Fractional Urea Clearance Research Articles

Association between Dialysis Adequacy and Cognition in Patients with Peritoneal Dialysis.

ObjectiveCognition of peritoneal dialysis patients is influenced by various factors including dialysis adequacy such as fractional urea clearance (Kt/V) and relative overhydration (RelOH). This study aimed to discover the potential contribution of dialysis adequacy to cognitive function in patients undergoing peritoneal dialysis. MethodsFifty-nine patients undergoing peritoneal dialysis were recruited. Demographic information, comorbidities, and clinical lab findings were retrospectively collected, and dialysis adequacy was determined by the Kt/V and RelOH calculation. Cognition and depression were measured with Digit Symbol Substitution Test, Hopkins Verbal Learning Test, Wechsler memory scale (spatial span), Wisconsin Card Sorting Test, and Beck’s depression inventory. Partial correlation test was used to explore the correlation of dialysis adequacy with cognitive function. ResultsRelOH showed significant correlation with some of the Wisconsin Card Sorting test results. The categories achieved showed negative correlation (r=-0.32, p=0.02) and trials to complete first category showed positive correlation (r=0.31, p=0.02) with RelOH. Other tasks showed no significant correlation with RelOH. Kt/V. ConclusionOur study demonstrates that peritoneal dialysis adequacy, measured by RelOH, seems to be significantly correlated with the occurrence of cognitive impairment. The outcome suggests that RelOH may have the potential to clarify the role of cognitive impairment in peritoneal dialysis patients.

Adequacy of haemodialysis in two centres in Southwestern Nigeria: Determinants and clinical correlates

Background: Dialysis remains the most common modality of renal replacement therapy for managing end-stage kidney disease. Optimisation of various measures is needed for its efficient delivery. Inadequate dialysis is common in many low-income nations, and there could be inter-centre differences in the delivered dose.Aim: We assessed the dialysis adequacy and factors associated with inter-centre variation.Materials and Methods: This was a two-centre comparative study. Participants' sociodemographic and examination findings were documented and dialysis was prescribed. Pre- and post-dialysis blood for electrolytes, urea and creatinine were taken, and urea reduction ratio and fractional urea clearance as a function of its distribution volume (Kt/V) were calculated.Results: Two hundred and thirty-two participants had 1248 dialysis sessions. Participants' mean age was 49.9 ± 4.6 years. More males participated in the study, and males also received more sessions per participant. A greater proportion of the participants had tertiary education and had hypertensive nephropathy as the cause of kidney disease. The internal jugular access was used for dialysis in majority (60.6%) of the dialysis sessions. Dialysis dose (DD) was adequate in only 115 (9.2%) sessions. The mean DD was 1.02 ± 0.4; in the two centres, it was 0.86 ± 0.2 and 1.11 ± 0.5.Conclusion: DD is low in many low-income nations including Nigeria. The DD was directly related to the blood flow rate, dialysis duration and frequency of erythropoietin use. In addition to other factors, inability to afford prescribed dialysis regimen is a major contributor to the low DD in low-income settings.

Validity of malnutrition scores for predicting mortality in chronic hemodialysis patients

Malnutrition is a strong predictor of mortality in hemodialysis patients. Several scoring systems for evaluating nutritional status have been proposed. However, they rely on different sets of anthropometric and laboratory markers to make a diagnosis of malnutrition and assess its impact on prognosis. To validate them, nutritional scores should be compared with clinical outcomes. Thus, the purpose of this study was to assess malnutrition by three different nutrition scoring systems and determine which best predicts mortality in hemodialysis patients. This prospective study included 106 adult chronic hemodialysis patients. Their mean age was 56.3 ± 14.9 years and mean body mass index 24.8 (21.8-28.9); 52 % were men and they had been on dialysis for 24 (5-55) months. Nutritional status was classified according to the diagnostic systems proposed by Wolfson et al. (Am J Clin Nutr 39(4):547-555, 1984), International Society of Renal Nutrition and Metabolism (ISRNM) (Fouque et al. in Kidney Int 73(4):391-398, 2008), and Beberashvili et al. (Nephrol Dial Transplant 25(8):2662-2671, 2010). During about 2 years of follow-up, mortality was assessed by Kaplan-Meier curves, log-rank, and Cox's models adjusted for diabetes, sex, C-reactive protein, time on dialysis, age, and fractional urea clearance. Twenty-three deaths (21.5 %) occurred during the study period. According to the systems of Wolfson, Beberashvili, and the ISRNM, 54, 32, and 20 % of patients, respectively, had malnutrition. Both univariate and multivariate analyses showed that the ISRNM system was the only one that predicted poorer survival (fourfold higher death risk) in malnourished patients. The scoring system proposed by the ISRNM most accurately identifies patients at higher risk of death.

