Epinephrine

Summary

Epinephrine is an adrenergic agonist that stimulates the sympathetic nervous system, which is also known as the fight or flight response. It activates alpha-1 receptors, which causes vasoconstriction and a subsequent increase in blood pressure. It also activates beta-1 receptors, which causes an increased heart rate and increased heart contractility. Remember, increased heart contractility is also called positive inotropy. The activation of beta-1 receptors eventually leads to an increase in cardiac output. Epinephrine also activates beta-2 receptors, causing bronchodilation.

Epinephrine can be used clinically to treat anaphylaxis, shock, and hypotension. It can also be given with lidocaine to improve lidocaine's effectiveness. Epinephrine can also treat asthma, heart block, and cardiac arrest.

Side effects of epinephrine include hypertension, tachycardia, and arrhythmias.

Key Points

• Epinephrine
  • Mechanism
    • Adrenergic Agonist
      • Activates Alpha-1 Receptors
        • Vasoconstriction
          • Increases Blood Pressure
          • Smooth muscle contraction in the blood vessels increases the pressure inside the arterial walls
      • Activates Beta-1 Receptors
        • Increases Heart Rate
        • Increases Myocardial Contractility
        • Increases Cardiac Output
          • The combined effects of increased heart rate and increased myocardial contractility lead to an overall increase in cardiac output, which is the amount of blood pumped by the heart per minute
      • Activates Beta-2 Receptors
        • Bronchodilation
          • Stimulation of beta-2 receptors relaxes bronchial smooth muscle to cause airway dilation
      • Stimulates Sympathetic Nervous System
        • Epinephrine is a key neurotransmitter in the sympathetic nervous system, also known as the "fight or flight" response
        • Stimulation of the sympathetic nervous system leads to increased alertness, increased heart rate and blood pressure, and other physiological changes that prepare the body for action
  • Clinical Use
    • Anaphylactic Shock (Severe Allergic Reactions)
      • Drug of choice; dilates airways and constricts systemic vasculature to restore normal blood pressure
      • Usually given IM
      • Can be repeated every 5-15 min if no response
      • Patients with a history of severe allergic reaction should always carry an EpiPen
        • Emergency administration can be given through clothing in the outer thigh
    • Given with Lidocaine (local anesthetic)
      • Vasoconstriction reduces blood flow to the area, reducing the risk of bleeding
      • Slows the absorption of the anesthetic and prolongs its action
    • Hypotension
      • Due to its vasoconstrictive effects
    • Heart Block
      • May be used to increase heart rate and maintain cardiac output in certain types of heart block
    • Shock
      • Epinephrine is used in the treatment of various types of shock (e.g., septic shock, cardiogenic shock) to improve blood pressure and perfusion to vital organs
    • Cardiac Arrest
      • Used in ACLS algorithm, believed to improve return of circulation and perfusion
    • Asthma
      • Can also help in other respiratory illnesses such as COPD and croup
  • Side Effects
    • Hypertension
      • Concurrent use with MAOIs increases the risk of hypertension
      • Monitor blood pressure during treatment
    • Arrhythmias
      • Epinephrine's stimulatory effects on the heart can sometimes lead to abnormal heart rhythms (arrhythmias), particularly in patients with underlying heart conditions
    • Tachycardia
      • Monitor heart rate during treatment