Anaphylaxis

[CEACCP 2004 Vol 4(4) "Anaphylaxis"]

Anaphylaxis is an example of type 1 hypersensitivity reaction

Mechanism of anaphylaxis

Step 1: Exposure to foreign antigen

Step 2: Stimulates the production of IgE antibodies

Step 3: IgE antibodies bind to mast cells and basophils

Step 4: Subsequent exposure, antigen binds to IgE antibodies on mast cells and basophiles
--> Degranulation of mast cells
--> Release of histamine, tryptase, slow-reacting substance A, leukotrienes and prostaglandins

NB:

Anaphylatoid reactions do not require previous exposure and do not involve IgE.

End result

• Increased mucous secretion
• Increased bronchial smooth muscle tone
• Increased vascular permeability

Clinically features

• Hypotension
• Airway oedema
• Bronchospasm

Initial presenting features in anaphylaxis

• No pulse detected, hypotension = 28%
• Difficulty inflating lung = 26%
• Flushing = 21%
• Coughing = 6%
• Rash = 4%
• Other presentations include:
  * Coughing
  * Desaturation
  * Cyanosis
  * ECG changes
  * Wheeze
  * Urticaria

Incidence and prognosis of anaphylaxis

• In Australia, incidence = 1 in 10,000 - 1 in 20,000
• Mortality = 5%
• In 80% of reactions, there had been no previous history
  * Especially with neuromuscular blocking agents
• Often starts 30-60 minutes after the start of anaesthetics, rather than at induction

Causes of life-threatening allergic reactions during anaesthesia

• Neuromuscular blocking agents = 70%
• Latex = 12.6%
• Colloid = 4.7%
• Induction agents = 3.6%
• Antibiotics = 2.6%
• Benzodiazepines = 2%
• Opioids = 1.7%
• Others = 2.5%
  * Including radiocontrast media, protamine, aprotonin, atropine, bone cement

Neuromuscular blocking agents

• Steroid-based NMB tend to cause anaphylactic reactions
• Benzylisoquinoliniums tend to cause anaphylatoid reactions
• 43% by suxamethonium
• 37% by vecuronium
• 7% by atracurium
• Most of the reactions occur on first exposure
  * Quaternary ammonium group found in NMB is also found in drugs, food, and cosmetics
  * Possible explanation for higher incidence of anaphylaxis to NMB in females

Latex

• Cross-reactivity between latex sensitivity and certain food
  * Especially bananas, chestnuts, and avocado

Colloid

• Risk is highest with gelatin solutions
• Also high risk with hyperosmolar solutions (e.g. mannitol)

Induction agents

• Severe reaction to thiopentone = 1 in 14,000 - 1 in 20,000
• Less with propofol
• Least with etomidate

Antibiotics

• Penicillins are most frequently implicated
• Cross-reactivity with cephalosporins = 8%
  * But cross-reactivity often incomplete
• In severe reaction, the antigen is usually the beta-lactam group

Opioids

• Usually anaphylatic reactions
• Morphine is usually implicated
• Reactions to synthetic opioids are rare
• Morphine, codeine, and meperidine can also cause dose-dependent non-immunological cutaneous histamine release