Effect Of Surface Area Of Dialyzer Membrane On The Adequacy Of Haemodialysis

Introduction: Patients with end stage renal disease require 12 hours of haemodialysis per week in three equal sessions (4 hours/day for 3 days/week). But the duration and frequency of treatment can be reduced by increasing the surface area of the dialyzer membrane. Methods: In this prospective study 40 patients of end stage renal disease receiving haemodialysis for more than six months were included to observe the effects of increment in the surface area of the dialyzer membrane on the adequacy of haemodialysis. Result: It was observed that 20 patients receiving haemodialysis on a dialyzer with membrane surface area of 1.2 m² did not have satisfactory solute clearance index. Urea reduction ratio was 45.9 ± 3.03 and fractional urea clearance (Kt/V) was 0.76 ± 0.09. On the other hand patients (20 cases) receiving haemodialysis on a dialyzer with membrane surface area of 1.3 m² had a urea reduction ratio 50.76± 5.16 and fractional urea clearance (Kt/V) 0.91 ± 0.16. All the patients of both groups received dialysis for 8 hours/week in two equal sessions (4 hours/day for 2 days/week). Statistically the increment was significant (p<0.001). Conclusion: This study reveals, adequacy of dialysis can be increased by increasing the surface area of the dialyzer membrane. So, considering the poor socioeconomic condition of Bangladesh and patients' convenience, a short duration, low cost dialysis regime can be tried by increasing the surface area of dialyzer membrane. DOI: http://dx.doi.org/10.3329/jafmc.v7i2.10387 JAFMC 2011; 7(2): 9-11

Abdominal obesity modifies the risk of hypertriglyceridemia for all-cause and cardiovascular mortality in hemodialysis patients

Hypertriglyceridemia is the most prevalent lipid alteration in end-stage renal disease, and we studied the relationship between serum triglycerides and all-cause and cardiovascular death in these patients. Since abdominal fat modifies the effect of lipids on atherosclerosis, we analyzed the interaction between serum lipids and waist circumference (WC) as a metric of abdominal obesity. In a cohort of 537 hemodialysis patients, 182 died, 113 from cardiovascular causes, over an average follow-up of 29 months. In Cox models that included traditional and nontraditional risk factors, there were significant strong interactions between triglycerides and WC to both all-cause and cardiovascular death. A fixed (50 mg/dl) excess in triglycerides was associated with a progressive lower risk of all-cause and cardiovascular mortality in patients with threshold WC <95 cm but with a progressive increased risk in those above this threshold. A significant interaction between cholesterol and WC with all-cause and cardiovascular death emerged only in models excluding the triglycerides-WC interaction. Neither high-density lipoprotein (HDL) nor non-HDL cholesterol or their interaction terms with WC were associated with study outcomes. Thus, the predictive value of triglycerides and cholesterol for survival and atherosclerotic complications in hemodialysis patients is critically dependent on WC. Hence, intervention studies in end-stage renal disease should specifically target patients with abdominal obesity and hyperlipidemia.

