Kt/V in CAPD by different estimations of V

Normalization of Clearances in Peritoneal Dialysis Using a Formula for Body Water Derived from an End-Stage Renal Disease Population

Objective

To compare body water (V) estimates from the Chertow formula (VC), which was derived in an end-stage renal disease population, to V estimates from the Watson formulas (VW) in continuous ambulatory peritoneal dialysis (CAPD) patients. To identify CAPD patients in whom VC is preferred to VW for clearance studies.

Design

Retrospective analysis of clearance studies.

Setting

Dialysis units of four academic medical centers.

Participants

302 subjects on CAPD.

Intervention

613 clearance studies by standard methods.

Main Outcome Measures

Comparisons between VC and VW, and between urea clearance normalized by VC [(Kt/VC)ur] and VW [(Kt/VW)ur].

Results

VC exceeded VW by 3.5 ± 1.6 L ( p < 0.001), or 9.6% on average. This degree of overestimation of VW is in the range of body water estimates found in CAPD subjects with severe volume overload (> 5% of body weight) in previous studies. Total (Kt/VW)ur exceeded total (Kt/VC)ur by 8.6%. By linear regression, VC = –0.589 + (1.112 x VW), r = 0.983. VW exceeded VC in only 12 studies. Young age, short height, low body weight, and low prevalence of diabetes characterized the studies with VW > VC. Total (Kt/VW)ur was adequate (≥ 2.0 weekly) in 276 studies. Among these, 74 studies had inadequate total (Kt/VC)ur (< 2.0 weekly). By logistic regression, the predictors of inadequate (Kt/VC)ur, when (Kt/VW)ur was adequate, included the presence of diabetes, great height, and long duration of CAPD.

Conclusions

VC provides estimates of body water exceeding those provided by VW in a great majority of CAPD patients. Consequently, approximately 25% of the clearance studies that are adequate when VW is used as the normalizing parameter may be inadequate when VC is used. VC may provide a more appropriate estimate of body water than VW in CAPD patients with volume overload.

In Search of the Ideal V

The ideal normalization parameter for urea and creatinine clearance is not yet known. The best current practices are to normalize urea clearance by anthropometric V, corrected for certain conditions such as edema, and creatinine clearance by BSA. Normalization parameters should be calculated using the actual weight. In addition, the ideal weight also should be used in underweight individuals.

Fractional Urea Clearance Estimates Using Two Anthropometric Formulas in Continuous Peritoneal Dialysis: Sex, Height, and Body Composition Differences

Objective

To compare estimates of urea volume (V) and KT/V obtained by the Watson and Hume anthropometric formulas, and to identify the similarities and differences between these estimates.

Design

Theoretical analysis applying wide variations in the determinants of anthropometric V (age, height, weight) in hypothetical women and men. Analysis of urea kinetic studies performed in patients on continuous peritoneal dialysis (CPD).

Setting

Four dialysis units in Albuquerque, two in Athens, and two in Thessaloniki.

Participants

Three hundred and two CPD patients who had 440 urea kinetic studies.

Intervention

Standard urea clearance was performed by 24-hour collections of urine and drained dialysate followed by blood sampling. V was estimated by both the Watson and Hume formulas.

Main Outcome Measures

Estimates of V and KT/V were compared separately in women and men by Student's t-test, linear regression, and limits of agreement (mean difference±2 SD). The agreement of the KT/V estimates was also tested by the kappa ratio using a value of 1.70 weekly as the lowest acceptable KT/V.

Results

The theoretical analysis indicated important disagreement only in extreme variations from the ordinary in height and, to a lesser extent, weight. Differences due to height variation were pronounced only in hypothetical women. CPD patient findings were as follows: in women, Watson V and weekly KT/V were 30.4±4.4 L and 2.10±0.61, respectively. Corresponding Hume estimates were 30.3±5.4 L and 2.12±0.66, respectively. Corresponding estimates for men were 40.5±5.7 L and 1.92±0.57 (Watson) plus 41.4±5.6 L and 1.88±0.57 (Hume), respectively. By linear regression, KT/VHume = -0.083 + 1.052 (KT/Vw8tson), r = 0.961 (women); and KT/VHume = -0.026 + 0.992 (KT/Vwatson), r = 0.985 (men). Limits of agreement were -1.41 L and 2.10 L for V, and -0.15 and 0.14 weekly for KT/V. In 94.3% of the cases, KT/Vw8tson and KT/VHume agreed (both >1.70 or both <1.70 weekly). Kappa ratio was 0.875 (excellent agreement). The concordant and discordant groups differed in height and degree of obesity, in agreement with the theoretical analysis.

