A patient with Graves’ disease exhibits symptoms of tachycardia, heat intolerance, and exophthalmos. Which drug is used to alter thyroid hormone levels prior to surgery?

Choice A rationale:

Hypertension is not a primary contraindication for mannitol use. While it's important to monitor blood pressure during mannitol administration, it's not the most concerning factor in this scenario.

Mannitol can even be used cautiously in hypertensive patients with conditions like intracranial hypertension or acute renal failure, where its benefits may outweigh the potential risks of exacerbating hypertension.

Choice B rationale:

Mannitol is actually indicated for the treatment of increased intracranial pressure (ICP). It works by drawing fluid from the brain tissues into the bloodstream, thereby reducing pressure within the skull.

Therefore, a patient with ICP would not be a concern for mannitol administration; rather, they would be a potential candidate for its use.

Choice D rationale:

While fluid volume overload can be a concern with mannitol use, it's typically managed with careful monitoring and fluid restriction.

The more significant concern in this scenario is congestive heart failure (CHF).

Choice C rationale:

Mannitol is contraindicated in patients with congestive heart failure (CHF). Here's why:

Increased Circulating Volume: Mannitol is an osmotic diuretic, meaning it draws fluid from the tissues into the bloodstream, increasing circulating blood volume. This can overload the already compromised heart in CHF patients, leading to worsening heart failure and pulmonary edema.

Elevated Blood Pressure: Mannitol can also cause a transient increase in blood pressure due to its osmotic effects. This can further strain the heart and worsen CHF symptoms.

Renal Impairment: CHF patients often have impaired renal function, which can reduce their ability to excrete mannitol effectively. This can lead to fluid retention and electrolyte imbalances, further complicating CHF management.

In summary, administering mannitol to a patient with CHF could potentially lead to:

Exacerbation of heart failure symptoms Pulmonary edema

Worsening renal function Electrolyte imbalances Increased risk of mortality

Therefore, it's crucial to avoid mannitol use in patients with CHF and to closely monitor fluid status and electrolytes in those who must receive it for other indications.

Choice A rationale:

Digoxin is a cardiac glycoside, not a calcium channel blocker. It works by increasing the force of contraction of the heart muscle and slowing the heart rate. However, it is not typically used as a first-line treatment for tachycardia. It's more commonly used to treat heart failure and atrial fibrillation.

Mechanism of action: Digoxin inhibits the sodium-potassium ATPase pump in cardiac cells, leading to an increase in intracellular calcium. This increased calcium availability enhances myocardial contractility. Digoxin also indirectly affects the autonomic nervous system, leading to a decrease in heart rate.

Key points:

Digoxin is not a calcium channel blocker.

It's used primarily for heart failure and atrial fibrillation.

Its mechanism of action involves increasing intracellular calcium and decreasing heart rate.

Choice B rationale:

Diltiazem (Cardizem) is a calcium channel blocker that is commonly used to treat tachycardia and manage heart rate. It works by blocking the movement of calcium into cardiac cells, which slows down the electrical conduction system of the heart and leads to a decrease in heart rate.

Mechanism of action: Diltiazem blocks L-type calcium channels in cardiac and vascular smooth muscle cells. This reduces calcium influx, leading to:

Decreased myocardial contractility Vasodilation (relaxation of blood vessels)

Negative chronotropic effect (decreased heart rate)

Negative dromotropic effect (slowed conduction through the AV node) Key points:

Diltiazem is a calcium channel blocker.

It's effective in treating tachycardia and managing heart rate.

Its mechanism of action involves blocking calcium channels, leading to various cardiovascular effects.

Choice C rationale:

Nitroglycerin is a vasodilator, not a calcium channel blocker. It works by relaxing the smooth muscle in blood vessels, which widens the vessels and allows more blood to flow through them. This can help to relieve chest pain (angina) and lower blood pressure, but it does not directly affect heart rate.

Mechanism of action: Nitroglycerin is metabolized to nitric oxide, which activates guanylate cyclase, leading to increased production of cyclic guanosine monophosphate (cGMP). cGMP causes smooth muscle relaxation, resulting in vasodilation.

Key points:

Nitroglycerin is a vasodilator, not a calcium channel blocker. It's primarily used for angina and hypertension.

Its mechanism of action involves nitric oxide-mediated vasodilation.

Choice D rationale:

Nitroprusside (Nipride) is a potent vasodilator, not a calcium channel blocker. It is typically used in critical care settings to manage severe hypertension or heart failure. It works by relaxing the smooth muscle in blood vessels, which widens the vessels and allows more blood to flow through them. This can help to lower blood pressure, but it does not directly affect heart rate.

Mechanism of action: Nitroprusside directly releases nitric oxide, leading to vasodilation. Key points:

Nitroprusside is a potent vasodilator, not a calcium channel blocker.

It's used in critical care settings for severe hypertension or heart failure.

Its mechanism of action involves direct nitric oxide release and vasodilation.