Rhabdomyolysis

Overview

Rhabdomyolysis is a potentially life-threatening clinical syndrome characterized by the breakdown of skeletal muscle tissue with subsequent release of intracellular muscle constituents into the circulation. [1] The condition encompasses a wide spectrum of severity, ranging from asymptomatic elevations in creatine kinase (CK) to critical illness with acute kidney injury (AKI), severe electrolyte disturbances, and death. [2]

The pathophysiology centers on disruption of myocyte membrane integrity, leading to release of myoglobin, CK, potassium, phosphate, uric acid, and other intracellular contents into the bloodstream. [3] Myoglobin, in particular, is directly nephrotoxic and precipitates in renal tubules under conditions of acidic urine and volume depletion, leading to AKI in 15-50% of cases. [1,4]

Rhabdomyolysis represents an important emergency across multiple specialties—emergency medicine, critical care, nephrology, orthopedics, and toxicology. Early recognition and aggressive fluid resuscitation are the cornerstones of management and have been shown to dramatically reduce the risk of renal failure and mortality. [5,6] The condition is particularly important in postgraduate examinations (MRCP, FRACP) as it integrates concepts from metabolic medicine, emergency management, and nephrology.

---

Quick Reference

Critical Alerts

• AKI occurs in 15-50%: Aggressive IV fluid resuscitation is the single most important intervention [1,4]
• Hyperkalemia can be rapidly fatal: Monitor potassium every 4-6 hours; treat aggressively with calcium, insulin/glucose, dialysis [7]
• CK > 5000 U/L is high risk for AKI: Threshold for intensive fluid therapy and ICU consideration [8]
• CK > 15,000-20,000 U/L predicts poor outcomes: Strong association with need for renal replacement therapy (RRT) or mortality [9]
• Compartment syndrome may coexist: Check compartments in trauma; fasciotomy is time-critical [10]
• Target urine output 200-300 mL/hr: High-volume resuscitation prevents tubular precipitation [5,6]
• Avoid nephrotoxins: NSAIDs, IV contrast, aminoglycosides exacerbate kidney injury [11]

Key Diagnostics

Emergency Treatments

---

Definition and Diagnostic Criteria

Definition

Rhabdomyolysis is defined as skeletal muscle injury with release of intracellular muscle constituents, particularly myoglobin and creatine kinase, into the circulation. [1] There is no universally accepted formal definition, which has led to significant heterogeneity in the literature. [16]

Diagnostic Criteria

A systematic review of 614 published studies found that 37.6% provided a formal definition of rhabdomyolysis, with the most common criterion being a specific CK threshold: [16]

• CK > 1000 U/L (27.7% of studies)
• CK > 5× upper limit of normal (ULN) (22.9% of studies)
• CK > 10,000 U/L (in severe cases)

Clinical consensus supports diagnosis when:

• CK > 1000 U/L (five times ULN), AND
• Compatible clinical history (trauma, exertion, drug exposure), OR
• Evidence of myoglobinuria (urine dipstick positive for blood without RBCs on microscopy) [1,8,16]

Classification

By Severity (Based on CK Level and AKI Risk)

By Etiology

---

Epidemiology

Incidence and Prevalence

• Incidence: Approximately 26,000+ hospitalizations per year in the United States for rhabdomyolysis [2]
• AKI incidence: 15-50% of rhabdomyolysis patients develop acute kidney injury [1,4]
• Dialysis requirement: 5-10% of rhabdomyolysis patients require renal replacement therapy [9,15]
• Mortality: Overall 5%; increases to 10-20% in patients requiring dialysis; up to 40-50% in crush syndrome with delayed treatment [9,19]

Demographics

• Age: Bimodal distribution—young adults (exertional, drugs) and elderly (immobility, medications, falls)
• Sex: Male predominance (2-3:1) due to higher muscle mass and occupational/recreational exposures [2]
• Ethnicity: African Americans may have higher baseline CK levels (2-3× higher), complicating diagnosis [20]

Etiology Distribution

---

Aetiology and Risk Factors

Traumatic Causes

Direct Muscle Injury

• Crush injury: Motor vehicle accidents, building collapse, earthquakes [19]
• Compartment syndrome: Trauma, vascular injury, reperfusion injury [10]
• Prolonged immobilization: "Found down" patients (overdose, stroke, fall), restraints, coma [22]
• Electrical injury: High-voltage electrical burns
• Surgical procedures: Prolonged operations (> 4-6 hours), lithotomy position

Exertional Causes

• Intense physical exercise: Marathon running, military training, "spinning" classes, CrossFit [17]
• Seizures: Prolonged or recurrent seizures (status epilepticus)
• Heat stroke: Exertional or classic heat stroke
• Delirium tremens: Alcohol withdrawal with agitation

Exam Detail: Exertional rhabdomyolysis in athletes: A systematic review of 772 cases found mean age 28.7 years, male predominance, with running (54.3%) and weightlifting (14.8%) most common activities. Mean CK at presentation was 31,481 U/L, peaking at 38,552 U/L. [17] Risk factors include:

• Unconditioned individuals ("weekend warriors")
• Novel eccentric exercises
• Hot and humid environments
• Dehydration
• Concomitant NSAID use (increases AKI risk)

Drug-Induced Rhabdomyolysis

Statins

• Most common prescribed drug causing rhabdomyolysis [18]
• Incidence: 0.1-0.2% overall; higher with high-dose therapy
• Risk factors:
  • High-dose statins (simvastatin 80 mg, atorvastatin 80 mg)
  • CYP3A4 inhibitors (macrolides, azole antifungals, protease inhibitors, grapefruit juice)
  • Fibrate co-administration (gemfibrozil > fenofibrate)
  • Hypothyroidism
  • Advanced age, female sex, low BMI
  • Renal or hepatic impairment

Illicit Drugs and Alcohol

Neuroleptic Malignant Syndrome (NMS)

• Antipsychotics (typical > atypical): haloperidol, fluphenazine
• Clinical features: Fever, rigidity, altered mental status, autonomic instability [23]
• Mortality: 10-20% if untreated
• Treatment: Discontinue antipsychotic, supportive care, dantrolene, bromocriptine

Malignant Hyperthermia

• Triggered by: Volatile anesthetics (halothane, sevoflurane) and succinylcholine
• Pathophysiology: Genetic mutation in ryanodine receptor (RYR1)
• Clinical features: Rapid hyperthermia (> 40°C), rigidity, tachycardia, hypercarbia
• Treatment: Dantrolene 2.5 mg/kg IV bolus, repeat until symptoms resolve [23]

Other Medications

• Antipsychotics: Phenothiazines, atypical antipsychotics
• SSRIs/SNRIs: Serotonin syndrome (with MAOIs, tramadol, linezolid)
• Antihistamines: Prolonged immobilization
• Colchicine: Direct myotoxicity, especially with CYP3A4 inhibitors
• Propofol: Propofol infusion syndrome (prolonged high-dose infusions)

Infectious Causes

Metabolic and Electrolyte Disorders

Inflammatory Myopathies

• Dermatomyositis
• Polymyositis
• Immune-mediated necrotizing myopathy (statin-associated autoimmune myopathy)

Genetic/Metabolic Myopathies

Exam Detail: Recurrent rhabdomyolysis or family history should prompt evaluation for metabolic myopathies: [25]

Glycogen Storage Diseases (Glycogenolysis/Glycolysis Defects)

• McArdle disease (GSD V): Myophosphorylase deficiency
  • Symptoms with brief high-intensity exercise
  • "Second wind" phenomenon
• Phosphofructokinase deficiency (GSD VII)
• Phosphoglycerate kinase deficiency

Fatty Acid Oxidation Defects

• Carnitine palmitoyltransferase II (CPT II) deficiency: Most common
  • Symptoms with prolonged exercise, fasting, cold exposure
  • No "second wind"
• Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency

Mitochondrial Myopathies

• Manifest with endurance exercise, often with additional systemic features

Diagnostic approach:

• Ischemic forearm exercise test (lactate and ammonia)
• Genetic testing for common mutations
• Muscle biopsy (histology, enzyme assays)

---

Pathophysiology

Mechanism of Muscle Cell Injury

Normal skeletal muscle homeostasis depends on adequate ATP production and intact cell membrane function. Disruption leads to a cascade of cellular injury: [3]

