Association of achieved dialysis dose with mortality in the hemodialysis study: an example of "dose-targeting bias"

Effects of Kt/Vurea on outcomes according to age in patients on maintenance hemodialysis

Background

The guidelines recommended target and minimum single-pool Kt/Vurea are 1.4 and 1.2, respectively, in hemodialysis patients. However, the optimal hemodialysis dose remains controversial. We investigated the effects of Kt/Vurea on patient outcomes according to age, with a focus on older patients.

Methods

This study used the hemodialysis quality assessment program and claims datasets. Patients were divided into four subgroups according to age (<65, 65-74, 75-84, and ≥85 years). Each group was divided into three subgroups according to Kt/Vurea : reference (ref) (1.2 ≤ Kt/Vurea ≤ 1.4), low (< 1.2), and high (> 1.4).

Results

The low, ref, and high Kt/Vurea groups included 1668, 8156, and 16 546 (< 65 years); 474, 3058, and 7646 (65-74 years); 225, 1362, and 4194 (75-84 years); and 14, 126, and 455 (≥85 years) patients, respectively. The low Kt/Vurea group had higher mortality rates than the ref Kt/Vurea group irrespective of age [adjusted hazard ratio (aHR), 95% confidence interval (CI): 1.23, 1.11-1.36; 1.14, 1.00-1.30; 1.28, 1.09-1.52; and 2.10, 1.16-3.98, in patients aged <65, 65-74, 75-84, and ≥85 years, respectively]. The high Kt/Vurea group had lower mortality rates than the ref Kt/Vurea group in patients aged <65 and 65-74 years (aHR, 95% Cl: 0.87, 0.82-0.92 and 0.93, 0.87-0.99 in patients aged <65 and 65-74 years, respectively).

Conclusions

These results support the current recommendations of a minimum Kt/Vurea of 1.2 even in patients age ≥85 years. In young patients, Kt/Vurea above the recommended threshold can be beneficial for survival.

Hemodiafiltration: a synergy yet to be convincing

The desperate attempt to improve mortality, morbidity, quality of life and patient-reported outcomes in patients on hemodialysis has led to multiple attempts to improve the different modes, frequencies, and durations of dialysis sessions in the last few decades. Nothing has been more appealing than the combination of diffusion and convection in the form of hemodiafiltration. Despite the concrete evidence of better clearance of middle weight molecules and better hemodynamic stability, tangible evidence to support the universal adoption is still at a distance. Survival benefits seen in selected groups who are likely to tolerate hemodiafiltration with better vascular access and with lower comorbid burden, need to be extended to real life dialysis patients who are older than the population studied and have significantly higher comorbid burden. Technical demands of initiation hemodiafiltration, the associated costs, and the incremental benefits targeted, along with patient-reported outcomes, need to be explored further before recommending hemodiafiltration as the mode of choice.

Can the response to dialysis treatment be predicted by using patient-specific modeling of fluid and solute exchanges? A multicentric evaluation

BACKGROUND

Parametric multipool kinetic models were used to describe the intradialytic trends of electrolytes, breakdown products, and body fluids volumes during hemodialysis. Therapy customization can be achieved by the identification of parameters, allowing patient-specific modulation of mass and fluid balance across dialyzer, capillary, and cell membranes. This study wants to evaluate the possibility to use this approach to predict the patient's intradialytic response.

METHODS

6 sessions of 68 patients (DialysIS© project) were considered. Data from the first three sessions were used to train the model, identifying the patient-specific parameters, that, together with the treatment settings and the patient's data at the session start, could be used for predicting the patient's specific time course of solutes and fluids along the sessions. Na+ , K+ , Cl- , Ca2+ , HCO3 - , and urea plasmatic concentrations and hematic volume deviations from clinical data were evaluated.

RESULTS

nRMSE predictive error is on average equal to 4.76% when describing the training sessions, and only increases by 0.97 percentage points on average in independent sessions of the same patient.

CONCLUSIONS

The proposed predictive approach represents a first step in the development of tools to support the clinician in tailoring the patient's prescription.

Clinical performance, intermediate and long-term outcomes of high-volume hemodiafiltration in patients with kidney failure

Hemodiafiltration (HDF), in which both convective and diffusion methods are combined, yields an increased overall solute clearance compared with hemodialysis (HD), specifically for medium and larger molecular weight uremic toxins. Due to uncertainty in the treatment effects, the nephrology community still perceives the implementation of HDF and the achievement of high convective volume as complex. In this article, we review practical aspects of the implementation of HDF that can effectively deliver a high-volume HDF therapy and assure clinical performance to most patients. We also present an overview of the impact of high-volume HDF (compared to HD) on a series of relevant biochemical, patient-reported, and clinical outcomes, including uremic toxin removal, phosphate, Inflammation and oxidative stress, hemodynamic stability, cardiac outcomes, nutritional effects, health-related quality of life, morbidity, and mortality.

Toward an individualized determination of dialysis adequacy: a narrative review with special emphasis on incremental hemodialysis

INTRODUCTION

The search for the 'perfect' renal replacement therapy has been paralleled by the search for the perfect biomarkers for assessing dialysis adequacy. Three main families of markers have been assessed: small molecules (prototype: urea); middle molecules (prototype β2-microglobulin); comprehensive and nutritional markers (prototype of the simplified assessment, albumin levels; composite indexes as malnutrition-inflammation score). After an era of standardization of dialysis treatment, personalized dialysis schedules are increasingly proposed, challenging the dogma of thrice-weekly hemodialysis.

AREAS COVERED

In this review, we describe the advantages and limitations of the approaches mentioned above, focusing on the open questions regarding personalized schedules and incremental hemodialysis.

EXPERT OPINION

In the era of personalized dialysis, the assessment of dialysis adequacy should be likewise personalized, due to the limits of 'one size fits all' approaches. We have tried to summarize some of the relevant issues regarding the determination of dialysis adequacy, attempting to adapt them to an elderly, highly comorbidity population, which would probably benefit from tailor-made dialysis prescriptions. While no single biomarker allows precisely tailoring the dialysis dose, we suggest using a combination of clinical and biological markers to prescribe dialysis according to comorbidity, life expectancy, residual kidney function, and small and medium-size molecule depuration.

