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 blocked 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.
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.
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.
Common causes to consider for the presentation of acute autonomic dysreflexia include:
Note that autonomic dysreflexia may also be caused
iatrogenically by staff clamping a catheter for a procedure such as a
bladder ultrasound or kinking catheter by accident in operating theatre
during a surgical procedure.
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 therefore 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 organ, such as the bladder or rectum. Pressure ulcers or other injuries such as fractures and urinary tract infections are also common causes. 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.
Pharmacological causes of autonomic dysreflexia are rare, but recently a case was reported in a patient receiving combination therapy with duloxetine and amitriptyline.
The patients blood pressure typically is significantly elevated (at least 20 to 40 mmHg above normal resting systolic level or 15 to 20 mmHg above resting systolic level in adolescents). It is important to remember that the BP for individuals with high paraplegia or tetraplegia may usually be low, around 90 to 100/60 mmHg while lying down and possibly lower whilst sitting. Therefore, patients with SCI may become symptomatic with BP in the normal range for the general population. Other symptoms may include any or all of the below:
Hypertension may be be severe enough to lead to a hypertensive crisis complicated by pulmonary oedema, 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.
Autonomic Dysreflexia is a serious condition that’s considered a medical emergency. It can be life-threatening and result in:
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