Anaphylaxis management
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Anaphylaxis Management
Anaphylaxis is a life-threatening systemic allergic (or non-allergic) reaction of acute onset with multiorgan involvement. Timely recognition and treatment are essential - half of anaphylactic fatalities occur within the first hour of exposure.
Pathophysiology
Anaphylaxis arises from activation of mast cells and basophils, primarily via IgE crosslinking and high-affinity IgE receptor aggregation. This triggers release of:
- Preformed mediators: histamine, tryptase, carboxypeptidase A, proteoglycans
- Newly generated mediators: prostaglandin D2, leukotrienes, platelet-activating factor, TNF-alpha
These cause vasodilation, increased vascular permeability, bronchoconstriction, and increased cardiac contractility - together producing the clinical syndrome.
Clinical Features
| System | Signs & Symptoms (Approximate Incidence) |
|---|---|
| Skin/Mucosa | Urticaria, flushing, pruritus, angioedema (80-90%) |
| ENT | Oropharyngeal/throat fullness (50%), tongue swelling, uvular edema |
| Respiratory | Dyspnea/wheezing (45-50%), laryngeal/pharyngeal edema (50-60%), stridor |
| Cardiovascular | Hypotension, tachycardia, syncope, cardiovascular collapse |
| GI | Nausea, vomiting, cramping, diarrhea |
| Neurologic | Anxiety, altered consciousness, seizure |
Classic progression: pruritus > urticaria/flushing > throat fullness + chest tightness + dyspnea > hypotension > loss of consciousness. Hoarseness or a "lump in the throat" signals impending life-threatening laryngeal edema.
Diagnosis
The diagnosis is clinical. Two or more body systems involved after allergen exposure strongly supports anaphylaxis. Formal criteria include:
- Acute onset of illness involving skin/mucosa PLUS one of: respiratory compromise, hypotension/collapse, or persistent GI symptoms
- Two or more of the above system findings occurring rapidly after exposure to a known allergen
- Known allergen exposure + hypotension alone in a high-risk patient
Lab Notes:
- Serum tryptase: peaks at 1 hour, may persist up to 4 hours. Has poor sensitivity (one-third of acute anaphylaxis cases have a normal level) - useful for later confirmation, not acute diagnosis
- Serum histamine: elevated for only 5-30 minutes, typically normal upon ED presentation
Common mimics to exclude: vasovagal syncope (distinguished by bradycardia), myocardial ischemia, acute severe asthma, hereditary angioedema (HAE), carcinoid, mastocytosis, panic attack, vocal cord dysfunction, foreign body airway obstruction
Management
Immediate Priority Actions
1. Epinephrine - First Line (No Absolute Contraindications)
Epinephrine is the medication of choice and must be given immediately. Antihistamines and corticosteroids must never replace or precede it.
| Route | Dose | Indication |
|---|---|---|
| IM - anterolateral thigh | Adults: 0.3-0.5 mg of 1:1000 solution; Children: 0.01 mg/kg (max 0.5 mg) | First-line for all cases |
| IV bolus | 5-10 mcg (hypotension), 0.1-1.0 mg (cardiovascular collapse) | Refractory or cardiovascular collapse |
| IV infusion | Titrate to maintain adequate BP | Protracted reactions requiring multiple IM doses |
| Sublingual | 0.5 mL of 1:1000 | Major airway compromise or hypotension when IV access unavailable |
- Repeat IM doses every 10-15 minutes as needed
- Severe anaphylaxis or need for repeated epinephrine doses are risk factors for biphasic anaphylaxis
2. Position
- Place patient in supine position (or left lateral decubitus if vomiting)
- Do not sit the patient upright or allow them to stand - this significantly worsens cardiovascular collapse
3. Airway
- Administer 100% oxygen
- Endotracheal intubation may be required for laryngeal edema
- If laryngeal edema does not respond rapidly to epinephrine: cricothyroidotomy or emergency tracheotomy
4. IV Fluids
