Key Takeaways
- Anaphylaxis is a severe, life-threatening allergic reaction involving multiple organ systems
- Epinephrine auto-injector dose: adult 0.3 mg, pediatric (under 30 kg / ~66 lbs) 0.15 mg
- Epinephrine is administered via auto-injector into the lateral (outer) thigh -- can be given through clothing
- Classic anaphylaxis triad: urticaria (hives), bronchospasm (wheezing/stridor), and hypotension (shock)
- Biphasic reactions can occur 4-12 hours after initial reaction -- patients need hospital monitoring
- Most common fatal food allergens: peanuts, tree nuts, and shellfish
- EMTs can assist with a patient's prescribed auto-injector or administer one per local protocol
Allergic Reactions & Anaphylaxis
Allergic reactions occur when the immune system overreacts to a foreign substance (allergen). While most allergic reactions are mild and self-limiting, anaphylaxis is a rapidly progressive, life-threatening emergency that demands immediate intervention.
Mild vs. Severe Allergic Reactions
| Feature | Mild Reaction | Severe Reaction (Anaphylaxis) |
|---|---|---|
| Skin | Localized hives, itching, redness | Widespread urticaria, flushing, angioedema |
| Respiratory | None or mild nasal congestion | Wheezing, stridor, throat tightness, dyspnea |
| Cardiovascular | Normal vital signs | Tachycardia, hypotension, weak pulse |
| GI | Mild nausea | Nausea, vomiting, abdominal cramping, diarrhea |
| Neurological | Alert and oriented | Anxiety, altered mental status, loss of consciousness |
| Onset | Minutes to hours | Usually rapid (within minutes) |
Anaphylaxis
Anaphylaxis involves two or more body systems and can progress to death within minutes if untreated. It is mediated by massive histamine release from mast cells and basophils.
Pathophysiology
- Vasodilation -- blood vessels dilate, causing hypotension
- Increased capillary permeability -- fluid leaks into tissues (edema, angioedema)
- Bronchospasm -- smooth muscle constriction in airways
- Increased mucus production -- further airway compromise
Signs and Symptoms of Anaphylaxis
- Skin: Urticaria (hives), flushing, angioedema (swelling of face, lips, tongue, throat)
- Respiratory: Wheezing, stridor, hoarseness, dyspnea, throat tightness
- Cardiovascular: Tachycardia, hypotension, weak/thready pulse, dizziness
- GI: Nausea, vomiting, abdominal pain, diarrhea
- Neurological: Anxiety, altered mental status, sense of impending doom
Common Allergens
- Foods: Peanuts, tree nuts, shellfish, fish, milk, eggs, soy, wheat
- Insect stings: Bees, wasps, hornets, fire ants
- Medications: Antibiotics (penicillin), NSAIDs, aspirin
- Other: Latex, contrast dye, exercise-induced
Epinephrine Auto-Injector
Epinephrine is the first-line and ONLY definitive treatment for anaphylaxis. It works by:
- Bronchodilation -- relaxes smooth muscle in airways
- Vasoconstriction -- increases blood pressure
- Reduces edema -- decreases capillary permeability
- Increases heart rate and contractility -- improves cardiac output
Dosing
| Patient | Dose | Auto-Injector Color |
|---|---|---|
| Adult (>30 kg / ~66 lbs) | 0.3 mg (1:1,000) | Yellow or orange |
| Pediatric (<30 kg / ~66 lbs) | 0.15 mg (1:1,000) | Green or teal |
Administration Steps
- Confirm signs/symptoms of anaphylaxis
- Obtain order from medical control (or follow standing orders/protocol)
- Remove safety cap from auto-injector
- Place tip firmly against lateral (outer) mid-thigh
- Can be administered through clothing -- do not delay to remove pants
- Press firmly until click is heard -- hold for 10 seconds
- Remove and massage injection site for 10 seconds
- Record the time of administration
- Reassess patient -- a second dose may be needed in 5-15 minutes if no improvement
Side Effects of Epinephrine
- Tachycardia, palpitations
- Anxiety, tremors
- Headache
- Nausea
- Pale skin (from vasoconstriction)
- These are expected and generally well-tolerated -- they are NOT reasons to withhold epinephrine in anaphylaxis
Biphasic Reactions
- Anaphylaxis symptoms can return 4-12 hours after initial resolution
- Occurs in approximately 20% of anaphylaxis cases
- This is why all anaphylaxis patients must be transported to the hospital for monitoring
- Second reaction may be more severe than the first
EMT Treatment for Anaphylaxis
- Remove the patient from the allergen source if safe to do so
- Maintain airway -- prepare for potential need for BVM ventilation
- Administer epinephrine auto-injector (assist with patient's own or per protocol)
- Administer high-flow oxygen (15 L/min via NRB)
- If signs of shock: lay patient supine with legs elevated (unless dyspnea prevents this)
- Monitor vitals continuously
- Rapid transport
- Be prepared to administer a second dose of epinephrine
The correct dose of epinephrine via auto-injector for an adult patient experiencing anaphylaxis is:
Where should an epinephrine auto-injector be administered?
A patient was stung by a bee 30 minutes ago and now has widespread hives, wheezing, and a blood pressure of 82/50. This presentation is BEST described as:
A biphasic anaphylactic reaction refers to:
Which of the following is TRUE regarding epinephrine administration for anaphylaxis?
A 10-year-old child weighing 25 kg is experiencing anaphylaxis after eating peanuts. What epinephrine auto-injector dose should be used?
After administering epinephrine to an anaphylaxis patient, the patient develops tachycardia, tremors, and anxiety. The EMT should:
Which mechanism of action makes epinephrine effective in treating anaphylaxis?
Which of the following are signs of anaphylaxis that would require epinephrine administration? (Select all that apply)
Select all that apply
The adult epinephrine auto-injector dose for anaphylaxis is ___ mg.
Type your answer below