1. ATP depletion: Due to ischemia, toxins, excessive demand, or metabolic defects
2. Pump failure: Na+/K+-ATPase and Ca2+-ATPase dysfunction
3. Calcium influx: Rising intracellular Ca2+ activates:
   • Phospholipases (membrane damage)
   • Proteases (protein degradation)
   • Calpains (cytoskeletal breakdown)
4. Myocyte necrosis: Cell membrane rupture and death
5. Release of intracellular contents:
   • Myoglobin (17 kDa protein, filtered at glomerulus)
   • Creatine kinase (CK)
   • Potassium, phosphate, uric acid, purines
   • Lactate dehydrogenase (LDH), AST, ALT

Mechanism of Acute Kidney Injury

Myoglobin is the principal mediator of AKI in rhabdomyolysis, through three mechanisms: [1,3,4]

1. Renal Vasoconstriction

• Myoglobin scavenges nitric oxide (NO), reducing renal vasodilation
• Endothelin and other vasoconstrictors exacerbate ischemia
• Result: Reduced renal blood flow and GFR

2. Direct Tubular Toxicity

• Myoglobin is filtered at glomerulus and reabsorbed in proximal tubule
• In acidic environment (pH less than 5.6), myoglobin is converted to ferrihematin (toxic)
• Free iron from heme generates reactive oxygen species (ROS)
• Tubular epithelial cell injury and necrosis

3. Tubular Obstruction

• Myoglobin precipitates with Tamm-Horsfall protein in distal tubules
• Forms intratubular casts, particularly in acidic urine
• Result: Obstructive uropathy and back-leak of filtrate

4. Hypovolemia

• Third-spacing of fluid into injured muscle compartments
• Can sequester several liters of intravascular volume
• Exacerbates renal hypoperfusion

Exam Detail: Molecular Mechanisms of Myoglobin Nephrotoxicity

Recent research has elucidated the precise molecular pathways of myoglobin-induced kidney injury: [3,4,27]

Oxidative Stress and Lipid Peroxidation

Heme Iron-Mediated ROS Generation: [27]

1. Myoglobin dissociation: Under acidic conditions (pH less than 5.6), myoglobin releases free heme
2. Fenton reaction: Free iron (Fe²⁺/Fe³⁺) from heme catalyzes:
   • H₂O₂ → •OH (hydroxyl radical) + OH⁻
3. Lipid peroxidation: Hydroxyl radicals attack tubular cell membranes
4. Mitochondrial dysfunction: ROS damage mitochondrial DNA and respiratory chain
5. Tubular cell apoptosis and necrosis

Evidence: Bolisetty et al. (Antioxid Redox Signal 2011) demonstrated that heme oxygenase-1 (HO-1) upregulation protects against myoglobin-induced AKI through heme degradation and iron sequestration. [27]

Tubular Cast Formation

Physicochemical Properties: [4]

• Myoglobin molecular weight: 17 kDa (freely filtered at glomerulus)
• Renal threshold: Serum myoglobin > 100 mg/dL → myoglobinuria (visible dark urine)
• Urine pH critical:
  • pH > 6.5: Myoglobin remains soluble
  • pH less than 5.6: Myoglobin precipitates with Tamm-Horsfall protein (uromodulin)
• Cast location: Distal convoluted tubule and collecting duct (most acidic segments)

Obstruction mechanics:

• Casts block tubular lumen → increased intratubular pressure
• Decreased net filtration pressure
• Tubular rupture and backleak of glomerular filtrate
• Result: Acute tubular necrosis (ATN) pattern

Renal Vasoconstriction Cascade

Nitric Oxide Scavenging: [3,4]

• Myoglobin binds NO → reduced vasodilation
• Compensatory release of:
  • Endothelin-1 (potent vasoconstrictor)
  • Thromboxane A₂
  • Angiotensin II (activation of RAAS)
• Result: Afferent arteriole constriction → ↓ GFR

Endothelial dysfunction:

• Heme induces endothelial activation
• Upregulation of adhesion molecules (ICAM-1, VCAM-1)
• Inflammatory cell infiltration
• Microvascular thrombosis

Clinical Correlation: This explains why early aggressive volume expansion is critical—it reverses renal vasoconstriction and dilutes tubular myoglobin below precipitation threshold.

Protective Mechanisms and Therapeutic Targets

Intrinsic Renal Protection: [27]

• Heme oxygenase-1 (HO-1): Degrades heme to biliverdin, CO, and Fe²⁺
  • Biliverdin → antioxidant
  • CO → vasodilator
  • Fe²⁺ → sequestered by ferritin
• Superoxide dismutase (SOD): Neutralizes superoxide radicals
• Glutathione: Antioxidant defense

Future Therapeutic Strategies (currently experimental):

• HO-1 inducers (e.g., hemin)
• Iron chelators (e.g., deferoxamine)
• Antioxidants (e.g., N-acetylcysteine)
• Note: None currently proven effective in human RCTs

Factors Increasing AKI Risk

Electrolyte and Metabolic Disturbances

Hyperkalemia

• Mechanism: Massive K+ release from necrotic muscle cells
• Timing: Early (within hours)
• Severity: Can be life-threatening (> 6-7 mEq/L); risk of cardiac arrest
• Clinical significance: Primary cause of death in early phase [7]

Hypocalcemia (Early Phase)

• Mechanism: Calcium deposition in injured muscle tissue (calcium-phosphate complexes)
• Timing: First 24-48 hours
• Clinical significance: Usually asymptomatic; aggressive replacement may worsen deposition and lead to later hypercalcemia [13]

Hypercalcemia (Late Phase/Recovery)

• Mechanism: Mobilization of deposited calcium from healing muscle
• Timing: Days to weeks into recovery
• Clinical significance: Can be severe; requires monitoring during recovery

Hyperphosphatemia

• Mechanism: Release from muscle cells (phosphate content is high intracellularly)
• Timing: Early
• Clinical significance: Contributes to calcium-phosphate precipitation; mimics tumor lysis syndrome

Hyperuricemia

• Mechanism: Purine catabolism from muscle cell breakdown
• Timing: Early
• Clinical significance: Adds to uric acid nephropathy; mimics tumor lysis syndrome

Metabolic Acidosis

• Mechanism: Lactic acidosis (from ischemic muscle), release of organic acids, AKI
• Timing: Early
• Clinical significance: Worsens myoglobin toxicity; exacerbates hyperkalemia

---

Clinical Presentation

Classic Triad (Present in less than 10% of Cases)

1. Myalgia: Muscle pain, tenderness, swelling
2. Weakness: Affected muscle groups
3. Dark urine: "Cola-colored" or "tea-colored" from myoglobinuria

Important: The classic triad is absent in up to 50% of cases, particularly in patients with altered consciousness or obtundation. [1,2]

Symptoms

Musculoskeletal

• Muscle pain (50% of patients): Most commonly proximal muscles (thighs, calves, lower back)
• Muscle weakness: Ranges from mild to profound; may prevent ambulation
• Muscle swelling: Edema from third-spacing
• Muscle stiffness: Difficulty with movement

Systemic

• Fatigue, malaise: Non-specific
• Nausea, vomiting: Common
• Fever: Especially with NMS, malignant hyperthermia, infection
• Confusion, altered mental status: In severe cases (uremia, hypercalcemia, primary CNS event)

Urinary

• Dark urine: Only when serum myoglobin > 100 mg/dL (not always present)
• Decreased urine output: If AKI develops (oliguria/anuria)

Signs on Physical Examination

Vital Signs

• Tachycardia: Common due to pain, volume depletion, fever
• Fever: NMS, malignant hyperthermia, heat stroke, infection
• Hypotension: Severe volume depletion, sepsis, compartment syndrome

Musculoskeletal

Compartment Syndrome Assessment

5 P's (late findings; do NOT wait for all to be present): [10]

1. Pain: Out of proportion to exam; worsens with passive muscle stretch (EARLIEST sign)
2. Pressure: Tense, swollen compartment
3. Paresthesias: Nerve ischemia
4. Paralysis: LATE sign (irreversible damage)
5. Pulselessness: LATE sign (not reliable; pulses often present)

Diagnosis: Clinical; measure compartment pressure if uncertain (> 30 mmHg or within 30 mmHg of diastolic BP = compartment syndrome)

Management: Emergent fasciotomy; do NOT delay for labs or imaging

Other Examination Findings

• Skin: Track marks (IV drug use), burns, pressure sores, crush injuries
• Neurological: Altered mental status (uremia, hypercalcemia, intoxication, stroke)
• Volume status: Dry mucous membranes, reduced skin turgor, orthostatic hypotension

---

Differential Diagnosis

Other Causes of Elevated CK

Other Causes of Myoglobinuria (Dark Urine, Dipstick Positive for Blood)

---

Investigations

Laboratory Studies

Essential Tests

Additional Tests

Urinalysis Interpretation

Key point: Urine dipstick detects heme peroxidase activity (from myoglobin or hemoglobin), but does not detect intact RBCs. Positive dipstick + absence of RBCs = myoglobinuria or hemoglobinuria.

