Autonomic Dysreflexia: Why a Normal Blood Pressure Can Be an Emergency

Autonomic dysreflexia: why a normal blood pressure reading can be an emergency

Here is the thing that gets people killed.

A man with a C5 injury arrives at an emergency department with a pounding headache and sweating above his collarbones. His blood pressure reads 150 over 95. A triage nurse looks at that number, sees mild hypertension, and puts him in the queue.

His usual resting systolic is 95.

He is 55 points above his own baseline. He is in a hypertensive emergency that can cause seizure, stroke, retinal haemorrhage or cardiac arrest, and the cause is almost certainly a kinked catheter that could be fixed in ninety seconds. But the number on the machine looks fine, because the number on the machine is being read against the general population rather than against him.

That is autonomic dysreflexia, and that misreading is the central danger of it. The condition itself is usually simple to resolve. What is not simple is getting the people around the person — including clinicians who do not see spinal cord injury often — to understand that a reading they consider normal is, for this person, a crisis.

We support people with spinal cord injury across New South Wales. We are not a clinical service, we do not write medical management plans, and nothing in this guide is medical advice. The person’s own autonomic dysreflexia management plan, written by their spinal unit, governs everything here. If you support somebody at risk and they do not have one, obtaining it is the most important thing you will do this month.

What is actually happening

Below a spinal cord injury, the body still works. Nerves still fire, reflexes still function, the sympathetic nervous system still responds to stimuli. What is lost is the brain’s ability to regulate any of it.

So when something noxious happens below the level of injury — a full bladder, a loaded bowel, an ingrown toenail, a tight sock — the spinal cord generates a sympathetic response. Blood vessels below the injury constrict sharply. Blood pressure rises.

In an intact nervous system, the brain detects that rise through the baroreceptors and sends descending signals to shut it down. After a spinal cord injury, those descending signals cannot get past the damaged segment. The brain detects the rise, tries to correct it, and the correction never arrives.

What the brain can do is act above the injury. So it dilates blood vessels in the head and neck and slows the heart through the vagus nerve, which is why the clinical picture is so distinctive: the person is flushed, sweating and congested above the injury level, pale and cold below it, with a pounding headache and often a slow pulse rather than a fast one.

Meanwhile the blood pressure keeps climbing, because the only thing that will stop it is removing the stimulus.

Why T6? The sympathetic outflow to the splanchnic circulation — the large blood vessels of the abdomen, which hold a substantial share of circulating blood volume — leaves the cord between roughly T6 and L2. An injury at or above T6 leaves that whole vascular bed able to constrict without any descending control, which is enough to drive a dangerous rise in pressure. Below T6, the response is usually too limited to produce a crisis.

Clinical guidance from the Consortium for Spinal Cord Medicine, published through the Paraplegia Veterans of America, states that autonomic dysreflexia occurs in people with injuries at or above T6, while noting that cases have been reported as low as T8. The practical implication: treat T6 as the threshold, but do not dismiss the possibility in somebody slightly below it.

The numbers that matter

The same guidance defines an episode as a sudden, significant rise in both systolic and diastolic pressure above the person’s usual levels, often accompanied by bradycardia. In adults with injuries above T6, a rise of 20 to 40 mmHg above baseline may signal autonomic dysreflexia. In adolescents, a systolic rise of more than 15 to 20 mmHg; in children, more than 15 mmHg.

Above baseline. Not above 140. Not above any population figure. Above their baseline.

This is why the single most useful piece of paper in the file is a record of the person’s usual resting blood pressure, measured when they are well. Many people with tetraplegia run resting systolic pressures in the 90s or low 100s, because the same loss of sympathetic control that causes dysreflexia also causes chronically low baseline pressure. For somebody whose normal is 95, a reading of 135 is a 40-point rise and an emergency. For somebody whose normal is 125, it is not.

If you support somebody at risk of autonomic dysreflexia and you do not know their baseline blood pressure, find out and write it down where everybody can see it. Put it on the front of the file, in the handover sheet, and on whatever the person carries.

The guidance indicates that in adults, systolic pressure of 150 mmHg or above is the point at which medication should be considered. Lower thresholds apply in children and adolescents — 120 mmHg under age 5, 130 for ages 6 to 12, 140 for adolescents. Those are clinical decisions made by clinicians; they are included here so that non-clinical people understand the urgency of the numbers they may be looking at.

What it looks like

• A pounding or bursting headache, often the first and most prominent symptom
• Sweating, flushing or goosebumps, mainly above the injury level, though sometimes below
• Nasal congestion
• Blurred vision, or spots in the visual field
• A slow pulse — though it may be only relatively slow
• Anxiety or a sense of apprehension, which people often describe as a feeling of dread they cannot explain
• Arrhythmias
• Cool, pale skin below the injury
• Sometimes nothing at all

That last point is important enough to name separately. Silent autonomic dysreflexia is real: some people have substantially raised blood pressure with no symptoms whatsoever. This is why blood pressure is checked when something seems off even in the absence of a headache, and why people with a history of silent episodes are advised to monitor more actively.

