Autonomic dysreflexia is a condition that emerges after a spinal cord injury, usually when the injury has occurred above the T6 level. The higher the level of the spinal cord injury, the greater the risk with up to 90% of patients with cervical spinal or high-thoracic spinal cord injury being susceptible. Dysregulation of the autonomic nervous system leads to an uncoordinated autonomic response that may result in a potentially life-threatening hypertensive episode when there is a noxious stimulus below the level of the spinal cord injury. In about 85% of cases, this stimulus is from a urological source such as a UTI, a distended bladder, or a clogged Foley catheter. There is a significantly increased risk of stroke by 300% to 400%. Autonomic dysreflexia can occur in susceptible individuals up to 40 times per day. The initial presenting complaint is usually a headache which can be severe. Susceptible individuals with spinal cord lesions above T6 who complain of a headache should immediately have their blood pressure checked. If elevated, a presumptive diagnosis of autonomic dysreflexia can be made. Prompt recognition and correction of the disorder, usually just by irrigating or changing the Foley catheter, can be life-saving.
The etiology is a spinal cord injury, usually above the T6 level. It is unlikely to occur if the level is below T10. The higher the injury level, the worse the severity of the cardiovascular dysfunction. The severity and frequency of autonomic dysreflexia episodes are also associated with the completeness of the spinal cord injury. Patients usually develop autonomic dysreflexia one month to one year after their injury. However, it has also been described in the first days or weeks after the original trauma. Objectively, an episode is defined as an increase in systolic blood pressure of 25 mm Hg.
Autonomic dysreflexia develops in 20% to 70% of patients with spinal cord injury above the T6 level and is unlikely to develop if the injury is below T10. Patients prone to this disorder will usually have a history of prior episodes, but health professionals need to be alert to an initial presentation without any prior history of autonomic dysreflexia.
Cutaneous or visceral stimulation below the level of the spinal cord injury, initiates afferent impulses that elicit reflex sympathetic nervous system activity. The sympathetic response leads to diffuse vasoconstriction, typically to the lower two-thirds of the body, and a rise in blood pressure. In an intact autonomic system, this increased blood pressure stimulates the carotid sinus leading to a parasympathetic outflow slowing the heart rate via vagal stimulation and causing diffuse vasodilation to balance the original increased sympathetic response. However, in the setting of a spinal cord injury, the normal compensatory parasympathetic response cannot travel below the level of the spinal cord injury, and generalized vasoconstriction continues below the level of injury leading to systemic hypertension. The compensatory parasympathetic response leads to bradycardia and vasodilation, but only above the level of the spinal cord injury.
The most common stimuli are distention of a hollow viscus, such as the bladder or rectum. Pressure ulcers or other injuries such as fractures and urinary tract infections are also common causes. Sexual intercourse can also be a stimulus. Medical procedures, surgeries, and labor and delivery are usually complicated in patients with a history of autonomic dysreflexia as well. Spinal cord injuries below T10 rarely result in autonomic dysreflexia because the splanchnic innervation remains intact and allows for compensatory parasympathetic dilation of the splanchnic vascular bed.
The manifestations are variable and include:
Hypertension may be asymptomatic or be severe enough to lead to a hypertensive crisis complicated by pulmonary edema, left ventricular dysfunction, retinal detachment, intracranial hemorrhage, seizures or even death. Bradycardia may also range from minor to resulting in cardiac arrest. Tachycardia is less common than bradycardia but may also occur along with cardiac arrhythmias and atrial fibrillation or flutter. If the patient has coronary artery disease, an episode may cause a myocardial infarction.
The combination of dangerously high blood pressure together with cerebral vasodilation puts the patient at high risk for a hemorrhagic stroke which can be life-threatening.
The evaluation includes obtaining a history of previous episodes, monitoring vital signs and watching for any developing signs and symptoms especially if there is a known trigger.
The key is first to identify patients at risk (spinal cord injury above T6 level) and recognize the key initial symptom which is usually a severe headache from cerebral vasodilation. Should this be encountered, the next step should be to check blood pressure. If elevated, then the patient is at high risk for an episode of autonomic dysreflexia.
