Anaphylaxis and Allergic Reactions

Anaphylaxis & Allergic Rxns - Defining Danger

• Anaphylaxis: A severe, potentially life-threatening, systemic hypersensitivity reaction. Characterized by rapid onset.
• Allergic Reaction: An exaggerated immune response to a typically harmless substance (allergen).
• Hypersensitivity Focus:
  • Type I (IgE-mediated): Most common in perioperative anaphylaxis. Involves mast cell and basophil degranulation releasing histamine and other mediators.
• Common Perioperative Triggers:
  • Neuromuscular Blocking Agents (NMBAs): e.g., Rocuronium, Suxamethonium.
  • Antibiotics: Especially β-lactams (penicillins, cephalosporins).
  • Latex: Gloves, catheters.
  • Chlorhexidine: Antiseptic skin preparation.
  • 📌 Mnemonic for Triggers: "Never Allow Lethal Complications" (NMBAs, Antibiotics, Latex, Chlorhexidine).

⭐ Neuromuscular blocking agents (NMBAs) are the most frequent cause of perioperative anaphylaxis.

Anaphylaxis & Allergic Rxns - Cascade Catastrophe

• Mechanisms:
  • IgE-mediated (Allergic): Type I hypersensitivity. Allergen cross-links IgE on mast cells/basophils → degranulation.
  • Non-IgE mediated (Anaphylactoid): Direct mast cell/basophil degranulation (e.g., opioids, NMBAs, contrast media).
• Key Mediators Released:
  • Histamine, tryptase (specific mast cell marker), leukotrienes ($LTC_4$, $LTD_4$), prostaglandins ($PGD_2$).
• Clinical Features (Systemic):
  • Cutaneous (Most common): Urticaria, angioedema, flushing, pruritus.
  • Respiratory: Bronchospasm, laryngeal edema, dyspnea, cough, wheeze.
  • Cardiovascular: Hypotension, tachycardia (can be bradycardia), arrhythmias, collapse.
  • GI: Nausea, vomiting, diarrhea, abdominal cramps.

⭐ Cardiovascular collapse can be the first and only sign of anaphylaxis under general anesthesia, especially in anesthetized patients.

• Severity Grading (Ring & Messmer):

Anaphylaxis & Allergic Rxns - Action Stations!

• Clinical Dx: Rapid hypotension, bronchospasm, urticaria, angioedema.
• DDx: High spinal, vasovagal, MI, PE.
• Labs: Serum tryptase (sample 0.5-2h post-onset; normal <11.4 ng/mL).
• Immediate Management:
  • Call for help! Stop trigger.
  • ABCDE approach:
    • Airway: Secure.
    • Breathing: 100% O2.
    • Circulation: IV fluids (Crystalloids 1-2L).
    • Drugs (see below). Exposure.
  • Pharmacotherapy: 📌 Epinephrine First!
    • Epinephrine: IM 0.3-0.5mg (1:1000). Repeat 5-15 min.
      • Refractory: IV Epi infusion 0.05-0.1 mcg/kg/min or slow IV bolus 5-20 mcg.
    • Antihistamines: H1 (Diphenhydramine 25-50mg IV) + H2 (Ranitidine 50mg IV).
    • Corticosteroids: Hydrocortisone 100-200mg IV.
    • Bronchodilators.

⭐ Serum tryptase: key diagnostic marker, peaks 1-2h post-onset; more specific than histamine.

Anaphylaxis & Allergic Rxns - Prevent & Protect

• Post-Acute Management & Documentation:
  • Observe for 6-12 hours (biphasic reaction risk).
  • Detailed documentation: suspected agents, timeline, vitals, treatment, response.
• Allergy Referral:
  • Indications: All suspected perioperative anaphylaxis cases.
  • Timing: Crucial for accurate testing.

  ⭐ Skin testing should ideally be performed 4-6 weeks after the anaphylactic event to allow IgE levels to normalize and avoid false negatives.

• Investigations:
  • Skin Prick Tests (SPT): Initial screen.
  • Intradermal Tests (IDT): More sensitive if SPT negative.
  • Specific IgE assays (e.g., RAST): Blood test for specific allergens.
  • Basophil Activation Test (BAT): Cellular test, useful in select cases.
• Prevention Strategies (Known/High-Risk):
  • Strict avoidance of confirmed allergens.
  • Premedication: Limited evidence; consider for radiocontrast media (corticosteroids, antihistamines).
  • Clear communication: Allergy bracelets, updated medical records, alert systems.

High‑Yield Points - ⚡ Biggest Takeaways

• NMBAs are the most common triggers for perioperative anaphylaxis.
• Reactions: IgE-mediated (true anaphylaxis) or non-IgE mediated (anaphylactoid).
• Key signs: sudden hypotension, bronchospasm, tachycardia, skin manifestations.
• Management: Stop agent, 100% O2, epinephrine (critical), IV fluids.
• Epinephrine is life-saving; use IV boluses (e.g., 10-100 mcg), consider infusion.
• Serum tryptase (peaks 1-2 hrs) confirms mast cell degranulation.
• Prior allergy, atopy, or multiple surgeries increase risk.