Weight status classification of patients on continuous peritoneal dialysis

We tested the agreement between classifications of the weight status of patients on peritoneal dialysis (PD) by body mass index (BMI) and by body fat (BF) content (BF/W, where W = actual weight), when BF was computed as BF = W - V/0.73 from the Sahlgrenska, Watson, or Hume anthropometric formulas estimating body water (V) in 933 patients on PD and 7,737 outpatients without hydration disorders. We used currently accepted cut-off values for classifying subjects as underweight, normal-weight, overweight, and obese by BMI and BF/W. We obtained these values: BMI: men on PD (n = 555), 25.5 +/- 4.3; men with normal renal function [NRF (n = 5,906)], 27.7 +/- 5.1; women on PD (n = 378), 25.9 +/- 6.1; women with NRF (n = 1,831), 28.3 +/- 6.5; BFSahlgrenska/W--men on PD, 0.238 +/- 0.063; men with NRF, 0.274 +/- 0.052; women on PD, 0.342 +/- 0.89; women with NRF, 0.366 +/- 0.075. We obtained these regressions: Women on PD BMI = 12.0832 + 38.9550 (BFSahlgrenska/W) -92.9252 (BFSahlgrenska/W)2 +254.0675 (BFSahlgrenska/W)3, r2 = 0.917; Men on PD BMI = 19.4729 - 29.1310 (BFSahlgrenska/W) +213.7045 (BFSahlgrenska/W)2, r2 = 0.888. From those regressions, the BMI value corresponding to the BFSahlgrenska/W cut-off for underweight was similar to the National Institutes of Health (NIH) BMI cut-off for underweight. The BMI value corresponding to the BFSahlgrenska/W cut-off for obesity was substantially lower than the NIH BMI cut-off for obesity. The kappa ratios of the classifications of weight status by BMI and BFSahlgrenska/W varied between 0.142 and 0.304 (poor agreement), with more than 50% of the subjects classified in a more obese weight category by BFSahlgrenska/W than by BMI. Classification of the subjects by BMI and by BFSahlgrenska/W in quintiles or quartiles led to much higher kappa ratios, particularly in women. The results were similar in subjects with NRF and with the use of the Watson and Hume formulas to estimate BF. The use of arbitrary cut-off values of BMI or anthropometric BF/W to classify PD patients or patients without edematous states as underweight, normal-weight, overweight, or obese leads to substantial disagreement between the two classifications. Classification of weight status by BMI or BF/W in quintiles or quartiles improves substantially the agreement between the two classifications and should be preferred.

Body composition evaluation in peritoneal dialysis patients using anthropometric formulas estimating body water

In adult patients on peritoneal dialysis (PD), estimates of body water (V), fat-free mass (FFM), and body fat (BF) can be obtained by using anthropometric formulas for estimating V. Estimates of V, FFM, and BF can also be obtained by using reference (standard) methods in which V is evaluated by a standard dilution method. To test whether the estimates obtained by the various methods agree, we analyzed published studies that measured V by a standard method in adult PD patients. We then calculated V, FFM, and BF by the Watson, Hume, Sahlgrenska, Chumlea, Lee, and Chertow formulas for the "average subject" in the published studies. We compared the standard and the anthropometric estimates using the limits-of-agreement method of Bland and Altman. Our analysis included six studies involving a total of 262 patients (89 women, 173 men). The six studies measured V by a reference method and allowed calculation of anthropometric V, FFM, and BF for the average patient. We calculated these values: VStandard, 36.8 +/- 4.7 L; VSahlgrenska, 36.9 +/- 4.3 L [p = nonsignificant (NS); Bland-Altman limits of agreement: -3.1 L to 3.3 L]; FFMStandard 50.9 +/- 5.2 kg; FFMSahlgrenska, 50.6 +/- 4.3 kg (Bland-Altman limits of agreement: -5.4 kg to 4.8 kg); BFStandard, 20.3 +/- 3.0 kg; BFSahlgrenska, 20.6 +/- 2.3 kg (Bland-Altman limits of agreement: -4.8 kg to 5.4 kg). Results obtained using the Watson, Hume, Chumlea, and Lee formulas also agreed with the standard estimates. The Chertow formula produced results that systematically overestimated the standard V and FFM values and that underestimated the standard BF. The Watson, Hume, Sahlgrenska, Chumlea, and Lee anthropometric formulas used to calculate V provide estimates of body composition that approximate those obtained using standard methods in PD patients with average body composition. Anthropometric estimates may cause large systematic errors in PD patients whose body composition varies from the average, particularly obese or overhydrated patients.

