Anaphylaxis: What to Do in the First Five Minutes

Anaphylaxis kills fast, and it usually kills through delay rather than through severity. The clinical decisions that matter most happen in the first five minutes, before the airway is lost and before circulatory collapse becomes irreversible. This is a walkthrough of those five minutes: what recognition actually looks like at the bedside, why epinephrine precedes every other intervention, and the positioning and observation decisions that quietly determine outcome.

Key points

• Anaphylaxis is a clinical diagnosis. Do not wait for hypotension, wheeze, or a known trigger — the majority of fatal cases were not recognised as anaphylaxis at first contact.
• Intramuscular epinephrine into the anterolateral thigh is the first action, not a later escalation. Antihistamines and corticosteroids treat neither airway obstruction nor shock.
• There is no absolute contraindication to epinephrine in anaphylaxis.
• Keep the patient supine (or in a position of comfort if dyspnoeic, left lateral if pregnant). Sudden upright posture has been associated with fatal cardiovascular collapse.
• Repeat epinephrine every 5–15 minutes if the response is inadequate; refractory cases need fluids and an infusion in a monitored setting.
• Observation duration is risk-stratified, not fixed. Every patient leaves with an autoinjector, a written action plan, and allergy follow-up.

Minute one: recognise it without a checklist

The clinical criteria for anaphylaxis are worth knowing precisely, but at the bedside they collapse into a simpler question: is this an acute-onset multisystem reaction, or a single-system reaction with hypotension or airway compromise after a likely allergen?

Three presentation patterns cover nearly everything you will see. The first is the classic one — sudden onset of skin or mucosal involvement (urticaria, flushing, lip or tongue swelling) plus either respiratory compromise or reduced blood pressure. The second is the multisystem picture after exposure to a likely allergen, where two or more of skin/mucosal, respiratory, cardiovascular, or persistent gastrointestinal symptoms appear together. The third is the trap: isolated hypotension after exposure to a known allergen for that patient, with no rash at all.

That third pattern matters because up to a fifth of anaphylaxis presentations have no cutaneous findings. Waiting for hives is a recognised cause of delayed treatment. Similarly, persistent vomiting and crampy abdominal pain after a sting or a food are cardiovascular-equivalent warning signs in children, not gastroenteritis.

Certain features should move you immediately: stridor, a hoarse or muffled voice, tongue or uvular swelling, a sense of impending doom, and — in the perioperative or infusion setting — unexplained hypotension or a sudden rise in airway pressures. Onset is typically within minutes to two hours of exposure; the faster the onset, the more severe the reaction tends to be.

What mimics it

Vasovagal syncope has bradycardia, pallor without urticaria, and no respiratory involvement. Acute asthma lacks the mucocutaneous and gastrointestinal features. Scombroid poisoning after fish produces flushing and headache with a histamine-like picture but a shared-meal history. Panic attacks and vocal cord dysfunction produce stridor-like noise without hypoxia or hypotension. None of these are harmed by a single dose of intramuscular epinephrine; the patient with unrecognised anaphylaxis is harmed by withholding it.

Minute two: epinephrine, intramuscular, anterolateral thigh

Epinephrine is the only intervention that addresses the whole pathophysiology at once. Alpha-1 agonism reverses vasodilatation and mucosal oedema; beta-1 agonism supports inotropy and chronotropy; beta-2 agonism produces bronchodilation and reduces further mediator release from mast cells and basophils. Nothing else in the tray does this.

Route and site are not interchangeable. The anterolateral thigh (vastus lateralis) achieves higher and faster peak plasma concentrations than the deltoid or subcutaneous administration, and intramuscular delivery is markedly more reliable than subcutaneous in a shocked patient with peripheral vasoconstriction. Give it through clothing if that is faster.

Intravenous bolus epinephrine is a different drug in practice — it is associated with dosing errors, hypertensive crisis, arrhythmia, and myocardial ischaemia. Reserve intravenous administration for cardiac arrest or for titrated infusion under monitoring in refractory shock.

There is no absolute contraindication. Elderly patients, patients with coronary disease, and pregnant patients all die of untreated anaphylaxis; the risk calculus favours the drug. Patients on beta-blockers may respond poorly, and glucagon is the recognised adjunct in that setting.

Antihistamines relieve itch and urticaria. Corticosteroids may modestly influence protracted reactions but have no demonstrated effect on the acute event, and the evidence that they prevent biphasic reactions is weak. Neither should ever be given instead of epinephrine or delay it, and reaching for the antihistamine first is one of the most consistent findings in fatality reviews.

Minute three: position the patient

This is the intervention most often skipped and one of the few with case-fatality evidence behind it. In distributive shock, venous return depends heavily on posture. Fatalities have been described in patients who were sat or stood up — moved to a chair, walked to a trolley, sent to the toilet — with sudden empty-ventricle collapse.

Lay the patient supine with legs elevated. If they are dyspnoeic or vomiting, allow a position of comfort or the recovery position, but do not have them stand or walk. In pregnancy, use the left lateral position to relieve aortocaval compression. Once supine, keep them supine until they are stable and monitored.

Minutes four and five: airway, access, oxygen, fluids

Remove the trigger where possible — stop the infusion, remove the stinger. Give high-flow oxygen. Establish large-bore intravenous access and give an aggressive crystalloid bolus, because massive fluid shifts into the interstitium mean these patients are functionally hypovolaemic, sometimes profoundly so.

Reassess at five minutes. If airway compromise, hypotension, or respiratory distress persist, repeat the intramuscular dose. Most patients respond to one or two doses; needing more than two identifies a patient who requires an infusion, critical care involvement, and consideration of adjuncts.

Anticipate the airway early. Angioedema of the tongue, oropharynx, or larynx can progress from voice change to complete obstruction quickly, and the window for intubation closes as tissue distorts. Call for the most experienced airway operator available at the first sign of stridor or voice change rather than after failure, and have a plan for a surgical airway.

Nebulised bronchodilators help persistent bronchospasm. Glucagon is used for patients on beta-blockade with refractory hypotension. Vasopressors are added for shock that does not respond to epinephrine infusion and fluids.

After the first five minutes: observation and discharge

Biphasic reactions — recurrence without re-exposure, typically within the first several hours — occur in a minority of patients but drive observation policy. Rigid fixed observation periods have given way to risk stratification. Longer, monitored observation is appropriate for patients who needed more than one dose of epinephrine, had severe or rapidly progressive features, had hypotension or airway involvement, have a history of biphasic reactions or poorly controlled asthma, or face barriers to returning for care. Low-risk patients with prompt, complete response to a single dose can often be observed for a shorter period.

Discharge is an intervention in itself. Every patient leaves with an epinephrine autoinjector prescription — two devices where indicated — and, critically, with a demonstration that they can actually use it. They leave with a written anaphylaxis action plan, clear advice to call emergency services after using it, avoidance counselling for the suspected trigger, and a referral to allergy or immunology for confirmatory testing and long-term management. Consider drawing a serum tryptase during the acute reaction with a convalescent baseline later, which can support the diagnosis retrospectively; a normal level never excludes anaphylaxis.

Document the timeline, the doses, and the response. That record is what allows the next clinician to stratify risk, and what allows the allergist to identify the trigger.

To rehearse this sequence under time pressure — including the atypical presentations that are missed most often — work through anaphylaxis with cited sources and a virtual patient at app.medicaltraining.ai.

Educational content for healthcare professionals. It is not medical advice and does not replace clinical judgement or local protocols.