A swan song for Kt/Vurea

Dialyzer clearance of urea multiplied by dialysis time and normalized for urea distribution volume (Kt/V_urea or simply Kt/V) has been used as an index of dialysis adequacy since more than 30 years. This article reviews the flaws of Kt/V, starting with a lack of proof of concept in three randomized controlled hard outcome trials (RCTs), and continuing with a long list of conditions where the concept of Kt/V was shown to be flawed. This information leaves little room for any conclusion other than that Kt/V, as an indicator of dialysis adequacy, is obsolete. The dialysis patient might benefit more if, instead, the nephrology community concentrates in the future on pursuing the optimal dialysis dose that conforms with adequate quality of life and on factors that are likely to affect outcomes more than Kt/V. These include residual renal function, volume status, dialysis length, ultrafiltration rate, the number of intra-dialytic hypotensive episodes, interdialytic blood pressure, serum potassium and phosphate, serum albumin, and C reactive protein.

Would prescribing target Kt dose adjusted for body surface area improve hemodialysis outcomes?

The use of Kt/V to prescribe and monitor hemodialysis adequacy remains the current standard, although it is increasingly questioned. Alternative proposals for dose prescription and monitoring have been advocated. In a noninterventional, prospective study reported in this issue, Maduell et al., utilizing online ionic dialysance, explore the association between outcome measures (mortality and hospitalization rates) and the extent to which delivered Kt dose achieved minimal target Kt doses calculated from individual estimates of body surface area.

Reporting of "dialysis adequacy" as an outcome in randomised trials conducted in adults on haemodialysis

Background

Clinical trials are most informative for evidence-based decision-making when they consistently measure and report outcomes of relevance to stakeholders, especially patients, clinicians, and policy makers. However, sometimes terminology used is interpreted differently by different stakeholders, which might lead to confusion during shared decision making. The construct dialysis adequacy is frequently used, suggesting it is an important outcome both for health care professionals as for patients.

Objective

To assess the scope and consistency of the construct dialysis adequacy as reported in randomised controlled trials in hemodialysis, and evaluate whether these align to the insights and understanding of this construct by patients.

Methods

To assess scope and consistency of dialysis adequacy by professionals, we performed a systematic review searching the Cochrane Central Register of Controlled Trials (CENTRAL) up to July 2017. We identified all randomised controlled trails (RCT) including patients on hemodialysis and reporting dialysis adequacy, adequacy or adequacy of dialysis and extracted and classified all reported outcomes. To explore interpretation and meaning of the construct of adequacy by patients, we conducted 11 semi-structured interviews with HD patients using thematic analysis. Belgian registration number B670201731001.

Findings

From the 31 included trials, we extracted and classified 98 outcome measures defined by the authors as adequacy of dialysis, of which 94 (95%) were biochemical, 3 (3%) non-biochemical surrogate and 2 (2%) patient-relevant. The three most commonly reported measures were all biochemical. None of the studies defined adequacy of dialysis as a patient relevant outcome such as survival or quality of life. Patients had a substantially different understanding of the construct dialysis adequacy than the biochemical interpretation reported in the literature. Being alive, time spent while being on dialysis, fatigue and friendliness of staff were the most prominent themes that patients linked to the construct of dialysis adequacy.

Conclusion

Adequacy of dialysis as reported in the literature refers to biochemical outcome measures, most of which are not related with patient relevant outcomes. For patients, adequate dialysis is a dialysis that enables them to spend as much quality time in their life as possible.

Unlike Kt, high Kt/V is associated with greater mortality: The importance of low V

INTRODUCTION

Kt/V has been used as a synonym for haemodialysis dose. Patient survival improved with a Kt/V>1; this target was subsequently increased to 1.2 and 1.3. The HEMO study revealed no significant relationship between Kt/V and mortality. The relationship between Kt/V and mortality often shows a J-shaped curve. Is V the confounding factor in this relationship? The objective of this study is to determine the relationship between mortality and Kt/V, Kt and body water content (V) and lean mass (bioimpedance).

METHODS

We studied a cohort of 127 prevalent haemodialysis patients, who we followed-up for an average of 36 months. Kt was determined by ionic dialysance, and V and nutrition parameters by bioimpedance. Kt/V, Kt corrected for body surface area (Kt/BSA) and target Kt/BSA were calculated. The mean data from 18,998 sessions were used as haemodialysis parameters, with a mean of 155 sessions per patient.

RESULTS

Mean age was 70.4±15.3 years and 61% were male; 76 were dialysed via an arteriovenous fistula and 65 were on online haemodiafiltration. Weight was 70.6 (16.8)kg; BSA 1.8 (0.25) m²; total body water (V) 32.2 (7.41) l and lean mass index (LMI) 11.1 (2.7)kg/m². Mean Kt/V was 1.84 (0.44); Kt 56.1 (7)l and Kt/BSA 52.8 (10.4)l. The mean target Kt/BSA was 49.7 (4.5)l. Mean Kt/BSA-target Kt/BSA +6.4 (7.0)l. Patients with a higher Kt/V had worse survival rates than others; with Kt this is not the case. Higher Kt/V values are due to a lower V, with poorer nutrition parameters. LMI and serum albumin were the parameters that best independently predicted the risk of death and are lower in patients with a higher Kt/V and lower V.

CONCLUSION

Kt/V is not useful for determining dialysis doses in patients with low or reduced body water. Kt or the Kt/BSA are proposed as an alternative.

Weekly Standard Kt/Vurea and Clinical Outcomes in Home and In-Center Hemodialysis

BACKGROUND AND OBJECTIVES

Patients undergoing hemodialysis with a frequency other than thrice weekly are not included in current clinical performance metrics for dialysis adequacy. The weekly standard Kt/Vurea incorporates treatment frequency, but there are limited data on its association with clinical outcomes.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We used multivariable regression to examine the association of dialysis standard Kt/Vurea with BP and metabolic control (serum potassium, calcium, bicarbonate, and phosphorus) in patients incidental to dialysis treated with home (n=2373) or in-center hemodialysis (n=109,273). We further used Cox survival models to examine the association of dialysis standard Kt/Vurea with mortality, hospitalization, and among patients on home hemodialysis, transfer to in-center hemodialysis.

