What Is Autonomic Dysreflexia? Key Information

Autonomic dysreflexia is a serious medical condition that can occur in people with a spinal cord injury, typically at or above the T6 level. It happens when a painful or irritating stimulus below the level of injury triggers a sudden, dangerous spike in blood pressure. This is a medical emergency that requires immediate attention. Without prompt treatment, it can lead to a stroke, seizure, or even death.

What Is Autonomic Dysreflexia and Why Does It Happen?

To understand autonomic dysreflexia, you first need to know a little about how the nervous system works. After a spinal cord injury, the brain’s normal communication with the body below the injury site is disrupted. This includes the autonomic nervous system, which controls involuntary functions like heart rate, blood pressure, and digestion.

Normally, when something irritating happens below the injury level—like a full bladder or an ingrown toenail—the body sends a pain signal up the spinal cord to the brain. The brain then tells the body to respond appropriately. In autonomic dysreflexia, that pain signal gets blocked at the level of the spinal cord injury. It cannot reach the brain, so the brain cannot send a calming signal back down.

Instead, a reflex kicks in. The blood vessels below the injury level constrict, or narrow, which drives blood pressure up rapidly. The body tries to compensate above the injury level by slowing the heart rate and widening blood vessels in the head and neck, but this is not enough to counteract the spike. The result is a dangerously high blood pressure that can escalate within minutes.

What Are the Most Common Triggers?

Any irritating stimulus below the level of the spinal cord injury can trigger an episode. The most common trigger by far is a distended bladder, meaning the bladder is full and cannot empty. This accounts for a large percentage of cases. A blocked or kinked urinary catheter is a frequent cause.

Bowel issues are the second most common trigger. Constipation, impacted stool, or even a digital stimulation procedure to trigger a bowel movement can set off an episode. Other triggers include pressure sores, ingrown toenails, tight clothing, skin burns or sunburn, insect bites, and even sexual activity. In women, labor and delivery can also trigger autonomic dysreflexia. Any surgical procedure below the level of injury, such as a minor cut or a urinary tract infection, carries the same risk.

What Are the Warning Signs and Symptoms?

Symptoms can be dramatic and frightening. The most common symptom is a sudden, pounding headache. The skin above the level of injury may become flushed, red, and sweaty, while the skin below the level of injury remains pale, cool, and dry. The person may experience goosebumps below the injury level and a stuffy nose.

One of the most critical signs is a rapid rise in blood pressure. For someone with a spinal cord injury, a normal resting blood pressure is often lower than average, around 90-110 systolic. During an episode of autonomic dysreflexia, the systolic blood pressure can spike to 200 mmHg or higher. This is a medical emergency. Other symptoms may include blurred vision, anxiety, nausea, and a slow heart rate, although the heart rate can sometimes be fast instead.

How Is Autonomic Dysreflexia Treated?

Immediate treatment is essential. The first step is to sit the person up as upright as possible to help lower blood pressure by allowing blood to pool in the legs. Loosen any tight clothing or constrictive devices. Then, check the blood pressure every few minutes.

The next step is to identify and remove the trigger. If the person has a urinary catheter, check it for kinks or blockages. If the bladder is distended and no catheter is present, catheterization may be necessary. If the trigger is likely bowel-related, check for impacted stool, but do not perform digital stimulation until blood pressure is under control and medical help is available, as this can worsen the episode.

If the blood pressure remains dangerously high after sitting up and checking the catheter, medication may be needed to lower it quickly. Topical nitroglycerin paste or a fast-acting blood pressure medication like nifedipine is often used in this setting. This is a situation where having an emergency plan and prescribed medication on hand is critical. Anyone who experiences autonomic dysreflexia should seek emergency medical care, even if the episode resolves, because the underlying trigger needs to be addressed.

Who Is at Risk for Autonomic Dysreflexia?

Autonomic dysreflexia only occurs in people with a spinal cord injury at or above the T6 level. T6 refers to the sixth thoracic vertebra in the upper back. The reason this level matters is anatomical. The nerve fibers that help control blood vessel tone in the large splanchnic bed—the blood vessels in the abdomen—exit the spinal cord around the T5 to T8 levels. An injury at or above T6 leaves this entire system disconnected from the brain, allowing the reflex to trigger.

People with injuries below T6 generally do not develop this condition because the reflex arc is disrupted. The risk of autonomic dysreflexia typically begins after the period of spinal shock, which is the initial flaccid phase immediately following an injury. This phase can last anywhere from a few weeks to a few months. Once spinal shock resolves, the risk of autonomic dysreflexia begins and can persist for life.

How Can Autonomic Dysreflexia Be Prevented?

Prevention is centered on avoiding the triggers. For most people, this means maintaining a strict bowel and bladder routine. A catheter that drains properly and is changed on schedule reduces the risk of a full bladder. Regular bowel programs help prevent constipation and impaction.

Daily skin checks are also essential. Pressure sores are a major trigger, and they can develop quickly in areas with reduced sensation. Wearing loose, comfortable clothing and checking for any cuts, blisters, or ingrown toenails can prevent many episodes. People with spinal cord injuries and their caregivers should be educated about these triggers and know the signs of an impending episode. Having an emergency action plan and blood pressure monitoring equipment at home is highly recommended.

When Should You Seek Emergency Help?

Any episode of autonomic dysreflexia with a sustained high blood pressure is a reason to call emergency services. If the systolic blood pressure remains above 150-160 mmHg after sitting up and attempting to relieve the trigger, immediate medical care is necessary. Do not wait to see if symptoms improve on their own.

Seek emergency care immediately if the person experiences severe headache, confusion, chest pain, difficulty breathing, or seizures. These can be signs of a stroke or other life-threatening complication. Autonomic dysreflexia does not resolve on its own while the trigger remains. It requires active intervention to lower blood pressure and find the cause.