A 78-year-old man with severe dementia is brought to the emergency department due to a daylong history of lethargy, fever, and vomiting. The patient lives in a nursing home, and his caregivers report that he has had poor oral intake over the last week. Medical history is significant for emphysema, heart failure with reduced ejection fraction, hypertension, and diabetes mellitus type 2. On physical examination, the patient is lethargic but arousable. Blood pressure is 60/30 mm Hg and pulse is 120/min and regular. The extremities are warm. Coarse rhonchi are heard over the right lower lung. After receiving several intravenous fluid boluses, the patient is given an intravenous infusion of an agent that increases peripheral vascular resistance, increases blood pressure, and decreases heart rate. Which of the following agents is most likely being described?

Question

A 78-year-old man with severe dementia is brought to the emergency department due to a daylong history of lethargy, fever, and vomiting.  The patient lives in a nursing home, and his caregivers report that he has had poor oral intake over the last week.  Medical history is significant for emphysema, heart failure with reduced ejection fraction, hypertension, and diabetes mellitus type 2.  On physical examination, the patient is lethargic but arousable.  Blood pressure is 60/30 mm Hg and pulse is 120/min and regular.  The extremities are warm.  Coarse rhonchi are heard over the right lower lung.  After receiving several intravenous fluid boluses, the patient is given an intravenous infusion of an agent that increases peripheral vascular resistance, increases blood pressure, and decreases heart rate.  Which of the following agents is most likely being described?

Quizplus · Accepted Answer

11ec160b_3b9b_f330_9249_e383844d2450_MD0001_00 Adrenergic agonists are often used to increase blood pressure in patients with shock. Phenylephrine is a selective alpha-1 agonist with no effect on alpha-2 receptors or beta receptors; it causes peripheral vasoconstriction, resulting in increased systemic vascular resistance (SVR) and increased blood pressure, but it has no direct effect on the heart. Drugs that increase blood pressure by increasing SVR are called pressors and are most useful in treating septic shock. Phenylephrine has indirect effects on the heart mediated via the baroreceptor reflex. Increased blood pressure stimulates firing of aortic and carotid baroreceptors. In response, the CNS increases parasympathetic output and decreases sympathetic output, which causes decreased heart rate and myocardial contractility. These reflexive changes slightly attenuate the initial increase in blood pressure and lead to overall reduced cardiac output. (Choices A and D) Dobutamine is primarily a beta-1 agonist with partial activity on beta-2 receptors and minimal effect on alpha receptors. It increases heart rate and myocardial contractility (via beta-1 stimulation) and causes mild vasodilation (via beta-2 stimulation) to decrease SVR. Milrinone is not an adrenergic agonist, but it inhibits phosphodiesterase 3 to increase myocardial contractility and cause peripheral vasodilation (decreases SVR). The combination of increased myocardial contractility (ie, inotropic effect) and reduced SVR induced by these drugs is most useful in treating cardiogenic shock. (Choice B) Dopamine stimulates dopamine-1 (located primarily in the renal arterioles), beta-1, and alpha-1 receptors, with the relative effects being dose dependent. High-dose dopamine primarily stimulates alpha-1 receptors to increase SVR and blood pressure; ongoing beta-1 receptor stimulation offsets the reflex-mediated decrease in heart rate, leaving the heart rate relatively unchanged. (Choice C) Epinephrine stimulates beta-1, beta-2, and alpha-1 receptors with dose-dependent effects. Low-dose epinephrine primarily stimulates beta-1 receptors, resulting in increased cardiac output due to increased heart rate and contractility. At low doses, the vasodilative beta-2-mediated effects are greater than the vasoconstrictive alpha-1-mediated effects, leading to a slight reduction in SVR. Educational objective: Phenylephrine is a selective alpha-1 agonist with no effect on alpha-2 or beta receptors. It causes peripheral vasoconstriction that increases systemic vascular resistance and blood pressure. It has no direct effect on the heart but stimulates a reflex-mediated decrease in heart rate and myocardial contractility.

A 78-Year-Old Man with Severe Dementia Is Brought to the Emergency