Adrenaline (Epinephrine)

Adrenaline, also known as epinephrine, is a hormone and medication that plays a critical role in the body’s fight-or-flight response. It is commonly used in medical emergencies to treat severe allergic reactions, asthma attacks, cardiac arrest, and other conditions.

Mechanism of Action

Adrenaline acts on various adrenergic receptors in the body, leading to different physiological responses:

  • Alpha-1 Adrenergic Receptors: Causes vasoconstriction, increasing blood pressure.
  • Beta-1 Adrenergic Receptors: Increases heart rate and force of cardiac contractions.
  • Beta-2 Adrenergic Receptors: Relaxes bronchial smooth muscle, leading to bronchodilation, and vasodilation in skeletal muscles.
  • Half-Life :
    • Intravenous (IV) Administration: The plasma half-life of adrenaline when administered intravenously is approximately 2 to 3 minutes.
    • Intramuscular (IM) Administration: When administered intramuscularly, the effects last longer due to slower absorption compared to intravenous administration.
  • Bioavailability :
    • Intravenous (IV) Administration: Adrenaline has 100% bioavailability when administered intravenously since it directly enters the systemic circulation.
    • Intramuscular (IM) and Subcutaneous (SC) Administration: The bioavailability of adrenaline is lower and more variable when administered via these routes.

Clinical Uses

  1. Anaphylaxis:
    • Mechanism: Adrenaline rapidly reverses the severe allergic reaction by vasoconstriction (reducing swelling), increasing blood pressure, and bronchodilation (easing breathing).
    • Dosage: 0.3-0.5 mg (0.3-0.5 mL of 1:1,000 solution) intramuscularly (IM) into the mid-outer thigh, may repeat every 5-15 minutes if necessary.
    • EpiPen for Adults and Children Over 30 kg (66 lbs):
      • Dose: 0.3 mg of adrenaline
      • Instructions: Inject into the outer thigh. It can be administered through clothing if necessary. Press Down Firmly Until a Click is Heard. Hold in place for about 3 seconds to ensure the full dose is delivered.
    • EpiPen Jr for Children 15-30 kg (33-66 lbs):
      • Dose: 0.15 mg of adrenaline
      • Instructions: The same as for the adult version, ensure the dose is administered correctly.
  2. Cardiac Arrest:
    • Mechanism: Stimulates the heart and improves blood flow to the brain and heart during resuscitation efforts.
    • Dosage: 1 mg (1:10,000 (0.1 mg/mL) intravenous (IV) push every 3-5 minutes during resuscitation. (1 mg = 10 mL of 1:10,000 solution)
  3. Septic Shock:
    • Mechanism: Increases blood pressure and cardiac output in patients with life-threatening low blood pressure due to sepsis.
    • Dosage: 0.01-0.5 mcg/kg/min IV infusion, titrated to achieve desired blood pressure.
  4. Severe Asthma Attacks:
    • Mechanism: Causes bronchodilation, improving airflow in and out of the lungs.
    • Dosage: 0.3-0.5 mg IM or subcutaneously (SC), may repeat every 20 minutes for up to three doses.

Adrenaline (epinephrine) infusion in (ICU)

Adrenaline (epinephrine) infusion is commonly used in the Intensive Care Unit (ICU) for patients experiencing severe hypotension, septic shock, or cardiogenic shock when other treatments are insufficient.

  1. Stock Solution: Adrenaline typically comes in ampoules of 1 mg/mL.
  2. Dilution: To prepare a 5 mg dose in 50 mL of dextrose solution:
    • Add 5 mg of adrenaline (5 mL of 1 mg/mL solution) to 45 mL of 5% dextrose solution.
    • This results in a final concentration of 0.1 mg/mL (100 mcg/mL).

Initial Dose Calculation

The initial infusion rate is often based on the patient’s weight and clinical condition. A common starting dose is 0.01 to 0.05 mcg/kg/min.

Administration:

  • The infusion is typically administered via a central venous catheter (CVC) to ensure rapid and consistent delivery.
  • Infusion rates are titrated based on the patient’s response, typically starting at a low dose and gradually increasing.

Monitoring

Patients on adrenaline infusion require continuous monitoring due to the potent effects of the medication:

  • Hemodynamic Monitoring: Blood pressure, heart rate, and ECG.
  • Urine Output: Indicator of renal perfusion.
  • Lactate Levels: Indicator of tissue perfusion and metabolic state.
  • Clinical Response: Regular assessment of the patient’s clinical status.

Adverse Effects

  • Common: Palpitations, tachycardia, anxiety, tremors, headache, dizziness.
  • Serious: Hypertensive crisis, arrhythmias, pulmonary edema, myocardial infarction.

Contraindications

  • Absolute: None in emergency situations where adrenaline is lifesaving.
  • Relative: Narrow-angle glaucoma, non-anaphylactic shock, labor (may inhibit uterine contractions).

References