Ionic dialysance: principle and review of its clinical relevance for quantification of hemodialysis efficiency

Ionic dialysance (D) is an online measured variable now available on several dialysis monitors to evaluate small-solute clearance. Based on conductivity measurements in the inlet and outlet dialysate, the principle of the measurement and the different measurement methods are described. Studies that have evaluated the reliability of ionic dialysance to assess dialysis efficiency are discussed. These studies are divided into two groups: the first comparing ionic dialysance to urea clearance and the second comparing Dt/V to Kt/V(urea), in which the uncertainties of the measurement of V(urea) could have misrepresented the relationship between Dt/V and Kt/V(urea). When Kt/V(urea) via the Daugirdas second-generation equation taking the rebound into account is considered, slight-even nonsignificant-differences are evidenced between Kt/V(urea) and Dt/V. Therefore, ionic dialysance should be considered as a valid measure in future guidelines for dialysis efficiency.     

Use of ionic dialysance to calculate Kt/V in pediatric hemodialysis

Online clearance (OLC) monitor measures conductivity difference between dialysate entering and leaving the dialyser. Derived ionic dialysance (ID) represents effective urea clearance from which Kt/V is calculated, allowing Kt/V monitoring at every treatment without blood sampling. We tested ID accuracy in children and provide recommendations for its use. Using Fresenius machines 2008?K with built-in OLC monitors, we studied 45 hemodialysis (HD) sessions and 168 calculated Kt/V results in 11 patients. Urea distribution volume (V), needed to calculate Kt/V from ID, was estimated using three methods: Mellits and Cheek (MC), KDOQI recommended total body water nomograms (TBWN) and OLC-derived independent from tested HD sessions. Reference spKt/V from pre- and post-HD BUN (Daugirdas) was compared with Kt/V calculated from ID using three different estimated V's. ID was accurate in calculating Kt/V in children when V derived from OLC was used (P?=?0.42), with absolute error 0.14?±?0.12. If TBWN-derived V was used, Kt/V was consistently underestimated by 0.32?±?0.22. TBWN-derived V can still be recommended for use with OLC for monitoring trend in Kt/V, if underestimation of spKt/V of average 0.3 is accounted for. MC-derived V results in even greater underestimation of spKt/V and therefore cannot be recommended for use with OLC.     

Energy metabolism,body composition,and urea generation rate in hemodialysis patients

Hemodialysis (HD) adequacy is currently assessed using normalized urea clearance (Kt/V), although scaling based on Watson volume (V) may disadvantage women and men with low body weight. Alternative scaling factors such as resting energy expenditure and high metabolic rate organ mass have been suggested. The relationship between such factors and uremic toxin generation has not been established. We aimed to study the relationship between body size, energy metabolism, and urea generation rate. A cross‐sectional cohort of 166 HD patients was studied. Anthropometric measurements were carried on all. Resting energy expenditure was measured by indirect calorimetry, fat‐free mass by bio‐impedance and total energy expenditure by combining resting energy expenditure with a questionnaire‐derived physical activity data. High metabolic rate organ mass was calculated using a published equation and urea generation rate using formal urea kinetic modeling. Metabolic factors including resting energy expenditure, total energy expenditure and fat‐free mass correlated better with urea generation rate than did Watson volume. Total energy expenditure and fat‐free mass (but not Watson Volume) were independent predictors of urea generation rate, the model explaining 42% of its variation. Small women (<mean V) had a significantly higher urea generation rate per kg than women with higher V. Similarly urea generation rate normalized to fat‐free mass was significantly greater in small women than in all others (significant only in comparison to larger men). Exercise‐related energy expenditure correlated significantly with urea generation rate. Energy metabolism, body composition and physical activity play important roles in small solute uremic toxin generation in HD patients and hence may impact on minimum dialysis requirements. Small women generate relatively more small solute toxins than other groups and thus may have a higher relative need for dialysis.     

