The Rule of Nines and What Comes After It

The rule of nines is a rapid field estimate of burn size in adults, and it is tested because everything downstream depends on it: fluid resuscitation, triage, and the decision to transfer. Getting the percentage roughly right and the consequences exactly right is the skill the exam is after.

Adult rule of nines

Nine regions of 9% plus 1% for the perineum gives 100%. Halves work as you would expect: the front of one leg is 9%, one whole arm's posterior surface is 4.5%.

The paediatric difference

Children are not small adults. The head is proportionally much larger and the legs proportionally smaller, and this is one of the most commonly tested adjustments in the topic.

Roughly: take 9% off each leg and give it to the head. The proportions shift gradually toward adult values through childhood, which is why the Lund–Browder chart — which is age-adjusted and more accurate — is the tool of choice in hospital, with the rule of nines reserved for rapid estimation.

Depth: what actually counts

Two traps live in that table. First, superficial burns are excluded from the TBSA used for fluid calculations — the classic item gives you a sunburned back and a scalded arm and expects you to count only the arm. Second, a painless burn is a worse burn, not a better one: absent sensation means the dermal nerve endings are destroyed.

Fluid resuscitation

The Parkland formula is the version most often taught and most often tested:

4 mL × body weight in kg × % TBSA (partial thickness and deeper) = volume of lactated Ringer's for the first 24 hours

Half of that volume is given in the first eight hours from the time of injury — not from the time the patient arrives — and the remaining half over the following sixteen hours.

Worked example: a 70 kg adult with 30% TBSA partial-thickness burns. 4 × 70 × 30 = 8,400 mL in 24 hours; 4,200 mL in the first eight hours from the burn, then 4,200 mL over the next sixteen.

The formula is a starting point, not a prescription

Calculated volumes are titrated to response, and the endpoint that matters is urine output — conventionally around 0.5 mL/kg/hour in adults and about 1 mL/kg/hour in children. Modern burn practice has moved toward lower initial volumes than the classic Parkland figure in many protocols because of the harms of over-resuscitation, so know the formula for the exam and know that clinical practice titrates.

Transfer criteria

The most examinable part of the topic. Referral to a burn centre is indicated for, among others:

• Partial-thickness burns over more than 10% TBSA
• Burns involving the face, hands, feet, genitalia, perineum or major joints
• Any full-thickness burn, at any age
• Electrical burns, including lightning injury
• Chemical burns
• Inhalation injury
• Burns in patients with pre-existing conditions that could complicate management or prolong recovery
• Burns with concomitant trauma, where the burn poses the greater immediate risk
• Burned children in facilities without qualified paediatric capability
• Patients requiring special social, emotional or rehabilitative support

Notice that several of these have nothing to do with size. A small full-thickness burn to the hand meets criteria; a large superficial sunburn does not.

Details that show up in stems

• Circumferential burns of a limb or the chest threaten perfusion and ventilation as oedema develops. Escharotomy is the intervention being hinted at.
• Inhalation injury clues: fire in an enclosed space, singed nasal hairs, facial burns, soot in the mouth or sputum, hoarseness, stridor. Airway comes before the fluid calculation, always.
• Electrical burns hide deep tissue destruction under normal-looking skin. Watch for rhabdomyolysis and cardiac dysrhythmias.
• Chemical burns need prolonged irrigation with water; brushing dry powder off first is part of the answer.
• Patterned or inconsistent burns — stocking-glove distributions, sharply demarcated immersion lines, a history that does not fit the injury — raise the question of non-accidental injury, and that is a mandated reporting item.
• Hypothermia is a real risk in large burns. Keep the patient warm.

Answering the calculation item

1. Total only the partial-thickness and deeper areas. Discard superficial burns.
2. Use the paediatric proportions if the patient is a young child.
3. Apply the formula, then halve it for the first eight hours.
4. Anchor the clock to the time of injury. If two hours have already passed, the first half is delivered over the remaining six.