- Large-volume crystalloid (2-4 L) for hypotension/shock
- Rapid fluid shifts from increased vascular permeability can result in significant intravascular volume loss
Second-Line Therapies
Antihistamines
- Relieve skin symptoms; no immediate effect on the hemodynamic reaction; may shorten reaction duration
- H1 blocker: Diphenhydramine 25-50 mg IM/IV (adults), 12.5-25 mg (children); or cetirizine 10 mg oral/IV
- H2 blocker (ranitidine or famotidine): may augment H1 blockade in severe cases
Corticosteroids
- No significant immediate effect and do not reliably prevent biphasic reactions
- Used to reduce potential late-phase responses (benefit is theorized, not firmly proven)
- Methylprednisolone 1-2 mg/kg IV or prednisone 1 mg/kg oral
Inhaled Beta-Agonists (e.g., salbutamol/albuterol)
- For resistant bronchospasm not responding to epinephrine
Glucagon
- For patients on beta-blockers with refractory bronchospasm or hypotension (beta-blockade blunts epinephrine response)
- Dose: 1-5 mg IV bolus slowly over 5 minutes, then infusion at 5-15 mcg/min
- Monitor for nausea/vomiting (protect airway)
Vasopressors (for refractory shock unresponsive to IV epinephrine)
- Norepinephrine, dopamine, dobutamine, or phenylephrine as alternatives/adjuncts if dysrhythmias limit epinephrine use
Anaphylaxis During General Anesthesia (Additional Steps)
| Step | Action |
|---|---|
| 1 | Stop antigen administration |
| 2 | Maintain airway, administer 100% O2 |
| 3 | Discontinue all anesthetic agents |
| 4 | Intravascular volume expansion (2-4 L crystalloid/colloid) |
| 5 | Epinephrine (5-10 mcg IV bolus for hypotension; 0.1-1.0 mg IV for cardiovascular collapse) |
Biphasic Anaphylaxis
- A second wave of mediator release peaking 8-11 hours after initial exposure, producing symptoms 3-4 hours after initial clinical resolution
- Incidence varies widely - clinically important biphasic reactions occur in approximately 4-5% of cases
- All patients treated for anaphylaxis should be observed until fully symptom-free
Observation & Disposition
Admit / prolonged observation (minimum 4-6 hours, ICU if severe) for patients with:
- Protracted anaphylaxis, hypotension, or airway involvement
- Unknown trigger
- IV epinephrine use or more than one IM epinephrine dose
- Poor outpatient social support
- All severe reactions warrant 24-hour ICU monitoring (recurrence risk)
Discharge criteria and must-do steps before discharge:
- Prescribe two self-injectable epinephrine autoinjectors and teach correct use
- Provide written emergency action plan
- Counsel on trigger avoidance and allergen contamination (especially food allergies)
- Recommend MedicAlert bracelet or equivalent
- Refer to allergist/immunologist for all patients; especially patients with Hymenoptera sensitivity for venom immunotherapy evaluation
- Switch beta-blockers to an alternative class in patients who had anaphylaxis on beta-blockers (blunts epinephrine response in future events)
Common Triggers (Pearls)
- Foods (nuts, shellfish, milk, eggs) - most common in children
- Medications (beta-lactam antibiotics, NSAIDs, radiocontrast media)
- Insect venom (Hymenoptera stings)
- Latex
- Allergen immunotherapy injections
- Idiopathic (significant proportion - no identified cause)
Recent Evidence Note
A 2026 systematic review (PMID 41701644) identified predictors of fatal anaphylaxis, reinforcing the importance of early epinephrine use and recognizing high-risk presentations. The 2023 Joint Task Force Anaphylaxis Practice Parameter (summarized in a 2025 Curr Opin Pediatr review) provides updated clinical pearls consistent with the above guidance.
Sources: Tintinalli's Emergency Medicine 9e, p. 110-113 | Rosen's Emergency Medicine 10e, p. 2383 | Washington Manual of Medical Therapeutics, p. 427 | Barash Clinical Anesthesia 9e, p. 630-631 | Textbook of Family Medicine 9e
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