RESULTS

After adjustment for potential confounders, patients with dialysis standard Kt/Vurea <2.1 had higher BPs compared with patients with standard Kt/Vurea 2.1 to <2.3 (3.4 mm Hg higher [P<0.001] for home hemodialysis and 0.9 mm Hg higher [P<0.001] for in-center hemodialysis). There were no clinically meaningful associations between dialysis standard Kt/Vurea and markers of metabolic control, irrespective of dialysis modality. There was no association between dialysis standard Kt/Vurea and risk for mortality, hospitalization, or transfer to in-center hemodialysis among patients undergoing home hemodialysis. Among patients on in-center hemodialysis, dialysis standard Kt/Vurea <2.1 was associated with higher risk (adjusted hazard ratio, 1.11; 95% confidence interval, 1.07 to 1.14) and standard Kt/Vurea ≥2.3 was associated with lower risk (adjusted hazard ratio, 0.97; 95% confidence interval, 0.94 to 0.99) for death compared with standard Kt/Vurea 2.1 to <2.3. Additional analyses limited to patients with available data on residual kidney function showed similar relationships of dialysis and total (dialysis plus kidney) standard Kt/Vurea with outcomes.

CONCLUSIONS

Current targets for standard Kt/Vurea have limited utility in identifying individuals at increased risk for adverse clinical outcomes for those undergoing home hemodialysis but may enhance risk stratification for in-center hemodialysis.

Impact of intradialytic exercise intensity on urea clearance in hemodialysis patients

Intradialytic exercise (IDE) has been shown to benefit dialysis efficacy; however, the effect of IDE intensity is unknown. Dialyzer urea clearance (K urea, mL/min) was significantly greater during both IDE protocols (55% and 70% maximal heart rate, HRmax), compared with no IDE (p < 0.05). No significant difference in K urea was found between IDE protocols (55% vs. 70% HRmax) (p > 0.05). Results show that higher intensity IDE has no additional benefit on K urea.

Hemodialysis Treatment Time: As Important as it Seems?

Hemodialysis treatment time and Kt/V can both be considered to be primary measures of hemodialysis adequacy, because when either goes to zero, mortality is certain in patients without residual kidney function. Treatment time is important, but it needs to be adjusted based on surface-area-normalized Kt/V, residual kidney function, and expected ultrafiltration rate. Rescaling dose of dialysis measured as Kt/V to body surface area prevents ultrashort dialysis in small patients, women, and children with minimal residual kidney function. Most if not all of the observational studies of associations between outcome and dialysis session length are probably confounded by dose targeting bias. Once adequate Kt/V (taking into account body surface area) has been provided, adequate dialysis time probably is most relevant in terms of limiting the need for a high fluid removal rate. The latter may adversely impact survival by causing recurrent ischemia to cardiovascular and other tissues. There is little high-quality evidence at this time to support a minimum 4-hour treatment time for all patients, regardless of body size, solute removal, or residual kidney function. On the other hand, there is little evidence that prolonging weekly treatment time up to 24 hours per week is harmful. The final decision regarding treatment time is best individualized, based on patient acceptability and experience, residual kidney function, body surface-area-normalized Kt/V, and expected ultrafiltration rate.

Test of the recommended dialysis dose on one-year mortality of nondiabetic maintenance hemodialysis patients; observations from a single dialysis unit

BACKGROUND

The optimal delivered dialysis dose has been of a great interest for the last three decades, though a clear cut point has not been reached yet. We aimed to evaluate the relationship between one-year mortality and the delivered dialysis dose, which was recommended by Kidney Disease Outcomes Quality Initiative (KDOQI), in our maintenance hemodialysis (MHD) patients.

METHODS

This was a single center, prospective observational study with one year of follow-up. Patients with extremes of age, BMI, residual renal function, diabetes mellitus, severe infection malignancy, and recent hospitalization within the last three months were excluded. Demographic, anthropometric, laboratory, and outcome data (mortality as the primary) were prospectively collected. Patients were classified into two groups according to baseline spKt/V levels; group 1 (n = 20): spKt/V ≤ 1.4, group 2 (n = 60): spKt/V > 1.4.

RESULTS

Median (IQR) age and hemodialysis vintage of all patients (M/F: 41/39) were 49.5 (29) years and 60 (94) months, respectively. Both groups had similar characteristics, with the exception of significantly higher BMI (24 vs. 21.7, p = 0.012), serum creatinine and uric acids, and lower spKt/V (1.30 vs. 1.71, p < 0.001) in group 1. Overall death occurred in seven (8.75%) patients (5 from group 1 and 2 from group 2). Patients in group 1 had significantly higher one-year mortality rate and shorter survival time (25% vs. 3.3%, p = 0.003 and 43.9 vs. 47.3 weeks, p = 0.003, respectively).

CONCLUSIONS

Higher spKt/V (>1.4) was associated with a lower one-year mortality in this small cohort of patients.

Antidepressants for treating depression in adults with end-stage kidney disease treated with dialysis

BACKGROUND

Depression affects approximately one-quarter of people treated with dialysis and is considered an important research uncertainty by patients and health professionals. Treatment for depression in dialysis patients may have different benefits and harms compared to the general population due to different clearances of antidepressant medication and the severity of somatic symptoms associated with end-stage kidney disease (ESKD). Guidelines suggest treatment of depression in dialysis patients with pharmacological therapy, preferably a selective serotonin reuptake inhibitor. This is an update of a review first published in 2005.

OBJECTIVES

To evaluate the benefit and harms of antidepressants for treating depression in adults with ESKD treated with dialysis.

SEARCH METHODS

We searched Cochrane Kidney and Transplant's Specialised Register to 20 January 2016 through contact with the Information Specialist using search terms relevant to this review.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing antidepressant treatment with placebo or no treatment, or compared to another antidepressant medication or psychological intervention in adults with ESKD (estimated glomerular filtration rate < 15 mL/min/1.73 m(2)).

