Evaluating a new method to judge dialysis treatment using online measurements of ionic clearance

New technology now supports direct online measurements of total dialysis dose per treatment, Kt. An outcome-based, nonlinear method for estimating target Kt in terms of ionic clearance measurements and body surface area (BSA) has been described recently. This is a validation study of the new method that evaluates the relationship between the (actual Kt-target Kt) difference and death risk. Patients with Kt measurements during March 2004 were identified (N=59,644). Target Kt was determined for each patient using the new method. Patients were then grouped by (actual Kt-target Kt) decile. They were also grouped by (actual URR-target URR) decile. Cox analysis-based risk profiles were constructed using those groupings. The (actual Kt-target Kt) difference profiles suggested improving death risk as Kt increased from below target to equal target. Risk ratios then flattened and remained so until (actual Kt-target Kt) reached the highest decile at which it appeared to improve, suggesting a possible biphasic profile. The (URR-target URR) risk profile was U-shaped. Death risk was related to the difference between the actual Kt and a target Kt value selected using the new nonlinear method. The method is therefore valid for prescribing and monitoring hemodialysis treatment.

The tortoise and hare on hemodialysis: Does slow and steady win the race?

The importance of hemodialysis session length relative to small solute (e.g., urea) clearance has been debated for many years. Longer session length augments clearance of larger molecules and may facilitate ultrafiltration; however, the independent effects of session length on survival and other outcomes are unknown. In this report, we review two recently published observational studies examining the association between hemodialysis session length and survival. Prospective clinical trials will be required to resolve the debate.

Association between prevalent care process measures and facility-specific mortality rates

BACKGROUND

Medical communities often develop practice guidelines recommending certain care processes intended to promote better clinical outcome among patients. Conformance with those guidelines by facilities is then monitored to evaluate care quality, presuming that the process is associated with and can be used reliably to predict clinical outcome. Outcome is often monitored as a facility-specific mortality rate (SMR) standardized to the mix of patients treated, also presuming that inferior outcome implies a suboptimal process. The U.S. Health Care Financing Administration monitors three practice guidelines, called Core Indicators, in dialysis facilities to assist management of its end-stage renal disease program: (1) patients' hematocrit values should exceed 30 vol%, (2) the urea reduction ratio (URR) during dialysis should equal or exceed 65%, and (3) patients' serum albumin concentrations should equal or exceed 3.5 g/dL.

METHODS

The associations of a facility-specific SMR were evaluated with the fractions of hemodialysis patients not conforming to (that is, at variance with) the Core Indicators during three successive years (1993 to 1995) in large numbers of facilities (394, 450, and 498) using one-variable and multivariable statistical models. Three related strategies were used. First, the association of the SMR with the fraction of patients not meeting the guideline was evaluated. Second, each facility was classified by whether its SMR exceeded the 80% confidence interval above 1.0 (worse than 1.0, Group 3), was less than the interval below 1.0 (better than 1.0, Group 1), or was within the interval (Group 2). The fraction of those patients who did not meet the Indicator guidelines was then evaluated in each group. Third, the ability of variance from Indicator guidelines to predict into which of the three SMR groups a facility would be categorized was evaluated.

RESULTS

SMR was directly correlated with variance from the Indicator guidelines, but the strengths of the associations were weak particularly for the hematocrit (R(2) = 2.2%, 5.6, and 2.2 for each of the 3 years) and URR Indicators (R(2) = 2.6, 0.6, 3.3). It was stronger for the albumin Indicator (R(2) = 11.6, 20.4, 21.8). The fractions of patients falling outside of the Indicator guidelines tended to be higher in the highest SMR group. The groups were not well separated, however, particularly for the hematocrit and URR Indicators, and there was substantial overlap between them. Finally, although the likelihood that a facility would be a member of the high or low SMR group was associated with fractional variance from Core Indicator guidelines, the strengths of association were weak, and the probability that a facility would be a member of the high or low group could not be easily distinguished from the probability that it would be a member of the middle group.

CONCLUSIONS

While there were statistical associations between SMR and the fraction of patients in facilities who were at variance with these guidelines, they were weak and variances from the guidelines could not be used reliably to predict high or low SMR. Such findings do not imply that measures reflecting anemia, dialysis dose, or medical processes that influence serum albumin concentration are irrelevant to the quality of care. They do suggest, however, that more attention needs be paid to these and other associates and causes of mortality among dialysis patients when developing care process indicator guidelines.

Changing hemodialysis thresholds for optimal survival

BACKGROUND

The urea reduction ratio (URR), a measure quantitating solute removal during hemodialysis, is the fractional reduction of the blood urea concentration during a single hemodialysis treatment. The URR is the principal measure of hemodialysis dose in the United States. Based on studies of patients dialyzed prior to 1994, a minimum URR value of 65% was recommended to optimize survival. Because of new hemodialysis technologies and evolving demographics of the hemodialysis population, the relationship between the amount of hemodialysis and mortality was examined in contemporary cohorts.

METHODS

This retrospective cohort included> 15,000 patients per year receiving hemodialysis during 1994 through 1997. Each patient's URR was averaged for the three months prior to the beginning of each year. Mortality odds ratios were calculated for patients by URR. To determine the URR value above which no further improvement in mortality was seen ("threshold"), spline functions were tested in logistic regression models, both unadjusted and adjusted for case mix measures. The strength of fit for URR, defined by a range of candidate thresholds from 55 to 75%, was evaluated in increments of 1% for each year using spline functions.

RESULTS

The median URR was 63.2, 65.4, 67.4, and 68.1% for 1994 through 1997, respectively. The median length of hemodialysis treatments increased only six minutes from the beginning to the end of the period of analysis. Using spline functions, the threshold URR values were 61.1, 65.0, 68.0, and 71.0% for 1994 through 1997 in models adjusted for case mix. The ratio of median URR to URR threshold decreased from 1.03 in 1994 to 0.97 in 1997.

CONCLUSIONS

From 1994 to 1997, the median URR and the URR threshold for mortality benefit increased. Although an increased need in the amount of hemodialysis may be a consequence of changes in patients' demographic characteristics, the likely explanation(s) is a change in the dialysis procedure and/or blood sampling favoring higher URR values without changing the amount of dialysis provided. The recommended minimum URR of 65% appears to be too low to confer an optimal mortality benefit in the context of current practices.

Prealbumin is as important as albumin in the nutritional assessment of hemodialysis patients

BACKGROUND

Although serum prealbumin is considered a valid indicator of nutritional status in hemodialysis patients, there is relatively little evidence that its determination is of major prognostic significance. In this study, we aimed to determine the independent association of serum prealbumin with survival in hemodialysis patients, after adjusting for serum albumin and other indicators of protein energy nutritional status.

METHODS

Serum prealbumin was measured in more than 1600 maintenance hemodialysis patients. We determined the correlations among prealbumin and other indicators of nutritional status, including serum albumin, and bioimpedance-derived indicators of body composition. The relationship between serum prealbumin and survival was determined using proportional hazards regression.