Conclusion

The Watson and Hume formulas provide similar estimates of V and KT/V in CPD patients. Differences may be noted only if women's height or, to a lesser extent, both sexes’ weight is at a great variance with the ordinary values.

Assessment of Fluid Status in Peritoneal Dialysis Patients

Objectives

To assess the influence of abnormalities in fluid status and body composition on agreement between multifrequency bioimpedance analysis (MF-BIA), segmental BIA (ΣBIA), the Watson formula, and tracer dilution techniques.

Design

Cross-sectional.

Setting

Multicenter.

Patients

40 patients (29 males, 11 females) on peritoneal dialysis (PD).

Main Outcome Measures

Agreement between the various techniques used to assess total body water (TBW) [MF-BIA, deuterium oxide (D2O), and the Watson formula] and extracellular water (ECW) [MF-BIA, bromide dilution (NaBr), and ΣBIA], also in relation to the relative magnitude of the body water compartments [ECW (NaBr):body weight (BW) and TBW (D2O):BW] and body composition (DEXA). Second, the relation between body water compartments with echocardiographic parameters.

Results

Wide limits of agreement were observed between tracer dilution techniques and MF-BIA [TBW (D2O – MF-BIA) 2.0 ± 3.9 L; ECW (NaBr – MF-BIA) –2.8 ± 3.9 L], which were related to the relative magnitude of the body water compartments: r = 0.70 for ECW and r = 0.40 for TBW. ΣBIA did not improve the agreement [ECW (NaBr – ΣBIA): 3.7 ± 2.9 L]. Also, wide limits of agreement were observed between D2O and the Watson formula (–2.3 ± 3.3 L). The difference between D2O and Watson was related to hydration state and to percentage of fat mass ( r = 0.70 and r = –0.53, p < 0.05). Both ECW and TBW as assessed by BIA and tracer dilution were related to echocardiographic parameters.

Conclusion

Wide limits of agreement were found between MF-BIA and ΣBIA with dilution methods in PD patients, which were related to hydration state itself. The disagreement between the Watson formula and dilution methods was related to both hydration state and body composition.

Accuracy of the estimation of V and the implications this has when applying Kt/Vurea for measuring dialysis dose in peritoneal dialysis

Background:

Current guidelines for the prescription of peritoneal dialysis dose rely on a single cut-off ‘minimal’ value of K t/ V. To apply this in the clinic, this requires an accurate estimation of V, the volume of urea distribution that equates to the total body water (TBW). This analysis sought to determine the accuracy to which V can be estimated.

Methods:

A literature search was undertaken of studies comparing TBW estimation using two or three of the following methods: isotopic dilution (gold standard), anthropometric equations (e.g. Watson formula) and bioimpedance analysis. Studies of healthy and dialysis populations of all ages were included. Mean differences and 95% limits of agreement (LOA) were extracted and pooled.

Results:

In 44 studies (31 including dialysis subjects), the between-method population means were typically within 1–1.5 L of each other, although larger bias was seen when applying anthropometric equations to different racial groups. However, the 95% LOA for all comparisons were consistently wide, typically ranging ±12–18% of the TBW. For a typical individual whose TBW is 35 L with a measured K t/ V of 1.7, this translates into a range of K t/ V 1.4–2.05.

Conclusions:

There are limitations to the accuracy of estimation of V which call into question the validity of applying a single threshold K t/ V value as indicative of adequate dialysis. This should be taken into account in guideline development such that if a target K t/ V was deemed appropriate that this should be expressed as a range; alternatively single targets should be avoided and dialysis dose should be determined according to patient need.

Validity of anthropometry- and impedance-based equations for the prediction of total body water as measured by deuterium dilution in Cameroonian haemodialysis patients

BACKGROUND & AIMS

There is no available information on the validity of anthropometry- and impedance-based equations for predicting total body water (TBW) in Cameroonian haemodialysis patients. This study aimed to validate and develop predictive equations of TBW for Cameroonian haemodialysis patients.

METHOD

TBW in 40 Cameroonian haemodialysis patients (28 men and 12 women) was measured by deuterium dilution and compared with the one predicted by 7 anthropometric and 9 BIA equations. Multiple linear regression analysis was used to develop an equation for predicting TBW as measured by deuterium, from anthropometric parameters.

