For a four-hour treatment, if a patient’s preweight is 72 kg and the target dry weight is 70 kg, the amount of fluid to be removed is best expressed as what rate in mL per hour?

• A. 1000 mL/hour
• B. 250 mL/hour
• C. 750 mL/hour
• D. 500 mL/hour

Answer: (D)

Determine how much fluid to remove and over how long. The fluid to be removed equals the difference between preweight and target dry weight: 72 kg − 70 kg = 2 kg, which is about 2 liters. Over a four-hour treatment, the ultrafiltration rate is 2 L ÷ 4 h = 0.5 L/h, i.e., 500 mL per hour. So the best expression is 500 mL/hour. This uses the idea that 1 kg of weight corresponds to roughly 1 liter of fluid, and the rate is the hourly amount removed.