RESULTS

The serum albumin was directly correlated with the serum prealbumin (r = 0.47, P < 0.0001), but still explained <25% of the variability in prealbumin. Prealbumin was inversely related to mortality, with a relative risk reduction of 6% per 1 mg/dL increase in prealbumin, even after adjusting for case mix, serum albumin, and other nutritional indicators. The increase in risk with lower serum prealbumin concentrations was observed whether the serum albumin was high or low.

CONCLUSION

In hemodialysis patients, the serum prealbumin provides prognostic value independent of the serum albumin and other established predictors of mortality in this population.

Predicting hemodialysis access failure with color flow Doppler ultrasound

Color flow doppler ultrasound examination of the hemodialysis access was conducted in 2,792 hemodialysis patients to evaluate its value in predicting hemodialysis access failure. After baseline assessment of vascular access function with clinical and laboratory tests including color flow doppler evaluation these patients were followed for a minimal of 6 months or until graft failure occurred (defined as surgery or angioplasty intervention, or graft loss). The patient demographics and vascular accesses were typical of a standard hemodialysis patient population. On the day of the color flow doppler examination systolic and diastolic blood pressure, hematocrit, urea reduction ratio, dialysis blood flow, venous line pressure at a dialysis blood flow of 250 ml/min, and access recirculation rate were measured. At the conclusion of the study 23.5% of the patients had access failure. Case mix predictors for access failure were determined using the Cox Model. Case mix predictors of access failure were race, non-white was higher than white (p < 0.005), younger accesses had a higher risk than older accesses (p < 0.025), accesses with prior thrombosis had a higher risk of failure (p=0.042), polytetrafluoroethylene (PTFE) grafts had a higher risk than native vein fistulae (p < 0.05), loop PTFE grafts had a higher risk than straight PTFE grafts (p < 0.025), and upper arm accesses had a higher risk than forearm accesses (p=0.033). Most significant, however, was decreased access blood flow as measured by color flow doppler (p < 0.0001). The relative risk of graft failure increased 40% when the blood flow in the graft decreased to less than 500 ml/min and the relative risk doubled when the blood flow was less than 300 ml/min. This study has shown that color flow doppler evaluation, quantifying blood flow in a prosthetic graft, can identify those grafts at risk for failure. In contrast, color doppler volume flow in native AV fistulae could not predict fistula survival. This technique is noninvasive, painless, portable, and reproducible. We believe that preemptory repair of an anatomical abnormality in vascular access grafts with decreased blood flow may decrease patient inconvenience, associated morbidity, and associated costs.

Comparing the urea reduction ratio and the urea product as outcome-based measures of hemodialysis dose

The urea reduction ratio (URR) and normalized treatment ratio (Kt/V) are related quantities that have become accepted measures of hemodialysis dose. Recent studies, however, have suggested that they combine two elements, both favorably associated with clinical outcome, as a single ratio. These elements, Kt and V, may offset each other, producing a complex quantity that does not reflect a true relationship between dialysis exposure and clinical outcome. This project explored and compared the associations of the URR and the ¿urea clearance x time¿ product (Kt) with mortality in a large sample of hemodialysis patients (37,108 patients) during 1998. Survival analyses using conventional techniques were the primary analytic tools. The relationship between URR and survival was U-shaped or J-shaped, with greater relative mortality at both extremes of the URR distribution than at its middle. Thus, identifying a threshold for adequate dialysis was not possible unless one considers also a threshold for overdialysis. Conversely, the association between Kt and outcome was much simpler, reflecting progressive improvement over the range of Kt evaluated here. These analyses suggest that such measures as URR and Kt/V are compound and complex, and that a simpler, more direct, measure, such as the Kt, should be considered to describe hemodialysis dose.

Vintage, nutritional status, and survival in hemodialysis patients

BACKGROUND

The link between dialysis "vintage" (length of time on dialysis in months to years) and survival has been difficult to define, largely because of selection effects. End-stage renal disease (ESRD) is thought to be a wasting illness, but there are no published reports describing the associations between vintage and body composition in hemodialysis patients.

METHODS

We explored the relationships among vintage, nutritional status, and survival in a 3009 patient cohort of prevalent hemodialysis patients. Body weight, total body water, body cell mass, and phase angle by bioelectrical impedance analysis were the body composition parameters of interest. We examined vintage as an explanatory variable in multiple linear regression analyses (adjusted for age, gender, race, and diabetes) using body composition parameters and biochemical indicators of nutritional status as dependent variables. Proportional hazards regression was used to evaluate the association of vintage and survival with and without adjustment for case mix and laboratory variables.

RESULTS

Dialysis vintage was 3.8 +/- 3.7 (median 2.6) years. Body composition parameters tended to be lower after dialysis year 2. Linear estimates per year of vintage beyond year 2 include -0.66 kg body wt (P < 0.0001), -0.17 kg total body water (P = 0.0003), -0.14 kg body cell mass (P < 0.0001), and -0.07 degrees phase angle (P < 0.0001). In unadjusted analyses, vintage was not associated with survival, either as a linear or higher order term. The adjustment for case mix yielded a vintage term associated with an increased relative risk (RR) of death (RR 1.04 (95% CI, 1.01 to 1.07 per year). A further adjustment for laboratory data yielded a RR of 1.06 (95% CI, 1.03 to 1.09 per year).

CONCLUSION

Dialysis vintage is related to nutritional status in hemodialysis patients, with vintage of more than years associated with a significant decline in all measured nutritional parameters. Cross-sectional analyses probably underestimate these effects. A year accrued on dialysis is associated with a 6% increase in the risk of death, all else equal. Longitudinal assessments of nutritional status, including body composition, are required to better understand the natural history of wasting with ESRD and its implications for long-term survival.

Quality-of-life evaluation using Short Form 36: comparison in hemodialysis and peritoneal dialysis patients

Short Form 36 (SF-36) is a well-documented health-related quality-of-life (HRQOL) instrument consisting of 36 questions compressed into eight scales and two primary dimensions: the physical and mental component scores. This tool was used to evaluate QOL among peritoneal dialysis (PD) and hemodialysis (HD) patients. The results of 16,755 HD and 1,260 PD patients (728 continuous ambulatory PD [CAPD] and 532 continuous cycling PD [CCPD]) completing an SF-36 during 1996 were analyzed. Three analyses of variance were performed, consisting of (1) no adjustment, (2) case mix (age, sex, race, and diabetes), and (3) case mix plus laboratory parameters. PD patients were younger (P < 0.001), a larger fraction were white (P < 0.001), fewer had diabetes (P < 0.001), and had lower serum albumin concentrations (P < 0.001) and higher creatinine, hemoglobin, and white blood cell count values (P < 0.001) than HD patients. Diabetes was present in a larger fraction of CCPD than CAPD patients (P < 0.001). HD and PD patients scored similarly for scales reflecting physical processes. PD patients scored higher for mental processes, but only after statistical adjustment for the laboratory measures. Scores on scales reflecting physical processes were worse, and those reflecting mental processes were better among CCPD than CAPD patients. HD and CAPD scores were similar. CCPD patients perceived themselves as more physically impaired but better adjusted than HD or CAPD patients. These descriptive data show that perception of QOL among PD and HD patients is similar before adjustment, but PD patients score higher for mental processes with adjustment. CCPD patients score worse for physical function and better for mental function than either CAPD or HD patients. We cannot, however, exclude the influence of therapy selection.