DATA COLLECTION AND ANALYSIS

Data were abstracted by two authors independently onto a standard form and subsequently entered into Review Manager. Risk ratios (RR) for dichotomous data and mean differences (MD) for continuous data were calculated with 95% confidence intervals (95% CI).

MAIN RESULTS

Four studies in 170 participants compared antidepressant therapy (fluoxetine, sertraline, citalopram or escitalopram) versus placebo or psychological training for 8 to 12 weeks. In generally very low or ungradeable evidence, compared to placebo, antidepressant therapy had no evidence of benefit on quality of life, had uncertain effects on increasing the risk of hypotension (3 studies, 144 participants: RR 1.72, 95% CI 0.75 to 3.92), headache (2 studies 56 participants: RR 2.91, 95% CI 0.73 to 11.57), and sexual dysfunction (2 studies, 101 participants: RR 3.83, 95% CI 0.63 to 23.34), and increased nausea (3 studies, 114 participants: RR 2.67, 95% CI 1.26 to 5.68). There were few or no data for hospitalisation, suicide or all-cause mortality resulting in inconclusive evidence. Antidepressant therapy may reduce depression scores during treatment compared to placebo (1 study, 43 participants: MD -7.50, 95% CI -11.94 to -3.06). Antidepressant therapy was not statistically different from group psychological therapy for effects on depression scores or withdrawal from treatment and a range of other outcomes were not measured.

AUTHORS' CONCLUSIONS

Despite the high prevalence of depression in dialysis patients and the relative priority that patients place on effective treatments, evidence for antidepressant medication in the dialysis setting is sparse and data are generally inconclusive. The relative benefits and harms of antidepressant therapy in dialysis patients are poorly known and large randomised studies of antidepressants versus placebo are required.

Association of Continuous-Equivalent Urea Clearances with Death Risk in Intermittent Hemodialysis

Background. Several reports describe favorable results from frequent hemodialysis, but due to the lack of unequivocal dose measures it is not clear whether the benefits are due to more efficient toxin removal or other factors. Methods. The associations with death risk of six continuous-equivalent urea clearance measures were compared in 57 conventional in-center hemodialysis treatment periods of 51 patients, together 114 patient years. The double pool dose measures were calculated with the Solute-Solver program and separately scaled to urea distribution volume or normalized with body surface area. Results. Mortality associated significantly with equivalent renal urea clearance (EKR) scaled to urea distribution volume (V) (p=0.033) and with EKR normalized with body surface area (BSA) (p=0.044) but not with V-scaled (p=0.059) nor BSA-normalized (p=0.183) standard clearance (stdK). Women had significantly higher normalized protein catabolic rate (nPCR), EKR/V, and stdK/V than men but slightly lower BSA-normalized dose measures and lower mortality. Protein catabolic rate and dialysis dose correlated positively with each other and with survival. Conclusions. The prognostically most valid continuous-equivalent clearance in the present material was EKR/V, calculated from double pool urea generation rate, distribution volume, and time-averaged concentration.

Kt/V (and especially its modifications) remains a useful measure of hemodialysis dose

Removal of small molecular weight solutes shows a strong relationship to hemodialysis outcomes. In contrast, survival with high-flux dialysis or hemodiafiltration is only slightly better than with low-flux hemodialysis. Despite laboratory evidence regarding toxicity of protein-bound uremic solutes, few data exist showing that increased removal of this class of molecules impacts outcomes. In the FHN trials, there was no effect of frequent dialysis, including frequent and long dialysis, on nutrition or control of anemia, outcomes expected to be sensitive to uremic toxin removal; the main benefit appeared to be better volume control. Scaling of hemodialysis dose to total body water may not be optimal. Kt/V scaling to body surface area and use of a continuous measure such as standard Kt/V reduces the likelihood of underdialysis of small patients, including children, and women. Minimum hemodialysis time may best be considered in respect to ultrafiltration rate, and a maximum target ultrafiltration rate unscaled to body size may be optimal. Intensive, extended dialysis may cause adverse effects to residual kidney function, and more information needs to be collected to better understand how urine volume modifies dose requirements, and how to maximize the chances of preserving residual kidney function.

Uraemic toxins and new methods to control their accumulation: game changers for the concept of dialysis adequacy

The current concept of an adequate dialysis based only on the dialysis process itself is rather limited. We now have considerable knowledge of uraemic toxicity and improved tools for limiting uraemic toxin accumulation. It is time to make use of these. A broader concept of adequacy that focusses on uraemic toxicity is required. As discussed in the present review, adequacy could be achieved by many different methods in combination with, or instead of, dialysis. These include preservation of renal function, dietary intake, reducing uraemic toxin generation rate and intestinal absorption, isolated ultrafiltration and extracorporeal adsorption of key uraemic toxins. A better measure of the quality of dialysis treatment would quantify the uraemic state in the patient using levels of a panel of key uraemic toxins. Treatment would focus on controlling uraemic toxicity while reducing harm or inconvenience to the patient. Delivering more dialysis might not be the best way to achieve this.

Intradialytic exercise in hemodialysis patients: a systematic review and meta-analysis

BACKGROUND AND OBJECTIVE

Hemodialysis (HD) patients are more inactive, leading to poor functional capacity and quality of life; this may be reversed with intradialytic exercise training. To systematically evaluate the efficacy and safety of intradialytic exercise for HD patients, we conducted a meta-analysis of the published randomized controlled trials.

DATA SOURCES AND METHODS

Medline, Embase, and Cochrane Central Register of Controlled Trials were systematically searched up to February, 2014. The reference lists of eligible studies and relevant reviews were also checked.

RESULTS

24 studies of 997 patients were included. Compared with control, intradialytic exercise significantly improve Kt/V (SMD = 0.27, 95% CI 0.01-0.53), peak oxygen consumption (VO(2peak)) (SMD = 0.53, 95% CI 0.30-0.76), and physical performance of physical function of life (SMD = 0.30, 95% CI 0.04-0.55). However, no significant improvements were found in the mental function of life. There was no significant difference with respect to musculoskeletal and cardiovascular complications between the intradialytic exercise groups and control groups. Further subgroup analysis found that, when the trial duration was more than 6 months, the intervention had significant effects on VO(2peak) (SMD = 0.89, 95% CI 0.56-1.22). However, when the trial duration was less than 6 months, the change of VO(2peak) was not significant (SMD = 0.19, 95% CI -0.13 to 0.51).