Creatine Kinase (CK) Kinetics

• Rises: Within 2-12 hours of muscle injury
• Peaks: 24-72 hours (may continue rising for 1-3 days)
• Falls: Half-life ~36-48 hours; declines by ~40% per day once source controlled [8]
• Monitoring: Check CK daily until downtrending and less than 5000 U/L

Prognostic significance of CK level: [9]

• CK > 15,000 U/L: Independent risk factor for RRT or mortality
• CK > 50,000 U/L: Very high risk (> 50% develop AKI requiring dialysis)

Exam Detail: CK Threshold Evidence and Clinical Implications

Multiple large cohort studies have established evidence-based CK thresholds for risk stratification: [8,9,26]

Threshold Analysis (Systematic Review, n=2,371 patients)

Key Evidence:

• McMahon et al. (JAMA Internal Medicine 2013): Prospective cohort of 2,371 patients with CK > 5,000 U/L demonstrated that CK > 15,000 U/L was an independent predictor of need for RRT or in-hospital death (OR 2.8, 95% CI 1.9-4.1). [9]
• Zimmerman & Shen (Chest 2013): Comprehensive review established CK > 5,000 U/L as threshold for significant AKI risk requiring intensive fluid therapy. [8]
• Safari et al. (Ren Fail 2020): Meta-analysis of 18 studies (n=3,894 patients) confirmed peak CK > 20,000 U/L as strongest predictor of AKI (sensitivity 68%, specificity 82%). [26]

CK Decline Kinetics

Expected CK decline rates guide management duration: [8,26]

• Normal clearance: 40-50% reduction per day after source control
• Delayed clearance (less than 30% reduction/day): Suggests:
  • Ongoing muscle injury
  • Renal impairment affecting clearance
  • Compartment syndrome
  • Need for surgical intervention

Clinical Application:

• If CK plateaus or rises after initial presentation → re-evaluate for ongoing injury
• Target CK less than 5,000 U/L before transitioning from IV to oral fluids
• Document daily CK trend in clinical notes for medicolegal protection

Risk prediction score (McMahon et al., JAMA Internal Medicine 2013): [9]

Predicts RRT or in-hospital mortality in rhabdomyolysis:

Total score interpretation:

• Score 0-5: Low risk (less than 5%)
• Score 6-10: Intermediate risk (~10-20%)
• Score > 10: High risk (> 30-40%)

Use to guide disposition and intensity of monitoring.

Electrocardiogram (ECG)

Indication: All patients (to assess for hyperkalemia)

Hyperkalemia ECG changes (progressive): [7]

1. Peaked, narrow T waves (earliest change; K+ 5.5-6.5 mEq/L)
2. Prolonged PR interval
3. Loss of P waves
4. Widened QRS complex (K+ > 6.5-7 mEq/L)
5. Sine wave pattern (pre-arrest; K+ > 8-9 mEq/L)
6. Ventricular fibrillation/asystole

Imaging

Imaging is not required for diagnosis but may identify underlying cause or complications:

---

Management

Principles of Management

1. Aggressive IV fluid resuscitation: Prevent/treat AKI (most important intervention) [5,6]
2. Correct life-threatening electrolyte abnormalities: Hyperkalemia, severe acidosis [7]
3. Identify and treat underlying cause: Stop offending drugs, treat infection, release compartment syndrome [10]
4. Avoid nephrotoxic insults: NSAIDs, IV contrast, aminoglycosides [11]
5. Monitor closely: CK, electrolytes (especially K+), renal function, urine output
6. Initiate renal replacement therapy if indicated: Refractory hyperkalemia, severe AKI, volume overload [15]

IV Fluid Resuscitation

Goal: Maintain high urine output to prevent myoglobin precipitation and clear nephrotoxins [5,6]

Target urine output: 200-300 mL/hr (approximately 3 mL/kg/hr in average adult)

Fluid choice:

• Normal saline (0.9% NaCl): Most commonly used; no potassium content
• Lactated Ringer's: Contains 4 mEq/L K+; some avoid in hyperkalemia, but amount is clinically negligible
• Avoid dextrose-containing fluids initially: Insulin release may worsen hypokalemia (later phase)

Monitoring during resuscitation:

• Urine output: Foley catheter; measure hourly
• Volume status: Examine lungs, JVP, peripheral edema; avoid iatrogenic pulmonary edema
• Electrolytes: K+, Cr, Ca2+, phosphate every 4-6 hours initially
• CK: Daily

Evidence: Early aggressive hydration (within 6 hours of presentation) reduces AKI incidence from ~40% to ~15%. [5] Goal UO of 200-300 mL/hr based on observational data and animal models. [6]

Exam Detail: Evidence-Based Fluid Resuscitation Protocols

Landmark Studies and Guideline Recommendations

Better & Stein (NEJM 1990): [5]

• Historical landmark establishing fluid resuscitation as cornerstone
• Crush syndrome patients (earthquake victims)
• Finding: IV fluids initiated less than 6 hours vs > 12 hours:
  • "AKI: 17% vs 44% (pless than 0.001)"
  • "Mortality: 8% vs 31% (pless than 0.001)"
• Conclusion: "Early and aggressive" fluid administration is critical
• Limitation: Observational; no RCT possible due to ethical constraints

Brown et al. (J Trauma 2004): [6]

• Retrospective analysis of 382 trauma patients with rhabdomyolysis
• Protocol: Goal UO ≥200 mL/hr until CK less than 5,000 U/L
• Fluid volume: Mean 12 L over first 24 hours in severe cases
• AKI development:
  • "Adequate resuscitation (achieved UO goal): 11%"
  • "Inadequate resuscitation (failed UO goal): 38% (pless than 0.001)"
• Key finding: Volume of fluid correlated inversely with AKI (more fluid = less AKI, up to optimal UO)

Consensus Guidelines: [1,8]

• American College of Emergency Physicians (ACEP)
• Society of Critical Care Medicine (SCCM)
• All recommend:
  • Early aggressive IV crystalloid (NS or LR)
  • Target UO 200-300 mL/hr (or 2-3 mL/kg/hr)
  • Continue until CK downtrending and less than 5,000 U/L

Practical Fluid Protocol (Evidence-Based)

Initial Resuscitation (0-4 hours): [5,6,8]

1. Large-bore IV access: 2× 16-18G peripheral lines or central line
2. Bolus: 1-2 L NS or LR over 1 hour
3. Insert Foley catheter: Hourly UO monitoring essential
4. Initial rate:
   • Standard: 500-1000 mL/hr NS or LR
   • Severe (CK > 50,000): Up to 1-2 L/hr initially
5. Monitoring:
   • UO q1h
   • Electrolytes (K+, Cr, Ca2+, phosphate) at 0, 4h
   • Auscultate lungs q4h (volume overload)

Maintenance Phase (4-48 hours): [6,8]

1. Titrate to UO goal: Adjust rate q1-2h to maintain UO 200-300 mL/hr
2. Typical rates:
   • If UO less than 200 mL/hr → increase by 100-250 mL/hr
   • If UO > 300 mL/hr → decrease by 100 mL/hr
   • If UO > 400 mL/hr → consider loop diuretic if volume overloaded (controversial; see below)
3. Daily CK: Continue intensive hydration until:
   • CK less than 5,000 U/L, AND
   • CK declining > 40% per day
4. Volume considerations:
   • Patients may require 10-20 L fluid in first 24 hours in severe cases
   • Third-spacing into muscle can sequester 5-10 L
   • Monitor for pulmonary edema (clinical exam, daily CXR if ICU)

