Hyperpyrexia

Overview

Hyperpyrexia means an extremely high body temperature. It is usually defined as a temperature of about 40°C (104°F) or higher. It is not the same as an ordinary fever. Hyperpyrexia is a medical emergency because the body can overheat and organs can be harmed if it is not treated quickly.

Hyperpyrexia is uncommon. Fever is common, but a temperature that reaches this very high level is rare and serious.

Anyone can be affected. Risk is higher in babies, older adults, people with weakened immune systems, people taking some medicines, and people exposed to extreme heat.

Symptoms

Common symptoms

• A very high temperature, about 40°C (104°F) or above
• Feeling very hot to touch
• Flushing, sweating, or hot and dry skin
• Fast heartbeat and fast breathing
• Confusion, drowsiness, or difficulty waking
• Severe headache or muscle aches
• Feeling sick or being sick
• Signs of dehydration, such as little urine, dry mouth, or dizziness

Symptoms in children

• Being unusually sleepy or hard to wake
• Poor feeding or fewer wet nappies
• Being very irritable or crying in an unusual way
• Fast breathing
• A seizure (fit)
• A fever in a baby under 3 months is an emergency even if the baby seems well

Symptoms in older adults

• New confusion or forgetfulness
• Weakness or falls
• Reduced appetite and drinking
• Dehydration
• The body may not feel very hot even when the person is seriously unwell

Causes

Main causes

• Serious infections, such as sepsis, meningitis, or encephalitis
• Heat illness or heat stroke
• Reactions to some medicines or recreational drugs
• A hormone storm, such as thyroid storm
• A rare inherited reaction to some anaesthetics
• Severe dehydration or burns
• Brain injury or bleeding in the brain

Risk factors

• Being a baby or an older adult
• Having a weakened immune system
• Working or exercising in very hot conditions
• Taking some medicines that affect body temperature
• Using recreational drugs
• Having certain long-term health conditions
• Having a family history of a rare reaction to anaesthetics

When to see a doctor

See a doctor urgently if:

• A temperature of 40°C (104°F) or higher
• Fever with confusion, drowsiness, or unusual behavior
• Fever with signs of dehydration
• Fever in someone with a weakened immune system
• Fever after recent heat exposure

Book a routine appointment if:

• Fevers that keep coming back
• Fevers with ongoing weight loss or night sweats
• Fevers after starting a new medicine — ask your provider before changing or stopping it
• Fever with pain when passing urine

Diagnosis

A healthcare provider will check the person’s temperature, ask about symptoms, medicines, heat exposure, and recent illness, and do a physical exam. They may do tests to find the cause.

Tests that may be done

• Blood tests
• Urine tests
• Chest X-ray or other imaging if needed
• A test of spinal fluid if meningitis is suspected
• A heart tracing (ECG) if needed

What to expect at your appointment

You may be seen quickly in an emergency department. Staff will check the temperature often, monitor breathing and heart rate, and start cooling if needed. They will also look for the cause and treat it.

Treatment

Hyperpyrexia is treated as an emergency. The goals are to cool the body safely and treat the cause. Treatment usually happens in a hospital.

Self-care at home

• Call your local emergency number if you think someone has hyperpyrexia.
• While waiting for help, move the person to a cool place and loosen extra clothing.
• Offer cool water only if the person is fully awake and able to swallow.
• Do not use ice baths, freezing water, or alcohol rubs.
• After recovery, rest, drink fluids, and follow up with your healthcare provider.

Medical treatments

Healthcare teams may use cooling blankets, cool mist, fans, and intravenous fluids. They treat the underlying cause, such as infection or heat illness. They monitor the heart, breathing, and brain function. Medicines may be used by the care team for specific causes, but do not take or give medicines without advice.

When is surgery considered?

Surgery is not a treatment for hyperpyrexia itself. It may be needed only if the underlying cause, such as an infection or injury, requires an operation.

Living with this condition

After an episode, you may need follow-up to check the cause and make sure your organs are working well. Avoid heavy heat exposure and strenuous activity until your provider says it is safe.

Lifestyle tips

• Drink water regularly, especially in hot weather
• Wear light clothing and stay in cool places during heatwaves
• Avoid the hottest part of the day for outdoor work or exercise
• Rest and monitor your temperature if you feel unwell
• Ask your pharmacist or provider to review your medicines

Diet and exercise

Eat and drink normally as you recover. Gentle activity is fine when you feel ready. Avoid hard exercise in heat until your healthcare provider says it is safe.

Mental health and emotional wellbeing

A very high fever can be frightening, and it is normal to feel anxious or worried afterward. Talk to your healthcare provider if these feelings continue. If you or someone else has thoughts of self-harm, call your local emergency number or a local crisis service immediately.

Prevention

Not all cases can be prevented, but you can lower the risk from heat and some infections.

Vaccines

Keep up with routine vaccines recommended by your local health service. They can prevent some infections that cause high fever.

Screening programmes

There is no routine screening test for hyperpyrexia. Regular check-ups for long-term conditions and a review of your medicines can help.

Complications

If left untreated

• Seizures
• Brain injury
• Organ damage or organ failure
• Coma
• Death

Long-term outlook

With quick treatment, many people recover well. The outlook depends on the cause and how fast care is given. Seeking help early gives the best chance.

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