Recognising and Treating Acute Anaphylaxis


Published: 08 February 2021

Over four million Australians (one in five) are affected by allergic disease. Allergic diseases include anaphylaxis, allergic rhinitis, asthma, eczema and others (Parliament of Australia 2020).

Anaphylaxis is the most severe type of allergic reaction. It is a potentially life-threatening medical emergency that requires urgent treatment (Allergy & Anaphylaxis Australia 2020).

Between 1997 and 2013, there have been 324 deaths related to anaphylaxis in Australia. Deaths caused by anaphylaxis are often preventable. Over the past five years, hospital admissions for anaphylaxis have increased by 46% (ACSQHC 2020).

What is Anaphylaxis?

Anaphylaxis is a severe generalised allergic reaction. Symptoms generally occur within 20 minutes to 2 hours after exposure to the allergen and may quickly escalate, with the potential to become life-threatening (Allergy & Anaphylaxis Australia 2020).

Note that not every person with an allergy will experience anaphylaxis (ASCIA 2019a).

The Australian Society of Clinical Immunology and Allergy (ASCIA) (2020a) defines anaphylaxis as:

  • ‘Any acute onset illness with typical skin features (urticarial rash or erythema/flushing, and/or angioedema), plus involvement of:
    • Respiratory and/or
    • Cardiovascular and/or
    • Persistent severe gastrointestinal symptoms; OR
  • Any acute onset of hypotension or bronchospasm or upper airway obstruction where anaphylaxis is considered possible, even if typical skin features are not present.’

Anaphylaxis Signs and Symptoms

anaphylaxis symptoms swelling tightness throat

The following symptoms suggest a mild to moderate allergic reaction. Note that these symptoms may precede anaphylaxis.

  • Swelling of the face, lips or eyes
  • Hives or welts
  • Tingling mouth
  • Abdominal pain and vomiting (which may indicate anaphylaxis caused by an insect allergy)
  • Localised swelling at sting site (in the case of an insect sting).

(ASCIA 2020a; ACSQHC 2020)

Anaphylaxis includes one or more of the following potentially life-threatening symptoms:

  • Swelling of the tongue
  • Difficulty swallowing or speaking
  • Swelling or tightness in the throat
  • Difficulty talking and/or a hoarse voice
  • Difficult or noisy breathing
  • Difficult or noisy breathing
  • A wheeze or persistent cough
  • Shortness of breath (increased respiratory rate)
  • Tachycardia
  • Hypotension with persistent dizziness or feeling faint
  • Collapse
  • Pallor and floppiness (in paediatrics)
  • Decreased level of consciousness or loss of consciousness
  • Cardiac arrest
  • Severe nausea
  • Severe diarrhoea
  • Abdominal pain and vomiting (which may indicate anaphylaxis caused by an insect allergy or injected drug allergy)

(ASCIA 2019; ACSQHC 2020)

Note that in up to 20% of anaphylactic reactions, skin and mucosal changes are minor or completely absent (ACSQHC 2019).

The severity of an anaphylactic reaction may be influenced by:

  • Exercise
  • Heat
  • Alcohol
  • Amount of food eaten and how it was prepared (in anaphylaxis caused by food).

(ASCIA 2019a)

Causes of Anaphylaxis

Anaphylaxis is most likely to be triggered by foods, medicines or insect stings (ASCIA 2020a).

The onset of symptoms may depend on the allergen triggering the reaction:

  • Reactions caused by food usually occur within one to two hours of ingestion.
  • Reactions caused by stings or injected medicines usually occur within 5 to 30 minutes.

(ASCIA 2020a)

About 10% of infants, 4 to 8% of children and 2% of adults experience food allergies. Although any food can cause an allergic reaction, 90% of reactions are triggered by:

  • Cow's milk
  • Eggs
  • Peanuts
  • Tree nuts
  • Sesame
  • Soy
  • Fish
  • Shellfish
  • Wheat.

(ASCIA 2019c)

anaphylaxis food peanuts
Most food-related anaphylactic reactions are triggered by one of nine foods, including peanuts.

Medicine-related anaphylaxis is most commonly caused by:

  • Antibiotics
  • Non-steroidal anti-inflammatory drugs (NSAIDs)
  • Contrast-induced anaphylactoid reactions
  • Immunotherapy.

(Nickson 2020)

Insect sting-related anaphylaxis is most commonly caused by honeybees, wasps or ants (Nickson 2020).

In more than 50% of cases, the trigger for anaphylaxis can not be identified (Nickson 2020).

Less common causes of anaphylaxis include:

  • Physical triggers such as exercise, heat, cold, or ultraviolet light
  • Biological fluids such as transfusions, immunoglobulin, antivenoms and semen
  • Latex rubber
  • Tick bites
  • Hormonal changes such as breastfeeding or menstruation
  • Dialysis membranes
  • Hydatid cyst rupture
  • Aeroallergens (animals and pollen)
  • Food additives such as preservatives and colours
  • Topic medications such as antiseptics

(Nickson 2020)

Those most likely to be allergic to latex are people who are frequently exposed to it, such as healthcare workers (ASCIA 2019b).

