Dosage Calculations: Expert Guides and Resources

No matter what initials you have after your name (RN, CNA, PA, and so on), you can bet you’ll see math on a daily basis if you’re going into (or are already in) a career in the medical field.Grasping some medical math basics — such as how to break down medical dosage problems into steps and use conversion factors — can simplify everyday situations all health care professionals face.

Whenever you’re administering intravenous (IV) infusions, you need to know the flow rate, infusion time, and total volume. Fortunately, calculating any one of these three variables is easy to do when you know the other two variables. Use the following equations: flow rate (mL/hr) = total volume (mL) ÷ infusion time (hr) infusion time (hr) = total volume (mL) ÷ flow rate (mL/hr) total volume (mL) = flow rate (mL/hr) × infusion time (hr) For example, if you must administer 1 L (1,000 mL) of fluid over 4 hours, use the first formula to calculate the flow rate, like so: flow rate (mL/hr) = total volume (mL) ÷ infusion time (hr) flow rate (mL/hr) = 1,000 ÷ 4 flow rate (mL/hr) = 250 The flow rate is 250 mL/hr.

Making sure that you correctly calculate a dose doesn’t matter much if the medication itself is incorrect or the dosing instructions are unclear. Some abbreviations in prescriptions are unacceptable because they cause ambiguity and confusion (the enemies of patient safety and quality healthcare!). For this reason, you don’t want to see these abbreviations on any medical orders you work with.