Anaphylaxis

Exam Cram

• Anaphylaxis is a systemic IgE Type 1 Hypersensitivity Reactions allergic reaction involving 2 or more body systems

• Presentation: rash, lip or throat swelling, hypotension, abdominal pain immediately after allergen exposure

• Investigations: raised serum tryptase

• Management: Adrenaline IM early 0.5mg (another can be given after 5 mins) & peri-arrest team

Outline

Background

• Anaphylaxis is caused by mast cells release of antihistamine from IgE Type 1, Hypersensitivity Reactions

• Anaphylaxis affects two body systems: e.g. respiratory (wheeze) and skin (rash)

Assessment

History

• Acute onset < 24hrs

• Sob, wheeze, rash, stridor, fatigue

• Post known triggers- antibiotics, food/ pet allergen

Examination

• Maculopapular rash

• Wheeze

• Stridor, tongue swelling

Investigations: 

• Serum tryptase: 

  • Levels peak at 6 hours

  • Sensitivity = 95%, specificity = 95%

• Raised WCC 

Diagnosis

Diagnostic criteria: clinical

Differentials: angioedema

Management

Acute

• Peri-arrest call & senior support, manage in resus or HDU

• Adrenaline: 500mcg IM stat & conside another in 5 minutes

• IVF for hypotension, airway adjuncts

Steroids and antihistamines have been removed from the algorithm because they were found to distract individuals from giving the adrenaline. Steroids and antihistamines take hours to act. It is hypothesised steroids reduce the risk of rebound anaphylaxis. 

Long term

• Epipen (IM adrenaline) in case of another attack

• Consider follow up with immunology for patch testing

• Stop ACE inhibitors (can worsen anaphylaxis)

Resources and References

Written 2024