Normalization of protein nitrogen appearance by various size indicators in patients on continuous peritoneal dialysis

Protein nitrogen appearance (PNA) estimated from urea nitrogen appearance (UNA) reflects dietary protein intake and is an important index of nutrition in peritoneal dialysis (PD). Normalization of PNA by several body size indicators has resulted in discrepancies between normalized PNA (nPNA) values and other nutrition indices in PD patients with varying weight status. To test whether a particular size indicator produces nPNA values that eliminate the discrepancies, we normalized PNA values obtained at the first clearance study in 925 PD patients by weight (W), by fat-free mass (FFM) obtained from body water, by lean body mass (LBM) derived from creatinine kinetics, by desirable weight (DW), by standard weight (SW), and by adjusted edema-fee body weight (aBW). We classified patients into three groups according to W/DW: an underweight group [group I: W/DW < 0.9, n = 147 (15.9%)], a normal-weight group [group II: 0.9 < or = W/DW < 1.2, n = 506 (54.7%)], and an obese group [group III: W/DW > or = 1.2, n = 272 (29.4%)]. The UNA and PNA increased progressively from group I to group III. The W, FFM, LBM, SW, and aBW also increased progressively, and the corresponding nPNA values decreased progressively from group I to group III--all at p < 0.001. The DW did not differ significantly between the three groups. The PNA values normalized by DW were 0.91 +/- 0.21 (group I), 0.96 +/- 0.24 (group II), and 1.07 +/- 0.25 (group III), p < 0.001. Of the six size indicators tested, only DW produced values of nPNA consistent with the nutrition status of PD patients with varying weight status. Our findings indicate that DW is the proper size indicator for normalizing PNA in PD patients.

Small solute clearances and nutrition indices in obese patients on continuous peritoneal dialysis

To investigate the relationship between obesity, small-solute clearances, and nutrition in continuous peritoneal dialysis (CPD), we compared clearances and nutrition indices between 270 obese and 502 normal-weight CPD patients. Degree of obesity was classified by the ratio of body weight (W) to desired weight (DW) at the first clearance study. The DWs were obtained from the tables of the Metropolitan Life Insurance Company, assuming a medium skeletal frame. The obese patients (group I) had W/DW > 1.2 (1.38 +/- 0.17), and the normal-weight patients (group II) had 0.9 < or = W/DW < or = 1.2 (1.05 +/- 0.08). Nutrition indices derived from urea nitrogen and creatinine excretion were normalized by both W and DW. The following variables differed between group I (first value) and group II: sex (women: 48.2% vs. 33.9%), W (87.6 +/- 14.4 kg vs. 68.2 +/- 8.7 kg), body surface area (1.95 +/- 0.22 m2 vs. 1.77 +/- 0.16 m2), body water by method of Watson (41.2 +/- 7.7 L vs. 36.3 +/- 5.5 L), body mass index (31.8 +/- 3.9 vs 24.3 +/- 2.0), protein nitrogen appearance (PNA: 62.9 +/- 17.6 kg in 24 h vs. 57.7 +/- 15.7 kg in 24 h), PNA normalized to DW (1.08 +/- 0.29 g/kg in 24 h vs. 0.96 +/- 0.26 g/kg in 24 h), creatinine excretion (CrEx: 1111 +/- 396 mg in 24 h vs. 991 +/- 348 mg in 24 h), CrEx/W (12.6 +/- 3.7 g/kg in 24 h vs. 15.4 +/- 4.5 g/kg in 24 h), CrEx/DW (17.3 +/- 5.3 g/kg in 24 h vs. 15.1 +/- 4.8 g/kg in 24 h), lean body mass (LBM: 49.3 +/- 13.8 kg vs. 43.6 +/- 11.9 kg), LBM/W (0.56 +/- 0.12 vs. 0.64 +/- 0.15), and LBM/DW (0.77 +/- 0.18 vs 0.67 +/- 0.16), all at p < or = 0.034. Marginal differences (0.10 > p > 0.05) were found in the diabetes prevalence (53.0% vs. 40.8%), height (165.9 +/- 11.7 cm vs. 167.4 +/- 9.8 cm), and serum albumin (3.64 +/- 0.55 g/dL vs. 3.53 +/- 0.62 g/dL). No differences were found in age, duration of CPD until the first clearance study, percent of subjects with anuria, Kt/V urea, creatinine clearance, blood urea nitrogen, serum creatinine, and PNA normalized to W. Obese CPD patients tend to have better nutrition indices than do normal-weight CPD patients with similar small-solute clearances. In obese subjects, normalization by W creates inappropriately low values for nutrition indices derived from urea nitrogen and creatinine excretion. Normalization of those indices by DW appears preferable.

