A one litre IV bag of normal saline has been running for 6 hours at a rate of 75 mL/h. The doctor orders the remaining contents to be run through in the next five hours. Calculate the new flow rate.

A one litre IV bag of normal saline has been running for 6 hours at a rate of 75 mL/h. The doctor orders the remaining contents to be run through in the next five hours. Calculate the new flow rate.

• A. 90 mL/h
• B. 120 mL/h
• C. 105 mL/h
• D. 110 mL/h

Answer: (D)

Start with what’s left to deliver and the time allotted. The bag has 1000 mL total. In 6 hours at 75 mL/h you’ve delivered 75 × 6 = 450 mL, so 1000 − 450 = 550 mL remains. The doctor wants that remaining volume delivered in 5 hours, so the new flow rate is 550 mL ÷ 5 h = 110 mL/h. Delivering at 110 mL per hour will complete the infusion in the requested time.

Start with what’s left to deliver and the time allotted. The bag has 1000 mL total. In 6 hours at 75 mL/h you’ve delivered 75 × 6 = 450 mL, so 1000 − 450 = 550 mL remains. The doctor wants that remaining volume delivered in 5 hours, so the new flow rate is 550 mL ÷ 5 h = 110 mL/h. Delivering at 110 mL per hour will complete the infusion in the requested time.