What actually is anaphylactic shock? An expert guide

Anaphylactic shock is what can happen when a severe systemic reaction,¹ usually allergic, progresses and makes your blood pressure drop suddenly.^1,2 Vital organs can’t get enough oxygen, which may be life-threatening.^1,2 It’s one of the reasons anaphylaxis – the name for this type of reaction – is a medical emergency.^1,2

Around 30% of people who have anaphylaxis go into shock, according to Anaphylaxis and Anaphylactic Shock, McMaster Textbook of Internal Medicine. And it can happen very fast.³ Read on to find out more about anaphylaxis and anaphylactic shock. This article covers the common causes, allergic and non-allergic, the signs and symptoms, what to do if it happens and how to manage the risk of anaphylactic shock in the future.

What happens when you go into anaphylactic shock?

Your immune system overreacts to some harmless trigger and floods your body with chemicals that dilate blood vessels and make them leaky. Your circulating blood volume can drop by 35% in around 10 minutes.³ The body compensates for the fall in blood pressure, until it can’t, then organs begin to fail.¹

The third and final stage is irreversible shock. The damage is done and treatment, however intensive, is unlikely to work.² You may go into cardiac arrest.⁴ That’s why it’s so important to recognize the early signs and symptoms (see below).

What should you do when someone’s in anaphylactic shock?

You’ll see that step 3 is to lie a person with anaphylaxis down. It’s vital not to let them sit up again (unless they’re having trouble breathing) because that can interfere with the flow of blood to the heart and itself cause anaphylactic shock.⁵  

1. Use an adrenaline nasal spray or auto-injector: If available, administer the first dose immediately. Instructions are usually printed on the device.¹ Make a note of the time.

2. Dial 999 right away: Say you suspect anaphylaxis or anaphylactic shock. Check for a medical alert bracelet or tag and share any critical allergy details you find.

3. Position the person properly:¹ Keep them lying flat with legs elevated – unless they’re pregnant, then place them on their left side. If they’re unconscious, put them in the recovery position. 

4. Monitor and consider a second dose of emergency medication:¹ If symptoms persist after 5 to 15 minutes and help hasn’t arrived, administer adrenaline again. Keep the person lying down, except if they’re having tryouble breathing. Keep the person lying down, except if they’re having tryouble breathing.

5. React quickly if their breathing or heart stops: Perform CPR.

6. Inform paramedics: Once help arrives, hand over the used nasal spray or auto-injector so they know exactly what medication has been administered.

What causes anaphylactic shock?

Food, insect venom, drug and latex allergies carry a higher risk of anaphylaxis and could cause anaphylactic shock. The immune system can overreact to other factors too, for instance exercise.¹ Sometimes the immune system isn’t involved, although the reaction may still be chemical or drug-related.^1,3 

Anaphylaxis can be a diagnostic challenge so the cause may remain unknown. Idiopathic anaphylaxis, as it’s called, accounts for around 10% of child cases and 30–60% of cases in adults, with more women affected than men.⁶

Which allergies can trigger anaphylactic shock?

Of the four allergies linked to anaphylaxis, drugs and insect venom are more likely to cause fatal anaphylactic shock, according to the clinical review Why do People Die of Anaphylaxis?⁵ Potential triggers include:^1,3

• Bee, wasp, yellow jacket or hornet stings³
• Antibiotics like penicillin⁴
• Muscle relaxants used in general anaesthetics⁵

With food allergies, the chances are higher of fatal respiratory arrest due to severely restricted airways.⁵

How can non-allergic triggers cause anaphylactic shock symptoms?

Anaphylaxis can follow a blood transfusion^3,7 or taking aspirin and other non-steroid anti-inflammatory drugs (NSAIDs), some opioids, chemotherapy and contrast agents for MRI scans and other medical imaging exams.¹ Sulfite food preservatives can cause it too.¹ So can exercise, alone or combined with an NSAID or food.⁷

Other factors can increase the risk of exercise-induced anaphylaxis, and therefore anaphylactic shock. These include hormonal changes, infections, stress and alcohol.¹

How can you spot the early signs of anaphylactic shock?

