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Independents' Day

Suspected anaphylaxis requires prompt treatment

How is anaphylaxis recognised?
What are the common triggers?
When should adrenaline be used?

How is anaphylaxis recognised?
What are the common triggers?
When should adrenaline be used?

Anaphylaxis is a severe, life-threatening, generalised or systemic hypersensitivity reaction. It is characterised by rapidly developing life-threatening airway and/or breathing and/or circulation problems usually associated with skin and/or mucosal changes.

Clinical presentations of allergy which are not life threatening should not be confused with anaphylaxis.

For example, allergic skin changes can be worrying or distressing for patients (and those treating them) but skin changes alone (urticaria with or without angioedema) without life-threatening airway, breathing or circulation problems are not anaphylaxis, and respond to antihistamines with or without corticosteroids. Most patients who have skin reactions alone, whether triggered by allergy (e.g. food allergy) or non-allergic (e.g. physical urticarias associated with heat, pressure of tight clothing), do not go on to develop anaphylaxis.

The presenting symptoms and signs of severe anaphylaxis and life-threatening asthma can be the same. If the patient has asthma-like features alone, the BTS/SIGN asthma guidelines should be followed.1

In January 2008, the Resuscitation Council UK published comprehensive guidelines on anaphylaxis and in April 2009 concise guidance was published by the Royal College of Physicians.2,3

What triggers anaphylaxis?

Food, drugs and stings are the most common triggers of anaphylaxis in the UK. Figures suggest that the incidence of anaphylaxis may be increasing. In 2007, 1,100 people were admitted to hospital in the UK suffering from anaphylaxis with food as the suspected cause, compared with 551 in 1997. Food triggers tend to be more common in children and drugs are far more common triggers in adults. Virtually any food or class of drug can be implicated. Nuts and fish are the most common food allergens. Muscle relaxants, antibiotics, NSAIDs and aspirin are the most common drug triggers. In many cases, no cause can be identified, so-called idiopathic anaphylaxis.

Less than 1% of all those who have anaphylaxis die from it. The risk of death is increased in those with pre-existing asthma, particularly if the asthma is poorly controlled or in those asthma patients who fail to use, or delay treatment with, adrenaline. There are approximately 20 anaphylaxis deaths reported each year in the UK. When anaphylaxis is fatal, death usually occurs within minutes of contact with the trigger. In a case series of 163 patients, fatal food reactions caused respiratory arrest typically after 30–35 minutes; insect stings caused collapse from shock after 10–15 minutes; and deaths caused by iv medication occurred most commonly within five minutes.4

Recognising anaphylaxis

Anaphylaxis is likely if a patient who is exposed to a known allergen develops a sudden illness (usually within minutes of exposure) with rapidly progressing skin changes (urticaria/angioedema typically) and life-threatening airway and/or breathing and/or circulation problems. The reaction is usually unexpected and often there is no identifiable trigger. A single set of criteria will not identify all anaphylactic reactions.

The Airway, Breathing, Circulation, Disability and Exposure (ABCDE) approach that is used in the immediate care of all critically ill patients is used to recognise and treat anaphylaxis. Treat life-threatening problems as soon as they are recognised (i.e. if there is a life-threatening airway problem treat this first, and then move on to assessing and treating breathing problems).


In the community it is essential to call an ambulance early. If you are working alone, ensure that help is coming as soon as possible. Resuscitation equipment and drugs to help with the rapid resuscitation of a patient with anaphylaxis must be immediately available in all clinical settings. All patients with suspected anaphylaxis should be monitored (e.g. by an ambulance crew) as soon as possible. Minimal monitoring includes pulse oximetry, non-invasive blood pressure and 3-lead ECG.

Patient positioning

Positioning of the patient is very important in anaphylaxis. For patients with airway and breathing problems the patient should be placed in a position where breathing is made easier. Lying flat with or without leg elevation is helpful for patients with a low blood pressure. If the patient feels faint, do not sit or stand them up - this can cause cardiac arrest.

Removing the trigger

Treatment must not be delayed if removing the trigger is not possible. Stop any drug suspected of causing anaphylaxis (e.g. stop iv infusion of an antibiotic). Remove the stinger after a bee sting. After food-induced anaphylaxis, do not make the patient vomit.

