Allergic Reactions and Anaphylaxis: Recognition and Emergency Management

Introduction

An allergic reaction is an immune system response to a typically harmless substance (allergen). Reactions range from mild localized symptoms to life-threatening anaphylaxis. Anaphylaxis is a severe, potentially fatal systemic allergic reaction with rapid onset. Prompt recognition and epinephrine administration are critical for survival.

Pathophysiology

Step	Process	Description
1	Sensitization	First exposure: B cells produce IgE specific to allergen; IgE binds to mast cells and basophils
2	Re-exposure	Allergen cross-links IgE on mast cells/basophils
3	Degranulation	Massive release of mediators: histamine, tryptase, leukotrienes, prostaglandins, PAF
4	Vasodilation	Widespread vasodilation causes hypotension, urticaria, angioedema
5	Bronchoconstriction	Smooth muscle contraction in airways
6	Increased permeability	Capillary leak leads to edema, third-spacing

Common Allergens

Food Allergens (Most Common in Children)

Allergen	Prevalence	Notes
Peanut	1-2% of children	Leading cause of fatal anaphylaxis
Tree nuts	0.5-1%	Almond, walnut, cashew, pistachio, pecan
Milk	2-3% of infants	Often outgrown by school age
Egg	1-2% of children	Many outgrow by adolescence
Wheat	0.1%	Often outgrown
Soy	0.1%	Often outgrown
Fish	0.1%	Persistent allergy
Shellfish	0.5-1%	Shrimp, crab, lobster; more common in adults
Sesame	0.1%	Increasing prevalence

Non-Food Allergens

Allergen	Common Sources	Reaction Pattern
Insect stings	Bee, wasp, hornet, yellow jacket, fire ant	Local or systemic; anaphylaxis in 0.5-5%
Latex	Gloves, balloons, medical devices	Contact urticaria to anaphylaxis
Medications	Penicillin (10% reported, 1% true), NSAIDs, ACEi, radiocontrast	Variable presentations
Exercise	Post-prandial exercise (specific food-dependent)	Anaphylaxis triggered by exercise after specific food
Idiopathic	Unknown trigger	Exclude other causes; treat same as known trigger

Allergic Reaction Severity Classification

Grading System

Grade	Symptoms	Management
1 (Mild)	Localized urticaria, mild itching, sneezing, rhinorrhea	Oral antihistamine, observation
2 (Moderate)	Generalized urticaria, angioedema (lips/eyes), nausea/cramping, wheezing	Oral/injectable antihistamine, consider epinephrine
3 (Severe/anaphylaxis)	Respiratory compromise, hypotension, dysphagia, hoarseness, dizziness, collapse	Epinephrine IM immediately, call 911
4 (Life-threatening)	Respiratory arrest, cardiac arrest, severe hypotension unresponsive to epinephrine	Aggressive resuscitation, epinephrine, IV fluids, airway management

Anaphylaxis Diagnosis

Clinical Criteria (National Institute of Allergy and Infectious Disease)

Criteria	One of the following with acute onset (minutes to hours) after exposure
Skin/mucosal	Generalized urticaria, itching-flushing, swollen lips-tongue-uvula AND at least one of:
Respiratory	Dyspnea, wheezing, stridor, hypoxemia
OR Hypotension	Reduced BP or associated symptoms (syncope, hypotonia, incontinence)

OR two or more (after likely exposure)
Skin/mucosal	Generalized urticaria, itching, flushing, swelling
Respiratory	Dyspnea, wheeze, stridor, hypoxemia
Cardiovascular	Hypotension, syncope, collapse
Gastrointestinal	Nausea, vomiting, cramping, diarrhea
OR Hypotension after known allergen	Isolated hypotension

ABC Assessment in Anaphylaxis

System	Assessment	Findings
Airway	Listen for stridor, hoarseness, dysphagia, drooling	Upper airway angioedema (laryngeal edema) - most feared
Breathing	Listen for wheezing, tachypnea, hypoxia, accessory muscle use	Bronchoconstriction, respiratory distress
Circulation	Check pulse, blood pressure, skin color	Hypotension, tachycardia, shock, cardiac arrest
Disability	Assess mental status, dizziness, lightheadedness	Cerebral hypoperfusion, impending collapse
Exposure	Full skin examination	Generalized urticaria, flushing, angioedema

Epinephrine (Adrenaline) Administration

Mechanism of Action

Receptor	Location	Effect	Clinical Benefit
Alpha-1	Vascular smooth muscle	Vasoconstriction	Reverses hypotension, angioedema
Beta-1	Heart	Increased heart rate, contractility	Improves cardiac output
Beta-2	Bronchial smooth muscle	Bronchodilation	Reverses wheezing, dyspnea
Beta-2	Mast cells	Inhibits mediator release	Halts progression