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) > or = 1.2. The dose of dialysis was considered adequate at weekly Kt/V urea > or = 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 > or = 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 > or = 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 micromol/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.

Weight deficit in patients on continuous ambulatory peritoneal dialysis

Small solute clearances were compared between two groups of patients on continuous ambulatory peritoneal dialysis (CAPD), an underweight group with a ratio of actual-to-ideal weight (W/IW) less than 0.9 and a normal-weight group with W/IW between 0.9 and 1.2 at the first clearance study after initiation of CAPD. Adequate clearance levels were set according to the K/DOQI guidelines. Duration of follow-up during CAPD and time on CAPD until the first clearance study was similar in the two groups. Initial weekly Kt/V urea and creatinine clearance also were similar. Kt/V urea values were adequate in 41.8% of the underweight subjects and 41.0% of the normal-weight subjects (not significant). Corresponding percentages for creatinine clearance were 36.4% and 39.7% (not significant). Serum creatinine and albumin concentration, creatinine excretion, and lean body mass estimated from creatinine kinetics were lower in the underweight group. Weight measurements from initiation of CAPD were available in 37 underweight patients. At initiation of CAPD, 31 subjects had W/IW less than 0.9, and 6 subjects had W/IW greater than 0.9. Chronic catabolic illness was present at CAPD initiation in 19 patients. Among the 37 patients, 17 lost weight and 6 gained weight during the course of CAPD. Compared with patients who lost weight, those who gained weight were younger (35.6 +/- 9.3 years old versus 58.4 +/- 15.0 years old; P = 0.0069) and had a higher percent of women (80.0% versus 11.8%; P = 0.0093), higher initial weekly Kt/V urea (2.58 +/- 0.50 versus 1.91 +/- 0.24; P = 0.0087), and a higher percent of adequate Kt/V urea (80.0% versus 11.8%; P = 0.0093). Small solute clearances do not differ between underweight CAPD patients and normal-weight CAPD patients. Underweight CAPD patients usually start CAPD with a weight deficit and have associated catabolic illnesses. Catabolic illness is the sole cause of weight deficit in 40% of the underweight CAPD patients and is present in the remaining 60%. The role of inadequate clearances in the development of weight deficit in CAPD populations is difficult to assess. It seems, however, that adequate Kt/V urea may be necessary for weight gain in underweight CAPD patients.