Cardiopulmonary resuscitation

If cardiac arrest occurs start cardiopulmonary resuscitation (CPR) immediately and follow current guidelines (see


Adrenaline is the most important drug for the treatment of anaphylaxis. It seems to work best when given early after the onset of the reaction but it is not without risk, particularly when given iv. Adverse effects are extremely rare with correct doses injected im.

Difficulties can arise if the clinical picture is evolving when the patient is first assessed. Adrenaline should be given to all patients with life-threatening features. If life-threatening features are absent but there are other features of a systemic allergic reaction, the patient needs careful observation and proportionate, symptomatic treatment using the ABCDE approach. Further doses of im adrenaline can be given at 5-minute intervals.

Ideally assessment of response to adrenaline should include monitoring of:

• pulse
• oxygen saturation
• blood pressure

The im route is best for most healthcare professionals administering adrenaline in the community setting as it provides a greater margin of safety, does not require iv access and is easier to learn. The best site for im injection is the anterolateral aspect of the middle third of the thigh. The injection needle needs to be long enough to ensure that the adrenaline is injected into muscle.

There is a much greater risk of causing harmful side-effects (e.g. arrhythmia, MI, severe hypertension, intracranial haemorrhage) when using iv adrenaline. This is why the im route is recommended for most healthcare providers.

Adrenaline autoinjectors are often given to patients at risk of anaphylaxis. There are only two doses of adrenaline autoinjector commonly available: 0.15 and 0.3 mg. If an adrenaline autoinjector is the only available adrenaline preparation when treating anaphylaxis, healthcare providers should use it.

Antihistamines and corticosteroids

These are second-line treatments for anaphylaxis.

Confirming diagnosis

Clinical history is the gold standard. Two case histories, one illustrating urticaria and the other anaphylaxis, are described in boxes 1 and 2respectively, attached.

A specific test to help confirm a diagnosis of anaphylaxis is measurement of mast cell tryptase. In anaphylaxis, mast cell degranulation leads to markedly increased blood tryptase concentrations. Tryptase levels in the blood may not increase until 30 minutes or more after the onset of symptoms, and peak 1-2 hours after onset. The half-life of tryptase is very short (approximately 2 hours), and concentrations may be back to normal within 6-8 hours, so timing of any blood samples is very important. Tryptase should be measured once a patient with suspected anaphylaxis is admitted to hospital.


Patients with suspected anaphylaxis (i.e. an airway, breathing or circulation problem) should be treated and then observed for at least 6 hours in a clinical area with facilities for treating medical emergencies. A longer period of observation is needed in the following situations:

• Slow onset and idiopathic anaphylaxis
• The patient has asthma. Poorly controlled asthma is a significant risk factor itself, and so all patients with a history of anaphylaxis, should have their asthma management reviewed and optimised, with a view to maximising compliance
• Continuing absorption of allergen
• Previous history of protracted reactions
• Poor social circumstances

Adrenaline autoinjectors

Allergen avoidance is the simplest first step towards preventing recurrence. An autoinjector device is appropriate for patients with a clear history of anaphylaxis, and an increased risk of recurrence. This includes idiopathic cases, or when it is difficult to avoid the trigger reaction e.g. stings and food-induced reactions in restaurants. Caution should be exercised in adults with ischaemic heart disease for whom the risk of using an adrenaline autoinjector may exceed the risk of not having one.

Referral to allergy specialists

All patients presenting with confirmed or suspected anaphylaxis should be referred to an allergy clinic with a view to:
• Confirming the diagnosis of anaphylaxis
• Identifying the cause, and thereby reducing the risk of future reactions. This may involve diagnostic skin prick and/or blood tests for specific IgE antibodies, and occasionally, cautious challenge testing (e.g. where a useful antibiotic is being avoided with a history not supportive of true anaphylaxis)
• Offering advice on allergen avoidance. If the allergen is a food, patients need to know what products are likely to contain it, and all the names that can be used to describe it. Where possible they also need to know how to avoid situations that could expose them to the allergen
• Defining a care plan and preparing the patient to manage future episodes themselves. Care plans decrease risk of recurrence. Patients need to be able to recognise the early symptoms of anaphylaxis, so that they can summon help quickly and prepare to use their emergency medication
• Training patients how to use adrenaline autoinjectors
• Advising patients on the use of MedicAlert bracelets, and providing letters for patients to use at the dentist, on holiday etc
• Desensitisation treatment can in some cases reduce future risks (e.g. wasp sting venom anaphylaxis)
Children should be referred to specialist paediatric allergy clinics. Specialist clinics are listed on the British Society for Allergy and Clinical Immunology (BSACI) website, see useful information box, below.


