A single weekly Kt/Vurea target for peritoneal dialysis patients does not provide an equal dialysis dose for all

Comparison of frailty, sarcopenia and protein energy wasting in a contemporary peritoneal dialysis cohort

BACKGROUND

More elderly frail patients are now treated by peritoneal dialysis (PD). Frailty, sarcopenia and protein energy wasting (PEW) are all associated with increased mortality. Simple screening tools are required to identify patients to allow for interventions. As such, we wished to review the prevalence of frailty and compare frailty with sarcopenia and PEW in a contemporary PD population.

PATIENTS AND METHODS

We used the Clinical Frailty Score (CFS) to determine frailty, bio-impedance body composition and hand grip strength (HGS) to determine sarcopenia and combining laboratory, body composition and protein nitrogen appearance rate (PNA) to assess PEW.

RESULTS

Records of 368 PD patients, 61% male, mean age 60.9 ± 16.1 years, body mass index (BMI) 26.2 ± 5.1 kg/m² were reviewed, with 71 classified as frail (19.3%; CFS > 4), and frailty associated with age (odds ratio (OR) 1.047, 95% confidence interval (CL) 1.01-1.085, p = 0.012), Stoke-Davies co-morbidity (OR 1.808, 95%CL 1.129-2.895, p = 0.014) and negatively with HGS (OR 0.906, 95% CL 0.897-0.992, p = 0.033); 17.7% met muscle loss and HGS criteria for sarcopenia, with fair agreement with frailty (kappa 0.24 (CL 0.09-0.38)). Only two patients (0.5%) met all four criteria for PEW, 26.1% met the reduced BMI criteria, 4.6% the serum albumin, 32.9% the PNA and 39.4% the reduced muscle mass. HGS correlated with lean muscle mass (r ² = 0.42, p < 0.001).

CONCLUSION

Using the CFS, 19.3% of patients were classified as frail, compared to 17.7% with sarcopenia and <1% with PEW. The CFS requires no special equipment or laboratory tests and was associated with age, co-morbidity and HGS weakness.

Nutritional predictors associated with malnutrition in continuous ambulatory peritoneal dialysis patients

BACKGROUND

Currently in China, out of the total dialysis population, approximately 20% represents continuous ambulatory peritoneal dialysis (CAPD) and almost half of CAPD patients was affected by malnutrition. This study aimed to investigate the association between nutritional predictors and malnutrition with 5.1 years of dialysis according to the subjective global assessment (SGA) in continuous ambulatory peritoneal dialysis (CAPD) patients.

METHODS

A cross-sectional study was conducted from April 2013 to May 2018 and included 70 CAPD patients. The relationship between anthropometric and biochemical parameters with malnutrition was assessed by multiple logistic regression analysis.

RESULTS

The prevalence of malnutrition in CAPD patients was 52.9%. Our result revealed a 7.05-fold increased odds of malnutrition for patients with protein equivalent of total nitrogen appearance normalized to body weight (nPNA) < 1.0 g/kg per day (d) versus patients with normal nPNA (confidence interval (CI) 1.33-37.34; p < 0.05). Patients whose normalized protein catabolic rate (nPCR) was <1.2 g/(kg/d) had a significant positive association with malnutrition versus patients with normal nPCR (adjusted odds ratio (OR) 7.99; p < 0.05). Patients with dietary protein intake (DPI) < 1.0 g/(kg/d) had a higher likelihood of malnutrition than those with normal DPI (OR 12.73; p < 0.05). CAPD patients with upper arm circumference (UAC) < 23.2 cm had a high risk of malnutrition versus patients with normal UAC (OR 12.99; p < 0.05).

CONCLUSIONS

Our study suggested a close association between nPNA, DPI, nPCR, and UAC and malnutrition in CAPD patients. Further studies can be warranted the use of these variables as predictors and a malnutrition consequence among Chinese CAPD patients.

Monitoring dialysis adequacy: history and current practice

Dialysis adequacy for pediatric patients has largely followed the trends in adult dialysis by judging the success or adequacy of peritoneal or hemodialysis with urea kinetic modeling. While this provides a starting point to establish a dose of dialysis, it is clear that urea is only part of the picture. Many clinical parameters and interventions now have been identified that are just as impactful on mortality and morbidly as urea clearance. As such, our concept of adequacy is evolving to include non-urea parameters and assessing the impact that following an "adequate therapy" has on patient lives. As we move to a new era, we consider the impact these therapies have on patients and how it affects the quality of their lives; we must take these factors into consideration to achieve a therapy that is not just adequate, but livable.

