Autonomic dysreflexia is a condition characterized by an abrupt and severe elevation in blood pressure. It occurs in individuals with spinal cord injuries, typically at or above the sixth thoracic vertebra (T6). This overreaction of the autonomic nervous system is a medical emergency that significantly impacts the cardiovascular system. The condition disrupts the body’s ability to regulate blood pressure, which in turn has a direct effect on heart rate.
The Cardiovascular Response to Autonomic Dysreflexia
An episode of autonomic dysreflexia begins with a painful or irritating stimulus below the level of the spinal cord injury. Because the injury blocks signals from reaching the brain, the sympathetic nervous system responds uncontrollably. This triggers widespread vasoconstriction, a narrowing of the blood vessels, which causes a rapid and dangerous spike in blood pressure.
The body has a built-in system to manage blood pressure through specialized sensors called baroreceptors, located in the walls of major arteries like the aorta and carotid arteries. These sensors detect the sharp rise in pressure and send signals to the brain. In response, the brain attempts to counteract the high blood pressure by sending signals down the vagus nerve, a component of the parasympathetic nervous system.
This signal from the brain instructs the heart to slow down. However, the spinal cord injury prevents the brain’s message to stop the vasoconstriction from reaching the lower body. The result is that the blood vessels below the injury level remain constricted, keeping blood pressure high, while the heart rate slows down significantly. This combination of severe hypertension and a slowed heart rate, known as bradycardia, is the characteristic cardiovascular response to autonomic dysreflexia.
Identifying the Signs and Symptoms
The most common initial symptom is a sudden, throbbing headache, which is a direct result of the rapid increase in blood pressure. Other classic signs include profuse sweating and skin flushing, typically appearing only above the level of the spinal cord injury. Goosebumps and a feeling of anxiety or unease are also frequently reported.
An indicator is a systolic blood pressure reading that is 20 to 40 mmHg or more above the individual’s usual baseline. For a person with a high-level spinal cord injury, whose typical blood pressure may be low, even a reading of 150 mmHg can signify a hypertensive crisis. This is accompanied by a noticeably slow and often pounding pulse, which is the physical manifestation of bradycardia.
While bradycardia is the hallmark response in the majority of confirmed cases, a fast heart rate, or tachycardia, can occur in some instances. This is less common and may be associated with other factors, but a slow heart rate combined with high blood pressure remains the most consistent diagnostic clue. Other possible symptoms include blurred vision, nasal congestion, and tightness in the chest.
Common Triggers Below the Injury Level
These triggers are often related to everyday bodily functions that have been disrupted by the injury. Identifying and managing these potential causes is a primary strategy for prevention.
The most frequent triggers are related to the bladder. A common cause is an overfull bladder, often caused by a kinked, clogged, or improperly draining urinary catheter. Urinary tract infections, bladder stones, or even minor irritation from catheterization procedures can initiate the dysreflexic response.
Bowel-related problems are another major category of triggers. Constipation and bowel impaction are common issues following spinal cord injury and can create the type of painful stimulus that leads to autonomic dysreflexia. Less frequent but still significant triggers can include skin-related problems like pressure sores, ingrown toenails, burns, or even restrictive clothing or leg straps.
Immediate Management Steps
Prompt action is required to lower blood pressure and prevent serious complications like stroke or seizure. The first step is to sit the person upright, raising their head to a 90-degree angle. This use of gravity helps to pool blood in the lower extremities, which can produce a drop in blood pressure.
Simultaneously, it is important to loosen or remove any restrictive items. This includes tight clothing, abdominal binders, compression stockings, or any straps that could be contributing to the problem.
The next step is a systematic search for the cause. The focus should be on the most common triggers first, beginning with the urinary system. Check for a blocked catheter, empty the leg bag, and if necessary, perform a bladder check to ensure it is not distended. If a bladder issue is not apparent, a careful check of the bowel and skin should follow.
Blood pressure and heart rate must be monitored continuously, ideally every two to five minutes. If the trigger cannot be identified and eliminated, or if the systolic blood pressure remains dangerously high (often cited as above 150 mmHg) despite removing the cause, it is time to seek emergency medical help.