The likelihood of autonomic dysreflexia is independently predicted by the level of the spinal cord lesion and the presence of neurogenic detrusor overactivity. Patients at high risk who are getting urodynamic testing should have continuous cardiovascular monitoring.
In the event of an episode, vital signs should be closely monitored, and recognition of the trigger should be immediately sought. Blood pressure should be checked at least every 5 minutes, and an arterial line should be considered. The noxious stimuli should be corrected as soon as possible. Bladder and bowel distension are the most common causes. Therefore, restoring bladder drainage is immediately recommended. If the patient has an indwelling catheter, it should be evaluated for malfunction or malpositioning, and a workup for a urinary tract infection should also be performed. A rectal exam should be performed to evaluate for impaction; however, this should be done with care as it can precipitate a worsening crisis due to the stimulation of the procedure. Sitting the patient upright and removing any tight clothing or constrictive devices will orthostatically help lower blood pressure by inducing pooling of blood in the abdominal and lower extremity vessels as well as removing any possible stimuli. If the trigger cannot be identified and initial maneuvers do not improve the systolic blood pressure below 150 mm Hg pharmacologic management should be initiated. Hypertension should be promptly corrected with agents that have a rapid onset but short duration of action. Examples are nitrates (either nitropaste or sublingual), nifedipine (oral or sublingual), sublingual captopril, intravenous hydralazine, intravenous labetalol (if the heart rate is not too slow), among others. Intravenous infusions such as nitroglycerine or clevidipine are also options; however, placement of an arterial line is recommended for close titration of the infusion.
Women with spinal cord injury who become pregnant are at risk for developing a dysreflexia episode during labor and delivery. In women with spinal cord injury, the symptoms of labor may only be some abdominal discomfort, increased spasticity, and autonomic dysreflexia. Epidural anesthesia has been reported to be the superior choice for control of autonomic dysreflexia during labor. For cesarean delivery or instrumentally assisted delivery, a spinal or epidural may be used. The American College of Obstetrics and Gynecology states that it is vital that any obstetrician caring for a patient with spinal cord injury be familiar with the complications related to such injuries.
Leakage of urine around catheters that are not obstructed is often due to bladder spasms that may be associated with dysreflexia episodes. For these cases, overactive bladder medications such as oxybutynin and mirabegron can be used. In severe cases, bladder wall injections of Botox can be used. Urinary infections may also cause bladder spasms without catheter blockage, but such spasms are usually transient and disappear when the UTI is successfully treated. Constipation may also be a contributing factor.
Patients with spinal cord injury and autonomic dysreflexia often undergo medical procedures and surgeries such as urologic instrumentations that can trigger dysreflexia episodes. General or regional anesthesia may be used for these procedures. Regional anesthesia in the form of a spinal anesthetic has the advantage of blocking both limbs of the reflex arc and thereby avoids autonomic dysreflexia. However, determining the level of anesthesia may be difficult, and placement of the spinal may be challenging in patients with spinal cord injuries. An epidural catheter may also be considered for longer cases as it has the advantage of being able to be “topped off.” Epidurals are subject to incomplete blocks and may be even more difficult to place. If general anesthesia is used and hypertension or other evidence of a dysreflexia episode develops, deepening the level of anesthesia by increasing the anesthetic agent often alleviates the episode. If however, the hypertension is not resolved by deepening the anesthetic, then antihypertensive medications should be used until the stimulus is withdrawn.
The use of 10 ml of 2% lidocaine administered intravesically 4-6 minutes prior to routine Foley catheter changes has been shown to reduce episodes of autonomic dysreflexia significantly.
Use of botox for chemodenervation of the bladder has also been shown to reduce autonomic dysreflexia in susceptible individuals.
Minocycline has been shown to have a neuroprotective effect in animal testing models, but has not yet been shown to have a similar clinical effect in humans.
Autonomic dysreflexia should be strongly suspected in any spinal cord injured patient with a lesion above T6 who complains of a headache. A blood pressure reading should be taken immediately, and corrective treatment started if the patient's blood pressure is significantly elevated as most spinal cord injured patients have low blood pressure. Bladder distension from urinary retention or a blocked Foley is the single most common cause of this disorder and irrigating or changing the catheter is often immediately curative. Quick recognition and rapid alleviation of the underlying stimulus may be life-saving.