Intermittent versus continuous renal replacement therapy in the ICU: impact on electrolyte and acid-base balance

Objectives: The maintenance of normal serum sodium, potassium and bicarbonate concentrations is a therapeutic goal of renal replacement therapy (RRT) in acute renal failure (ARF). The aim of this study was to determine whether this goal is best achieved with intermittent hemodialysis (IHD) or continuous venovenous hemodiafiltration (CVVHDF). Design: Retrospective controlled study. Setting: Tertiary intensive care unit. Patients: Consecutive patients with ARF treated with IHD (n = 47) or CVVHDF (n = 49). Interventions: Measurement of daily morning sodium, potassium and bicarbonate concentrations after the initiation of RRT for up to 2 weeks of treatment. Measurements and results: Before RRT, abnormal thigh or low) values were frequently observed for sodium (42.6% vs 39.6%; NS) potassium (23.4% vs 45.8%; NS) and bicarbonate (63.2% vs 54.3%; NS). After treatment, however, CVVHDF, but not IHD, significantly increased mean sodium concentrations (p = 0.0001). CVVHDF was also more likely to normalize the serum sodium than IHD (76.2% vs 47.8% p = 0.0001). The mean potassium concentrations of both groups significantly decreased (p = 0.019 vs p = 0.0075, difference: NS). However, CVVHDF more frequently reduced the incidence of hypokalemia (1.9% vs 7.1%, p = 0.0006). CVVHDF but not IHD significantly increased mean bicarbonate concentrations (p = 0.016) in the first 48 h, and more frequently normalized them (71.5% vs 59.2, p = 0.0073). Conclusions: Serum sodium and potassium, and arterial bicarbonate, concentrations are frequently abnormal in ARF patients before and during renal replacement. Normalization of these values, however, is achieved more frequently with CVVHDF than with IHD.