Classifying the Burn
Two numbers drive every decision — depth (guides healing & surgery) and size / % total body surface area (TBSA) (guides fluids, transfer & prognosis). Only partial- and full-thickness burns are counted when calculating TBSA for fluids.
| Depth | Layers | Appearance / clinical | Healing |
|---|---|---|---|
| Superficial (1°) | Epidermis only | Red, dry, painful, blanches on pressure; no blisters | ~7 days, no scar (not counted in TBSA) |
| Superficial partial (2°) | Epidermis + superficial (papillary) dermis; adnexa preserved | Blisters, moist, very painful, blanches | 10–14 days, minimal/no scar |
| Deep partial (2°) | Epidermis + deep (reticular) dermis; few adnexa left | Mottled/marbled, drier, less painful, sluggish/absent blanching | 2–3 weeks, scarring ± contracture |
| Full thickness (3°) | All layers (± fat/muscle in 4°) | Charred / leathery / waxy white, dry, insensate (painless), does not blanch | Needs excision & grafting; heals with contracture |
📐 Estimating burn size (TBSA)
- Wallace "rule of 9s" (adults) — head 9%, each arm 9%, each leg 18%, anterior trunk 18%, posterior trunk 18%, perineum 1%.
- Lund–Browder chart — the most accurate, especially in children, because it corrects for age: an infant's head is relatively large (~18%) and the legs relatively small, changing with growth.
- Palm rule — the patient's palm + fingers ≈ 1% TBSA — quick for small or scattered burns.
Pathophysiology
Jackson's three concentric zones of a burn wound
Zone of coagulationCentral, irreversible necrosis — coagulated protein, no perfusion
Zone of stasisSurrounding, at-risk but salvageable — good resuscitation, avoiding hypotension/hypoxia can save it; poor resuscitation converts it to necrosis (burn "deepens")
Zone of hyperaemiaOutermost — vasodilated, viable, recovers
The systemic response — a biphasic time course
EBB phase (0–48 h) — hypovolaemicMassive capillary leak & oedema → ↓ intravascular volume, ↓ cardiac output, ↑ SVR. This is the resuscitation window — but avoid over-resuscitation ("fluid creep").
FLOW phase (>48 h) — hypermetabolicHyperdynamic circulation (↑ CO), a doubling of metabolic rate, catabolism, protein loss, immunosuppression & sepsis risk — persists until wounds are healed.
Why the "flow" phase matters to the anaesthetist: the hypercatabolic patient is tachycardic, warm and fluid-hungry at baseline, has ↑ drug clearance and altered protein binding, and is prone to hypothermia and infection — which is exactly why these patients are best posted first on the list and kept aggressively warm.