Acid-base profile in patients on PD

Secular trends in dialysis dose in peritoneal dialysis (PD) and modes of dialysis delivery [automated PD (APD) versus continuous ambulatory PD (CAPD)] require a reexamination of acid-base status in patients treated with these renal replacement modalities. We explored steady-state acid-base profile and its determinants in 175 patients on CAPD and 77 patients on APD. The majority (62% to 70%) of patients had serum bicarbonate levels in the normal range, and a minority (17% to 27%) had values just above 28 mEq/L. Only a small percentage (10% to 12%) of patients in either the CAPD or the APD groups had a serum HCO3 less than 22 mEq/L, an indication of the successful correction of acidosis in most patients. The anion gap was elevated (16 mEq/L) in the majority of patients on CAPD and APD and bore an inverse relationship to serum HCO3 and a direct relationship to serum albumin and serum phosphate. In CAPD patients, but not APD patients, a significant inverse relationship was observed between the anion gap and peritoneal permeability as assessed by four-hour D/Pcreatinine. The correction of acidosis in PD appears to be predominantly achieved by the continuous supplementation of alkali via dialysis, with residual renal function not differentiating the degree of correction. Steady-state serum bicarbonate in patients on CAPD appeared to be responsive to the underlying peritoneal membrane permeability characteristics of the patient that govern alkali loss and gain, but the higher dialysate volumes in APD appear to override this effect. Higher albumin, blood urea nitrogen (BUN), and phosphate in patients with lower HCO3 suggest a discrepancy between daily acid load and dialysis dose.