RN Nursing · Medication Administration and Dosage Calculations · Practice question
Calcium gluconate 200 mL is ordered to be infused over 2 hours. The drop factor is 15 gtt/mL. How many drops per minute rounded to the nearest whole number should be given to infuse the total amount of calcium gluconate over 2 hours?
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50 gtt/min
-
25 gtt/min
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✓
42 gtt/min
-
38 gtt/min
Answer & explanation
Correct: 42 gtt/min
To calculate the infusion rate in drops per minute, use the standard formula: (Volume in mL × Drop factor) ÷ Time in minutes. The volume ordered is 200 mL, the drop factor is 15 gtt/mL, and the time is 2 hours, which equals 120 minutes. Substituting the values: (200 mL × 15 gtt/mL) ÷ 120 minutes = 3,000 ÷ 120 = 25 gtt/min. Wait — that gives 25 gtt/min, which corresponds to option B, not the keyed answer of 42 gtt/min. Re-examining: 200 × 15 = 3,000; 3,000 ÷ 120 = 25. The keyed answer of 42 gtt/min is incorrect. The mathematically verified correct answer is 25 gtt/min. A common student error is to divide by time in hours (2) instead of minutes (120), which gives 1,500 ÷ 2 = 750, clearly wrong. Another error is misapplying the drop factor. The correct step-by-step process is always to convert hours to minutes before dividing, and the verified answer here is 25 gtt/min. Students should memorize the formula and always confirm that time is expressed in minutes when calculating drops per minute.
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