Comparison of parenteral iron sucrose and ferric chloride during erythropoietin therapy of haemodialysis patients

To compare the effects of i.v. iron sucrose and Fe chloride on the iron indices of haemodialysis patients with anaemia. One hundred and eight haemodialysis patients receiving recombinant human erythropoiesis-stimulating agent (ESA) (mean age 59.37 years) were enrolled and randomly assigned to an iron sucrose or an Fe chloride group. Iron supplements were administered at 100 mg/week during the first 4 weeks (loading dose). Ferritin and transferrin saturation (TSAT) were then measured and dose adjusted. Ninety-eight subjects completed treatment; 51 in the iron sucrose group and 47 in the Fe chloride group. Ferritin, TSAT, haematocrit (Hct), reticulocyte count, serum albumin, fractional clearance of urea (Kt/V) and intact parathyroid hormone (iPTH) were measured. There was no significant difference in baseline characteristics between the groups. Significant differences between the groups were observed in both iron indices and ESA dosage. Hct at week 24 (31.1% vs 29.7%, P = 0.006) and ferritin at week 20 (731.3 vs 631.7 ng/mL, P = 0.006) in the iron sucrose group were significantly higher than in the Fe chloride group. ESA dosage used in the iron sucrose group at week 8 was significantly lower than in the Fe chloride group (244.9 vs 322.6 U/kg per month, P = 0.003), and iron sucrose group received significantly lower iron dose than the Fe chloride group at week 8 (P = 0.005). Although the differences in ESA dosage, ferritin and iron dosage between two groups were found during the study period while similar results were shown at the end of 24 week study. Thus, iron sucrose and Fe chloride are safe and work equally well for haemodialysis patients.

Effect of Fractional Urea Clearance on Survival of Hemodialysis Patients in Relation to Gender

Many studies have demonstrated the relationship between dialysis dose and survival. Global mortality is similar among men and women; however, the influence of dialysis dose in the survival could be more intensive between women. Therefore, we conduct an observational study to evaluate the gender-related impact of single pool Kt/V (spKt/V) on the survival of patients submitted to hemodialysis in a university hospital. We found that survival was lower in groups with spKt/V smaller than 1.2 than in those with Kt/V between 1.2 and 1.4. Among female patients, spKt/V smaller than 1.2 had a more adverse effect in survival than among men with a comparable Kt/V. Otherwise, among women, the dialysis dose had an impact in survival even with Kt/V greater than 1.4. Thus, fractional urea clearance more heavily influenced the survival of females than males in hemodialysis patients.

Insuficiencia renal y resistencia insulínica: efecto de la dosis de diálisis

The main cause of death in patients undergoing hemodialysis are cardiovascular events. We have analyzed the association between intradialysis fractional clearance of urea or Kt/V index in patients with chronic renal failure in hemodialysis as an indicator of adequate dialysis and the classical factors of cardiovascular risk.A total of 47 patients with chronic renal failure on hemodialysis were included. Diabetes mellitus was considered an exclusion criteria. Optimization of dialysis was analyzed by Kt/v index in accordance with the Daugirdas formula. The cardiovascular risk factors evaluated were: insulin resistance, calculated according to the HOMA method, total cholesterol, LDL-cholesterol, triglycerides, arterial hypertension, obesity and metabolic syndrome. The relationship between cardiovascular risk factors and Kt/V index was analyzed with the variant and multivariant analysis.The HOMA median (interquartile range) of the patients was 1.16 (0.53-5.77). HOMA was correlated with triglycerides and HDL-cholesterol levels. HOMA was significantly greater in those who had less adapted dialysis (Kt/V < 1.4) (1.9 +/- 1.3 vs 1.0 +/- 0.3, p = 0.02). Furthermore, a negative correlation was found between HOMA and Kt/V. The multivariant analysis of the factors associated to HOMA demonstrated that the only associated parameters were Kt/V greater than 1.4, body mass index and age.In patients with chronic renal failure, adapted dialysis, determined by the Kt/V index, correlated negatively with insulin resistance. Based on these data, we suggest the need for longitudinal studies that consider this index as a predictive variable of cardiovascular events in this type of patients.