Exploring the reverse J-shaped curve between urea reduction ratio and mortality

BACKGROUND

Although accepted worldwide as valid measures of dialysis adequacy, neither the Kt/V (urea clearance determined by kinetic modeling) nor the urea reduction ratio (URR) have unambiguously predicted survival in hemodialysis patients. Because the ratio Kt/V can be high with either high Kt (clearance x time) or low V (urea volume of distribution) and V may be a proxy for skeletal muscle mass and nutritional health, we hypothesized that the increase in the relative risk of death observed among individuals dialyzed in the top 10 to 20% of URR or Kt/V values might reflect a competing risk of malnutrition.

METHODS

A total of 3,009 patients who underwent bioelectrical impedance analysis were stratified into quintiles of URR. Laboratory indicators of nutritional status and two bioimpedance-derived parameters, phase angle and estimated total body water, were compared across quintiles. The relationship between dialysis dose and mortality was explored, with a focus on how V influenced the structure of the dose-mortality relationship.

RESULTS

There were statistically significant differences in all nutritional parameters across quintiles of URR or Kt/V, indicating that patients in the fifth quintile (mean URR, 74.4 +/- 3.1%) were more severely malnourished on average than patients in all or some of the other quintiles. The relationship between URR and mortality was decidedly curvilinear, resembling a reverse J shape that was confirmed by statistical analysis. An adjustment for the influence of V on URR or Kt/V was performed by evaluating the Kt-mortality relationship. There was no evidence of an increase in the relative risk of death among patients treated with high Kt. Higher Kt was associated with a better nutritional status.

CONCLUSION

We conclude that the increase in mortality observed among those patients whose URR or Kt/V are among the top 10 to 20% of patients reflects a deleterious effect of malnutrition (manifest by a reduced V) that overcomes whatever benefit might be derived from an associated increase in urea clearance. Identification of patients who achieve extremely high URR (>75%) or single-pooled Kt/V (>1.6) values using standard dialysis prescriptions should prompt a careful assessment of nutritional status. Confounding by protein-calorie malnutrition may limit the utility of URR or Kt/V as a population-based measure of dialysis dose.

Body weight-for-height relationships predict mortality in maintenance hemodialysis patients

BACKGROUND

Protein-energy malnutrition is a strong predictor of mortality in maintenance hemodialysis (MHD) patients. This association has generally been described for serum chemistry measures of protein-energy malnutrition. We hypothesized that body weight-for-height relationships also predict survival in MHD patients.

METHODS

During the last three months of 1993, data were obtained on 12,965 men and women concerning clinical characteristics (height, postdialysis weight, age, gender, race, and presence or absence of diabetes mellitus) and laboratory measurements (predialysis serum albumin, creatinine and cholesterol, and the urea reduction ratio). Patient survival during the next 12 months was evaluated retrospectively.

RESULTS

In comparison to values for normal Americans determined from the National Health and Nutrition Evaluation Survey II data, weight-for-height relationships tended to be slightly lower than normal in African American men and women and Caucasian men undergoing MHD and were normal or slightly greater in the taller Caucasian women. In both men and women, the mortality rate decreased progressively as the patients' weight-for-height increased. MHD patients who weighed more than normal had the lowest mortality rates. After adjustment for clinical characteristics and laboratory measurements, the inverse relationship between mortality rates and weight-for-height percentiles was still highly significant for patients within the lower 50th percentile of body weight-for-height. Serum albumin correlated directly with weight-for-height in patients in the lower 50th percentile of weight-for-height. Serum creatinine and cholesterol correlated directly with weight-for-height in the entire population of men and women. In contrast, the urea reduction ratio was inversely correlated with weight-for-height.

CONCLUSIONS

These data indicate that weight-for-height is a strong predictor of 12-month mortality in male and female MHD patients. Multivariate analyses indicate that body weight-for-height is an independent predictor of higher mortality in those patients who are in the lower 50th percentile for this measurement.

The urea [clearance x dialysis time] product (Kt) as an outcome-based measure of hemodialysis dose

BACKGROUND

The normalized treatment ratio [Kt/V = the ratio of the urea clearance x time product to total body water] and the urea reduction ratio (URR) have become widely accepted measures of dialysis dose. Both are related to and derived from pharmacokinetic models of blood urea concentration during the dialysis cycle. Theoretical reconsideration of the models revealed that the premise about V on which they rest (that is, that V is a passive diluent with no survival-associated properties of its own) is flawed if the intended use of the models is for profiling clinical outcome (for example, mortality) rather than estimating urea concentration. As a proxy for body mass, V has survival-associated properties of its own. Thus, indexing clearance x time to body size could create an offsetting combination whereby one measure favorably associated with survival (Kt) is divided by another (for example, V). Observed clinical paradoxes support that interpretation. For example, patients with a low body mass have both higher URR and higher mortality than heavier patients. Increasing mortality is often observed at high URR, suggesting the possibility of "over-dialysis." Black patients tend to be treated at lower URR than whites but enjoy better survival on dialysis. Therefore, clearance x time was evaluated as an outcome-based measure of dialysis dose, not indexed to V, and various body size estimates were evaluated as separate and distinct measures.

METHODS

The retrospective sample included 17,141 black and white hemodialysis patients treated three times per week. Logistic regression analysis was used to evaluate death odds in age-, gender-, race-, and diabetes-adjusted models. Kt and five body size estimates (total body water or V, body weight, body weight adjusted for height, body surface area, and body mass index) were evaluated using two analytical strategies. First, all of the measures were treated as continuous variables to explore different statistical models. Second, Kt and the body size measures were divided into groups to construct risk profiles.

RESULTS

All evaluations revealed improving death odds with increasing Kt (whether adjusted for the body size estimates or not) and also with increasing body size (whether adjusted for Kt or not) for each estimate of size. Significant statistical interactions of Kt with gender, but not Kt with race, were observed in all models. There were no statistical interactions, suggesting that higher Kt was routinely required with increasing body size. Separate risk profiles for males and females suggested a higher Kt threshold for males.

CONCLUSIONS

The urea clearance x time is a valid outcome-based measure of dialysis dose and is not confounded by indexing it to an estimate of body size, which has outcome-associated properties of its own. Dialysis prescriptions for males and females should be regarded separately, but there appears no need to make a distinction between the races.