Comparisons of Kt/V evaluated using an online method and calculated from urea measurements in patients on intermittent hemodialysis

Kt/V(urea) (Kt/V) depends on the method applied for its evaluation. Our aim was to compare Kt/V obtained using the conductivity online method and that calculated from urea measurements. Studies were carried out in 40 patients. A stable dialysis schedule was maintained during the study. Online Kt/V was measured every week or 4 consecutive months. Single pool Kt/V (spKt/V) was calculated from urea estimations in the fourth week of the first month and in the last week of the fourth month of studies, using the formulas: (1)spKt/V = -ln(Ct/Co), where Ct is the postdialysis urea concentration obtained at the end of dialysis, Co the predialysis urea concentration obtained before the start of the blood pump; (2)spKt/V = -ln(R - 0.008 x t - f x UF/W), where R is the Ct/Co, t the duration of HD session, f=1.0, UF is the ultrafiltration volume (l), W is the body weight after the HD session; and (3)spKt/V + -ln(R - 0.008 x t) + (4 - 3.5 x R) x UF/W. The equilibrated Kt/V (eKt/V) was calculated as (3)spKt/V - {0.47 x [(3)spKt/V]/t} + 0.02. Correlation analysis was performed between all obtained Kt/V. Weekly online Kt/V was stable during 4 months of studies. In the first month, the respective values of online Kt/V, (1)spKt/V, (2)spKt/V, (3)spKt/V, and eKt/V were 1.15+/-0.14, 1.16+/-0.14, 1.38+/-0.17, 1.36+/-0.20, and 1.22+/-0.13. In the fourth month, these values were 1.17+/-0.14, 1.16+/-0.17, 1.38+/-0.22, 1.35+/-0.20, and 1.22+/-0.18. The respective values of Kt/V, estimated in the first and fourth month, were not different and showed a positive correlation: the highest one occurred between online Kt/V estimated at the indicated study periods (r=0.713, p=0.0000). Online Kt/V was significantly lower than (2)spKt/V, (3)spKt/V, and eKt/V. Correlation coefficients between online Kt/V, spKt/V, and urea reduction ratio did not exceed 0.490. Our studies show that Kt/V obtained using online monitoring indicates a lower intermittent hemodialysis adequacy that those calculated from urea measurements. This difference has to be remembered in application of results to clinical practice.     

Half the V by 120: A practical approach to the prevention of the dialysis disequilibrium syndrome

The dialysis disequilibrium syndrome (DDS) results from osmotic shifts between the blood and the brain compartments. Patients at risk for DDS include those with very elevated blood urea nitrogen, concomitant hypernatremia, metabolic acidosis, and low total body water volumes. By understanding the underlying pathophysiology and applying urea kinetic modeling, it is possible to avoid the occurrence of this disorder. A urea reduction ratio (URR) of no more than 40%–45% over 2 h is recommended for the initial hemodialysis treatment. The relationship between the URR and Kt/V is useful when trying to model the dialysis treatment to a specific URR target. A simplified relationship between Kt/V and URR is provided by the equation: Kt/V = −ln (1 − URR). A URR of 40% is roughly equivalent to a Kt/V of 0.5. The required dialyzer urea clearance to achieve this goal URR in a 120-min treatment can simply be calculated by dividing half the patient's volume of distribution of urea by 120. The blood flow rate and dialyzer mass transfer coefficient (K₀A) required to achieve this clearance can then be plotted on a nomogram. Other methods to reduce the risk of DDS are reviewed, including the use of continuous renal replacement therapy.     

Complementary parameter for dialysis monitoring based on UV absorbance

An optical on-line monitoring system aimed at the estimation of dialysis dose has been tested clinically. The natural logarithmic slope is used to calculate Kt/V(urea) from ultraviolet (UV)-absorbance measurements. Errors in the calculation of Kt/V(urea) may appear due to changes in blood and dialysate flow or due to disturbances when the slope is used to estimate dialysis dose. This study introduces a new parameter for dialysis monitoring that may be used as a complementary parameter, the area under UV-absorbance curve (AUCa), to reflect a total solute removal during dialysis. The aim was to investigate the relationship between this new dialysis on-line monitoring parameter, AUCa, and the total removal of a few solutes. Fifteen patients were monitored during hemodialysis using UV absorbance at the wavelength of 297 nm. All spent dialysate passed through a flow cuvette in a spectrophotometer and then further to a collection tank where solute concentrations in the entire spent dialysate were determined. The AUCa at 297 nm was compared with the total amount of removed solute in the tank (reference method). The result shows strong correlations between AUCa and the total removal of urea, urate, creatinine, and phosphate during a given treatment and less strong correlation in all 15 patients together. A first indication of a new, possible, complementary parameter in hemodialysis treatment is presented, the AUCa, prospected to estimate solute removal.     

