Epinephrine Infusion for Angioedema in an 18-Year-Old Male Weighing 125 Pounds
For this 18-year-old male (57 kg) with severe angioedema requiring continuous epinephrine infusion, prepare 1 mg (1 mL) of 1:1000 epinephrine in 250 mL D5W (yielding 4 mcg/mL) and infuse at 1-4 mcg/min initially, titrating up to a maximum of 10 mcg/min based on clinical response. 1
Initial Intramuscular Epinephrine
Before initiating an infusion, ensure the patient has received adequate intramuscular epinephrine first. For this patient weighing 57 kg (125 lbs), administer 0.3-0.5 mg (0.3-0.5 mL) of 1:1000 epinephrine intramuscularly into the anterolateral thigh, repeated every 5-10 minutes as necessary. 2 Since the patient weighs more than 30 kg, the adult dosing applies. 1
Epinephrine infusion should only be considered when the patient fails to respond to multiple intramuscular epinephrine injections and aggressive volume resuscitation. 1 This is critical—IV epinephrine carries significant risk of potentially lethal arrhythmias and should be reserved for profoundly hypotensive patients or those in cardiorespiratory arrest. 1
Preparation of Epinephrine Infusion
Two standard preparation methods are available:
Primary method: Add 1 mg (1 mL) of 1:1000 epinephrine to 250 mL of D5W, yielding a concentration of 4 mcg/mL. 1, 3 Infuse at 1-4 mcg/min initially (15-60 drops per minute with a microdrop apparatus where 60 drops/min = 1 mL = 60 mL/h). 1
Alternative method (if infusion pump available): Add 1 mg (1 mL) of epinephrine to 100 mL of saline, yielding a 1:100,000 solution (10 mcg/mL). 1, 3 Administer at an initial rate of 30-100 mL/h (5-15 mcg/min). 1
Dosing and Titration
- Starting dose: 1-4 mcg/min (or 5-15 mcg/min with alternative preparation) 1, 3
- Maximum dose: 10 mcg/min 1, 3
- Titration: Adjust based on clinical response (blood pressure, heart rate, respiratory status) and signs of epinephrine toxicity 1
- Monitoring frequency: Blood pressure and pulse every minute initially, with continuous electrocardiographic monitoring if available 1, 3
Critical Concurrent Management
Aggressive intravenous fluid resuscitation is mandatory. Administer 1-2 liters of normal saline rapidly in this adult patient (5-10 mL/kg in the first 5 minutes), as angioedema with anaphylaxis causes profound intravascular volume depletion. 3 Large volumes up to 30 mL/kg in the first hour may be required. 3
Airway management takes priority. If pharyngeal or laryngeal involvement is present or worsening, consider early intubation before complete airway obstruction occurs. 3, 4 Epinephrine should be administered if there is any concern for laryngeal edema. 4
Adjunctive Medications (Second-Line)
These should never delay epinephrine administration but can be added:
- Diphenhydramine: 50 mg IV (1-2 mg/kg) 1, 3
- Ranitidine: 50 mg IV diluted in D5W over 5 minutes 1, 3
- Methylprednisolone: 1-2 mg/kg IV every 6 hours to prevent biphasic reactions 3
- Inhaled albuterol: 2.5-5 mg nebulized if bronchospasm is present and resistant to epinephrine 1
The combination of H1 and H2 antihistamines is superior to H1 alone, but both have much slower onset than epinephrine and are strictly second-line. 1
Refractory Hypotension
If hypotension persists despite epinephrine infusion at maximum dose and adequate fluid resuscitation:
- Add vasopressin: 0.01-0.04 units/min (prepare as 25 units in 250 mL D5W or normal saline) 3
- Alternative: Norepinephrine infusion may be used, prepared as 1 mg in 100 mL saline at 30-100 mL/h (5-15 mcg/min) 1, 3
Monitoring and Observation
- Continuous hemodynamic monitoring is essential when IV epinephrine is used 1
- Monitor blood pressure, heart rate, oxygen saturation every 5-15 minutes during titration 3
- Assess tissue perfusion markers: mental status, urine output, capillary refill 3
- Observe for 24 hours after severe angioedema requiring IV epinephrine, as biphasic reactions occur in 1-7% of patients 3
Critical Pitfalls to Avoid
Do not use IV epinephrine as first-line treatment. It should only be administered after failure of several intramuscular epinephrine injections and volume replacement. 1 The risk of lethal arrhythmias is significant. 1
Do not delay epinephrine for antihistamines or corticosteroids. These are ineffective as monotherapy and have much slower onset. 1, 4
Do not assume all angioedema is allergic. Bradykinin-mediated angioedema (ACE inhibitor-induced, hereditary, or acquired) does not respond to epinephrine, antihistamines, or corticosteroids. 5 However, in an emergency presentation with airway compromise, epinephrine should still be administered while the etiology is being determined. 4
Do not administer repeated injections at the same site, as vasoconstriction may cause tissue necrosis. 2