Perioperative anaphilaxis.

    Anaphylaxis is a severe, potentially life-threatening systemic hypersensitivity reaction. The estimated incidence of perioperative anaphylaxis is 1 in 10,000–20,000 anesthetic procedures.

    Approximately 60–70% of the perioperative anaphylaxis cases are IgE mediated. IgE-mediated anaphylaxis is caused by the cross-linking of IgE resulting in degranulation of mast cells and basophils. It results in the release of mediators like histamine, prostaglandins, proteoglycans, and cytokines. Non-IgE mediated allergic reaction is because of IgG or immune complex complement mediated pathways.

    In the perioperative setting, the common agents involved in IgE-mediated anaphylaxis are antibiotics, latex and neuromuscular blocking agents (NMBAs), and less commonly, colloids, hypnotic agents, opioids, dyes, and chlorhexidine.

    Grades of Severity:

1. Generalized cutaneous signs: erythema, urticaria, with or without angioedema
2. Moderate multiorgan involvement with cutaneous signs, hypotension and tachycardia, bronchial hyper-reactivity, cough, difficulty in breathing.
3. Severe life-threatening multiorgan involvement: cardiovascular collapse, tachycardia or bradycardia, arrhythmias, bronchospasm. Cutaneous signs may be present or occur only after the arterial blood pressure recover
4. Cardiac and/or respiratory arrest

    Diagnosis:

Arterial blood gas, renal and liver function tests. Measurement of serum tryptase, a protease released by mast cell degranulation, provides additional diagnostic clue and should be performed whenever feasible. Total serum tryptase levels above 25 μg/L suggest an IgE-related mechanism. Elevated plasma histamine level correlates with signs and symptoms of anaphylaxis.

    Treatment:

    Airway - high flow oxygen should be given. Intubation could be difficult. This may require an emergency cricothyroidotomy.

    Epinephrine in an initial dose of 10–20 μg IV for grade II anaphylactic reaction and 100–200 μg IV for grade III reactions can be used. Additional doses, if required, should not be delayed. If the patient requires repeated boluses, a continuous infusion (0.05–0.4 μg kg-1 min-1) should be started. If intravenous access is not available, epinephrine can be injected intramuscularly at the lateral thigh till IV access is established.

    Intravenous Fluid Resuscitation involves repeated boluses of 20 mL kg-1 intravenous isotonic crystalloids, to fill the dilated peripheral vessels and to compensate for plasma leakage to extravascular space.

    Vasopressors like norepinephrine or vasopressin may be used.

    Glucagon may be given in a dose of 1–5 mg in adults and 20–30 μg kg-1 to a maximum of 1 mg in children intravenously over 5 minutes.

    Beta-adrenergic agonists such as salbutamol or nebulized epinephrine can be used to treat bronchospasm.

    Sugammadex, a reversal agent for rocuronium and vecuronium, may reverse anaphylaxis triggered by rocuronium.

    Hydrocortisone 200 mg IV bolus (or 5 mg kg-1) is followed by 100 mg (2.5 mg kg-1) IV every 6 hours or methylprednisolone 125 mg IV is given every 6 hours.

    Mild nonanaphylactic reactions, with skin manifestations can be treated with H1 antihistamines (diphenhydramine 25–50 mg or 0.5–1 mg kg-1 IV or dexchlorpheniramine 5 mg IV) with H2 antihistamines (ranitidine 50 mg IV).