To replace nasogastric losses, an IV of normal saline with potassium chloride is ordered. If 640 mL must infuse over 8 hours with a drop factor of 15 gtt/mL, what is the IV flow rate in gtt/min?

To replace nasogastric losses, an IV of normal saline with potassium chloride is ordered. If 640 mL must infuse over 8 hours with a drop factor of 15 gtt/mL, what is the IV flow rate in gtt/min?

• A. 80 mL/hr
• B. 100 mL/hr
• C. 20 gtt/min
• D. 25 gtt/min

Answer: (C)

In gravity IV calculations, the flow rate in drops per minute is found by multiplying the volume to be infused by the drop factor, then dividing by the total time in minutes. Here, 640 mL over 8 hours equals 80 mL per hour, or 80 mL/hour. Multiply by the drop factor: 80 mL/hour × 15 gtt/mL = 1200 gtt/hour. Convert to minutes: 1200 gtt/hour ÷ 60 min/hour = 20 gtt/min. So the IV rate is 20 gtt/min. Using the direct formula gives the same result: (640 mL × 15 gtt/mL) ÷ (8 hours × 60 min/hour) = 20 gtt/min. The other options don’t use the drop factor and time in the correct way.

In gravity IV calculations, the flow rate in drops per minute is found by multiplying the volume to be infused by the drop factor, then dividing by the total time in minutes. Here, 640 mL over 8 hours equals 80 mL per hour, or 80 mL/hour. Multiply by the drop factor: 80 mL/hour × 15 gtt/mL = 1200 gtt/hour. Convert to minutes: 1200 gtt/hour ÷ 60 min/hour = 20 gtt/min. So the IV rate is 20 gtt/min. Using the direct formula gives the same result: (640 mL × 15 gtt/mL) ÷ (8 hours × 60 min/hour) = 20 gtt/min. The other options don’t use the drop factor and time in the correct way.