Dextrose 5% in water (D5W) 1 liter is to be infused. The rate is set at 75 mL/hour for the first 6 hours, then reduced to 50 mL/hour. How long will it take to deliver the full 1 liter?

Dextrose 5% in water (D5W) 1 liter is to be infused. The rate is set at 75 mL/hour for the first 6 hours, then reduced to 50 mL/hour. How long will it take to deliver the full 1 liter?

• A. 15 hours
• B. 16 hours
• C. 17 hours
• D. 18 hours

Answer: (C)

When a infusion uses two different rates, handle it step by step. First, see how much volume is delivered in the initial period: 6 hours at 75 mL per hour equals 6 × 75 = 450 mL. The remaining volume to infuse is 1000 mL − 450 mL = 550 mL. Now switch to the lower rate: 550 mL ÷ 50 mL per hour = 11 hours. Add the initial 6 hours to get the total time: 6 + 11 = 17 hours. Thus, the full liter will be delivered in 17 hours.

When a infusion uses two different rates, handle it step by step. First, see how much volume is delivered in the initial period: 6 hours at 75 mL per hour equals 6 × 75 = 450 mL. The remaining volume to infuse is 1000 mL − 450 mL = 550 mL. Now switch to the lower rate: 550 mL ÷ 50 mL per hour = 11 hours. Add the initial 6 hours to get the total time: 6 + 11 = 17 hours. Thus, the full liter will be delivered in 17 hours.