A 35-year-old woman is admitted 8 hours after a severe crush injury to her left forearm. She complains of severe pain in the forearm despite adequate analgesia. On examination, the forearm is tense and swollen; pain is elicited on passive extension of the fingers. Compartment pressure in the flexor compartment is measured at 38 mmHg; her diastolic blood pressure is 65 mmHg. Urine dipstick shows 3+ protein and is dark brown. What is the most important immediate complication to prevent?

Explanation

## Pathophysiology of Crush Injury and Compartment Syndrome **Key Point:** Crush injury with compartment syndrome triggers massive muscle necrosis and rhabdomyolysis, releasing myoglobin into the circulation. The immediate life-threatening complication is acute kidney injury (AKI) from myoglobin precipitation in renal tubules. ## Compartment Pressure Assessment | Parameter | Value | Interpretation | | --- | --- | --- | | Compartment pressure | 38 mmHg | Elevated | | Diastolic BP | 65 mmHg | Delta P = 65 − 38 = 27 mmHg | | Threshold for fasciotomy | Delta P ≤ 30 mmHg | **Fasciotomy indicated** | **High-Yield:** When Delta P (diastolic BP − compartment pressure) is ≤30 mmHg, tissue perfusion is critically compromised and fasciotomy is mandatory. ## Rhabdomyolysis Cascade ```mermaid flowchart TD A[Crush injury + Compartment syndrome]:::outcome --> B[Muscle necrosis]:::action B --> C[Myoglobin release]:::action C --> D[Dark brown urine]:::outcome D --> E{Myoglobin in renal tubules}:::decision E -->|Acidic urine, dehydration| F[Myoglobin precipitation]:::action F --> G[Acute tubular necrosis]:::outcome G --> H[Acute kidney injury]:::urgent B --> I[Hyperkalemia from cell lysis]:::urgent I --> J[Cardiac dysrhythmias]:::urgent ``` ## Immediate Management Priorities **High-Yield:** In rhabdomyolysis-associated compartment syndrome, the order of urgency is: 1. **Fasciotomy** — prevent further muscle necrosis 2. **Aggressive IV hydration** — dilute urine, maintain glomerular filtration, prevent myoglobin precipitation 3. **Urine alkalinization** (sodium bicarbonate) — myoglobin is less soluble in acidic urine; alkaline urine promotes solubility and renal excretion 4. **Monitor potassium** — rhabdomyolysis causes hyperkalemia; ECG monitoring and calcium gluconate/insulin-glucose standby 5. **Avoid NSAIDs and nephrotoxic drugs** — further renal injury ## Why AKI Is the Most Important Immediate Complication **Clinical Pearl:** Myoglobin-induced acute kidney injury can develop within hours of crush injury and is the leading cause of death in crush syndrome. Mortality from rhabdomyolysis-associated AKI ranges from 10–50% depending on severity and management. - **Volkmann's contracture** (option A) is a late sequela (weeks to months) resulting from ischemic muscle fibrosis; it is prevented by timely fasciotomy but is not the immediate life threat. - **Sensory loss** (option D) occurs only if fasciotomy is delayed beyond 6–8 hours; nerve damage is late, not immediate. - **Sepsis** (option C) is a potential complication of tissue necrosis but develops over days; AKI is immediate (hours). **Mnemonic: CRASH** — **C**rush injury, **R**habdomyolysis, **A**cute kidney injury, **S**evere hyperkalemia, **H**yperphosphatemia. [cite:Harrison 21e Ch 335; Orthopedic Surgery Essentials Ch 2]