What are the symptoms and treatment of anaphylaxis?

Anaphylaxis: Symptoms and Treatment

Anaphylaxis is a life-threatening systemic allergic reaction with sudden onset (minutes to hours) that requires immediate intramuscular epinephrine administration—the only first-line, life-saving treatment—and should never be delayed when anaphylaxis is suspected. 1, 2

Clinical Recognition: Multi-System Involvement

Anaphylaxis typically involves two or more organ systems simultaneously, though rapidly progressive reactions may present with isolated cardiovascular collapse before cutaneous manifestations appear. 1, 2

Cutaneous Manifestations (Most Common)

• Skin and mucosa: Generalized urticaria, itching, flushing, hives, swelling of lips/tongue/uvula, diffuse erythema 1
• Conjunctivae: Itching, swelling, redness 1
• Critical caveat: Cutaneous signs may be delayed or completely absent in rapidly progressive anaphylaxis with cardiovascular collapse 2

Respiratory Symptoms

• Upper airway: Hoarseness, throat itching/tightness, stridor, laryngeal edema 1
• Lower airway: Dyspnea, wheeze, bronchospasm, chest tightness, cough, cyanosis, hypoxemia 1

Cardiovascular Manifestations (Most Dangerous)

• Tachycardia, hypotension, weak/thready pulse, chest pain 1
• Dizziness, syncope, collapse, incontinence, shock 1
• Hallmark pathophysiology: Up to 50% of intravascular fluid can shift to extravascular space within 10 minutes, causing distributive shock 2, 3

Gastrointestinal Symptoms

• Nausea, crampy abdominal pain, persistent vomiting, diarrhea 1

Neurological Signs

• Sense of impending doom, headache, altered mental status, confusion, tunnel vision 1
• Behavioral changes in infants 1

Diagnostic Criteria: When to Diagnose Anaphylaxis

Anaphylaxis is highly likely when ANY ONE of these three criteria is met: 1

1. Acute onset with skin/mucosal involvement PLUS either respiratory compromise OR reduced blood pressure/end-organ dysfunction 1

2. Two or more systems involved after allergen exposure: (a) skin/mucosal tissue, (b) respiratory compromise, (c) reduced blood pressure/associated symptoms, OR (d) persistent GI symptoms 1

3. Reduced blood pressure alone after exposure to a known allergen for that patient 1

Critical principle: The more rapidly anaphylaxis develops after exposure, the more likely it is severe and life-threatening. 2

Immediate Treatment Algorithm

Step 1: Recognize and Act Immediately

• Epinephrine is the ONLY first-line medication and must not be delayed 1, 2, 4
• When in doubt, it is better to give epinephrine—delayed administration increases risk of death and hypoxic-ischemic encephalopathy 1, 2

Step 2: Epinephrine Administration

• Route: Intramuscular injection in the mid-outer thigh (vastus lateralis muscle) 1
• Dose:
  • Adults: 0.3-0.5 mg (0.3-0.5 mL of 1:1000 solution) 1, 3
  • Children: 0.01 mg/kg, maximum 0.3 mg prepubertal, up to 0.5 mg in teenagers 1, 2
• Autoinjector doses: 0.15 mg for young children, 0.3 mg for older children/adults 1

Step 3: Repeat Dosing if Needed

• Repeat epinephrine every 5-15 minutes as necessary to control symptoms 1
• Approximately 6-19% of pediatric patients require a second dose 1
• If no response and EMS arrival exceeds 5-10 minutes, repeat dose should be considered 1

Step 4: Positioning and Support

• Place patient supine (on back) with legs elevated, unless respiratory distress or vomiting present 1
• Never allow standing, walking, or running—sudden position changes can precipitate cardiovascular collapse 1

Step 5: Activate Emergency Response

• Call 911/EMS immediately in community settings or resuscitation team in healthcare settings 1
• Transport to emergency department, preferably by EMS vehicle, for monitoring and additional treatment 1

Additional Supportive Measures

Secondary Medications (Never Replace Epinephrine)

• H1-antihistamines: Valuable for mild reactions but should never delay epinephrine 5
• Glucocorticoids: May prevent biphasic reactions but have minimal acute benefit 6, 5
• Volume resuscitation: Crystalloids initially, colloids for severe shock 5
• Inhaled beta-2 agonists: For persistent bronchospasm 5
• Supplemental oxygen and IV fluids as needed 1

Observation Period

• Monitor for 4-10 hours depending on severity, as biphasic reactions occur in 1-7% of cases 6, 5

Common Triggers

Pediatric Population

• Foods (most common): Peanuts, tree nuts, milk, eggs, shellfish, fish 1
• Insect stings (Hymenoptera venom) 1, 3
• Medications, especially antibiotics 1
• Vaccines rarely trigger anaphylaxis 1

Critical Pitfalls to Avoid

Diagnostic Errors

• Vasovagal reaction mimicry: Unlike anaphylaxis, vasovagal reactions have bradycardia (not tachycardia), no urticaria, cool/pale skin, and normal/elevated blood pressure 1
• Missing anaphylaxis without skin findings: Rapidly progressive reactions may present with isolated cardiovascular collapse 2
• Other mimics include acute asthma, panic attacks, myocardial infarction, pulmonary embolism 1, 7, 8

Treatment Errors

• Delaying epinephrine while giving antihistamines or steroids first—this is the most common fatal error 1, 2
• Using subcutaneous instead of intramuscular route (IM provides faster absorption) 1
• Administering epinephrine in the arm instead of thigh (thigh provides higher plasma levels) 1
• Allowing patient to stand or walk (can precipitate fatal cardiovascular collapse) 1

High-Risk Patients Requiring Extra Vigilance

• Adolescents with concomitant severe or poorly controlled asthma 1
• Patients on beta-blockers (may blunt response to epinephrine and mask early signs) 7, 5
• Patients on ACE inhibitors (may worsen angioedema) 7

Post-Acute Management Essentials

All patients require: 2

• Prescription for epinephrine autoinjector with training on use 2
• Referral to allergist-immunologist for trigger identification 2
• Education on anaphylaxis recognition and emergency action plan 2
• Trigger avoidance counseling 2