Anaphylaxis: Recognition and Emergency Management

Core Review

Definition

Anaphylaxis is a severe, life-threatening, generalized (systemic) hypersensitivity reaction that is rapid in onset and may cause death. It is a Type I hypersensitivity reaction (IgE-mediated) that results in massive release of inflammatory mediators (histamine, leukotrienes, prostaglandins, tryptase) from mast cells and basophils.

Key characteristics:

• Rapid onset (minutes to hours after exposure)
• Involves TWO or more organ systems (or isolated severe respiratory or cardiovascular compromise)
• Life-threatening without immediate treatment

Anaphylaxis vs. Mild Allergic Reaction:

Pathophysiology

Anaphylaxis occurs through a cascade:

1. Sensitization: Previous exposure to an allergen → IgE antibodies produced → IgE binds to mast cell and basophil surfaces
2. Re-exposure: The same allergen binds to IgE on the mast cell surface → cross-linking of IgE receptors → mast cell degranulation
3. Mediator release:
   • Histamine: Vasodilation, increased vascular permeability (urticaria, angioedema, hypotension), bronchoconstriction
   • Leukotrienes and prostaglandins: Sustained bronchoconstriction, mucus secretion, vasodilation
   • Tryptase: Mast cell activation marker (can be measured in blood; clinical utility is retrospective diagnosis)
   • Platelet-activating factor (PAF): Bronchoconstriction, increased vascular permeability
4. Clinical effects:
   • Increased vascular permeability → urticaria, angioedema, laryngeal edema
   • Vasodilation → hypotension, vascular collapse
   • Bronchoconstriction → wheezing, respiratory distress
   • GI smooth muscle contraction → nausea, vomiting, diarrhea, cramping

Triggers in the Dental Setting

Common allergens encountered in dentistry include:

• Latex: Gloves, rubber dam, prophylaxis cups, blood pressure cuffs, some local anesthetic cartridges (latex-containing stoppers). Latex allergy prevalence has decreased with increased use of non-latex products.
• Local anesthetics: True IgE-mediated allergy is EXTREMELY RARE with amide local anesthetics (lidocaine, articaine, mepivacaine, bupivacaine, prilocaine). Most reported "allergies" are actually vasovagal reactions, epinephrine-related tachycardia, or toxicity from inadvertent intravascular injection. Ester anesthetics (benzocaine, procaine) have a higher allergy risk due to their PABA metabolite but are rarely used for injection.
• Antibiotics: Penicillin and cephalosporins are the most common antibiotic allergens. Always ask about antibiotic allergies before prescribing. Cross-reactivity between penicillin and cephalosporins is approximately 1-5%.
• NSAIDs: Aspirin, ibuprofen, naproxen — can trigger anaphylactoid (non-IgE mediated) reactions via cyclooxygenase pathway.
• Chlorhexidine: Rare but increasingly recognized cause of anaphylaxis.
• Acrylic monomers (methyl methacrylate): Contact dermatitis is common; anaphylaxis is rare.

Clinical Presentation

Anaphylaxis involves two or more organ systems. The NBDHE expects recognition of multi-system involvement:

Skin/Mucosal (present in 80-90% of cases):

• Urticaria (hives): raised, erythematous, intensely pruritic wheals
• Angioedema: swelling of the lips, tongue, periorbital area, face, neck. If laryngeal involvement: stridor (inspiratory, high-pitched), hoarseness, difficulty swallowing, sensation of a "lump in the throat"
• Flushing: generalized erythema
• Pruritus: generalized itching

Respiratory (present in 70% of cases):

• Bronchospasm: wheezing (expiratory), chest tightness, dyspnea, coughing
• Laryngeal edema: stridor, voice changes (hoarseness), airway obstruction (this is the most common cause of death from anaphylaxis)
• Rhinitis: sneezing, nasal congestion, rhinorrhea

Cardiovascular (present in 45% of cases):

