Phenylephrine vs Ephedrine in Medical Settings

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Questions and Answers

What is the primary function of atrial natriuretic peptide (ANP)?

To regulate fluid and electrolyte balance (correct)

To stimulate the Bainbridge reflex

To decrease heart rate

To increase blood pressure

Why are ANP levels difficult to draw in ICUs?

Due to the lack of stretch receptors in the atria

Due to the long half-life of ANP

Due to quick breakdown caused by atrial stretch (correct)

Due to the low concentration of ANP in the blood

What is the effect of atrial stretch on heart rate?

Decreases heart rate by up to 75%

Has no effect on heart rate

Increases heart rate by up to 75% (correct)

Increases blood pressure

What is the Bainbridge reflex responsible for?

Increasing heart rate in response to atrial stretch Signup and view all the answers

What is the role of the vasomotor center in blood pressure regulation?

To detect changes in blood pressure Signup and view all the answers

What is the result of the cerebral ischemic response?

Excitation of basal constrictor and cardioaccelerated neurons Signup and view all the answers

What is the effect of low blood volume on heart rate?

Increases heart rate Signup and view all the answers

What is the effect of atrial stretch on atrial irritability?

Increases atrial irritability Signup and view all the answers

Why would phenylephrine be preferred over ephedrine for a patient with coronary artery disease?

Phenylephrine does not increase heart rate as much Signup and view all the answers

What is a limitation of using ephedrine in patients with CHF?

They may not have a significant response to it Signup and view all the answers

What is a common use of ephedrine in medical settings?

To temporarily increase blood pressure and heart rate to overcome a specific event Signup and view all the answers

What is a concern with using ephedrine in the CVICU?

It may deplete catecholamine stores Signup and view all the answers

Why is ephedrine not commonly used in the ICU?

It is too short-acting and not typically given by infusion Signup and view all the answers

What is a characteristic of ephedrine's effect on blood pressure?

It causes a rapid increase in blood pressure, followed by a drop Signup and view all the answers

Why is ephedrine used in anesthesia?

As a bridge to get past a certain issue Signup and view all the answers

What is important for clinical students to understand when using medications?

The rationale for using medications and alternative options Signup and view all the answers

What is the primary function of the baroreceptor reflex?

To maintain blood pressure and cardiac output within normal physiologic ranges Signup and view all the answers

What type of nerve endings are baroreceptors?

Spray-type nerve endings Signup and view all the answers

Through which nerve do the signals from the aorta transmit to the nucleus tractus solitarius in the medulla?

Vagus nerve Signup and view all the answers

What is the effect of phenylephrine on heart rate?

It decreases heart rate due to its alpha one agonist activity Signup and view all the answers

What is the role of the baroreceptors in response to changes in arterial blood pressure?

To respond rapidly to changes in arterial blood pressure within the physiologic blood pressure range Signup and view all the answers

What is the effect of ephedrine on heart rate?

It maintains a high heart rate due to its alpha one and beta one activity Signup and view all the answers

What is the location of the nucleus tractus solitarius?

In the medulla Signup and view all the answers

What is the purpose of the baroreceptor reflex in situations such as physical exercise or stress?

To maintain blood pressure and cardiac output within normal physiologic ranges Signup and view all the answers

What happens to arterial pressure after an hour due to diuresis caused by increased volume and pressure?

It returns to normal Signup and view all the answers

What is the primary function of triamterene hydrochlorothiazide as a blood pressure medication?

Causing diuresis Signup and view all the answers

What is the result of increased sodium intake on renal output?

Increased output of water and salt Signup and view all the answers

What is the term for the return of arterial pressure to the equilibrium point?

Near infinite gain principle Signup and view all the answers

What happens in individuals with chronic essential hypertension?

They have a reset equilibrium point Signup and view all the answers

What is the effect of Lasix on blood pressure?

It decreases blood pressure Signup and view all the answers

What is the primary mechanism of chronic control of blood pressure?

Renal output of water and salt Signup and view all the answers

What is required to change the long term mean arterial pressure level?

A change in one or both of the basic determinants of long term arterial pressure Signup and view all the answers

What is the term for chronic changes in arterial pressure lasting for days or months?

Natriuresis Signup and view all the answers

What is an example of individuals with altered long term arterial pressure regulation?