Many people who have lived with this for years will tell you they know before any of it shows. A particular feeling, a specific quality of unease. Believe them. A person who says “I think I’m going into dysreflexia” is a more reliable instrument than anything in the room.

What triggers it

The clinical guidance groups triggers as follows, and the ordering matters because it tells you where to look first.

Urinary — and bladder distension is the most common cause of all. Blocked, kinked or misplaced catheters. Bladder overfilling. Bladder stones. Urological procedures. Detrusor-sphincter dyssynergia. Lithotripsy. Urinary tract infection.

Bowel — the second most common cause. Bowel distension or faecal impaction. Haemorrhoids. Gastrointestinal procedures. Appendicitis, gallstones, gastric ulcers.

Skin and musculoskeletal. Tight clothing, tight shoes, anything with a seam or a strap pressing. Sharp objects. Blisters, burns, sunburn, frostbite. Ingrown toenails. Insect bites. Pressure injuries.

Reproductive. Intercourse and ejaculation. Electroejaculation. Scrotal compression. Epididymitis. Sexually transmitted infections. Menstruation. Vaginitis. Pregnancy, and especially labour and delivery.

Systemic. Deep vein thrombosis. Pulmonary embolism. Fractures — including fractures the person cannot feel. Heterotopic ossification. Surgery and invasive procedures. Functional electrical stimulation. Stimulants, alcohol, excess caffeine, diuretics. Substance use. And deliberate induction by athletes, known as “boosting”.

Two practical observations from that list.

First, a fracture the person cannot feel can present as autonomic dysreflexia. So can a deep vein thrombosis and so can an acute abdomen. Dysreflexia is sometimes the only signal the body can send about something serious below the injury level, which is why recurrent or unexplained episodes need proper investigation rather than just resolution.

Second, boosting deserves naming because it is a real practice. Some athletes with spinal cord injury deliberately induce dysreflexia before competing, because the raised blood pressure improves performance. It is prohibited and it is genuinely dangerous — people have had strokes doing it.

What to do: the first two minutes

What follows is the general shape of the response described in clinical guidance. Follow the person’s own management plan where it differs. Steps involving catheterisation, rectal examination, medication or anything invasive are clinical tasks for appropriately trained and authorised people, performed under that plan — not things a support worker improvises.

1. Sit them up. If the person is lying down, sit them upright. Lower their legs if possible. This uses gravity to drop blood pressure and it is the single most effective thing available to a non-clinician. Do it first, before anything else, before taking a blood pressure, before making a phone call.

2. Loosen everything. Clothing, abdominal binder, compression stockings, leg bag straps, shoes, anything tight. Any constrictive device comes off or comes loose.

3. Check the blood pressure and pulse. And compare it to the person’s baseline, not to a general population range.

4. Look at the bladder. It is the most common cause by a wide margin. If there is an indwelling or suprapubic catheter, check the entire length of the tubing for kinks, folds, obstruction or a leg bag that is full, twisted, or clamped. Check the catheter is actually draining. Check the bag is below bladder level. A substantial proportion of episodes end right here, within seconds, because somebody straightened a tube.

5. Then the bowel. If the bladder is clear and symptoms persist, a loaded bowel or faecal impaction is the next consideration. Anything involving rectal examination or stool removal is a clinical task under the person’s plan — and worth knowing that performing it can transiently worsen dysreflexia, which is why guidance advises topical anaesthetic first and stopping if symptoms escalate.

6. Then look everywhere else. Skin under straps and seams. Feet and toenails. Pressure areas. Anything new.

7. Keep monitoring. Guidance suggests blood pressure and pulse checks every two to five minutes until stable.

8. Call for help, early. See below.

9. Watch for the crash afterwards. Once the trigger is removed, blood pressure can fall — sometimes sharply, and especially if medication has already been given or a very full bladder has been suddenly drained. If the person becomes hypotensive, lie them down and raise their legs. The guidance specifically flags monitoring during bladder drainage for this reason.

10. Document it. What happened, what the readings were, what was done, what worked, how long it took.

When to call 000, and what to say

Call 000 if: the blood pressure stays high after sitting the person up and clearing the obvious triggers; the symptoms are severe; there is chest pain, visual disturbance, altered consciousness or seizure; the cause cannot be found; or the person’s management plan says to.

Do not wait to see if it settles. The risk is stroke and it does not announce itself.