Self-reported functional status: an important predictor of health outcomes among end-stage renal disease patients

A contemporary focus on outcomes assessment has provided affirmation that patient functional status is both an important outcome of medical care and an important predictor of longer term outcomes such as morbidity and/or mortality. Monitoring functional status among end-stage renal disease (ESRD) patients is particularly critical because the cycle of physical deconditioning experienced by renal patients is both insidious and malignant. Over the past several years, patient self-report instruments have been used with increasing frequency to assess functioning. Among ESRD patients, such self-reports have reliably predicted mortality and some morbidity. Additionally, renal patients' self-reported functioning is also correlated with the results of several commonly performed laboratory tests. Based on these findings, measures of self-reported functional status might be considered a practical adjunct to regular patient assessments. They could be routinely used for purposes that might include: identifying the particular areas of functioning and well-being that need improvement; screening for subtle changes in health status; establishing physical status baselines; and corroborating the effectiveness of physical activity interventions. Overall, ESRD patients' self-report of their functioning appears to secure, synthesize, and standardize data about patient health status that is unavailable through any other mechanism. Such information may be essential to medicine's primary missions of promoting health and preserving life.

Relationship between urea reduction ratio, demographic characteristics, and body weight for patients in the 1996 National ESRD Core Indicators Project

The 1996 Health Care Financing Administration's (HCFA) Core Indicators Project for in-center, hemodialysis patients collects information on the quality of care delivered in four clinical areas that were anticipated to predict patient outcomes. Included among these clinical performance measurements is the delivered dose of hemodialysis, measured by the fractional reduction of urea achieved during a single hemodialysis session (urea reduction ratio [URR]). A random sample (N = 7,310) of adult (aged > or =18 years), in-center hemodialysis patients was selected, and a one-page data collection form for each patient was sent to the dialysis facility in which care was provided during the last quarter of 1995. The dialysis facilities provided information for 6,861 (94%) patients, and at least one paired predialysis and postdialysis blood urea nitrogen (BUN) concentration was reported for 6,655 (97%) of these patients. The URR of this cohort was 65.5% +/- 8.0% (mean +/- SD), and 41% of patients had a URR less than 65%. The mean dialysis session length was 203 minutes, and more than half of the patients received dialysis with a dialyzer membrane with a KUf less than 10 mL/mm Hg/h. The patients with a URR less than 65% had a mean body weight approximately 10 kg greater than patients with a URR of 65% or greater. This relationship was present for all demographic characteristics studied, including age, gender, race, and primary cause of end-stage renal disease (ESRD). Patients receiving dialysis for less than 6 months were more likely to have a URR less than 65% than patients on dialysis for longer periods. By multivariate analysis, variables significantly associated with a delivered URR less than 65% were body weight in the heaviest quartile (odds ratio [OR] = 6.1), male gender (OR = 2.6), on dialysis therapy less than 6 months (OR = 2.5), youngest quartile of age (<49 years) (OR = 2.0), lowest quartile of serum albumin values less than 3.6 g/dL (bromcresol green method) or less than 3.3 g/dL (bromcresol purple method) (OR = 1.6), black (OR = 1.5), dialyzed with a dialyzer KUf less than 20 mL/mm Hg/h (OR = 1.8), lowest quartile hematocrit (<29.7%) (OR = 1.2), and shorter dialysis session length (OR = 1.02/min). In conclusion, both patient-specific demographic variables and treatment-specific parameters are significantly associated with ESRD patients receiving a URR less than 65%. Furthermore, these data suggest statistically significant linkages between the delivered dose of hemodialysis and other independent outcome predictors such as serum albumin concentration. Prospective study is required to determine whether intervention strategies to improve the delivered dose of hemodialysis will affect this outcome predictor or whether serum albumin and dialysis dose share a common cause not amenable to increasing the URR.

Associates of mortality among peritoneal dialysis patients with special reference to peritoneal transport rates and solute clearance

The current report describes the distributions of selected demographic and biochemical parameters, clearance, and other transport values among patients undergoing peritoneal dialysis (PD) and evaluates the associates of mortality using those values, with and without clearance and peritoneal equilibration test (PET) data. All patients receiving PD on January 1, 1994 were selected (n = 2,686). Patients who switched to another form of dialysis during the study period were removed from the study at the time of therapy change. Working files were constructed from the clinical database to include demographic, laboratory, and outcome data. Laboratory data were available in only 1,603 patients and were used to evaluate the biochemical associates of mortality after merging the biochemical, demographic, and outcome data. Patients with clearance data or PET studies underwent a second analysis to assess the effects of peritoneal and renal clearance on survival. The analysis of demographic and laboratory data confirmed the importance of age and serum albumin concentration as predictors of death. Residual renal function (RRF) was strongly correlated with survival, but peritoneal clearance was not. Several possible explanations for the lack of correlation between peritoneal clearance and survival are discussed. The data suggest that RRF and peritoneal clearance may be separate and not equivalent quantities. Substantial work is required to confirm or refute these findings, because the information is essential to establish the adequate dose of PD in patients with various degrees of RRF.

Acute-phase inflammatory process contributes to malnutrition, anemia, and possibly other abnormalities in dialysis patients

The target organ failures associated with uremia are most often considered to be caused by processes other than uremia per se. Heart disease, for example, is considered the product of hypertension, lipid abnormalities, and so forth, rather then the uremic state. Erythropoietin deficiency, blood loss, and iron deficiency are believed to cause anemia, rather than the uremic state. Malnutrition is believed to be the product of poor nutrient intake and perhaps nutrient losses, rather than uremia per se. This article reviews evidence suggesting that anemia and malnutrition share a common cause; the acute-phase inflammatory process that is a normal host-defense mechanism. Given the high prevalence of heart disease among patients with end-stage renal disease (ESRD), data indicating activation of the acute-phase process in patients with kidney failure, and emerging evidence that the process has a significant role in the risk for cardiovascular disease among patients without kidney failure, there is a strong likelihood that heart disease will share with anemia and malnutrition the acute-phase state as a contributing cause. Thus, instead of disconnected target organ failures, each with different antecedent causes, we see emerging the likelihood of a unifying pathobiology for uremia. The antecedents of morbidity and mortality appear as a web of organ failures connected by a common pathobiology. Whereas each failure likely has contributing causes other than the acute-phase state, they probably share the state as a causative, contributing, or exacerbating factor.

Primary associates of mortality among dialysis patients: trends and reassessment of Kt/V and urea reduction ratio as outcome-based measures of dialysis dose

Information from a large clinical database was used to construct time trends for the leading associates of mortality among dialysis patients. The changing strengths of association of those measures with mortal risk were also evaluated. Strength did not change in meaningful ways for serum albumin, creatinine, or anion gap concentrations. It declined for the urea reduction ratio (URR), however, as prevalent values of the URR increased. Irrational patterns of association between the URR and other measures suggested reevaluation of the urea kinetic method for prescribing and judging dialysis dose. Two premises on which the urea kinetic equations rest are not valid if the context for their use is clinical outcome instead of predicting blood urea nitrogen (BUN) concentration. Rigorous use of the Kt/V criterion for dialysis dose could lead to clinical judgment errors, particularly underdialysis for small or malnourished persons. Changes for prescribing dose and judging therapy are recommended.

Dose of hemodialysis and survival: differences by race and sex

CONTEXT

Although blacks receive lower doses of hemodialysis than whites, their survival when receiving dialysis treatment is better than that for whites. Previous studies of the relationship between the dose of dialysis and patient survival have not controlled for differences in patient characteristics.

