Diagnosis and treatment of anaphylaxis should follow a structured ABCDE approach:

• Airway problems
• Breathing problems
• Circulation problems
• Disability problems
• Exposure

Patients may present with an airway, breathing or circulatory problem or any combination.

Airway problems - Airway problems are caused by swelling of the throat and/or the tongue due to angioedema. This can result in breathing and/or swallowing problems. The patient may feel as though their throat is closing up.

A hoarse voice or stridor can also be indicative of airway problems. Stridor is a high pitched noise on inspiration caused by obstruction of the upper airway.

Breathing problems - Patients experiencing an anaphylactic reaction are likely to begin to wheeze, have an increased respiratory rate and develop shortness of breath. The increased effort associated with breathing is likely to make the patient tired. The patient may become confused due to hypoxia (lack of oxygen).

Later signs of breathing problems include cyanosis, a bluish discolouration of the skin due to poor circulation or oxygenation, and respiratory arrest.

Circulation problems - Circulation problems are caused by reduced myocardial contractility, increased heart rate, vasodilation and increased vascular permeability causing capillary leakage of fluid. Capillary leakage can result in tissue swelling or oedema.

Circulation problems can present as:

• Low blood pressure causing faintness, dizziness or collapse.
• Increased pulse rate or tachycardia
• Circulatory collapse which would present as pale and clammy skin along with a rapid pulse followed by hypotension
• Reduced or loss of consciousness
• Bradycardia can be a late feature often preceding cardiac arrest
• Cardiac arrest

Disability problems - Disability problems are associated with the patient's neurological status. Reduced brain perfusion may present as confusion, agitation or loss of consciousness. These changes are directly related to the airway, breathing or circulatory problems discussed previously.

Exposure - Determining a patient's exposure requires assessment of any skin or mucosal changes. Changes to the skin or mucosa are present in more than 80% of anaphylactic reactions.

Dermatological changes can be either subtle or dramatic and are often the first presenting feature of a reaction. Changes can affect either the skin or mucosa or both and may present as flushing, erythema, urticaria or angio-oedema.

• Erythema is a superficial red rash that can be either patchy or generalised.
• Urticaria can appear anywhere on the body presenting as a red, raised and itchy rash
• Angioedema is swelling of the dermis, subcutaneous tissue or mucosa. It is most commonly affects the eye lids, lips and occasionally the mouth and throat.

Skin changes can cause anxiety and distress to patients but skin changes without life-threatening airway, breathing or circulatory problems do not indicate an anaphylactic reaction.

Confirmed or suspected anaphylaxis should always be treated as a medical emergency as cardio-respiratory collapse can be fatal if not managed urgently.