What is the immediate management of a suspected allergic reaction that could progress to anaphylaxis?

Immediate Management of Suspected Allergic Reaction Progressing to Anaphylaxis

Administer intravenous epinephrine 50 mcg (0.5 mL of 1:10,000 solution) immediately as first-line treatment while simultaneously securing the airway with 100% oxygen and removing all potential causative agents. 1

Initial Response (First 60 Seconds)

• Call for help immediately and note the time 2, 1
• Remove all potential allergens including IV colloids, latex, chlorhexidine, and antibiotics 2, 1
• Secure the airway and administer 100% oxygen via facemask; intubate if necessary 2, 1
• Elevate the patient's legs if hypotension is present to improve venous return 2, 1
• Start CPR immediately if cardiac arrest is imminent, following Advanced Life Support Guidelines 2, 1

Epinephrine Administration (The Definitive Treatment)

Intravenous route (when IV access available):

• Adults: 50 mcg IV (0.5 mL of 1:10,000 solution) as initial bolus 2, 1
• Repeat every 3-5 minutes as needed for severe hypotension or bronchospasm 1, 3
• Start continuous IV infusion if multiple boluses are required: 1 mg (1 mL of 1:1000) in 250 mL D5W = 4 mcg/mL, infuse at 1-4 mcg/min initially, titrate up to 10 mcg/min 1
• Pediatric IV dosing: 1 mcg/kg (0.1 mL/kg of 1:10,000 solution), titrated to response 2, 1

Intramuscular route (if IV access unavailable):

• >12 years: 500 mcg IM (0.5 mL of 1:1000 solution) into anterolateral thigh 2, 4
• 6-12 years: 300 mcg IM (0.3 mL of 1:1000 solution) 2
• <6 years: 150 mcg IM (0.15 mL of 1:1000 solution) 2

Critical point: Epinephrine has alpha-agonist (vasoconstriction), beta-agonist (inotropy, bronchodilation), and mediator release inhibition properties, making it the only drug that addresses all pathophysiologic mechanisms of anaphylaxis 1. Do not delay administration while attempting to confirm the diagnosis 5, 6.

Aggressive Fluid Resuscitation

• Administer normal saline 0.9% or lactated Ringer's solution at high rate through large-bore IV cannula 2, 1
• Adults: 1-2 L at 5-10 mL/kg in first 5 minutes, up to 7 L may be required 1
• Pediatric: up to 30 mL/kg in first hour 1
• Rationale: Increased vascular permeability can transfer 50% of intravascular fluid to extravascular space within 10 minutes 1

Secondary Pharmacologic Management (Only After Epinephrine)

Adjunctive medications:

• Chlorphenamine (diphenhydramine) 10-50 mg IV for histamine-mediated component 2, 1, 3
• Hydrocortisone 200 mg IV (or methylprednisolone 125 mg IV) 2, 1, 3
• H2-blocker: ranitidine 50 mg IV or famotidine 20 mg IV 3

For persistent hypotension despite epinephrine:

• Consider alternative vasopressor such as metaraminol or norepinephrine infusion (0.05-0.5 mcg/kg/min) 2, 1, 3

For persistent bronchospasm:

• Salbutamol IV infusion or metered-dose inhaler via breathing-system connector 2, 1
• Consider IV aminophylline or magnesium sulfate 2

Diagnostic Workup (Do Not Delay Treatment)

Mast cell tryptase sampling protocol:

• First sample: As soon as feasible after resuscitation starts (5-10 mL clotted blood) 2, 1
• Second sample: 1-2 hours after symptom onset 2, 1, 7
• Third sample: At 24 hours or in convalescence to establish baseline 2, 1, 7
• Label all samples with time and date 2

Observation Period

• Monitor for biphasic reactions for 4-12 hours depending on risk factors 8
• Arrange immediate transfer to Critical Care area for continued monitoring 2, 1
• Extended observation required for patients with oropharyngeal or laryngeal involvement 3

Critical Pitfalls to Avoid

• Do not delay epinephrine while waiting for cutaneous signs—28% of anaphylaxis cases lack skin manifestations, and isolated hypotension occurs in 10% of cases 1, 3
• Do not assume tachycardia will be present—bradycardia occurs in 10% of anaphylaxis cases 1, 7
• Do not use IM route when IV access is available in monitored settings—IV allows precise titration 1
• Do not rely solely on antihistamines and steroids—these are adjuncts only and should never replace epinephrine 3, 6
• Exclude equipment failure (misplaced tracheal tube) before attributing all symptoms to anaphylaxis 2, 1
• Recognize delayed presentations—symptoms typically develop within minutes but can occur up to 1 hour after exposure with certain agents (latex, antibiotics, IV colloids) 1, 7

Recognition Pearls

• Cardiovascular collapse is the most common presentation during anesthesia (50.8% of cases), often without cutaneous signs 1
• Cutaneous signs (flushing, urticaria) are present in only 72% of cases 1, 7
• Bronchospasm occurs in 39.8% of allergic anaphylaxis cases 1
• Angioedema is observed in approximately 12% of cases 7