OBJECTIVE

To examine the association of mortality with the dose of hemodialysis for clusters of patients categorized by race and sex.

DESIGN

Retrospective analysis of laboratory data and mortality outcomes from 1994, using a national database of hemodialysis patients.

PATIENTS

A total of 18144 black and white patients receiving hemodialysis 3 times weekly who either lived the entire year receiving hemodialysis or died.

MAIN OUTCOME MEASURES

The fractional reduction of urea in a single dialysis session as the measured hemodialysis dose (urea reduction ratio [URR]) after controlling for race, sex, age, and diabetes mellitus. Mortality was determined by strata of URRs and albumin and creatinine levels.

RESULTS

Across all age categories, blacks had lower URRs than whites, and men had lower URRs than women. In an age-adjusted model for evaluating interactions among URRs, race, sex, and diabetes, the association of URR with mortality risk was weak among blacks, particularly black men. After adjustment for age and diabetes, death probability curves were most steep for white women with URR values less than 60%. The death probability curves were least steep for black men. There was no meaningful difference between death probability and albumin or creatinine concentration among the race by sex clusters.

CONCLUSION

Using URR, the usual measure of hemodialysis dose, the assumption that the association between dialysis dose and survival is uniform across demographic groups appears incorrect. Comparisons of the quality of dialysis patient care should not rely on URR alone to predict patient survival.

C-reactive protein as an outcome predictor for maintenance hemodialysis patients

BACKGROUND

The possible association between inflammatory processes and other outcome measures in ESRD patients led us to measure the blood C-reactive protein (CRP) concentration in a large sample of hemodialysis patients, and to evaluate its statistical relationship with other common laboratory measures and patient survival. This was performed in a prospective, observational analysis with mortality as the principal outcome measure.

METHODS

One thousand fifty-four routine blood samples, collected from as many patients during June and July 1995 (one sample per patient), were randomly selected for measurement of CRP, prealbumin, and other routine laboratory measures. Six months after the initial blood tests, patient survival was determined: Logistic regression analysis was the primary statistical tool used to evaluate laboratory associations with odds of death. Bivariate regression and correlation analyses were performed using all available data.

RESULTS

The distribution of CRP values was skewed; approximately 35% of the values exceeded the upper limit of the laboratory's reference range. Serum albumin and prealbumin concentrations both correlated with the serum creatinine concentration (r = 0.378 and r = 0.347, respectively; P's < 0.001), and were inversely associated with the CRP (r = -0.254 and r = -0.354, respectively; P's < 0.001). CRP was also inversely associated with blood hemoglobin concentrations (r = -0.235; P < 0.001). Using multiple regression analysis to further explore these relationships, the serum creatinine concentration was inversely associated with CRP (r = -0.140; P < 0.001). However, after adjustment for the linkage of the serum creatinine with the serum albumin concentration (r = -0.378; P < 0.001), no relationship with creatinine was observed. Before and after adjustment for serum albumin and prealbumin concentration, the ferritin concentration correlated directly with CRP (r = 0.148; P < 0.001). Ferritin was inversely and highly correlated with total iron binding capacity (r = -0.516; P < 0.001). Independent associations of hemoglobin with albumin (t = 7.16; P < 0.001), prealbumin (t = 2.39; P = 0.017), and CRP (t = -4.27; P < 0.001) were observed. Also, the dose of erythropoietin was directly associated with the CRP concentration, before (r = 0.081, P = 0.009) and after (t = 2.03, P = 0.042) adjustment for the serum albumin and iron concentrations. CRP correlated directly with neutrophil (r = 0.318; P < 0.001) and platelet counts (r = 0.180; P < 0.001), but was weakly and inversely correlated with the lymphocyte count (r = -0.071; P = 0.04). A logistic regression analysis performed using the laboratory variables revealed a strong, independent, and inverse relationships between the serum albumin and creatinine concentrations, total lymphocyte count, and the odds risk of death. In this model, no significant relationship was observed between the odds risk of death and CRP.

CONCLUSIONS

The data presented herein suggest that: (1) strong predictable associations exist among laboratory proxies for malnutrition, anemia, and the acute phase reaction, and (2) the pathobiology implied by these laboratory abnormalities influence patients' mortal risk primarily through depletion of vital body proteins, not inflammation.

Bioimpedance norms for the hemodialysis population

More than 3,000 hemodialysis patients were examined with single-frequency bioelectrical impedance analysis (BIA). Distributions of resistance, reactance, phase angle (PA), and estimates of total body water (TBW) and body cell mass (BCM) by BIA were determined, and compared with traditional laboratory markers of nutritional status. Bioimpedance parameters and body composition estimates differed significantly by age, sex, race, and diabetic status. PA and BCM correlated directly with serum creatinine, albumin, and prealbumin concentrations. Population-based norms for bioimpedance parameters and estimates of body composition are provided.

Anemia in hemodialysis patients: variables affecting this outcome predictor

Despite the prevalent use of recombinant human erythropoietin (rhEPO), anemia is a frequent finding in hemodialysis patients. The goal of this study was to evaluate the impact of anemia on patient survival and characterize the determinants of hematopoiesis that may be amenable to therapeutic manipulation to enhance rhEPO responsiveness and reduce death risk. Patient characteristics and laboratory data were collected for 21,899 patients receiving hemodialysis three times per week in dialysis centers throughout the United States in 1993. Hemoglobin concentrations (Hb) < or =80 g/L were associated with a twofold increase in the odds of death (odds ratio = 2.01; P = 0.001) when compared with Hb 100 to 110 g/L. No improvement in the odds of death was afforded for Hb >110 g/L. Using multiple linear regression, variables of rhEPO administration (rhEPO dose and percentage of treatments that rhEPO was administered), variables of iron status (serum iron, transferrin saturation, and ferritin), variables of nutritional status (serum albumin and creatinine concentration), and the dose of dialysis (urea reduction ratio) were found to be significantly associated with hemoglobin concentration (P < 0.001). Age, race, and gender were also found to be significantly associated with hemoglobin concentrations (P < 0.001). From this report, the following conclusions may be made. (1) Anemia may be predictive of an increased risk of mortality in some hemodialysis patients. (2) Hemoglobin concentrations > 110 g/L are not associated with further improvements in the odds of death. (3) Laboratory surrogates of iron stores, nutritional status, and the delivered dose of dialysis are predictive of hemoglobin concentration. Whether manipulation of the factors that improve anemia will also enhance the survival of patients on hemodialysis is unknown and should be evaluated by prospective, interventional studies.

