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Easy Ways to remember Epinephrine (Low, Int, high Dose)

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These videos are designed for medical students studying for the USMLE step 1. Feel free to comment and suggest what you would like to see in the future, and I will do my best to fulfill those requests.

This video talks about epinephrine it’s different receptors and how epinephrine works at different dosage so let’s get right into it epinephrine has four receptors alpha 1 alpha 2 beta 1 and beta 2 what is the function of alpha 1 primarily primarily alpha 1 is responsible for basal constriction primarily alpha 2 is responsible for decreasing sympathetic flow

What about beta 1 primarily it affects us to increase heart rate and beta 2 would be vasodilation and bronchodilation so those are the primary effects and it’s important to categorize those like that to be able to understand how epinephrine works at different level of dosage and there’s three levels low dose intermediate dose and high dose so let’s talk about

Low dosage first at low dosage a lot of people say that epinephrine behaves as isoproterenol okay what is as a paternal isoproterenol is actually a beta agonist a non-selective beta agonist so it does not matter if it’s beta 1 or beta 2 they’re going to be equally stimulated in a super turn but that’s as a paternal and i’ll tell you why people make that make

The conclusion that epinephrine acts like as a paternal in a bit later but let’s talk about our receptors first just based on receptors epinephrine has a higher effect on the beta receptors than the alpha receptors so will have a higher effect on beta 1 beta 2 then alpha 1 and alpha 2 and if you ask me which of these two beta receptors epinephrine has a greater

Effect at low dose my answer is going to be beta 1 there is going to be a greater beta 1 effect than beta 2 then why do people say that low dose of epinephrine is like isoproterenol because that really is not the case is it epinephrine at low dose has a greater beta1 effect than beta-2 where i support eronel beta-1 and beta-2 has equal effects and will understand

That by looking at these two graphs so what do we have here we have blood pressure and we have heart rate now this is our time on our x-axis so this is our blood pressure kind of average blood pressure right here and this is where we’re infusing low dose of epinephrine okay for both the graphs so what we see is happening to our heart rate let’s talk about how at

First because it’s easier to understand we know that beta 1 has a lot of effect at low dose so as soon as we infuse epinephrine into our system at low dose the beta 1 receptors is going to be stimulated and the beta 1 is going to increase the contractility of the heart and we’re going to have increased heart rate that’s the easy one what about beta 2 what’s going

To happen to our blood pressure okay now there’s two receptors in the sympathetic system which takes care of blood pressure to caranas there’s three ways it can change first of all is that beta blood pressure is affected by alpha one receptors how because it’s a vasoconstrictor it’s affected by beta 1 beta 2 receptor how because it causes the opposite of alpha 1

Which is vasodilation again there is also reflux so if heart rate is increased a reflex is going to cause the blood pressure to increase or decrease and accordingly so why is the blood pressure going down at low dose of epinephrine the reason for that is we establish right at the beginning we said that the alpha receptors has less effect than beta 1 beta receptors

Okay so in a war between alpha and beta this is going to alpha is going to try to vasoconstrict where beta is going to visit dilate but since more beta is going to be active the beta is going to win over alpha okay so the beta 2 receptor is going to win over alpha and beta 2 receptor is going to cause vasodilation and the heart rate is – sorry the blood pressure

Is going to fall again through our beta 1 receptors at low dose of epinephrine so at low dose of epinephrine the beta 1 are being active right here we have increased heart rate and through beta 2 receptors by winning the war between alpha 1 and beta 2 the blood pressure is going to drop because beta beta receptors has a greater effect at low dose then at a higher

Dose so now let’s talk about our intermediate dose in our intermediate dose we are going to have alpha receptors equal to our beta receptors i always like to start with heart rate or beta first so let’s talk about heart rate heart rate is predominantly affected by beta 1 receptors and since alpha 1 is equal to alpha 2 we’re going to see an increase in heart rate

So imagine this is where the infusion happened and the heart rate at intermediate dose is going to be increased okay what about blood pressure so at intermediate dose alpha receptors is going to be equal to beta receptors then it’s fair to say that alpha 1 is going to be equal to beta 2 as a result what’s going to happen alpha 1 is will try to increase the blood

Pressure beta 1 it will try to decrease the blood pressure right as a result they’re going to equal each other out and we’re going to see a flatline right here we’re going to see the blood pressure not changing even though the infusion probably happened right here so that’s what’s going to happen at intermediate level now let’s talk about high level at high dose

We’re going to have greater alpha receptors than beta 1 so now what’s going to happen to our heart rate and our blood pressure so at high dose for high dose let’s talk about blood pressure first we know that alpha is going to have greater effect than beta so what are the two receptors that are acting for for determining the blood pressure they’re going to be

Primarily they’re going to be alpha 1 and beta 2 and who is going to win the fight alpha 1 at high dose alpha 1 is going to win the fight so what’s going to alpha 1 going to try to do alpha 1 will try to basic and strict as a result of blood pressure is going to increase so imagine the sub blood pressure right here so it should be straight and let’s say this is

Where infusion happened and we’re going to see increase in blood pressure and that is through alpha 1 now let’s talk about heart rate whenever we’re talking about heart rate who is going to win the fight over alpha and beta obviously it’s going to be alpha so beta is not going to increase the heart rate as much so as a result because blood pressure is going up and

Because beta 1 is not as stimulated like the low dosage we are going to have the heart is going to try to compensate for the increased blood pressure as a result we’re going to see a drop in heart rate as we’re increasing high dosage of epinephrine at this level at high dosage epinephrine works as norepinephrine so if you were to draw a heart rate or blood pressure

Graph or norepinephrine it would look exactly like how it is looking at high blood pressure

Transcribed from video
Easy Ways to remember Epinephrine (Low, Int, high Dose) By 100lyric