Severe Drop in Blood Pressure (Severe Hypotension)

What counts as dangerously low blood pressure

Blood pressure is written as two numbers: systolic (pressure when the heart beats) over diastolic (pressure between beats). Low blood pressure (hypotension) is usually defined as below 90/60 mmHg. Many healthy, fit people live with readings around 90/60 and feel well, so a number alone is not the problem.

Blood pressure is dangerously low when it causes poor blood flow to organs. Doctors look for:

• systolic pressure below 90 mmHg, or a mean arterial pressure below 65 mmHg
• a drop of 40 mmHg or more from a person's usual systolic pressure
• signs of poor organ perfusion: confusion, cold mottled skin, little urine, rising lactate in the blood

This state is called shock.

Warning signs of a severe drop

• dizziness, lightheadedness or fainting
• confusion, drowsiness or agitation
• pale, cold, clammy or blotchy skin; blue lips
• fast, weak pulse (often above 100 beats per minute)
• fast, shallow breathing
• nausea, thirst
• passing little or no urine
• blurred vision

Causes of a sudden, severe drop in blood pressure

Other causes

• Medicines: too much blood pressure medicine, diuretics, nitrates (especially combined with erectile dysfunction drugs such as sildenafil), sedatives and opioid overdose
• Severe dehydration from heat, illness or not drinking, especially in older adults
• Vasovagal fainting: a sudden reflex drop in heart rate and pressure triggered by pain, fear, standing long or the sight of blood. It is usually harmless and brief.
• Postural hypotension: a drop when standing up, common with age, dehydration, Parkinson's disease and diabetes

What to do right now

1. Call 911 or your local emergency number if someone has signs of shock.
2. Lay the person flat and raise their legs about 30 cm (12 in), unless this causes pain or breathing difficulty, or there is a head, neck or spine injury.
3. Use an epinephrine auto-injector if anaphylaxis is suspected.
4. Control any bleeding with firm, direct pressure.
5. Keep them warm with a blanket, but do not overheat.
6. Do not give food or drink, which may cause choking or delay surgery.
7. Start CPR if they stop breathing normally.

For a simple faint with prompt recovery, lie down with legs raised, then sit up slowly after several minutes and drink water once fully alert.

How doctors find the cause

In hospital, care starts with stabilizing blood pressure while looking for the cause:

• continuous monitoring of blood pressure, heart rate, oxygen and urine output
• blood tests: blood count, lactate, kidney function, electrolytes, cardiac troponin, blood cultures, glucose, cortisol if adrenal crisis is possible
• ECG and chest X-ray
• bedside ultrasound of the heart, lungs and belly
• CT scan for internal bleeding or pulmonary embolism

Treatment

Treatment depends on the cause:

• IV fluids for dehydration, sepsis and bleeding
• Blood transfusion and stopping the bleeding by surgery or endoscopy
• Antibiotics within the first hour for septic shock
• Epinephrine for anaphylaxis
• Vasopressors (medicines that tighten blood vessels, such as norepinephrine) in intensive care when fluids are not enough
• Treatments for the heart: reopening a blocked artery, controlling a rhythm problem
• IV hydrocortisone for adrenal crisis
• Clot-busting drugs or procedures for major pulmonary embolism
• Stopping or adjusting medicines that caused the drop

Outlook

Outcome depends on the cause and how quickly treatment starts. Shock that is recognized and treated early is often reversible. Prolonged shock damages the kidneys, brain, heart and other organs and can be fatal, which is why early signs should never be ignored.

Frequently asked questions

What is a dangerously low blood pressure?

There is no single number, but a systolic pressure below 90 mmHg with symptoms such as fainting, confusion, cold clammy skin or a fast weak pulse is dangerous. A sudden drop of 40 mmHg or more from your usual level is also concerning, even if the reading is above 90.

What causes a sudden drop in blood pressure?

Common causes include dehydration, blood loss, severe infection (sepsis), allergic reactions (anaphylaxis), heart problems such as heart attack or arrhythmia, blood clots in the lungs, adrenal crisis and medicines. A simple faint (vasovagal reaction) is the most common harmless cause.

What should I do if my blood pressure drops suddenly?

Lie down and raise your legs. If you have confusion, chest pain, breathlessness, cold clammy skin, fever, bleeding or symptoms that do not improve within a few minutes, call 911 or your local emergency number. Do not drive yourself.

Is low blood pressure worse than high blood pressure?

Long-term, high blood pressure causes more harm, raising the risk of stroke and heart attack. But a sudden severe drop in blood pressure is an immediate emergency because organs are not getting enough blood. Chronically low pressure without symptoms is usually harmless.

Can dehydration cause a severe drop in blood pressure?

Yes. Severe vomiting, diarrhea, heat exposure or not drinking enough reduces blood volume, which can cause dizziness, fainting and, in severe cases, shock. Older adults, young children and people on diuretics are most at risk.