Development of a population-specific regression equation to estimate total body water in hemodialysis patients

We have previously shown that the impedance index (height corrected resistance) is a valid and reliable correlate of total body water (TBW) in hemodialysis patients. We estimated TBW by single frequency bioelectrical impedance analysis (BIA) in 3009 in-center hemodialysis patients, and developed an ESRD-specific TBW equation from routinely available demographic and anthropometric variables. The mean +/- SD age was 60.5 +/- 15.5 years; 47% were female, 47% African-American, and 36% diabetic. Dialysis duration was 3.8 +/- 3.7 years. Mean TBW was 40.8 +/- 9.3 kg, 56 +/- 9% of body weight. A stepwise linear regression equation was fit on a two-thirds random sample, deriving significant parameter estimates for the variables age, gender, height, weight, diabetic status, weight squared, and the cross-products of age and gender, age and weight, gender and weight, and height and weight. The equation was then validated in the remaining one-third sample, and compared with TBW estimates by the Watson and Hume-Weyer formulae. TBW estimated by our equation (40.6 +/- 8.6 kg) was not significantly different from the BIA TBW (40.5 +/- 9.3 kg). In contrast, TBW estimated by the Watson (37.0 +/- 7.6 kg) and Hume-Weyer (37.9 +/- 7.7 kg) formulae underestimated TBW by a mean of 3.5 and 2.6 kg, respectively. A population-specific equation provides superior prediction of TBW in hemodialysis patients. The use of formulae developed and validated in non-uremic populations may result in underestimates of TBW in patients with ESRD, and potentially, overestimates of dialysis dose approximated by the clearance-time to TBW ratio (Kt/V).

Modeling mortality risk in hemodialysis patients using laboratory values as time-dependent covariates

Proportional hazards analyses assume that the magnitude of mortality risk for a predictor variable remains proportional over time. In a time-dependent model, the explanatory variable violates this assumption, and repeat observations are required to accommodate the change in risk that occurs over time. Using a retrospective cohort design, we tested the following laboratory values for a time-by-covariate interaction: hematocrit (HCT), serum albumin (ALB), and serum creatinine (CR). A random sample of 4,083 hemodialysis patients whose specimens were analyzed in a central laboratory over a 3-year period served as the study group. Using the baseline observation, we discovered significant probability values for the interaction terms TIME*CR (P = 0.013) and TIME*ALB (P < 0.01). The beta coefficient for TIME*HCT was not significant, indicating that the proportional hazard assumption was not violated by this covariate. Based on these results, we fitted a multivariate regression model containing two time-dependent covariates (CR and ALB) using a data structure that incorporated repeat observations of these laboratory values. Patients with high ALB levels experienced the lowest mortality risk. Similarly, serum CR levels were higher in long-term survivors. This analysis verifies the clinical importance of monitoring ALB and CR levels over time and the hazard of using a single laboratory observation to make long-term projections. Additionally, the predictive values of the time-dependent covariates ALB and CR affirm the significance of nutritional approaches directed toward maintaining visceral and somatic protein content throughout renal replacement therapy.

Thoughts about judging dialysis treatment: mathematics and measurements, mirrors in the mind

This article considers the contributions of the urea kinetic parameters, , Kt/V and nPCR, to beliefs about judging dialysis treatment. The values calculated from any set of data depend on the model (eg, 1 pool, 2 pool, or so forth) and the mathematics used to derive the values. Yet, the medical community debates the value of Kt/V at which patients should be treated even as they debate the mathematics by which Kt/V should be calculated. The resulting ambiguities about proper targets and methods may actually frustrate large-scale clinical quality enhancement initiatives. The casual use of mathematical models can mislead unwary clinicians and compromise quality enhancement. For example, the observation that a high Kt/V is associated with a high nPCR leads to the widespread belief that improving Kt/V must substantially improve nutritional status. The association, however, results mainly, if not solely, from mathematical coupling rather than biological cause and effect. The misguided belief could contribute to ineffective treatment of malnourished patients. Complicated mathematical models are useful tools for describing and evaluating evolving concepts about the physical properties of dialysis and for estimating the effects of new therapies. However, the changing nature of concepts, and therefore the mathematical models designed to support them, makes clinical care ideas that attempt to shoehorn old concepts into new equations. It is the result of the dialysis treatment, not the mathematical path by which it is achieved, that is associated with improved patient health. Consequently, clinical care should be guided by simple measurements that reflect the outcome of the treatment, not by mathematical parameters.

Nutritional assessment with bioelectrical impedance analysis in maintenance hemodialysis patients

Protein energy malnutrition is common among persons with ESRD and contributes substantially to morbidity and mortality. The usual methods of nutritional assessment, such as anthropometry, can be misleading because of altered tissue hydration. Bioelectrical impedance analysis (BIA) has been recommended by some as a practical nutritional assessment tool but has not been validated in patients with ESRD. Thirty-three stable patients on maintenance hemodialysis were evaluated in an ambulatory clinical research center with simultaneous BIA, dual-energy x-ray absorptiometry, and deuterium oxide (D2O) and sodium bromide (NaBr) isotope dilution studies. Standard determinations of total body water (TBW) and body cell mass (BCM) were obtained and compared with values estimated by BIA. Two separate outpatient BIA measurements were also obtained approximately 2 wk before and after the clinical research center evaluation. BCM estimated by BIA was directly correlated (r = 0.92, P < 0.0001) with BCM determined by DEXA and NaBr. TBW estimated by BIA was directly correlated (r = 0.96, P < 0.0001) with TBW determined by deuterium oxide dilution. The reactance to resistance ratio (Xc/R) derived from BIA was inversely correlated (r = -0.73, P < 0.0001) with the extracellular water/TBW ratio determined by NaBr/D2O. Bland-Altman analyses showed that for TBW, BIA was in excellent agreement with D2O dilution. BCM was modestly underestimated by BIA compared with the dual-energy x-ray absorptiometry/NaBr standard and was adjusted by linear regression. The coefficients of variation on repeated BIA measurements were below 4%, demonstrating test-retest reliability. BIA is a valid and reliable method of nutritional assessment in maintenance hemodialysis patients.

Death risk predictors among peritoneal dialysis and hemodialysis patients: a preliminary comparison

Variables associated with survival among 1,522 peritoneal dialysis patients and 16,404 hemodialysis patients who received treatment during 1992 were evaluated. Analysis was performed separately for the treatment types and for the combined patient group. In general, the associates of survival appear similar among patients receiving peritoneal or hemodialysis. Important variables appear related to nutrition, acid-base status (which is related to nutrition), and age.

The association of intradialytic parenteral nutrition administration with survival in hemodialysis patients

Hemodialysis patients who had received intradialytic parenteral nutrition (IDPN) during 1991 were identified. These patients were compared with unexposed controls after adjusting for demographic variables, baseline renal diagnosis, diabetic status, serum albumin (ALB), creatinine (CRE), and urea reduction ratio. At lower levels of ALB (< or = 3.4 g/dL), treatment with IDPN was associated with a reduction in the odds of death at 1 year, an effect that became stronger at lower levels of CRE (< or = 8.0 mg/dL). In contrast, treatment with IDPN in patients with normal ALB was associated with increased mortality. Time trend analyses of ALB and CRE demonstrated progressive increases toward pretreatment levels in IDPN recipients that were not evident in control subjects. These time trend data suggest that in undernourished hemodialysis patients, IDPN can effect the serum levels of valid biochemical surrogates of visceral and somatic protein nutrition. Albeit retrospective, the improvement in survival at year's end among patients with ALB < or = 3.4 g/dL suggests that malnutrition and its attendant ill effects in hemodialysis patients may respond to aggressive therapeutic intervention, such as IDPN. These important findings should be prospectively confirmed in a randomized clinical trial.

