Life-threatening systemic type 1 hypersensitivity reaction leading to compromise of airway and/or breathing and/or circulation usually associated with skin or mucosal changes
Epidemiology of anaphylaxis
Common: incidence is around 1 in 20,000 per year
Causes of anaphylaxis
Essentially any foreign material can start a type 1 hypersensitivity reaction but the common ones are:
Food
Peanuts (and other nut types)
Pulses
Fish and shellfish
Drugs
Antibiotics
Non-steroidal anti-inflammatory drugs (NSAIDs)
Radiological contrast media
Venom
Wasp or bee stings
Risk factors for anaphylaxis
Allergic rhinitis
Asthma
Eczema
Pathophysiology of anaphylaxis
Sensitisation phase
Immune system encounters allergen and makes immunoglobulin E (IgE) against it
No clinical features occur
Effector phase
Allergen cross-links IgE on surface of mast cells
Causes widespread degranulation and release of histamine which mediates inflammatory bronchospasm, vasodilatation, increased capillary permeability, and tissue oedema
Presentation of anaphylaxis
Acute onset: exact speed will depend on the trigger; IV medications will cause a more rapid onset than orally ingested triggers
Airway
Stridor
Hoarse voice
Dysphagia
Breathing
Respiratory distress
Dyspnoea
Wheeze
Cyanosis
Circulation
Pale
Clammy
Light-headedness
Tachycardia
Hypotension
Disability
Confusion
Agitation
Loss of consciousness
Exposure
Urticaria
Angioedema
Video on the basic management of anaphylaxis
Differential diagnosis of anaphylaxis
Airway
Foreign body inhalation
Croup (children only)
Epiglotitis
Laryngospasm
Breathing
Asthma
Circulation
Syncope
Septic shock
Neurogenic shock
Hypovolaemic shock
Cardiogenic shock
Obstructive shock
Investigation of anaphylaxis
Arterial blood gas (ABG)
Full blood count
Urea & electrolytes
Mast cell tryptase
Take three samples taken as soon as possible, after 1-2 hours and after 24 hours
Useful in making a retrospective diagnosis but the absence of a rise does not exclude anaphylaxis
Initial management of anaphylaxis
Shout for help
Call an anaesthetist early and request the difficult airway trolley
If necessary put out a cardiac arrest call
Remove allergen if possible
Lie patient flat and raise their legs
Give adrenaline intramuscular (IM) and repeat after 5 min if no/minimal response to previous dose
Adult and child >12 years: 500 micrograms (0.5 ml of 1:1,000)
Child 6-12 years: 300 micrograms (0.3 ml of 1:1,000)
Child <6 years: 150 micrograms (0.15 ml of 1:1,000)
Patients on beta blockers may exhibit an attenuated response to adrenaline so consider giving glucagon 1-2 mg IV or IM
Assess patient from an ABCDE perspective
Maintain a patent airway: use manoeuvres, adjuncts, supraglottic or definitive airways as indicated
If evidence of impending airway compromise exists, give nebulised adrenaline as a temporising measure
Deliver oxygen to maintain saturations (SpO2) 94-98%
Attach monitoring
Pulse oximetry
Non-invasive blood pressure
Three-lead cardiac monitoring
Obtain IV access and take bloods
Give IV fluid challenge and repeat as necessary; large volumes may be required
Adult: 500-1000 ml
Child: 20 ml/kg
Give chlorphenamine IM or slow IV
Adult & child >12 years: 10 mg
Child 6-12 years: 5 mg
Child 6 months – 6 years: 2.5 mg
Child <6 months: 0.25 mg/kg
Give hydrocortisone IM or slow IV
Adult & child >12 years: 200 mg
Child 6-12 years: 100 mg
Child 6 months – 6 years: 50 mg
Child <6 months: 25 mg
Consider nebulised salbutamol 5 mg and/or ipratropium bromide 0.5 mg if evidence of wheeze on auscultation
Further management of anaphylaxis
Observe for at least six hours
Beware biphasic reactions
Advise patient to return immediately if symptoms reoccur
Provide three day prescription of oral steroid and anti-histamine
