How many milliliters equivalent per hour of sodium am I removing in an 80 kg patient undergoing Continuous Renal Replacement Therapy (CRRT) with a fluid dose of 1000 mL per hour?

Sodium Removal Rate in CRRT

In an 80 kg patient receiving CRRT at an effluent dose of 1000 mL/hour, you are removing approximately 140 mEq of sodium per hour, which is equivalent to approximately 900 mL of plasma sodium per hour (assuming standard dialysate/replacement fluid sodium concentration of 140 mEq/L).

Understanding Sodium Removal Mechanics

The sodium removal during CRRT depends on the sodium concentration gradient between the patient's blood and the dialysate/replacement fluid being used 1, 2:

• Standard CRRT fluids contain 140 mEq/L of sodium 3, 4, 2
• At steady state, when patient serum sodium equals fluid sodium (140 mEq/L), there is no net sodium removal—only replacement 2, 5
• Sodium removal occurs only when there is a concentration gradient between blood and dialysate/replacement fluid 2, 6

Calculating Net Sodium Removal

The actual sodium removal rate depends on your patient's current serum sodium level 2, 5:

• If serum sodium = 140 mEq/L: Net sodium removal = 0 mEq/hour (isonatremic exchange)
• If serum sodium = 150 mEq/L: Net sodium removal ≈ 10 mEq/hour × effluent rate factor
• If serum sodium = 130 mEq/L: Net sodium addition ≈ 10 mEq/hour × effluent rate factor

At 1000 mL/hour effluent rate with standard 140 mEq/L fluids, the sodium flux approximates the concentration difference multiplied by the clearance rate 2, 6.

Clinical Implications for Sodium Management

The 1000 mL/hour effluent dose (12.5 mL/kg/hr in your 80 kg patient) is below the recommended minimum of 20-25 mL/kg/hr for adequate CRRT dosing 1, 7. This translates to 1600-2000 mL/hour for an 80 kg patient 1.

Managing Hyponatremia During CRRT

When treating severe hyponatremia (serum sodium <120 mEq/L), standard 140 mEq/L fluids will cause excessively rapid correction 4, 5:

• Target correction rate: ≤6-8 mEq/L per 24 hours to prevent osmotic demyelination syndrome 7, 4, 5
• Use customized low-sodium fluids (119-126 mEq/L) by adding sterile water to commercial solutions 4, 2, 5
• Monitor serum sodium every 4-6 hours during correction 7, 5

Managing Hypernatremia During CRRT

For hypernatremia correction, the opposite approach applies 2, 6:

• Add calculated amounts of 30% NaCl to dialysate/replacement fluid to create a sodium concentration slightly below the patient's current level 2, 6
• Aim for gradual correction to prevent cerebral edema from rapid osmotic shifts 2, 6

Electrolyte Monitoring During CRRT

Beyond sodium, intensive CRRT commonly causes other electrolyte derangements that require monitoring 1:

• Hypophosphatemia (60-80% prevalence): Associated with negative patient outcomes 1
• Hypokalemia (up to 25% prevalence): Particularly with prolonged CRRT 1
• Hypomagnesemia (60-65% incidence): Exacerbated by citrate anticoagulation 1

Use dialysis solutions containing potassium (4 mEq/L), phosphate, and magnesium to prevent these deficiencies rather than relying on intravenous supplementation 1.

Common Pitfalls

• Assuming net sodium removal occurs at all serum sodium levels: Remember that at isonatremia (140 mEq/L), you are only replacing sodium, not removing it 2, 5
• Using inadequate CRRT dosing: Your 1000 mL/hour rate is subtherapeutic; increase to at least 1600 mL/hour (20 mL/kg/hr) for adequate clearance 1
• Failing to adjust fluid sodium concentration in dysnatremia: Standard fluids will cause dangerous correction rates in severe sodium disorders 4, 5
• Neglecting other electrolyte losses: Phosphate, potassium, and magnesium depletion are nearly universal with intensive CRRT and require proactive prevention 1