Example B Suppose the medication is ordered based on the patient's weight in kilograms. You know the patient's weight is 168 pounds and you need to convert the weight into kilograms To make this conversion, follow these steps:
1. Set up a fraction with the weight in pounds on top and the unknown weight in kilograms on the bottom:
\[
\frac{168 \mathrm{lb}}{x \mathrm{~kg}}
\]
2. Next set up a fraction with the standard equivalent. See Table 52-4. Make sure that for this fraction you use units of measure on the top and the bottom that match the units of measure on the top and the bottom of the first fraction:
\[
\frac{2.2 \mathrm{lb}}{1 \mathrm{~kg}}
\]
3. Then set up a proportion with both fractions:
\[
\frac{168 \mathrm{lb}}{x \mathrm{~kg}}=\frac{2.2 \mathrm{lb}}{1 \mathrm{~kg}}
\]
4. Now cross multiply. Multiply the bottom left number by the top right number, and multiply the top left number by the bottom right number:
\[
x \times 2.2 \mathrm{lb}=168 \mathrm{lb} \times 1 \mathrm{~kg}
\]
5. To solve for $x$, divide both sides of the equation by $2.2 \mathrm{lb}$; then do the arithmetic, canceling out like terms in the top and bottom of each fraction and then dividing 168 by 2.2 :
\[
\begin{aligned}
\frac{x \times 2.2 \mathrm{~kb}}{2.21 \mathrm{~b}} & =\frac{168 \mathrm{k} \times 1 \mathrm{~kg}}{2.2 \mathrm{~kb}} \\
x & =76.36 \mathrm{~kg}
\end{aligned}
\]
6. Follow the rules of rounding. To round to the nearest tenth, the 6 in the hundredth column is greater than 5 so you would round the answer to $76.4 \mathrm{~kg}$. To round to the nearest whole number you would round to the nearest tenth $76.4 \mathrm{~kg}$ and since the 4 is less than 4 in the tenths column the nearest whole number would be $76 \mathrm{~kg}$.

Your Turn You need to prepare a solution for the licensed practitioner to clean a wound. He asks for $3 \frac{1}{2}$ fluid ounces (fl oz) of saline to be placed in a sterile bowl. Your container of saline is marked in milliliters (mL). Use these steps to make the conversion:
1. Set up a fraction with the ordered dose on the top and the unknown amount on the bottom.
2. Next, set up a fraction with the standard equivalent. See Table 52-4. Make sure that for this fraction you use units of measure on the top and the bottom that match the units of measure on the top and the bottom of the first fraction.
3. Then set up a proportion with both fractions.
4. Now cross multiply. Multiply the bottom left number by the top right number, and multiply the top left number by the bottom right number.
5. To solve for $x$, cancel out like terms in the top and bottom of each fraction, then do the arithmetic.
6. Round to the nearest whole number.
If you followed each step correctly, you find that you need $105 \mathrm{~mL}$ of saline.
DOSAGE CALCULATIONS
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