Epinephrine Auto-Injectors

Device	Dose (Adult)	Dose (Child)	Needle length
EpiPen	0.3 mg (1:1000, 0.3 mL)	0.15 mg (1:2000, 0.15 mL) for 15-30 kg	Standard
Auvi-Q	0.3 mg	0.15 mg for 15-30 kg; 0.1 mg for 7.5-15 kg	Shorter (audio-guided)
Adrenaclick	0.3 mg	0.15 mg	Standard
Symjepi	0.3 mg	0.15 mg	Pre-filled syringe

Administration Technique

Step	Instruction
1	Remove auto-injector from case
2	Form fist around device (do not touch needle end)
3	Remove safety cap (blue/safety release)
4	Place orange/red tip against outer mid-thigh (can inject through clothing)
5	Swing and push firmly until click heard/felt
6	Hold for 3 seconds
7	Remove and massage injection site for 10 seconds
8	Note time of administration
9	Call 911 (tell them epinephrine was given)
10	Prepare for second dose if no response in 5-15 minutes

Why Intramuscular (IM) in the Thigh

Route	Advantage	Disadvantage
IM thigh (vastus lateralis)	Rapid absorption, highest peak concentration	Pain at injection site
IM deltoid	Acceptable alternative	Lower peak concentration
Subcutaneous	Too slow in anaphylaxis	Delayed absorption, lower blood levels
Intravenous	Rapid onset	Risk of arrhythmia, hypertension (only in ICU setting)
Endotracheal	Alternative if no IV access	Erratic absorption

Epinephrine Dosing

Weight	Dose	Auto-Injector
>30 kg (adult/child)	0.3 mg IM	Adult auto-injector
15-30 kg (child)	0.15 mg IM	Junior auto-injector
7.5-15 kg (infant/toddler)	0.1 mg IM	0.1 mg device or drawn manually from ampule
<7.5 kg (infant)	0.01 mg/kg IM	Draw up manually (1:1000 solution)

Side Effects of Epinephrine

Side Effect	Mechanism	Significance
Palpitations	Beta-1 effect	Self-limited, resolves rapidly
Tremor	Beta-2 effect	Transient
Anxiety/fear	CNS effect	May mimic anaphylaxis progression
Headache	Vasoconstriction + increased BP	Transient
Hypertension	Alpha-1 effect	Usually brief
Tachyarrhythmia	Beta-1 effect	Rare in patients without underlying heart disease
Myocardial ischemia	Increased demand + vasoconstriction	Rare; risk-benefit favors epinephrine in anaphylaxis

Epinephrine is NOT Contraindicated in Anaphylaxis

Myth	Reality
Epinephrine is dangerous in elderly/hypertensive	Risk of anaphylaxis death far exceeds risk of epinephrine side effects
Epinephrine should be saved for severe reactions	Early epinephrine improves outcome even in moderate reactions
Antihistamines are equivalent	Antihistamines do NOT reverse airway obstruction or hypotension
Wait to see if symptoms worsen	Anaphylaxis can progress rapidly; treat immediately

Antihistamines

H1 Antihistamines

Drug	Onset	Duration	Route	Indication
Diphenhydramine (Benadryl)	15-30 min	4-6 hours	PO, IM, IV	Urticaria, pruritus
Cetirizine (Zyrtec)	1 hour	24 hours	PO	Mild-moderate allergic symptoms
Loratadine (Claritin)	1-3 hours	24 hours	PO	Mild allergic symptoms
Fexofenadine (Allegra)	1-3 hours	24 hours	PO	Mild allergic symptoms

H2 Antihistamines

Drug	Mechanism	Use in Anaphylaxis
Famotidine (Pepcid)	Blocks H2 receptors on gastric mucosa and blood vessels	May be used as adjunct to H1 blocker and epinephrine
Ranitidine (Zantac)	Same as famotidine	Off market in US (NDMA contamination)

Role of Antihistamines in Anaphylaxis

Aspect	Role
Effectiveness for anaphylaxis	Treats only histamine-mediated symptoms (urticaria, flushing)
Does NOT treat	Airway edema, bronchoconstriction, hypotension, shock
Onset	Too slow for acute management
Recommendation	Adjunct ONLY after epinephrine; epinephrine is first-line

Biphasic Anaphylaxis

Feature	Description
Definition	Recurrence of anaphylaxis symptoms after initial resolution WITHOUT re-exposure to trigger
Incidence	1-20% of anaphylaxis cases
Onset	Typically 1-8 hours after initial reaction (can be up to 72 hours)
Duration of second phase	Usually shorter than first
Severity	Can be equal to or more severe than initial reaction
Risk factors	Severe initial reaction, delayed epinephrine, need for >1 epinephrine dose, unknown trigger, hypotension, food allergy

Biphasic Reaction Management

Aspect	Recommendation
Observation period	4-8 hours after symptom resolution for most patients
High-risk observation	12-24 hours for patients with severe reactions, multiple epinephrine doses, or significant comorbidities
Discharge	Prescribe epinephrine auto-injectors; provide action plan
Follow-up	Allergy specialist evaluation within 2-4 weeks

