A 35-year-old woman is admitted 6 hours after a flame burn affecting 40% of her body surface area (BSA). Physical examination reveals erythematous skin with blistering on the trunk and limbs; some areas show a leathery, dark appearance with no blanching. She is alert and oriented. Her current urine output is 0.6 mL/kg/hr on Parkland resuscitation. Which depth of burn is most likely affecting the dark, non-blanching areas?

Explanation

## Burn Depth Classification Burn depth is classified by the **anatomical layer of skin and underlying tissue** involved. The clinical appearance and response to stimuli are key diagnostic features. ## Burn Depth Table | **Depth** | **Anatomical Layer** | **Appearance** | **Blanching** | **Pain** | **Healing** | |---|---|---|---|---|---| | **Superficial (1st)** | Epidermis only | Red, dry | Yes | Severe | 3–7 days, no scar | | **Superficial Partial (2nd)** | Epidermis + superficial dermis | Red, blistered, wet | Yes | Severe | 2–3 weeks, minimal scar | | **Deep Partial (2nd)** | Epidermis + deep dermis | Pale, mottled, blistered | Slow/no | Decreased | 3–6 weeks, hypertrophic scar | | **Full-thickness (3rd)** | Entire dermis + subcutaneous | Leathery, dark, charred | **No** | **Absent** | Requires grafting, scar | | **Subdermal (4th)** | Muscle, bone, fascia | Charred, eschar | No | Absent | Requires amputation/extensive surgery | ## Key Clinical Feature: Non-Blanching **Key Point:** The **dark, leathery, non-blanching appearance** is pathognomonic for **full-thickness (third-degree) burns**. - **Full-thickness burns** destroy the entire dermis and epidermis. - **No viable skin appendages** remain (hair follicles, sweat glands, nerve endings). - **No blanching** on pressure because there is no viable capillary bed to blanch. - **No pain** because nerve endings are destroyed. - **Eschar** (dead tissue) is leathery, dark brown to black, and inelastic. **High-Yield:** Blanching is a sign of **viable tissue** with intact microcirculation. Non-blanching = dead tissue = full-thickness. ## Mnemonic: FBSD (Full-thickness Burn Severity Descriptor) - **F** — Full-thickness (all layers of skin) - **B** — Blanching: **No** (this is the key discriminator) - **S** — Sensation: **Absent** (no pain) - **D** — Dark, leathery, charred appearance ## Clinical Implications 1. **Full-thickness burns do NOT heal by re-epithelialization** — they require **skin grafting** (autograft or allograft). 2. **Eschar must be removed** (escharotomy or debridement) to assess underlying tissue and prevent infection. 3. **Contractures and hypertrophic scarring** are common complications. 4. **Circumferential full-thickness burns** on the chest or limbs may require **escharotomy** to relieve compartment syndrome or allow chest wall expansion. ## Why This Patient Has Full-Thickness Burns - **Leathery, dark appearance** = eschar (dead tissue). - **No blanching** = no viable capillary bed. - **Flame burn** (high-temperature exposure) typically causes full-thickness injury in the zone of maximum heat. [cite:ATLS 10e Chapter 7 — Burns; Sabiston Textbook of Surgery 21e Chapter 72]