I find dimentional analysis to be the easiest way to work out dosage calculations. It lines up really nice, and you just have to multiply the fractions. If you follow these 3 rules for your calculations, it's simple. Step 1: Start out with what you're looking for (just put the units of measurement first without any numbers to get your thoughts straight). Step 2: Your next numerator has to have the same unit of measurement as your previous denominator (this is so you can cancel them out). Step 3: When you are left with only the units of measurement you are looking for, you are done...just do the math straight across.The problem reads: Ordered: Heparin 18 units per kg per hr in a continuous infusion. Available: Heparin 25,000 units in a 500 mL D5W. Patient's weight: 70kg.a. How many units per hr are ordered? U/ hr = 18 U/ kg/hr X 70 kg/ 1 (I use a 1 as a filler when nothing else goes there. It's not really needed in this case, but in a more complicated problem, it helps) = 1260/ 1 = 1260 U/ hr b. The nurse will set the flow rate at how many mL per hr? mL/ hr = 500 mL/ 25,000 U X 1260 U/ hr = 630,000/ 25,000 = 25.2 --> 25 mL/ hr I had this typed in Word so I could should the fractions better and how you cancel out the units of measurement, but I couldn't figure out how to attach it lol. Anyway, I hope this makes sense.