Autonomic hyperreflexia syndrome is a condition marked by an overreaction of the body’s autonomic (involuntary) nervous system. It is a medical emergency that can lead to life-threatening complications if not addressed promptly. This syndrome primarily affects individuals with a spinal cord injury, causing a sudden and dangerous spike in blood pressure and a slowed heartbeat, among other changes to the body’s automatic functions.
Underlying Causes and Mechanisms
The cause of autonomic hyperreflexia is a spinal cord injury, most often at or above the sixth thoracic vertebra (T6). The autonomic nervous system (ANS) is responsible for regulating involuntary functions like blood pressure and heart rate. An injury at the T6 level or higher disrupts communication between the brain and the body below the injury.
When a painful or irritating stimulus occurs below the spinal cord lesion, nerve signals travel up the spinal cord but are blocked from reaching the brain. This blockage triggers an uncontrolled response from the sympathetic nervous system, the part of the ANS managing the “fight or flight” reaction. The result is vasoconstriction (a tightening of blood vessels) in the lower body, which causes a rapid and severe increase in blood pressure.
The brain attempts to counteract this by activating the parasympathetic nervous system, which handles “rest and digest” functions. It sends signals to slow the heart rate and dilate blood vessels. Because of the spinal cord injury, these calming signals cannot travel past the lesion. This leads to conflicting symptoms, such as a slow pulse and sweating above the injury level, while blood pressure remains high below it.
Common Triggers and Symptoms
An episode is set off by a noxious stimulus below the level of the spinal injury, even if the individual cannot feel pain from it. The most frequent triggers are related to the bladder, accounting for about 85% of episodes. Common causes include:
- A blocked urinary catheter or an overfull bladder
- Urinary tract infections
- An overstretched or irritated bowel, constipation, or fecal impaction
- Pressure sores, burns, cuts, or insect bites
- Clothing that is too tight or restrictive
Other triggers can include fractures, sexual activity, and extreme temperature changes.
Symptoms appear quickly. The primary sign is a sudden, pounding headache accompanied by a rapid increase in systolic blood pressure. Individuals experience profuse sweating and flushed, red skin above the level of their spinal cord injury.
Additional symptoms include goosebumps, nasal congestion, anxiety, and blurred vision. While blood pressure rises, the heart rate may slow down (bradycardia). Below the level of injury, the skin may appear pale and cool. Some individuals experience silent autonomic hyperreflexia, where blood pressure rises without other noticeable symptoms.
Immediate Response and Medical Management
An episode of autonomic hyperreflexia requires immediate action. The first step is to have the person sit upright with their legs dangling down. This simple change in posture uses gravity to help pool blood in the legs and can bring blood pressure down. Any tight or restrictive clothing, socks, or binders should be loosened or removed.
The next step is to identify and remove the triggering stimulus. Since bladder issues are the most common cause, check for a kinked urinary catheter or determine if the bladder needs to be emptied. A check for bowel impaction should also be performed. Blood pressure should be monitored every two to five minutes during this process.
If the trigger cannot be removed quickly or if systolic blood pressure remains high (above 150 mmHg), medical intervention is necessary. Healthcare providers may use fast-acting medications to lower blood pressure, such as nitrates or other antihypertensive drugs. The goal is to reduce blood pressure to prevent complications while the search for the cause continues.
Long-Term Complications and Prevention Strategies
Uncontrolled episodes of autonomic hyperreflexia can lead to major health consequences. The spikes in blood pressure significantly increase the risk of:
- Stroke
- Seizures
- Retinal hemorrhage (bleeding in the eye)
- Pulmonary edema (fluid in the lungs)
- Cardiac arrest
Preventative care is centered on avoiding known triggers. This involves a consistent bladder and bowel management program to prevent over-distension or impaction. For individuals using catheters, ensuring they are draining properly is a daily necessity. Regular and thorough skin checks are also important to identify and treat pressure sores, ingrown toenails, or other sources of irritation before they can trigger an episode.
Wearing properly fitting clothes and shoes that do not cause pressure is another preventative measure. Managing pain and preventing urinary tract infections are also part of a comprehensive plan. Educating the individual and their caregivers about the signs, triggers, and immediate responses empowers them to act quickly and reduce the frequency of events.