Phenylephrine vs Ephedrine in Medical Settings

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.

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.