What is Autonomic Hyperreflexia?

Autonomic hyperreflexia is a potentially dangerous overreaction of the autonomic nervous system to a stimulus, leading to increased blood pressure and a slow heart rate. If the patient does not receive immediate treatment, the outcome can be fatal. This condition is most commonly seen in people with spinal cord injuries, usually above the level of the T6 vertebra. It can also sometimes occur as a part of a medication reaction, response to brain injury, or drug overdose.

In a patient with autonomic hyperreflexia, a painful stimulus attempts to travel up the spinal cord and cannot complete the path to the brain, resulting in a signal sent to the autonomic nervous system. It goes into overdrive in response to the stimulus. The patient's blood pressure will rapidly spike, while the heart rate falls. In addition, the skin will flush and patients usually report headaches and anxiety. These symptoms can onset very rapidly in a previously stable patients.

For patients with spinal cord injuries, the usual culprit is loss of control over the bowels. The patient cannot strain to eliminate feces or urine, causing distension of the gut or bladder. This will eventually trigger a pain response as the body tries to signal the brain to alert it to a problem. When that signal cannot reach the brain, the patient can enter autonomic hyperreflexia. Other types of unpleasant stimuli in different patients may be root causes as well.

Treatment for this condition requires immediately stabilizing the patient and addressing the stimulus. The patient might be instructed to remove tight, restrictive clothing, and sit up, while dangling the legs over the edge of a bed or table. Medications are available to bring the blood pressure down and control the heart rate. If the patient has a fecal impaction or a distended bladder, a care provider can catheterize the bladder or digitally extract the feces to remove pressure and make the patient feel more comfortable.

Once the patient is stable, the flushing, headache, and other symptoms should start to resolve. Patients with spinal cord injuries need to be especially aware of signs of autonomic hyperreflexia, which usually appears in the first year after injury if it is going to occur. Anything unusual should be reported to a doctor so he can determine if the patient needs to receive treatment. It can be helpful to keep track of bowel and urinary health, to catch failure to eliminate before it triggers an episode of autonomic hyperreflexia.