FACTORS AFFECTING ACID-BASE HOMEOSTASIS IN CAPD PATIENTS

Since metabolic acidosis in uremic patients appears to affect protein metabolism, cardiac function and bone disease, its complete correction seems to be necessary. CAPD enables a certain degree of correction, however a substantial amount of patients still present acid base derangements. Several studies have dealt with acid base balance in peritoneal dialysis reporting a considerable interpatient and intertreatment variability. In this study a complete analysis of factors affecting acid base homeostasis in CAPD patients has been performed. This analysis demonstrated that residual renal function is not the key factor for acid base homeostasis, nevertheless, in patient with a high residual urine volume, bicarbonate loss should be taken into account. A weak but statistically significant negative correlation was recorded between arterial blood bicarbonate and the calculated metabolic acid production. Bicarbonate levels decrease with the increase of metabolic acid production and patients with a higher protein intake are more prone to develop metabolic acidosis. Dialysate lactate concentration in spent dialysate was dependent on length of dwell time and did not correlate to lactate blood levels which were normal in all subjects. Regression analysis revealed that dialysate bicarbonate concentration at 4, 6 and 12 hours tightly correlated to the one of arterial blood. On the contrary ultrafiltration volume did not influence dialysate bicarbonate concentration. Therefore, since bicarbonate loss depends on drained volume multiplied by dialysate bicarbonate concentration, it is evident that ultrafiltration plays a key role on dialytic base gain. In conclusion, the non adequate correction of metabolic acidosis mostly depends on high metabolic acid production and high ultrafiltration.