NAPLEX Question of the Week: Calculations

Calculations are a daily task performed by pharmacists in nearly all settings and is an important portion of the NAPLEX.

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A 45-year-old mechanically ventilated woman is receiving propofol for sedation. The drug is provided as 10 mg/mL propofol and is being delivered at 200 mg/h. Propofol is commercially provided in a 10% lipid emulsion vehicle. How many calories per day is the patient receiving via the propofol infusion assuming constant rate?

a. 100

b. 144

c. 264

d. 528

Propofol is commonly used as a sedative in mechanically ventilated critically ill patients. The rate of administration for this use frequently provides significant lipid kcal (1.1kcal/mL) and should be taken into account when calculating kcal and lipid administration. In patients receiving PN concomitantly, IV lipid emulsion may need to be held or the rate of administration cut while the patient is receiving propofol. Clevidipine is an intravenous antihypertensive medication that is also provided in lipid emulsion, and when it is used, fat calories provided by the formulation should be taken into account.

Answer d is correct. Calculation is as follows:

Propofol being infused at 200 mg/h/10 mg/mL = 20 mL/h

20 mL/h × 24 h/d = 480 mL/d

480 ml/d x 1.1 kcal/ml = 528 kcal

Calculations should be a major component of your studying in the new year. They could be asked in a number of question formats including the constructed response format, where you would have to do the complete calculation and type in the answer. Therefore it is important to be disciplined and not "cheat" by looking at the answer in a practice problem until the very end after putting in the work to get to the final answer. Don't worry if you are rusty as it may have been a while since you did some significant calculation problems. It will get easier with practice, practice, practice!

Have a great week. Be sure and rest and relax some over the holiday season so you will be ready to roll come January 2020. You will graduate soon enough and take the NAPLEX!

Dr. B

Christopher M. Bland

Clinical Associate Professor, University of Georgia College of Pharmacy

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