Nutritional Markers during Peritoneal Dialysis: Data from the 1998 Peritoneal Dialysis Core Indicators Study

Objective

This analysis explores the nutritional status of adult U.S. peritoneal dialysis (PD) patients.

Design

The Peritoneal Dialysis Core Indicators Study is a prospective cross-sectional prevalence survey describing the care provided to a random sample of adult U.S. PD patients.

Methods and Population

Prevalence data were collected from a national random sample of 1381 adult PD patients participating in the United States End Stage Renal Disease (ESRD) program.

Results

The median age of these patients was 55 years, 61% were Caucasian; the leading cause of ESRD was diabetes mellitus. Age, sex, size, peritoneal permeability, dialysis adequacy, and nutritional indices did not differ between patients on continuous ambulatory PD and patients on automated PD. The dialysis prescriptions employed achieved mean weekly Kt/V urea (wKt/V) and creatinine clearance (wCCr) values of 2.22 ± 0.57 and 67.8 ± 22.5 L/1.73 m2/week, respectively. The PD patients were large, with a mean body weight of 77 ± 21 kg and body mass index (BMI) of 27 ± 8.6 kg/m2. The mean serum albumin of these patients was 3.5 ± 0.51 g/dL, and 43% of values fell below the National Kidney Foundation Dialysis Outcomes Quality Initiative's desired range. The PD patients had a normalized protein equivalent of nitrogen appearance (nPNA) of 1.0 ± 0.57 g/kg/day, a normalized creatinine appearance rate (nCAR) of 17 ± 7.3 mg/kg/day, and an estimated lean body mass (%LBM) of 62% ± 18% of body weight. Serum albumin correlated positively with patient size, nCAR, and nPNA, but negatively with age, the presence of diabetes mellitus, female gender, erythropoietin dose, the creatinine dialysate-to-plasma ratio results of peritoneal equilibration testing, and the dialysis portion of the wCCr. The duration of ESRD experience correlated negatively with both serum albumin and patient size, although these relationships were complex.

Conclusion

Peritoneal dialysis patients generally have marginal serum albumin levels, a finding incongruent with alternative measures of nutritional status, such as weight, BMI, and creatinine generation. Serum albumin is reduced in patients with high peritoneal permeability ( i.e., rapid transporters) and, because these patients generally have higher than average wCCr values, serum albumin is inversely correlated with the dialysis component of the wCCr. The presumptive nutritional indicators (BMI, %LBM, nPNA, and serum albumin) provide disparate estimates, varying from 10% to 50% for the prevalence of nutritionally stressed PD patients.

Nutrition Indices in Obese Continuous Peritoneal Dialysis Patients with Inadequate and Adequate Urea Clearance

♦ Objective

To test whether better nutrition is associated more with adequate urea clearance than with inadequate urea clearance in obese patients on continuous peritoneal dialysis (CPD).

♦ Design

Retrospective analysis of clearance and nutrition indices in obese CPD patients. Only obese patients were analyzed. Obesity was defined as a ratio of actual weight to desired weight (W/DW) ≥ 1.2. The dose of dialysis was considered adequate at weekly Kt/V urea ≥ 2.0. Small solute clearances and nutrition indices were compared between patients with weekly Kt/V urea < 2.0 and patients with weekly Kt/V urea ≥ 2.0 at the first clearance study.

♦ Setting

Four university-affiliated and two private dialysis units in Canada and the United States.

♦ Patients

A total of 270 CPD patients with W/DW ≥ 1.2 at the first clearance study.

♦ Results

Among the 270 obese CPD patients, 157 (58.1%) were underdialyzed (weekly Kt/V urea 1.66 ± 0.22) and 113 (41.9%) had adequate dialysis (weekly Kt/V urea 2.51 ± 0.47) at the first clearance study. Creatinine clearance values also differed between the underdialyzed and adequately dialyzed obese groups (55.6 ± 15.2 vs 87.6 ± 29.8 L/1.73 m2 weekly, respectively, p < 0.001). The underdialyzed group contained fewer women (39.5% vs 60.2%, p < 0.001) and more patients with anuria (35.0% vs 8.8%, p < 0.001), and had higher serum urea (20.7 ± 6.9 vs 18.2 ± 5.3 mmol/L, p = 0.001) and serum creatinine (974 ± 283 vs 734 ± 275 μmol/L, p < 0.001), marginally lower serum albumin (35.8 ± 5.2 vs 37.2 ± 6.4 g/L, p = 0.082), lower urea nitrogen excretion (5778 ± 2290 vs 7085 ± 2238 mg/24 hr, p < 0.001) and indices derived from urea nitrogen excretion (protein nitrogen appearance and normalized protein nitrogen appearance), and lower creatinine excretion (1034 ± 349 vs 1217 ± 432 mg/24 hr, p < 0.001) and indices derived from creatinine excretion (lean body mass normalized to actual or desired weight) than the adequately dialyzed group.

♦ Conclusion

Nutrition indices derived from urea nitrogen and creatinine excretion are worse in underdialyzed than in adequately dialyzed obese CPD patients. This finding may have clinical importance, despite the mathematical coupling between small solute clearances and excretion rates in cross-sectional studies, because of evidence from other studies that small solute excretion rate in cross-sectional studies is a robust independent predictor of outcome in CPD.