3. Old stuff
          3.1. Old pharm stuff (pre 2009)
              3.1.7. Anaesthetics
 3.1.7.5. Anaphylaxis 

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