What is the initial management of anaphylactic shock?

Initial Management of Anaphylactic Shock

Immediately administer intramuscular epinephrine 0.3-0.5 mg (1:1000 concentration) into the anterolateral thigh for adults, or 0.01 mg/kg for children (maximum 0.5 mg), as this is the cornerstone of anaphylaxis treatment and the only first-line therapy that can be lifesaving. 1, 2, 3

Immediate First-Line Actions

Epinephrine Administration

• Inject epinephrine IM into the lateral aspect of the mid-thigh using 1:1000 concentration (1 mg/mL), as this route produces rapid peak plasma concentrations and is preferred over subcutaneous injection due to faster onset and superior effectiveness 1, 2, 4
• Repeat the dose every 5-15 minutes as needed if symptoms persist or recur, as many patients require multiple doses 1, 2, 5
• Use epinephrine autoinjectors when available: adult devices deliver 0.3 mg, pediatric devices deliver 0.15 mg 1

Positioning and Oxygen

• Position the patient supine with legs elevated unless respiratory distress makes this impossible, as this improves venous return 2
• Provide supplemental high-flow oxygen and monitor oxygen saturation continuously 2

Vascular Access and Fluid Resuscitation

• Establish intravenous access immediately and administer a rapid bolus of crystalloid fluid: 500-1000 mL for adults or 20 mL/kg for children 2
• Monitor vital signs continuously (blood pressure, heart rate, respiratory rate, oxygen saturation) as cardiovascular and respiratory status can deteriorate rapidly 1, 2

Advanced Management for Refractory Shock

IV Epinephrine for Severe Hypotension

• If severe hypotension or shock persists despite IM epinephrine and fluid resuscitation, administer IV epinephrine 0.05-0.1 mg (using 1:10,000 concentration) slowly over several minutes 1, 2
• For ongoing shock, initiate an epinephrine infusion at 5-15 μg/min and titrate to clinical response, as continuous infusion is more effective than bolus dosing for persistent hypotension 1, 2

Airway Management

• Assess for airway obstruction continuously, as obstructive airway edema can develop rapidly 1
• Perform early intubation if airway compromise is evident; in severe cases, emergency cricothyroidotomy or tracheostomy may be required 1, 6

Second-Line Adjunctive Therapies

Antihistamines

• Administer H1-antihistamine: diphenhydramine 25-50 mg IV/IM (1-2 mg/kg for children) 2
• Add H2-antihistamine: ranitidine 50 mg IV (or famotidine 20 mg IV if ranitidine unavailable), as the combination of H1 + H2 antagonists provides superior symptom control compared to H1 alone 2

Corticosteroids

• Consider methylprednisolone 1-2 mg/kg IV every 6 hours (typically 40 mg IV every 6 hours for adults) or oral prednisone 0.5 mg/kg for less severe cases 1, 2
• Corticosteroids provide no acute benefit but may prevent biphasic or protracted reactions, particularly in patients with asthma, severe anaphylaxis, or idiopathic anaphylaxis 1, 2

Bronchodilators

• If bronchospasm persists despite epinephrine, administer albuterol nebulization 2.5-5 mg in 3 mL saline 2

Special Clinical Situations

Patients on Beta-Blockers

• If the patient is taking beta-blockers and remains unresponsive to epinephrine, administer glucagon 1-5 mg IV (20-30 μg/kg for children, maximum 1 mg) over 5 minutes, followed by an infusion of 5-15 μg/min 1, 2
• Glucagon bypasses beta-receptor blockade and can reverse refractory hypotension 1

Cardiac Arrest from Anaphylaxis

• Initiate standard CPR and advanced cardiac life support immediately 1
• Administer high-dose IV epinephrine: 1-3 mg (1:10,000 dilution) slowly over 3 minutes, then 3-5 mg over 3 minutes, followed by an infusion of 4-10 μg/min 1, 2
• For pediatric cardiac arrest, use 0.01 mg/kg (0.1 mL/kg of 1:10,000) every 3-5 minutes; consider higher doses (0.1-0.2 mg/kg of 1:1000) for refractory arrest 1, 2
• Prolonged resuscitation efforts are encouraged, as outcomes are more favorable in anaphylaxis-related cardiac arrest compared to other causes 1

Critical Pitfalls to Avoid

• Never delay epinephrine administration while waiting for IV access or giving antihistamines first, as delayed epinephrine is associated with increased mortality 2, 4, 5
• Do not use subcutaneous epinephrine as the initial route, as it has delayed onset compared to IM injection 4
• Avoid confusing epinephrine concentrations: use 1:1000 (1 mg/mL) for IM injection and 1:10,000 (0.1 mg/mL) for IV administration to prevent dosing errors 7
• Do not rely on antihistamines or corticosteroids as primary treatment, as they have no role in acute stabilization 2

Observation and Disposition

• Observe patients for at least 6 hours or until clinically stable, as biphasic reactions can occur but are unpredictable 2
• Prescribe an epinephrine autoinjector at discharge and provide thorough education on self-administration technique 1, 2
• Arrange follow-up with an allergist-immunologist for diagnostic evaluation, trigger identification, and long-term management planning 1