RN Nursing · Intravenous Therapy · Practice question
Insert the numeric response only. The physician orders an IV of 40 mEq of potassium chloride in 500 mL 0.9% NS to infuse over 4 hours. Calculate the flow rate in milliliters per hour.
Answer & explanation
Correct:
To calculate an intravenous flow rate in milliliters per hour, divide the total volume to be infused by the total number of hours over which it is to run. The order specifies 500 mL to infuse over 4 hours. Dividing 500 mL by 4 hours gives 125 mL per hour. The potassium chloride concentration (40 mEq) is relevant for safety considerations but does not change the volume-per-hour calculation, because the entire 500 mL bag is the vehicle and the rate is based solely on volume over time. A common student error is to attempt to factor in the drug concentration or to convert the time into minutes and then forget to convert back, yielding an answer in mL per minute rather than mL per hour. Another mistake is dividing 4 into 40 (the milliequivalents) rather than into 500 (the volume). It is also worth noting clinically that 40 mEq of potassium chloride in a peripheral IV requires careful monitoring for phlebitis and cardiac effects, and the standard maximum recommended rate for peripheral potassium infusion is generally 10 mEq per hour, so this order would warrant a clinical alert — but the mathematical answer to the flow rate question is 125 mL per hour.
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