Which rate is correct for 150 mL/hr with a 15 gtt/mL drop factor?

Which rate is correct for 150 mL/hr with a 15 gtt/mL drop factor?

• A. 36 gtt/min
• B. 40 gtt/min
• C. 38 gtt/min
• D. 42 gtt/min

Answer: (C)

This tests converting a volume-per-hour infusion into drops per minute using the drop factor. The formula is gtt/min = (volume in mL per hour) × (drop factor in gtt/mL) ÷ 60. Plugging in 150 mL/hr and 15 gtt/mL: 150 × 15 = 2250 drops per hour. Divide by 60 minutes gives 2250 ÷ 60 = 37.5 gtt/min. You round to the nearest whole drop, so 37.5 becomes 38 gtt/min. An alternate view: 150 mL/hr is 2.5 mL/min (since 150 ÷ 60 = 2.5). Multiply by 15 gtt/mL to get 2.5 × 15 = 37.5 gtt/min, which also rounds to 38 gtt/min. Therefore, the correct rate is 38 gtt/min.

This tests converting a volume-per-hour infusion into drops per minute using the drop factor. The formula is gtt/min = (volume in mL per hour) × (drop factor in gtt/mL) ÷ 60.

Plugging in 150 mL/hr and 15 gtt/mL: 150 × 15 = 2250 drops per hour. Divide by 60 minutes gives 2250 ÷ 60 = 37.5 gtt/min. You round to the nearest whole drop, so 37.5 becomes 38 gtt/min.

An alternate view: 150 mL/hr is 2.5 mL/min (since 150 ÷ 60 = 2.5). Multiply by 15 gtt/mL to get 2.5 × 15 = 37.5 gtt/min, which also rounds to 38 gtt/min. Therefore, the correct rate is 38 gtt/min.