What is the recommended hydration rate in mL/min of normal saline (sodium chloride 0.9%) for an obese patient with rhabdomyolysis and an adjusted body weight of 96.6 kg?

Fluid Hydration Rate for Rhabdomyolysis in Obese Patient

For an obese patient with rhabdomyolysis and an adjusted body weight of 96.6 kg, the recommended hydration rate is approximately 16.7 mL/min of normal saline (0.9% NaCl), which translates to 1000 mL/hour during the initial resuscitation phase.

Initial Aggressive Fluid Resuscitation Protocol

• Start with 0.9% normal saline at 1000 mL/hour (16.7 mL/min) immediately upon establishing IV access 1
• This aggressive rate should be maintained during the initial resuscitation phase to achieve the target urine output 1
• If resuscitation extends beyond 2 hours, reduce the infusion rate by at least 50% (to approximately 500 mL/hour or 8.3 mL/min) to prevent volume overload 1

Target Urine Output and Monitoring

• The critical therapeutic goal is achieving a urine output of ≥300 mL/hour (5 mL/min), which is approximately 3.1 mL/kg/hour for this patient's adjusted body weight 1, 2
• Insert a bladder catheter immediately to monitor hourly urine output unless urethral injury is suspected 1
• This target is 6-10 times higher than the standard oliguria threshold used in general acute kidney injury definitions 1

Fluid Type Selection

• Use only 0.9% normal saline (sodium chloride 0.9%) for initial volume expansion 3, 1
• Avoid potassium-containing solutions such as Lactated Ringer's, Hartmann's solution, or Plasmalyte A, as potassium levels can increase markedly after muscle reperfusion even with intact renal function 1
• Avoid starch-based fluids due to their association with increased rates of acute kidney injury and bleeding 1

Severity-Based Fluid Requirements

• For severe rhabdomyolysis (which this patient has, given the context of obesity and likely elevated creatine kinase), administer >6 liters of intravenous fluids per 24-hour period 1, 4
• This translates to an average continuous rate of >250 mL/hour (4.2 mL/min) over 24 hours, though initial rates should be higher as described above 1

Adjustments Based on Body Weight Considerations

• The adjusted body weight of 96.6 kg should be used for calculating fluid requirements in this obese patient 3
• The adjusted body weight formula accounts for the fact that metabolic needs of adipose tissue are less than lean body mass: aBW = actual weight + [(standard weight - actual weight) × 0.25] 3
• Obese patients undergoing prolonged procedures are at particularly high risk for rhabdomyolysis due to increased compressive pressure from body weight 5, 6

Critical Monitoring Parameters

• Monitor creatine phosphokinase (CPK) levels serially - if CPK rises above 5,000 U/L, institute aggressive hydration and consider mannitol diuresis 6
• Perform repeated assessments of plasma myoglobin, CPK, potassium, calcium, and phosphate levels 1
• Monitor urine pH and maintain at approximately 6.5 1
• Assess volume status carefully with continuous cardiac output monitoring to avoid over- or under-resuscitation 1

Adjunctive Therapies to Avoid

• Do NOT routinely use sodium bicarbonate for urinary alkalinization, as current evidence does not demonstrate benefit over aggressive crystalloid resuscitation alone 1
• Do NOT routinely use mannitol, as studies suggest little additional benefit compared to crystalloid resuscitation alone and it is potentially nephrotoxic 1
• Mannitol may only benefit patients with markedly elevated CK (>30,000 U/L), though this benefit remains undefined 1

When to Escalate Care

• If urine output remains <300 mL/hour despite aggressive hydration at 1000 mL/hour, prepare for early renal replacement therapy 4
• Intermittent hemodialysis is the preferred modality for rapid potassium clearance 1
• Continue intravenous fluids until CPK levels decrease to <1,000 U/L 2

Critical Pitfalls to Avoid

• Delayed fluid resuscitation is associated with higher risk of acute kidney injury - start fluids immediately 1
• Inadequate initial fluid rates - many clinicians underestimate the volume needed; 1000 mL/hour is appropriate for severe rhabdomyolysis 1, 2
• Using potassium-containing fluids can precipitate fatal cardiac arrhythmias in the setting of muscle breakdown 1
• Failure to monitor hourly urine output can lead to missed intervention windows for renal replacement therapy 4