A healthcare provider orders a continuous IV infusion of Nitroglycerin to run at 15 mcg/min. The pharmacy supplies a solution of 50 mg of Nitroglycerin in 500 mL of D5W. At what rate (in mL/hr) should the nurse set the infusion pump?

1. A

   3 mL/hr

2. B

   6 mL/hr

3. C

   9 mL/hr

4. D

   15 mL/hr

Appeared in: NORCET 9 Prelims-2025

Explanation

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• The calculation requires a three-step process: determining drug concentration, calculating the hourly dose, and then finding the infusion rate.
• First, convert the available drug (50 mg in 500 mL) to a standard concentration. 50 mg is 50,000 mcg. Dividing 50,000 mcg by 500 mL gives a concentration of 100 mcg/mL.
• Next, convert the ordered dose from minutes to hours. An order of 15 mcg/min is equivalent to 900 mcg/hr (15 mcg × 60 min).
• Finally, divide the required hourly dose by the concentration to get the rate in mL/hr: 900 mcg/hr ÷ 100 mcg/mL = 9 mL/hr.

Why Other Options Were Wrong

• Option A: An infusion rate of 3 mL/hr would only deliver 300 mcg of Nitroglycerin per hour (3 mL/hr × 100 mcg/mL), which is equivalent to 5 mcg/min. This is one-third of the prescribed dose.
• Option B: An infusion rate of 6 mL/hr would deliver 600 mcg of Nitroglycerin per hour (6 mL/hr × 100 mcg/mL), which is equivalent to 10 mcg/min. This is two-thirds of the prescribed dose.
• Option D: An infusion rate of 15 mL/hr would deliver 1500 mcg of Nitroglycerin per hour (15 mL/hr × 100 mcg/mL), which is equivalent to 25 mcg/min. This is significantly higher than the prescribed dose and could cause profound hypotension.

Related Visual

• Visual 1: Flowchart - A flowchart illustrating the step-by-step process of IV infusion calculation: 1. Find concentration (mcg/mL), 2. Find hourly dose (mcg/hr), 3. Divide hourly dose by concentration to get mL/hr.
• Visual 2: Infographic - An infographic showing the formula: Rate (mL/hr) = [Dose (mcg/min) x 60 min/hr] / [Concentration (mcg/mL)].
• Visual 3: Image - A picture of an infusion pump with the screen displaying a rate of '9 mL/hr' to reinforce the correct answer visually.

Clinical Relevance

• Nursing practice connection: Knowing IV infusion rate calculation for continuous medication administration helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
• Accurate medication calculation is a fundamental nursing responsibility and is critical for patient safety. Errors can lead to underdosing (ineffective treatment) or overdosing (toxicity and adverse effects).
• Nitroglycerin is a high-alert medication. Its primary effect is vasodilation, which can cause a rapid drop in blood pressure. An incorrect, high dose can lead to severe hypotension, reflex tachycardia, and myocardial ischemia.
• Most hospital policies require independent double-checks by two registered nurses for the setup and rate changes of high-alert medications like Nitroglycerin.

How to Approach the Question

• First, identify the question type. This is an analytical question requiring a drug dosage calculation.
• Identify the given information: Ordered dose (15 mcg/min), available solution (50 mg in 500 mL), and the desired unit for the answer (mL/hr).
• Standardize the units. The order is in 'mcg', but the supply is in 'mg'. Convert mg to mcg (1 mg = 1000 mcg).
• Calculate the concentration of the drug in the IV bag in mcg per mL.
• Calculate the total amount of drug needed per hour based on the per-minute order.
• Use the standard formula: Infusion Rate (mL/hr) = [Total Dose Required per Hour] / [Concentration of Drug per mL]. Perform the final division to find the answer.

Concept Tested & Keywords

• Concept Tested: IV infusion rate calculation for continuous medication administration.
• Stem keywords: Nitroglycerin, IV infusion, mcg/min, mg, mL, D5W, infusion pump, mL/hr
• Lead-in keywords: At what rate

Question ID

Qp_9e7z9CNMesyb9ZoqT7P

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