Weight-to-BSA Conversion Formula
BSA scales with weight to the 0.67 power, not linearly.
- 0.67: Formula exponent (allometric power law)
- kg: Input unit (body weight)
- m²: Output unit (surface area)
- Oncology: Common use (chemo dosing)
Why a power law, not linear scaling
Surface area grows slower than mass as an animal gets larger.
Placeholder: small pets have proportionally more surface area per kg.
Species-Specific BSA Constant
The constant K adjusts the formula per species body shape.
- 10.1: Canine K (dogs)
- 10.0: Feline K (cats)
- 10.5: Equine K (horses)
- cm²/g^0.67: Units (scaled constant)
Choosing the right constant
Placeholder: constant reflects average body geometry per species.
Placeholder: wrong constant skews dose estimates.
BSA (m²) Calculation Result
The computed BSA value becomes the dosing reference point.
- ~0.3 m²: Small dog BSA (5 kg)
- ~0.7 m²: Medium dog BSA (20 kg)
- ~1.4 m²: Large dog BSA (50 kg)
- 3 decimals: Precision (clinical rounding)
Reading the BSA output
Placeholder: BSA result feeds directly into dose calculation.
Placeholder: always double-check units before dosing.
Chemo Dose (mg/m²) Application
Target dose per m² multiplies by BSA for total mg administered.
- 10-300 mg/m²: Typical range (protocol dependent)
- Dose × BSA: Formula (total mg)
- Nearest 0.1 mg: Rounding (syringe precision)
- Every visit: Recheck (weight changes)
From target dose to syringe
Placeholder: multiply mg/m² target by patient BSA for total dose.
Placeholder: recalculate BSA at every treatment visit.
Why BSA Dosing Differs From mg/kg
BSA tracks metabolic rate better than raw body weight.
- Overdose: mg/kg risk (small patients)
- Safer scaling: BSA benefit (across sizes)
- Oncology: Adopted by (human & vet)
- Extremes: Limitation (very small/large)
Metabolic scaling rationale
Placeholder: metabolic rate correlates with surface area, not mass.
Placeholder: BSA dosing reduces toxicity risk in small patients.