A 35-year-old woman is admitted 4 hours after a tibia fracture sustained in a fall from height. She complains of severe leg pain and swelling. On examination, pain is elicited with passive dorsiflexion of the foot. Compartment pressure in the anterior compartment is measured at 48 mmHg. Her serum creatinine is 1.0 mg/dL and urine myoglobin is positive. What is the most important immediate intervention to prevent acute kidney injury?

Explanation

## Rhabdomyolysis and Acute Kidney Injury Prevention **Key Point:** In compartment syndrome with rhabdomyolysis, the dual priorities are (1) emergency fasciotomy to stop ongoing muscle breakdown, and (2) aggressive IV hydration to prevent myoglobin-induced acute tubular necrosis (ATN). ## Pathophysiology of Myoglobin-Induced AKI Myoglobin released from damaged muscle: 1. Filters freely at the glomerulus 2. Precipitates in acidic urine (pH <5.6) 3. Obstructs renal tubules → ATN 4. Generates free radicals → tubular injury **High-Yield:** The most effective prevention is **high-volume saline hydration** (target urine output 200–300 mL/hour) to maintain tubular flow and prevent myoglobin precipitation. Fasciotomy must be performed urgently to halt ongoing rhabdomyolysis. ## Management Strategy for Rhabdo-Associated AKI | Intervention | Rationale | Evidence | | --- | --- | --- | | **Emergency fasciotomy** | Stop ongoing muscle necrosis and myoglobin release | Essential; prevents progression | | **IV saline 0.9% at 500 mL/hour** | Maintain urine output 200–300 mL/hour; dilute myoglobin | Gold standard | | **Target urine output** | Prevent myoglobin precipitation in tubules | Reduces AKI incidence from 50% to <5% | | **Sodium bicarbonate** | Alkalinize urine (target pH >6.5); reduce myoglobin precipitation | Adjunctive; less evidence than hydration alone | | **Loop diuretics** | ~~Increase urine output~~ | **Contraindicated**; worsen dehydration and electrolyte imbalance | | **Mannitol** | ~~Osmotic diuresis~~ | **Contraindicated** in rhabdo; worsens hyperkalemia and volume depletion | **Clinical Pearl:** The compartment pressure of 48 mmHg in a symptomatic patient (pain on passive stretch) is an indication for fasciotomy. This will stop the source of myoglobin release. Simultaneous aggressive hydration is critical to prevent AKI. ## Why Hydration Targets Matter **Mnemonic — RhabdoHydration:** **R**igorous IV fluids, **A**ggressive urine output (200–300 mL/hr), **B**icarbonate (adjunctive), **D**on't use diuretics, **O**bserve K^+^ and creatinine. ```mermaid flowchart TD A[Crush injury + compartment syndrome + myoglobinuria]:::outcome --> B[Emergency fasciotomy]:::urgent B --> C[Aggressive IV saline 0.9%]:::action C --> D[Target urine output 200-300 mL/hr]:::action D --> E{Urine pH?}:::decision E -->|<6.5| F[Add sodium bicarbonate if needed]:::action E -->|>6.5| G[Continue hydration, monitor K+ and Cr]:::action F --> G G --> H[Prevent myoglobin precipitation and AKI]:::outcome ``` **Warning:** Loop diuretics and mannitol are **contraindicated** in rhabdomyolysis. They worsen volume depletion, reduce renal perfusion, and exacerbate hyperkalemia—all of which increase AKI risk.