RESULTS

Pure errors in predicting TBW showed unacceptable value for all equations tested. In all the cases, unacceptable discrepancies at individual level for clinical purposes were noted. The following equation was developed and showed a better agreement with the deuterium dilution method: TBW = 13.8994 + 0.0017 × Age +0.3190 × Weight +1.8532 × Sex.

CONCLUSION

Further development and cross-validation of anthropometric and BIA prediction equations specific to African heamodialysis patient are needed. Meanwhile, the equation developed in this study which provided a better agreement with the isotope dilution could be use for Cameroonian haemodialysis patients.

The prescription of peritoneal dialysis

In addition to the maintenance of normal extracellular electrolyte composition, the prescription of continuous peritoneal dialysis (CPD) should address four other specific issues: (i) prevention of uremia by achievement of adequate clearance of azotemic substances, (ii) prevention of progressive expansion of the extracellular volume by adequate peritoneal ultrafiltration, (iii) prevention of loss of residual renal function, and (iv) prevention of deterioration of the peritoneal membrane structure and function. Urea clearance, in the form of Kt/V(Urea), is the index of removal of azotemic substances proposed by current guidelines. The target total (renal plus peritoneal) Kt/V(Urea) is >or=1.7 weekly. To provide the desired peritoneal Kt/V(Urea) (K(p)t/V(Urea)), the prescription of peritoneal dialysis must provide a daily drain volume (Dv) defined by the clearance equations as Dv = V x (K(p)t/V(Urea))/(D/P(Urea)), where V is body water obtained from published anthropometric formulas, K(p)t/V(Urea) = (1.7 - renal Kt/V(Urea))/7 and D/P(Urea) is the dialysate-to-plasma urea concentration ratio at the dwell time prescribed. Computer programs obtain the relevant D/P(Urea) values from formal studies of peritoneal transport. In the absence of these studies (for example, at initiation of CPD), D/P(Urea) values can be obtained from published studies with similar dwell times. Body size, indicated by V, is the major determinant of the K(p)t/V(Urea) limit provided by a given CPD schedule. Other obstacles to achievement of adequate urea clearance are created by poor patient compliance, inaccuracies of the anthropometric formulas estimating V, and mechanical complications of CPD that lead to retention of dialysate in the body. The main requirements for the prescription of adequate ultrafiltration are knowledge of the individual peritoneal transport characteristics, monitoring of urinary volume, and restriction of dietary sodium intake. Excessive dietary sodium intake is the major cause of extracellular volume expansion in CPD. Ideally, sodium intake should be kept at the level of total (peritoneal plus renal) sodium removal. Preventing the loss of residual renal function involves avoidance of nephrotoxic influences in the form of medications, radiocontrast agents, urinary obstruction and infection, and possibly other influences, such an elevated calcium-phosphorus product and anemia. Use of the lowest dialysate dextrose concentration that will allow adequate ultrafiltration is currently the most widespread practical measure of prevention of peritoneal membrane deterioration. Formulation of biocompatible dialysate is a major ongoing research effort and may greatly enhance the success of CPD in the future.

Online Conductivity Monitoring: Validation and Usefulness in a Clinical Trial of Reduced Dialysate Conductivity

Relatively low dialysate conductivity (Cndi) may improve outcomes by reducing the overall sodium burden in dialysis patients. Excess sodium removal, however, could lead to hemodynamic instability. We performed a randomized controlled trial of reduction of Cndi. For the study, 28 patients were randomized to maintenance of Cndi at 13.6 mS/cm (equivalent to 135 mmol/L of Na+) or serial reduction of Cndi in steps of 0.2 mS/cm, guided by symptoms and blood pressure. Sodium removal estimated from pre- and postplasma concentrations correlated well with removal measured by conductivity monitoring as ionic mass balance (R2 0.66, p < 0.0001). Of the 16 patients randomized to reduction of Cndi, 6 achieved Cndi 13.4 mS/cm, 6 achieved 13.2 mS/cm, and 4 achieved 13.0 mS/cm. No episodes of disequilibrium occurred. Interdialytic weight gain was reduced from 2.34 +/- 0.10 kg to 1.57 +/- 0.11 kg (p < 0.0001). Predialysis systolic blood pressure fell from 144 +/- 3 mm Hg to 137 +/- 4 mm Hg (p < 0.05). The reduction in convective sodium removal was balanced by an increase in diffusive sodium removal (95 +/- 9 mmol cf. 175 +/- 14 mmol, p < 0.0001). Reduction in Cndi monitored by IMB is safe and practical and leads to improved interdialytic weight gains and blood pressure control, while avoiding excessive sodium removal.

