## Rule of Nines for Adult BSA Estimation **Key Point:** The Rule of Nines is the most widely used method for rapid estimation of burn surface area in adults and is essential for triage and fluid resuscitation calculations. ### Standard Adult Distribution | Body Region | Percentage of BSA | | --- | --- | | Head and neck | 9% | | Each upper limb (arm + forearm + hand) | 9% | | Chest | 9% | | Abdomen | 9% | | Each lower limb (thigh + leg + foot) | 18% | | Back and buttocks | 18% | | Perineum/genitalia | 1% | | **Total** | **100%** | **High-Yield:** Each upper limb = 9% (not 4.5%, which is a common misconception). The 9% represents the entire limb from shoulder to fingertips. **Mnemonic:** **"9-18 Rule"** — Head/trunk regions = 9% each; lower limbs = 18% each. **Clinical Pearl:** The Rule of Nines is most accurate for adults and children >10 years. In young children (<5 years), the head represents a larger percentage (~18%) and lower limbs represent less (~13.5% each), requiring the **Lund and Browder Chart** for more precise estimation. **Warning:** Do not confuse the 9% for the entire upper limb with 4.5% for half the limb or anterior/posterior surface alone.
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