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

To compare the effect of lactate vs. bicarbonate-buffered replacement fluids on electrolyte mass balance during isovolemic continuous veno-venous hemofiltration (CVVH).

Randomized controlled study with double cross over.

Intensive care unit of a tertiary university hospital.

Eight patients with acute renal failure (ARF).

Isovolemic CVVH (2L/hr of replacement fluid) was performed in random order with either bicarbonate or lactate-buffered replacement fluid delivered pre-filter.

Sodium, potassium, chloride, magnesium, and phosphate, were measured in each sample. There was a mass gain of sodium, which was similar under both conditions (bicarbonate: 23.3+/-4.9 mmol/hr, lactate: 22.7+/-3.5 mmol/hr). Mass chloride gains occurred with bicarbonate-buffered replacement fluid only (12.8+/-5.3 mmol/hr), while there was an overall net loss of chloride with lactate fluids (-2.5+/-5.2 mmol/hr), resulting in a significant difference in chloride mass balance (p<0.0001). Magnesium mass balance was negative with bicarbonate buffer only (-0.6+/-0.2 mmol/hr) and also differed significantly from that obtained with lactate fluids (-0.1+/-0.2 mmol/hr, p<0.0001). Phosphate losses (bicarbonate: -1.7+/-0.7 mmol/hr, lactate: -1.7+/-0.5 mmol/hr) were equivalent with both buffers. Potassium mass balance was neutral.

Mass balance during isovolemic CVVH is significantly affected by the type of replacement fluid administered prefilter. Isovolemic CVVH is not isonatremic and the use of bicarbonate-buffered fluid results in a significant accumulation of chloride and a loss of magnesium.