A 28-year-old woman with 45% TBSA thermal burns (estimated by Lund and Browder chart) is admitted to the burn unit. The resident calculates fluid requirements using the Parkland formula and initiates resuscitation. To confirm the adequacy of fluid resuscitation and validate the initial TBSA estimate, which investigation is most appropriate?

Explanation

## Validation of Fluid Resuscitation Adequacy in Burns **Key Point:** Urine output is the most reliable **real-time indicator** of adequate tissue perfusion and the appropriateness of fluid resuscitation volume in acute burns. It is the gold standard endpoint for titrating Parkland formula-based resuscitation. ### Parkland Formula and Resuscitation Endpoints **Parkland Formula:** $$\text{Fluid (mL)} = 4 \times \text{TBSA%} \times \text{Body weight (kg)}$$ - Given over 24 hours: first half in first 8 hours, second half over next 16 hours - Uses **Lactated Ringer's solution** (crystalloid) ### Urine Output Targets (Resuscitation Endpoints) | Patient Type | Target Urine Output | Monitoring Interval | |--------------|-------------------|---------------------| | **Adult** | 0.5 mL/kg/hr | Hourly | | **Child (< 30 kg)** | 1 mL/kg/hr | Hourly | | **Electrical burn** | 75–100 mL/hr (or 200 mL/hr if myoglobinuria) | Continuous | **High-Yield:** Urine output is the **investigation of choice** because: 1. It reflects real-time tissue perfusion and organ perfusion 2. It guides **dynamic titration** of fluid rate (increase if < target, decrease if > target) 3. It prevents both **under-resuscitation** (shock, organ failure) and **over-resuscitation** (compartment syndrome, pulmonary edema) 4. It is non-invasive and continuously available ### Why Urine Output Validates TBSA Estimate - If urine output is **persistently low** despite adequate fluid infusion → TBSA may be **underestimated** → increase fluids - If urine output is **excessive** with minimal fluid input → TBSA may be **overestimated** → decrease fluids - Mismatch between expected and observed urine output signals need to **reassess TBSA** and adjust Parkland calculation **Clinical Pearl:** Oliguria (< 0.5 mL/kg/hr in adults) in the first 24–48 hours of burn resuscitation is a sign of inadequate fluid delivery and increased risk of acute kidney injury, sepsis, and multi-organ failure. **Mnemonic:** **BURN URINE** — Burn resuscitation endpoints use Urine output as the Real-time Indicator for Normalization of tissue Endoperfusion. [cite:Park 26e Ch 12]