What is the treatment algorithm for anaphylactic shock?

Anaphylactic Shock Treatment Algorithm

Immediate First-Line Treatment

Intramuscular epinephrine 0.01 mg/kg (maximum 0.5 mg adults, 0.3 mg children) of 1:1000 solution injected into the anterolateral thigh is the immediate first-line treatment for anaphylactic shock and must be administered without delay. 1

Initial Management Steps

• Administer IM epinephrine immediately upon recognition of anaphylaxis—delays in administration are a risk factor for fatal outcomes 1
• Inject into the lateral thigh (vastus lateralis muscle), not subcutaneous tissue, as IM administration provides faster and more reliable absorption 1, 2
• Activate emergency medical services (EMS) immediately, as patients may require advanced interventions including intubation, IV fluids, and vasopressors 1
• Position patient supine with legs elevated to improve venous return in hypotensive shock 3

Repeat Dosing Protocol

• Repeat IM epinephrine every 5-15 minutes if symptoms persist or worsen 1
• If EMS arrival will exceed 5-10 minutes and patient has not responded to initial dose, administer a second dose 1
• Approximately 7-18% of patients require more than one dose of epinephrine 1

Transition to IV Epinephrine (Refractory Cases Only)

IV epinephrine should only be used when IM epinephrine has failed after multiple doses, in profound hypotension unresponsive to IV fluids, or during cardiac arrest from anaphylaxis. 1, 3

IV Bolus Administration

• Initial dose: 0.05-0.1 mg (50-100 mcg) of 1:10,000 concentration administered slowly over several minutes 3
• This represents only 5-10% of the cardiac arrest dose to minimize risk of lethal arrhythmias 3
• Continuous hemodynamic monitoring is mandatory—including continuous ECG, blood pressure every minute, and pulse oximetry 1, 3

IV Infusion Protocol (Preferred for Refractory Shock)

• Preparation method: Add 1 mg (1 mL) of 1:1000 epinephrine to 1000 mL of 0.9% normal saline 1
• Starting rate: 2 mcg/min (2 mL/min or 120 mL/hour) 1
• Titrate upward to maximum 10 mcg/min (10 mL/min or 600 mL/hour) based on blood pressure, heart rate, and oxygenation 1
• IV infusion allows careful titration and avoids risks of repeated boluses 3

Adjunctive Therapies (Second-Line Only)

These medications do not substitute for epinephrine and should never delay its administration 1, 4:

Volume Resuscitation

• Aggressive IV fluid boluses are mandatory—anaphylactic shock can cause up to 37% loss of circulating blood volume due to capillary leak 5
• Administer 1-2 liters of normal saline rapidly in adults (20 mL/kg boluses in children) 1

Antihistamines

• Diphenhydramine 1-2 mg/kg (25-50 mg in adults) IV or IM 1
• Ranitidine 1 mg/kg IV (or cimetidine 4 mg/kg)—combination H1 + H2 blockade is superior to H1 alone 1

Bronchodilators

• Albuterol 2.5-5 mg nebulized for bronchospasm resistant to epinephrine 1

Corticosteroids

• Methylprednisolone 1-2 mg/kg/day IV every 6 hours (or prednisone 0.5 mg/kg PO for less severe cases) 1
• May prevent biphasic or protracted reactions but have no acute benefit 1

Special Circumstances

Beta-Blocker Therapy

• Glucagon 1-5 mg IV over 5 minutes (20-30 mcg/kg in children, max 1 mg) followed by infusion at 5-15 mcg/min 1, 3
• Use aspiration precautions as glucagon causes nausea and vomiting 1

Refractory Hypotension

• Dopamine 400 mg in 500 mL D5W at 2-20 mcg/kg/min, titrated to blood pressure with continuous monitoring 1, 3

Cardiac Arrest from Anaphylaxis

• High-dose IV epinephrine: 1-3 mg (1:10,000) IV over 3 minutes, then 3-5 mg over 3 minutes, then 4-10 mg/min infusion 1
• Pediatric dosing: 0.01 mg/kg (0.1 mL/kg of 1:10,000) every 3-5 minutes, escalating to 0.1-0.2 mg/kg for refractory arrest 1
• Prolonged resuscitation efforts are warranted—outcomes are better in anaphylaxis than other causes of arrest due to younger, healthier patients 1
• Consider atropine and transcutaneous pacing for asystole or pulseless electrical activity 1

Observation Period

• Minimum 4-6 hours observation in emergency department for all patients, as 17% experience delayed deterioration 1
• Extended observation (up to 24 hours) for severe reactions, delayed epinephrine administration, or history of biphasic reactions 1
• 53% of delayed deteriorations require epinephrine, with 69% occurring within 4 hours of ED arrival 1

Critical Pitfalls to Avoid

• Never delay epinephrine while administering antihistamines or steroids—this is the most common fatal error 1, 4
• Do not use subcutaneous epinephrine—absorption is slower and less reliable than IM 1, 2
• Do not administer IV epinephrine too rapidly—give boluses slowly over several minutes to prevent lethal arrhythmias 3
• Never confuse concentrations—use 1:1000 (1 mg/mL) for IM and 1:10,000 (0.1 mg/mL) for IV 3, 6
• Do not use vasodilators like isosorbide, which worsen hypotension in anaphylactic shock 5
• There are no absolute contraindications to epinephrine in anaphylaxis, even in elderly patients with cardiac disease—the benefits outweigh risks 1