Chronic dialysis treatment: clinical outcome and related processes of care

The selection of primary clinical outcome by which to evaluate the success of a therapy is discussed. Outcome should be relevant to the treatment, important to the patient and to the public health, and easy to measure with little associated variance. The odds of death is chosen as the primary outcome by which to evaluate chronic dialysis treatment because the purpose of dialysis is to preserve life. The odds of death is then correlated with the processes of care, which themselves may be measurable and therefore viewed as outcome of other processes. A general model for outcome research using existing data and for evaluating the relationships among processes and outcome is discussed using a large patient cohort analysis as an example. The analysis suggests that two dimensions of the care process account for most of the explainable death odds difference among patients: a dialysis intensity-related dimension and a nutrition-related dimension. Experience has suggested that knowledge of these principles combined with simple measurements has, over time, led dialysis professionals to increase the intensity of the dialysis treatment they deliver. That was not the case for the nutrition-related dimension. We speculate that these professionals understand, from prior knowledge, how to control dialysis intensity but do not possess similar knowledge about nutritional therapeutics for dialysis patients. Therefore, a better understanding of nutritional therapeutics will be required to achieve maximum reduction of mortality rates.

Survival of hemodialysis patients in the United States is improved with a greater quantity of dialysis

The mortality rate for hemodialysis patients in the United States is higher than in other industrialized countries. Some attribute this to insufficient quantities of prescribed and delivered dialysis. A multicenter study in Dallas dialysis centers (Dallas Nephrology Associates) was begun in 1989 to assess the impact of increasing the delivered quantity of dialysis on mortality in subsequent years. Dialysis dose was measured by urea kinetic modeling. Kt/V, reflecting the fractional volume of body water clearance of urea during a dialysis treatment, was purposefully increased from 1.18 starting in 1989 to 1.46 in 1992. Additionally, the dialysis dose measured by the urea reduction ratio, the fractional reduction of blood urea nitrogen concentration caused by a dialysis treatment, increased from 63.0% to 69.6% between 1990 and 1992. Outcome analytical methods included both crude and standardized mortality rates and mortality ratios standardized to large end-stage renal disease databases at the United States Renal Data System and at National Medical Care, Inc. Crude mortality rates at Dallas Nephrology Associates decreased from 22.5% in 1989 to 18.1% in 1992. In comparison, between 1990 and 1992 the urea reduction ration in National Medical Care facilities increased from 57.1% to 62.5%. During that time crude mortality rates decreased from 21.8% to 19.5%. Crude mortality in the United States remained essentially unchanged in the same time period. By 1992, Dallas Nephrology Associates and National Medical Care had standardized mortality ratios of 0.77 and 0.74, respectively, compared with the US dialysis population, indicating almost 30% fewer observed deaths than expected. Monitoring dialysis dose by urea kinetic modeling or urea reduction ratio are equally effective in predicting improvement in patient survival. Improved survival is possible in the US end-stage renal disease program with greater amounts of dialysis. This strategy can save an estimated 8,000 to 16,000 lives per year.

The urea reduction ratio and serum albumin concentration as predictors of mortality in patients undergoing hemodialysis

BACKGROUND

Among patients with end-stage renal disease who are treated with hemodialysis, solute clearance during dialysis and nutritional adequacy are determinants of mortality. We determined the effects of reductions in blood urea nitrogen concentrations during dialysis and changes in serum albumin concentrations, as an indicator of nutritional status, on mortality in a large group of patients treated with hemodialysis.

METHODS

We analyzed retrospectively the demographic characteristics, mortality rate, duration of hemodialysis, serum albumin concentration, and urea reduction ratio (defined as the percent reduction in blood urea nitrogen concentration during a single dialysis treatment) in 13,473 patients treated from October 1, 1990, through March 31, 1991. The risk of death was determined as a function of the urea reduction ratio and serum albumin concentration.

RESULTS

As compared with patients with urea reduction ratios of 65 to 69 percent, patients with values below 60 percent had a higher risk of death during follow-up (odds ratio, 1.28 for urea reduction ratios of 55 to 59 percent and 1.39 for ratios below 55 percent). Fifty-five percent of the patients had urea reduction ratios below 60 percent. The duration of dialysis was not predictive of mortality. The serum albumin concentration was a more powerful (21 times greater) predictor of death than the urea reduction ratio, and 60 percent of the patients had serum albumin concentrations predictive of an increased risk of death (values below 4.0 g per deciliter). The odds ratio for death was 1.48 for serum albumin concentrations of 3.5 to 3.9 g per deciliter and 3.13 for concentrations of 3.0 to 3.4 g per deciliter. Diabetic patients had lower serum albumin concentrations and urea reduction ratios than nondiabetic patients.

CONCLUSIONS

Low urea reduction ratios during dialysis are associated with increased odds ratios for death. These risks are worsened by inadequate nutrition.

Race and diabetes as death risk predictors in hemodialysis patients

Case mix and laboratory predictors of death risk were evaluated in 17,185 hemodialysis patients. The laboratory variables most closely associated with the increased death risk borne by diabetic patients (relative to non-diabetics) and White patients (relative to non-Whites) were identified. The analyses of laboratory death risk predictors were similar to those previously reported. Serum albumin concentration is the most powerful death risk predictor among all of the variables, both case mix and laboratory. Statistical models including only case mix variables reveal both race (RRWhites = 1.42) and diabetes (RRdiabetes = 1.43) as significant predictors. Adding creatinine, albumin, and BUN concentrations to the model eliminated diabetes as a significant predictor. Creatinine and albumin accounted for most of the change. Adding only creatinine eliminated race. The data suggest that reduced visceral and somatic protein mass and/or metabolism may be important determinants of mortality in dialysis patients. Because differences in the concentrations of creatinine and albumin explain much of the risk associated with being White or diabetic, differences in nutritional status may explain the reduced survival observed in those groups. Therefore, clinicians should not simply accept without question the notion that diabetics and Whites are doomed to inferior survival.

Increased serum aluminum. An independent risk factor for mortality in patients undergoing long-term hemodialysis

The annual mortality rate among patients receiving long-term hemodialysis has been rising over the past decade. The prevalences of known risk factors such as older age, male sex, duration of dialysis, presence of diabetes, coronary artery disease, or hypertension do not seem to have changed during this time. However, evidence suggests that an increased body aluminum level may have an adverse effect on survival even in the absence of overt aluminum toxic reaction. Therefore, we evaluated the correlation between serum aluminum levels and mortality in 10 646 patients undergoing long-term hemodialysis. Mortalities were 18% higher for patients with serum aluminum levels between 1520 and 2220 nmol/L and progressively increased to 60% higher for patients with aluminum levels above 7410 nmol/L. Serum aluminum level was an important predictor of survival even after other known risk factors had been controlled. These data strongly suggest that patients undergoing long-term hemodialysis should have periodic surveillance of the serum aluminum levels, and in those patients who have plasma levels of 1520 to 2220 nmol/L or higher, one should seriously consider discontinuing aluminum salts and giving therapy to decrease body aluminum level if it is found to be increased.

