Pharmacology

Epinephrine

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Epinephrine (adrenaline) is an incredibly versatile catecholamine. It can be administered through intravenous, subcutaneous, intramuscular, and inhalational routes. It treats a myriad of clinical conditions ranging from anaphylaxis and croup to bronchospasm and afterload enhancement in cardiopulmonary arrest. Epinephrine is routinely added to local anesthetics to provide localized vasoconstriction, but literature is also showing that its adrenergic effects are independently conferring a degree of analgesia.

Epinephrine’s mechanism of action is highly dependent on its dose – “beta” agonist effects are seen first followed by “alpha” agonist effects. For this reason, it’s important to understand how the adrenergic system ACTUALLY works rather than thinking “epi increases blood pressure.”  I use this medication ALL the time in cardiothoracic anesthesiology and in the ICU for patients with systolic dysfunction (especially in right heart failure). Beta effects allow me to increase a patient’s chronotropy (heart rate) and inotropy (contractility) while simultaneously promoting vasodilation of the vascular smooth muscle (decreased afterload). The net effect? Promoting forward flow!

Some points to think about: epinephrine can create a lactic acidosis even in aerobic conditions due to the accumulation of pyruvate and saturation of the PDH/TCA pathways. Systolic anterior motion (SAM) of the mitral valve misdiagnosed as anaphylaxis and treated with epinephrine can lead to hemodynamic collapse. Patients who are taking beta blockers (especially mixed agents like labetalol) may not manifest the typical hemodynamic responses one would expect with high doses of epinephrine. It’s important to consider how the simultaneous adrenergic agonism/antagonism will present clinically.

Drop me a comment below with questions!

2 Comments

  1. Hi! From my understanding, norepi is used to maintain adequate blood pressure, whereas epi is used to increase heart rate and contractility. I’m curious as to what the indications are when selecting epi vs norepi gtt in cardiac patients? I know that each have different effects on afterload and so I’m guessing that may have something to do with it? I work peds and almost all of our kids are on milrinone gtt and epi, but have rarely ever seen norepi used. I read your post about milrinone and how it can cause hypotension, which is why I’m interested in why epi is favored over norepi as wouldn’t you have double the effect? Thanks a bunch!

    • The combination of milrinone and epinephrine screams “right heart support” (at least in the adult population) since milrinone works synergistically with catecholamines like epinephrine to improve inotropy. Sometimes the systemic hypotension isn’t significant, so afterload enhancement isn’t necessary. I’ve certainly had situations where I run milrinone with vasopressin to offset the systemic hypotension.

      Like all things in medicine, patients sometimes respond differently and/or to varying degrees. Just have to address the issues as they come up.

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