Disagreement between height/weight classifications of underweight, normal weight, and obesity in peritoneal dialysis patients

Peritoneal dialysis (PD) patients are classified as underweight, normal weight, or obese by height/weight indices including body mass index (BMI) and the body weight/desired weight (W/DW) ratio. We compared these classifications of degree of obesity in 378 women and 555 men on PD. We used these cut-off values: for underweight, BMI < or = 18.5 and W/DW < or = 0.9; for obesity, BMI > or = 30.0 and W/DW > or = 1.2. The W/DW values were calculated assuming first a small frame, then a medium frame, and finally a large frame for all subjects. Regardless of sex or skeletal frame, BMI correlated highly with W/DW (r value between 0.98 and 0.99); however, the range of BMI values corresponding by linear regression to the normal range of W/DW (0.9-1.2) was narrower than the range of "normal" BMI (18.5-30.0). Consequently, regardless of sex or skeletal frame, smaller fractions of the patient population were classified as underweight or obese by BMI standards than by W/DW standards. The degree of agreement of the classifications of subjects as underweight, normal weight, or obese by BMI and W/DW was evaluated by Cohen's kappa ratio. The kappa ratio varied between 0.47 and 0.58, indicating a reasonable--but not high--degree of agreement beyond chance. The highest kappa ratios were obtained assuming a medium skeletal frame for both women and men. Substantial discrepancies are observed in the classification of PD patients as underweight, normal weight, or obese by BMI and W/DW. Further research is needed to identify the height/weight index that has the strongest association both with clinical outcomes and with other, more precise measurements of body fat content.

The relation between nutrition indices and age in patients on continuous ambulatory peritoneal dialysis receiving similar small solute clearances

OBJECTIVE

To analyze the effect of age on nutrition indices in subjects on the same continuous ambulatory peritoneal dialysis (CAPD) schedule.

METHODS

We analyzed 613 sets of clearance values and nutrition indices in 302 CAPD patients. Small solute clearances included urea clearance (Kt/Vurea) and creatinine clearance (Ccr). Nutrition indices included body mass index (BMI), serum albumin, urea and creatinine, 24-h urea nitrogen and creatinine excretion in urine plus dialysate, protein nitrogen appearance (PNA), PNA normalized by standard weight (nPNA), lean body mass (LBM) computed by creatinine kinetics, and LBM/Weight. CAPD subjects were classified in 4 age quartiles (Q): Group Q1, age 33.7 +/- 7.6 years, N = 149; group Q2, age 49.5 +/- 3.8 years, N = 158; group Q3, age 61.5 +/- 2.6 years, N = 154; and group Q4, age 72.1 +/- 5.4 years, N = 152. Group comparison was done by one-way ANOVA or chi-square. Predictors of low nutritional parameters were identified by logistic regression. Selected variables were compared by linear regression.

RESULTS

Mean Kt/Vurea and Ccr were above the current adequacy standards and did not differ between the age quartiles. In contrast, older quartiles had, in general, lower nutrition indices than younger quartiles. However, the youngest quartile had the lowest BMI. By logistic regression, young age was a predictor of low BMI, while advanced age was a predictor of low creatinine and urea nitrogen excretion, low nPNA, and low LBM/Weight. The regressions of nPNA on Kt/Vurea differed between the age quartiles. By these regressions, the youngest quartile had higher nPNA values for the same Kt/Vurea than the oldest quartile in the clinically relevant range of Kt/Vurea and nPNA values.

CONCLUSIONS

Nutrition indices are worse in older than in younger CAPD patients with the same small solute clearances. Nutrition of CAPD patients is adversely affected by age and requires special attention in the older age group.

A population-specific formula predicting creatinine excretion in continuous peritoneal dialysis

OBJECTIVE

The Cockroft-Gault formula was shown to systematically overestimate the decline in creatinine excretion with age in continuous peritoneal dialysis (CPD) patients and is, therefore, not suitable for studying creatinine excretion. The purpose of the present study was to develop and test a population-specific formula predicting average creatinine excretion in CPD.

