Clinical Guides
Anaphylaxis
A clinically focused guide to rapid anaphylaxis recognition, immediate intramuscular adrenaline, physiological resuscitation, risk-based observation and prevention of recurrence in Indian practice.
MedNext Academy | 14 min read
Anaphylaxis
A clinically focused guide to rapid anaphylaxis recognition, immediate intramuscular adrenaline, physiological resuscitation, risk-based observation and prevention of recurrence in Indian practice.
Summary
Anaphylaxis is an acute systemic hypersensitivity reaction capable of causing fatal airway, breathing or circulatory compromise within minutes. It is a clinical diagnosis and may occur without urticaria, flushing or angioedema. When a compatible exposure is followed rapidly by bronchospasm, laryngeal symptoms or hypotension, treatment must begin before laboratory confirmation. The decisive first-line medicine is adrenaline given intramuscularly into the mid-anterolateral thigh. Call for skilled help, stop the trigger when safe, position the patient appropriately, give oxygen and crystalloid according to physiology, monitor continuously, and repeat intramuscular adrenaline after about five minutes if life-threatening features persist.
Adrenaline should not be displaced by antihistamines, corticosteroids, nebulised bronchodilators or attempts to obtain intravenous access. Those interventions either treat limited components or have uncertain benefit. Refractory shock after repeated correctly administered intramuscular doses and adequate fluid resuscitation needs critical-care support and a titrated intravenous adrenaline infusion, never an improvised intravenous bolus. After recovery, the work is not finished: record the entire timeline, consider timed tryptase sampling without delaying treatment, observe according to severity and recurrence risk, supply an emergency plan and arrange allergy assessment.
Indian services must plan for variable ambulance times, uneven availability of allergy specialists and adrenaline auto-injectors, and the role-specific requirements of vaccination programmes. Every clinic that administers a potential trigger needs in-date adrenaline, dose charts, oxygen, resuscitation equipment, trained staff and a rehearsed transfer route. Management advice must be adapted to local capability while retaining the universal safety sequence: recognise physiological danger, inject intramuscular adrenaline promptly, reassess, escalate and prevent recurrence.
How Common Is It?
Measured anaphylaxis frequency varies widely because diagnostic criteria, triggers, age groups, health systems and methods of case capture differ. Emergency-department records miss episodes treated in the community; administrative codes may include non-anaphylactic allergy; and fatal reactions can be misclassified as asthma, arrhythmia or unexplained collapse. International guidance reports increasing recognition and healthcare use, but it does not justify importing one country's incidence into India. India does not yet have a comprehensive, population-representative national anaphylaxis registry using a single validated case definition, so a precise national rate would create false certainty.
Foods are prominent triggers in children and young adults, whereas medicines and insect venom account for a larger share in many adult series. Antibiotics, analgesics, anaesthetic agents, radiocontrast and biological medicines are important healthcare-associated causes. Exercise, alcohol, acute infection, sleep loss and medicines such as non-steroidal anti-inflammatory drugs may act as cofactors, so the same exposure may not provoke the same severity every time. Vaccination-associated anaphylaxis is rare, but rarity does not reduce the need for preparedness because treatment delay can be catastrophic. An event after immunisation is temporally associated until formal causality assessment; it must not automatically be attributed to the vaccine.
The most actionable burden measure for an Indian service is process reliability rather than a headline prevalence: percentage of clinical areas with complete kits, median time from recognition to intramuscular adrenaline, correct dose and route, documented reassessment, appropriate observation, discharge education and allergy referral. Audits should state their denominator, setting and case definition. Under-recognition and delayed adrenaline are more credible safety concerns than whether a local count matches a foreign epidemiological estimate.
Risk Factors
Risk of having anaphylaxis is distinct from risk of a severe or fatal outcome. A previous systemic reaction to the same trigger, a confirmed food, venom or medicine allergy, and exposure to a sensitising agent increase recurrence probability. Atopy alone does not predict every reaction, and a family history is not evidence that a person is allergic to a particular drug or food. Mast-cell disorders, elevated baseline tryptase, cardiovascular disease, poorly controlled asthma and older age can increase the clinical consequences or complicate resuscitation. Pregnancy changes positioning and transfer priorities but does not make intramuscular adrenaline contraindicated.