Bioelectric impedance vector distribution in peritoneal dialysis patients with different hydration status

BACKGROUND

In continuous ambulatory peritoneal dialysis (CAPD), total body water (TBW) is estimated by functions of body weight, and by equations of bioelectric impedance analysis (BIA). These procedures may be biased with abnormal tissue hydration. We validated vector BIA (BIVA) patterns of hydration in CAPD patients, based on direct measurements of resistance (R) and reactance (Xc) (RXc graph) without knowledge of the body weight.

METHODS

Cross-sectional study in 200 adult CAPD patients from two groups: 149 patients (77 males and 72 females) without edema (BMI 24.3 kg/m2), and 51 (29 males and 22 females) with pitting edema (BMI 24.6 kg/m2). Single frequency (50 kHz), whole-body impedance vector was measured with both empty and filled peritoneal cavity. Vector distribution was compared with that from 726 healthy subjects, 1116 hemodialysis patients, and 50 nephrotic patients, all with a same BMI. The performance of BIVA was compared with indications of four anthropometry and four conventional BIA equations for TBW.

RESULTS

TBW estimates from anthropometry (Watson, Hume and Weyers, Chertow, and Johansson formulas) were misleading, indicating the same hydration in edema. TBW estimates from BIA equations indicated a 10% excess TBW in edema. BIVA were very sensitive to fluid overload, as both R (by 10%) and Xc (by 40%) were reduced in patients with edema (regardless of peritoneal filling). The vector distribution of individual CAPD patients without edema was superposable to that of the healthy, gender-specific, reference population (50%, 75%, and 95% tolerance ellipses, RXc graph) and close to the hemodialysis, presession distribution. Vectors from patients with edema were displaced downward on the RXc graph, out of the 75% ellipse (88% sensitivity and 87% specificity), and close to vectors from nephrotic patients.

CONCLUSION

CAPD prescription would keep or bring vectors of patients back into the 75% reference ellipse (border for progression from latent to apparent overhydration across the lower pole) regardless of body weight. Whether CAPD patients with vector within the target ellipse have better outcome needs longitudinal evaluation.

Estimates of body water, fat-free mass, and body fat in patients on peritoneal dialysis by anthropometric formulas

BACKGROUND

Anthropometric formulas that are used to estimate body water in peritoneal dialysis patients can also be used to estimate fat-free mass and body fat. Evaluation of body composition by the anthropometric formulas rests on two assumptions: (1) fat contains no water, and (2) the water content of the fat-free mass is constant (72%).

METHODS

We compared estimates of body water, fat-free mass, and body fat by anthropometric formulas to estimates employing dilution of tracer substances to measure body water and standard methods to analyze body composition in studies performed on peritoneal dialysis patients. We also analyzed the potential errors of the estimates of body composition by the formulas.

RESULTS

Estimates of the average body composition provided by the anthropometric formulas agreed with estimates provided by the standard methods. However, these formulas have the potential of introducing large errors when estimating body composition in individuals differing from the average subject, either because the anthropometric formulas do not account for major determinants of body composition, such as physical exercise, nutrition, and catabolic illness, or because these formulas systematically overestimate body water in subjects who are obese or experiencing volume excess.

CONCLUSION

Anthropometric formulas currently in existence can provide only approximations of body composition and may be the sources of large errors in evaluating body composition in peritoneal dialysis patients. The potential errors include estimates of body water. These errors may alter the interpretation of urea kinetic studies in certain categories of peritoneal dialysis patients (e.g., obese subjects).

Discrepancies between adequacy goals in peritoneal dialysis: role of gender

BACKGROUND

The National Kidney Foundation-Dialysis Outcome Quality Initiative (NKF-DOQI) recommends a weekly creatinine clearance (CrCl) of 60 L/wk/1.73 m2 or greater and a Kt/V of 2.0 or greater as peritoneal dialysis (PD) adequacy standards. It has been described that approximately one quarter of patients may have discrepancies between these goals. The purpose of this study is to identify associated factors in patients reaching both criteria, none, or only weekly Kt/V, where K is clearance, t is time, and V is volume.

METHODS

We studied 64 patients and their adequacy results in a cross-sectional analysis. Patients were divided in three groups. Group 1 reached both weekly Kt/V and CrCl criteria. Group 2 did not reach either criteria. Group 3 reached only the weekly Kt/V criterion. A new weekly Kt/V also was calculated, assigning to all patients a male V. One patient who met only the CrCl criterion was excluded.