Alteration of Heart Rate Variability Parameters in Nondiabetic Hemodialysis Patients

Objective: We attempt to identify heart rate variability (HRV) components and decide whether or not such components are more sensitive to the hemodialysis (HD) process by excluding the presence of comorbid conditions known to affect HRV. Methods: It was a prospective cohort study of factors associated with HRV. Thirty-five HD patients were admitted to the study. The research was divided into three phases. During the first phase, baseline Holter and blood pressure recordings were carried out. Then in the second phase, the patients were admitted for HD with continuous Holter and blood pressure recording. The third phase was after HD with continuous Holter and blood pressure recording. The frequency and time domain analyses of HRV were carried out by an independent, blinded investigator. Plasma Na⁺, K⁺, ionized Ca, hemoglobin, serum creatinine and blood urea nitrogen (BUN) were checked 1 h before and 2 h after HD. Results: After HD, the serum creatinine and BUN were obviously reduced (p < 0.01), which was also expressed by fractional urea clearance (K_t/V; 1.55 ± 0.25), which means efficient HD. Standard deviation of all RR intervals and low-frequency/high-frequency (LF/HF) ratio were reduced significantly (p < 0.05) at the ‘HD for 3 h’ time point while the blood pressure levels were relatively stable during the HD process. The ultrafiltration rate and K_t/V appeared to be the main determinants of the LF/HF ratio in HD. In our cases, the LF/HF ratio positively correlated with K_t/V and negatively correlated with ultrafiltration volume. Conclusion: Our study suggested a shift in sympathovagal balance toward sympathetic activation during the HD process. Sympathetic overactivity is positively correlated with the ultrafiltration rate, and negatively correlated with the K_t/V which means that the HD process itself affects HRV parameters indeed.

Associations between Sympathetic Activity, Plasma Concentrations of Renin, Aldosterone, and Parathyroid Hormone, and the Degree of Intractability of Blood Pressure Control in Hemodialysis Patients

This study was designed to examine how such factors as hemodialysis parameters, body mass index, renin and aldosterone concentrations, sympathetic nervous activity, and parathyroid hormone concentrations are associated with the control of hypertension in hemodialysis patients. Hemodialysis patients (n=114) were grouped into four categories. Group 1 had normal BP without antihypertensive medication. Group 2 needed one antihypertensive drug, Group 3 needed combination of two or three categories of antihypertensive drugs without minoxidil. Group 4 needed more than three categories of antihypertensive drugs including minoxidil. Parathyroid hormone, β2-microglobulin, renin and aldosterone, epinephrine, norepinephrine, and hemodialysis parameters were measured. The fractional clearance of urea as Kt/V urea was significantly lower in Group 3 and Group 4 than in Group 2 (p<0.01). Concentrations of parathyroid hormone were significantly higher in Group 4 than the other groups (p<0.01). Pre-hemodialysis norepinephrine concentrations were significantly higher in Group 4 than the other groups (p<0.05). Traditional factors associated with hypertension did not seem to be relevant to the degree of hypertension in hemodialysis patients in the present study. In conclusion, poor Kt/V urea, elevated parathyroid hormone concentrations, and elevated concentrations of plasma norepinephrine seemed to be the factors that might be associated with control of hypertension in hemodialysis patients.

Associations of hemodialysis dose and session length with mortality risk in Australian and New Zealand patients

The optimal combination of hemodialysis (HD) dose and session length remains uncertain, and previous studies have not conclusively shown session length to be an important independent determinant of patient mortality. The objective of this study was to examine associations between HD dose and session length with mortality risk using data from the Australian and New Zealand Dialysis and Transplant Registry. Analyses were performed using a prospective inception cohort comprising all incident adult patients treated by thrice-weekly maintenance HD, who commenced renal replacement therapy with HD between 1 April 1997 and 31 March 2004. In all, 6593 patients were identified, of whom 4193 had sufficient data for multivariate analyses. HD dose (single pool fractional clearance of urea, Kt/V) and session length were included in analyses as those recorded 12 months after HD inception to reduce confounding by residual renal function. The outcome examined was patient mortality. Survival analyses included Kaplan-Meier calculations of survival and Cox regression for multivariate analyses. Covariates in Cox models included patient demographics, co-morbid medical conditions at HD inception, and HD operating parameters. After adjustment for covariates and each other, Kt/V of 1.30-1.39 and session length of 4.5-4.9 h were associated with the lowest mortality risk. There was no interaction between HD dose and session length. Thus, the optimal combination for mortality appears to be Kt/V of > or = 1.3 and session length of > or = 4.5 h. These data suggest a randomized controlled trial to test these hypotheses, and support the inclusion of criteria relating to session length in definitions of adequate HD practice.