CONCLUSION

Intradialytic exercise can improve Kt/V, VO(2peak), and the physical quality of life, and intradialytic exercise is safe for HD patients. Therefore, we put forward the suggestion that clinical guideline be updated to inform clinicians on the benefits of intradialytic exercise on HD patients.

Dialysis dosing for chronic hemodialysis: beyond Kt/V

Current views regarding hemodialysis adequacy reach beyond indices of small solute removal such as Kt/V. Nevertheless, new Kt/V-based constructs such as the standard Kt/V, which adjusts not only for dialysis frequency, but which also represents removal of sequestered solutes rather than easily removed urea, continue to be useful. The scaling of dialysis dose to measures of size other than body water results in higher recommended doses of dialysis for children, small patients, and women, compared with the current body water-based scaling approach. Aside from small solute removal, increasing weekly time on dialysis results in slower removal of fluid with better tolerance and with increased removal of phosphorus, although both salt and water and phosphorus control often respond to efforts to reduce intake. The intermediate term benefits of removing larger middle molecules such as beta-2-microglobulin appear to be modest, and the benefits of removal of protein-bound uremic toxins remain to be proved in controlled trials.

Dose of hemodialysis and survival: a marginal structural model analysis

BACKGROUND

Observational studies have consistently demonstrated the survival benefits of a greater dialysis dose in maintenance hemodialysis (MHD) patients, whereas randomized controlled trials have shown conflicting results. The possible causal impact of dialysis dose on mortality needs to be investigated using rich cohort data analyzed with novel statistical methods such as marginal structural models (MSMs) that account for time-varying confounding and exposure.

METHODS

We quantified the effect of delivered dose of hemodialysis (HD) [single-pool Kt/V (spKt/V)] on mortality risk in a contemporary cohort of 68,110 patients undergoing HD 3 times weekly (7/2001- 9/2005). We compared conventional Cox proportional hazard and MSM survival analyses, accounting for time-varying confounding by applying longitudinally modeled inverse-probability-of-dialysis-dose weights to each observation.

RESULTS

In conventional Cox models, baseline spKt/V showed a weak negative association with mortality, while higher time-averaged spKt/V was strongly associated with lower mortality risk. In MSM analyses, compared to a spKt/V range of 1.2 - <1.4, a spKt/V range of <1.2 was associated with a higher risk of mortality [HR (95% CI) 1.67 (1.54 - 1.80)], whereas mortality risks were significantly lower with higher spKt/V [HRs (95% CI): 0.74 (0.70-0.78), 0.63 (0.59-0.66), 0.56 (0.52-0.60), and 0.56 (0.52-0.61) for spKt/V ranges of 1.4 - <1.6, 1.6-<1.8, 1.8 - <2.0, and ≥2.0, respectively]. Thus, MSM analyses showed that the greatest survival advantage of a higher dialysis dose was observed for a spKt/V range of 1.8-<2.0, and the dialysis dose-mortality relationship was robust in almost all subgroups of patients.

CONCLUSIONS

Higher HD doses were robustly associated with greater survival in MSM analyses that more fully and appropriately accounted for time-varying confounding.

Physiological monitoring and control in hemodialysis: state of the art and outlook

Medical devices for monitoring and feedback control of physiological parameters of the dialysis patient were introduced in the early 1990s. They have a wide range of applications, aiming at increasing the safety and ensuring the efficiency of the treatment, and at an improved restoration of physiological conditions, leading to an overall reduction in morbidity and mortality. Such devices include sensors for the measurement of temperature, optical parameters and sound speed in blood, and electrical characteristics of the human body, and other parameters. Essential for the development of these devices is a detailed understanding of the pathophysiological background of a therapeutical problem. There is still a large potential to introduce new devices for further therapy improvement and automation. Also, the size of the hemodialysis market appears attractive; however, a new product has to meet several specific requirements in order to also become commercially successful. This review describes the therapeutic and technical principles of several available devices, reports on concepts for possible future devices, and presents a short overview on the market environment.

Dialysis frequency versus dialysis time, that is the question

We reviewed a number of prospective randomized and multiple retrospective cohort studies of different dialysis prescriptions: longer dialysis time, at a frequency of at least three times a week, or a frequency of daily hemodialysis with a shorter dialysis time. Interestingly, the retrospective analyses have generally found significant survival benefits in the intensive dialysis groups, whereas more modest effects were observed in the prospective randomized controlled trials. The reason for this discrepancy may be related to the retrospective nature of the studies and possible selection bias; for example, the patients who were prescribed more frequent dialysis may have had more difficulties with volume control or high blood pressure. In contrast, the randomized controlled trials of increased dialysis frequency, which have shown indirect and modest benefits in complex coprimary end points, have small sample sizes and are plagued with difficulties in recruitment and compliance with the randomly allocated more frequent dialysis. This review, which attempts to balance the potential benefits of more frequent dialysis with the burden on the patient's lifestyle, an increased risk of access malfunction, as well as societal costs of such intensive dialysis prescriptions, concludes in favor of the conventional three times per week dialysis (at a minimum) but at longer dialysis times than is currently prescribed based on the Kt/Vurea metric alone.

Dialysis dose and intradialytic hypotension: results from the HEMO study

BACKGROUND

Intradialytic hypotension (IDH) is common and is associated with increased morbidity and mortality in chronic hemodialysis patients. A higher dialysis 'dose' may generate transient intradialytic osmotic gradients, predisposing to intracellular fluid shifts and resulting in hypotension.

STUDY DESIGN

We performed a post hoc analysis of the HEMO study, a multicenter trial that randomized chronic hemodialysis patients to high versus standard Kt/V and higher versus lower membrane flux. In order to achieve dose targets, per protocol, adjustments were made in membrane efficiency, blood flow or dialysate flow before changing session length. Detailed hemodynamic and urea kinetic modeling data were abstracted from 1,825 individuals. The primary outcome was the occurrence of hypotensive events necessitating clinical intervention (saline infusion, lowering of ultrafiltration rate or reduced blood flow).