RESULTS

Groups 2 and 3 had significantly less residual renal function (RRF) than group 1 (residual CrCl, 5.50 and 1.33 versus 37.3 L/wk/1.73 m2, respectively; P < 0.001). Other differences, such as age, weight, peritoneal membrane transport, nutritional parameters, or number of patients with diabetes, were not significantly different. Group 3 made up 19% of patients and was predominantly females. Conversely, group 2 was predominantly males. Using a male V, we obtained a weekly Kt/V below the NKF-DOQI recommendations for group 3 (1.9 versus 2.2; P < 0.05).

CONCLUSION

Conservation of RRF was the main factor in reaching both PD adequacy criteria. Discrepancies were frequent, accounting for 19% of our population. Female gender explained why patients reached weekly Kt/V only. This difference disappeared when we calculated Kt/V using a male V.

Feasibility of adequate solute clearance in obese patients on peritoneal dialysis: a cross-sectional study

BACKGROUND

It is widely assumed that obese patients are poorly suited for peritoneal dialysis (PD). Mathematical models predicting weight limits to achieve adequate solute clearance in anuric patients on continuous ambulatory PD therapy do not apply to the majority of obese patients on PD therapy.

METHODS

To define the extent to which obesity or large body size interferes with successful PD, the feasibility of achieving adequate solute clearance, defined by the Kidney Disease Outcomes Quality Initiative (K/DOQI) guidelines, was studied. We reviewed prospectively recorded data for 25 obese patients (body mass index > or = 29) from a group of 58 prevalent PD patients treated in an inner-city ambulatory dialysis center. Adequacy of solute clearances was assessed by comparing weekly Kt/V and weekly creatinine clearance (WCC) with those recommended by the K/DOQI. Adequacy also was examined separately for large patients, defined as those with total-body water (TBW) by the Watson and Watson equation of 48 L or greater. Similar analyses were performed separately for 10 anuric obese patients.

RESULTS

Eighty four percent and 88% of the 25 obese patients achieved K/DOQI targets for weekly Kt/V and WCC, respectively. Among the 10 anuric obese patients, 90% and 70% achieved these targets. Only 60% of those with TBW of 48 L or greater met the Kt/V target.

CONCLUSION

PD remains a viable option for obese patients with end-stage renal disease. It is possible for the majority of obese patients on PD therapy to achieve solute clearances recommended by the K/DOQI.

Independent effects of residual renal function and dialysis adequacy on dietary micronutrient intakes in patients receiving continuous ambulatory peritoneal dialysis

BACKGROUND

Dialysis patients are at risk of vitamin and mineral deficiencies, not only because of losses during chronic hemodialysis or peritoneal dialysis but also because of low intakes.

OBJECTIVE

The objective was to determine the importance of urea clearance (calculated as K(t)/V) and residual renal function (RRF) in predicting micronutrient intakes in a large cohort of patients receiving continuous ambulatory peritoneal dialysis (CAPD).

DESIGN

We conducted a survey of dietary intakes in 242 CAPD patients and divided them into 3 groups according to their weekly urea clearance and RRF: WD group (n = 84), a urea clearance >/= 1.7 and a glomerular filtration rate (GFR) >/= 1 mL x min(-1) x 1.73 m(-2); DD group (n = 71), a urea clearance >/= 1.7 and a GFR < 1 mL x min(-1) x 1.73 m(-2); and ID group (n = 87), a urea clearance < 1.7.

RESULTS

Most of the patients had intakes of water-soluble vitamins and minerals that were lower than the recommended dietary allowance; most intakes were significantly higher in the WD group than in the DD and ID groups, except those of niacin and calcium. After age, sex, body weight, and the presence of diabetes were controlled for, total weekly urea clearance and the GFR (but not peritoneal dialysis urea clearance) were significantly associated with intakes of vitamins A and C, the B vitamins, and minerals (calcium, phosphate, iron, and zinc). Low intakes of vitamins and minerals with low RRF and urea clearance were the result of reduced overall food intakes, except for thiamine, vitamin B-6, and folic acid, which were deficient in the diet.

CONCLUSIONS

Supplementation with most water-soluble vitamins and minerals, including iron and zinc, should be considered in CAPD patients, especially those with low RRF and low urea clearance. The optimal dose needs to be determined.

