What is the next best step for a patient with a crush injury, dark-colored urine, and impaired renal function?

Immediate Management of Crush Injury with Suspected Rhabdomyolysis

Order a 1 L crystalloid bolus STAT (Answer B) as the immediate priority, followed by creatine kinase measurement to confirm rhabdomyolysis and guide ongoing management. 1

Rationale for Aggressive Fluid Resuscitation First

The clinical presentation—crush injury, dark-colored urine (myoglobinuria), and doubling of creatinine on hospital day 1—indicates rhabdomyolysis with evolving acute kidney injury. Early and aggressive crystalloid infusion is the cornerstone of preventing progression to acute renal failure and is most effective when initiated within 6 hours of injury. 2, 3

• Fluid resuscitation takes precedence over diagnostic testing because the therapeutic window is narrow, and delayed treatment significantly increases mortality risk (10-50% with severe AKI). 2
• The Kidney International guidelines recommend infusing 0.9% saline at 1 L/hour initially for crush victims, with 3-6 L total in the first 24 hours depending on clinical response. 1
• Volume expansion corrects hypovolemia from third-spacing into damaged muscle, maintains renal perfusion, and dilutes nephrotoxic myoglobin to prevent tubular cast formation. 1, 4

Why Creatine Kinase Should Be Ordered Immediately After (But Not Instead Of) Fluids

• CK measurement (Answer A) is essential for confirming rhabdomyolysis and assessing severity, but should not delay fluid resuscitation. 5, 3
• CK levels >5,000 IU/L confirm rhabdomyolysis; levels >75,000 IU/L indicate >80% risk of acute kidney injury requiring intensive monitoring. 5
• Serial CK measurements guide the duration and intensity of fluid therapy. 5

Why Mannitol Is NOT the Next Best Step

Mannitol (Answer D) should NOT be ordered at this point because:

• Current evidence shows no additional benefit of mannitol over crystalloid resuscitation alone for preventing acute kidney injury in crush syndrome. 1
• Mannitol is potentially nephrotoxic, particularly in hypovolemic patients or those with established renal dysfunction. 1, 6
• The FDA label warns that mannitol can cause irreversible renal failure, especially in patients with pre-existing renal disease or those receiving other nephrotoxic agents. 6
• Mannitol requires close monitoring of fluid status and electrolytes, which may be impossible in the acute resuscitation phase. 1
• If mannitol is considered at all, it should only be given AFTER volume status is stabilized and urine flow is confirmed, not as initial therapy. 3, 4

Why Nephrology Consultation Is Premature

• Renal replacement therapy consultation (Answer C) is premature at this stage because the patient has not yet received adequate fluid resuscitation. 1
• RRT is indicated for life-threatening complications (severe hyperkalemia, refractory acidosis, fluid overload) or persistent anuria despite aggressive fluid therapy—none of which have been established yet. 1
• Early aggressive fluid resuscitation may prevent the need for dialysis entirely. 2, 3

Critical Monitoring After Fluid Bolus

Once the fluid bolus is initiated, immediately order:

• Creatine kinase STAT to confirm diagnosis and assess severity. 5, 3
• Complete metabolic panel including potassium, calcium, phosphate to detect life-threatening hyperkalemia or hypocalcemia. 1, 5
• Urine output monitoring (goal >200-300 mL/hour initially to flush myoglobin). 1, 4
• ECG to assess for hyperkalemia-induced arrhythmias. 5

Fluid Management Algorithm

• Continue 0.9% normal saline at 1 L/hour initially, then taper by at least 50% after 2 hours based on clinical response. 7
• Avoid Lactated Ringer's or other potassium-containing fluids as potassium levels may rise markedly even with intact renal function. 7
• Avoid starch-based colloids due to increased risk of AKI and bleeding. 1, 7
• Target urine output of 200-300 mL/hour until myoglobinuria clears. 1, 4

Common Pitfalls to Avoid

• Delaying fluid resuscitation to obtain diagnostic tests first—this misses the critical therapeutic window. 2, 3
• Ordering mannitol before volume resuscitation—this can worsen renal injury in hypovolemic patients. 1, 6
• Using potassium-containing fluids—hyperkalemia is a major cause of early mortality in crush syndrome. 7
• Premature nephrology consultation before adequate resuscitation attempt—most cases can be prevented with early aggressive fluids. 1, 2