RESULTS

Intradialytic hypotensive events occurred more frequently in the higher-Kt/V group (18.3 vs. 16.8%; p < 0.001). Participants randomized to higher-target Kt/V had a greater adjusted risk of IDH than those randomized to standard Kt/V [odds ratio (OR) 1.12; 95% confidence interval (CI) 1.01-1.25]. Higher vs. lower dialyzer mass transfer-area coefficient for urea and rate of urea removal were associated with greater adjusted odds of IDH (OR 1.15; 95% CI 1.04-1.27 and OR 1.05; 95% CI 1.04-1.06 per mg/dl/h, respectively).

CONCLUSIONS

Higher dialysis dose, at relatively constrained treatment times, may associate with an increased risk of IDH. These findings support the possibility that rapidity of intradialytic reductions in plasma osmolality may play an important role in mediating hemodynamic instability during dialysis.

Dialysis time, survival, and dose-targeting bias

Dialysis time is increasingly being appreciated as an important measure of dialysis adequacy. Increased dialysis time leads to better control of volume excess, to reduced occurrence of intradialytic hypotension, and to better control of serum phosphorus. Nevertheless, the amount of benefit obtainable by moderate increases in dialysis time in patients following a three-times-per-week schedule has not been well established, and the analysis is confounded by associations between prescribed and/or delivered dialysis time and factors related to patient mortality.

Dialysis dose scaled to body surface area and size-adjusted, sex-specific patient mortality

BACKGROUND AND OBJECTIVES

When hemodialysis dose is scaled to body water (V), women typically receive a greater dose than men, but their survival is not better given a similar dose. This study sought to determine whether rescaling dose to body surface area (SA) might reveal different associations among dose, sex, and mortality.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Single-pool Kt/V (spKt/V), equilibrated Kt/V, and standard Kt/V (stdKt/V) were computed using urea kinetic modeling on a prevalent cohort of 7229 patients undergoing thrice-weekly hemodialysis. Data were obtained from the Centers for Medicare & Medicaid Services 2008 ESRD Clinical Performance Measures Project. SA-normalized stdKt/V (SAN-stdKt/V) was calculated as stdKt/V × ratio of anthropometric volume to SA/17.5. Patients were grouped into sex-specific dose quintiles (reference: quintile 1 for men). Adjusted hazard ratios (HRs) for 1-year mortality were calculated using Cox regression.

RESULTS

spKt/V was higher in women (1.7 ± 0.3) than in men (1.5 ± 0.2; P<0.001), but SAN-stdKt/V was lower (women: 2.3 ± 0.2; men: 2.5 ± 0.3; P<0.001). For both sexes, mortality decreased as spKt/V increased, until spKt/V was 1.6-1.7 (quintile 4 for men: HR, 0.62; quintile 3 for women: HR, 0.64); no benefit was observed with higher spKt/V. HR for mortality decreased further at higher SAN-stdKt/V in both sexes (quintile 5 for men: HR, 0.69; quintile 5 for women: HR, 0.60).

CONCLUSIONS

SA-based dialysis dose results in dose-mortality relationships substantially different from those with volume-based dosing. SAN-stdKt/V analyses suggest women may be relatively underdosed when treated by V-based dosing. SAN-stdKt/V as a measure for dialysis dose may warrant further study.

The controversies of diagnosing and treating hypertension among hemodialysis patients

This review discusses 10 current controversies regarding the dialysis patient with hypertension. The clinician is faced with a dilemma at the bedside on how to evaluate blood pressure and treat this condition in a patient on long-term hemodialysis. The evidence base to give firm recommendations is thin, but the epidemiological evidence tells us to do nothing. This appears to be an incorrect strategy, at least based on what we know today. Evaluating home BP in every dialysis patient, evaluating volume status on a regular basis, and treating hypertension predominantly with nonpharmacological strategies are worthwhile.

Erythropoietin-stimulating agents in chronic kidney disease: a response to hyporesponsiveness

Hyporesponsiveness to erythropoietin stimulating agents occurs frequently, and may be observed at initiation of treatment or during maintenance therapy. An inverse relationship between hyporesponsiveness and incident cardiovascular events has been reported. It is related at least in part to co-morbidity and its occurrence requires a search for the cause. Treatment of anemia in hyporesponsive patients should be individualized, with consideration given to the indication for ESA therapy, the target hemoglobin for therapy, and maximal dose limitations.

Limitations of analyses based on achieved blood pressure: lessons from the African American study of kidney disease and hypertension trial

Blood pressure (BP) guidelines that set target BP levels often rely on analyses of achieved BP from hypertension treatment trials. The objective of this article was to compare the results of analyses of achieved BP to intention-to-treat analyses on renal disease progression. Participants (n=1094) in the African-American Study of Kidney Disease and Hypertension Trial were randomly assigned to either usual BP goal defined by a mean arterial pressure goal of 102 to 107 mm Hg or lower BP goal defined by a mean arterial pressure goal of ≤92 mm Hg. Median follow-up was 3.7 years. Primary outcomes were rate of decline in measured glomerular filtration rate and a composite of a decrease in glomerular filtration rate by >50% or >25 mL/min per 1.73 m(2), requirement for dialysis, transplantation, or death. Intention-to-treat analyses showed no evidence of a BP effect on either the rate of decline in glomerular filtration rate or the clinical composite outcome. In contrast, the achieved BP analyses showed that each 10-mm Hg increment in mean follow-up achieved mean arterial pressure was associated with a 0.35 mL/min per 1.73 m(2) (95% CI: 0.08 to 0.62 mL/min per 1.73 m(2); P=0.01) faster mean glomerular filtration rate decline and a 17% (95% CI: 5% to 32%; P=0.006) increased risk of the clinical composite outcome. Analyses based on achieved BP lead to markedly different inferences than traditional intention-to-treat analyses, attributed in part to confounding of achieved BP with comorbidities, disease severity, and adherence. Clinicians and policy makers should exercise caution when making treatment recommendations based on analyses relating outcomes to achieved BP.