Quantitating Dialysis in the Home Hemodialysis Patient: A Simple and Practical Approach

Home hemodialysis is the most cost-effective form of dialysis and is associated with the lowest mortality. Home hemodialysis patients are usually highly motivated, independent, and actively employed. Because of the minimal supervision they require and the fact that they are not in a controlled environment, it is easy to overlook the measurement of their dialysis adequacy. We studied 6 home hemodialysis patients and demonstrated that blood urea measured 30 min before the end of dialysis (Ct-30) is equivalent to that measured 30 min after the end of dialysis (Ct+30). The Kt/V results using Ct-30, Kt/V(Ct-30), were almost equivalent to Kt/V(Ct+30) (p = 0.5). The Kt/V Kt/V(Ct) using blood urea measured at the end of dialysis (Ct) significantly overestimated Kt/V(Ct-30) and Kt/V(Ct+30) (p = 0.007) The calculated percent reduction of urea (PRU) was about 5% less when using Ct-30 compared with Ct (p = 0.001). Taking blood samples 30 min before the end of dialysis for urea kinetics is more convenient for the home dialysis patients, since no other technical aspects of dialysis need their attention. The samples can be delivered to the laboratory the following day, because the blood may be stored in heparinized tubes at 4°C without deterioration of urea and creatinine concentrations. The Kt/V(Ct-30) was almost equal to Kt/V(Ct+30), so there is no longer any concern for the errors introduced by urea rebound. The blood pump must be reduced to 80 mL/min for about 10 sec to eliminate the errors due to fistula and cardiopulmonary recirculation. A simple programmable calculator will facilitate the calculation of accurate results using the Daugirdas second-generation formula.     

What is a surrogate marker for optimal dialysis?

To find a surrogate marker to obtain optimal dialysis delivery from the viewpoint of nutrition, 180 maintenance hemodialysis patients (109 males/71 females) were enrolled between October 1999 and June 2006 at our kidney center. In the 449 hemodialysis treatments, ultrapure dialysis solutions and high-flux synthetic membranes were utilized. Parameters were measured by Kt/V(urea) and postdialysis urea rebound, Kc (the cellular membrane clearance for urea), urea clear space (CS), %creatinine generation rate, %lean body mass, total body water, and so on. We examined the correlation between dialysis delivery and nutritional parameters: Kt/V(urea) and postdialysis urea rebound were found to be strongly and negatively correlated with nutritional parameters. However, Kc and CS have shown positive and strong correlations with nutritional parameters such as %creatinine generation rate, %lean body mass, and total body water as well. In addition, the age factor was correlated with Kt/V(urea) positively, and it influenced Kc and CS negatively. As a conventional dialysis parameter, Kt/V(urea) did not reflect nutrition, but Kc was found to improve nutrition due to the increase of the dialysis delivery. Therefore, Kc might be a reliable surrogate marker for optimal dialysis.     

We Should Strive for Optimal Hemodialysis: A Criticism of the Hemodialysis Adequacy Concept

Adequacy of hemodialysis is frequently equated with Kt/V_urea , the amount of urea clearance (K) multiplied by time (t) and divided by urea distribution volume (V). Several formulas have been developed to calculate Kt/V_urea from the pre‐ and post‐dialysis urea concentrations. In three‐times‐weekly hemodialysis, a single pool (spKt/V_urea) value of 1.3 per treatment is commonly considered to indicate adequate therapy.
Despite providing the recommended spKt/V_urea of 1.3 per treatment, short dialysis with rapid ultrafiltration is associated with multiple intradialytic and interdialytic complications. Patients experience cramps, nausea, vomiting, headaches, fatigue, hypotensive episodes during dialysis, and hangover after dialysis; patients remain fluid overloaded with subsequent poor blood pressure control, left ventricular hypertrophy, diastolic dysfunction, and high cardiovascular mortality.
According to Webster's dictionary, "optimal" means most desirable or satisfactory; "adequate" means sufficient for a specific requirement or barely sufficient or satisfactory. Optimal dialysis is the method of dialysis yielding results that cannot be further improved. New approaches, including hemeral quotidian or long nocturnal dialysis, provide opportunities to abandon the notion that adequate dialysis is "good enough" for our patients. Optimal dialysis should be our goal. Dialysis sessions should be long and frequent enough to provide excellent intra‐ and interdialytic tolerance of hemodialysis, normalization of serum calcium and phosphorus, blood pressure control, normal myocardial morphology and function, and hormonal balance, and to eliminate all, even subtle, uremic symptoms.     

