Overview: Allergic & Anaphylactic Reactions
Allergies are immune reactions to foreign substances. Most are minor (itching, hives), but some can rapidly become life-threatening. This lesson covers the spectrum from localized allergies to anaphylactic shock requiring immediate epinephrine injection.
Critical: Anaphylaxis is a medical emergency. Epinephrine MUST be given immediately — it's the first-line treatment, not a last resort.
Key Points
Anaphylaxis is a severe, rapid-onset allergic reaction affecting multiple body systems
Epinephrine is the FIRST-line treatment for anaphylaxis, not diphenhydramine (Benadryl)
Common wilderness triggers: bee/wasp/fire ant stings, food allergies, medications
Biphasic anaphylaxis: most second waves occur within the first hours, but recurrence is possible up to 72 hours later; all anaphylaxis requires evacuation
Time is critical: symptoms develop in minutes; treatment is lifesaving
Allergic Reaction Spectrum
Immune Mechanism
- IgE-mediated: Immunoglobulin E antibodies bind to mast cells. When allergen exposure occurs, mast cells degranulate (break open), releasing histamine and other mediators.
- Histamine effects:
- Causes blood vessel leakage (edema/swelling)
- Increases vascular permeability
- Causes bronchoconstriction (airway narrowing)
- Causes vasodilation (blood vessel widening)
- Triggers itch and hives
Mild (Localized) Allergic Reaction
- Signs: Skin-only symptoms at or near the site of sting/contact — hives (urticaria), itching, mild erythema (redness). No symptoms anywhere else in the body.
- Example: Mosquito bite that itches and causes small raised bump
- Treatment:
- Diphenhydramine (Benadryl) 25-50mg orally
- Hydrocortisone cream topically for itch
- Ice/cool compress
- Monitoring: Watch closely for at least 30 minutes, and keep rechecking — be alert for any spread beyond the site or new symptoms in other body systems (progression means anaphylaxis)
More Than Skin-Only = Anaphylaxis
- Treat as ANAPHYLAXIS if ANY of the following after likely allergen exposure:
- Any lower-airway involvement — wheezing, chest or throat tightness, difficulty breathing
- Signs in 2 or more body systems (e.g., hives PLUS nausea or swelling of lips/tongue/face)
- Any cardiovascular sign — dizziness, faintness, weak pulse, collapse
- Treatment:
- Epinephrine IMMEDIATELY — do not wait to see if it gets worse
- Antihistamines (diphenhydramine 25-50mg) only AFTER epinephrine, as an adjunct for skin symptoms — they do not treat anaphylaxis
Severe (Anaphylaxis)
Definition: Severe, rapid-onset allergic reaction involving ≥2 body systems OR a single life-threatening reaction
- Criteria for anaphylaxis:
- Skin involvement (hives/flushing) PLUS respiratory symptoms (wheezing, stridor, dyspnea) OR cardiovascular symptoms (hypotension, dizziness, syncope)
- OR: Respiratory OR cardiovascular symptoms alone if known allergen exposure
- THIS IS A MEDICAL EMERGENCY
Anaphylaxis Recognition
Signs & Symptoms
- Skin: Urticaria (hives) throughout body, flushing, pruritus (intense itching)
- Respiratory:
- Bronchospasm: wheezing, shortness of breath, chest tightness
- Upper airway edema: stridor (high-pitched breathing), voice changes, difficulty swallowing
- Dyspnea (shortness of breath)
- Cardiovascular:
- Hypotension (low blood pressure): dizziness, syncope (fainting), shock
- Tachycardia (rapid heart rate)
- Chest pain or palpitations
- GI: Nausea, vomiting, cramping, diarrhea
- Neurologic: Anxiety, confusion, sense of impending doom
Time Course
- Onset: Usually within MINUTES (up to 1 hour) of allergen exposure
- Faster onset = more severe reaction
- Symptoms within 5 min = severe, life-threatening
- Symptoms 15-30 min = more time to intervene
- Why speed matters: Rapid swelling of airway can obstruct breathing. Shock develops quickly. This is URGENT.
Common Triggers in Wilderness
- Insect stings (MOST COMMON):
- Hymenoptera (bees, wasps, hornets)
- Fire ants
- Anaphylaxis risk: ~1% of sting victims
- Food: Peanuts, tree nuts, shellfish, eggs, milk
- Medications: Penicillin, NSAIDs, aspirin
- Latex: From gloves, equipment
- Venom: Snake venom (rare)
Biphasic Anaphylaxis
- What: Second wave of anaphylactic symptoms after the initial reaction resolves — most occur within the first hours, but recurrence is possible up to 72 hours later
- Frequency: 5-20% of anaphylaxis cases
- Why: More mast cells degranulating or continued allergen effect
- Clinical importance: ALL anaphylaxis patients MUST be evacuated and monitored in hospital. Can't predict who will have biphasic reaction.
EpiPen (Epinephrine Auto-Injector) Administration
As a wilderness first aider, your role is to help a patient use their OWN prescribed epinephrine auto-injector — the device and prescription belong to them, and you are assisting them with their own medication. Many states also protect trained laypersons who give epinephrine in an emergency; know the rules where you live and travel.