• Tachycardia (compensatory; may progress to bradycardia in severe cases)
• Hypotension (the most dangerous cardiovascular sign)
• Dizziness, lightheadedness
• Syncope
• Cardiovascular collapse (shock)

Gastrointestinal (present in 45% of cases):

• Nausea, vomiting
• Diarrhea
• Abdominal cramping

Neurologic:

• Anxiety, agitation
• Sense of impending doom
• Confusion
• Loss of consciousness

The "Impending Doom" Sign: Patients experiencing anaphylaxis often report a profound sense that "something is terribly wrong" or "I feel like I'm going to die." This is a real clinical finding, not just anxiety, and should be taken extremely seriously.

Emergency Management Protocol

Step 1: RECOGNIZE

Identify the multi-system involvement that suggests anaphylaxis. If a patient develops urticaria + bronchospasm, or angioedema + hypotension, or any two systems involved within minutes of a potential allergen exposure, diagnose anaphylaxis and act immediately.

Step 2: ACTIVATE EMS

Call 911 IMMEDIATELY. Anaphylaxis is a life-threatening emergency that requires hospital-level care even if epinephrine produces initial improvement. Biphasic anaphylaxis (recurrence of symptoms hours after initial resolution) occurs in up to 20% of cases.

Step 3: ADMINISTER EPINEPHRINE (FIRST-LINE, NO DELAY)

Epinephrine is THE single most important treatment for anaphylaxis. There is NO contraindication to epinephrine in anaphylaxis — the risk of untreated anaphylaxis far outweighs any theoretical risk of epinephrine administration.

Epinephrine Dosing:

• Concentration: 1:1,000 (1 mg/mL)
• Dose for ADULTS: 0.3-0.5 mg (0.3-0.5 mL of 1:1,000 solution)
• Dose for CHILDREN: 0.01 mg/kg (max 0.3 mg per dose)
• Route: INTRAMUSCULAR (IM) — into the anterolateral thigh (vastus lateralis muscle)
• Can be repeated every 5-15 minutes if symptoms persist

Why IM into the thigh?

• Rapid absorption compared to subcutaneous (SC) route (IM achieves peak plasma concentrations faster)
• The thigh muscle is large, easily accessible, and well-vascularized
• SC administration is NO LONGER recommended for anaphylaxis (slower absorption, less reliable)

Why the anterolateral thigh specifically?

• Large muscle mass
• Accessible even in clothed patients
• Away from major nerves and vessels
• Can be self-administered (EpiPen is designed for thigh)

Epinephrine's Mechanism in Anaphylaxis:

• Alpha-1 adrenergic agonism → vasoconstriction → increases blood pressure, decreases mucosal edema (especially laryngeal)
• Beta-1 adrenergic agonism → increases heart rate and contractility
• Beta-2 adrenergic agonism → bronchodilation
• Inhibits further mast cell mediator release

Epinephrine addresses ALL the life-threatening features of anaphylaxis simultaneously — no other drug does this. Antihistamines and corticosteroids are SECONDARY, adjunctive treatments.

Step 4: POSITION THE PATIENT

• If the patient is dyspneic (difficulty breathing, wheezing): Position semi-upright to facilitate respiratory effort
• If the patient is hypotensive (low blood pressure, lightheaded): Position supine with legs elevated (to improve venous return)
• If the patient is vomiting or has altered consciousness: Left lateral recumbent (recovery position) to prevent aspiration
• Do NOT sit or stand the patient up suddenly — this can cause "empty ventricle syndrome" and precipitate cardiovascular collapse

Step 5: AIRWAY AND OXYGEN

• Open and maintain the airway
• Administer high-flow oxygen (10-15 L/min via non-rebreather mask)
• Be prepared for airway compromise: laryngeal edema can make intubation extremely difficult; early intubation may be life-saving in the hospital setting
• In the dental setting: maintain airway, provide oxygen, and allow EMS to manage the airway definitively

Step 6: ADJUNCTIVE MEDICATIONS (Secondary)

