Phosphatemic control during acute renal failure: intermittent hemodialysis versus continuous hemodiafiltration

Background: Achieving "adequacy of dialysis" includes the maintenance of normal serum phosphate concentrations and is an important therapeutic goal in the treatment of acute renal failure (ARF). It is unknown whether this goal is best achieved with intermittent or continuous renal replacement therapy. Methods: We compared the effects of continuous veno-venous hemodiafiltration (CVVHDF) and intermittent hemodialysis (IHD) on serum phosphate concentrations using daily morning blood tests in 88 consecutive intensive care patients half of which were treated with IHD and half with CRRT. Results: Mean patient age was 54 +/- 14 years for IHD and 60 +/- 14 years for CVVHDF(NS). However, patients who received CVVHDF were more critically ill (mean APACHE II scores: 24.4 +/- 5.1 for IHD vs. 29.2 +/- 5.7 for CVVHDF; p<0.003). Before treatment, the serum phosphate concentration was 2.04 +/- 0.16 mmoll L for IHD and 1.96 +/- 0.17 mmoll L for CVVHDF (NS), with abnormal values in 79.4% of IHD patients and in 64.8% of CVVHDF patients (NS). During treatment, CVVHDF induced a greater reduction in serum phosphate (p=0.02) during the first 48 hours and conferred superior subsequent control of hyperphosphatemia (achieved in 64.6% of observations during CVVHDF vs. 41.8% during IHD; p<0.0001). The serum phosphate concentration was also more likely to be within the normal range during CVVHDF (55.3% vs .36.2%; p<0.0001). There was a trend toward more frequent hypophosphatemia (9.3% vs. 5.6%; P<0.1) during CVVHDF. Conclusions: Abnormal serum phosphate concentrations are frequent in ARF patients before and during renal replacement, however, normalization of phosphatemia is achieved more frequently with CVVHDF.