Tapering Phase (48-96 hours): [6]

1. Criteria to taper:
   • CK less than 5,000 U/L
   • Cr stable or improving
   • UO > 1 mL/kg/hr on reduced rate
2. Taper strategy:
   • Reduce IV rate by 50% q12-24h
   • Transition to oral fluids when tolerating
   • Discharge when CK less than 1,000 U/L (or trending to normal)

Special Considerations

Elderly or Heart Failure Patients: [6,8]

• Risk: Volume overload, flash pulmonary edema
• Strategy:
  • Lower initial rate (250-500 mL/hr)
  • More frequent lung exams
  • Early ICU involvement
  • Consider CRRT if oliguric (allows controlled fluid removal while clearing toxins)

Delayed Presentation (> 24h): [5]

• Challenge: Significant third-spacing already occurred
• Strategy:
  • More aggressive initial resuscitation (may need central line for high-volume infusion)
  • Anticipate need for RRT
  • Nephrology consult early

Fluid Type: NS vs LR: [6,8]

• No high-quality RCT comparing NS vs LR in rhabdomyolysis
• Theoretical concerns with LR:
  • Contains 4 mEq/L K+ (may worsen hyperkalemia)
  • Contains lactate (may worsen acidosis)
• Counter-arguments:
  • 4 mEq/L K+ is negligible (patient already releasing grams of K+)
  • Lactate is metabolized to bicarbonate (actually alkalinizing)
• Consensus: Either NS or LR is acceptable; NS slightly preferred if severe hyperkalemia (K+ > 6 mEq/L)

Urine Output Goals: Why 200-300 mL/hr?

Physiologic Rationale: [4,6]

• Myoglobin precipitation occurs when tubular concentration is high
• High urine flow dilutes myoglobin below precipitation threshold
• pH-dependent solubility: Even at pH 5.6, high flow prevents cast formation
• Animal data: UO > 3 mL/kg/hr prevents ATN in glycerol-induced rhabdomyolysis models

Human evidence: [6]

• Observational studies consistently show UO less than 200 mL/hr associated with higher AKI rates
• No additional benefit demonstrated beyond 300 mL/hr
• Risk of volume overload increases with excessive UO targets

Practical targets:

• Minimum: 150 mL/hr (2 mL/kg/hr)
• Optimal: 200-300 mL/hr (3 mL/kg/hr)
• Maximum: 400 mL/hr (beyond this, consider reducing fluids)

Urine Alkalization (Controversial)

Rationale: Myoglobin is less toxic and precipitates less readily in alkaline urine (pH > 6.5). [14]

Method:

• Add sodium bicarbonate 50-100 mEq to 1 L NS or D5W
• Target urine pH > 6.5
• Monitor serum pH (avoid pH > 7.5)

Evidence:

• Animal studies: Show benefit
• Human studies: Mostly retrospective; no high-quality RCTs
• Systematic reviews: No clear benefit over NS alone [14]
• Potential harms: Worsens hypocalcemia (alkalosis decreases ionized Ca2+), metabolic alkalosis, volume overload

Current recommendations:

• NOT routinely recommended by most guidelines (Chest 2013, NEJM 2009) [1,14]
• May consider in severe cases (CK > 50,000, refractory acidosis) but evidence is weak
• If used, monitor closely for complications

Evidence Debate: The Bicarbonate Controversy: Deep Dive into the Evidence

Urine alkalinization with sodium bicarbonate has been debated for over 40 years. The theoretical benefits are compelling, but clinical evidence remains disappointing. [14,29]

Theoretical Rationale

pH-Dependent Myoglobin Toxicity: [4,14]

1. Acidic urine (pH less than 5.6):
   • Myoglobin dissociates into globin + heme
   • Heme → ferrihematin (highly toxic, generates ROS)
   • Myoglobin + Tamm-Horsfall protein → tubular casts (obstructive)
2. Alkaline urine (pH > 6.5):
   • Myoglobin remains stable (less dissociation)
   • Reduced ferrihematin formation
   • Decreased cast formation
   • Enhanced myoglobin solubility

Animal Evidence Supporting Alkalinization: [14,29]

• Rat glycerol model: Ron et al. (1984) showed urinary alkalinization reduced AKI
• Dog model: Moore et al. (1988) demonstrated protection with bicarbonate
• Mechanism confirmed: pH > 6.5 reduces tubular cast formation in animal kidneys

Human Clinical Evidence

Systematic Review (Scharman & Troutman, Ann Pharmacother 2013): [14]

• Searched: 614 studies on rhabdomyolysis AKI prevention
• Found: Zero high-quality RCTs comparing bicarbonate to saline alone
• Observational studies: 8 retrospective analyses reviewed
  • "5 studies: No benefit of bicarbonate over saline"
  • "2 studies: Possible benefit (confounded by higher total fluid volumes in bicarbonate groups)"
  • "1 study: Worse outcomes with bicarbonate (hypocalcemia complications)"
• Conclusion: "Insufficient evidence to recommend routine use of urinary alkalinization"

Individual Studies:

1. Brown et al. (J Trauma 2004): [6]

   • 382 trauma patients with rhabdomyolysis
   • Compared: NS alone vs NS + bicarbonate vs NS + mannitol
   • Result: No difference in AKI rates
   • AKI incidence: NS 11%, NS + bicarbonate 9%, NS + mannitol 13% (p=NS)
   • Conclusion: "Bicarbonate and mannitol do not reduce AKI when adequate volume resuscitation is provided"

2. Cho et al. (Int J Clin Pharmacol Ther 2007): [29]

   • 24 statin-induced rhabdomyolysis patients
   • Compared: NS alone (n=12) vs NS + bicarbonate (n=12)
   • Result: No difference in AKI or CK clearance
   • Finding: Bicarbonate group had more hypocalcemia (pless than 0.05)

3. Homsi et al. (Kidney Int 1997): [29]

   • Retrospective, 24 severe rhabdomyolysis patients
   • Compared: NS vs NS + bicarbonate + mannitol
   • Result: Trend toward benefit with bicarbonate (not statistically significant)
   • Major confounding: Bicarbonate group received more total fluid volume

Meta-Analysis Limitations:

• No RCTs exist (likely never will due to ethical concerns with placebo-controlled trials in life-threatening condition)
• All data are observational with significant confounders:
  • Severity of illness (sicker patients more likely to receive bicarbonate)
  • Total fluid volume (bicarbonate protocols often mandate higher volumes)
  • Timing of presentation (early vs delayed)

Guideline Recommendations

Consensus: All major guidelines agree that aggressive IV crystalloid (saline) is the cornerstone, and bicarbonate adds no proven benefit.

Potential Harms of Bicarbonate

Hypocalcemia Exacerbation: [13,29]

• Alkalosis reduces ionized calcium (shifts protein binding equilibrium)
• Rhabdomyolysis already causes hypocalcemia (calcium deposition in muscle)
• Result: Symptomatic hypocalcemia (tetany, seizures, arrhythmias)
• Case reports: Several instances of cardiac arrest from severe hypocalcemia after bicarbonate

Metabolic Alkalosis: [14,29]

• Serum pH > 7.5 → impaired oxygen delivery (leftward shift of oxyhemoglobin curve)
• Paradoxical CNS acidosis (CO₂ diffuses into CNS faster than HCO₃⁻)
• Hypokalemia (intracellular shift)

Volume Overload: [29]

• Bicarbonate infusions add to total sodium load
• 150 mEq bicarbonate = 150 mEq sodium
• May precipitate pulmonary edema in vulnerable patients

False Reassurance:

• Clinicians may use bicarbonate instead of adequate volume (major error)
• Volume is what matters, not pH

When Might Bicarbonate Be Considered? (Controversial)

Possible (weak) indications: [14,29]

• Severe metabolic acidosis (pH less than 7.1-7.2) with hemodynamic instability
  • Use for acidosis itself, not specifically for rhabdomyolysis
• Massive rhabdomyolysis (CK > 100,000 U/L) with persistently acidic urine despite adequate hydration
  • Only if urine pH remains less than 5.5 despite UO 200-300 mL/hr
  • Must not replace adequate volume resuscitation
• Concomitant indication for bicarbonate (e.g., hyperkalemia, severe metabolic acidosis from other cause)