The incidence of anaphylaxis is increasing. Early recognition of life-threatening airway, breathing or circulation problems and treatment with im adrenaline is essential. All patients with confirmed anaphylaxis or suspected anaphylaxis should be referred to an allergy clinic.

Diagnostic skin pricks Useful information

Resuscitation Council UK
Full detailed guideline on anaphylaxis

British Society for Allergy and Clinical Immunology
Lists specialist clinics in the UK

The Anaphylaxis Campaign
Useful information for patients, carers and healthcare professionals

Podcasts by Dr Jasmeet Soar and Dr David J. Unsworth
Aimed at primary care on the initial treatment and follow up of patients with anaphylaxis

The MedicAlert Foundation
A registered charity that provides identification bracelets for patients with allergies and other medical conditions


Dr Jasmeet Soar
Consultant in anaesthesia and intensive care medicine

Dr David J. Unsworth
Consultant in immunology and allergy

Southmead Hospital
North Bristol NHS Trust

Key points Box 1: Idiopathic, non-allergic (physical) urticaria

A 35-year-old woman was referred to the allergy clinic after frequent visits over several years to her GP and the emergency department (ED) with florid urticaria, occasionally with lip or tongue angioedema. Hot baths and tight clothing were recognised as (physical/non-allergic) factors which made the grumbling daily rash much worse. The most recent episode had started three weeks ago. She was diagnosed with anaphylaxis in the ED even though review of ED records showed a normal blood pressure, pulse oximetry, and ECG. Adrenaline, chlorphenamine, and hydrocortisone had been given with benefit. Prednisolone had been given for home use. An adrenaline autoinjector was also provided. When seen in the allergy clinic, the patient was convinced that fish eaten several hours before the onset of the rash had been the recent trigger. The same fish had been eaten many times before without problems. She was distressed that once the oral prednisolone had been stopped, the tendency to daily itchy hives had recurred. On examination, dermatographism was readily demonstrable.

Comment: The history is of idiopathic, non-allergic (likely physical/intrinsic) urticaria. Subsequent blood tests excluded fish allergy. A normal diet was recommended. Routine blood tests showed a normal total IgE concentration, and normal C3/4. A daily long-acting antihistamine was prescribed. The patient was given a clinic handout explaining the mechanisms behind
non-allergic urticaria. The GP was informed that the adrenaline autoinjector was not required. The patient was advised to avoid NSAIDs. She was reassured that the urticaria typically goes into remission and can remain so for many years.

Box 2: IgE-mediated anaphylaxis to wasp venom

A 23-year-old man was stung on the neck by a wasp while cycling. Within minutes he felt faint and unwell. He also had an itchy scalp, and hives. He had asthma and felt wheezy so stopped to use his inhaler. The local emergency department was only a few hundred yards away and a passer by helped him to get there in a car. On his arrival about 10 minutes after the sting, he could barely stand. His blood pressure was low (60/30 mm Hg). Anaphylaxis was correctly diagnosed. Immediate resuscitation included oxygen, 0.5 mg im adrenaline, and a salbutamol nebuliser. His breathing and blood pressure improved over the next 5-10 minutes. He was also given chlorphenamine and hydrocortisone. He was admitted for observation overnight, and referred to the allergy clinic for review.

In the allergy clinic six weeks later, the suspected diagnosis of wasp hypersensitivity presenting as anaphylaxis was confirmed by skin prick testing. (The photograph, below, shows a wheal and flare reaction down to 10 µg/ml concentration of wasp venom). An adrenaline autoinjector was prescribed, and the patient and his partner trained in its use. A MedicAlert bracelet was provided. The patient admitted poor compliance with his asthma treatment and the importance of using his inhaled steroid was stressed.

The patient was successfully enrolled for day case subcutaneous desensitising injections of purified wasp venom.

Box 1 Box 2

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