Modeled urea distribution volume and mortality in the HEMO Study

BACKGROUND AND OBJECTIVES

In the Hemodialysis (HEMO) Study, observed small decreases in achieved equilibrated Kt/V(urea) were noncausally associated with markedly increased mortality. Here we examine the association of mortality with modeled volume (V(m)), the denominator of equilibrated Kt/V(urea).

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Parameters derived from modeled urea kinetics (including V(m)) and blood pressure (BP) were obtained monthly in 1846 patients. Case mix-adjusted time-dependent Cox regressions were used to relate the relative mortality hazard at each time point to V(m) and to the change in V(m) over the preceding 6 months. Mixed effects models were used to relate V(m) to changes in intradialytic systolic BP and to other factors at each follow-up visit.

RESULTS

Mortality was associated with V(m) and change in V(m) over the preceding 6 months. The association between change in V(m) and mortality was independent of vascular access complications. In contrast, mortality was inversely associated with V calculated from anthropometric measurements (V(ant)). In case mix-adjusted analysis using V(m) as a time-dependent covariate, the association of mortality with V(m) strengthened after statistical adjustment for V(ant). After adjustment for V(ant), higher V(m) was associated with slightly smaller reductions in intradialytic systolic BP and with risk factors for mortality including recent hospitalization and reductions in serum albumin concentration and body weight.

CONCLUSIONS

An increase in V(m) is a marker for illness and mortality risk in hemodialysis patients.

Can rescaling dose of dialysis to body surface area in the HEMO study explain the different responses to dose in women versus men?

BACKGROUND AND OBJECTIVES

In the Hemodialysis (HEMO) Study, the lower death rate in women but not in men assigned to the higher dose (Kt/V) could have resulted from use of "V" as the normalizing factor, since women have a lower anthropometric V per unit of surface area (V/SA) than men.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The effect of Kt/V on mortality was re-examined after normalizing for surface area and expressing dose as surface area normalized standard Kt/V (SAn-stdKt/V).

RESULTS

Both men and women in the high-dose group received approximately 16% more dialysis (when expressed as SAn-stdKt/V) than the controls. SAn-stdKt/V clustered into three levels: 2.14/wk for conventional dose women, 2.44/wk for conventional dose men or 2.46/wk for high-dose women, and 2.80/wk for high-dose men. V/SA was associated with the effect of dose assignment on the risk of death; above 20 L/m(2), the mortality hazard ratio = 1.23 (0.99 to 1.53); below 20 L/m(2), hazard ratio = 0.78 (0.65 to 0.95), P = 0.002. Within gender, V/SA did not modify the effect of dose on mortality.

CONCLUSIONS

When normalized to body surface area rather than V, the dose of dialysis in women in the HEMO Study was substantially lower than in men. The lowest surface-area-normalized dose was received by women randomized to the conventional dose arm, possibly explaining the sex-specific response to dialysis dose. Results are consistent with the hypothesis that when dialysis dose is expressed as Kt/V, women, due to their lower V/SA ratio, require a higher amount than men.

Association of hemodialysis treatment time and dose with mortality and the role of race and sex

BACKGROUND

The association of survival with characteristics of thrice-weekly hemodialysis (HD) treatment, including dose or duration of treatment, has not been completely elucidated, especially in different race and sex categories.

STUDY DESIGN

We examined associations of time-averaged and quarterly varying (time-dependent) delivered HD dose and treatment time and 5-year (July 2001-June 2006) survival.

SETTING & PARTICIPANTS

88,153 thrice-weekly-treated HD patients from DaVita dialysis clinics.

PREDICTORS

HD treatment dose (single-pool Kt/V) and treatment time.

OUTCOMES & OTHER MEASUREMENTS

5-Year mortality.

RESULTS

Thrice-weekly treatment time < 3 hours (but > or = 2.5 hours) per HD session compared with > or = 3.5 hours (but < 5 hours) was associated with increased death risk independent of Kt/V dose. The greatest survival gain of higher HD dose was associated with a Kt/V approaching the 1.6-1.8 range, beyond which survival gain was minimal, nonexistent, or even tended to reverse in African American men and those with 4-5 hours of HD treatment. In non-Hispanic white women, Kt/V > 1.8 continued to show survival advantage trends, especially in time-dependent models.

LIMITATIONS

Our results may incorporate uncontrolled confounding. Achieved Kt/V may have different associations than targeted Kt/V.

CONCLUSIONS

HD treatment dose and time appear to have different associations with survival in different sex or race groups. Randomized controlled trials may be warranted to examine these associations across different racial and demographic groups.

On Small Solute Clearance and Patient Outcomes: Evidential Practice or Observational Trepidation?

Recent guidelines on peritoneal dialysis adequacy set a minimum target for small solute clearance at Kt/V urea 1.70. While evidence from both observational studies and randomized controlled trials (RCTs) supports such a minimum target, there continues to be debate over what role small solute clearance plays in determining patient outcome. Current ANZDATA Registry results from Australia and New Zealand add fuel to this debate by demonstrating a significant nonlinear U-shaped relationship between peritoneal small solute clearance and patient survival. The ANZDATA results indicate that patients with too low or too high peritoneal Kt/V urea may be at significant risk of death compared to those with a peritoneal Kt/V urea between 1.70 and 2.00. As these results are somewhat at odds with results from published RCTs, we will examine the level of evidence from the observational setting that is the ANZDATA Registry and contrast it against the level of evidence from RCTs, particularly the ADEMEX trial. New results from the ADEMEX study are presented as a possible explanation for the paradoxical U-shaped results seen in the ANZDATA study.

Key comorbid conditions that are predictive of survival among hemodialysis patients

BACKGROUND AND OBJECTIVES

Abstracting information about comorbid illnesses from the medical record can be time-consuming, particularly when a large number of conditions are under consideration. We sought to determine which conditions are most prognostic and whether comorbidity continues to contribute to a survival model once laboratory and clinical parameters have been accounted for.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Comorbidity data were abstracted from the medical records of Dialysis Outcomes and Practice Pattern Study (DOPPS) I, II, and III participants using a standardized questionnaire. Models that were composed of different combinations of comorbid conditions and case-mix factors were compared for explained variance (R(2)) and discrimination (c statistic).

