Version 1.0 — Published September 2026
Quick Answer
Severe anaphylaxis is repeatedly tested on NEET PG under anaesthesia, medicine, and emergency medicine — the WAO clinical criteria, IM epinephrine first-line, perioperative trigger profile, biphasic observation, tryptase workup, and discharge planning appear almost every cycle. A 38-year-old woman with sudden itching, facial and tongue swelling, stridor, wheeze, urticaria, and shock (HR 135, BP 68/40, SpO2 88 percent) ten minutes after IV cefazolin in the post-anaesthesia bay needs the following 9-step workflow:
- Recognise anaphylaxis — WAO criterion 1 satisfied — skin plus airway plus shock after a probable allergen.
- STOP the trigger — discontinue the cefazolin infusion; label all administered drugs.
- Call for help — anaesthesia consultant, code team, and prepare a difficult airway trolley.
- Position — supine with legs elevated; if severe respiratory distress, allow sitting.
- IM epinephrine 0.5 mg (0.5 mL of 1:1000) into vastus lateralis — repeat every 5-15 min if inadequate response.
- High-flow oxygen at 15 L via non-rebreather; prepare for early intubation for progressive angioedema.
- Two large-bore IV access and rapid crystalloid bolus 1-2 L; add norepinephrine for refractory shock; add glucagon 1-5 mg IV if on beta-blocker.
- Adjuncts AFTER epinephrine — H1 antihistamine, corticosteroid, nebulised salbutamol for bronchospasm.
- Observation, tryptase within 3 hours, allergist referral at 4-6 weeks, EpiPen prescription, action plan, medical ID.
The case
A 38-year-old female schoolteacher is transferred to the post-anaesthesia care unit at 10:15 following an uneventful right knee arthroscopy for meniscal repair under spinal anaesthesia (bupivacaine 15 mg intrathecal). She has no known drug allergies, is on no regular medications, and has no personal or family history of atopy or asthma. Pre-incision IV cefazolin 2 g was given at 09:20 as prophylaxis; a second dose has just been started at 10:22 as per the four-hour redosing protocol for a longer-than-expected procedure.
At 10:32 the recovery nurse pages the anaesthetist for sudden itching, facial swelling and difficulty in breathing that began within a minute of the second cefazolin dose starting. By the time the anaesthetist arrives at the bedside 90 seconds later, the picture has escalated rapidly.
Examination on arrival — patient sitting bolt upright in the bed, distressed, diaphoretic, using accessory muscles. Speech is single-word and hoarse. Temperature 36.9 degrees C, pulse 135/min regular thready, respiratory rate 32, BP 68/40, SpO2 88 percent on 4 L nasal cannula. Capillary refill 5 seconds. Extremities cold and mottled.
Airway — audible inspiratory stridor; visible angioedema of the periorbital region, lips and tongue with tongue protruding partially past the incisors; drooling; swelling still visibly progressing.
Breathing — diffuse bilateral polyphonic wheeze with reduced air entry; no crackles; no pneumothorax signs.
Circulation — thready peripheral pulse; hypotension unresponsive to a 500 mL crystalloid bolus in the last two minutes; cool clammy skin.
Skin — diffuse blanching urticarial wheals across the anterior chest, upper abdomen, both arms, and neck; palms erythematous; angioedema of face and upper airway as above.
CNS — anxious, mildly confused, mentating in short sentences with distress about breathing.
The anaesthetist recognises the pattern — perioperative anaphylaxis grade IV (severe cardiovascular and respiratory compromise) most likely to the cefazolin dose. The cefazolin infusion is stopped immediately, the code team is called, the difficult airway trolley is brought to the bedside, and IM epinephrine is prepared.
The three time-critical principles
Principle 1 — Epinephrine first, always, no exceptions. IM epinephrine into the anterolateral thigh (vastus lateralis) is the single life-saving intervention. It reverses vasodilation, mucosal oedema, bronchospasm, and stabilises mast cells all at once. Delaying it for antihistamines, steroids, or intubation preparation is the single commonest cause of anaphylaxis-related death.
Principle 2 — Airway before intubation. Progressive angioedema converts a manageable airway into an impossible airway within minutes. Prepare a difficult-airway trolley, call for the most senior available anaesthetist, and consider awake fibreoptic intubation while the airway is still patent. Have a surgical airway (cricothyroidotomy) kit open and ready. Do not wait for the airway to fail.