Epinephrine Mechanism
- Alpha-1 effects: Vasoconstriction (raises blood pressure, reverses shock)
- Beta-1 effects: Increased heart rate and contractility (improves cardiac output)
- Beta-2 effects: Bronchodilation (opens airways, reverses bronchospasm)
- Net result: Reverses the cardinal signs of anaphylaxis (hypotension, bronchospasm, angioedema)
EpiPen Dosing
- Adult auto-injector: 0.3 mg
- EpiPen Jr (pediatric): 0.15 mg, for children approximately 15-30 kg (33-66 lbs)
- Smaller children <15 kg: 0.15 mg or specialty pediatric dosing
Injection Technique
- Site: Lateral mid-thigh (outer aspect of thigh, halfway between hip and knee)
- Advantage of thigh: Good muscle mass for absorption, easily accessible (even through pants if necessary), far from vital structures
- Steps:
- Remove blue safety release cap (at top)
- Hold auto-injector firmly with orange tip (needle) pointing DOWN
- Swing and push orange tip firmly against lateral thigh at 90° angle (straight into thigh)
- HOLD in place for 3 seconds (per current auto-injector labeling)
- Remove the injector — massaging the injection site is no longer recommended
- Can inject through clothing: Denim/fabric won't block needle
Practice: Know how to use your EpiPen before you need it. Carry trainer (practice) auto-injector on trips to review technique.
Onset & Duration
- Onset: 5-15 minutes
- Duration: 20-30 minutes
- Can repeat: EpiPen can be given every 5-15 minutes if no improvement or symptoms recur
- Carry multiple: Persons with known anaphylaxis risk should carry ≥2 EpiPens
Side Effects
- Palpitations (feeling heart beating forcefully)
- Tremor, shakiness
- Headache, anxiety
- These are expected and temporary. Far better than death from anaphylaxis.
Anaphylaxis Field Management
Treatment Priority: Epinephrine FIRST
CRITICAL: Give epinephrine BEFORE diphenhydramine (Benadryl). Epinephrine is first-line. Do not delay for other medications.
- Immediate: Epinephrine IM (intramuscular in thigh)
- Then follow with:
- Oral diphenhydramine 25-50mg for skin symptoms
- Help the patient use their own inhaler for persistent wheeze — after epinephrine, never instead of it
Patient Positioning
- Respiratory distress: Sitting upright (easier breathing)
- Hypotension/shock: Supine (flat); raising the legs may help if breathing is not impaired (anaphylaxis-specific guidance — blood pools when the patient stands)
- Nausea/vomiting risk: Recovery position (on side) if unconscious
- NEVER stand or sit the patient up abruptly — sudden position changes can cause fatal collapse in anaphylaxis
Complete Field Management
- Recognize anaphylaxis — don't wait for "confirmation"
- Give epinephrine IM immediately (0.3 mg adult, 0.15 mg child)
- Position patient (upright if respiratory distress, supine if shock)
- Give supplemental oxygen if available
- Follow with diphenhydramine for skin symptoms
- Monitor vital signs and airway continuously
- URGENT EVACUATION — all anaphylaxis requires hospital evaluation
Biphasic Reaction Monitoring
- Even if patient improves dramatically after epinephrine, symptoms can recur — most often within the first hours, but possibly up to 72 hours later
- NO field observation is adequate — hospital monitoring required
- Patient must be evacuated even if feeling well
What NOT to Do
- DO NOT: Give oral fluids if airway swelling (aspiration risk)
- DO NOT: Use only antihistamines thinking it will stop anaphylaxis (it won't)
- DO NOT: Delay evacuation if patient "feels better" after epinephrine
- DO NOT: Refuse epinephrine due to side effects (dying is worse)
Case Scenarios
Scenario 1: Bee Sting with Anaphylaxis on Trail
Setting: A hiker is stung by multiple bees while hiking. Within 5 minutes, develops rapid wheezing, hives spreading across body, and swelling of lips. She's becoming anxious and short of breath. You have her EpiPen in the group first aid kit.
Recognition: Anaphylaxis — stung, rapid onset of respiratory (wheezing) + skin (hives) involvement. This is ANAPHYLAXIS.
Immediate Actions:
- Get EpiPen from first aid kit
- Remove blue cap, position with orange tip toward thigh
- Inject IM into lateral thigh (can go through pants)
- Hold 3 seconds, then remove
- Position upright (respiratory distress)
- Monitor airway — if swelling worsens, be ready to manage airway
Follow-up:
- Give diphenhydramine if available (for skin symptoms, after epinephrine)
- Help her use her own inhaler if wheezing continues — after epinephrine, never instead of it
- URGENT evacuation — activate emergency services
- Watch for biphasic reaction during evacuation
Scenario 2: Unknown Food Allergen at Camp
Setting: A backpacker accidentally eats trail mix containing peanuts (known allergy) shared by groupmate. 15 minutes later, throat feels tight, she's dizzy, and breaking out in hives. She has an EpiPen but says "Maybe I'm overreacting."
Recognition: Anaphylaxis — known allergen exposure, throat tightness (airway involvement), dizziness (cardiovascular), hives (skin). Signs meeting anaphylaxis criteria.
Key point: Don't hesitate due to patient minimizing symptoms. Rapid progression is likely.
Management:
- Get EpiPen immediately, do NOT delay
- Inject into thigh
- Position supine (flat) — legs may be raised if breathing is not impaired; never let the patient stand or sit up abruptly
- Oral diphenhydramine after epinephrine (adjunct for skin symptoms only)
- Prepare for helicopter evacuation (dizziness suggests cardiovascular involvement)
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Lesson Summary
Key Concepts
Anaphylaxis is severe allergic reaction affecting multiple body systems; life-threatening emergency
Epinephrine is FIRST-line treatment; give immediately IM to lateral thigh
EpiPen adult = 0.3 mg, pediatric = 0.15 mg
Common triggers: bee/wasp stings, food allergies, medications
Rapid onset (minutes) = emergency; speed of epinephrine delivery is critical
Biphasic reaction: most occur within the first hours, but possible up to 72 hours later; always evacuate
Position patient: upright if respiratory distress, supine if shock