A 57-year-old man is admitted to the burn unit after he was brought to the emergency room following an accidental fire in his house. His past medical history is unknown due to his current clinical condition. Currently, his blood pressure is 75/40 mmHg, pulse rate is 140/min, and respiratory rate is 17/min. The patient is subsequently intubated and started on aggressive fluid resuscitation. A Swan-Ganz catheter is inserted to clarify his volume status. Which of the following hemodynamic parameters would you expect to see in this patient?

Cardiac output: ↓, systemic vascular resistance: ↑, pulmonary artery wedge pressure: ↓

Cardiac output: ↓, systemic vascular resistance: ↔, pulmonary artery wedge pressure: ↔

Cardiac output: ↑, systemic vascular resistance: ↑, pulmonary artery wedge pressure: ↔

Cardiac output: ↑, systemic vascular resistance: ↓, pulmonary artery wedge pressure: ↔

Cardiac output: ↔, systemic vascular resistance: ↔, pulmonary artery wedge pressure: ↔

A 53-year-old man presents to the office for a routine examination. The medical history is significant for diabetes mellitus, for which he is taking metformin. The medical records show blood pressure readings from three separate visits to fall in the 130–160 mm Hg range for systolic and 90–100 mm Hg range for diastolic. Prazosin is prescribed. Which of the following are effects of this drug?

Vasodilation, bladder sphincter relaxation

Vasodilation, decreased heart rate, bronchial constriction

Vasodilation, increased peristalsis, bronchial dilation

Vasoconstriction, bladder sphincter constriction, mydriasis

Vasoconstriction, increase in AV conduction rate, bronchial dilation

A 77-year-old man with refractory shock has been under treatment in an intensive care unit for last 7 days. Despite the best possible management by the team of physicians and intensivists, he fails to show improvement. After discussion with his relatives and obtaining informed consent from them, the team administers to him a novel drug, an adrenergic agonist that produces positive chronotropic effects and inotropic effects and stimulates the release of renin from the kidneys. The drug does not have any other adrenergic effects. Which of the following second messengers is most likely to be responsible for the actions of the novel drug?

Cyclic adenosine monophosphate (cAMP)

Cyclic guanosine monophosphate (cGMP)

Inositol 1,4,5-triphosphate (IP3)

A 73-year-old man presents to his primary care physician with chest pain. He noticed the pain after walking several blocks, and the pain is relieved by sitting. On exam, he has a BP 155/89 mmHg, HR 79 bpm, and T 98.9 F. The physician refers the patient to a cardiologist and offers prescriptions for carvedilol and nitroglycerin. Which of the following describes the mechanism or effects of each of these medications, respectively?

Increased contractility; Decreased endothelial nitric oxide

Decreased cGMP; Increased venous resistance

Increased heart rate; Decreased arterial resistance

A 70-year-old man comes to the physician for the evaluation of pain, cramps, and tingling in his lower extremities over the past 6 months. The patient reports that the symptoms worsen with walking more than two blocks and are completely relieved by rest. Over the past 3 months, his symptoms have not improved despite his participating in supervised exercise therapy. He has type 2 diabetes mellitus. He had smoked one pack of cigarettes daily for the past 50 years, but quit 3 months ago. He does not drink alcohol. His current medications include metformin, atorvastatin, and aspirin. Examination shows loss of hair and decreased skin temperature in the lower legs. Femoral pulses are palpable; pedal pulses are absent. Which of the following is the most appropriate treatment for this patient?

Percutaneous transluminal angioplasty

Vasopressors and inotropes for USMLE Step 3: High-Yield Pharmacology Lessons

Receptor Review - The Body's Buttons

Receptor	Primary Location(s)	Primary Effect
α1	Vascular smooth muscle, Pupillary dilator	↑ Vasoconstriction, ↑ SVR, Mydriasis
α2	Presynaptic nerve terminals, CNS	↓ Norepinephrine release, ↓ Sympathetic outflow
β1	Heart (SA/AV nodes, myocardium)	↑ Heart Rate, ↑ Contractility, ↑ Conduction
β2	Lungs, Vascular & Uterine smooth muscle	Bronchodilation, Vasodilation (↓ SVR)
D1	Renal & Mesenteric arteries	Vasodilation, ↑ Renal blood flow
V1	Vascular smooth muscle	Vasoconstriction (via $G_q$ pathway)

⭐ Exam Favorite: Dopamine's effects are dose-dependent: low doses target D1 (renal vasodilation), moderate doses β1 (↑ contractility), and high doses α1 (vasoconstriction).

The Pressure Crew - Meet the Agents

Drug	Receptor Activity	Primary Clinical Use	Key Adverse Effect
Norepinephrine	α1 > β1	Septic shock (1st line)	Peripheral ischemia
Epinephrine	β > α (low dose); α > β (high dose)	Anaphylaxis, Cardiac Arrest	Tachyarrhythmias
Phenylephrine	α1 only	Neurogenic shock, Anesthesia-induced hypotension	Reflex bradycardia
Dopamine	Dose-dependent: D > β1 > α1	Symptomatic bradycardia, Shock (not 1st line)	Tachyarrhythmias
Dobutamine	β1 > β2	Acute decompensated HF, Cardiogenic shock	Hypotension (β2), Tachyphylaxis
Vasopressin	V1 agonist	Septic shock (adjunct), Asystole	Coronary/mesenteric ischemia

⭐ In patients with cardiogenic shock, dobutamine can paradoxically cause hypotension if the patient is hypovolemic, as its β2-mediated vasodilation may outweigh its β1-mediated increase in cardiac output.

Shock Scenarios - The Right Drug, Right Time

Clinical decision-making for shock requires rapid identification of the underlying cause to guide pharmacotherapy. The primary goal is to restore tissue perfusion by targeting mean arterial pressure (MAP) > 65 mmHg.

⭐ In early, hyperdynamic septic shock ("warm shock"), cardiac output is paradoxically high due to peripheral vasodilation and a compensatory ↑ heart rate. As shock progresses, cardiac function deteriorates.

High‑Yield Points - ⚡ Biggest Takeaways

Phenylephrine, a pure α1 agonist, causes potent vasoconstriction and can lead to reflex bradycardia.

Norepinephrine is the first-line vasopressor for septic shock, with strong α1 and moderate β1 activity.

Epinephrine has dose-dependent effects: β-receptor effects dominate at low doses, while α-receptor effects dominate at high doses. It is the drug of choice for anaphylaxis.

Dobutamine is a primary β1 agonist that increases inotropy and is used in cardiogenic shock.

Milrinone, a PDE-3 inhibitor, increases intracellular cAMP, leading to increased inotropy and vasodilation.

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