A patient's dry weight is 154.0 lb (70 kg) and their pre-treatment weight is 158.4 lb (72 kg). How many mL/hour must they lose to reach their dry weight during a four-hour treatment?

To determine how many mL/hour the patient needs to lose to reach their dry weight during a four-hour treatment, we first need to calculate the total weight that must be lost. The patient's pre-treatment weight is 158.4 lb, and their dry weight is 154.0 lb.

The difference between these two weights is:

158.4 lb - 154.0 lb = 4.4 lb

Next, we convert this weight loss into kilograms:

4.4 lb / 2.2046 = approximately 2 kg

Since 1 liter of fluid approximately weighs 1 kg, the patient must lose around 2 liters of fluid (2,000 mL) to reach their dry weight.

Now, to find out how many mL/hour the patient must lose over a four-hour treatment:

2,000 mL / 4 hours = 500 mL/hour

This calculation shows that to achieve the desired weight loss to reach dry weight within the four-hour treatment, the patient must lose 500 mL/hour. Thus, the answer is 500 mL/hour.