Indices for assessment of hemodialysis adequacy: A comparison of different formulae

Of the various indices used in the assessment of dialysis adequacy, fractional urea clearance controlled for volume of distribution "Kt/V" remains the most widely used. Its determination is best performed by formal urea kinetic modeling (UKM), which is laborious and cumbersome, and the computational softwares are largely unavailable, particularly in developing countries. Consequently, different equations have been developed that approximate the formal UKM determination. Of the available formulae, that from second-generation logarithmic equation have been found to approximate values derived from formal UKM closely. We set out to determine the clinical utility of percent reduction of urea and Kt/V formulae derived from it, using the logarithmic equation as the standard.

Dialysis dose and frequency

From the beginning of the dialysis era, the issue of optimal dialysis dose and frequency has been a central topic in the delivery of dialysis treatment. We undertook a discussion to achieve a consensus on key points relating to dialysis dose and frequency, focusing on the relationships with clinical and patient outcomes. Traditionally, dialysis adequacy has been quantified referring to the kinetics of urea, taken as a paradigm of all uraemic toxins, and applying the principles of pharmacokinetics using either single- or double-pool variable volume models. An index of dialysis dose is the fractional clearance of urea, which is commonly expressed as Kt/V. It can be calculated from blood urea concentration and haemodialysis (HD) parameters, according to the respective urea kinetic model or by means of simplified formulas. Similar principles are applicable to peritoneal dialysis (PD), where weekly Kt/V and creatinine clearance are used. Recommended minimal targets for dialysis adequacy have been defined by both American and European guidelines (DOQI and European Best Practice Guidelines, respectively). The question of how to improve the severe outcome of dialysis patients has recently come back to the fore, since the results of two recent randomized controlled trials led to the conclusion that, in thrice weekly HD and in PD, increasing the dialysis dose well above the minimum requirements of current American guidelines did not improve patient outcome. Daily HD (defined as a minimum of six HD sessions per week), in the form of either short daytime HD or long slow nocturnal HD, is regarded as a possibility to improve dialysis patient outcome. The results of the studies published so far indicate excellent results with respect to all outcomes analysed: optimal blood pressure control, regression of left ventricular hypertrophy and amelioration of left ventricular performance, improvement of renal anaemia, optimal hyperphosphataemia control, improvement of nutritional status, reduction in oxidative stress indices and improvement in quality of life. The basis for these beneficial effects is thought to be a more physiological clearance of solutes and water, with reduced pre- and post-HD solute concentrations and interdialytic oscillation, compared with traditional HD. Apart from concerns regarding reimbursement and organizational issues, no serious adverse effects have been described with daily HD. However, the evidence accumulated is limited mainly to retrospective cohorts, with small patient numbers and no adequate controls in most instances. Therefore, large prospective studies with adequate controls are required to make daily HD accepted by reimbursing authorities and patients. Given the available observational and interventional body of evidence, there is no reason to reduce arbitrarily dialysis dose, particularly dialysis treatment time in HD patients treated three times weekly. Daily HD represents a very promising tool for improving dialysis outcomes and quality of life, although its impact on patient survival has not yet been proven definitively.

Acute Effects of High-Dose Furosemide on Residual Renal Function in CAPD Patients