These are NOT substitutes for epinephrine. Administer AFTER epinephrine:

Antihistamines:

• Diphenhydramine (Benadryl): 25-50 mg IM or IV (adults); 1 mg/kg (children)
• An H1-receptor antagonist — reduces urticaria and pruritus but does NOT reverse bronchospasm or hypotension
• Takes 15-30 minutes for onset; delayed effect

Corticosteroids:

• Methylprednisolone 125 mg IV, or prednisone 50 mg PO
• Onset is 4-6 hours (too slow for acute management)
• Role: May prevent biphasic (late-phase) reaction
• NOT a life-saving acute intervention

Bronchodilators (for persistent bronchospasm):

• Albuterol: 2-4 puffs via metered-dose inhaler with spacer
• Beta-2 agonist — relaxes bronchial smooth muscle
• Adjuvant to epinephrine, not a replacement

Step 7: MONITOR AND SUPPORT

• Monitor vital signs continuously (BP, pulse, RR, SpO₂)
• Be prepared to initiate CPR if cardiac arrest occurs
• Document all drugs administered (name, dose, route, time)
• Transfer care to EMS with a clear handoff

Prevention in the Dental Setting

• Allergy history: Meticulously document all allergies (drug, latex, environmental) in the medical history. Update at every visit.
• Latex precautions: For latex-allergic patients:
  • Use non-latex (nitrile) gloves
  • Remove all latex-containing items from the operatory
  • Use latex-free rubber dam, latex-free prophylaxis cups, latex-free BP cuffs
  • Schedule as the first patient of the day (minimize airborne latex particles from previous patients)
• Drug allergies:
  • Verify antibiotic allergies before prescribing
  • For local anesthetic "allergy" reports: carefully assess the nature of the reported reaction. Many are vasovagal or epinephrine-related. True amide LA allergy is extremely rare.
  • If a true allergy is suspected, refer to an allergist for testing
• Emergency preparedness: Epinephrine auto-injectors (e.g., EpiPen) should be available in the emergency kit and all staff trained on their use

Clinical Application

Scenario: 10 minutes after administering 2% lidocaine with 1:100,000 epinephrine for quadrant scaling, a 48-year-old female patient develops generalized urticaria (hives on arms, chest, and neck), periorbital swelling (angioedema), and reports "I can't breathe... my chest feels tight." You auscultate bilateral wheezing. BP: 88/54, pulse: 112, SpO₂: 91%.

Diagnosis: Anaphylaxis — skin (urticaria, angioedema), respiratory (bronchospasm, dyspnea), and cardiovascular (hypotension, tachycardia) involvement.

Management:

1. Activate EMS — call 911 immediately
2. Epinephrine: 0.3 mg (0.3 mL of 1:1,000) IM into the anterolateral thigh
3. Position: Semi-upright (respiratory distress is the dominant symptom, but BP is low — monitor for deterioration)
4. Oxygen: 15 L/min via non-rebreather mask
5. Monitor: BP, pulse, SpO₂ continuously. If no improvement in 5 minutes, repeat epinephrine 0.3 mg IM.
6. Adjunctive: Diphenhydramine 50 mg IM (if available and after epinephrine)
7. Transfer: Handoff to EMS with complete documentation

Common Traps

• TRAP: Administering antihistamines (diphenhydramine) FIRST instead of epinephrine. Epinephrine is the only life-saving drug. Antihistamines do NOT reverse bronchospasm or hypotension.
• TRAP: Using SC route for epinephrine. Current guidelines recommend IM into the anterolateral thigh for more rapid and reliable absorption.
• TRAP: Not calling 911 because the patient "improved" after epinephrine. Biphasic anaphylaxis can occur hours later. All anaphylaxis patients need emergency department evaluation.
• TRAP: Administering epinephrine 1:10,000 IV in the dental setting. The IV concentration is for cardiac arrest in a hospital setting. The dental emergency kit contains 1:1,000 for IM use.