Body Surface Area Calculation for an 18.85 kg, 5-Year-Old Girl According to BNFC
According to the British National Formulary for Children (BNFC), the body surface area (BSA) for an 18.85 kg, 5-year-old girl should be calculated using the Gehan and George equation: BSA (m²) = 0.0235 × (height [cm])^0.42246 × (weight [kg])^0.51456. 1
Calculation Methods for BSA
- The BNFC recommends the Gehan and George equation for calculating BSA in pediatric patients as it is derived from the greatest number of study subjects and provides more accurate results 1
- Without height information provided in the question, we must consider alternative weight-based formulas that are validated against standard methods 2
- For children weighing less than 30 kg (like this 5-year-old girl weighing 18.85 kg), BSA can be estimated using weight-based formulas that have been validated against the Mosteller formula 3
Weight-Based BSA Estimation
- A simplified weight-based formula that correlates well with the Mosteller formula is: BSA (m²) = (4W + 7)/(90 + W), where W is weight in kg 3
- Using this formula for the 18.85 kg child: BSA = (4 × 18.85 + 7)/(90 + 18.85) = 82.4/108.85 = 0.757 m² 3
- Another validated approach is the Meeh-type equation which has shown 99.2% correlation with the Mosteller formula in pediatric populations 2
Clinical Implications of BSA Calculation
- Accurate BSA calculation is particularly important for medications with narrow therapeutic indices, such as chemotherapeutic agents 1
- The BSA method is preferred over simple weight-based (mg/kg) dosing for many pediatric medications as it more closely follows physiological parameters 4
- For this 5-year-old girl weighing 18.85 kg, using BSA-based dosing would help optimize drug delivery while minimizing potential toxicity 5
Limitations and Considerations
- BSA calculations have limitations, particularly in children with abnormal body proportions or nutritional status 1
- The Mosteller formula has been shown to underestimate BSA by approximately 4.06% in the pediatric population, with greater imprecision in infants and neonates 6
- When height measurements are unavailable, weight-based formulas provide a practical alternative but should be used with awareness of their limitations 2