Secondary Medications for Anaphylaxis

Glucocorticoids

Drug	Dose	Onset	Rationale
Methylprednisolone	1-2 mg/kg IV/IM (max 125 mg)	4-6 hours	May prevent biphasic reaction (controversial)
Prednisone	40-60 mg PO	4-6 hours	Oral alternative for after stabilization
Dexamethasone	0.3-0.6 mg/kg IV/IM	4-6 hours	Alternative

Beta-Agonists

Drug	Dose	Indication
Albuterol (salbutamol)	2.5-5 mg nebulized or 2-4 puffs MDI	Wheezing, bronchospasm (NOT first-line; epinephrine is)
Continuous nebulized albuterol	10 mg/hour	Refractory bronchospasm

IV Fluids

Fluid	Initial Bolus	Indication
Normal saline (0.9% NaCl)	20 mL/kg (adults 1-2 L)	Hypotension, shock, capillary leak
Lactated Ringer’s	Same as NS	Alternative if NS unavailable
Repeat	As needed based on response	Titrate to blood pressure and perfusion

Vasopressors

Agent	Indication
Epinephrine infusion (IV drip)	Refractory hypotension despite IM epinephrine and IV fluids
Dopamine	Alternative vasopressor if epinephrine drip unavailable
Vasopressin	Third-line for refractory shock

Glucagon for Beta-Blocked Patients

Aspect	Details
Indication	Anaphylaxis in patient taking beta-blockers (epinephrine may be less effective)
Dose	1-5 mg IV/IM (adults); 20-50 mcg/kg (children)
Mechanism	Bypasses blocked beta-receptors; increases heart rate and blood pressure
Repeat	Can be given every 5-10 minutes as needed
Side effects	Nausea, vomiting, hyperglycemia

Allergy Action Plans

Components of an Action Plan

Component	Description
Patient identification	Name, date of birth, photo (for children)
Known allergens	List of confirmed triggers
Mild reaction instructions	Oral antihistamine, monitor
Moderate reaction instructions	Oral antihistamine, consider epinephrine, call physician
Severe reaction instructions	Immediate epinephrine, call 911, second dose if needed
Emergency contacts	Physician, local ED, family contacts
Medication list	Epinephrine auto-injectors, antihistamines, expiration dates
Activation instructions	When to call ambulance (any respiratory or cardiovascular symptom)
School/work orders	Permission for others to administer epinephrine
Follow-up plan	Schedule allergy specialist appointment

Prevention and Long-Term Management

Allergen Avoidance

Allergen	Avoidance Strategy
Food	Read labels carefully, ask about ingredients when eating out, beware of cross-contamination
Insect stings	Avoid floral areas, perfumes, bright colors in warm months; wear closed shoes
Latex	Use non-latex gloves, inform healthcare providers
Medications	Maintain list of allergies, wear medical alert bracelet

Immunotherapy

Type	Method	Duration	Indication
Subcutaneous immunotherapy (SCIT)	Weekly injections of allergen extract, then monthly	3-5 years	Stinging insect venom, environmental allergens
Sublingual immunotherapy (SLIT)	Daily tablets under tongue	3-5 years	Grass pollen, ragweed, house dust mites
Oral immunotherapy (OIT)	Daily ingestion of food allergen	Ongoing	Peanut (FDA-approved for children 4-17)

Medical Alert Identification

Item	Use
Medical alert bracelet	Engraved with allergies, carries epinephrine
Wallet card	Detailed medical history, medications
Smartphone medical ID	Emergency access without unlocking
School/work emergency forms	Action plans, medication authorization

Special Populations

Children

Aspect	Consideration
Epinephrine dosing	Weight-based: 0.01 mg/kg IM
Auto-injector availability	Age-appropriate doses (0.1 mg, 0.15 mg, 0.3 mg)
School training	Train school nurse and staff in epinephrine administration
Growth monitoring	Re-evaluate auto-injector dose as child grows
Outgrowing allergies	Many children outgrow milk, egg, soy, wheat allergies

Elderly

Aspect	Consideration
Comorbidities	Cardiovascular disease may make reaction more dangerous
Medications	Beta-blockers, ACE inhibitors may complicate treatment
Frailty	Falls risk during syncope
Medication interactions	Multiple medications may interact with epinephrine

Pregnancy

Aspect	Consideration
Fetal risk	Anaphylaxis causes maternal hypotension -> fetal hypoxia
Epinephrine	Use is indicated (no absolute contraindication)
Positioning	Left lateral position to maintain uterine perfusion
IV fluids	Aggressive fluid resuscitation

Summary: Anaphylaxis Management Algorithm

Time	Action
Immediate	Assess ABCs, remove trigger if possible
0-1 minute	Administer epinephrine IM in thigh
1-5 minutes	Call 911, position patient supine with legs elevated
5-15 minutes	Repeat epinephrine if no improvement
0+ minutes	Give antihistamine as adjunct
5+ minutes	Give corticosteroids (controversial for acute phase)
15+ minutes	Nebulized albuterol for refractory wheezing
Any time	IV fluids if hypotension present
Ongoing	Monitor for biphasic reaction
Discharge	Prescribe epinephrine auto-injectors, action plan, allergy follow-up