## Rule of Nines for Adult BSA Estimation **Key Point:** The Rule of Nines is the most widely used rapid method for estimating total body surface area (TBSA) affected by burns in adults. ### Adult Distribution (Rule of Nines) | Body Region | Percentage | | --- | --- | | Head and neck | 9% | | Each arm (anterior + posterior) | 9% | | Chest | 9% | | Abdomen | 9% | | Each leg (anterior + posterior) | 18% | | Genitalia | 1% | | **Total** | **100%** | **High-Yield:** Each upper limb = 9% (not 4.5% for one side alone). The 9% includes both anterior and posterior surfaces of the entire arm from shoulder to fingertips. **Clinical Pearl:** This rule allows rapid field assessment and triage decisions. Burns >20% TBSA in adults (>10% in children and elderly) require fluid resuscitation and transfer to a burn centre. **Mnemonic:** **"9-18-9 Rule"** — Head 9%, Arms 9% each, Legs 18% each, Trunk 18% (chest + abdomen combined).
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