A 28-year-old woman is admitted 6 hours after sustaining a 35% TBSA deep partial and full thickness burn from a house fire. She has been resuscitated with Lactated Ringer's solution according to the Parkland formula. Her current urine output is 0.3 mL/kg/hour, blood pressure is 110/70 mmHg, heart rate is 98 bpm, and serum sodium is 148 mEq/L. What is the most appropriate next step in fluid management?

Explanation

## Burn Resuscitation Endpoints and Fluid Titration **Key Point:** Urine output is the primary real-time marker of adequate tissue perfusion and resuscitation in burn patients. Target urine output varies by burn depth and patient factors. ### Target Urine Output in Burns | Patient Type | Target Urine Output | Rationale | | --- | --- | --- | | **Adult with thermal burn** | 0.5 mL/kg/hour | Maintains renal perfusion and prevents myoglobinuria precipitation | | **Adult with electrical burn** | 0.75–1 mL/kg/hour | Risk of myoglobinuria; higher output needed | | **Pediatric patient** | 1 mL/kg/hour | Higher metabolic rate | | **Inhalation injury present** | 0.5–1 mL/kg/hour | Increased fluid requirements | **High-Yield:** Current urine output of **0.3 mL/kg/hour is inadequate** (target = 0.5 mL/kg/hour for thermal burns). This indicates **under-resuscitation** despite normal vital signs — a classic trap in burn management. **Clinical Pearl:** Vital signs (BP, HR) may remain deceptively normal in the early phase of under-resuscitation due to compensatory mechanisms. Urine output is more sensitive and earlier indicator of tissue hypoperfusion. ### Why Hypernatremia Is Present (But Not the Primary Problem) Serum sodium of 148 mEq/L reflects: - Evaporative water loss from the burn wound - Relative free water deficit (Lactated Ringer's has sodium 130 mEq/L, which is hypotonic relative to normal plasma) - This is **expected and self-limited** if resuscitation is adequate **Mnemonic:** **FLUID TITRATION** — Urine output is the **primary endpoint**; vital signs and labs are secondary. Increase fluids if UOP < target; decrease if UOP > target + signs of over-resuscitation (pulmonary edema, compartment syndrome). ## Why This Answer Is Correct 1. Urine output of 0.3 mL/kg/hour is **below target** (0.5 mL/kg/hour for thermal burns) 2. Vital signs are currently stable, but this does not mean adequate resuscitation — tissue perfusion may still be compromised 3. **Increasing Lactated Ringer's infusion** is the appropriate response to achieve target urine output 4. Hypernatremia will self-correct once adequate perfusion is restored; it is not the primary problem to address [cite:ATLS 10th Edition Ch 5; Sabiston 21e Ch 73]