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

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

DESIGN: Randomized controlled study with double cross over.

SETTING: Intensive care unit of a tertiary university hospital.

PATIENTS AND PARTICIPANTS: Eight patients with acute renal failure (ARF).

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

MEASUREMENTS AND RESULTS: 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.

CONCLUSIONS: 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.