Principle 3 — Trigger identification is a discharge-time obligation, not an acute-time distraction. In the perioperative setting several drugs have been given simultaneously — antibiotic, muscle relaxant, opioid, colloid, latex, chlorhexidine. During resuscitation, label everything, save the infusion bags and syringes, send tryptase, and refer to an allergist at 4-6 weeks. Do not guess the culprit at the bedside — a wrong guess is worse than none because it directs future avoidance at the wrong drug.
Investigations
Bedside (within 5 minutes)
- Continuous cardiac monitoring, pulse oximetry, non-invasive BP every minute — track response to epinephrine.
- Airway assessment — Mallampati, mouth opening, thyromental distance; grade the airway as anticipated difficult given tongue and floor-of-mouth oedema.
- ECG — sinus tachycardia at 135, no ischaemic changes; watch for arrhythmia after epinephrine.
- Arterial blood gas (drawn during IV cannulation) — pH 7.24, pCO2 32, pO2 55 (on 4 L nasal cannula), lactate 5.6 mmol/L — mixed respiratory and metabolic acidosis with hyperlactataemia from shock.
Laboratory (send during initial resuscitation)
- Serum tryptase — the single most useful confirmatory test. Send within 15-60 minutes of onset (peaks 1-2 hours), a second sample at 3 hours (still elevated), and a third convalescent sample at 24 hours or later (patient's baseline). Peak tryptase greater than 11.4 microgram/L OR greater than 1.2 x baseline plus 2 microgram/L confirms mast cell activation.
- CBC, urea, creatinine, electrolytes, LFTs — baseline for ITU admission.
- Coagulation — INR, aPTT; anaphylaxis-related coagulopathy is uncommon but described.
- Blood group and cross-match — precautionary given planned ICU stay.
- Save the drug ampoule, infusion bag, giving set — sequester for later allergist review.
Interpretation — the diagnosis is clinical; laboratory tests confirm mast cell activation and guide the culprit hunt but must never delay treatment.
Diagnosis
Perioperative anaphylaxis grade IV (severe cardiovascular and respiratory compromise) — WAO clinical criterion 1 satisfied (acute-onset skin plus airway plus circulatory collapse minutes after IV cefazolin re-dose) — culprit most likely cefazolin (temporal association, second dose in the same patient) — for immediate IM epinephrine 0.5 mg into vastus lateralis, high-flow oxygen, prepare for early airway control including surgical airway back-up, rapid crystalloid resuscitation, adjunctive H1 antihistamine, corticosteroid and nebulised salbutamol after epinephrine, serial tryptase, ICU admission, allergist referral at 4-6 weeks and formal discharge planning with EpiPen prescription, medical ID bracelet, and written action plan.
Management — first ten minutes, definitive drainage, and post-episode
First ten minutes — stabilisation
- STOP the cefazolin infusion. Label all administered drugs; save ampoules and infusion bags.
- Position — supine with legs elevated (Trendelenburg) unless dyspnoea prevents this, in which case sitting up.
- IM epinephrine 0.5 mg (0.5 mL of 1:1000) into the anterolateral thigh (vastus lateralis) — the single life-saving step. Repeat every 5-15 minutes if the response is inadequate. Do NOT give subcutaneously (delayed absorption in shock) and do NOT give as an IV bolus at 1:1000 concentration (risk of ventricular arrhythmia and hypertensive crisis).
- High-flow oxygen at 15 L via non-rebreather to keep SpO2 above 94 percent.
- Two large-bore (16G) IV access lines; rapid crystalloid bolus 1-2 L over 5-10 minutes; refractory hypotension needs 20-40 mL/kg.
- Prepare for early intubation with a difficult-airway trolley — smaller endotracheal tubes (size 6.0-7.0), video laryngoscope, awake fibreoptic set, surgical airway (cricothyroidotomy) kit open. Call the most senior available anaesthetist. Avoid nasal intubation (bleeding into a swollen airway is catastrophic).
- Norepinephrine 0.05 microgram/kg/min titrated to MAP above 65 mmHg if BP fails to respond after two IM epinephrine doses and adequate fluid.
