Ilyas K. Colombowala, MD, FACC, FHRS
Cardiac Electrophysiology · Houston, TX · colombowala.com
EP Staff Education

Emergency

Anaphylaxis in the EP Lab

Acute hypersensitivity reactions in the EP lab usually come from contrast, antibiotics, or latex. Recognition fast, IM epinephrine first, the rest in parallel. Most cases respond to a single IM dose; biphasic reactions and refractory shock are the bad outcomes to anticipate.

Indications

  • ▸New onset rash, urticaria, angioedema, bronchospasm, or hemodynamic instability after contrast, antibiotic, latex exposure, or new IV medication
  • ▸Bronchospasm with hypotension during a case in a patient with no obvious cardiac cause
  • ▸Sudden cardiovascular collapse without evidence of bleeding, tamponade, or arrhythmia

Equipment / drugs

  • ▸Epinephrine 1:1000 (IM) — 0.3–0.5 mg IM for adults, into the lateral mid-thigh
  • ▸Epinephrine 1:10,000 (IV) — bolus 50–100 µg or infusion 2–10 µg/min for refractory shock
  • ▸Antihistamines: diphenhydramine 25–50 mg IV (H1) + famotidine 20 mg IV (H2)
  • ▸Methylprednisolone 125 mg IV or hydrocortisone 100 mg IV
  • ▸Albuterol nebulizer 5 mg or MDI for bronchospasm
  • ▸IV fluids: 1–2 L crystalloid wide open for distributive shock
  • ▸Glucagon 1–5 mg IV for patients on beta-blockers with refractory hypotension

Pitfalls

  • ▸Giving IV epinephrine first when IM is the appropriate first dose — IV epi is for refractory shock, not initial treatment
  • ▸Treating with diphenhydramine alone — antihistamines are adjuncts, not primary therapy
  • ▸Under-dosing epinephrine — the right dose is 0.3–0.5 mg IM (adult), not 0.1 mg
  • ▸Failing to recognize biphasic reactions — symptoms can recur 4–12 hours after initial resolution; observation is mandatory
  • ▸Missing the diagnosis in patients on beta-blockers, in whom tachycardia and bronchospasm may be blunted

Recognizing it

Anaphylaxis in the EP lab is usually triggered by something administered during or just before the case. The common culprits:

  • Iodinated contrast — the most common in EP labs that use contrast for venograms or angiograms
  • Antibiotics — particularly cefazolin given pre-procedure
  • Latex — increasingly rare in modern labs but still a possibility for patients with spina bifida history, healthcare workers, food allergies (kiwi, banana, avocado)
  • Heparin (rare) — heparin-induced anaphylactic reactions exist but are uncommon
  • Protamine reversal — bradykinin-mediated reactions in patients with prior NPH-insulin or vasectomy exposure
  • Local anesthetics — true allergy is rare but does occur (esters more than amides)
  • Chlorhexidine — sometimes the missed culprit when skin prep happens just before the reaction

The clinical picture in adults typically involves at least two of:

  • Skin/mucous membrane: urticaria, flushing, angioedema (lips, tongue, face)
  • Respiratory: wheezing, stridor, bronchospasm, dyspnea, hypoxia
  • Cardiovascular: hypotension, tachycardia (or bradycardia in severe), shock
  • Gastrointestinal: nausea, vomiting, abdominal cramps (less common in lab settings)

A reasonable working definition for the EP lab: any new respiratory or hemodynamic problem temporally associated with a new exposure, especially with skin findings, is anaphylaxis until proven otherwise.

What it isn’t

A few mimics that can be confused with anaphylaxis:

  • Vasovagal reaction — bradycardia + hypotension, but no urticaria, no bronchospasm, and responds to fluids + atropine
  • Sedation-related hypotension — falls with sedation initiation, no rash, no bronchospasm
  • Contrast reaction (non-anaphylactic) — distinct from anaphylactic-contrast reaction; usually mild rash or nausea without hemodynamic compromise. See contrast reaction.
  • Latex reaction (contact) — local skin findings only, no systemic involvement
  • Pulmonary embolism during the case — sudden cardiovascular collapse but no urticaria, no bronchospasm characteristic of anaphylaxis

When in doubt, treat as anaphylaxis. Delayed epinephrine is the most common pattern in fatal cases.

The first 90 seconds

The single most important intervention is IM epinephrine. Everything else runs in parallel:

  1. Stop the offending agent. Pause contrast, stop the antibiotic infusion, remove latex products if suspected.
  2. IM epinephrine 0.3–0.5 mg into the lateral mid-thigh (vastus lateralis). 1:1000 concentration. Repeat every 5–15 minutes as needed; second doses are required in 10–20% of cases.
  3. Call for help. Anesthesia (if not already in the room), code team if hemodynamics are collapsing.
  4. Position. Supine with legs elevated for shock; sitting up if respiratory distress dominates.
  5. High-flow oxygen. Non-rebreather mask at 15 L/min.
  6. IV fluid bolus. 1–2 L crystalloid wide open. Anaphylactic shock is distributive — they need volume.
  7. Continuous monitoring. Already set up in the lab — keep it on.