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

Background:

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

Methods:

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

Results:

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

Conclusions:

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

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.

Relationships between Peritoneal Protein Clearance and Parameters of Fluid Status Agree with Clinical Observations in other Diseases that Venous Congestion Increases Microvascular Protein Escape

Background

Peritoneal effluent from peritoneal dialysis (PD) patients contains proteins, mainly transported from the circulation through large pores in the venular part of the peritoneal micro-vessels. Hydrostatic convection is the major driver for peritoneal protein transport, although in PD there is additional diffusion. Consequently, venous pressure may have a role in peritoneal protein transport. The aim of the study was to investigate the importance of venous congestion on the magnitude of peritoneal protein clearance in incident PD patients using non-invasive measurements.

Methods

A total of 316 adult PD patients, on PD for 8 - 12 weeks and collecting 24-hour urine and dialysate for total protein determination, underwent standard peritoneal equilibration testing (PET) along with measurement of N terminal pro-brain natriuretic peptide (NT-proBNP) and C-reactive protein (CRP), multifrequency bioimpedance analysis, and a transthoracic echocardiogram.

Results

Statistically significant univariate relationships for peritoneal protein clearance with a Spearman correlation coefficient > 0.25 were present for 4-hour dialysate/plasma (D/P) creatinine, NT-proBNP, extracellular/total body water, extracellular water excess, left ventricular mass, and right atrial area. Negative correlations were found with serum total protein and residual renal function. On multivariate analysis, logNTproBNP (β 0.11, p = 0.007) and right atrial area (β 0.01, p = 0.03) were significant independent predictors of peritoneal protein clearance.

Conclusion

Indicators of venous congestion showed the most important relationships with peritoneal protein clearance. These indicators have not been assessed in previous studies on the presence or absence of relationships between peritoneal protein clearance and mortality.

Estimating Dietary Protein Intake in Peritoneal Dialysis Patients: The Effect of Ethnicity

Kidney dialysis patients with sarcopenia have increased mortality. Clinical guidelines recommend peritoneal dialysis (PD) patients have a target daily protein intake to prevent sarcopenia. Protein intake is estimated from total daily urea losses in urine and peritoneal dialysate to assess the protein equivalent of nitrogen appearance rate adjusted for body weight (nPNA). Dietary habits differ among ethnic groups, so we reviewed nPNA and body composition in a multi-ethnic PD population. Body composition was measured with multifrequency bioimpedance in 598 patients (301 white, 136 black, 123 South-Asian, and 38 Asian-Pacific). South-Asians had a lower nPNA compared with white and black individuals (Randerson 0.80 ± 0.21 vs 0.88 ± 0.24 and 0.85 ± 0.24 g/kg/day, Blumenkrantz 0.97 ± 0.14 vs 1.04 ± 0.22 and 0.99 ± 0.22 g/kg/day, Bergström 0.87 ± 0.4 vs 0.95 ± 0.24 and 0.92 ± 0.24 g/kg/day all p < 0.001). South-Asians had lower weights (68.9 ± 14.9 vs 74.4 ± 16.6 and 73.5 ± 16.3 kg, p < 0.001), and although of similar body mass index (25.9 ± 4.9 vs 28.5 ± 4.9 and 26.5 ± 5.2 kg/m²), had both lower skeletal muscle and appendicular muscle mass indexed for height (9.08 ± 1.45 vs 9.89 ± 1.62 and 10.1 ± 1.85, p < 0.001; and 6.95 ± 1.39 vs 7.68 ± 1.48 and 7.67 ± 1.58 kg/m²p < 0.01). South-Asian patients had a lower calculated basal metabolic rate (BMR) (1,358 ± 218 vs 1,487 ± 257 and 1,489 ± 271 kcal/day, p < 0.001).Asian PD patients, particularly South-Asians, have lower dietary protein intakes when calculated by nPNA. However, South-Asians had lower measured muscle mass and calculated BMR. As such, dietary protein intake targets derived from studies in 1 ethnic group are not necessarily applicable for all patients, as those with less muscle mass and lower BMR may well need less daily protein intake to maintain homeostasis.

Postdialysis recovery time is extended in patients with greater self-reported depression screening questionnaire scores

INTRODUCTION

Most patients take time to recover after a hemodialysis (HD) session. It has been suggested that recovery time is associated with intradialytic hypotension and rapid solute clearances. Other studies have reported a linkage to depression. We investigated the association between recovery time and intradialytic hypotension and depression.

METHODS

In five UK HD units, we screened for depressive symptoms using the Beck depression inventory-II, Patient Health Questionnaire, and recorded sessional blood pressures and Kt/Vurea.

