Medication Calculation Based on Body Surface Area (BSA)
A pediatric nurse is preparing to administer chemotherapy to a 8-year-old child weighing 25 kg with a height of 120 cm. The oncologist has ordered cyclophosphamide 400 mg/m² IV. Using the Mosteller formula for BSA calculation, what is the correct dose of cyclophosphamide for this child?
The nurse must calculate the body surface area using the Mosteller formula: BSA (m²) = √[(height in cm × weight in kg) ÷ 3600], then multiply by the ordered dose per m².
1320 mg
2365 mg✓ 정답
3280 mg
4340 mg
해설
The correct dose is 365 mg. Using the Mosteller formula, BSA = √[(120 cm × 25 kg) ÷ 3600] = √(3000/3600) = √0.8333 ≈ 0.9129 m². Then, 0.9129 m² × 400 mg/m² = 365.16 mg, which rounds to 365 mg. The other options result from errors in BSA calculation or in multiplying the BSA by the ordered dose.
This is a medication calculation question that requires a two-step process. First, use the Mosteller formula to calculate the child's body surface area (BSA). Second, multiply the calculated BSA by the ordered dose per square meter to find the total dose.
Step 1: Calculate the BSA using the Mosteller Formula
BSA (m²) = √[(height in cm × weight in kg) ÷ 3600]
Plug in the child's measurements: * Height = 120 cm * Weight = 25 kg
The oncologist's order is for cyclophosphamide 400 mg/m².
Total Dose = BSA (m²) × Ordered Dose (mg/m²) Total Dose = 0.9129 m² × 400 mg/m² Total Dose = 365.16 mg, which rounds to 365 mg.
Clinical Significance of BSA-Based Dosing
BSA-based dosing is standard for chemotherapeutic agents such as cyclophosphamide because BSA correlates more closely with metabolic rate, cardiac output, and drug clearance than weight alone, providing a safer dosing strategy in pediatric oncology. Avoid premature rounding of the intermediate BSA value, and always have a second nurse independently verify calculations for high-alert medications such as chemotherapy.
Pediatric BSA-Based Chemotherapy CalculationUsing the Mosteller Formula for Safe Dosing
To calculate the dose, first determine the body surface area (BSA) using the Mosteller formula: √[(height in cm × weight in kg) ÷ 3600]. For a child 120 cm and 25 kg, the BSA is 0.9129 m².
Next, multiply the calculated BSA by the ordered dose per square meter. The order is for cyclophosphamide400 mg/m². The total dose is 0.9129 m² × 400 mg/m² = 365.16 mg. In clinical practice, this is often rounded based on pharmacy or institutional policy.
Caution
Never round intermediate BSA values prematurely, as this can lead to significant under- or overdosing. Always verify the final calculated dose with a second nurse and consult pharmacy for high-alert medications like chemotherapy.
Body Surface Area (BSA) — A measurement used for many clinical purposes, including calculating chemotherapy doses, expressed in square meters (m²).
Mosteller Formula — A simplified formula for estimating BSA: √[(height in cm × weight in kg) ÷ 3600].
Cyclophosphamide — An alkylating agent chemotherapy drug often dosed based on body surface area.