Salt insensitive patients and chronically hypertensive patients Signup and view all the answers

What is the effect of an increase in salt and water intake on blood pressure in salt-sensitive individuals?

A moderate increase in blood pressure Signup and view all the answers

What is the effect of potassium chloride on blood pressure?

It decreases blood pressure Signup and view all the answers

What is a contraindication for the use of potassium chloride salt substitute?

Renal failure Signup and view all the answers

What is a factor that contributes to salt sensitivity?

Loss of functional nephrons Signup and view all the answers

What is the relationship between salt intake and blood pressure?

Directly proportional Signup and view all the answers

What is the effect of an increase in total peripheral resistance on blood pressure?

It elevates blood pressure Signup and view all the answers

Study Notes

Coronary Artery Disease and Medications

For patients with coronary artery disease and a heart rate of 80, phenylephrine is preferred over ephedrine because it does not increase heart rate as much.
Ephedrine can increase heart rate and is not ideal for patients with coronary artery disease.
Ephedrine does not work on people with Addison's disease or those who have depleted catecholamine vesicles due to drug abuse.

Use of Ephedrine in Medical Settings

Ephedrine can be redosed if the initial dose does not have the desired effect, but its short-acting nature makes it less practical for use in the ICU.
Patients with CHF may already be catecholamine depleted and may not have a significant response to ephedrine.
Ephedrine is typically used to temporarily increase blood pressure and heart rate to overcome a specific event, such as deep anesthesia without surgical stimulation.
Ephedrine can lead to tachyphylaxis, where its effectiveness decreases with repeated use.

Baroreceptor Reflex and Blood Pressure Regulation

The baroreceptor reflex is a mechanism through which the body responds to changes in arterial blood pressure.
Baroreceptors are specialized nerve endings found in the walls of large arteries such as the carotid sinus and the wall of the aortic arch.
The reflex aims to keep blood pressure and cardiac output within normal physiologic ranges.
The baroreceptor reflex is responsible for regulating blood pressure during normal daily activities, as well as in situations such as physical exercise or stress.

Phenylephrine and Baroreceptors

Phenylephrine is an alpha one agonist, causing vasoconstriction and not affecting beta receptors, leading to an increase in stretch in baroreceptors and resulting in a decrease in heart rate.
Ephedrine has both alpha one and beta one activity, offsetting the effect of the baroreceptors and maintaining a high heart rate.

ANP and BNP Levels

Atrial natriuretic peptide (ANP) levels are difficult to draw in ICUs due to quick breakdown, caused by atrial stretch and used as a mechanism to excrete sodium and water.
Brain natriuretic peptide (BNP) levels are easier to draw, as they last longer and are similarly affected by atrial and ventricular stretch, often indicating pulmonary artery pressure and right ventricular pressure.

Bainbridge Reflex and Neurological Control of Blood Pressure

Atrial stretch increases atrial irritability through the Bainbridge reflex, leading to an increase in heart rate and potentially causing atrial pacemakers other than the sinus node to take over.
The Bainbridge reflex increases heart rate when blood volume is increased, and stretch receptors in the atria elicit the Bainbridge reflex, transmitting a signal to the vagus nerve and the medulla of the brain.

Principles of Arterial Pressure Control and Hypertension

The return of arterial pressure to the equilibrium point is known as the near infinite gain principle for control of arterial pressure.
Individuals without chronic essential hypertension can handle an increase in fluid and salt load, diuresing off the extra water to return to the equilibrium point.
Hypertension occurs when there is a reset in the equilibrium point or the level of the renal output curve for salt and water shifts.

Chronic Effects of Salt and Water on Blood Pressure

Chronic changes in arterial pressure lasting for days or months are referred to as natriuresis or pressured diurese.
Chronic control of blood pressure is primarily mediated by renal output of water and salt.
An increase in pressure leads to an increase in renin, causing angiotensin 2 to become a powerful basal constrictor and increasing systemic vascular resistance.

Salt Sensitivity and Blood Pressure

Salt sensitivity can affect blood pressure, causing significant increases in arterial pressure for some individuals.
Individuals with excessive secretion of anti-nutrient hormones or kidney injury are considered to be salt sensitive.
Moderate increases in salt intake can have a significant effect on blood pressure for salt-sensitive individuals.

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Description

This quiz compares the effects of phenylephrine and ephedrine on heart rate in patients with coronary artery disease. It also discusses the limitations of ephedrine in certain medical conditions.