METHODS

Creatinine excretion in urine plus dialysate was measured in 925 CPD patients. Forty patients were excluded because of evidence of noncompliance. The remaining 885 subjects were randomly grouped into a derivation group (n = 432) and a validation group (n = 453). Stepwise multiple linear regression models were used to predict creatinine excretion in the derivation group. The candidate variables, chosen because they were previously shown to be predictors of creatinine excretion in CPD, included weight (W), age (A), gender (G), diabetes (D), and interaction terms between these four variables. Estimates of creatinine excretion from the best-fit regression formula (CrExcr1) and from the Cockroft-Gault formula (CrExcr2) were compared to creatinine excretion (CrExcr) in the validation group.

RESULTS

The best-fit regression model in the derivation group included all four candidate variables (W, A, G, D), but no interaction terms. This model was as follows: CrExcr1 = 302.150 - 4.380A + 171.234G - 39.041D + 11.730W (r2 = 0.477, p < 0.001). In the validation set, CrExcr = -15.795 + 0.988CrExcr1 (r2 = 0.447, p < 0.001), and CrExcr = -303.823 + 0.732CrExcr2 (r2 = 0.340, p < 0.001). When the differences between measured and predicted creatinine excretion did not take into account the sign of each individual difference, CrExcr - CrExcr1 = 201 +/- 156 mg/24 hours, and CrExcr - CrExcr2 = 235 +/- 174 mg/24 hr (p < 0.001) in the validation group. When the sign of the difference was taken into account, CrExcr - CrExcr1 = -28 +/- 149 mg/24 hr, and CrExcr - CrExcr2 = 63 +/- 295 mg/24 hr (p < 0.001).

CONCLUSIONS

A population-specific formula predicting creatinine excretion in CPD was derived. This formula has greater accuracy than the Cockroft-Gault formula and can be used in studies of creatinine excretion in CPD.

Outcomes of Severe Methanol Intoxication Treated with Hemodialysis: Report of Seven Cases and Review of Literature

To identify factors associated with the outcome of severe methanol intoxication treated with hemodialysis, we analyzed the clinical course of 7 patients admitted with serum methanol level higher than 50 mg/dL, and therefore requiring hemodialysis. Four patients (group A) had adverse outcomes (1 death, 3 severe neurological deficits and/or blindness) and 3 patients (group B) had no adverse outcomes. Compared to group B, group A appeared to have a longer delay between ingestion of methanol and arrival at the emergency department (ED), a longer wait in the ED until ethanol infusion was started (3.6 ± 2.7 vs 1.3 ± 0.9 hr, p < 0.05), and, on admission, higher serum methanol (504 ± 219 vs 321 ± 228 mg/dL, p < 0.05), higher serum osmolality (460.5 ± 98.2 vs 397.6 ± 52.3 mOsm/kg, p < 0.05), higher serum osmolal gap (162.6 ± 76.7 vs 105.6 ± 52.9 mOsm/kg, p < 0.05), lower arterial pH (6.86 ± 0.08 vs 7.38 ± 0.16, p < 0.01), lower serum bicarbonate (4.6 ± 1.6 vs 19.9 ± 5.7 mmol/L, p < 0.01), and higher serum anion gap (36.5 ± 1.3 vs 14.3 ± 6.7 mEq/L, p < 0.01). Delay in the ED until hemodialysis was started did not differ (group A 6.4 ± 2.6 hr, group B 5.3 ± 3.5 hr), while duration of hemodialysis until serum methanol levels became permanently undetectable was longer in group A (15.0 ± 0.5 vs 8.4 ± 4.4 hr, p < 0.01). The ingested dose of methanol and the delay between ingestion and initiation of therapy to block methanol metabolism (ethanol infusion) and remove methanol from the body (hemodialysis) appear to be the critical factors influencing the outcome of methanol intoxication. Early diagnosis and initiation of treatment before substantial parts of the ingested methanol have been metabolized are of paramount importance in ensuring a favorable outcome.

