In a male patient with a high‑energy femur fracture from a tractor crush injury, which is the most appropriate next step: check serum creatine kinase, obtain PSA and place a Foley catheter, perform renal ultrasound, check hemoglobin A1c, or obtain urine electrolytes and calculate FeNa?

Immediate Management of High-Energy Femur Fracture with Crush Injury

Check serum creatine kinase immediately – this is the single most critical next step in a patient with a high-energy tractor crush injury and femur fracture to assess for rhabdomyolysis and guide aggressive fluid resuscitation. 1, 2

Rationale for Creatine Kinase Measurement

In crush injuries and high-energy trauma, elevated creatine kinase (CK) is the primary biomarker for detecting rhabdomyolysis, which can lead to acute kidney injury, compartment syndrome, hyperkalemia, and death if not recognized and treated early. 1, 3, 4

• CK levels >1,000 IU/L indicate rhabdomyolysis, and levels >75,000 IU/L are associated with >80% incidence of acute kidney injury requiring aggressive intervention. 1
• CK is a superior early predictor of acute renal failure compared to serum creatinine or urinary myoglobin in trauma patients – in one study, 93% of patients who developed AKI had elevated CK at admission versus only 60% with elevated creatinine. 4
• Direct trauma from being rolled over by a tractor causes massive muscle injury, releasing myoglobin that precipitates in renal tubules and causes AKI. 3

Why the Other Options Are Incorrect

• PSA and Foley placement – While Foley catheterization is important for monitoring urine output after rhabdomyolysis is confirmed, PSA has no role in acute trauma management and this combination is not the priority diagnostic step. 2
• Renal ultrasound – Imaging is not indicated for initial assessment of crush-related AKI; ultrasound is appropriate for suspected obstructive causes or chronic kidney disease, neither of which applies here. 1
• Hemoglobin A1c – This assesses chronic glycemic control over 3 months and has no role in acute trauma evaluation. 1
• Urine electrolytes and FeNa – While these help differentiate prerenal from intrinsic AKI in medical patients, they are not the initial diagnostic priority in crush injury where the mechanism (rhabdomyolysis) is clinically obvious and requires immediate CK measurement. 5, 6

Immediate Management Algorithm After CK Confirmation

If CK is elevated (>1,000 IU/L), initiate aggressive fluid resuscitation immediately:

• Administer >6 liters of 0.9% normal saline per day for severe rhabdomyolysis (CK >30,000 IU/L). 2
• Target urine output of ≥300 mL/hour (approximately 3-5 mL/kg/hour) to ensure myoglobin clearance. 2
• Avoid potassium-containing fluids (Lactated Ringer's, Hartmann's solution) as potassium levels rise markedly after reperfusion even with intact renal function. 2
• Place Foley catheter to monitor hourly urine output once rhabdomyolysis is confirmed. 2

Monitor for life-threatening complications:

• Check serum potassium, calcium, phosphorus, and creatinine every 6-12 hours in severe cases. 2
• Assess for compartment syndrome by examining for pain with passive stretch, paresthesias, paresis, and compartment pressure >30 mmHg. 1
• Treat hyperkalemia emergently if present (bicarbonate may be used for life-threatening hyperkalemia, though not routinely for rhabdomyolysis itself). 2

Common Pitfalls to Avoid

• Delaying fluid resuscitation – Early aggressive hydration is the only proven intervention to prevent AKI in rhabdomyolysis; delayed treatment dramatically increases AKI risk. 2, 3
• Using bicarbonate routinely – Current evidence does not support urinary alkalinization over aggressive crystalloid resuscitation alone, and bicarbonate can worsen hypocalcemia. 2
• Relying on serum creatinine alone – Creatinine rises later than CK and is less sensitive for early detection of muscle injury and impending AKI. 4
• Ignoring compartment syndrome – Crush injuries carry high risk; clinical signs (pain, paresthesias, paresis) must be assessed every 30-60 minutes in the first 24 hours. 1