- Glucagon 1-5 mg IV bolus followed by 5-15 microgram/min infusion if the patient is on a beta-blocker (bypasses the beta-adrenergic receptor blockade).
- Adjuncts AFTER epinephrine — H1 antihistamine (chlorpheniramine 10 mg IV or diphenhydramine 25-50 mg IV) — H2 antihistamine (ranitidine 50 mg IV or famotidine 20 mg IV, weak evidence) — corticosteroid (hydrocortisone 200 mg IV or methylprednisolone 125 mg IV, mainly to reduce protracted or biphasic reactions, weak evidence) — nebulised salbutamol 2.5-5 mg for persistent bronchospasm.
- Send serial tryptase, arterial blood gas, and admit to ICU for at least 24 hours of monitored observation.
Refractory cases
- Vasopressin 0.03 units/min or methylene blue 1-2 mg/kg IV for vasoplegic shock resistant to catecholamines.
- ECMO in extreme refractory cardiogenic-anaphylactic shock (rare, tertiary centres only).
- Continued epinephrine infusion at 2-10 microgram/min under invasive monitoring.
Definitive care
- ICU admission for 24 hours after any grade III-IV reaction, primarily to detect a biphasic reaction (8-72 hours later, typically 8-10 hours).
- Serial tryptase at less than 1 hour, at 3 hours, and 24 hours or later.
- Airway management plan — extubation only when tongue and pharyngeal oedema have resolved (typically 12-24 hours); leak test around the deflated cuff before extubation.
- Steroid taper oral prednisolone 40 mg once daily for 3-5 days if biphasic risk high.
- Discharge with two EpiPens, medical ID, printed anaphylaxis action plan, and allergist appointment at 4-6 weeks for skin prick, intradermal, and specific IgE testing.
Complications
Acute
- Death from asphyxiation (airway obstruction) or cardiovascular collapse if epinephrine is delayed.
- Anoxic brain injury from prolonged hypoxaemia.
- Myocardial infarction — either from anaphylactic shock coronary hypoperfusion or Kounis syndrome (allergic coronary vasospasm).
- Post-epinephrine arrhythmia — SVT, ventricular ectopy, rare VT in the elderly or in patients receiving IV boluses.
Subacute
- Biphasic reaction — recurrence of symptoms 1-72 hours after the initial episode without re-exposure; up to 20 percent incidence; more common after severe or refractory presentations.
- Protracted anaphylaxis — sustained symptoms lasting more than 24 hours despite treatment.
- Post-intubation laryngeal injury and hoarseness.
Long-term
- Anaphylaxis recurrence on re-exposure to an unidentified trigger — case-fatality approaches 10 percent.
- Anxiety and food/drug avoidance behaviour — often disproportionate to actual risk; benefits from allergist counselling.
India-specific context
- Cefazolin and augmentin dominate perioperative anaphylaxis triggers in Indian series because pre-incision antibiotic prophylaxis is nearly universal and NMBAs are used less liberally than in Western practice.
- EpiPen cost and availability — auto-injectors are expensive (Rs 5,000-8,000 per pen) and not universally stocked. Prefilled syringes with 1:1000 epinephrine plus written instructions and family training are the practical alternative in government-hospital and rural settings.
- Traditional first-aid delays — patients or families sometimes attempt oral remedies before presenting to hospital, delaying epinephrine by critical minutes. Public awareness campaigns from ICAAI (Indian College of Allergy, Asthma and Immunology) are important.
- PMJAY emergency and tertiary allergy testing coverage — increasing but uneven; allergist access is limited outside metro tertiary centres, so telehealth follow-up and printed action plans matter.
- Latex anaphylaxis — still relevant in Indian hospitals using latex gloves; healthcare workers themselves are a high-risk group.
How NEET PG tests anaphylaxis
Pattern 1 — First-line drug question: Drug of choice in anaphylaxis? Intramuscular epinephrine 0.5 mg (0.5 mL of 1:1000) into the vastus lateralis.
Pattern 2 — The route trap: Never subcutaneous (delayed absorption in shock); never IV at 1:1000 (arrhythmia risk); IV at 1:10,000 only in refractory shock or arrest under monitoring.
