A 60 kg patient is to be given intravenous Nitroglycerin (NTG) at the rate of 10 micrograms per minute. A 50 ml syringe contains 25 milligrams of NTG. The rate of syringe infusion pump will be set at

1. A

   2.4 ml/hr

2. B

   1.2 ml/hr.

3. C

   1.8 ml/hr

4. D

   0.6 ml/hr

Appeared in: GMCH - 2015

Explanation

• The calculation requires finding the drug concentration first: 25 mg in 50 ml is 25,000 mcg in 50 ml, which equals 500 mcg/ml.
• Next, the prescribed dose rate (10 mcg/min) must be converted to an hourly rate: 10 mcg/min * 60 min/hr = 600 mcg/hr.
• Finally, the infusion rate is calculated by dividing the hourly dose by the concentration: 600 mcg/hr ÷ 500 mcg/ml = 1.2 ml/hr.
• The patient's weight is irrelevant information (a distractor) for this specific calculation.

Why Other Options Were Wrong

• Option A: A rate of 2.4 ml/hr would deliver 1200 mcg/hr, or 20 mcg/min, which is double the prescribed dose.
• Option C: A rate of 1.8 ml/hr would deliver 900 mcg/hr, or 15 mcg/min.
• Option D: A rate of 0.6 ml/hr would deliver 300 mcg/hr, or 5 mcg/min, which is half the prescribed dose.

Related Visual

Clinical Relevance

• Nursing practice connection: Use the key finding related to Intravenous Drug Dose Calculation to guide bedside assessment, documentation, and the next nursing action.
• Accurate drug calculation is a critical nursing skill to prevent medication errors, which can have severe consequences for patient safety.
• Nitroglycerin is a high-alert medication. Nurses must be vigilant in monitoring for its primary side effect, hypotension, and be prepared to intervene.
• What if? If the order was for 10 mcg/kg/min, the calculation would change. The total dose would be 10 mcg * 60 kg = 600 mcg/min. The hourly rate would then be (600 mcg/min * 60 min/hr) / 500 mcg/ml = 72 ml/hr. This highlights the importance of distinguishing between fixed-rate and weight-based dosing.

How to Approach the Question

• Identify the goal: The question asks for the infusion pump rate in ml/hr.
• Extract the given values: Desired dose (10 mcg/min), available drug (25 mg in 50 ml).
• Check for consistent units. The desired dose is in mcg, but the available drug is in mg. Convert mg to mcg (1 mg = 1000 mcg).
• Calculate the concentration of the drug solution (mcg/ml).
• Convert the desired dose from per minute to per hour (multiply by 60).
• Apply the formula: Rate (ml/hr) = Hourly Dose (mcg/hr) / Concentration (mcg/ml).

Concept Tested & Keywords

• Concept Tested: Intravenous Drug Dose Calculation
• Stem keywords: Nitroglycerin (NTG), intravenous, 10 micrograms per minute, 25 milligrams, 50 ml, syringe infusion pump
• Lead-in keywords: rate will be set at
• Clinical cues: Patient weight of 60 kg is a distractor as the dose is not weight-based.

Question ID

Q7jW6z6nmQcsmtfQUjl5Rr

Copy ID

Reference Book

E6 Pharmacology Nurses Shanbhag 3e pp. 56-58, 54-56