Infusion of 500 ml normal saline over 6 hours requires how many drops per minute when the drop factor is 15 drops per ml?

Appeared in: RUHS, Jaipur, M.Sc Nursing Entrance Exam-2019

Explanation

derived using the standard formula for calculating IV drip rates: Flow Rate (gtt/min) = (Total Volume in mL × Drop Factor) / Time in minutes.
First, the total infusion time must be converted from hours to minutes: 6 hours × 60 minutes/hour = 360 minutes.
Next, the values are substituted into the formula: (500 mL × 15 gtt/mL) / 360 minutes.
This calculation results in 7500 / 360, which equals 20.83 gtt/min.
Since it is impossible to administer a fraction of a drop, the rate is rounded to the nearest whole number, which is 21 gtt/min.

Option A: This result would be obtained from an incorrect calculation, possibly by dividing the total drops (7500) by an incorrect time, such as approximately 326 minutes instead of 360.
Option C: This result would be obtained from an incorrect calculation, possibly by dividing the total drops (7500) by an incorrect time, such as approximately 441 minutes (about 7.35 hours) instead of 360.
Option D: This option incorrectly uses the drop factor (15) as the final answer, completely disregarding the total volume and time for the infusion.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain IV flow rate calculation as background academic context rather than a clinical decision trigger.
Accurate calculation of IV flow rates is a fundamental nursing skill crucial for patient safety. Administering fluids too quickly can lead to fluid overload, while administering them too slowly can result in dehydration or delayed therapeutic effect.
Nurses must always double-check their calculations and, if possible, have another nurse verify them, especially for critical medications or vulnerable patients (e.g., pediatric, elderly, cardiac, or renal patients).
What if the infusion was for a pediatric patient? A microdrip set (60 gtt/mL) would likely be used for more precise control. The rate would then be (500 mL × 60 gtt/mL) / 360 min = 83 gtt/min.

How to Approach the Question

Identify this as a calculation question requiring a specific formula.
Extract all the necessary values from the stem: Total Volume (500 mL), Total Time (6 hours), and Drop Factor (15 gtt/mL).
Recall the standard formula for IV drip rate: (Volume × Drop Factor) / Time.
Ensure all units are consistent for the formula. Convert the time from hours to minutes (6 hours × 60 = 360 minutes).
Substitute the values into the formula: (500 × 15) / 360.
Perform the calculation and round the final answer to the nearest whole number, as partial drops cannot be administered.

Concept Tested & Keywords

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E6 Pharmacology Nurses Shanbhag 3e p. 54-56

E6 Nursing Fundamentals Potter Perry 12e Part 5 p. 93-95

E6 Nursing Fundamentals Taylor p. 799-801

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