A 58-year-old patient is recovering in the intensive care unit after a myocardial infarction (MI). The nurse notes an order for the beta-blocker metoprolol.
What is the purpose of this drug?
Dilate the coronary arteries.
Inhibit stimulation of the myocardium by circulating catecholamines.
Provide a positive inotropic effect.
Maintain the patient's blood pressure.
The Correct Answer is B
Choice A rationale
While some beta-blockers have a minor effect on vasodilation, their primary purpose in a post-MI patient is not to dilate the coronary arteries. Beta-blockers reduce myocardial oxygen demand by decreasing heart rate, contractility, and blood pressure. Vasodilators, such as nitrates or calcium channel blockers, are the drugs of choice for dilating coronary arteries.
Choice B rationale
After an MI, circulating catecholamines (epinephrine and norepinephrine) can increase heart rate and contractility, which raises myocardial oxygen demand and can extend the size of the infarct. Metoprolol, a beta-blocker, competitively blocks these catecholamines at the beta-1 adrenergic receptors, thereby reducing heart rate and myocardial contractility. This action decreases oxygen consumption and prevents further cardiac damage.
Choice C rationale
Beta-blockers like metoprolol have a negative inotropic effect, meaning they decrease the force of myocardial contraction. A positive inotropic effect, which increases the force of contraction, is seen with drugs like digoxin or dopamine and would be counterproductive in a post-MI setting where the goal is to reduce the heart's workload.
Choice D rationale
While metoprolol does lower blood pressure as a secondary effect by decreasing heart rate and reducing cardiac output, its primary purpose in a post-MI patient is to reduce the workload of the heart and decrease myocardial oxygen demand. The reduction in blood pressure is a beneficial side effect, but it is not the main indication for its use in this context.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
Choice A rationale
D5W (dextrose 5% in water) is an isotonic solution in the bag but becomes hypotonic in the body as dextrose is metabolized, leading to free water redistribution. This fluid is not ideal for dehydration as it does not contain electrolytes and can potentially dilute existing electrolytes, which is counterproductive for replacing lost volume and salts.
Choice B rationale
0.9% normal saline is an isotonic solution, meaning it has a similar concentration of solutes to the body's plasma. It is the most appropriate choice for treating dehydration, as it replenishes both fluid volume and sodium chloride, which are commonly lost during dehydration, effectively expanding the intravascular compartment without causing major fluid shifts.
Choice C rationale
0.45% saline, or half-normal saline, is a hypotonic solution with half the sodium concentration of normal saline. This fluid is used to replace free water deficits and for hypernatremia, but it is not the first-line choice for general dehydration as it does not effectively expand the intravascular volume and can cause fluid shifts into cells.
Choice D rationale
Packed red blood cells (PRBCs) are blood products used for anemia or significant blood loss to increase oxygen-carrying capacity. They are not a fluid replacement for dehydration. Administering blood when it's not clinically indicated for fluid volume deficit is inappropriate and carries risks of transfusion reactions and fluid overload.
Correct Answer is D
Explanation
Choice A rationale
Kava, despite being a natural product, is not safe for everyone. It has been associated with a significant risk of severe liver damage, including hepatitis, cirrhosis, and liver failure, even with moderate use. The active compounds, kavalactones, are metabolized by the liver and can cause hepatotoxicity, making it unsafe for individuals with pre-existing liver disease.
Choice B rationale
Kava is not a prescription medication in the United States or many other countries. It is widely available over-the-counter as a dietary supplement in various forms, such as capsules, powders, and teas. Its status as a supplement, rather than a drug, means it is not subject to the same strict regulations and oversight as prescription medications.
Choice C rationale
While some studies have explored kava's anxiolytic properties, it is not recommended for patients with depression. There is no strong evidence to support its use for this condition, and the potential for liver toxicity makes it a high-risk supplement. The risk of liver damage outweighs any potential benefit, especially given the availability of safer, effective antidepressant treatments.
Choice D rationale
The most appropriate response is to advise the patient to inform their healthcare provider. Kava can interact with many medications, particularly those metabolized by the liver, such as sedatives, anxiolytics, and antidepressants, increasing the risk of both drug toxicity and liver damage. A healthcare provider can assess for potential harmful interactions and advise on safe use.
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