Creatinine excretion in continuous peritoneal dialysis: a systematic error of the Cockroft-Gault formula

We investigated the hypothesis that the rate of loss of creatinine excretion with age in peritoneal dialysis (PD) patients differs from the rate predicted from the Cockroft-Gault formula (Cr(Pred)) by analyzing creatinine excretion data obtained from clearance studies of 925 patients on continuous ambulatory PD therapy with an age range of 12 to 91 years. Measured creatinine generation (Cr(Meas)) is the sum of creatinine excretion in urine plus dialysate (Cr(Excr)) plus an estimated metabolic degradation of creatinine. The effect of age on Cr(Excr) and the differences Cr(Excr) - Cr(Pred) and Cr(Meas) - Cr(Pred) were analyzed by linear regression. In 373 women, Cr(Excr) = W(16.9360 - 0.084A), r = -0.342, P < 0.001 (where W is weight in kilograms and A is age in years). The regression slope was one half of the slope in the Cockroft-Gault formula. Cr(Excr) - Cr(Pred) = -413.91 + 4.78A, r = 0.300, P < 0.001. Cr(Meas) - Cr(Pred) = -176.36 + 4.37A, r = 0.278, P < 0.001. In 552 men, Cr(Excr) = W(21.079 - 0.108A), r = -0.338, P < 0.001. The regression slope was approximately one half of the slope in the Cockroft-Gault formula. Cr(Excr) - Cr(Pred) = -493.25 + 6.28A, r = 0.267, P < 0.001. Cr(Meas) - Cr(Pred) = -66.41 + 3.63A, r = 0.143, P = 0.001. The rate of loss of creatinine excretion with age is one half of the rate predicted by the Cockroft-Gault formula in both women and men on PD therapy. Therefore, the difference between excretion (or measured generation) of creatinine and creatinine generation predicted by the Cockroft-Gault formula is not constant, but increases with age. The Cockroft-Gault formula systematically overestimates the effect of age on creatinine excretion in PD patients and is not suitable for predicting creatinine excretion in these subjects.

Water and small solute excretion in continuous peritoneal dialysis patients with lean body mass exceeding 90% of body weight as estimated from creatinine kinetics

Lean body mass computed from creatinine kinetics (LBM) is an index of somatic nutrition and correlates with other nutrition indices in CAPD. However, LBM exceeding 90% of body weight (LBM/W > or = 0.9) may be an index of non-compliance, rather than nutrition. To test this hypothesis, we analyzed fluid and solute excretion in 40 CAPD patients with LBM/W > or = 0.9 (group A). The comparison group (group B) consisted of 885 CAPD patients with LBM/W < 0.9. Group A was younger (38.3+/-14.8 vs 54.7+/-14.7 yr) and had a lower percent of women (23.5% vs 41.1%) and diabetic subjects (17.5% vs 42.6%) than group B (at P < or = 0.019). Group A also had lower body mass index (22.7+/-2.7 vs 25.8+/-5.1 kg/m2, P <0.001) and serum albumin (33.0+/-6.7 vs 35.2+/-5.5 g/L, P = 0.014). Despite similar prescribed daily fill volumes (group A 8.3+/-2.4, group B 8.5+/-2.2 L/24 h) and similar D/P urea and creatinine values, group A had higher daily drain volume (11.0+/-3.6 vs 9.6+/-2.1 L/24 h, P < 0.001). Renal clearances were similar, while peritoneal and total clearances were apparently higher in group A. Creatinine excretion was higher in group A (27.4+/-5.1 vs 13.6+/-4.1 mg/kg x 24 h, P < 0.001), with a large part of the excess creatinine excretion in group A being accounted for by peritoneal excretion. The combination of an apparently high daily ultrafiltration volume (2.7 L/24 h on the average), unrealistically high creatinine excretion rate, and relatively poor nutrition (low body mass index and serum albumin) in group A is consistent with non-compliance. We suggest that the finding of LBM/W > or = 0.9 during a clearance study in CAPD should trigger an investigation for non-compliance.

Effect of preventing Staphylococcus aureus carriage on rates of peritoneal catheter-related staphylococcal infections. Literature synthesis

OBJECTIVE

To determine whether specific preventive measures reduce the rate of peritoneal catheter-related infections and peritoneal catheter loss due to Staphylococcus aureus.