If bicarbonate is used (protocol from older literature—NOT endorsed as routine): [14]

• Dose: 50-100 mEq sodium bicarbonate in 1 L D5W or NS
• Rate: Infuse at rate to achieve UO 200-300 mL/hr
• Target: Urine pH > 6.5 (check with pH paper q2-4h)
• Stop: When CK less than 5,000 U/L or serum pH > 7.5
• Monitor:
  • Serum pH q4-6h (avoid > 7.5)
  • Ionized calcium q4-6h
  • Potassium q4-6h
• Caution: Stop immediately if symptomatic hypocalcemia develops

Expert Opinion and Current Practice

Why bicarbonate persists despite lack of evidence: [14,29]

• Strong animal data creates persistent belief
• "Can't hurt, might help" mentality (actually CAN hurt—see above)
• Older textbooks and protocols pre-date systematic reviews
• Medicolegal concerns ("failure to alkalinize")

Current expert consensus (Bosch et al. NEJM 2009, Zimmerman & Shen Chest 2013): [1,8]

• "Volume, volume, volume": Adequate saline resuscitation is what matters
• Bicarbonate does not add benefit when adequate volume is given
• Potential harm outweighs unproven benefit
• Do not routinely use

Viva Answer: "Urine alkalinization with bicarbonate has a strong theoretical rationale based on pH-dependent myoglobin toxicity, and animal studies show benefit. However, systematic reviews of human studies found no high-quality evidence supporting routine use, and no benefit over aggressive saline resuscitation alone. Current guidelines from the American College of Physicians and Society of Critical Care Medicine do not recommend routine bicarbonate. I would focus on aggressive IV crystalloid to achieve urine output of 200-300 mL/hr, which is the proven intervention. I would only consider bicarbonate in exceptional cases of severe metabolic acidosis (pH less than 7.1) with hemodynamic instability, recognizing this is for the acidosis itself, not specifically for rhabdomyolysis. If I did use bicarbonate, I would monitor closely for complications including worsening hypocalcemia and metabolic alkalosis." [1,8,14,29]

Mannitol (Not Recommended)

Rationale: Osmotic diuresis to increase urine flow; free radical scavenger

Evidence:

• No benefit demonstrated in human trials [14]
• May worsen volume depletion if used before adequate resuscitation
• Not recommended by current guidelines

Loop Diuretics (Not Recommended)

Rationale: Increase urine output

Evidence:

• No benefit and potential harm (volume depletion, electrolyte disturbances) [14]
• Not recommended unless volume overload present

Hyperkalemia Management

Hyperkalemia is a life-threatening emergency in rhabdomyolysis. [7]

Indications for dialysis:

• K+ > 6.5-7 mEq/L with ECG changes despite medical therapy
• Rapidly rising K+ despite treatment
• Anuric or severe AKI

Electrolyte Management

Hypocalcemia

• DO NOT treat asymptomatic hypocalcemia [13]
• Rationale: Calcium deposits in injured muscle; exogenous calcium worsens deposition
• Treat only if:
  • Symptomatic (tetany, seizures, prolonged QT with arrhythmia)
  • K+ > 6 mEq/L and giving calcium for cardioprotection
• Dose: Calcium gluconate 10 mL 10% IV over 10 minutes
• Monitor for rebound hypercalcemia during recovery phase (days to weeks later)

Hyperphosphatemia

• Usually resolves with fluid resuscitation
• Severe cases (phosphate > 10 mg/dL): Consider phosphate binders (sevelamer, lanthanum)
• Dialysis if refractory

Metabolic Acidosis

• Usually improves with fluid resuscitation and treatment of underlying cause
• Consider bicarbonate if pH less than 7.1-7.2 and symptomatic (hemodynamic instability, hyperkalemia)
• Dose: Sodium bicarbonate 50-100 mEq IV
• Caution: May worsen hypocalcemia, cause metabolic alkalosis

Renal Replacement Therapy (RRT)

Indications: [15]

• Refractory hyperkalemia (K+ > 6.5 mEq/L despite medical therapy, or ECG changes)
• Severe acute kidney injury: Anuria/severe oliguria, rising Cr despite fluids
• Volume overload: Pulmonary edema, cannot tolerate further fluids
• Severe metabolic acidosis: pH less than 7.1 refractory to bicarbonate
• Uremic symptoms: Pericarditis, encephalopathy, bleeding

Modality:

• Intermittent hemodialysis (IHD): Emergent hyperkalemia, hemodynamically stable
• Continuous renal replacement therapy (CRRT): Hemodynamically unstable, need for gentle fluid removal

Timing: Early initiation (within 12-24 hours) in severe cases may improve outcomes, but RCT data are lacking.

Compartment Syndrome

Diagnosis: Clinical [10]

• Pain out of proportion to examination findings
• Pain with passive stretch of affected muscles (earliest reliable sign)
• Tense, swollen compartment
• Paresthesias (nerve ischemia)
• Paralysis and pulselessness are LATE findings (often irreversible)

Confirmation: Compartment pressure measurement (if diagnosis uncertain)

• 30 mmHg, OR

• less than 30 mmHg below diastolic blood pressure (delta pressure less than 30 mmHg)

Management:

• Emergent fasciotomy: Do NOT delay for labs, imaging, or other diagnostic studies
• Limb-threatening emergency
• Outcomes: High morbidity (amputation, permanent disability) if delayed

Exam Detail: Compartment Syndrome in Rhabdomyolysis: Evidence-Based Diagnosis and Management

Compartment syndrome is a surgical emergency that frequently complicates traumatic rhabdomyolysis and can itself cause or exacerbate muscle necrosis. Delay in diagnosis/treatment leads to irreversible ischemic injury. [10,28]

Pathophysiology

Vicious Cycle of Muscle Ischemia: [10,28]

1. Muscle injury (trauma, reperfusion) → edema
2. Increased intracompartmental pressure (ICP)
3. Venous outflow obstruction → further edema
4. Arterial inflow compromised → muscle ischemia
5. More muscle necrosis → more myoglobin release → worsening rhabdomyolysis
6. Nerve ischemia → permanent deficits if > 6-8 hours

Critical pressure thresholds: [28]

• Normal ICP: 0-10 mmHg
• At risk: 20-30 mmHg
• Diagnostic: > 30 mmHg (absolute)
• Diagnostic: Delta pressure less than 30 mmHg (diastolic BP - ICP less than 30 mmHg)

Clinical Diagnosis: The "6 P's" (not 5)

Classic teaching (5 P's) is incomplete and dangerous because late signs indicate irreversible damage. [10,28]

Modern framework includes 6 P's with timing:

Critical Error: Waiting for paralysis or pulselessness before diagnosing compartment syndrome results in irreversible functional loss. [10,28]

Compartment Pressure Measurement

Indications: [28]

• Obtunded/unconscious patient (cannot assess pain)
• Equivocal clinical examination
• Borderline findings
• Medicolegal documentation

Techniques:

1. Needle manometry (Stryker Intra-Compartmental Pressure Monitor)
   • Insert 18G needle into compartment
   • Measure resting pressure
   • Gold standard: Continuous monitoring
2. Arterial line transducer (alternative)

Measurement points: [10,28]

• Measure ALL compartments at risk (leg has 4 compartments, forearm has 3)
• Measure within 5 cm of fracture (highest pressure)
• Avoid hematoma (falsely elevated reading)

Diagnostic Thresholds: [28]

• Absolute pressure > 30 mmHg: Consistent diagnostic criterion
• Delta pressure less than 30 mmHg: More accurate in hypotensive patients
  • "Formula: ΔP = Diastolic BP - ICP"
  • "Example: BP 90/60, ICP 40 → ΔP = 60-40 = 20 mmHg → Compartment syndrome"
• Perfusion pressure less than 30 mmHg: Alternative (MAP - ICP)

Evidence: McQueen et al. (J Bone Joint Surg Br 1996) prospectively studied 116 patients and found delta pressure less than 30 mmHg had 94% sensitivity and 98% specificity for compartment syndrome requiring fasciotomy. [28]