Pattern 3 — The site trap: Anterolateral thigh (vastus lateralis) is preferred over deltoid because absorption is faster and more reliable.
Pattern 4 — The adjunct hierarchy: Antihistamines, corticosteroids and beta-2 agonists are adjuncts AFTER epinephrine, never substitutes.
Pattern 5 — The beta-blocker trap: In refractory anaphylaxis on a beta-blocker, add glucagon 1-5 mg IV to bypass the beta-adrenergic blockade.
Pattern 6 — The tryptase question: Peak tryptase greater than 11.4 microgram/L or greater than 1.2 x baseline plus 2 microgram/L confirms mast cell activation; peaks 1-2 hours, falls by 6 hours; useful in perioperative and idiopathic cases.
Pattern 7 — The biphasic observation question: Monitor for 24 hours after severe or refractory reactions because 20 percent are biphasic (recurrence 1-72 hours, typically 8-10 hours later, without re-exposure).
Pattern 8 — The perioperative trigger question: Commonest culprits are neuromuscular blockers (rocuronium, suxamethonium), antibiotics (cefazolin, other beta-lactams, vancomycin), latex, chlorhexidine, and blue dyes.
Pattern 9 — The discharge planning question: Two auto-injectors, medical ID, written action plan, allergist referral at 4-6 weeks (earlier tests have false negatives from mast cell depletion).
Pattern 10 — The WAO criteria question: ANY ONE of three scenarios — skin plus airway/shock/GI; hypotension/bronchospasm after known allergen even without skin signs; reduced BP after known allergen.
Key takeaways
- WAO clinical criteria — any one of three scenarios diagnoses anaphylaxis; skin signs are absent in up to 20 percent of fatal cases.
- IM epinephrine 0.5 mg into vastus lateralis is first-line and life-saving.
- Never delay epinephrine for antihistamines or steroids or intubation preparation.
- Never give epinephrine subcutaneously in anaphylaxis; never bolus IV 1:1000.
- Fluids, oxygen, airway preparation, and second-line vasopressors follow.
- Glucagon for beta-blocker patients unresponsive to epinephrine.
- Serial tryptase at less than 1 hour, at 3 hours, and 24 hours or later.
- Biphasic reactions in up to 20 percent; observe severe cases 24 hours.
- Discharge with two EpiPens, medical ID, printed action plan, and allergist referral at 4-6 weeks.
- In perioperative anaphylaxis, save all drugs and infusion bags for allergist workup.
Frequently Asked Questions
What are the World Allergy Organization clinical criteria for diagnosing anaphylaxis?
The World Allergy Organization (WAO) 2020 clinical criteria, adopted by AAAAI, EAACI, and NBEMS-aligned Indian emergency protocols, allow anaphylaxis to be diagnosed if ANY ONE of three scenarios is present. Criterion 1 — acute onset (minutes to a few hours) of an illness with involvement of the skin, mucosal tissue, or both AND at least one of respiratory compromise, reduced blood pressure or end-organ dysfunction, or severe gastrointestinal symptoms. Criterion 2 — acute onset of hypotension, bronchospasm, or laryngeal involvement after exposure to a KNOWN or highly probable allergen for that patient, even in the ABSENCE of typical skin involvement. Criterion 3 — reduced BP after exposure to a known allergen for that patient (age-specific hypotension thresholds). Absence of urticaria does not exclude anaphylaxis — up to 20 percent of fatal anaphylaxis cases have no cutaneous signs at all, which is one reason perioperative anaphylaxis under drapes is so easily missed until frank cardiovascular collapse.
Why is intramuscular epinephrine the first-line drug in anaphylaxis and why not subcutaneous or intravenous?
Intramuscular epinephrine into the anterolateral thigh (vastus lateralis) is the first-line, life-saving intervention. Adult dose 0.5 mg (0.5 mL of 1:1000); paediatric dose 0.01 mg/kg to a maximum of 0.3 mg; may be repeated every 5-15 minutes. Alpha-1 reverses vasodilation and mucosal oedema, beta-1 increases inotropy and chronotropy, beta-2 relaxes bronchial smooth muscle, and it stabilises mast cells reducing further mediator release. IM into the thigh gives faster and more reliable absorption than subcutaneous (subcutaneous fat is poorly perfused during shock — peak levels take 30-40 minutes vs 8-10 minutes IM) and faster than IM into the deltoid. Intravenous epinephrine is reserved for refractory shock or arrest because bolus IV at 1 mg/mL carries a high risk of ventricular arrhythmia, hypertensive crisis, and myocardial ischaemia; when IV is used, it is at markedly diluted concentrations — 5-10 microgram boluses (0.1 mL of 1:10,000) titrated to response, or an infusion at 2-10 microgram/min under invasive monitoring.
