Anaphylaxis is a severe, life-threatening, generalised or systemic hypersensitivity reaction that is likely when both of the following criteria are met:
- Sudden onset and rapid progression of symptoms
- Life-threatening airway and/or breathing and/or circulation problems.
Skin and/or mucosal changes (flushing, urticaria, angio-oedema) can also occur but are absent in a significant proportion of cases.
Initial Rapid Assessment and Management
The management of anaphylaxis requires airway management, early administration of adrenaline (preferably in the anterolateral aspect of the middle third of the thigh) and aggressive fluid resuscitation. Intubation may be required in severe cases.
The initial management is as follows:
- Remove any allergen that may be present and call for help.
- Administer IM adrenaline
- Treat life-threatening features using the standard Airway, Breathing, Circulation, Disability, Exposure (ABCDE) approach
- Administer high-flow oxygen using a mask with an oxygen reservoir
- All patients should be monitored with pulse oximetry, non-invasive blood pressure monitoring and a 3-lead ECG
- Lying the patient flat with legs elevated can help relieve hypotension
- Patients who are breathing normally and unconscious should be placed on their side in the recovery position, and their breathing should be monitored continuously.
Adrenaline
Adrenaline is the most important drug for the treatment of anaphylactic reactions. As an alpha-adrenergic receptor agonist, it reverses peripheral vasodilatation and reduces oedema. Its beta-adrenergic effects dilate the bronchial airways, increase the force of myocardial contraction and suppresses histamine and leukotriene release. Adrenaline should be the first drug administered, and the IM route is best for most individuals.
The age-related doses of IM adrenaline given in anaphylaxis are:
- Child under 6 years: 150 mcg (0.15 mL of 1:1000)
- Child 6-12 years: 300 mcg (0.3 mL of 1:1000)
- Child >12: 500 mcg (0.5 mL of 1:1000)
- Adult: 500 mcg (0.5 mL of 1:1000)
The latest APLS guidelines recommend the use of nebulised adrenaline in the presence of stridor and/or wheeze.
A repeat dose of adrenaline should be given after 5 minutes if Airway/ Breathing/ Circulation problems persist.
Adrenaline may be administered in life-threatening anaphylactic reactions, even when the following relative contraindications are present:
- Coronary artery disease
- Uncontrolled hypertension
- Serious ventricular arrhythmias
- Second stage of labour
Patients who are taking beta-blockers can be resistant to the effects of adrenaline in anaphylaxis. Animal studies and case reports have suggested that glucagon can be used to overcome the effects of the beta-blockade if initial doses of adrenaline are unsuccessful.
Intravenous adrenaline must be used only in certain specialist settings and only by those skilled and experienced in its use.
Intravenous Fluid Challenge
An intravenous fluid challenge is recommended if there are signs of shock present:
- The ALS guidelines recommend a fluid challenge with 500-1000 mL of warmed crystalloid solution for adults (e.g. Hartmann’s or 0.9% saline)
- The APLS guidelines recommend a fluid challenge with 20 mL/kg of warmed crystalloid.
Corticosteroids and antihistamines
Corticosteroids and/or antihistamines are no longer recommended for the initial acute management of anaphylaxis, and they should be used only after initial resuscitation.
The age-related doses of chlorphenamine that may be given after initial resuscitation are:
- Child under 6 months: 10 mg IM or IV slowly
- Child months-6 years: 2.5 mg IM or IV slowly
- Child 6-12 years: 5 mg IM or IV slowly
- Child >12 years and adults: 200 mg IM or IV slowly.
The age-related doses of hydrocortisone that may be given after initial resuscitation are:
- Child under 6 months: 25 mg IM or IV slowly
- Child months-6 years: 50 mg IM or IV slowly
- Child 6-12 years: 100 mg IM or IV slowly
- Child >12 years and adults: 200 mg IM or IV slowly.
Serum mast-cell tryptase
The mast cell tryptase test, which is also referred to as the tryptase test, is a useful indicator of mast cell activation and can help confirm the diagnosis of anaphylaxis in cases where the diagnosis is uncertain.
Tryptase is the major protein part of mast cells. Mast cells degranulate in anaphylaxis, causing a rise in blood tryptase levels. Levels usually rise about 30 minutes after the onset of symptoms, peak at 1-2 hours, and concentrations can be back to normal levels within 6-8 hours.
Ideally, three timed samples should be taken:
- As soon as possible after resuscitation commenced
- At 1-2 hours after onset of symptoms
- At 24 hours (gives a baseline level)
Observation
Adult patients should be observed for a period of 6-12 hours from the onset of symptoms, depending on their response to emergency treatment.
Children under 16 years of age with anaphylaxis should be admitted under the care of a paediatric team rather than just receiving treatment in the emergency department.
Follow-up
All patients who have suffered an episode of confirmed or suspected anaphylaxis should be referred to a specialist allergy service consisting of healthcare professionals with the skills and competencies necessary to accurately investigate, diagnose, monitor and provide ongoing management of and patient education about suspected anaphylaxis. They should also be offered an appropriate adrenaline injector as an interim measure before the specialist allergy service appointment.
Thank you to the joint editorial team of www.mrcemexamprep.net for this article.
