Understanding Anaphylaxis
Anaphylaxis is a severe, potentially life-threatening allergic reaction that affects multiple body systems simultaneously. It develops rapidly, often within minutes of allergen exposure, and requires immediate treatment with epinephrine. The NREMT tests your ability to recognize anaphylaxis, differentiate it from mild allergic reactions, and administer appropriate treatment.
Pathophysiology
In anaphylaxis, the immune system overreacts to an allergen by releasing massive amounts of histamine and other chemical mediators from mast cells and basophils. These chemicals cause:
- Vasodilation: Blood vessels dilate, causing hypotension (distributive shock)
- Increased capillary permeability: Fluid leaks from blood vessels into tissues, causing edema
- Bronchoconstriction: Airway smooth muscle contracts, causing wheezing and dyspnea
- Upper airway edema: Swelling of the tongue, lips, and throat can cause airway obstruction
Signs and Symptoms
Skin: Urticaria (hives), flushing, angioedema (swelling of face, lips, tongue, throat), pruritus (itching)
Respiratory: Wheezing, stridor, dyspnea, hoarseness, sensation of throat closing, cough
Cardiovascular: Tachycardia, hypotension, dizziness, syncope, weak/thready pulse
GI: Nausea, vomiting, abdominal cramping, diarrhea
Neurological: Anxiety, altered mental status, feeling of impending doom
Mild Allergic Reaction vs. Anaphylaxis
A mild allergic reaction involves only the skin (hives, itching, mild swelling) without respiratory or cardiovascular compromise. These patients should be monitored closely because mild reactions can progress to anaphylaxis.
Anaphylaxis involves TWO or more body systems (skin + respiratory, skin + cardiovascular, respiratory + cardiovascular) OR isolated severe respiratory or cardiovascular compromise after known allergen exposure. Any respiratory distress or hypotension after allergen exposure should be treated as anaphylaxis.
EMT Treatment
- Remove the allergen if possible (remove stinger by scraping, stop IV medication)
- Epinephrine auto-injector: Administer 0.3 mg IM (adult) or 0.15 mg IM (pediatric under 66 lbs) in the lateral thigh. This is the ONLY definitive treatment for anaphylaxis at the EMT level. Do not delay epinephrine for any other intervention.
- Oxygen: High-flow via non-rebreather mask
- Position: Supine with legs elevated if hypotensive (to improve venous return). Sitting upright if in respiratory distress. If both, find a compromise position.
- Monitor: Reassess vitals every 5 minutes. Be prepared for a second dose of epinephrine if symptoms recur (biphasic anaphylaxis)
- Transport: Rapid transport to the emergency department
Common Allergens
Most common triggers for anaphylaxis: insect stings (bees, wasps, hornets), foods (peanuts, tree nuts, shellfish, milk, eggs), medications (penicillin, NSAIDs, sulfa drugs), and latex. However, any substance can potentially cause anaphylaxis, and some cases have no identifiable trigger (idiopathic anaphylaxis).
Key NREMT Points
- Epinephrine has NO absolute contraindications in anaphylaxis. Always give it.
- The most common cause of death from anaphylaxis is delayed epinephrine administration
- Biphasic reactions can occur 4 to 12 hours after the initial reaction, which is why hospital observation is important
- Patients with known allergies should carry two epinephrine auto-injectors