A 35-year-old woman is admitted 8 hours after a tibia fracture sustained in a fall from height. She develops severe leg swelling, pain on passive toe extension, and compartment pressure measured at 38 mmHg (diastolic BP 65 mmHg). She undergoes urgent fasciotomy. Over the next 24 hours, she develops dark urine, a serum creatinine rise from 0.9 to 2.8 mg/dL, and serum potassium of 6.2 mEq/L. What is the most appropriate immediate intervention to prevent acute kidney injury?

Explanation

## Rhabdomyolysis and Acute Kidney Injury Post-Fasciotomy **Key Point:** Compartment syndrome from crush injury causes muscle necrosis (rhabdomyolysis), releasing myoglobin into the bloodstream. Myoglobin precipitates in renal tubules, causing acute tubular necrosis (ATN) and acute kidney injury (AKI). ### Pathophysiology of Rhabdomyolysis-Induced AKI 1. **Muscle injury** → Release of myoglobin, potassium, phosphate, uric acid 2. **Myoglobinuria** → Dark/cola-colored urine (as in this case) 3. **Tubular precipitation** → Myoglobin + acidic urine → crystal formation in renal tubules 4. **Tubular obstruction + direct toxicity** → Acute tubular necrosis 5. **Hyperkalemia** → Cardiac arrhythmias (life-threatening) ### Clinical Features in This Patient | Finding | Significance | |---------|---------------| | Dark urine | Myoglobinuria (pathognomonic) | | Creatinine 0.9 → 2.8 mg/dL in 24 hrs | Rapid decline in GFR; ATN | | K^+^ 6.2 mEq/L | Hyperkalemia (normal: 3.5–5.0); risk of arrhythmia | | Compartment syndrome + crush injury | Massive rhabdomyolysis | **High-Yield:** The combination of crush injury, compartment syndrome, myoglobinuria, and hyperkalemia is a **medical emergency requiring immediate intervention**. ### Management Strategy ```mermaid flowchart TD A[Crush injury + compartment syndrome]:::outcome --> B[Rhabdomyolysis develops]:::urgent B --> C[Dark urine + ↑K+ + ↑Cr]:::urgent C --> D[Immediate interventions]:::action D --> E["1. IV K+ lowering agents<br/>(Ca gluconate, insulin-dextrose, NaHCO3)"]:::action D --> F["2. Aggressive IV hydration<br/>(target urine output 200-300 mL/hr)"]:::action D --> G["3. Alkalinize urine<br/>(sodium bicarbonate to pH > 6.5)"]:::action E --> H[Stabilize cardiac membrane<br/>& shift K+ intracellularly]:::outcome F --> I[Dilute myoglobin,<br/>prevent precipitation]:::outcome G --> J[Myoglobin more soluble<br/>in alkaline urine]:::outcome H --> K[Prevent arrhythmias]:::action I --> L[Preserve renal function]:::action ``` ### Immediate Management Priorities **1. Treat Hyperkalemia (Life-Threatening)** | Agent | Mechanism | Onset | Duration | |-------|-----------|-------|----------| | **Calcium gluconate** | Stabilizes cardiac membrane | Immediate (1–3 min) | 30–60 min | | **Insulin 10 U + Dextrose 25 g IV** | Shifts K^+^ into cells | 10–20 min | 4–6 hours | | **Sodium bicarbonate 50–100 mEq IV** | Shifts K^+^ into cells + alkalinizes urine | 30–60 min | 2–4 hours | | **Furosemide** | Urinary K^+^ excretion | 1–2 hours | Variable | **Clinical Pearl:** Calcium gluconate is given **first** because it provides immediate cardiac protection while other agents take effect. It does NOT lower K^+^ but prevents fatal arrhythmias. **2. Aggressive IV Hydration** - **Target:** Urine output 200–300 mL/hour (or 1–1.5 L/day) - **Fluid:** Normal saline (0.9% NaCl) or Ringer's lactate - **Rationale:** Dilutes myoglobin, reduces tubular concentration, and promotes urinary excretion - **Monitoring:** Foley catheter, strict I/O, daily weights, CVP if needed **3. Urine Alkalinization** - **Target pH:** > 6.5 (ideally 7.0–8.0) - **Method:** Sodium bicarbonate 50–100 mEq IV, then continuous infusion - **Rationale:** Myoglobin is more soluble in alkaline urine; reduces precipitation in tubules - **Caution:** Risk of hypokalemia and hypernatremia; monitor electrolytes closely **4. Monitoring** - Serum K^+^, creatinine, phosphate, uric acid, CK (creatine kinase) - Urine myoglobin, color, pH - ECG for hyperkalemia changes (peaked T waves, widened QRS) ### Why Each Distractor Is Wrong **Option 1 (Correct):** Addresses both hyperkalemia (immediate cardiac risk) and AKI prevention (hydration + alkalinization). **Option 2 (Hemodialysis):** Hemodialysis is reserved for: - Refractory hyperkalemia despite medical management - Severe metabolic acidosis - Fluid overload with pulmonary edema - Creatinine > 5–6 mg/dL or oliguria lasting > 5–7 days It is **not** the first-line intervention. Medical management (K^+^ lowering, hydration) must be initiated immediately. **Option 3 (Furosemide + fluid restriction):** Furosemide alone is insufficient for K^+^ management and may worsen AKI by reducing renal perfusion. Fluid restriction is **contraindicated** in rhabdomyolysis; aggressive hydration is required. This approach risks worsening renal failure. **Option 4 (Allopurinol):** Allopurinol reduces uric acid production and is useful for **prevention** of uric acid nephropathy in tumor lysis syndrome. However, in acute rhabdomyolysis: - It does not address hyperkalemia (immediate life threat) - It does not prevent myoglobin precipitation - It is not first-line therapy Allopurinol may be used as adjunctive therapy but is not the immediate intervention. **Mnemonic: CRASH-M for Rhabdomyolysis Management** - **C**alcium gluconate (cardiac stabilization) - **R**apid IV hydration (dilute myoglobin) - **A**lkalinize urine (sodium bicarbonate) - **S**hift K^+^ intracellularly (insulin-dextrose) - **H**emodialysis (if refractory) - **M**onitor electrolytes and renal function **Tip:** In exams, recognize that rhabdomyolysis + hyperkalemia is a **medical emergency**. The correct answer will always include immediate K^+^ lowering AND aggressive hydration. Dialysis, allopurinol, and diuretics are secondary interventions. [cite:Harrison 21e Ch 283; Campbell's Operative Orthopaedics 13e Ch 42]