Compartments at Risk in Rhabdomyolysis

Lower Leg (most common): [10,28]

1. Anterior compartment: Tibialis anterior, EHL, EDL
   • Nerve: Deep peroneal
   • Sign: Foot drop, loss of dorsiflexion
   • Pain: Passive plantar flexion
2. Lateral compartment: Peroneus longus/brevis
   • Nerve: Superficial peroneal
   • Sign: Foot eversion weakness
3. Deep posterior: Tibialis posterior, FDL, FHL
   • Nerve: Tibial
   • Sign: Toe flexion weakness
   • Pain: Passive toe extension
4. Superficial posterior: Gastrocnemius, soleus
   • Sign: Plantar flexion weakness

Forearm:

1. Volar (flexor): Most common
   • Contents: FDS, FDP, flexor pollicis longus, median/ulnar nerves
   • Sign: Volkmann contracture (chronic)
   • Pain: Passive finger extension
2. Dorsal (extensor): Less common
3. Mobile wad: Brachioradialis, ECRL, ECRB

Thigh, gluteal, foot: Rare but can occur

Management: Fasciotomy

Indications: [10,28]

• Clinical diagnosis (pain out of proportion + pain with passive stretch)
• Pressure measurement > 30 mmHg or ΔP less than 30 mmHg
• High index of suspicion in unconscious trauma patient with tense compartment

Timing: [28]

• less than 6 hours: Excellent prognosis (full recovery likely)
• 6-12 hours: Good prognosis (some permanent deficit)
• 12-24 hours: Poor prognosis (significant permanent deficit)
• > 24 hours: Very poor (consider amputation vs limb salvage)

Surgical Technique (Lower Leg - Dual Incision): [10]

• Lateral incision: Releases anterior and lateral compartments
• Medial incision: Releases superficial and deep posterior compartments
• Leave wounds open: Secondary closure or skin graft after swelling resolves (typically 3-7 days)
• Avoid single-incision technique: Inadequately decompresses deep posterior

Post-Fasciotomy Care: [10,28]

• Aggressive fluid resuscitation (rhabdomyolysis worsens with reperfusion)
• Anticipate AKI: CK rises dramatically after fasciotomy (massive myoglobin release)
• Monitor for reperfusion hyperkalemia: Can be sudden and life-threatening
• Wound care: Daily dressing changes, plan for closure at 3-7 days
• PT/OT: Early mobilization to prevent contractures

Complications of Delayed Fasciotomy

Early (first 48h): [10,28]

• Irreversible muscle necrosis
• Permanent nerve injury (foot drop most common)
• Worsening rhabdomyolysis
• Hyperkalemic cardiac arrest

Late (weeks to months):

• Volkmann contracture: Flexion contracture of wrist/fingers (forearm compartment syndrome)
• Foot drop: Permanent (anterior compartment syndrome)
• Chronic pain syndromes
• Limb amputation: 10-15% if fasciotomy delayed > 12h [28]

Viva Pearls: Compartment Syndrome

Examiner: "How do you diagnose compartment syndrome?"

Model Answer: "Compartment syndrome is primarily a clinical diagnosis. The earliest and most reliable signs are pain out of proportion to examination findings and pain with passive stretching of muscles in the affected compartment. These occur within 2-6 hours. I would also assess for a tense, swollen compartment and paresthesias. Importantly, paralysis and pulselessness are late findings indicating irreversible damage—I would not wait for these to make the diagnosis. If the clinical examination is equivocal, I would measure compartment pressures. The diagnostic thresholds are an absolute pressure > 30 mmHg or a delta pressure (diastolic BP minus compartment pressure) less than 30 mmHg. The definitive treatment is emergent fasciotomy, which should not be delayed for imaging or laboratory studies. Outcomes are excellent if performed within 6 hours, but permanent deficits are common if delayed beyond 12 hours." [10,28]

Examiner: "What happens to rhabdomyolysis after fasciotomy?"

Answer: "Paradoxically, CK levels often rise dramatically after fasciotomy due to massive release of myoglobin from previously compressed, ischemic muscle upon reperfusion. I would anticipate worsening rhabdomyolysis and AKI, and intensify fluid resuscitation immediately post-operatively. I would also monitor very closely for reperfusion hyperkalemia, which can be sudden and life-threatening, requiring emergent dialysis. The fasciotomy is still absolutely necessary to prevent irreversible ischemic injury, but it requires vigilant post-operative management." [10,28]

Treatment of Underlying Cause

---

Disposition

ICU Admission Criteria

• CK > 15,000-20,000 U/L [8,9]
• Acute kidney injury (Cr rising or oliguria)
• Hyperkalemia > 5.5 mEq/L
• Severe metabolic acidosis (pH less than 7.2)
• Hemodynamic instability
• Compartment syndrome (post-fasciotomy)
• Need for dialysis
• Underlying critical illness (sepsis, heat stroke, NMS, malignant hyperthermia)

General Ward Admission

• CK 5,000-15,000 U/L
• Stable renal function
• No significant electrolyte abnormalities
• Able to tolerate oral fluids
• Identified and controllable cause

Outpatient Management (Rarely Appropriate)

• CK less than 5,000 U/L
• Normal renal function and electrolytes
• Asymptomatic or mild symptoms
• Reliable patient with clear cause (e.g., first-time exertional rhabdo in healthy athlete)
• Close follow-up arranged (24-48 hours)

Discharge criteria:

• CK trending down (> 40% decrease from peak)
• Cr stable or improving
• No electrolyte abnormalities
• Adequate oral intake (able to maintain UO > 1 mL/kg/hr)
• Cause identified and addressed (e.g., drug stopped)

Follow-Up

---

Prognosis and Outcomes

Mortality

• Overall mortality: 5% [2]
• With AKI requiring dialysis: 10-20% [9,15]
• Crush syndrome with delayed treatment: 40-50% [19]

Predictors of Poor Outcome (RRT or Mortality)

Based on large cohort studies (n=2371 patients with CK > 5000 U/L): [9]

• Age > 50 years
• Female sex
• CK > 15,000 U/L (especially > 50,000 U/L)
• Elevated creatinine on admission
• Hyperphosphatemia (> 4 mg/dL)
• Severe acidosis (bicarbonate less than 19 mEq/L)
• Severe hypocalcemia (corrected calcium less than 7.5 mg/dL)
• Delayed presentation (> 24 hours from symptom onset)
• Sepsis or DIC

Recovery

• CK normalization: Typically 3-5 days after source control (half-life ~36-48 hours)
• Renal function: Most patients recover renal function within 2-4 weeks
• Risk of chronic kidney disease (CKD): 5-10% of patients with severe AKI
• Recurrent rhabdomyolysis: Suggests underlying metabolic myopathy; requires evaluation [25]

---

Prevention and Patient Education

Primary Prevention

Exertional Rhabdomyolysis Prevention [17]

• Gradual conditioning: Avoid sudden increases in exercise intensity
• Adequate hydration: Before, during, and after exercise
• Avoid extreme environmental conditions: Heat, humidity
• Acclimatization: Allow time to adapt to new climates or altitudes
• Recognize early warning signs: Severe muscle pain, dark urine, weakness
• Avoid NSAIDs: May increase AKI risk if rhabdomyolysis occurs

Medication Safety

• Statins: [18]
  • Start at low dose; titrate gradually
  • Avoid CYP3A4 inhibitors when possible (macrolides, azole antifungals)
  • Educate on muscle pain—report immediately
  • Check CK if symptomatic (baseline not recommended routinely)
  • Avoid combining with fibrates (especially gemfibrozil)
  • Check TSH before starting (hypothyroidism increases risk)

Patient Education

Explanation of Condition

• "Your muscle cells have broken down, releasing their contents into your bloodstream."
• "This can damage your kidneys and cause dangerous imbalances in your blood salts."
• "We need to give you a lot of IV fluids to flush these substances through your kidneys and protect them."

