How to Use Conversion in Nursing Math

Knowing how to convert medication doses safeguards your patients.
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Nurses need to know how to convert measurements to administer medications and fluids. A physician orders medication with the dose written in milligrams (mg), for example. To administer the medication you must draw it up in a syringe. But syringes aren't marked in milligrams. You must convert the milligram dose to an amount that you can measure in a syringe, measuring cup or other device, such as a milliliter or cubic centimeter.

Step 1

Read the physician's order to see if you need to do a medication dose conversion. A typical order might say to give a dose such as 5 mg of a medication, or to give 1.5 teaspoons of a liquid. To determine the first, you need to know how many milligrams of the medication are in 1 milliliter or cc. To determine the second, you need to know how many milliliters are in a teaspoon.

Step 2

Figure out the type of dose conversion you need by checking the syringe or other administering device, such as a measuring cup. Most medications will be given in syringes or medication cups marked in milliliters or cubic centimeters. Milliliters and ccs are two different names for the same amount; 1 cc equals 1 ml. A typical syringe might have both designations or one or the other.

Step 3

Determine how to convert your dose. You may need to multiply to get the dose you need, or you might need to divide. If, for example, the 5-mg medication dose ordered is for a medication that comes mixed at a concentration of 2.5 mg per ml, you will need to multiply, because you need more medication than is in 1 ml. If the medication comes mixed with 10 mg per ml, you will need to divide. In many conversions, you need to do both multiplication and division.

Step 4

Do the math, using a calculator if necessary. A typical conversion will go like this. The order states to give 6 mg of medication. The bottle you have contains 2 mg per ml. You need to determine how many milligrams are in each milliliter, because your syringes are marked in milliliters. You can do this in one of two ways. Divide 2 into 6, which equals 3. You need 3 x 1 ml, or 3 ml. Alternatively, divide 1 ml by 2 mg to determine how many milligrams of medication are in 1 ml. You find that 1 milliliter contains 0.5 milligrams of medication. Since you need to give 6 mg of medication, multiply 6 x 0.5. The answer is 3. You will give 3 ml of medication.

Step 5

Double-check your math. Even if the pharmacy sends up a medication with the dose already computed, check it yourself. If a dose seems too large -- for example, if you need several syringes to give a single medication dose -- check the order again. Rarely should you need to use more than one syringe to dispense a medication, or give more than two pills at one time, the American Society of Hospital Pharmacists warns.

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