🧠 The Rule of 9s: Burn Assessment Made Easy for Medical Exams
When a patient presents with burns, one of the first things you’re expected to determine is the total body surface area (TBSA) affected. The Rule of 9s is a quick, clinical tool used to estimate this, and it shows up on nearly every Step 2 CK, EM rotation, and surgery shelf exam.
Today, we’ll break it down using visuals, mnemonics, and formulas that stick.
🔢 What Is the Rule of 9s?
The Rule of 9s divides the adult body into sections, each worth a multiple of 9%. These are added up to quickly estimate TBSA affected by burns.
🧍♂️ Rule of 9s Chart for Adults
| Body Region | TBSA (%) |
|---|---|
| Head and neck | 9% |
| Each arm | 9% |
| Each leg | 18% |
| Anterior torso | 18% |
| Posterior torso | 18% |
| Perineum / genitalia | 1% |
🧠 KOTC Tip: “Head is 9, each limb and side is 9 or 18”
🧑⚕️ Pediatric Variation
Pediatric patients have larger heads proportionally
Use Lund-Browder chart for accuracy in children
💧 Fluid Resuscitation: Parkland Formula
Used for patients with burns >20% TBSA
Parkland Formula:
💧 4 mL x body weight (kg) x % TBSA burned
→ Give half in first 8 hours, rest over 16 hours
📌 Example:
70 kg adult with 30% TBSA:
4 x 70 x 30 = 8400 mL total fluids
🧠 High-Yield Scenarios
| Scenario | Likely TBSA | Key Management |
|---|---|---|
| Burns to anterior trunk + both legs | 18 + 18 + 18 = 54% | Fluids + ICU transfer |
| Burns to arm and neck | 9 + 9 = 18% | Likely outpatient unless inhalation risk |
| Electrical burn, small area | Small TBSA | Still monitor for rhabdo, EKG, myoglobinuria |
📌 Before You Go…
Burns are hot topics on exams—so burn this into your memory 🔥
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