Reaction severity is influenced by dose, route and speed of exposure. Intravenous administration can produce faster, more severe reactions than oral exposure. Cofactors include exertion, fever or infection, alcohol, sleep deprivation and non-steroidal anti-inflammatory medicines; their contribution should be recorded rather than assumed. Beta-blockers or angiotensin-converting-enzyme inhibitors may complicate selected reactions or their treatment, but prescribed cardiovascular medicines should not be stopped casually without a clinician balancing competing risk. Poor asthma control is particularly important in food-triggered respiratory reactions.
System risks are preventable. These include adrenaline stored far from the treatment area, missing paediatric dose charts, confusion between 1 mg/mL and dilute cardiac-arrest preparations, use of the subcutaneous route, failure to record dose time, allowing a hypotensive patient to stand, and transferring without a trained escort. Delayed presentation, more than one adrenaline dose, severe respiratory compromise, unknown trigger, continuing absorption, previous biphasic reaction, limited supervision and long travel to emergency care raise concern after initial recovery. They should influence observation and discharge decisions rather than being converted into a single prediction score.
Diagnosis
History
Reconstruct the episode in minutes, not vague phases. Record the suspected exposure, route, amount, time, first symptom, order of organ involvement, cofactors and every treatment with response. Ask about voice change, throat closure, stridor, wheeze, cough, hypoxaemia, faintness, collapse, confusion, hives, flushing, swelling, severe cramping and repetitive vomiting. Establish previous reactions, asthma control, mast-cell disease, cardiovascular disease, pregnancy and relevant medicines. Ask witnesses because shock and hypoxia impair recall. A known or highly probable allergen followed rapidly by bronchospasm, laryngeal involvement or hypotension can satisfy diagnostic criteria even without skin findings.
Examination
Assess airway, breathing, circulation and consciousness simultaneously while help is summoned. Listen for hoarseness, stridor, wheeze or a silent chest; measure respiratory rate and oxygen saturation; assess pulse, blood pressure, capillary refill and mental state. Inspect skin and mucosa without delaying resuscitation or causing heat loss. Repeat observations after every intervention because anaphylaxis evolves quickly. Document the patient's position. Pallor, bradycardia and rapid recovery while supine favour a vasovagal event, whereas persistent respiratory or circulatory compromise demands emergency treatment.
Investigations
No investigation rules in anaphylaxis quickly enough to precede adrenaline. Use ECG, pulse oximetry, frequent blood pressure and capnography when available to guide resuscitation. Timed mast-cell tryptase samples may support later specialist assessment, particularly after hypotension or an uncertain adult presentation, but a normal result does not exclude anaphylaxis. Record sample timing relative to onset. Test glucose and perform other studies only for competing diagnoses or complications. Preserve medicine, infusion, vaccine and batch details. Allergy skin tests, specific IgE and challenge procedures belong to later specialist evaluation and must never be performed during the acute event.
Differential Diagnosis
Vasovagal syncope commonly follows pain, fear or injection and produces nausea, sweating, pallor, bradycardia and improvement after lying flat. It does not usually cause sustained bronchospasm, laryngeal swelling or progressive shock. Panic and hyperventilation can cause dyspnoea, tingling and dizziness, yet objective hypoxaemia, wheeze, stridor or hypotension require another explanation. Acute severe asthma may present without rash and can coexist with anaphylaxis. When a plausible allergen exposure and systemic compromise are present, give intramuscular adrenaline rather than waiting for diagnostic purity.
Other immediately dangerous mimics include pulmonary embolism, acute coronary syndrome, arrhythmia, sepsis, haemorrhage and obstructive shock. Upper-airway obstruction may result from a foreign body, infection or inducible laryngeal obstruction. Bradykinin-mediated angioedema, including hereditary disease or an ACE-inhibitor reaction, usually lacks urticaria and may not respond to adrenaline; threatened airway still requires expert emergency management. Scombroid toxicity can affect several people eating the same fish, while food poisoning usually has a different timeline and lacks laryngeal or circulatory features.
Perioperative collapse demands parallel evaluation for haemorrhage, anaesthetic complications, embolism and allergy to every agent or material, including antibiotics, neuromuscular blockers, chlorhexidine, latex and dyes. After vaccination, consider an immunisation stress response, breath-holding, hypoglycaemia or seizure, but do not let that differential delay treatment when airway, breathing or circulation criteria are met. Flushing or local urticaria alone is not necessarily anaphylaxis. The safest approach is to treat the life-threatening physiology promptly while continually testing alternative explanations.