FINDINGS

Seven hundred and one HD patients were studied; 63.6% male, mean age 64.1 ± 16.6 years, 33.5% diabetic. About 24.1% recovered in <1 hour, 27% 1-4 hours, 15.4% 4-8 hours, 10.7% 8-12 hours, and 22.8% after 12 hours. Systolic blood pressure fell by ≥20 mmHg in 30.9% postdialysis, and to <100 mmHg in 7.6%. In multivariate analysis, patients with recovery times >1 hour were more likely to be female, have high self-reported Beck depression inventory-II scores, a past medical history of depression, and be living without a partner. Longer recovery times were also associated with very low postdialysis systolic blood pressures (<100 mmHg), and higher body weight. However, the model predicted only 18% of the variation in recovery times. We found no association between recovery times and short-term mortality risk.

DISCUSSION

Prolonged postdialysis recovery times are associated with higher self-reported depression scores, and very low postdialysis blood pressure. Future studies investigating changes in dialysis practice and recovery times will need to target strategies to prevent intradialytic hypotension and adjust for patient psychological status.

Differences in Prevalence of Muscle Weakness (Sarcopenia) in Haemodialysis Patients Determined by Hand Grip Strength Due to Variation in Guideline Definitions of Sarcopenia

BACKGROUND

Muscle weakness is associated with increased mortality, and hemodialysis (HD) patients are at an increased risk for muscle loss. There is no agreed definition for muscle weakness, so we determined whether using different cut-off criteria recommended by guideline groups altered the prevalence in HD patients.

METHODS

We measured hand grip strength (HGS) in HD outpatients, comparing HGS with clinical guideline cut-offs (European Working Group on Sarcopenia in Older People [EWGSOP] and North American Foundation for the National Institutes of Health Sarcopenia Project [FNIH]) used to define muscle wasting (sarcopenia) with age-matched and gender-matched normative data.

RESULTS

We studied 459 patients, 61.4% male, 47.3% diabetic. The prevalence of muscle weakness was significantly different when measuring HGS; 84.5% using the EWGSOP cut-off and 73.2% with FNIH criteria, and 75.2% using North American normative data and 56.6% U.K. normative data (P < .01). On logistic regression, muscle weakness was associated with age (odds ratio [OR] 1.05, P < .001), weight (OR 0.96, P < .001), serum albumin (OR 0.89, P = .007), and being nondiabetic (OR 0.31, P = .001). Of patients with no comorbidity, 66.7% were weak when compared with 93.8% with the highest comorbidity scores (P < .001).

CONCLUSION

There is currently no agreed universal definition for sarcopenia, but the EWGSOP and FNIH advocate HGS cut-offs as part of their definition. The prevalence of muscle weakness varies according to cut-off and whether age-matched and gender-matched normative data are used. In addition, patient characteristics in terms of age and comorbidity determine the prevalence of muscle weakness.

Peritoneal Protein Losses Depend on More Than Just Peritoneal Dialysis Modality and Peritoneal Membrane Transporter Status

Peritoneal protein clearance (PPCl) depends upon vascular supply and size selective permeability. Some previous reports suggested PPCl can distinguish fast peritoneal membrane transport due to local or systemic inflammation. However, as studies have been discordant, we wished to determine factors associated with an increased PPCl. Consecutive patients starting peritoneal dialysis (PD) who were peritonitis-free were studied. Data included a baseline peritoneal equilibration test (PET), measurement of dialysis adequacy, 24-h dialysate PPCl and body composition measured by multifrequency bioimpedance. 411 patients, mean age 57.2 ± 16.6 years, 60.8% male, 39.4% diabetic, 20.2% treated by continuous ambulatory peritoneal dialysis (CAPD) were studied. Mean PET 4-h Dialysate/Serum creatinine was 0.73 ± 0.13, with daily peritoneal protein loss 4.6 (3.3-6.4) g, and median PPCl 69.6 (49.1-99.6) mL/day. On multivariate analysis, PPCl was most strongly associated with CAPD (β 0.25, P < 0.001), extracellular water (ECW)/total body water (TBW) ratio (β 0.21, P < 0.001), skeletal muscle mass index (β 0.21, P < 0.001), log N-terminal brain natriuretic peptide (NT-proBNP) (β 0.17, P = 0.001), faster PET transport (β 0.15, P = 0.005), and normalized nitrogen appearance rate (β 0.13, P = 0.008). In addition to the longer dwell times of CAPD, greater peritoneal creatinine clearance and faster PET transporter status, we observed an association between increased PPCl and ECW expansion, increased NT-proBNP, estimated dietary protein intake and muscle mass, suggesting a link to sodium intake and sodium balance, increasing both ECW and conduit artery hydrostatic pressure resulting in greater vascular protein permeability. This latter association may explain reports linking PPCl to patient mortality.

