Anaphylaxis

Question 1

Define anaphylaxis

Answer 1

Acute life-threatening multisystem syndrome caused by sudden release of mast cell-and-basophil-derived mediators into the circulation

Question 2

What are the causes/risk factors of anaphylaxis?

Answer 2

Immunogenic:
• IgE binds to the antigen.
• Antigen-bound IgE then activates FcR receptors on mast cells and basophils.
• This leads to the release of inflammatory mediators such as histamine.
• These mediators subsequently increase the contraction of bronchial smooth muscles, trigger vasodilation, increase the leakage of fluid from blood vessels, and cause heart muscle depression.

Non-immunogenic: 
• These substances cause immediate mast cell/ basophil degranulation without the reliance on antibodies to do so. 
• Contrast media 
• Vancomycin 
• ACEi 

Common Allergens: 
• Penicillin 
• Radiological contrast agents 
• Latex 
• Insect stings 
• Egg 
• Peanuts 
• Shellfish  
• Fish

Question 3

What are the symptoms of anaphylaxis?

Answer 3

• Acute onset of symptoms.
• History of allergen exposure.
• Wheeze, shortness of breath or sensation of choking.
• Swelling of lips and face.
• Pruritus, rash.
• Biphasic reactions occur 1–72 h after the first reaction in up to 20% of patients

Question 4

What are the signs of anaphylaxis?

Answer 4

• Tachypnoea, wheeze, cyanosis due to bronchoconstriction.
• Inspiratory stridor –severe airway obstruction.
• Swollen upper airways and eyes, rhinitis, conjunctival injection.
• Urticarial rash (erythematous wheals).
• Hypotension, tachycardia due to vasodilation and shock.

Question 5

What investigations are carried out for anaphylaxis?

Answer 5

diagnosis often clinical

To confirm the diagnosis, the following investigations may be carried out after initiating treatment:
• Serum Tryptase - a few hours after admission and treatment. Elevated in patients with anaphylaxis, but it is delayed after the onset by a few hours.
• Plasma Histamine - preferably measured within 30 minutes of suspected anaphylaxis. Elevated.
• Urinary Histamine Metabolites - elevated; measured several hours after the onset of the anaphylaxis.
NB: Normal levels of these mediators do not exclude the presence of anaphylaxis.

After the Attack:
• Allergen skin testing - identifies allergen. It should be performed by an allergy specialist, because of the risk of anaphylaxis and the skill required for proper interpretation.
• IgE Immunoassays - radioallergosorbent test (RAST) to identify food-specific IgE in theserum.

Question 6

What is the management for anaphylaxis?

Answer 6

• Remove exposure to the allergen.
• ABCDE Resuscitation. Secure airway and give 100% O2. Inform ITU and anaesthetics if the patient’s airway is at risk or if the patient needs immediate/ imminent escalation.
• Adrenaline IM (0.5 mL of 1:1000). This can be repeated every 10 min according to response of pulse and BP.
• Antihistamine IV (10mg chlorpheniramine).
• Steroids IV (100mg hydrocortisone).
• IV crystalloid or colloid to maintain blood pressure. If hypotensive, lie patient flat with head tilted down.
• Treat bronchospasm with salbutamol/ipratropium inhaler. Aminophylline IV infusion may be required.
• Advice: Educate on use of adrenaline pen for IM administration. Provide Medicalert bracelet.
• Make note in patient’s notes and drug charts. Referral to an allergy specialist for identification of the culprit allergen and education in allergen avoidance

Question 7

What are the complications of anaphylaxis?

Answer 7

• Respiratory failure
• Shock
• Death