What are the ICU admission criteria for a patient with severe rhabdomyolysis, indicated by significantly elevated Creatine Kinase (CK) levels and high risk of acute kidney injury?

ICU Admission Criteria for Rhabdomyolysis

Patients with severe rhabdomyolysis should be admitted to the ICU when they require aggressive fluid resuscitation exceeding 6 liters per day with hourly urine output monitoring targeting ≥300 mL/hour, have high probability of requiring renal replacement therapy, or demonstrate life-threatening electrolyte derangements. 1

Severity Assessment Requiring ICU Admission

Creatine Kinase Thresholds:

• Peak CK ≥5,000 U/L is 83% sensitive for predicting AKI requiring renal replacement therapy, though specificity is only 55% 2
• CK levels 43 times higher than 5,000 U/L (approximately >215,000 U/L) indicate extreme severity with high risk of AKI requiring RRT 1
• However, CK alone is not a specific or early predictor—it often peaks between admission and day 3 in 91% of cases, making it a delayed finding 2

McMahon Score:

• A McMahon score ≥6 calculated on admission is 86% sensitive and 68% specific for predicting need for RRT, providing more timely risk stratification than waiting for peak CK 2
• This score allows earlier identification of patients who may benefit from ICU-level monitoring and high-volume fluid resuscitation 2

Absolute ICU Admission Indications

Fluid Resuscitation Requirements:

• Need for >6 liters of IV fluids per day with hourly monitoring mandates ICU admission 1, 3
• Target urine output of ≥300 mL/hour (approximately 3-5 mL/kg/hour for a 70 kg patient—6-10 times higher than standard oliguria threshold) requires bladder catheterization and continuous monitoring only feasible in ICU 1, 3

Renal Complications:

• High probability of requiring renal replacement therapy 1
• Acute kidney injury occurs in 43% of rhabdomyolysis patients, with stage 3 AKI carrying 50% mortality 4
• Urine output remaining <300 mL/hour despite aggressive hydration indicates impending need for RRT 1

Life-Threatening Electrolyte Derangements:

• Risk of hyperkalemia, hypocalcemia, and hyperphosphatemia requiring close monitoring 1
• These electrolyte abnormalities can cause fatal cardiac arrhythmias if not promptly identified and corrected 1, 5

ICU Management Protocol

Immediate Interventions:

• Establish IV access and infuse 0.9% normal saline at 1000 mL/hour initially, reducing by at least 50% if resuscitation exceeds 2 hours to avoid volume overload 3
• Insert bladder catheter for hourly urine output monitoring unless urethral injury is suspected 3
• Avoid potassium-containing solutions (Lactated Ringer's, Hartmann's, Plasmalyte A) as potassium levels may increase markedly after reperfusion 3
• Avoid starch-based fluids due to association with increased AKI rates 3

Monitoring Parameters:

• Serial laboratory assessments of CK, creatinine, BUN, and electrolytes every 6-12 hours 1, 5
• Maintain urine pH at approximately 6.5 1, 3
• Continuous cardiac monitoring for arrhythmias secondary to electrolyte derangements 1

Renal Replacement Therapy Preparation:

• Early initiation of RRT is indicated if urine output remains <300 mL/hour despite aggressive hydration 1
• Intermittent hemodialysis is the preferred modality for rapid potassium clearance 1, 3
• Delaying RRT can lead to irreversible kidney damage and increased mortality 1, 5

Critical Pitfalls to Avoid

Delayed Recognition:

• Delayed fluid resuscitation increases risk of AKI—initiation should occur as early as possible after muscle injury 1, 3
• In one study, 44% of rhabdomyolysis patients with AKI did not receive nephrology consultation, likely contributing to worse outcomes 4

Inadequate Monitoring:

• Failure to monitor hourly urine output can lead to missed intervention windows 1
• Inadequate serial electrolyte monitoring can result in fatal cardiac arrhythmias 1, 5

Inappropriate Interventions:

• Do not routinely use mannitol—studies show little additional benefit compared to crystalloid resuscitation alone, and it is potentially nephrotoxic 3
• Mannitol may only benefit patients with CK >30,000 U/L, though this benefit remains undefined and is contraindicated in oligoanuria 3, 5
• Urinary alkalinization with bicarbonate is not recommended—current evidence does not demonstrate benefit over aggressive fluid resuscitation alone 3
• Large doses of bicarbonate can worsen hypocalcemia by decreasing free calcium levels 3

Clinical Context Considerations

While the KDIGO AKI guideline suggests considering ICU admission for stage 2 AKI, the clinical context must guide decision-making 6. For rhabdomyolysis specifically, ICU admission is warranted when the patient requires the intensive monitoring and aggressive fluid management outlined above, regardless of formal AKI staging. Patients with potentially reversible causes without features of severe sepsis or shock may not require ICU admission even with elevated CK, provided they can receive adequate fluid resuscitation and monitoring on a step-down unit 6.

Overall mortality in hospitalized rhabdomyolysis patients is 16%, with significantly prolonged length of stay in the presence of AKI 4, emphasizing the importance of early aggressive management in an ICU setting for severe cases.