Limitations in anthropometric calculations of total body water in patients on peritoneal dialysis

Having an accurate estimation of total body water (TBW) is essential for the evaluation of dialysis efficacy in peritoneal dialysis (PD) patients. In this study, TBW volumes were measured by tritium dilution (TBW(THO)) in 165 PD patients and compared with TBW calculations according to the Watson formulas. An alternative anthropometric formula based on the present PD population was also developed and validated in an independent sample of 29 PD patients. Furthermore, the relation between TBW(THO) and body surface area (BSA) according to the formula of Gehan was analyzed. Body composition was assessed by a four-compartment model, based on measurements of TBW(THO) and total body potassium. Mean values of TBW by the Watson formulas were almost identical to TBW(THO), and the correlation coefficient for the relationship of calculated to measured volumes was 0.89 (P = 0.001). However, both anthropometric formulas-the Watson formulas as well as the new, alternative one-overestimated TBW in obese patients and vice versa in lean patients. Similarly, TBW was underestimated in patients who were overhydrated. The correlation coefficient between TBW(THO) and BSA was 0.708 for males and 0.797 for females (P = 0.0001 for both). In obese patients, the relationship was even closer (r = 0.924 and 0.911, respectively). In conclusion, anthropometric formulas to calculate TBW showed a considerable intraindividual variability compared with measured values. This was related to body composition features, such as degree of obesity and hydration. In contrast, BSA correlated closely to TBW in obese individuals. TBW as estimated by anthropometric formulas must be analyzed with caution, especially in the very obese or very lean patient.

Diameter of inferior caval vein and impedance analysis for assessment of hydration status in peritoneal dialysis

In 19 stable peritoneal dialysis (PD) patients, hydration status was evaluated by measurement of vena cava diameter (VCD) and bioelectrical impedance analysis (BIA) variables: intracellular water (ICW), extracellular water (ECW), and total body water (TBW). We investigated whether BIA can replace VCD. VCD did not correlate with TBW but correlated moderately with ECW/TBW (r = 0.42; 0.025 < p < 0.05) and ICW/ECW (r = -0.47; p < 0.025). Patients with underhydration (n = 4; VCD <8 mm/m2) revealed limits for BIA variables as ICW/ECW (>1.50) and ECW/TBW (<0.40). The same held true for overhydration (n = 5; VCD >11.5 mm/m2): ICW/ECW (<1.50) and ECW/TBW (>0.40). Although the positive predictive value of ICW/ECW and ECW/TBW for both under- and overhydration was only 50% and 54%, respectively, there were no false negative values. Although BIA cannot replace VCD in PD patients, the reverse holds true as well. Combining BIA and VCD may lead to a better estimation of hydration status because both techniques provide complementary information.

Comparing different methods of assessing body composition in end-stage renal failure

BACKGROUND

Accurate measurement of nutritional status in patients with end-stage renal disease is important because of its clear association with prognosis. Total body water (TBW) has additionally been recently recognized as an independent prognostic value because of its relationship with hypertension and cardiac morbidity. The current study was designed to assess the utility of surrogate markers of nutritional state and TBW in patients with end-stage renal disease.

METHODS

Fifty-four patients with renal disease were studied. TBW obtained using the deuterium dilution technique was compared with estimates derived from anthropometric measures of TBW, including 58% body weight, Watson equations, and bioelectrical impedance analysis (BIA). Anthropometrically derived fat-free mass (FFM) was compared with BIA-derived estimates. Total body nitrogen (TBN) measurements were correlated with TBW estimates and BIA-derived resistance.

RESULTS

TBW was significantly underestimated by the Watson equation (mean difference, -1.751 L, P = 0.01) and the 58% body weight approximation significantly overestimated it (mean difference, 1.792 L, P = 0.04). The Kushner BIA estimation of TBW did not significantly differ from that of the gold standard determined from D2O dilution (mean difference, -1.221 L, P = 0.12) and was also the method that showed the best agreement with the D2O estimate. However, the limits of agreement were large. Accurate prediction equations for FFM (FFM = -21.768 + 0.001 x ht2 + 6630.669 x 1/R + 0.312 x wt, R2 = 0.95) and TBN (TBN = -668.324 - 3.963 x age + 10.133 x wt + 0. 045 x ht2 + 32141.457 x 1/R, R2 = 0.91) were derived from BIA obtained resistance.

CONCLUSIONS

The estimation of TBW varies significantly depending on the method of calculation. BIA is the most accurate surrogate marker for the measurement of both TBW and other parameters of body composition.

