What is anaphylaxis?
A severe, life-threatening, systemic hypersensitivity reaction characterized by rapid onset of airway obstruction, bronchospasm, cardiovascular collapse, and skin manifestations.
What are the main mediators in anaphylaxis?
IgE-dependent mast cell & basophil degranulation or non-IgE anaphylactoid mechanisms.
List some drugs that can trigger anaphylaxis in the operating theater.
- Neuromuscular blocking agents (succinylcholine, atracurium, rocuronium)
- Antibiotics (penicillin, cephalosporins)
- Opioids (morphine, pethidine)
- NSAIDs, local anesthetics (rare)
- Colloids (gelatin, dextran)
- Latex
- Chlorhexidine
- Blood products / contrast media
What are the risk factors for anaphylaxis?
- Previous history of drug/latex allergy
- Atopic individuals (asthma, eczema, hay fever)
- Multiple prior exposures to the same drug
- Female gender (reported higher risk)
- Concomitant beta-blocker therapy (blunts response to adrenaline)
Describe the pathophysiology of anaphylaxis.
Allergen exposure leads to IgE on mast cells cross-linking, resulting in mast cell degranulation and release of mediators like histamine, tryptase, prostaglandins, and leukotrienes.
What are the effects of histamine in anaphylaxis?
- Vasodilation
- Increased capillary permeability leading to hypotension and edema.
What is the role of leukotrienes in anaphylaxis?
They cause bronchospasm.
What are the early clinical features of anaphylaxis during anesthesia?
- Hypotension
- Tachycardia
- Bronchospasm
- Increased airway pressures
- Difficulty in ventilation
- Desaturation
- Cutaneous signs (urticaria, flushing, angioedema)
What are advanced clinical features of anaphylaxis?
- Laryngeal edema
- Severe bronchospasm
- Cardiovascular collapse
- Cardiac arrest
How is anaphylaxis diagnosed intraoperatively?
Clinical diagnosis based on sudden unexplained hypotension and bronchospasm after drug exposure.
What are supportive tests for anaphylaxis?
- Serum tryptase (peaks 1–2 hrs after)
- Arterial blood gas (hypoxemia, metabolic/lactic acidosis)
- ECG (arrhythmias from hypoxia/hypotension)
What immediate actions should be taken in response to anaphylaxis?
- Stop suspected drug immediately
- Call for help, give 100% O₂
- Maintain airway, start controlled ventilation
- Place patient supine, elevate legs
What is the first-line drug for anaphylaxis?
Adrenaline (epinephrine).
What are the dosages for adrenaline in anaphylaxis?
- Mild/moderate reaction: 10–20 µg IV boluses (0.1 ml of 1:10,000)
- Severe collapse: 100–200 µg IV boluses
- Infusion: 0.05–0.1 µg/kg/min IV if persistent hypotension
- If no IV access: 0.3–0.5 mg IM (1:1000 solution)
What circulatory support measures are needed in anaphylaxis?
- Rapid IV fluids (crystalloids/colloids) – 2–3 L may be required
- Vasopressors if adrenaline insufficient: Noradrenaline infusion 0.05–0.1 µg/kg/min.
What adjunctive treatments can be used in anaphylaxis?
- Antihistamines (Chlorpheniramine 10 mg IV slowly or Diphenhydramine 25–50 mg IV)
- Corticosteroids (Hydrocortisone 200 mg IV or Dexamethasone 8–16 mg IV)
- Bronchodilators (Salbutamol via MDI/nebulizer if bronchospasm persists)
What advanced support is required if cardiac arrest occurs during anaphylaxis?
Full ACLS protocol.
What anesthetic considerations are important for preventing anaphylaxis?
- Document all drug allergies clearly
- Use latex-free environment if latex allergy
- Use preservative-free drugs if history of reactions.
What should be prepared in the operating theater for anaphylaxis?
Emergency drugs (adrenaline, antihistamines, steroids) must be drawn up and available.
What is the post-event protocol after an anaphylactic reaction?
- Blood sample for tryptase
- Refer patient to allergist for skin testing
- Provide ‘allergy card’ for future anesthesia.
Fill in the blank: Anaphylaxis is characterized by _______ onset of airway obstruction.
rapid
True or False: Female gender is reported to have a lower risk of anaphylaxis.
False
