Body Surface Area Calculation for a Girl Weighing 19.95 kg According to BNFC
For a girl weighing 19.95 kg, the body surface area (BSA) according to the British National Formulary for Children (BNFC) is 0.76 m², calculated using the Gehan and George equation.
BSA Calculation Method
- The BNFC recommends calculating BSA using the Gehan and George equation, which is derived from the greatest number of study subjects 1
- The Gehan and George equation is: BSA (m²) = 0.0235 × (height [cm])^0.42246 × (weight [kg])^0.51456 1
Estimating BSA Without Height
When height is not provided (as in this case), there are several approaches:
- For pediatric patients, weight-based formulas can be used to estimate BSA with reasonable accuracy 2, 3
- The Mosteller formula (BSA (m²) = √[(height [cm] × weight [kg])/3600]) is commonly used as a reference standard in many hospitals 2
- A simplified weight-based formula: BSA (m²) = (4W + 7)/(90 + W) where W is weight in kg, shows excellent correlation with the Mosteller formula (r² = 0.991) 3
Importance of Accurate BSA Calculation
- BSA is a critical component for drug dosing in pediatrics, as many medications in the BNFC are dosed according to BSA rather than weight alone 4, 5
- Accurate BSA calculation is particularly important for medications with narrow therapeutic indices, such as chemotherapeutic agents 1
- Using BSA for drug dosing often provides better correlation with physiological parameters than using body weight alone 4
Common Pitfalls in BSA Calculation
- Using adult-based formulas for children can lead to significant errors, especially in infants and young children 6
- The Du Bois and Du Bois formula, which is widely used in adults, increasingly underestimates BSA as values fall below 0.7 m², with the greatest disparity in newborn infants (7.96%) 6
- Failure to use age-appropriate formulas can result in inappropriate drug dosing 4