Calculated nitrogen balance in hemodialysis patients: influence of protein intake

BACKGROUND

Optimal nutrient intake is important in the maintenance of a positive nitrogen balance in hemodialysis (HD) patients. The objectives of this study were (1) to assess the influence of two levels of protein intakes on nitrogen balance in stable adult HD patients, and (2) to identify a minimum level of protein intake that would result in a negative nitrogen balance, so that preliminary recommendations may be made in Indian patients on maintenance HD (MHD).

METHODS

Stable, adult, nondiabetic MHD patients were recruited after informed consent into a cross over trial with a high-protein (HP) diet [1.2 g/kg ideal body weight (IBW)/day), followed by a low-protein (LP) diet (0.6 g/kg IBW/day] after appropriate periods of equilibration; for both diets, 50% of protein was of high biological value, and calorie intake was 35 kCal/kg IBW/day. Duplicate meals and residues were weighed, homogenized, and stored at -20 degrees C for analysis of dietary N by the Kjeldahl method, used to check the consistency of the N content of the diet supplied. Pre- and post- (30-minute equilibrated) blood urea samples were drawn, and details of weights and other HD parameters were recorded. Interdialytic urine collections for urea were obtained. N input came from dietary protein calculated as 16% of the weight of biological protein; N output was calculated using blood-side urea measurements and urinary urea excretion and was the sum of urea N (UN) and nonurea N (NUN) losses (assumed to be equal to 0.031 g N/kg/day).

RESULTS

Fifteen patients were recruited. Twelve patients completed both limbs of the study. The mean age was 30.3 +/- 12.7 years. The body mass index was 18.9 +/- 2.4. Serum albumin was 3.8 +/- 0.35 g/dL, and Kt/V (equilibrated) was 1.17 +/- 0.3 g/dL. Protein consumed was 1.06 +/- 0.18 g/kg IBW/day in the HP limb versus 0.61 +/- 0.1 g/kg IBW/day in the LP limb (P = 0.000). Energy intake was 33 +/- 6.5 vs. 32.8 +/- 6. 7 kCal/kg IBW/day, respectively (P = 0.8). The normalized protein N appearance (nPNA) was 0.88 +/- 0.2 g/kg/day in the HP limb versus 0. 78 +/- 0.2 g/kg/day in the LP limb (P = 0.02). Dietary N was 73.5 +/- 15.3 g in the HP week and 42.5 +/- 7.5 g in the LP week (P = 0. 000). The difference between this and the sum of (UN + NUN) losses over the week was 29 +/- 13.2 g versus 1.2 +/- 8.1 g, respectively (P = 0.001), showing a strong, uniformly positive nitrogen balance with HP diet and neutral to negative nitrogen balance with LP diet. The ratio of dietary protein intake (DPI) to nPNA was significantly lower (anabolic) in the HP limb (0.7 +/- 0.2 vs. 1.12 +/- 0.3, P = 0. 000). On a scatter plot of nPNA to DPI, a catabolic relationship was demonstrated below a DPI of 0.75 g/kg/day (95% CI, 0.65 to 0.85 g/kg/day).

CONCLUSION

A DPI of approximately 1.1 g/kg/day produces a positive nitrogen balance and 0.6 g/kg/day a neutral to negative nitrogen balance, demonstrating protein anabolism as a function of protein intake. It is suggested that a protein intake of 0.85 g/kg/day should be considered unsafe. These conclusions apply in stable nondiabetic adult HD patients in the setting of adequate dialysis and adequate calorie intake.

Mortality and technique failure in patients starting chronic peritoneal dialysis: results of The Netherlands Cooperative Study on the Adequacy of Dialysis. NECOSAD Study Group

BACKGROUND

Recent studies have shown an association between small solute clearance and patient survival. Thus far, little attention has been paid to the potential effects of fluid overload. The aim of this study was to determine the relative importance of baseline patient and treatment characteristics to mortality and technique failure in patients starting peritoneal dialysis.

METHODS

One hundred and eighteen consecutive new patients were included in this prospective multicenter cohort study. Cox proportional hazards regression was used to predict mortality and technique failure.

