An infusion bag of dobutamine contains 250 milligram / 250 millilitre. It is to be infused at the rate of 3 microgram / kg / minute to a 70 kg man. The rate of infusion in millilitre / hour (calculated to the nearest millilitre) will be:

1. A

   32

2. B

   26

3. C

   21

4. D

   13

Appeared in: GMCH - 2016

Explanation

• The calculation correctly determines the final infusion rate by converting the weight-based dose (mcg/kg/min) to a total hourly dose (mg/hr) and then dividing by the drug concentration (mg/mL).
• First, the total dose is calculated: 3 mcg/kg/min * 70 kg = 210 mcg/min.
• This is converted to an hourly rate in mg: (210 mcg/min * 60 min/hr) / 1000 mcg/mg = 12.6 mg/hr.
• The drug concentration is 250 mg / 250 mL = 1 mg/mL.
• The infusion rate is then calculated as: 12.6 mg/hr / 1 mg/mL = 12.6 mL/hr.
• Rounding 12.6 to the nearest whole number gives 13 mL/hr.

Why Other Options Were Wrong

• Option A: This value is incorrect and likely results from a significant miscalculation, possibly involving incorrect unit conversions or misplaced decimal points.
• Option B: This value is incorrect. It may arise from calculation errors, such as doubling the final answer or miscalculating the hourly dose conversion.
• Option C: This value is incorrect. A common error is to confuse the total dose in mcg/min (210) and then perform an incorrect division, for example, dividing by 10 (210 / 10 = 21), instead of following the correct conversion and rate calculation formula.

Related Visual

Clinical Relevance

• Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain IV infusion rate calculation for a weight-based medication as background academic context rather than a clinical decision trigger.
• Accurate dosage calculation is a critical nursing skill to ensure patient safety, especially with potent vasoactive drugs like dobutamine, where small errors can lead to significant changes in heart rate and blood pressure.
• It is a standard and best practice to have a second nurse independently verify any high-alert medication calculation before administration to prevent medication errors.
• What if the drug concentration was different, for example, 500 mg in 250 mL? The concentration would be 2 mg/mL. The final rate would be 12.6 mg/hr ÷ 2 mg/mL = 6.3 mL/hr, which rounds to 6 mL/hr. This shows how concentration directly impacts the final rate.

How to Approach the Question

• First, identify all the given values in the problem: the drug, the concentration (250 mg/250 mL), the prescribed dose (3 mcg/kg/min), and the patient's weight (70 kg).
• Next, identify what the question is asking for: the infusion rate in millilitres per hour (mL/hr).
• Follow a systematic, step-by-step approach. Start by calculating the total dose the patient needs per minute.
• Convert the units to match the final answer required. Here, convert mcg/min to mg/hr.
• Calculate the drug concentration from the information on the infusion bag.
• Use the standard formula: Rate (mL/hr) = Dose (mg/hr) / Concentration (mg/mL).

Concept Tested & Keywords

• Concept Tested: IV infusion rate calculation for a weight-based medication.
• Stem keywords: dobutamine, infusion, 250 milligram / 250 millilitre, 3 microgram / kg / minute, 70 kg, millilitre / hour
• Lead-in keywords: rate of infusion

Question ID

QVHGZ7-SKlZB0xQHkQv6eS

Copy ID

Reference Book

E6 Pharmacology Nurses Shanbhag 3e p. 56-58

E6 Pharmacology KD Tripathi OneStop 9e p. 181-183