Start with the surface area, not the formula
Every burn fluid estimate begins with one number: the percent of total body surface area burned (TBSA). The Rule of Nines is the bedside shorthand — 9% per arm, 18% per leg, 18% front and back torso, 9% head, 1% perineum — and you count partial- and full-thickness burns, not simple erythema. Children break the rule: the head is proportionally larger and the legs smaller, so the percentages shift with age.
The formula is a starting estimate, not a prescription
Three formulas share the same shape — Lactated Ringer's over 24 hours, half in the first 8 hours from the time of injury and half over the next 16. They differ only in the per-kilogram coefficient: classic Parkland at 4 mL/kg/%TBSA, Modified Brooke at 2, and the ABLS consensus starting point at 2 in adults and 3 in children. None of them is the dose. Each is the rate you start at and then adjust.
Why the volumes came down
Resuscitating all the way to the full Parkland estimate reliably over-delivers fluid — “fluid creep” — and that excess drives abdominal and extremity compartment syndromes, pulmonary edema, and conversion of burns to deeper injuries. That is why the American Burn Association and most modern protocols start at the lower 2 mL/kg estimate and titrate up only when the patient asks for it.
Children and the obese need different inputs
Two groups break the simple formula. Children carry a higher surface-area-to-mass ratio and less reserve, so formal resuscitation is considered at a lower threshold — roughly 10–15% TBSA versus 20% in adults — and a given burn is classified more severely. In obesity, total body weight badly over-estimates volume because adipose tissue holds little water; the common fix is an adjusted body weight [ideal + 0.4 × (actual − ideal)], unless the high BMI is muscle rather than fat.
Titrate to urine output
Whatever formula and weight you start from, urine output is the readout that matters — about 0.5 mL/kg/hr in adults and 1 mL/kg/hr in children. Reassess hourly and move the rate up or down. The formula gets you to the right order of magnitude; the patient gets you the rest of the way.
Where Master Anesthesia comes in
The Burns calculator in Master Anesthesia works the way you'd actually reason through it — tap the burned regions on an adult or pediatric body to build the TBSA, pick your formula, and read the first-8-hour and next-16-hour targets, already age-aware and adjusted for obesity. See the Burn Resuscitation Calculator.