Around 80-90% of people get skin symptoms during a sudden severe reaction, according to the World Allergy Organization,¹ and it usually affects other parts of the body too. Anaphylactic shock could happen at the start but tends to develop shortly afterwards.³ Look out for these warning signs, in any combination:

• Hives rash, itchy, flushed or pale skin¹
• Swollen tongue or throat¹
• Wheezing and difficulty breathing¹
• Nausea, vomiting or diarrhoea¹
• Weak or rapid pulse¹
• Drop in blood pressure (hypotension) and shock¹
• Dizziness or fainting¹
• Sense of impending doom⁴

Anaphylaxis symptoms can subside and then reappear in a second wave. It’s called biphasic anaphylaxis.³ And it's why you should always go to the emergency room even if you start to feel better.

What does anaphylactic shock itself look and feel like?

When someone’s in anaphylactic shock their skin may be cold and pale,^3,4 even though they’re sweating.³ Their heart may start racing, breathing may become rapid and crackly,⁸ and it’s possible they’ll lose control of their bowels.³ Disorientation and agitation are also common.⁴

The end point of anaphylactic shock can be a slowing of the heart rate, unconsciousness and cardiac arrest.⁴

4 differences between anaphylaxis and anaphylactic shock

Here’s a quick reminder, in case you’re still confused about which term to use when:

How do you prevent or manage the risk of anaphylactic shock?

If you suspect an allergy or have had an anaphylactic reaction, allergy testing can help identify the trigger. You’ll need to avoid it and carry emergency medication. Allergy immunotherapy could be an option too.¹ Essentially, it’s about minimising the risks while having an action plan ready in case it happens.¹

Find out what could trigger anaphylactic shock for you

Your GP may suggest a skin prick test, blood test or challenge test to pinpoint your allergy.^1,2,3 Depending on the trigger, Precision Allergy Molecular Diagnosis (PAMD@) is a more detailed blood test that may help assess your anaphylaxis risk.⁹ Some peanut and insect sting allergens are more likely triggers.⁹

Understand other risk factors for anaphylaxis and anaphylactic shock

Apart from having a high-risk allergy, your doctor will ask if any of these factors apply to you:¹⁰

• anaphylaxis in the family
• a previous anaphylactic attack
• having heart problems or asthma, particularly if uncontrolled
• mastocytosis

Always carry emergency medication

Adrenaline is the first-line treatment¹ and around 10% of severe systemic allergic reactions need more than one dose, according to the review Use of Multiple Epinephrine Doses in Anaphylaxis.¹¹ In the ambulance or at hospital, you may also have intravenous fluids and oxygen for anaphylactic shock.^2,3

Keep two adrenaline nasal sprays or auto-injectors with you at all times in case of a life-threatening allergic reaction.¹ Make sure they’re in date and stored correctly. 

Discuss with your doctor whether allergy immunotherapy could help

Allergy immunotherapy uses regular doses of an allergen to retrain the immune system so it becomes more tolerant. It can lower the risk of anaphylaxis for people allergic to bee and wasp stings (hymenoptera), ¹² or to peanut¹⁵. Your doctor can tell you if it might be a suitable treatment.

Share your allergy action plan³

Work with the doctor to create a personalized action plan and share it with school or work, family and caregivers. Then everyone will know what trigger it is you have to avoid. Most importantly, they’ll be able to act fast in case of anaphylaxis and how to administer emergency medication.

The short version

Anaphylactic shock is when blood pressure drops suddenly during a severe allergic reaction (anaphylaxis), cutting off oxygen to vital organs.^1,2 About 30% of anaphylaxis cases lead to shock and it can be life-threatening without prompt treatment.^1,3

Drug and insect venom allergies are most likely to cause fatal anaphylactic shock.⁵ Other triggers include food, latex, exercise and certain chemicals. Anaphylaxis symptoms usually affect more than one part of the body, from the skin to airways, breathing and circulation.¹ Someone in anaphylactic shock might look pale and sweaty, and be disorientated.^3,4

If you’re at risk of anaphylaxis and anaphylactic shock, it’s important to avoid your trigger, carry emergency medication and have an action plan.^1,3 Using an adrenaline nasal spray or auto-injector immediately can limit the severity of the reaction.¹ Call an ambulance and lie down with legs raised, even if you start to feel better.^1,5