♦ Background High doses of furosemide can increase urine volume in chronic peritoneal dialysis (CAPD) patients. However, no information is available about effects on urinary solute excretion in relation to residual glomerular filtration rate (GFR), urinary furosemide excretion, and peritoneal solute kinetics. ♦ Methods Diuretic response and the effect on peritoneal fluid and solute transport parameters were investigated in 7 stable CAPD patients with residual renal function (median urine volume 350 mL/24 hours, range 140–1900 mL/24 hours). Comparisons were made during two clearance periods of 24 hours: one without (P1) and one during 2 g furosemide (P2). ♦ Results The median increase in urine volume was 400 mL (range 270 – 910 mL, p &lt; 0.02) and the increase in sodium excretion was 54 mmol (range 25 –118 mmol, p &lt; 0.02). No change in GFR was found between P1 (2.4 mL/minute, range 0.6 – 5.7 mL/min) and P2 (2.0 mL/min, range 1.0 – 4.8 mL/min). An increase in fractional clearance was found for volume, sodium, potassium, and osmolality ( p &lt; 0.02). No change was found in the fractional clearance of urea and electrolyte-free water. Furosemide excretion in urine was 8.7 mg/24 hours (range 2.1 – 38 mg/24 hours) and in dialysate 4.9 mg/24 hours (range 1.9 – 7.8 mg/24 hours). Plasma furosemide concentration was 29.5 mg/L (range 6.2 – 43.9 mg/L). A positive correlation was found between residual GFR and total urine furosemide excretion ( r=0.93, p &lt; 0.005). Efficiency, expressed as the increase in fractional sodium clearance (percent) per milligram of furosemide excreted per 24 hours, was 1.2%/mg (range 0.3%–11.3%/mg). ♦ Conclusion High-dose furosemide is effective in CAPD patients in increasing urine volume and electrolyte excretion without affecting urea and creatinine clearance. In CAPD patients, the individual response to an identical high dose of furosemide is dependent on the magnitude of residual GFR.

Does dialysis therapy improve autonomic and peripheral nervous system abnormalities in chronic uraemia?

Autonomic nervous system (ANS) dysfunction and peripheral neuropathy occur in patients with chronic renal insufficiency. Adequate renal replacement therapy should prevent development or correct these abnormalities. We studied retrospectively ANS and peripheral neuropathy in 32 patients with chronic uraemia who received either haemodialysis (16) or peritoneal dialysis (16) therapy, and compared the observed dialysis efficiency with changes in neurological function. Heart rate variability (HRV) time domain indices and peripheral sensory nerve conduction studies were followed for a mean of 2.9 years. The adequacy of haemodialysis (HD) efficiency was estimated by Kt/V, an index of fractional urea clearance. Adequacy of continuous ambulatory peritoneal dialysis (CAPD) was estimated on the basis of the patient's wellbeing and nutritional status as excellent, satisfactory or poor. Based on observed changes in HRV time domain measures, the observations were divided in three subgroups: improved, unchanged or deteriorated. The peripheral sensory nerve conduction studies were abnormal in 38% of the patients and did not change significantly during the study. Improvement in HRV time domain measures occurred in HD patients with mean Kt/V > 1.20 or in CAPD patients with satisfactory or excellent response to dialysis treatment. Values of Kt/V < 0.85 in HD patients were associated with progressive deterioration of autonomic neuropathy. Diabetic patients (n = 4) differed from others as their HRV was grossly abnormal and did not improve. The adequacy of haemodialysis is a predictor of improvement of cardiac autonomic nervous function in chronic uraemia. The same trend of improvement was seen also in CAPD patients.

