A unit of autologous blood 480 mL is to be infused over 3 hours using a giving set that delivers 15 drops/mL. What is the drip rate in gtt/min?

A unit of autologous blood 480 mL is to be infused over 3 hours using a giving set that delivers 15 drops/mL. What is the drip rate in gtt/min?

• A. 39 gtt/min
• B. 41 gtt/min
• C. 40 gtt/min
• D. 42 gtt/min

Answer: (C)

The key idea is converting the prescribed volume and time into a flow rate using the drop factor. First find the rate in milliliters per minute: 480 mL over 180 minutes (3 hours) equals 480/180 = 2.666... mL/min. Convert that to drops per minute with the given drop factor of 15 drops per mL: 2.666... mL/min × 15 gtt/mL = 40 gtt/min. The same calculation can be done directly by (480 mL × 15 gtt/mL) / 180 min = 40 gtt/min. So the drip rate is 40 gtt/min.

The key idea is converting the prescribed volume and time into a flow rate using the drop factor. First find the rate in milliliters per minute: 480 mL over 180 minutes (3 hours) equals 480/180 = 2.666... mL/min. Convert that to drops per minute with the given drop factor of 15 drops per mL: 2.666... mL/min × 15 gtt/mL = 40 gtt/min. The same calculation can be done directly by (480 mL × 15 gtt/mL) / 180 min = 40 gtt/min. So the drip rate is 40 gtt/min.