Nursing care
Allergic Reactions and Anaphylaxis nursing care: what to assess and what to do first
Written and reviewed by Dana Whitfield, RN, MSN · 5 min read · Updated September 2026
Short answer
Anaphylaxis is a rapid, severe, multi-system allergic reaction that can cause airway compromise and shock within minutes. The first action is intramuscular epinephrine into the lateral thigh — before antihistamines, before corticosteroids, and before further assessment. Delay for any other intervention risks a fatal outcome.
What it is and why it happens
An allergic reaction ranges from mild and localised, such as hives or itching after a drug or food exposure, to anaphylaxis, a severe, rapidly progressing systemic reaction. In anaphylaxis, mast cells and basophils release histamine and other mediators throughout the body in response to an allergen the immune system has previously been sensitised to, whether that is a medication, a food, a venom, or latex.
The physiological result is what makes anaphylaxis dangerous: widespread vasodilation and increased vascular permeability drop blood pressure fast, while bronchoconstriction and airway oedema threaten breathing at the same time. This combination of airway compromise and circulatory collapse, arriving within minutes of exposure, is what separates anaphylaxis from a routine allergic reaction and from most other acute deteriorations you will see on a ward.
Common triggers on an inpatient unit include IV antibiotics such as penicillins and cephalosporins, contrast media, blood products, and latex gloves or equipment, so exposure can happen mid-shift without warning.
How it presents — what you will actually see
Look for rapid onset across more than one body system: skin changes such as hives, flushing, or angioedema of the lips and face; respiratory signs including stridor, wheeze, throat tightness, or a hoarse voice; and cardiovascular signs such as hypotension, tachycardia, and dizziness or collapse. Gastrointestinal symptoms — cramping, vomiting, diarrhoea — can appear alongside the others.
Onset is typically within minutes of exposure, though it can be delayed up to an hour or more depending on the route and allergen, and IV-administered triggers tend to act fastest. Patients often describe a sense of impending doom before objective signs are fully apparent, and that subjective report should be taken seriously rather than dismissed as anxiety.
Not every case includes a rash. Airway and circulatory collapse can occur with minimal or no visible skin involvement, so absence of hives does not rule anaphylaxis out if respiratory or cardiovascular signs are present.
Nursing assessment priorities
Airway and breathing come first: listen for stridor or wheeze, check for voice change or throat tightness, and assess oxygen saturation immediately. A rapidly swelling airway can close within minutes, so this assessment cannot wait for a full set of vitals to be charted first.
Move quickly to circulation: check blood pressure and heart rate, and look for signs of shock such as pallor, delayed capillary refill, or altered mental status. Identify and stop the suspected trigger the moment anaphylaxis is suspected — halt an infusion, remove a dressing, or note the last medication given — since ongoing exposure worsens the reaction.
Assess skin and gastrointestinal symptoms as supporting evidence, but do not let their absence delay recognition. Call for help immediately, since anaphylaxis management needs more than one set of hands: someone to give epinephrine, someone to secure the airway and IV access, and someone to call the rapid response or emergency team.
Interventions and what to do first
Give epinephrine first, intramuscularly, into the lateral thigh — this is the single most important intervention and it happens before anything else, including antihistamines and corticosteroids. IM injection into the vastus lateralis achieves faster, more reliable absorption than subcutaneous or arm injection, and delay to give an antihistamine first is a recognised cause of preventable death in anaphylaxis.
After epinephrine, call for emergency assistance, position the patient supine with legs elevated unless they are struggling to breathe, and administer high-flow oxygen. Establish or maintain IV access and give fluids to support blood pressure, since capillary leak from histamine release can cause rapid volume loss into the tissues.
Antihistamines and corticosteroids follow as adjuncts, easing skin symptoms and helping prevent a biphasic reaction, but they act too slowly to reverse airway closure or shock and must never substitute for epinephrine. Repeat epinephrine doses every 5 to 15 minutes if symptoms persist, and prepare for advanced airway management if stridor or swelling worsens.
Complications to watch for
Airway obstruction from laryngeal oedema is the most immediately life-threatening complication, and it can progress from mild voice change to complete closure within minutes, so continuous reassessment of airway patency is essential even after the first epinephrine dose.
Refractory hypotension and cardiovascular collapse can persist despite fluids and repeated epinephrine, particularly in patients on beta-blockers, who may respond poorly to standard doses and require glucagon as an adjunct. Watch closely for a biphasic reaction: symptoms that resolve and then recur, typically within 4 to 12 hours but occasionally later, which is why observation continues well after the patient appears stable.
Cardiac arrest can occur from either airway loss or circulatory collapse if treatment is delayed, underscoring why the first dose of epinephrine cannot wait for a confirmed diagnosis or a full assessment.
Patient teaching before discharge
Confirm the patient knows their confirmed or suspected trigger and can name it clearly, since avoidance is the primary prevention strategy going forward. Prescribe and teach the use of an epinephrine auto-injector if one is indicated, including the injection site, technique, and the instruction to call emergency services immediately after use even if symptoms improve.
Explain the biphasic reaction risk in plain terms: symptoms can return hours after they seem to have resolved, so the patient should seek care again if any allergic symptoms reappear, even after a normal-seeming recovery. Recommend a medical alert bracelet or similar identification, particularly for drug or food allergies likely to recur in a future clinical setting.
Arrange allergy referral or testing where appropriate, and make sure the allergy is documented clearly and visibly in the patient's medical record so that future clinicians, especially those prescribing medication, see it before it becomes a repeat exposure.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our reduction of risk potential practice questions are the closest set to what this page covers.
One question from the reduction of risk potential set
Four hours after a cardiac catheterization via the right femoral artery, the nurse notes the client's right dorsalis pedis pulse is now faint and the foot is cool and pale. What is the nurse's priority action?
Rationale
A pulse that was present and is now faint, with a cool, pale extremity distal to the puncture site, is arterial occlusion until proven otherwise — a limb-threatening complication that needs the provider now. Documenting and rechecking wastes the window, warming treats the symptom and masks the change, and asking the client to move the ankle neither restores flow nor gives you new information.
Answer: C
Common questions
What is the first drug given in anaphylaxis?
Epinephrine, given intramuscularly into the lateral thigh. It is given before antihistamines or corticosteroids, since it is the only drug that reliably reverses airway swelling and circulatory collapse quickly enough to prevent death.
Why intramuscular and not subcutaneous?
IM injection into the vastus lateralis achieves faster and more reliable absorption than subcutaneous injection, which matters when minutes determine whether the airway stays open. This is a frequently tested distinction on the NCLEX.
Can anaphylaxis occur without a rash?
Yes. Airway and cardiovascular signs can dominate with little or no visible skin involvement, so a patient without hives can still be in anaphylaxis if they have stridor, wheeze, or hypotension after a likely trigger.
What is a biphasic reaction?
A recurrence of anaphylaxis symptoms after apparent resolution, typically within 4 to 12 hours but sometimes later. It is the reason patients are observed for a period after treatment rather than discharged as soon as symptoms settle.
Why might epinephrine work poorly in some patients?
Patients on beta-blockers can have a blunted response to standard epinephrine dosing and may need glucagon as an adjunct if hypotension persists despite repeated doses and fluids.
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