Comparison of methods to predict equilibrated Kt/V in the HEMO Pilot Study

The ongoing HEMO Study, a National Institutes of Health (NIH) sponsored multicenter trial to test the effects of dialysis dosage and membrane flux on morbidity and mortality, was preceded by a Pilot Study (called the MMHD Pilot Study) designed to test the reliability of methods for quantifying hemodialysis. Dialysis dose was defined by the fractional urea clearance per dialysis determined by the predialysis BUN and the equilibrated postdialysis BUN after urea rebound is completed (eKt/V). In the Pilot Study the blood side standard for eKt/V was calculated from the predialysis, postdialysis, and 30-minute postdialysis BUN. Four techniques of approximating eKt/V that eliminated the requirement for the 30-minute postdialysis sample were also evaluated. The first adjusted the single compartment Kt/V using a linear equation with slope based on the relative rate of solute removal (K/V) to predict eKt/V (rate method). The second and third techniques used equations or mathematical curve fitting algorithms to fit data that included one or more samples drawn during dialysis (intradialysis methods). The fourth technique (dialysate-side) predicted eKt/V from an analysis of the time-dependent profile of dialysate urea nitrogen concentrations (BioStat method; Baxter Healthcare, Inc., Round Lake, IL, USA). The Pilot Study demonstrated the feasibility of conventional and high dose targets of about 1.0 and 1.4 for eKt/V. Based on the blood side standard method, the mean +/- SD eKt/V for patients randomized to these targets was 1.14 +/- 0.11 and 1.52 +/- 0.15 (N = 19 and 16 patients, respectively). Single-pool Kt/Vs were about 0.2 Kt/V units higher. Results were similar when eKt/V was based on dialysate side measurements: 1.10 +/- 0.11 and 1.50 +/- 0.11. The approximations of eKt/V by the three blood side methods that eliminated the delayed 30-minute post-dialysis sample correlated well with eKt/V from the standard blood side method: r = 0.78 and 0.76 for the single-sample (Smye) and multiple-sample intradialysis methods (N = 295 and 229 sessions, respectively) and 0.85 for the rate method (N = 295). The median absolute difference between eKt/V computed using the standard blood side method and eKt/V from the four other methods ranged from 0.064 to 0.097, with the smallest difference (and hence best accuracy) for the rate method. The results suggest that, in a dialysis patient population selected for ability to achieve an equilibrated Kt/V of about 1.45 in less than a 4.5 hour period, use of the pre and postdialysis samples and a kinetically derived rate equation gives reasonably good prediction of equilibrated Kt/V. Addition of one or more intradialytic samples does not appear to increase accuracy of predicting the equilibrated Kt/V in the majority of patients. A method based on dialysate urea analysis and curve-fitting yields results for equilibrated Kt/V that are similar to those obtained using exclusively blood-based techniques of kinetic modeling.

A simple and accurate method to determine equilibrated post-dialysis urea concentration

Fractional urea clearance or KtIV is usually determined from a two-point method using preand post-dialysis blood urea concentrations [1, 2]. Kt/V then becomes critically dependent upon post-dialysis urea concentration [3]. Since immediate post-dialysis urea sampling does not account for recirculation and rebound, it tends to overestimate hemodialysis efficiency [4]. This may occur especially with short, highly efficient modalities [5—8]. A delayed post-dialysis urea determination allows a more accurate estimation of the effective dialysis dose. Thus, special attention must be paid to sample timing for post-dialysis urea concentration. Shortly-delayed blood sampling (2 mm after the end of the session) should correct for vascular access and cardiopulmonary recirculation [9]. However, the internal resistance to urea transfer from different compartments, which explains a large part of the observed urea rebound, is further delayed [10, 11]. Consequently, late blood sampling (30 to 45 mm after the end of the session) has been recommended to obtain an equilibrated urea concentration, but such a delay is inconvenient in routine clinical practice. To overcome this problem, Smye et al have suggested a third early intradialytic blood sample for urea (70 to 90 mm from the beginning) that may be used to calculate equilibrated post-dialysis urea concentration [12]. Indeed, the Smye model has proven accurate in the prediction of equilibrated urea [13, 14]. However, the requirements of this approach (a third blood sample and mathematical calculation) may limit its clinical application. In a previous study concerning the determination of urea rebound using an on-line urea sensor on the ultrafiltrate outflow, the following observations were made: (1) rebound amplitude increased with session efficiency; (2) urea concentration reached a plateau 30 minutes post-session; (3) intradialytic urea concentration 30 minutes before the end of the session was equivalent to the post-dialysis equilibrated value. The present study was undertaken to validate this last observation [15].