DESIGN

Structured literature synthesis.

METHODS

Relevant studies were identified by MEDLINE search, from personal files, and from the reference lists of retrieved articles. We analyzed English-language studies on treatment targeted at S. aureus, with at least 10 subjects and at least 3 months of follow-up, and data on staphylococcal peritoneal dialysis catheter infections. We excluded noncontrolled studies. Two investigators abstracted data using a structured form.

RESULTS

We evaluated six studies with concurrent controls and eight studies with historical controls. In one randomized, placebo-controlled, blinded study, periodic nasal mupirocin ointment reduced the rate of staphylococcal exit-site infection from 0.42 to 0.12 episodes/patient-year (p = 0.006), but had no effect on the rates of staphylococcal tunnel infection, peritonitis, or catheter loss. In one randomized study without placebo control, periodic oral rifampin reduced the rate of staphylococcal exit-site infection from 0.65 to 0.22 epi/pt-yr (p = 0.011), but had no effect on the rate of staphylococcal peritonitis. In another nonblinded, randomized, controlled study, the use of either rifampin or mupirocin was associated with low rates of staphylococcal catheter infections and catheter loss. In one study with historical controls, the rate of staphylococcal exit-site infection and peritonitis was lower after oral rifampin prophylaxis. In seven other studies comparing nasal or exit-site mupirocin to historical controls, the rate of staphylococcal exit-site infection decreased from 0.17 to 0.05 epi/pt-yr, the rate of staphylococcal peritonitis decreased from 0.18 to 0.06 epi/pt-yr, and the rate of catheter loss decreased from 0.09 to 0.05 epi/pt-yr during the mupirocin period.

CONCLUSION

The literature provides strong evidence that staphylococcal carriage prophylaxis using either oral rifampin or mupirocin ointment in the nares or exit site reduces significantly the rate of exit-site infection due to Staphylococcus aureus. Weaker evidence based on studies with historical controls suggests that rifampin or mupirocin prophylaxis also reduces the rate of staphylococcal peritonitis and peritoneal catheter loss. Studies with a stronger level of evidence are needed to verify this last point.

Renal clearances in continuous ambulatory peritoneal dialysis: differences between diabetic and non-diabetic subjects

We analyzed the effect of diabetes on the decline of residual renal function during the course of CAPD in a cross-sectional study including 105 diabetic subjects (41 women) who had 207 clearance studies and 125 non-diabetic subjects (50 women, 265 clearance studies). CAPD duration was 11.5+/-10.5 months in the diabetic group (DG) and 16.8+/-18.6 months in the non-diabetic group (NDG, P < 0.001). The DG had lower urine volume than the NDG (0.52+/-0.46 vs 0.61+/-0.50 L/24-h, P < 0.05), while urine-to-plasma concentration ratio was higher in the DG for creatinine (13.5+/-9.4 vs 11.5+/-11.0, P <0.05) and did not differ for urea. Weekly renal Kt/V urea (DG 0.51+/-0.57, NDG 0.53+/-0.49) and Ccr (DG 31.0+/-28.7 NDG 29.3+/-26.5 L/1.73 m2) did not differ. The slopes of the regressions of CAPD duration on renal clearances did not differ. These regressions allowed estimates of the time, from the onset of CAPD, at which renal clearances become negligible. These estimates differed for both urea clearance (DG 35.3, NDG 50.5 months) and creatinine clearance (DG 43.2, NDG 57.6 months). The slope of the regression of renal urea clearance on renal creatinine clearance was steeper in the DG, suggesting a higher renal creatinine clearance in the DG than in the NDG when renal urea clearance is the same in the two groups. Subtle differences in the rate of decline of renal function can be detected between diabetic and non-diabetic subjects on CAPD by detailed statistical analysis. These findings are supportive of the studies which have identified diabetes mellitus as a predictor of loss of residual renal function during the course of CAPD. In addition, the relationship between the renal urea and creatinine clearances differs between diabetic and nondiabetic subjects on CAPD. Therefore, the dose of CAPD required for adequate total clearances may differ between diabetic and non-diabetic subjects.

