A 45-year-old man comes to the emergency department due to a 2-day history of dyspnea, orthopnea, and ankle swelling. This morning, he also had nausea, vomiting, and a headache. Blood pressure is elevated, and physical examination shows pulmonary crackles and bilateral pitting edema up to the knees. A sodium nitroprusside infusion is begun. Which of the following left ventricular pressure/volume relationships best represents the effects of this therapy?*Solid line = before nitroprusside; dashed line = during nitroprusside infusion.

Question

A 45-year-old man comes to the emergency department due to a 2-day history of dyspnea, orthopnea, and ankle swelling.  This morning, he also had nausea, vomiting, and a headache.  Blood pressure is elevated, and physical examination shows pulmonary crackles and bilateral pitting edema up to the knees.  A sodium nitroprusside infusion is begun.  Which of the following left ventricular pressure/volume relationships best represents the effects of this therapy?*Solid line = before nitroprusside; dashed line = during nitroprusside infusion.

Quizplus · Accepted Answer

11ec160b_3c92_fd28_9249_0902536aac18_MD0001_00 This patient most likely has acute heart failure due to systemic hypertension, which can be treated with an infusion of sodium nitroprusside. Sodium nitroprusside is a short-acting agent that causes balanced vasodilation of the veins and arteries; as such, it decreases left ventricular (LV) preload and afterload, allowing for maintenance of cardiac output (unchanged stroke volume) at a lower LV pressure (decreased LV work). LV contractility is essentially unchanged. Of the choices given, only graph E shows a reduction in both LV end-diastolic volume (preload) and LV systolic pressure (afterload) without a decrease in stroke volume. (Choice A) This graph depicts unchanged preload with increased stroke volume due to an increase in LV contractility (point 3 is moved upward and to the left). The slight increase in afterload occurs secondary to the increase in contractility. Such changes are expected with the administration of a positive inotrope with minimal vasodilatory/vasoconstrictive effect (eg, digoxin). (Choice B) This graph depicts increased preload with an increase in stroke volume and no change in contractility. The increase in afterload is secondary to the increase in stroke volume (higher stroke volume increases systolic pressure). Such changes are consistent with the Frank-Starling response to increased preload. (Choice C) This graph depicts an increase in preload and afterload with a reduction in stroke volume and no change in contractility. Such changes are detrimental in heart failure and would be expected with a vasoconstrictor affecting both the veins and arteries but with no effect on the myocardium (eg, the alpha-1 agonist phenylephrine). (Choice D) This graph depicts a decrease in preload and stroke volume with a minimal reduction in afterload and no change in contractility. These changes are expected with predominantly venous dilators such as nitrates (eg, nitroglycerin, isosorbide mononitrate, isosorbide dinitrate). Sodium nitroprusside differs from nitrates in that it generates nitric oxide in the bloodstream rather than in the venous smooth muscle, creating a balanced vasodilatory effect on both the arteries and veins. Educational objective: Sodium nitroprusside is a short-acting agent that causes balanced vasodilation of the veins and arteries to decrease both left ventricular (LV) preload and afterload. The balanced vasodilation allows for maintenance of stroke volume and cardiac output at a lower LV pressure (lower cardiac work).

A 45-Year-Old Man Comes to the Emergency Department Due to a 2-Day