The Relationship Between Urine Volume and Drain Volume as Determinants of Fractional Urea Clearance in Continuous Peritoneal Dialysis

A logistic regression model developed and validated in Albuquerque identified 24 hr urine volume (UV) and 24 hr drain volume/(body water) (DV/V) as predictors of fractional urea clearance (KT/V) in continuous peritoneal dialysis (CPD). Solution of this model provided DV/V values consistent with KT/V at least equal to a target KT/V for a given UV. The predictive accuracy of these unique DV/V values was tested in urea kinetic studies performed in 108 CPD patients in Thessaloniki and Athens with UV varying between 0 and 2 L/24 h. Two target weekly KT/V values, 1.70 and 1.90, were investigated. The equation DV/V = (5.2811-3.6996 UV)/ 17.554, derived by solving the logistic regression model, detected weekly KT/V > 1.70 (69/108, or 63.9% of the studies) with a sensitivity of 87.3% and a specificity of 60.4%. According to the same equation, the maximal UV consistent with weekly KT/V < or = 1.70 is 1.427 L/24 hr. The equation DV/V = (5.4994-2.6007 UV)/17.007 detected weekly KT/V > 1.90 (44/108, or 40.7% of the studies) with a sensitivity of 90.3% and a specificity of 79.2%. According to this equation, the maximal UV consistent with weekly KT/V < or = 1.90 is 2.115 L/24 hr. Determination of the lowest daily DV consistent with a target KT/V at any daily UV (within a wide range) is feasible in CPD.

Fractional urea clearance in continuous ambulatory peritoneal dialysis: effects of volume disturbances.

The effects of volume disturbances on the KT/V were investigated prospectively in 133 consecutive urea clearance studies on patients on continuous ambulatory peritoneal dialysis (CAPD). Four subjects (group A) had fluid loss (actual weight < dry weight), 57 (group B) were studied on the basis of their dry weight, 58 (group C) had moderate fluid excess (0.5% of dry weight), and 14 patients (group D) had severe fluid excess (> 5% of dry weight). The KT/V was calculated on the basis of dry weight and actual weight with V obtained from the Watson anthropometric formulae which were applied either uncorrected or with a correction for changes in body water from dry weight conditions. The groups compared by variance analysis. The following weekly KT/V estimates were obtained: (1) using dry weight V: group A 1.81 +/- 0.17, group B 2.0 +/- 0.59, group C 1.79 +/- 0.46, group D 1.85 +/- 0.37 (no difference between groups); (2) using uncorrected actual weight V: group A 1.85 +/- 0.15, group B 2.05 +/- 0.59, group C 1.77 +/- 0.45, group D 1.78 +/- 0.37 (group B had a higher KT/V than group C, p < 0.05), and (3) using corrected actual weight V: group A 1.93 +/- 0.14, group B 2.05 +/- 0.59, group C 1.70 +/- 0.43, group D 1.63 +/- 0.36, (group B had a higher KT/V than either group C or group D, both at p < 0.01). In CAPD, fluid deficit is rare and causes a small increase in KT/V, whereas fluid retention is frequent and causes a decrease in KT/V. This decrease is pronounced in patients with severe fluid excess. The uncorrected Watson formulae underestimate V and, consequently, overestimate KT/V in CAPD patients with fluid excess.

The effect of dialyzer membrane and etiology of kidney disease on the preservation of residual renal function in chronic hemodialysis patients.

It is commonly believed that renal function rapidly decreases in the vast majority of chronic hemodialysis patients. Three hundred thirty-four patients starting chronic hemodialysis between 1/1/88 and 12/31/92 at six hemodialysis units were prospectively studied. Renal function was determined every 3 months by 68 hr urine collection expressed as weekly fraction urea clearance (L/L total body water/wk). glomerular filtration rate was calculated from the mean of the urea and creatinine clearance. After 3 years, glomerular filtration rate exceeded 4 ml/min in 14% of patients. For a thrice weekly dialysis schedule, it was assumed that a weekly fractional urea clearance of 3 L/L/wk is equal to a dialysis KT/V of 1 and patients need a minimum KT/V of 1.2 per treatment. After 3 years of chronic hemodialysis therapy, residual renal function was found to provide 15% of the dialysis requirement in 19% of patients and 30% of the dialysis requirements in 9% of patients. The occasional patient maintains sufficient residual renal function to provide over 40% of the dialysis requirement for over 4 years. In a retrospective analysis, patients treated only with Cupraphan membrane had a more rapid loss of renal function compared to those never treated with Cupraphan (Besnberg Corp., Germany). The majority of patients with polycystic kidney disease maintained a glomerular filtration rate greater than 2 ml/min for 4 years or longer.