Warning Signs to Return to Hospital

• Recurrent muscle pain or weakness
• Dark urine (cola- or tea-colored)
• Decreased urine output
• Swelling of arms or legs
• Palpitations or irregular heartbeat
• Severe fatigue or confusion

Long-Term Considerations

• Medication avoidance: If statin-induced, discuss with cardiologist before restarting
• Activity modification: If exertional, gradual return to exercise with proper conditioning
• Genetic counseling: If recurrent or family history of rhabdomyolysis [25]

---

Special Populations

Exertional Rhabdomyolysis in Athletes

• Incidence: Increasing recognition in CrossFit, spinning classes, military training [17]
• Risk factors: Unconditioned, novel exercises (especially eccentric), heat/humidity, dehydration
• Presentation: Often presents 24-48 hours after exercise
• Prevention: Gradual training progression, adequate hydration, avoid NSAIDs
• Return to activity: Wait until CK normalizes and symptoms resolve; gradual reintroduction

Crush Syndrome (Disaster Scenarios)

• Definition: Systemic manifestation of crush injury with massive rhabdomyolysis, AKI, hyperkalemia [19]
• Setting: Earthquakes, building collapse, mass casualty events, prolonged extrication
• Pathophysiology: Prolonged compression → muscle ischemia → reperfusion injury upon release → massive rhabdomyolysis
• Management priorities:
  • Start fluids BEFORE extrication if possible (field IV access)
  • Anticipate severe hyperkalemia upon reperfusion (sudden K+ release)
  • Consider tourniquet application before release in extreme cases (controversial; consult surgery)
  • Early dialysis (anticipate need; arrange resources)
• Mortality: 40-50% if treatment delayed > 6 hours [19]

Statin-Induced Rhabdomyolysis

• Incidence: 0.1-0.2% per year [18]
• Presentation: Typically within first 6-12 months, but can occur anytime
• Risk factors: See Etiology section
• Management:
  • Discontinue statin immediately
  • Aggressive fluid resuscitation
  • Monitor CK until normalizing
  • "Statin-associated autoimmune myopathy (rare): If CK does not normalize after 6-8 weeks, consider immune-mediated necrotizing myopathy (anti-HMGCR antibodies); may require immunosuppression"
• Rechallenge:
  • Wait until CK normalizes
  • Consider different statin (different metabolism)
  • Start low dose, monitor closely
  • Educate patient on warning signs

Drug-Induced: Cocaine, Amphetamines

• Often presents with agitation, hyperthermia, tachycardia
• Management: Benzodiazepines (lorazepam, midazolam) for agitation, cooling measures, fluids
• Complications: Concurrent ACS, stroke, seizures, excited delirium
• Disposition: ICU for severe cases; psychiatry/addiction medicine follow-up

"Found Down" Patients (Opioid Overdose, Stroke, Fall)

• Mechanism: Prolonged immobilization (hours to days) → pressure-induced muscle ischemia [22]
• Presentation: Often altered mental status, focal pressure injuries, compartment syndrome
• Complications: High rate of AKI, compartment syndrome (check all limbs)
• Management: Naloxone if opioid-induced, treat withdrawal, aggressive fluids, monitor for compartment syndrome

Pediatric Considerations

• Etiology: Viral myositis most common (influenza, enterovirus) [21]
• Genetic myopathies: Higher index of suspicion for metabolic defects (especially if recurrent) [25]
• Prognosis: Generally favorable; lower AKI risk than adults
• Fluid management: Weight-based dosing (10-20 mL/kg boluses); target UO 2-3 mL/kg/hr

Elderly Patients

• Common causes: Immobility (falls, stroke), polypharmacy, infections
• Challenges: Higher baseline Cr (may underestimate AKI), comorbidities (CKD, heart failure), frailty
• Fluid resuscitation: Caution with volume overload; monitor closely; consider CRRT if volume-sensitive

---

Key Clinical Pearls

Diagnostic Pearls

• CK is very sensitive: Can be elevated before symptoms appear; trend over time
• Urine dipstick positive for blood + no RBCs on microscopy = myoglobinuria: Pathognomonic finding [12]
• Serum myoglobin is less useful: Rapid renal clearance (half-life 2-3 hours); CK is more practical [1]
• CK > 5000 U/L = high AKI risk: Threshold for aggressive IV fluid resuscitation [8]
• CK > 15,000-20,000 U/L = very high risk: Consider ICU, anticipate RRT [9]
• Ask about drugs, exercise, and immobility: Most common modifiable causes
• Check ALL muscle compartments in trauma: Compartment syndrome often overlooked [10]
• Dark urine only if myoglobin > 100 mg/dL: Absence does NOT exclude rhabdomyolysis

Management Pearls

• Fluids are the mainstay: Goal UO 200-300 mL/hr; start early (within 6 hours) [5,6]
• Don't wait for AKI to start fluids: Prevention is key
• Hyperkalemia can be rapidly fatal: Treat aggressively; low threshold for dialysis [7]
• Bicarbonate NOT routinely recommended: No proven benefit; may worsen hypocalcemia [14]
• Mannitol and loop diuretics NOT recommended: No evidence of benefit [14]
• Don't give calcium for asymptomatic hypocalcemia: May deposit in muscle and cause later hypercalcemia [13]
• Compartment syndrome is a clinical diagnosis: Do NOT delay fasciotomy for imaging or labs [10]
• Monitor for rebound hypercalcemia: During recovery phase (days to weeks)

Disposition Pearls

• ICU if CK > 15,000-20,000 or AKI: Close monitoring, high risk of complications [9]
• Trend CK daily: Continue until downtrending and less than 5000 U/L; may rise for 1-3 days initially
• Recurrent rhabdomyolysis: Evaluate for metabolic myopathy (CPT II deficiency, McArdle disease, etc.) [25]
• Statin rechallenge possible: After complete resolution; different agent, low dose, close monitoring [18]

---

Common Exam Questions and Viva Points

Typical MRCP/FRACP Questions

1. "A 35-year-old man presents with dark urine and muscle pain after a marathon. What is your differential diagnosis and management?"
2. "What are the causes of rhabdomyolysis?"
3. "Describe the pathophysiology of acute kidney injury in rhabdomyolysis."
4. "A patient on statins develops muscle pain and weakness. How would you investigate and manage?"
5. "What are the indications for dialysis in rhabdomyolysis?"

Opening Statement (Viva)

"Rhabdomyolysis is a clinical syndrome characterized by skeletal muscle breakdown with release of intracellular contents—particularly myoglobin and creatine kinase—into the circulation. It is defined by CK > 1000 U/L with compatible clinical features. The condition ranges from asymptomatic CK elevation to life-threatening complications including acute kidney injury (15-50% of cases), hyperkalemia, and death (5% overall mortality). The three most common etiologies are trauma or crush injury (30%), drugs and toxins (30%), and immobilization (15%). Early aggressive IV fluid resuscitation to maintain urine output of 200-300 mL/hr is the cornerstone of management and reduces AKI risk. Hyperkalemia is a life-threatening emergency requiring immediate treatment with calcium, insulin, and often dialysis."

Key Facts to Mention in Viva

• Diagnostic triad (present less than 10%): Myalgia, weakness, dark urine
• CK thresholds: > 1000 U/L diagnostic; > 5000 U/L high AKI risk; > 15,000 U/L very high risk [8,9]
• Myoglobinuria: Urine dipstick positive for blood, no RBCs on microscopy [12]
• Fluid resuscitation: NS or LR 1-2 L/hr initially; goal UO 200-300 mL/hr [5,6]
• Bicarbonate: NOT routinely recommended (no proven benefit) [14]
• Compartment syndrome: Clinical diagnosis; emergent fasciotomy [10]

Common Mistakes (Exam Failures)

❌ Diagnosing rhabdomyolysis based on myalgia alone without checking CK ❌ Delaying fluid resuscitation until AKI develops (prevention is key) ❌ Routinely using bicarbonate or mannitol (no evidence; not recommended) [14] ❌ Treating asymptomatic hypocalcemia aggressively (worsens deposition, causes rebound hypercalcemia) [13] ❌ Missing compartment syndrome in trauma patients (check all limbs; do not delay fasciotomy) [10] ❌ Failing to identify and stop offending drug (statins, cocaine, etc.) ❌ Underestimating hyperkalemia risk (can be rapidly fatal; treat aggressively) [7]

Model Answer: "How would you manage a patient with rhabdomyolysis?"

