How to calculate child dose using BSA

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Burgaña A, Abellana R, Yordanov SZ, Kazan R, Pérez Ortiz AM, Ramos CC, Hernández CG, Rivero MM, Gonçalves AQ, Padilla E, Pérez J, García-Puig R, Perez-Porcuna TM. Burgaña A, et al. Int J Parasitol Drugs Drug Resist. 2019 Dec;11:95-100. doi: 10.1016/j.ijpddr.2019.10.005. Epub 2019 Nov 11. Int J Parasitol Drugs Drug Resist. 2019. PMID: 31759244 Free PMC article.

This review will discuss how to solve nursing dosage and calculations on body surface area!

Body surface area is used to help calculate the most accurate medication dosage for a patient. For example, some medications ordered for a pediatric patient may be based on body surface area (BSA) and strong medications, such as chemo agents (anticancer medications).

This review will demonstrate step-by-step how to calculate the following:

• Body surface area of a patient based on weight and height (both kilograms, centimeters, pounds, and inches will be reviewed)
• Calculating the child’s dose based on the child’s BSA and the normal adult dose
• Calculating the amount of medication you will administer based on the patient’s BSA and physician’s order

Calculating BSA is based on the patient’s weight and height. It can be calculated using a nomogram (a diagram that gives you the BSA of the patient) or specific formulas, which is what this review will cover.

In addition, it’s important to know that body surface area is expressed in m2, square meter, which means that body surface is the amount of square meters of a person’s body.

When solving these BSA problems you will need a calculator that configures square roots of numbers, round per your program’s guidelines, and memorize some formulas.

Therefore, before solving body surface area you need to commit to memory the following formulas below.

**The first two formulas will help you calculate the body surface area and you will select which formula to use based on if the scenario gave you the patient’s weight and height in the household or metric system.

• You will use the FIRST formula below if the weight and height are in kilograms (kg) and centimeters (cm).
• You will use the SECOND formula below if the weight and height are in pounds (lbs) and inches (in).

The last formula will help you calculate a child’s dose based on the child’s BSA and the normal adult dose.

Lecture on Body Surface Area Medication Calculations

Problem 1:

Your patient weighs 163 lbs and is 5 feet 7 inches. What is the patient’s BSA?

First, pull from the scenario the most important information you need to solve the problem.

• Weight: 163 lbs
• Height: 5 feet 7 inches
  • Based on this information, you will be using the second formula above.

Now let’s solve:

Problem 2:

Your patient weighs 27.2 kg and is 91 cm. What is the patient’s BSA?

First, pull from the scenario the most important information you need to solve the problem.

• Weight: 27.2 kg
• Height: 91 cm
  • Based on this information, you will be using the first formula above.

Now let’s solve:

Problem 3:

A pediatric patient is ordered a medication dose of 10 mg/ m2/day by mouth for 7 days. The patient weighs 46 lbs. and is 3 feet 9 inches. What is the daily dose of medication the patient will receive?

First, pull from the scenario the most important information you need to solve the problem.

• Weight: 46 lbs.
• Height: 3 feet 9 inches
  • Based on this information, you will be using the second formula above.
• Physician’s order: 10 mg/ m2/day
• Solve for: daily dose

Now let’s solve:

Problem 4:

A pediatric patient is 65 lbs. and 4 feet 5 inches. The physician orders an oral medication that has a normal adult dose of 250 mg. How many mg of this medication will be administered?

First, pull from the scenario the most important information you need to solve the problem.

• Weight: 65 lbs.
• Height: 4 feet 5 inches
  • Based on this information, you will be using the second formula above.
• Normal adult dose: 250 mg
• Solve for: child’s dose…mg to be administered

Now let’s solve:

Problem 5:

A pediatric patient has a body surface area of 0.88 m2. The physician orders an IV medication that has a normal adult dose of 125 mg. You’re supplied with a vial that reads 30 mg/mL. How many mL will you administer to this patient?

First, pull from the scenario the most important information you need to solve the problem.

• Patient’s BSA: 0.88 m2
• Normal adult dose: 125 mg
• You’re supplied with a vial that reads: 30 mg/mL
• Solve for: mL you will administer

Now let’s solve:

Test your knowledge: Body Surface Area Practice Questions