Diagnosing Anaphylaxis

Immunoglobulin E (IgE) are antibodies produced by the immune system. The plasma cell produces IgE-antibodies that bind to a specific allergen via the Fragment antigen-binding region. If you have an allergy, your immune system overreacts to an allergen by producing IgE (ASCIA 2020b).

Diagnosis involves testing for raised antibodies in response to a particular allergen that is given. This can be performed through tests such as:

  • Full blood count with differential
  • Eosinophil count
  • Total serum immunoglobulin levels
  • Skin tests
  • Challenge tests
  • Radio-Allergo-Sorbent Test (RAST).

(ASCIA 2020b)

One of the difficulties with recognising an anaphylactic reaction is that there are many differential diagnoses. Some of these include:

  • Idiopathic urticaria
  • Isolated angioedema
  • Dystonic reactions that mimic swollen tongue
  • Acute oesophageal reflux
  • Peptide-secreting tumours
  • Alcohol-related flushing
  • Epileptic seizures
  • Stroke
  • Vasovagal syncope
  • Systemic inflammatory response syndrome
  • Shock
  • Asthma
  • Panic disorders
  • Globus hystericus
  • Laryngospasm
  • Vocal cord dysfunction
  • Scombroid fish poisoning
  • Serum sickness
  • Pheochromocytoma
  • Systemic mastocytosis.

(Nickson 2020)

Treatment of an Anaphylactic Reaction

For the most up-to-date guidelines for immediate treatment and management of anaphylactic reactions, refer to ASCIA’s Guidelines - Acute Management of Anaphylaxis.

What is Adrenaline?

Adrenaline (epinephrine) is the first-line treatment of anaphylaxis. It is the only effective treatment and reduces hospitalisation and death (ACSQHC 2020). It works by:

  • Reducing airway mucosal oedema
  • Inducing bronchodilation
  • Inducing vasoconstriction
  • Increasing the strength of cardiac contraction.

(ASCIA 2020a)

Adrenaline also has a relatively short half-life (plasma half-life of approximately two to three minutes). Some patients may experience adverse effects such as transient pallor, palpitations or headache after administration (EMC 2020).

Monitoring the Patient After an Anaphylactic Reaction

The patient should not be allowed to stand or walk until they are haemodynamically stable.

  • Patients who received one dose of adrenaline should wait for at least one hour
  • Patients who received several doses of adrenaline should wait for at least four hours.

(ASCIA 2020a)

The patient should be closely monitored (which means to increase the frequency of observations) for at least 4 hours following their last dose of adrenaline, as there is potential for relapse. Increase the frequency of overnight observations or consider critical care if the patient is haemodynamically unstable. Overnight observation is recommended if the patient:

  • Experienced a severe or protracted (e.g. repeated doses of adrenaline or IV fluid resuscitation) reaction
  • Has a history of severe or protracted anaphylaxis
  • Has a concomitant illness such as asthma or arrhythmia
  • Lives alone or remotely from medical care
  • Presented for care late in the evening.

(ASCIA 2020a)

Any person with anaphylaxis should have an anaphylaxis management plan. Training and education, as well as an emergency kit containing medication such as adrenaline, should be provided to the patient and their family (ACSQHC 2020).

The Acute Anaphylaxis Clinical Care Standard

The Australian Commission on Safety and Quality in Health Care is currently in the process of finalising a new Acute Anaphylaxis Clinical Care Standard. This standard aims to reduce differences in care received by people who experience an anaphylactic reaction (ACSQHC 2019).

According to the draft document released in 2020, the standard comprises the following eight Quality Statements:

Quality Statement 1: Prompt recognition of anaphylaxis Patients displaying the symptoms of anaphylaxis are assessed rapidly, especially if they have a history of allergy or have been exposed to an allergic trigger.
Quality Statement 2: Immediate injection of intramuscular adrenaline Adrenaline is administered without delay if a patient is having an anaphylactic reaction or suspected anaphylactic reaction. Adrenaline is administered before any other treatment, including asthma medicine, corticosteroids and antihistamines.
Quality Statement 3: Correct patient positioning Patients experiencing an anaphylactic reaction are laid flat. If they are having difficulty breathing, they can sit with their legs extended. Patients are not permitted to stand or walk until they have been assessed as safe to do so.
Quality Statement 4: Access to a personal adrenaline injector in all healthcare settings Patients have access to their own adrenaline injectors at all times when receiving care and can self-medicate if required.
Quality Statement 5: Observation time following anaphylaxis Patients who have experienced an anaphylactic reaction are monitored for at least four hours following their last dose of adrenaline, in a healthcare facility. In accordance with ASCIA’s Acute Management of Anaphylaxis Guidelines, overnight observation may be required.
Quality Statement 6: Discharge management Prior to discharge from a healthcare facility, patients receive:
  • An anaphylaxis action plan
  • An adrenaline injector or prescription (if there is a re-exposure risk)
  • Education on allergy management strategies
  • Arrangements for a consultation with their general practitioner and a clinical immunology/allergy specialist

(ACSQHC 2020a)

Note: This information is subject to change when the final version of the standard is released.

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