RESULTS

There were 33 deaths and 44 technique failures. The two-year patient survival was 77%, and the two-year technique survival was 64%. Age, systolic blood pressure, and the absolute quantity of small solutes removed at baseline were independent predictors of mortality. A one-year increase in age was associated with a relative risk (RR) of death of 1.05 (95% CI, 1.01 to 1.09) and a 10 mm Hg rise in systolic blood pressure, with a RR of 1.42 (95% CI, 1.17 to 1.73). The removal of 1 mmol/week/1.73 m2 of urinary and dialysate creatinine was associated with a RR of death of 0.95 (95% CI, 0.92 to 0.98) and 0.93 (95% CI, 0.89 to 0.98). The removal of urea had a similar association with the RR of death. Predictors for technique failure were urine volume, peritoneal ultrafiltration, and systolic blood pressure.

CONCLUSIONS

Dialysate solute removal was an independent predictor of mortality. The association between systolic blood pressure and mortality shows that the maintenance of fluid balance and the removal of small solutes deserve equal attention.

Evaluating volume status in hemodialysis patients

Accurate determination of the volume and distribution of body fluids in end stage renal disease patients will permit improved assessment of dry weight and strategies for optimal fluid removal. Certain biochemical markers and anatomical measures have been proposed as markers of dry weight, but these markers primarily reflect the volume of the intravascular compartment and may not reflect total body volume status. Noninvasive determination of total body water and extracellular fluid volumes using bioimpedance analyses has also been proposed for assessment of dry weight, but such determinations do not yet have sufficient accuracy for routine use. Several devices have been recently developed for continuously monitoring changes in blood volume on-line during routine hemodialysis. Such blood volume monitors cannot be used to determine dry weight directly; however, continuous monitoring of blood volume can be used to detect fluid overload because intradialytic changes in blood volume are small in hemodialysis patients who are overhydrated. Furthermore, continuous monitoring of blood volume can be used to predict symptoms resulting from intradialytic hypovolemia. The combined use of blood volume monitoring and time-dependent ultrafiltration and dialysate sodium profiles will be used increasingly in the future to assist in the prevention of hypotension and symptoms that result from intradialytic hypovolemia, especially when automated systems for controlling intradialytic blood volume are individualized and shown to be safe and effective.

Ambulatory blood pressure monitoring in dialysis patients and estimation of mean interdialytic blood pressure

To define blood pressure (BP) patterns and control in dialysis patients, 48-hour ambulatory BP monitoring was performed in 36 hemodialysis and 18 peritoneal dialysis patients. Monitoring began during a dialysis session for hemodialysis patients. Data revealed significantly lower diastolic BP (DBP) and lower diastolic load (percentage of diastolic values > 90 mm Hg) in hemodialysis patients compared with peritoneal dialysis patients (80.6 mm Hg v 88.8 mm Hg, respectively, [P < 0.03] and 26% v 45%, respectively [P < 0.03]) for the 48-hour period. When the 2 days were analyzed separately, the difference in diastolic pressures and loads was significant only for the first (dialysis) day. Similarly, trends toward lower systolic BP (SBP) and systolic load in hemodialysis patients existed throughout monitoring and were greater in magnitude during the first day. BP data were fit to a random-coefficient growth curve model to detect periodicity. This sensitive model did not detect diurnal variation of BP in either group. The incidence of hypotension did not differ between the two groups (2.0% v 1.0% of total observations, hemodialysis v peritoneal dialysis). In the hemodialysis group, the proportion of hypotensive observations was significantly greater during the 4 hours postdialysis compared with other periods (5.6% v 1.6%; P < 0.02), a finding that likely reflects the practice of holding antihypertensives until after hemodialysis. However, patient diaries did not reflect hypotensive symptoms during this time. In the hemodialysis group, mean BP and predialysis BP did not correlate with interdialytic sodium load or weight gain. Predialysis and postdialysis BP (recorded by dialysis nurses) correlated significantly with mean BP. Predialysis SBP overestimated mean SBP by an average of 10 mm Hg, while postdialysis SBP underestimated mean SBP by an average of 7 mm Hg. To create formulas to estimate mean SBP and DBP in hemodialysis patients, multiple linear regression was used to model these variables against age, sex, race, and average prehemodialysis/posthemodialysis BP. The model achieved a high degree of fit (r2 = 0.72 for SBP; r2 = 0.65 for DBP), demonstrating that prehemodialysis and posthemodialysis BP can be used to predict mean BP in hemodialysis patients. In summary, our data show the absence of a diurnal variation of BP in dialysis patients and lower BP in hemodialysis patients compared with peritoneal dialysis patients. Among hemodialysis patients, more hypotension occurred after dialysis compared with other periods, and predialysis and postdialysis BP can be used to model mean BP levels.