What to say, in this order:

“This is autonomic dysreflexia in a person with a spinal cord injury at [level]. Their normal blood pressure is [baseline]. It is now [reading]. This is a hypertensive emergency.”

Say those words. The reason to lead with the baseline is precisely the misreading described at the start of this guide: a paramedic or triage nurse who has not seen spinal cord injury recently may look at 150 over 95 and not register urgency. The baseline reframes the number, and it is the difference between immediate attention and a wait.

Bring the management plan. Bring the medication list. If the person carries a wallet card, hand it over — clinical guidance specifically recommends people at risk carry one, and the reason is this exact conversation.

Two clinical cautions worth passing on to ambulance and ED staff:

• If the person has taken sildenafil or a similar medication in the last 24 hours, nitrates must be avoided. The guidance names this explicitly and suggests a short-acting alternative instead. This is a question somebody needs to ask and the person may not volunteer.
• Sudden bladder decompression after medication has been given can cause hypotension. Order of operations matters.

After it resolves

Clinical guidance advises monitoring for at least two hours after resolution, because episodes recur — often because the trigger was partially rather than fully resolved. People managing an episode at home should watch symptoms and blood pressure across that window and seek immediate care if it comes back.

Then, and this is the step most often skipped: work out why it happened. Review the trigger with the person and everybody who supports them. Adjust the plan. If it was a kinked catheter, what about the setup made that possible. If it was a loaded bowel, is the bowel programme adequate or is it being rushed. If it was a tight strap, who put it on.

An episode with no identified cause, or episodes that keep happening, warrant proper medical evaluation. The guidance notes that recurrent dysreflexia may reflect worsening bladder dysfunction or the development of a syrinx — a fluid-filled cavity in the cord that can cause progressive neurological deterioration. Recurrent dysreflexia is a signal, not just a nuisance.

Pregnancy and labour

This deserves its own section because the stakes are high and the knowledge gap is wide.

Pregnancy is a listed trigger, and labour and delivery particularly so. Uterine contractions are a powerful noxious stimulus below the injury level, and a woman with an injury at or above T6 can go into severe dysreflexia during labour — which can be mistaken for pre-eclampsia, since both present with hypertension.

The distinction matters because the treatment differs. Clinical guidance advises that pregnant patients who have had an episode be referred to their obstetric provider, and that hospital admission be considered where an obstetric complication is suspected.

Anyone with an injury at or above T6 who is pregnant or planning pregnancy needs this flagged with both the obstetric team and the spinal service well before delivery, with a written plan. It is also one of the reasons epidural anaesthesia is often recommended in labour for this group — it blocks the afferent stimulus. That is a conversation for the treating team, not a website, but it is a conversation that needs to happen early rather than at 3am in a birth suite.

Prevention, which is most of the work

Almost all of this is bladder and bowel. Which means prevention is mostly about doing those two things properly and not rushing them.

Bladder. Catheterise on schedule rather than when convenient. Do not let the bladder overfill. Check tubing and bag position routinely, not only when something is wrong. Keep bags below bladder level. Treat infections promptly. Maintain the renal surveillance the spinal service recommends.

Bowel. Run the programme consistently, at the same time, with enough time allocated. A bowel programme that is habitually rushed because the shift is short is a dysreflexia risk, and it is also a funding question — if the plan does not fund the time the programme takes, that is something to raise at the plan reassessment rather than absorb.

Skin. Daily checks. Pressure injuries are a listed trigger and they are often found during a dysreflexia episode rather than before it.

Clothing and equipment. Nothing tight. Check under straps, bindings and seams. Watch shoes, particularly where feet have swollen.

Feet and toenails. Regular podiatry. An ingrown toenail is a small problem that can produce a hypertensive emergency.

The things that are easy to miss. New medication. Caffeine load. Alcohol. A fracture nobody noticed. A urinary tract infection without the usual symptoms.

What every support worker needs to have

If you manage a service or coordinate supports for somebody at risk, this is the list.

• The person’s written autonomic dysreflexia management plan, from their spinal unit, current, in the file and accessible on every shift.
• Their baseline blood pressure, recorded, visible, and known to every worker.
• A working blood pressure monitor in the house, with workers who can use it and who know the baseline to compare against.
• Every worker trained to recognise it and to sit the person up, including casuals and agency staff. Not a one-off induction — repeated.
• A clear escalation rule: what triggers 000, who else to call, and the authority to call without seeking permission first.
• The script for what to say to paramedics, written down.
• The wallet card the person carries, current.
• Documentation of every episode, with triggers and response, reviewed for pattern.
• Enough funded time for bowel and bladder care to be done properly, because rushing them is what causes the episodes.

The last one is the one providers least like to talk about and it is the most consequential. A great many dysreflexia episodes in supported accommodation trace back to a routine being compressed into a shift that was too short.