Death risk in hemodialysis patients: the predictive value of commonly measured variables and an evaluation of death rate differences between facilities

Logistic regression analysis was applied to a sample of more than 12,000 hemodialysis patients to evaluate the association of various patient descriptors, treatment time (hours/treatment), and various laboratory tests with the probability of death. Advancing age, white race, and diabetes were all associated with a significantly increased risk of death. Short dialysis times were also associated with high death risk before adjustment for the value of laboratory tests. Of the laboratory variables, low serum albumin less than 40 g/L (less than 4.0 g/dL) was most highly associated with death probability. About two thirds of patients had low albumin. These findings suggest that inadequate nutrition may be an important contributing factor to the mortality suffered by hemodialysis patients. The relative risk profiles for other laboratory tests are presented. Among these, low serum creatinine, not high, was associated with high death risk. Both serum albumin concentration and creatinine were directly correlated with treatment time so that high values for both substances were associated with long treatment times. The data suggest that physicians may select patients with high creatinine for more intense dialysis exposure and patients with low creatinine for less intense treatment. In a separate analysis, observed death rates were compared with rates expected on the basis of case mix for these 237 facilities. The data suggest substantial volatility of observed/expected ratios when facility size is small. Nonetheless, a minority of facilities (less than or equal to 2%) may have higher rates than expected when compared with the pool of all patients in this sample. The effect of various laboratory variables on mortality is substantial, while relatively few facilities have observed death rates that exceed their expected values. Therefore, we suggest that strategies designed to improve the overall mortality statistic for dialysis patients in the United States would be better directed toward improving the quality of care for all patients, particularly high-risk patients, within their usual treatment settings rather than trying to identify facilities with high death rate for possible regulatory intervention.

Death risk in hemodialysis patients: the predictive value of commonly measured variables and an evaluation of death rate differences between facilities

Logistic regression analysis was applied to a sample of more than 12,000 hemodialysis patients to evaluate the association of various patient descriptors, treatment time (hours/treatment), and various laboratory tests with the probability of death. Advancing age, white race, and diabetes were all associated with a significantly increased risk of death. Short dialysis times were also associated with high death risk before adjustment for the value of laboratory tests. Of the laboratory variables, low serum albumin less than 40 g/L (less than 4.0 g/dL) was most highly associated with death probability. About two thirds of patients had low albumin. These findings suggest that inadequate nutrition may be an important contributing factor to the mortality suffered by hemodialysis patients. The relative risk profiles for other laboratory tests are presented. Among these, low serum creatinine, not high, was associated with high death risk. Both serum albumin concentration and creatinine were directly correlated with treatment time so that high values for both substances were associated with long treatment times. The data suggest that physicians may select patients with high creatinine for more intense dialysis exposure and patients with low creatinine for less intense treatment. In a separate analysis, observed death rates were compared with rates expected on the basis of case mix for these 237 facilities. The data suggest substantial volatility of observed/expected ratios when facility size is small. Nonetheless, a minority of facilities (less than or equal to 2%) may have higher rates than expected when compared with the pool of all patients in this sample. The effect of various laboratory variables on mortality is substantial, while relatively few facilities have observed death rates that exceed their expected values. Therefore, we suggest that strategies designed to improve the overall mortality statistic for dialysis patients in the United States would be better directed toward improving the quality of care for all patients, particularly high-risk patients, within their usual treatment settings rather than trying to identify facilities with high death rate for possible regulatory intervention.

Formaldehyde kinetics and bacteriology in dialyzers

The kinetics of formaldehyde washout in new and reused dialyzers with 2% (w/v) and 4% formaldehyde solution was studied. Using a standard method of rinsing, the concentration of formaldehyde decreases exponentially, but the rate of decrease and the steady-state level depends on the type of dialyzer. The residual quantity of formaldehyde using a 4% solution is more than twice that seen with a 2% solution in similar dialyzers. Bacteriological tests on water-adapted, formaldehyde-resistant organisms indicate that a significant proportion of these organisms can survive a 4-hr incubation with 4% formaldehyde at 20 degrees C. However, increasing the temperature of incubation to 40 degrees C or the addition of ethanol up to 8% (v/v) improved the bacteriological efficacy of formaldehyde. Under these conditions, a 1% formaldehyde solution allows eradication of all organisms tested. Similar results were observed in multiple-use dialyzers inoculated with the same organisms. There was no effect of incubation at 40 degrees C on the in vitro clearance determinations of new and reused dialyzers.

The quality of life of patients with end-stage renal disease

We assessed the quality of life of 859 patients undergoing dialysis or transplantation, with the goal of ascertaining whether objective and subjective measures of the quality of life were influenced by case mix or treatment. We found that 79.1 per cent of the transplant recipients were able to function at nearly normal levels, as compared with between 47.5 and 59.1 per cent of the patients treated with dialysis (depending on the type). Nearly 75 per cent of the transplant recipients were able to work, as compared with between 24.7 and 59.3 per cent of the patients undergoing dialysis. On three subjective measures (life satisfaction, well-being, and psychological affect) transplant recipients had a higher quality of life than patients on dialysis. Among the patients treated with dialysis, those undergoing treatment at home had the highest quality of life. All quality-of-life differences were found to persist even after the patient case mix had been controlled statistically. Finally, the quality of life of transplant recipients compared well with that of the general population, but despite favorable subjective assessments, patients undergoing dialysis did not work or function at the same level as people in the general population.

Which mathematical model to study uremic toxicity? National Cooperative Dialysis Study

Mathematical modelling advantages and limitations to study dialysis adequacy are evaluated, the use of the single pool urea model in the guidance of the National Cooperative Dialysis Study (NCDS) is described, and therapeutic control results from the Control phase of the NCDS are reported. The relevance of using urea as a target compound and the practicality of modelling its levels in clinical settings using a single pool model are discussed. The NCDS involves intensive participation of 8 geographically separate centers to control BUN at two weekly time averaged concentrations (50 +/- 5 and 100 +/- 5 mg/dl) using standard clinical dialyzers and two different lengths of dialysis (3 and 4.5 hr) in the presence of .8-1.4 g/kg/day protein intake. Control phase data on 195 patients indicates a remarkable level of clinical precision and method reproducibility as well as a high degree of patient compliance. Patient urea volumes averaged 39.8 +/- 8.9 liters, net rates of daily protein catabolism were 1.06 +/- .17 g/kg; daily weight gain: .96 +/0 .43 kg; and dialyzer clearances to maintain patients in the control phase for 3 to 6 months were 168 +/- 44 ml/min. Clearances required to randomize patients into four experimental groups ranged 40-250 ml/min. Less than 1/4 of dialyzers were larger than 1.8 m2 and were not specific to any experimental group.