What is the role of adjunctive antihistamines, corticosteroids and bronchodilators in anaphylaxis?
Adjunctive therapies are given AFTER intramuscular epinephrine and never as a substitute for it. H1-blockers (diphenhydramine, cetirizine, chlorpheniramine) reduce cutaneous itch, urticaria and flush but do NOT reverse airway obstruction or shock; onset 30-60 minutes. H2-blockers (ranitidine, famotidine) are proposed to have additive effect on cutaneous symptoms in combination with H1-blockers, though evidence is weak. Corticosteroids (methylprednisolone, hydrocortisone) have onset of several hours and do NOT treat the acute reaction; their historical role was reduction of biphasic and protracted anaphylaxis, though recent meta-analyses have downgraded this recommendation. Nebulised beta-2 agonists treat bronchospasm not reversed by epinephrine. Glucagon 1-5 mg IV bolus followed by 5-15 microgram/min infusion bypasses the beta-adrenergic receptor and is used in patients on beta-blockers where epinephrine has blunted effect. For refractory hypotension despite epinephrine and fluid, add a second vasopressor (norepinephrine, dopamine, vasopressin) and consider methylene blue for vasoplegic shock resistant to catecholamines.
How does perioperative anaphylaxis differ from community anaphylaxis and what triggers must the anaesthetist consider?
Perioperative anaphylaxis differs in three important ways. First, the classical cutaneous signs may be masked or delayed under surgical drapes, making the earliest signs cardiovascular (unexplained tachycardia or hypotension) or ventilatory (rising airway pressures, difficulty ventilating). Second, several drugs are given simultaneously, complicating culprit identification. Third, the patient is often already sedated and may be on vasoactive drugs that mask the shock picture. Trigger prevalence — neuromuscular blocking agents (rocuronium, suxamethonium), latex, antibiotics (cefazolin and other beta-lactams, vancomycin), colloids, chlorhexidine, and blue dyes. Indian series show a higher share for antibiotics because pre-incision prophylaxis is nearly universal. Diagnosis rests on the clinical criteria (recognising them despite draped presentation), obtaining serial serum tryptase, and referring the patient to an allergist 4-6 weeks after the event for formal skin prick, intradermal testing, and specific IgE assays. Documentation on the case sheet, a wristband alert, and a written patient letter are essential — repeat exposure to an unidentified culprit has a case-fatality rate approaching 10 percent.
What discharge and follow-up steps are essential after any episode of anaphylaxis?
Six mandatory elements. First, observation for biphasic reaction — up to 20 percent of anaphylaxis is biphasic. Severe or refractory initial reactions warrant 24 hours of monitored observation; a fully resolved mild-moderate reaction can be discharged after 4-6 hours if there is safe transport, a responsible adult at home, and clear return advice. Second, two epinephrine auto-injectors (EpiPen 0.3 mg for adults; EpiPen Jr 0.15 mg for children 10-25 kg). In India, auto-injectors have limited availability and are expensive; prefilled syringes with 1:1000 epinephrine plus written instructions and family training are a practical alternative. Third, trigger identification — send serum tryptase within 3 hours and refer to an allergist at 4-6 weeks for skin prick, intradermal, and specific IgE testing. Fourth, a written anaphylaxis action plan. Fifth, a medical ID bracelet or card. Sixth, patient and family education — recognise early symptoms, always inject early rather than waiting for shock, call ambulance after every injection, avoid known trigger.
This content is for educational purposes for NEET PG exam preparation. It is not a substitute for professional medical advice, diagnosis, or treatment. Clinical information has been reviewed by qualified medical professionals.
Written by: NEETPGAI Editorial Team
Reviewed by: Pending SME Review
Last reviewed: September 2026
