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Decreased cardiac contractility
13%
29/225
Increased left ventricular end-diastolic pressure
8%
18/225
Decreased stroke volume
29%
66/225
Decreased pulmonary capillary wedge pressure
46%
103/225
Increased systemic vascular resistance
2%
4/225
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Nitroprusside, a medication commonly used in the treatment of hypertensive emergencies, is the most likely agent described in the question stem. It acts as both a venous and arterial vasodilator, leading to decreases in both preload (reflected in the left ventricular end-diastolic pressure and pulmonary capillary wedge pressure) and afterload (systemic vascular resistance). Nitroprusside is a short acting antihypertensive agent that allows for excellent minute-to-minute control of blood pressure. It is particularly useful in the treatment of hypertensive emergencies or acute congestive heart failure. Although decreases in both preload and afterload are seen with its administration, its effect on preload is thought to be relatively greater, leading to moderate venous pooling. The primary limitation to the use of nitroprusside is its metabolism to cyanide and development of associated toxicity. Sanders discusses the management of hypertensive emergencies. He states that prompt treatment with antihypertensives and close monitoring is essential, with a goal of reducing diastolic pressure either 20-25% or to 100-110 mmHg over one hour. The author cautions against lowering blood pressures too quickly, which can exacerbate the patient's symptoms and decrease blood flow to end organs, resulting in damage. Cohn et al. provide an excellent overview of clinically significant direct-acting vasodilators. Nitroprusside is almost exclusively used in the intensive care setting to lower blood pressure in hypertensive crises or when left ventricular function is failing secondary to increased work against elevated systemic pressures. Illustration A depicts the vasodilating mechanism of action of nitroprusside. Incorrect Answers: Answer 1: Nitroprusside does not have a direct effect on cardiac contractility; instead a reflex increase in cardiac contractility might be expected in this scenario. Answer 2: Nitroprusside causes a decrease in left ventricular end diastolic pressure through venous vasodilation and resulting decreased preload. Answer 3: Nitroprusside lowers both preload and afterload, resulting in a maintenance of cardiac stroke volume. Answer 5: Through arterial vasodilation, systemic vascular resistance (afterload) is decreased in response to nitroprusside.
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