What is the appropriate management of anaphylactic shock?

Management of Anaphylactic Shock

Immediately administer intramuscular epinephrine 0.3-0.5 mg (1:1000 dilution) into the anterolateral thigh, repeat every 5 minutes as needed, while simultaneously establishing IV access and beginning aggressive fluid resuscitation with 1-2 liters of normal saline—this is the only intervention proven to reduce mortality. 1

Immediate First-Line Management (First 5 Minutes)

Epinephrine Administration

• Route: Intramuscular into the anterolateral thigh (vastus lateralis) is superior to deltoid injection, producing higher and more rapid peak plasma levels 2
• Dose:
  • Adults: 0.3-0.5 mg of 1:1000 dilution (or use EpiPen 0.3 mg autoinjector)
  • Children: 0.01 mg/kg (maximum 0.3 mg; use EpiPen Jr 0.15 mg if <25 kg)
• Repeat: Every 5 minutes until symptoms resolve—do not hesitate to give multiple doses 2, 1
• Critical point: There are no absolute contraindications to epinephrine in anaphylaxis 2

Concurrent Resuscitative Measures

1. Position patient supine with legs elevated (never upright—this can precipitate cardiovascular collapse) 3
2. Establish IV access immediately
3. Administer high-flow oxygen at 6-8 L/min 2
4. Begin aggressive fluid resuscitation: 1-2 L normal saline rapidly in adults (5-10 mL/kg in first 5 minutes; children may require up to 30 mL/kg in first hour) due to massive capillary leak 2

Second-Line Interventions (After Epinephrine)

For Refractory Hypotension

If hypotension persists despite 2-3 IM epinephrine doses and volume resuscitation:

IV Epinephrine Options:

• Bolus: 0.05-0.1 mg (1:10,000 dilution) IV slowly over 3 minutes with continuous cardiac monitoring 1
• Infusion: 1-4 mcg/min initially, titrate up to 10 mcg/min (prepare 1 mg in 250 mL D5W = 4 mcg/mL) 2
• Warning: IV epinephrine carries risk of lethal arrhythmias—use only for profound hypotension unresponsive to IM doses and fluids, with continuous hemodynamic monitoring 2

If Still Refractory:

• Dopamine: 400 mg in 500 mL D5W at 2-20 mcg/kg/min, titrate to maintain SBP >90 mmHg 2

Adjunctive Medications (Never Delay Epinephrine)

H1 + H2 Antihistamine Combination (superior to H1 alone):

• Diphenhydramine 25-50 mg IV/IM (1-2 mg/kg in children) 2
• Plus Ranitidine 50 mg IV over 5 minutes (1 mg/kg in children) or Cimetidine 4 mg/kg IV 2

For Bronchospasm Resistant to Epinephrine:

• Albuterol 2.5-5 mg nebulized in 3 mL saline, repeat as needed 2

Corticosteroids (may prevent biphasic/protracted reactions but no acute benefit):

• Methylprednisolone 1-2 mg/kg IV every 6 hours, or
• Prednisone 0.5 mg/kg PO for less severe cases 2
• Consider especially for patients with asthma or history of idiopathic anaphylaxis 2

Special Circumstances

Patients on Beta-Blockers:

• Glucagon 1-5 mg IV over 5 minutes, then infusion at 5-15 mcg/min (may cause vomiting—aspiration precautions) 2
• These patients may be refractory to epinephrine and require higher doses

Cardiac Arrest from Anaphylaxis

If patient arrests, use high-dose IV epinephrine with standard ACLS:

• Initial: 1-3 mg (1:10,000) IV over 3 minutes
• Then: 3-5 mg IV over 3 minutes
• Then: 4-10 mg/min infusion 2
• Children: 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 1:1,000) for refractory asystole/PEA 2

Additional measures:

• Massive volume expansion is mandatory 2
• Consider atropine and transcutaneous pacing for asystole/PEA 2
• Prolonged resuscitation is encouraged—outcomes are better in anaphylaxis than other causes of arrest, especially in young patients with healthy hearts 2

Airway Management

Early intubation is critical if oropharyngeal/laryngeal edema develops—this can progress rapidly 1. Have cricothyrotomy equipment immediately available as surgical airway may be required if edema prevents intubation 2, 1.

Common Pitfalls to Avoid

1. Delaying epinephrine while giving antihistamines/steroids first—this is the most common fatal error 4, 5
2. Using subcutaneous instead of IM route—IM thigh absorption is faster 2
3. Sitting patient upright—this can cause "empty ventricle syndrome" and sudden death 3
4. Giving IV epinephrine too early—reserve for true refractory shock after multiple IM doses 2
5. Inadequate fluid resuscitation—patients may require several liters due to massive third-spacing 2

Observation and Disposition

• No reliable predictors of biphasic reactions exist based on initial presentation 2
• Observation period must be individualized based on severity, number of epinephrine doses required, distance to emergency care, and response to treatment 2, 6
• Risk factors for biphasic reactions: severe initial reaction, need for >1 epinephrine dose 6
• Discharge all patients with epinephrine autoinjector and proper training 2, 3