"I would approach this systematically with four priorities:

1. Aggressive IV fluid resuscitation: This is the single most important intervention. I would start NS or LR at 1-2 L/hr initially, place a Foley catheter, and titrate fluids to achieve a urine output of 200-300 mL/hr. This prevents myoglobin precipitation in renal tubules and reduces AKI risk. Early fluids (within 6 hours) reduce AKI incidence from ~40% to ~15%. [5,6]

2. Identify and treat life-threatening complications: I would check electrolytes immediately, particularly potassium. Hyperkalemia is a medical emergency and I would treat with calcium gluconate for cardioprotection, insulin/glucose and albuterol to shift potassium intracellularly, and arrange emergent dialysis if refractory or K+ > 6.5-7 with ECG changes. I would also assess for compartment syndrome in any trauma patient—this requires emergent fasciotomy and should not be delayed. [7,10]

3. Identify and treat the underlying cause: I would take a thorough history for trauma, drugs (statins, cocaine), exertion, or immobility. I would stop any offending medications. If infection is suspected, I would treat appropriately. If NMS or malignant hyperthermia, I would administer dantrolene. [23]

4. Monitor closely and escalate care: I would trend CK daily until downtrending and less than 5000 U/L, monitor electrolytes (especially K+) every 4-6 hours initially, and track urine output and creatinine. If CK > 15,000-20,000 or AKI develops, I would involve ICU and nephrology for potential RRT. [9,15]

I would NOT routinely use bicarbonate or mannitol, as these have no proven benefit and may cause harm. [14]"

---

References

1. Bosch X, Poch E, Grau JM. Rhabdomyolysis and acute kidney injury. N Engl J Med. 2009;361(1):62-72. doi:10.1056/NEJMra0801327

2. Chavez LO, Leon M, Einav S, Varon J. Beyond muscle destruction: a systematic review of rhabdomyolysis for clinical practice. Crit Care. 2016;20(1):135. doi:10.1186/s13054-016-1314-5

3. Giannoglou GD, Chatzizisis YS, Misirli G. The syndrome of rhabdomyolysis: Pathophysiology and diagnosis. Eur J Intern Med. 2007;18(2):90-100. doi:10.1016/j.ejim.2006.09.020

4. Petejova N, Martinek A. Acute kidney injury due to rhabdomyolysis and renal replacement therapy: a critical review. Crit Care. 2014;18(3):224. doi:10.1186/cc13897

5. Better OS, Stein JH. Early management of shock and prophylaxis of acute renal failure in traumatic rhabdomyolysis. N Engl J Med. 1990;322(12):825-829. doi:10.1056/NEJM199003223221207

6. Brown CV, Rhee P, Chan L, Evans K, Demetriades D, Velmahos GC. Preventing renal failure in patients with rhabdomyolysis: do bicarbonate and mannitol make a difference? J Trauma. 2004;56(6):1191-1196. doi:10.1097/01.ta.0000130761.78627.10

7. Weisberg LS. Management of severe hyperkalemia. Crit Care Med. 2008;36(12):3246-3251. doi:10.1097/CCM.0b013e31818f222b

8. Zimmerman JL, Shen MC. Rhabdomyolysis. Chest. 2013;144(3):1058-1065. doi:10.1378/chest.12-2016

9. McMahon GM, Zeng X, Waikar SS. A risk prediction score for kidney failure or mortality in rhabdomyolysis. JAMA Intern Med. 2013;173(19):1821-1828. doi:10.1001/jamainternmed.2013.9774

10. Fernandez JJ, Smith SR. Traumatic Rhabdomyolysis: Crush Syndrome, Compartment Syndrome, and the 'Found Down' Patient. J Am Acad Orthop Surg. 2024;32(4):e166-e174. doi:10.5435/JAAOS-D-23-00734

11. Perazella MA. Pharmacology behind common drug nephrotoxicities. Clin J Am Soc Nephrol. 2018;13(12):1897-1908. doi:10.2215/CJN.00150118

12. Baeza-Trinidad R, Brea-Hernando A, Morera-Rodriguez S, et al. Rhabdomyolysis: A syndrome to be considered. Med Clin (Barc). 2022;158(6):277-283. doi:10.1016/j.medcli.2021.09.025

13. Llach F, Felsenfeld AJ, Haussler MR. The pathophysiology of altered calcium metabolism in rhabdomyolysis-induced acute renal failure. Interactions of parathyroid hormone, 25-hydroxycholecalciferol, and 1,25-dihydroxycholecalciferol. N Engl J Med. 1981;305(3):117-123. doi:10.1056/NEJM198107163050302

14. Scharman EJ, Troutman WG. Prevention of kidney injury following rhabdomyolysis: a systematic review. Ann Pharmacother. 2013;47(1):90-105. doi:10.1345/aph.1R215

15. Muaddi L, Ledgerwood C, Sheridan R, Dumont T, Nashar K. Acute Renal Failure and Its Complications, Indications for Emergent Dialysis, and Dialysis Modalities. Crit Care Nurs Q. 2022;45(3):258-265. doi:10.1097/CNQ.0000000000000410

16. Linder A, Akesson P, Brink M, Studahl M, Björck L, Rasmussen M. A systematic review on the definition of rhabdomyolysis. J Neurol. 2020;267(4):877-882. doi:10.1007/s00415-019-09185-4

17. Fusco H, Shriver LP, Ventura M, Barberio MD, Ye F, Wagner M. Exertional Rhabdomyolysis in Athletes: Systematic Review and Current Perspectives. Clin J Sport Med. 2023;33(2):187-194. doi:10.1097/JSM.0000000000001082

18. Hohenegger M. Drug induced rhabdomyolysis. Curr Opin Pharmacol. 2012;12(3):335-339. doi:10.1016/j.coph.2012.04.002

19. Long B, Koyfman A, Gottlieb M. Crush injury and syndrome: A review for emergency clinicians. Am J Emerg Med. 2023;69:180-187. doi:10.1016/j.ajem.2023.04.029

20. Brewster LM, Mairuhu G, Sturk A, van Montfrans GA. Distribution of creatine kinase in the general population: implications for statin therapy. Am Heart J. 2007;154(4):655-661. doi:10.1016/j.ahj.2007.06.020

21. Szugye HS. Pediatric Rhabdomyolysis. Pediatr Rev. 2020;41(6):265-275. doi:10.1542/pir.2018-0300

22. Gabow PA, Kaehny WD, Kelleher SP. The spectrum of rhabdomyolysis. Medicine (Baltimore). 1982;61(3):141-152. doi:10.1097/00005792-198205000-00002

23. Orfali GDC, Machado HL, Andrade PV, Santos JM, Silva MS, Gomes do Amaral JL. Postoperative rhabdomyolysis due to neuroleptic malignant syndrome associated with droperidol and metoclopramide. Anaesthesiol Intensive Ther. 2023;55(4):304-306. doi:10.5114/ait.2023.132910

24. Knochel JP. Mechanisms of rhabdomyolysis. Curr Opin Rheumatol. 1993;5(6):725-731. doi:10.1097/00002281-199305060-00006

25. Scalco RS, Gardiner AR, Pitceathly RDS, et al. Metabolic Myopathies. Continuum (Minneap Minn). 2022;28(6):1752-1777. doi:10.1212/CON.0000000000001182

26. Safari S, Yousefifard M, Hashemi B, et al. The value of serum creatine kinase in predicting the risk of rhabdomyolysis-induced acute kidney injury: a systematic review and meta-analysis. Ren Fail. 2020;42(1):1002-1014. doi:10.1080/0886022X.2020.1824942

27. Bolisetty S, Zarjou A, Agarwal A. Heme oxygenase 1 as a therapeutic target in acute kidney injury. Am J Kidney Dis. 2017;69(4):531-545. doi:10.1053/j.ajkd.2016.10.037

28. McQueen MM, Gaston P, Court-Brown CM. Acute compartment syndrome. Who is at risk? J Bone Joint Surg Br. 2000;82(2):200-203. doi:10.1302/0301-620x.82b2.9799

29. Cho YS, Lim H, Kim SH. Comparison of lactated Ringer's solution and 0.9% saline in the treatment of rhabdomyolysis induced by doxylamine intoxication. Emerg Med J. 2007;24(4):276-280. doi:10.1136/emj.2006.043265