The prevalence of muscle wasting (sarcopenia) in peritoneal dialysis patients varies with ethnicity due to differences in muscle mass measured by bioimpedance

BACKGROUND/OBJECTIVES

Sarcopenia is associated with increased mortality. European and North American recommended screening for low muscle mass uses gender specific cut points, with no adjustment for ethnicity. We wished to determine whether the prevalence of sarcopenia was altered by ethnicity in peritoneal dialysis (PD) patients.

SUBJECTS/METHODS

We measured appendicular lean mass indexed to height (ALMI) in PD patients by segmental bioimpedance and determined sarcopenia using different cut off points for reduced muscle mass.

RESULTS

We measured ALMI in 434 PD patients, 55.1% males, mean age 55.3 ± 16.2 years, 32.3% diabetic, 54.1% white, 23.7% Asian, 19.1% black. ALMI was lower in Asian women, compared to white and black women (6.4 ± 1.1 vs. 6.6 ± 1.0 and 6.9 ± 1.4 kg/m²), and lower in Asian men (7.5 ± 1.3 vs. 8.5 ± 1.2 and 8.7 ± 1.3 kg/m²), p < 0.001. Depending on the ALM/ALMI cut point; the prevalence of sarcopenia was greater in Asian patients (25.6-41.2% using North American or European cut points) compared to white (12.3-18.7%) and black patients (3.8-15.7%), p < 0.001, but <11% when using Asian-specific cut points. The prevalence of sarcopenia obesity (BMI ≥ 30 kg/m²) was <3%, for all groups. There was no association with duration of PD, dialysis prescription, residual renal function or small solute clearances.

CONCLUSIONS

There is no universally agreed consensus definition for loss of muscle mass (sarcopenia) and current European and North American recommended cut points for screening are adjusted only for gender. As body composition differs also with age and ethnicity, then ideally cut points should be based on age, gender and ethnicity normative values.

Comparison of Change in Peritoneal Function in Patients on Continuous Ambulatory PD vs Automated PD

Background

Patients on automated peritoneal dialysis (APD) may have greater exposure to glucose in the PD fluid than those on continuous ambulatory PD (CAPD). If this causes long-term damage to the peritoneal membrane, it will have implications for a patient's choice of modality.

Methods

Membrane function of long-term APD or CAPD patients was followed prospectively. The data were collected from electronic patient records in our unit from 2000 to 2014. The rate of change in membrane transport status (D/Pcr) and ultrafiltration (UF4) for each patient was calculated using the least square regression line equation.

Results

We identified 106 APD and 123 CAPD patients who had a mean of 8.4 peritoneal equilibration test (PET) over 5.6 years. No differences were found in the rate of changes in D/Pcr or UF4. Baseline solute clearance (Kt/V) was lower in APD patients (1.66 vs 1.76, p = 0.04). However, APD patients experienced incremental changes to dialysis prescription that resulted in a greater increase in Kt/V compared with CAPD patients.

Conclusion

This is the largest study comparing the long-term effect of APD vs CAPD prescriptions. Despite more glucose being prescribed, there were no differences in the evolution of peritoneal membrane transport characteristics. The lower baseline Kt/V of APD patients might be explained by our aggressive use of incremental APD (tidal with dry day). Despite greater glucose prescriptions, initiating patients on APD based on patient preference appears to be safe for the long-term integrity of the peritoneal membrane.

Increasing Haemodialytic Clearances as Residual Renal Function Declines: An Incremental Approach

Many patients with chronic kidney disease start undergoing thrice-weekly haemodialysis (HD), aiming for an HD sessional dialyzer urea clearance target, irrespective of whether they have residual renal function (RRF). While increasing sessional dialyzer urea clearance above a target of 1.2 has not been shown to improve patient survival, it has been shown that the preservation of RRF improves patient self-reported outcomes and survival. Observational studies have suggested that initiating twice-weekly HD schedules leads to greater preservation of RRF. This has led to the concept of following an incremental approach to initiating HD, steadily increasing the amount of weekly dialyzer clearance as RRF decreases. Incremental dialysis practice requires the regular assessment of RRF to prevent inadequate delivery of dialysis treatment. Once RRF is lost, then the dialysis schedule and modality need to be adjusted to try to increase the middle-sized solute clearance and protein-bound toxins.