Management
Call an emergency or resuscitation team, stop a suspected infusion if this can be done instantly, and keep the patient under direct observation. Position most patients flat with legs raised; use the left lateral position in pregnancy, the recovery position if unconscious but breathing, and cautious supported sitting only when severe respiratory distress makes lying flat impossible. Do not permit sudden standing or walking. Give intramuscular adrenaline into the mid-anterolateral thigh without delay: 0.01 mg/kg of 1 mg/mL solution, up to 0.5 mg. For most adults, 0.5 mg is the usual healthcare dose. Repeat after approximately five minutes when airway, breathing or circulatory problems continue. Record the time and response to every dose.
Deliver high-concentration oxygen, attach monitoring and obtain intravenous or intraosseous access without postponing adrenaline. Give rapid isotonic crystalloid boluses for hypotension or poor perfusion and reassess for further fluid, taking age and cardiac or renal disease into account. Begin standard cardiopulmonary resuscitation if arrest occurs. Inhaled beta-2 agonist can supplement treatment for persistent bronchospasm; nebulised adrenaline may be used by experienced teams for upper-airway obstruction. Neither replaces intramuscular adrenaline. Antihistamines can be considered later for troublesome cutaneous symptoms once physiological compromise is controlled. Routine corticosteroids do not provide immediate rescue and should not distract from resuscitation.
Persistent compromise after two correctly administered intramuscular doses should trigger early critical-care and anaesthetic support. Check diagnosis, dose, concentration, injection site, positioning and fluid resuscitation. A titrated intravenous adrenaline infusion with continuous monitoring is an expert intervention for refractory anaphylaxis; unmonitored bolus injection is dangerous. After stabilization, plan observation, documentation, trigger avoidance, emergency medication, education and referral before discharge.
Prescribing Information
For intramuscular treatment use adrenaline 1 mg/mL, historically labelled 1:1,000. The dose is 0.01 mg/kg; because the solution contains 1 mg in each millilitre, the numerical dose in milligrams equals the volume in millilitres. A 15 kg child therefore receives 0.15 mg, or 0.15 mL, while the maximum dose is 0.5 mg. Follow a current age- or weight-based local chart where exact weighing is impossible. Inject through clothing if necessary into the outer mid-thigh. Do not give subcutaneously and do not waste time diluting an intramuscular dose. Check the label aloud to prevent confusion with more dilute cardiac-arrest preparations.
Transient tremor, pallor, anxiety, headache and palpitations can follow an appropriate dose and are not reasons to withhold repeat treatment from a patient with continuing life-threatening features. Serious hypertension, arrhythmia, myocardial ischaemia and pulmonary oedema are more likely after dosing or route errors, especially an intravenous bolus. There is no absolute contraindication to intramuscular adrenaline in life-threatening anaphylaxis. A patient taking a beta-blocker with refractory shock may require specialist consideration of glucagon, with protection against vomiting and monitoring of glucose and haemodynamics.
At discharge, decide whether adrenaline auto-injectors are indicated under the current specialist or local pathway. Device strengths and availability vary, and some Indian patients may face major cost or supply barriers. Prescribe only with hands-on training, a written action plan, expiry checks and advice to seek emergency care after use. An auto-injector is not a substitute for ambulance activation or observation. Review all interacting or suspected medicines through the allergy pathway; never stop essential cardiovascular treatment solely because it appears on a generic risk list.
When to Refer
Every patient treated for suspected anaphylaxis needs transfer to an emergency-capable service unless already in one. Urgent anaesthetic or critical-care input is required for progressive airway swelling, silent chest, persistent hypoxaemia, shock, arrhythmia, more than one intramuscular adrenaline dose or any need for an intravenous vasopressor infusion. Obstetric, paediatric or cardiology support should be added according to physiology and comorbidity, without delaying core resuscitation. A referral handover should include the suspected trigger, exposure route, symptom sequence, vital-sign trend, positioning, exact adrenaline concentration, dose, route, site and times, fluids, adjuncts and response.
After recovery, refer to a specialist allergy service to identify the likely trigger, evaluate alternatives, interpret tryptase, decide on testing, reduce unnecessary avoidance and construct a prevention plan. Referral urgency rises after an unknown trigger, recurrent episodes, occupational exposure, venom reaction, suspected medicine or perioperative allergy, severe food reaction, mast-cell disease concern or major difficulty accessing emergency care. Children need dietetic input when food avoidance could impair nutrition. Perioperative referrals require the full anaesthetic chart and every product used, not just the drug administered immediately before collapse.
