Electrolyte mass balance during CVVH: lactate vs. bicarbonate-buffered replacement fluids

Area of Science:

• Nephrology
• Critical Care Medicine
• Biochemistry

Background:

• Continuous veno-venous hemofiltration (CVVH) is a common renal replacement therapy in intensive care units.
• The composition of replacement fluids, particularly buffer type, may influence electrolyte balance during CVVH.
• Understanding these effects is crucial for optimizing fluid management in critically ill patients.

Purpose of the Study:

• To compare the effects of lactate- versus bicarbonate-buffered replacement fluids on electrolyte mass balance during isovolemic CVVH.
• To determine the impact of different buffer types on sodium, potassium, chloride, magnesium, and phosphate balance.

Main Methods:

• A randomized controlled study with a double cross-over design was conducted.
• Eight patients with acute renal failure (ARF) undergoing isovolemic CVVH were included.
• Replacement fluids (bicarbonate or lactate-buffered) were administered pre-filter at a rate of 2 L/hr.

Main Results:

• Sodium mass balance was similar between bicarbonate and lactate fluids.
• Bicarbonate fluids led to significant chloride gain (12.8+/-5.3 mmol/hr) and magnesium loss (-0.6+/-0.2 mmol/hr).
• Lactate fluids resulted in chloride loss (-2.5+/-5.2 mmol/hr) and minimal magnesium change (-0.1+/-0.2 mmol/hr). Phosphate losses were equivalent, and potassium balance was neutral.

Conclusions:

• The buffer type of pre-filter replacement fluid significantly alters electrolyte mass balance during isovolemic CVVH.
• Isovolemic CVVH with bicarbonate-buffered fluids is not isonatremic, leading to chloride accumulation and magnesium depletion.
• Careful selection of replacement fluid is necessary to manage electrolyte disturbances in patients undergoing CVVH.