In Mosteller's approach, the BSA is multiplied by which baseline daily maintenance fluid to obtain daily maintenance?

• A. 1000 mL/day
• B. 1500 mL/day
• C. 2000 mL/day
• D. 2500 mL/day

Answer: (B)

Mosteller's approach estimates maintenance fluid needs by scaling with body surface area, since metabolic rate and insensible losses tend to follow surface area rather than weight alone. In this method, you take the patient’s body surface area (in square meters) and multiply it by a fixed baseline maintenance fluid of 1500 mL per square meter per day. That product gives the daily maintenance fluid.

For example, a patient with a BSA of 0.8 m^2 would need about 0.8 × 1500 = 1200 mL/day, while a patient with 1.2 m^2 would need about 1800 mL/day. The fixed 1500 mL per m^2 baseline is used specifically because it scales with size, whereas flat values (like 1000, 2000, or 2500 mL/day) don’t account for differences in body size and would misestimate maintenance needs across patients.