RESULTS

Seventeen comorbid conditions account for 96% of the total explained variance that would result if 45 comorbidities that were expected to be predictive of survival were added to a demographics-adjusted survival model. These conditions together had more discriminatory power (c statistic 0.67) than age alone (0.63) or serum albumin (0.60) and were equivalent to a combination of routine laboratory and clinical parameters (0.67). The strength of association of the individual comorbidities lessened when laboratory/clinical parameters were added, but all remained significant. The total R(2) of a model adjusted for demographics and laboratory/clinical parameters increased from 0.13 to 0.17 upon addition of comorbidity.

CONCLUSIONS

A relatively small list of comorbid conditions provides equivalent discrimination and explained variance for survival as a more extensive characterization of comorbidity. Comorbidity adds to the survival model a modest amount of independent prognostic information that cannot be substituted by clinical/laboratory parameters.

Considerations in the statistical analysis of hemodialysis patient survival

The association of hemodialysis dosage with patient survival is controversial. Here, we tested the hypothesis that methods for survival analysis may influence conclusions regarding dialysis dosage and mortality. We analyzed all-cause mortality by proportional hazards and accelerated failure time regression models in a cohort of incident hemodialysis patients who were followed for 9 yr. Both models identified age, race, heart failure, physical functioning, and comorbidity scores as important predictors of patient survival. Using proportional hazards, there was no statistically significant association between mortality and Kt/V (hazard ratio 0.72; 95% confidence interval 0.45 to 1.14). In contrast, using accelerated failure time models, each 0.1-U increment of Kt/V improved adjusted median patient survival by 3.50% (95% confidence interval 0.20 to 7.08%). Proportional hazard models also yielded less accurate estimates for median survival. These findings are consistent with an additive damage model for the survival of patients who are on hemodialysis. In this conceptual model, the assumptions of the proportional hazard model are violated, leading to underestimation of the importance of dialysis dosage. These results suggest that future studies of dialysis adequacy should consider this additive damage model when selecting methods for survival analysis. Accelerated failure time models may be useful adjuncts to the Cox model when studying outcomes of dialysis patients.

Comparison of proposed alternative methods for rescaling dialysis dose: resting energy expenditure, high metabolic rate organ mass, liver size, and body surface area

A number of denominators for scaling the dose of dialysis have been proposed as alternatives to the urea distribution volume (V). These include resting energy expenditure (REE), mass of high metabolic rate organs (HMRO), visceral mass, and body surface area. Metabolic rate is an unlikely denominator as it varies enormously among humans with different levels of activity and correlates poorly with the glomerular filtration rate. Similarly, scaling based on HMRO may not be optimal, as many organs with high metabolic rates such as spleen, brain, and heart are unlikely to generate unusually large amounts of uremic toxins. Visceral mass, in particular the liver and gut, has potential merit as a denominator for scaling; liver size is related to protein intake and the liver, along with the gut, is known to be responsible for the generation of suspected uremic toxins. Surface area is time-honored as a scaling method for glomerular filtration rate and scales similarly to liver size. How currently recommended dialysis doses might be affected by these alternative rescaling methods was modeled by applying anthropometric equations to a large group of dialysis patients who participated in the HEMO study. The data suggested that rescaling to REE would not be much different from scaling to V. Scaling to HMRO mass would mandate substantially higher dialysis doses for smaller patients of either gender. Rescaling to liver mass would require substantially more dialysis for women compared with men at all levels of body size. Rescaling to body surface area would require more dialysis for smaller patients of either gender and also more dialysis for women of any size. Of these proposed alternative rescaling measures, body surface area may be the best, because it reflects gender-based scaling of liver size and thereby the rate of generation of uremic toxins.

Surface-area-normalized Kt/V: a method of rescaling dialysis dose to body surface area-implications for different-size patients by gender

Dialysis is measured as Kt/V, which scales the dose (Kt) to body water content (V). Scaling dialysis dose to body surface area (S(dub)) has been advocated, but the implications of such rescaling have not been examined. We developed a method of rescaling measured Kt/V to S(dub) and studied the effect of such alternative scaling on the minimum adequacy values that might then be applied in male and female patients of varying body size. We examined anthropometric estimates of V and S (Watson vs. Dubois estimates) in 1765 patients enrolled in the HEMO study after excluding patients with amputations. An S-normalized target stdKt/V was defined, and an adequacy ratio (R) was computed for each patient as R = D/N where D = delivered stdKt/V (calculated using the Gotch-Leypoldt equation for stdKt/V) and N = the S-normalized minimum target value. In the HEMO data set, we determined the extent to which baseline (prerandomization) stdKt/V values would have exceeded such an S-based minimum target stdKt/V. The median V(wat):S(dub) ratios were significantly higher in men (21.34) than in women (18.50). The average of these (20) was used to normalize the current suggested minimally adequate value (stdKt/V > or = 2.0/week) to the S-normalized target value (stdKt/S > or = 40 L/M(2)), assuming that average modeled V = average anthropometric V. To achieve this S-normalized target, the required single-pool (sp) Kt/V was always higher in women than in men at any level of body size. For small patients (V(wat) = 25L), required stdKt/V values were 2.05 and 2.21/week for men and women, respectively, corresponding to spKt/V values of 1.31 and 1.52/session. On the other hand, large (V(wat) = 50L) male patients would need spKt/V values of only 1.0/session. Prerandomization baseline dialysis sessions in the HEMO study were found to meet such a new S-based standard in almost all (766/773) men and in 885/992 women. An analysis of scaling dose to anthropometrically estimated liver size (L) showed similar gender ratios for V(wat):L and V(wat):S(dub), providing a potential physiologic explanation underpinning S-based scaling. S-based scaling of the dialysis dose would require considerably higher doses in small patients and in women, and would allow somewhat lower doses in larger male patients. Current dialysis practice would largely meet such an S-based adequacy standard if the dose were normalized to a V(wat):S(dub) ratio of 20.