How should anaphylactic shock be managed, including intramuscular epinephrine dosing for adults and children, adjunctive medications, fluid resuscitation, airway management, and observation?

Anaphylactic Shock Management

Immediately administer intramuscular epinephrine 0.3-0.5 mg (1:1000) for adults or 0.01 mg/kg (maximum 0.3 mg) for children into the anterolateral thigh, and repeat every 5-15 minutes as needed—this is the only first-line treatment that prevents death from anaphylaxis. 1, 2

Immediate Initial Management

Epinephrine Administration (First-Line Treatment)

• Adults and children ≥30 kg: Administer 0.3-0.5 mg (0.3-0.5 mL of 1:1000 solution) intramuscularly into the anterolateral thigh 1, 2
• Children <30 kg: Administer 0.01 mg/kg (maximum 0.3 mg) intramuscularly into the anterolateral thigh 1, 2
• Repeat dosing: Every 5-15 minutes as needed for persistent or recurrent symptoms 1, 3
• Autoinjector dosing: 0.3 mg for adults/children >30 kg; 0.15 mg for children 15-30 kg 1

Critical Positioning and Monitoring

• Position patient supine with legs elevated unless respiratory distress prevents this—sudden standing or sitting can cause fatal cardiovascular collapse 3
• Establish close hemodynamic monitoring immediately, as cardiovascular and respiratory status can deteriorate rapidly 1
• Activate emergency medical services (EMS) immediately for all cases of anaphylaxis 1

Airway Management

• Immediately refer to a provider with advanced airway expertise given the potential for rapid oropharyngeal or laryngeal edema 1
• Prepare for emergency cricothyroidotomy or tracheostomy if airway obstruction develops, as standard intubation may be impossible 1
• Administer high-flow supplemental oxygen and monitor oxygen saturation continuously 3

Advanced Resuscitation for Severe Cases

Fluid Resuscitation

• Establish large-bore IV access immediately 3
• Administer 500-1000 mL crystalloid bolus for adults (20 mL/kg for children) rapidly 3
• Continue aggressive fluid resuscitation as hypotension often requires multiple liters 3

IV Epinephrine (For Refractory Shock)

When anaphylactic shock persists despite IM epinephrine and fluid resuscitation:

• IV bolus: 0.05-0.1 mg (50-100 mcg) of 1:10,000 solution administered slowly, repeated as needed 1, 4
• IV infusion: Start at 5-15 mcg/min and titrate to response for refractory or recurrent shock 1, 3
• Mandatory continuous cardiac monitoring during IV administration to detect arrhythmias 4
• Critical safety warning: Use only 1:10,000 concentration (0.1 mg/mL) for IV route—using 1:1000 concentration IV can cause fatal arrhythmias 4

Persistent Bronchospasm

• If bronchospasm is unresponsive to epinephrine, administer albuterol nebulization 2.5-5 mg in 3 mL saline 3

Adjunctive Medications (Second-Line Only)

These medications provide no acute benefit and should never delay or replace epinephrine 1, 3:

H1-Antihistamine

• Diphenhydramine 25-50 mg IV/IM for adults (1-2 mg/kg for children) 3, 4

H2-Antihistamine

• Ranitidine 50 mg IV for adults (1 mg/kg for children), or famotidine 20 mg IV if ranitidine unavailable 3, 4
• Combination H1 + H2 antagonists provide superior symptom control compared to H1 alone 3

Corticosteroids

• Methylprednisolone 1-2 mg/kg IV (typically 40 mg IV every 6 hours for adults) to potentially prevent biphasic or protracted reactions 3, 4
• Alternative: Hydrocortisone 100 mg IV 3
• Important caveat: Corticosteroids have no proven benefit in acute anaphylaxis or cardiac arrest from anaphylaxis 1

Special Situations

Cardiac Arrest from Anaphylaxis

• Perform standard BLS and ACLS with immediate epinephrine administration as the priority 1
• Administer high-dose epinephrine: 1-3 mg IV (1:10,000) over 3 minutes, then 3-5 mg over 3 minutes if needed 3
• No proven benefit from antihistamines, inhaled beta-agonists, or IV corticosteroids during cardiac arrest 1

Patients on Beta-Blockers (Refractory to Epinephrine)

If hypotension persists despite multiple epinephrine doses and adequate fluid resuscitation:

• Glucagon 1-5 mg IV over 5 minutes (20-30 mcg/kg for children, maximum 1 mg) 3, 4
• Follow with glucagon infusion 5-15 mcg/min 3, 4
• Rationale: Beta-blockers prevent epinephrine's cardiac effects; glucagon bypasses beta-receptors 3

Observation and Disposition

Observation Period

• Observe for minimum 4-6 hours after symptom resolution 3
• Extend observation for patients with:
  • Severe anaphylaxis requiring multiple epinephrine doses 3
  • Persistent airway symptoms 3
  • History of biphasic reactions 3
• Biphasic reactions occur in 7-18% of cases but are unpredictable and may occur outside typical observation windows 1, 5

Discharge Protocol

Every patient must receive:

• Two epinephrine autoinjectors with hands-on training in proper use 3
• Prednisone 1 mg/kg daily (maximum 60-80 mg) for 2-3 days 3
• H1-antihistamine for 2-3 days 3
• H2-antihistamine twice daily for 2-3 days 3
• Written anaphylaxis action plan 3
• Allergist referral within 1-2 weeks 3

Critical Pitfalls to Avoid

• Never delay epinephrine while administering antihistamines or corticosteroids—delays in epinephrine administration may be fatal 6, 7
• Never use 1:1000 epinephrine concentration IV—this causes life-threatening arrhythmias; only use 1:10,000 for IV route 4
• Never allow patients to stand or sit up suddenly during treatment—this can cause immediate cardiovascular collapse and death 8
• Never inject epinephrine into buttocks, digits, hands, or feet—this can cause tissue necrosis and serious infections 2
• Never discharge patients prematurely, especially those with airway involvement or requiring multiple epinephrine doses 3
• Never prescribe corticosteroids alone without epinephrine autoinjectors—epinephrine is the only medication that treats acute anaphylaxis 3