After the first epi

Within minutes, adjuncts can be started:

  • Antihistamines:
    • Diphenhydramine 25–50 mg IV (H1 blocker)
    • Famotidine 20 mg IV (H2 blocker) — adding H2 to H1 is more effective than H1 alone
  • Corticosteroid:
    • Methylprednisolone 125 mg IV, or hydrocortisone 100 mg IV
    • The steroid won’t help in the acute moment but may reduce the biphasic recurrence rate
  • Bronchodilator if bronchospasm:
    • Albuterol 5 mg nebulized, or 4–8 puffs MDI
    • Ipratropium 0.5 mg nebulized as an add-on if persistent
  • Glucagon 1–5 mg IV for patients on beta-blockers with refractory hypotension — overcomes the receptor blockade
  • Continued IV fluids — patients can need 4–6 L over the first hour in severe cases

Refractory shock

If hemodynamics aren’t improving after IM epinephrine and fluid:

  • IV epinephrine infusion — 2–10 µg/min titrated to MAP > 65
  • Repeat IM epinephrine every 5–15 minutes (no upper limit in the acute setting)
  • Vasopressin 1–2 unit IV bolus or 0.04 units/min infusion as add-on pressor
  • Norepinephrine as an alternative or add-on
  • Consider methylene blue 1–2 mg/kg IV in vasoplegic shock refractory to catecholamines
  • Airway: have anesthesia at the head of the bed; intubate if airway edema is progressing or work-of-breathing is failing

Cardiovascular collapse and arrest

Anaphylactic cardiac arrest follows standard ACLS, with two important additions:

  • Higher epinephrine doses are reasonable — there is no upper limit
  • Aggressive volume resuscitation — much more than typical ACLS fluid administration
  • Consider ECMO consult for refractory shock or arrest in centers where it’s available

Survival from anaphylactic arrest is meaningfully better than from cardiac-cause arrest, often because the underlying physiology is reversible.

Biphasic reactions

This is the underappreciated risk. Up to 20% of anaphylaxis episodes recur 4–12 hours after apparent resolution, sometimes more severely than the initial event. Therefore:

  • Minimum 4-hour observation after symptom resolution for mild cases
  • 8–24-hour observation for moderate to severe reactions, including those requiring repeat epinephrine
  • Patient discharge education — recognition of recurrence, when to call 911
  • Epinephrine auto-injector prescription before discharge — and instruction on use
  • Outpatient allergy follow-up to identify the culprit and counsel on future avoidance

Special populations

Patients on beta-blockers

The cardiac and respiratory response to epinephrine is blunted. They may need:

  • Higher epinephrine doses
  • Glucagon 1–5 mg IV as a beta-receptor bypass — this is the unique addition
  • More aggressive fluid resuscitation
  • Lower threshold for IV pressors

Patients with known severe allergy and a history of biphasic reactions

Pre-treatment doesn’t reliably prevent contrast anaphylaxis, but it reduces severity in many cases:

  • Prednisone 50 mg PO at 13, 7, and 1 hour before exposure
  • Diphenhydramine 50 mg PO 1 hour before
  • See contrast reaction for a more detailed premedication protocol

Pregnant patients

Anaphylaxis treatment in pregnancy is essentially unchanged — epinephrine first, fluids, oxygen, supportive care. The risk to the fetus from a treated anaphylactic mother is much less than from an untreated one.

Documentation

Every anaphylactic event in the lab requires:

  • Detailed timeline — exposure → onset → first epi → response
  • Suspected agent — what was given just before, in what order
  • All medications administered — doses, routes, times
  • Outcome — full recovery, ICU transfer, intubation, death
  • Allergy band placed before discharge
  • Allergy clinic referral

Adding the suspected agent to the patient’s allergy list with a clear description (e.g., “Iohexol — anaphylaxis 2026-05-24, required IM epinephrine and IV fluid resuscitation”) protects future encounters across the health system.

Last reviewed by Dr. Colombowala on May 24, 2026.

Clinical-reference content, not medical advice. This page is written for EP staff and does not create a doctor-patient relationship. It does not replace institutional policy, current device manuals, or attending direction during a case. See the full disclaimer.

© 2026 Ilyas K. Colombowala, MD. All rights reserved. Reproduction, redistribution, or republication of this content in any form without written permission is prohibited.

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