Observation must be risk-based. Current current guidelines guidance permits consideration of discharge after two hours from complete resolution only when response was rapid to a single early dose, the person already has and can use prescribed auto-injectors, and safe adult supervision exists. At least six hours is advised after two intramuscular doses or a previous biphasic reaction; at least twelve hours is advised after severe reactions needing more than two doses and for specified higher-risk circumstances. These thresholds begin after symptoms resolve and must be extended when local travel, supervision or access makes recurrence unsafe.
Red Flags
Hoarseness, tongue swelling, stridor, inability to complete sentences, silent chest, cyanosis, falling oxygen saturation, hypotension, poor perfusion, confusion, collapse or cardiac arrest are immediate threats. Give intramuscular adrenaline and activate resuscitation. Do not wait for rash, because severe anaphylaxis can lack skin manifestations. Sudden deterioration after a medicine, sting, food, infusion, anaesthetic or vaccine is enough to begin parallel diagnosis and treatment when airway, breathing or circulation are affected. A patient who appears calmer after lying down may still be in compensated shock; reassess objective physiology.
Failure to improve after a correctly delivered dose, or renewed compromise after initial improvement, is a red flag. Repeat intramuscular adrenaline after about five minutes when indicated, treat hypoxia and intravascular depletion, and call critical care early. A biphasic reaction is recurrence after apparent resolution without a new exposure. It is not reliably predicted by one feature, but severe initial illness, delayed adrenaline and multiple doses increase concern. Continuing allergen absorption, severe asthma, late presentation, pregnancy, poor supervision and long distance from emergency care further lower the threshold for prolonged monitoring.
Treatment errors are also emergencies: wrong concentration, intravenous bolus, subcutaneous injection, late repeat dosing, failure to position safely or an empty kit can cause preventable harm. Antihistamine response does not prove the episode was mild, and steroid administration does not prevent the need for observation. At discharge, absence of a written plan, inaccessible rescue medication, no allergy referral or inability to return promptly should stop an otherwise premature discharge. Recurrent unexplained episodes, hypotension after an insect sting, or persistently raised baseline tryptase warrant specialist assessment for mast-cell disease.
Indian Clinical Context
Anaphylaxis readiness must work across tertiary hospitals, small nursing homes, dental clinics, diagnostic centres, infusion units, schools and outreach vaccination sites. Each location should keep in-date adrenaline 1 mg/mL, appropriate syringes and needles, a visible weight-based chart, oxygen and airway equipment, crystalloid, monitoring where feasible, and a direct plan for ambulance or receiving-facility transfer. Stock should be protected from light and excessive heat and checked on a named schedule. Simulation should include recognition without rash, dose calculation, safe positioning, repeat dosing, documentation and handover. Purchasing a kit without recurrent rehearsal is not preparedness.
MoHFW role-specific instructions govern Indian immunisation sessions. Frontline vaccinators should follow the current operational pathway for authorised initial intramuscular adrenaline, medical-officer notification, urgent transfer and AEFI documentation. Record vaccine or medicine name, manufacturer, batch, diluent, administration site and route, time of exposure, onset, all vital signs, each treatment and the outcome. A severe event following vaccination must enter the national reporting and investigation process; surveillance records temporal association and does not by itself establish causation. Clear communication protects both patients and confidence in immunisation.
Access to auto-injectors and allergy testing is uneven and cost-sensitive. A discharge plan must therefore specify what the patient can actually obtain, who can train the family, and where emergency care is reachable. Where a device is unavailable, specialist advice is needed rather than an improvised home ampoule-and-syringe plan. Translate trigger avoidance and emergency instructions into a language the patient understands, account for food labelling and cross-contact realities, and give schools or workplaces role-specific written plans. Remote residence, monsoon travel, ambulance delay and overnight access should influence observation decisions. International observation or prescribing recommendations are evidence references, not substitutes for current Indian law, programme documents and local clinical capacity.
NMC Competency Mapping
Anaphylaxis integrates emergency medicine, pharmacology, internal medicine, paediatrics, anaesthesiology and community medicine. At knowledge level, learners should define a rapid systemic hypersensitivity reaction, explain mast-cell mediator effects, recognise that skin signs may be absent, and distinguish IgE-mediated allergy from non-IgE mechanisms and non-allergic adverse effects. Pharmacology learning includes alpha- and beta-adrenergic actions, why thigh intramuscular delivery is preferred, the 1 mg/mL concentration, weight-based dosing, expected adverse effects and the danger of an intravenous bolus.
