Define Anaphylaxis under Anaesthesia. Describe its clinical features and management.

Definition & Triggers

Anaphylaxis is a severe, life-threatening systemic hypersensitivity reaction. Under anaesthesia it is usually caused by drugs given intravenously — most commonly neuromuscular blocking agents (especially suxamethonium), antibiotics, chlorhexidine and latex — and, because the patient is draped and unconscious, it may present atypically and be recognised late.

Immediate management of anaesthetic anaphylaxis: stop the trigger and call for help, secure the airway with 100% oxygen, give adrenaline, give large-volume IV fluids, and add adjuncts (with a later tryptase).

Clinical Features

Features under anaesthesia include cardiovascular collapse (severe hypotension, tachycardia — often the first and most prominent sign), bronchospasm (high airway pressures, difficult ventilation, wheeze), cutaneous signs (flushing, urticaria, angioedema — may be hidden by drapes), and desaturation. Cardiovascular collapse and bronchospasm may dominate.

Management

Management is immediate: stop the likely trigger and call for help; secure the airway and give 100% oxygen; give adrenaline (the key drug — IM, or titrated IV boluses under monitoring for severe reactions); give large volumes of IV fluid (for the profound vasodilatation/capillary leak); and add adjuncts (antihistamine, corticosteroid). Later, take serial tryptase samples to confirm the reaction and refer for allergy testing to identify the culprit.

Grading & the Central Role of Adrenaline

Anaphylactic reactions vary in severity from mild cutaneous signs to life-threatening cardiovascular collapse and bronchospasm, and under anaesthesia the milder cutaneous features are often hidden by the drapes, so the reaction may first announce itself as sudden, profound hypotension or as unexpectedly high airway pressures. Whatever the presentation, adrenaline is the single most important treatment, because it simultaneously reverses the key problems — it constricts blood vessels to counter the vasodilatation, supports the heart, relieves bronchospasm and reduces further mediator release. Antihistamines and corticosteroids have only an adjunctive, later role, and the common, dangerous error is to reach for them first; the correct instinct is early adrenaline, oxygen and large volumes of intravenous fluid while the trigger is removed and help summoned.

• Anaphylaxis: severe systemic hypersensitivity; anaesthetic triggers — muscle relaxants (esp. Suxamethonium), antibiotics, chlorhexidine, latex.
• Features: cardiovascular collapse (often first), bronchospasm/high airway pressures, flushing/urticaria (may be hidden), desaturation.
• Manage: stop trigger, call help, airway + 100% O₂, adrenaline (first-line), large-volume IV fluids, adjuncts.
• Antihistamine/steroid are adjuncts — don’t delay adrenaline.
• Later: serial tryptase to confirm + allergy referral to identify the culprit.