Body mass index in patients with amputations on peritoneal dialysis: error of uncorrected estimates and proposed correction

"Weight-height" indices including percent of ideal weight (%IW) and body mass index (BMI) are used to estimate degree of obesity in populations and are predictors of survival in dialysis patients. Amputation affects the relationship between weight and height independently of the degree of obesity. Corrections of both %IW and BMI for amputation have been published, but a National (U.S.) computer nutrition program used in the authors' institution uses only the correction for %IW. This study had two parts: (1) To test whether the weight-height cut-off values for weight deficit (%IW 90%, BMI 20 kg/m2) and obesity (%IW 120%, BMI 30 kg/m2) are compatible, we performed linear regression of BMI on %IW in peritoneal dialysis (PD) patients without amputations. In 349 men, BMI = 0.834 + 0.226 (%IW), r = 0.979. From this regression, the 95% confidence interval (CI) of BMI is 19.2-23.1 kg/m2 if %IW is 90%, and 26.1-29.9 kg/m2 if %IW is 120%. In 260 women, BMI = 2.194 + 0.184 (%IW), r = 0.974. From this regression, the 95% CI of BMI is 15.7-21.8 kg/m2 if %IW is 90%, and 21.3-27.3 kg/m2 if %IW is 120%. (2) To identify the direction and magnitude of the error of uncorrected BMI (BMIu) in dialysis patients with amputations, we analyzed weight-height indices in two groups of men by the computer nutrition program, which corrects %IW, but not BMI for amputation, and by the corrected BMI (BMIc) formula. In group A (amputation without height loss, n = 11), %IW = 110.2% +/- 16.9%, BMIu = 23.6 +/- 2.7 kg/m2, BMIc = 26.4 +/- 3.8 kg/m2 (p < 0.001, BMIc vs BMIu), and 5 of the 11 BMIu values fell below the 95% confidence band of the regression of BMI on %IW in patients without amputations. In group B (amputation with loss of height, n = 6), %IW = 92.7% +/- 19.9%, BMIu = 33.9 +/- 10.7 kg/m2, BMIc = 22.1 +/- 4.4 kg/m2 (p < 0.005, BMIc vs BMIu), and 5 of the 6 BMIu values fell above the 95% confidence band of the regression of BMI on %IW in patients without amputations.

CONCLUSIONS

(1) The weight deficit cut-offs for %IW and BMI are compatible in non amputated men and women. (2) The obesity cut-offs for %IW and BMI are compatible in non amputated men, but not in non amputated women. (3) Amputation without height loss decreases BMIu, while amputation with height loss increases, in general, BMIu. (4) BMI should be corrected in PD patients with amputations.

Peritoneal dialysis in the next millennium

The main thrust of research will be the prevention of renal disease and its progression to the end-stage state (ESRD); such efforts will reduce or even reverse the present epidemic of ESRD by the middle of the 21(st) Century. In the meantime, the number of ESRD patients will continue to increase and, unless xenotransplantation and cloning of one's own kidneys using stem cells will provide an alternative, the various modes of dialysis will continue to be the principle treatment for an increasing numbers of ESRD patients. Peritoneal dialysis (PD) has achieved success at certain salient points and, to advance further, the next generation of nephrologists will have to build on these. They include the following: PD is the treatment of choice for children; it has low rates of peritonitis; it has similar (or in some countries, better) survival rates than hemodialysis; it has lower costs; it has adequate clearances through the introduction of automated PD; and it is an effective treatment for those awaiting a kidney transplant. This report presents the authors' views concerning the areas in which PD will improve in the future. These include (1) a reduction in technique failure rates that will allow us to maintain a larger number of patients on PD for 10 years or more; (2) prevention of long-term changes of the peritoneal membrane through the use of more "friendly" solutions; (3) prevention of malnutrition; (4) the development of better peritoneal access devices; and (5) the increased use of PD as the treatment of first choice for most ESRD patients.