At skills level, the student should perform an ABC assessment, summon help, position an adult, child or pregnant patient safely, calculate and draw up intramuscular adrenaline, identify the injection site, state the five-minute reassessment interval and begin oxygen, monitoring and fluid resuscitation. A simulation should test whether adrenaline precedes cannulation, antihistamine and paperwork. The learner should recognize refractory physiology, request senior or critical-care support, initiate a structured handover and document exposure, onset, dose times and response. Independent intravenous adrenaline prescribing is beyond an undergraduate unsupervised role.
Community-medicine competence includes maintaining emergency readiness at immunisation sessions, distinguishing an AEFI from established vaccine causation, preserving batch details, and reporting through the current national pathway. Longitudinal care requires safe discharge information, referral and avoidance of an inaccurate permanent allergy label. Departments should map these outcomes to the version of the NMC curriculum and local logbook actually in force rather than inventing one highly specific code. Assessment should combine case interpretation, dose calculation, communication and observable emergency actions, because recall of a drug name alone does not demonstrate safe performance.
Key Exam Pearls for NEET PG
Anaphylaxis is diagnosed clinically. Acute skin or mucosal involvement plus respiratory compromise, hypotension or severe gastrointestinal features is one pattern; bronchospasm, laryngeal involvement or hypotension after a known or highly probable allergen may establish the diagnosis even without a rash. The first-line treatment is adrenaline 1 mg/mL injected intramuscularly into the mid-anterolateral thigh at 0.01 mg/kg, maximum 0.5 mg. Repeat after about five minutes if dangerous airway, breathing or circulation features persist. Keep a shocked patient flat, use left lateral positioning in pregnancy, and do not allow walking.
Oxygen, monitoring and rapid isotonic crystalloid for shock are concurrent measures. A bronchodilator treats residual bronchospasm but not vasodilatory shock or laryngeal oedema. Antihistamines are for later cutaneous symptoms; corticosteroids are not immediate rescue. Intravenous adrenaline bolus is unsafe outside exceptional expert circumstances. Refractory anaphylaxis requires confirmation of correct intramuscular dosing, adequate fluid and an expert titrated infusion. Serum tryptase can support later evaluation but a normal value does not exclude the diagnosis and sampling never delays treatment.
Vasovagal syncope favours pallor, sweating, bradycardia and rapid improvement supine. Anaphylaxis favours persistent respiratory or circulatory compromise. Biphasic recurrence can follow apparent recovery without re-exposure, so observation is based on severity, number of doses, timing, asthma, continuing absorption, previous biphasic events and access to care. Every survivor needs a documented trigger history, written action plan and allergy referral. In immunisation questions, AEFI means an event after vaccination, not proof of causation; Indian session readiness requires trained staff, adrenaline, transfer linkage and reporting.
Frequently Asked Questions
Should intramuscular adrenaline be withheld from an older patient with coronary artery disease?
No. Life-threatening anaphylaxis has no absolute contraindication to correctly dosed intramuscular adrenaline. Delaying treatment leaves hypoxia and shock untreated and may be more dangerous to the myocardium. Give the thigh dose, monitor closely, provide oxygen and fluid according to physiology, and involve critical care early. Avoid an intravenous bolus, which carries a much greater dosing and arrhythmia risk.
When should a repeat dose of adrenaline be given during anaphylaxis?
Reassess continuously and repeat intramuscular adrenaline after approximately five minutes when life-threatening airway, breathing or circulatory problems persist. Record the exact time, concentration, dose, route and response. After two appropriate doses, seek expert critical-care support early, confirm correct thigh delivery and treat hypoxia and intravascular depletion while preparing monitored escalation for refractory shock.
How long should a patient be observed after an anaphylactic reaction resolves?
For adults, current guidance recommends 6 to 12 hours of observation from symptom onset after emergency treatment, with the exact period depending on the response. A shorter period may be considered only when the reaction was promptly and easily controlled and appropriate post-reaction care is in place. Children under 16 should be admitted under a paediatric medical team. Local travel and access can justify longer observation.
Why is referral to an allergy service necessary after emergency recovery?
Emergency treatment controls the episode but does not reliably identify the trigger or prevent recurrence. Specialist review reconstructs exposures, interprets tryptase, selects appropriate skin, blood or challenge testing, distinguishes true allergy from an inaccurate label, advises avoidance, considers auto-injectors and supplies a personalized plan. Perioperative, medicine, venom and unexplained reactions especially require complete records and targeted evaluation.
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