYSFUNCTION SUCH AS SILDENAFIL (VIAGRA), VARDENAFIL (LEVITRA) HAS BEEN TAKEN IN LAST 24 HOURS, OR TADALAFIL (CIALIS) HAS BEEN TAKEN WITHIN THE LAST 48 HOURS OR 96 HOURS IN THE ELDERLY (Refer to Manufacturers Product Information for further pharmaceutical information because extremely severe reductions in BP may occur).
Administer one spray of glyceryl trinitrate (GTN) (400 mcg Nitrolingual Pump Spray),
OR if spray is unavailable, place half GTN tablet (300 mcg Anginine) under tongue,
or apply one 5 mg/24 hours GTN Transdermal Patch to chest or upper arm (patch should be removed as soon as hypertension resolves).
Monitor BP; if little or no effect in 5 to 10 minutes, administer a second spray or other half tablet of Anginine under tongue. Be cautious, particularly with elderly patients, when administering GTN spray or tablet as sudden hypotension may result, particularly if cause is quickly remedied.
If symptomatic hypotension (low BP) occurs lay the person down and elevate the legs or tilt bed down. Dosage may be titrated by removing the transdermal patch or by spitting out residual spray or tablet with hypotensive effect being shorter lasting.
Up to 3 doses can be given in 30 minutes (if BP remains elevated or rises rapidly intravenous medication may be indicated - see below).
DO NOT USE SILDENAFIL (VIAGRA), VARDENAFIL (LEVITRA), TADALAFIL (CIALIS) OR OTHER DRUG IN THE PDE 5 INHIBITOR (NITRIC OXIDE ENHANCER) CLASS WITHIN 24 HOURS OF TAKING GTN SPRAY OR TABLETS.
Alternative (Short Acting) Oral Agents If GTN spray, tablets or patch are unavailable, or contraindicated due to recent use of medication for erectile dysfunction within the last 24 hours (or 48 to 96 hours if Cialis) and depending on age (see guidelines above), an alternative (short-acting) antihypertensive agent, such as captopril should be used. Captopril, administered sublingually as a 25mg tablet (taking about 3 minutes to dissolve under the tongue), has been shown to effectively lower BP within 15 minutes of administration. ADVANTAGES OF SUBLINGUAL ADMINISTRATION OF CAPTOPRIL ARE THAT THE DRUG ENTERS THE GENERAL CIRCULATION DIRECTLY, WITH THERAPEUTIC CONCENTRATIONS AND ONSET OF ACTION ACHIEVED MORE RAPIDLY. IN ADDITION, THE PARTIALLY DISSOLVED TABLET MAY BE SPAT OUT IF THERE IS A VERY RAPID REDUCTION IN BP. Nifedipine capsules (bite and swallow), which were previously used in this situation are no longer available, having been withdrawn due to risks that have been associated with use in the able-bodied population with angina, or hypertension. The pharmacokinetics of nifedipine oral tablets is less ideal for rapid reduction in BP with delayed onset and longer action.
Prognosis The cause of autonomic dysreflexia 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 managing autonomic dysreflexia in adults, children, and pregnant women. There is also a consumer version of this guideline.
Note: Medical conditions MUST always be diagnosed by a medical professional. The following information is structured to provide basic information to HWH Support Workers and Clinical Care Managers.