News and Traditional Indications from Short Daily Dialysis: Different Schemes to Optimized ESF Response

Dialysis adequacy indexed by Kt/V in hemodialysis (HD) patients is recommended as a single-pool Kt/V of at least 1.2 per session thrice weekly. But many patients cannot achieve this adequacy target. Although dialysis time is the most important as a factor influencing Kt/V, it is difficult to prolong dialysis time in practice because of its economic impact and poor patient compliance.
Objective:  The aim of this study is to investigate the effect of increasing blood flow rate on dialysis adequacy in HD patients with low Kt/V.
Methods:  This study enrolled 36 HD patients with single-pool Kt/V <1.2 per session thrice weekly, which was measured in dialyzer blood flow rate of 230 mL/min. We increased 15% of blood flow rate in patients <65 kg of body weight and 20% in patients >65 kg. And then we compared Kt/V and urea reduction ratio (URR) between before and after increasing blood flow rate.
Results:  The mean age was 48 ± 11 years (23–73 years), and the number of males was 25. Of the total patients, 24 patients had dry weight <65 kg. Mean dialysis duration was 52 ± 50 months (3–216 months). Mean Kt/V before increasing blood flow rate was 1.02 ± 0.09. It increased to 1.14 ± 0.12 after increasing blood flow rate (p < 0.001). Of the total 36 patients, 13 patients (36.1%) achieved adequacy target (Kt/V ≤ 1.2). Mean URR before increasing blood flow rate was 56.9 ± 4.0%. It also increased to 60.8 ± 4.1% (p < 0.001).
Conclusion:  Our data suggest that increasing blood flow rate by 15–20% of previous flow rate is effective in achieving dialysis adequacy in HD patients with low Kt/V.     

Comparative Study between Classic and Newer Methods for the Evaluation of Hemodialysis Adequacy

Aim:  The comparative study of hemodialysis (HD) adequacy of Kt/V measurement between classic method (Daugirdas formula) and urea sensor monitor (online).
Patients and methods:  30 patients with end-stage renal failure undergoing dialysis were studied. A comparative evaluation of HD adequacy during the same session was done with two different methods: (1) blood samples were drawn in the beginning and in the end of HD session for the measurement of blood urea nitrogen (BUN) and after measurement of HD adequacy by 3rd generation Daugirdas formula and (2) urea sensor monitor use for continuous HD adequacy measurement during HD session.
Results:  There was statistically significant correlation of Kt/V Daugirdas with Kt/V online (r = 0.8, p < 0.001). Also there was statistically significant correlation between solute removal index (SRI), Kt/V Daugirdas (r = 0.81, p < 0.001) and Kt/V online (r = 0.92, p < 0.001). From nutrition indices that were measured, the protein catabolic rate (PCR) had marginal negative correlation with the two compared adequacy indices, Kt/V Daugirdas (r = −0.24, p < 0.03), and Kt/V online (r = −0.17, p < 0.03) although the nPCR (normalized PCR) had marginal positive correlation (r = 0.35, p < 0.05) (r = 0.42, p < 0.05).
Conclusions:  The use of online urea sensor monitors contributes to the easy measurement of adequacy and nutrition indices and hence complicated mathematical formulas are not necessary. The results of these measurements are reliable and comparable with classic methods of HD adequacy evaluation.     

Measurement of Hemodialysis Adequacy in a Changing World

Defining adequacy of dialysis remains an elusive goal. The application of the Kt/V_urea concept to clinical dialysis was a major improvement in trying to define a dialysis dose. Intuitively, the Kt/V concept makes a great deal of sense: the urea clearance of the dialyzer during dialysis (K), multiplied by the time (t) of dialysis, divided by the patient's urea distribution volume (V) ought to give the best number to compare the efficiency of dialyses that patients receive. There are, however, many pitfalls associated with the whole Kt/V_urea concept.     

Inherent Errors in the Quantitation of Dialysis Delivery: Implications For CAPD and Daily Hemodialysis

When compared to intermittent dialysis, the theoretical advantages of continuous dialysis may be less important than its practical disadvantage: the inability to accurately quantify dialysis. With intermittent dialysis the change in blood urea nitrogen over the course of the treatment allows the ratio of K (urea clearance) to V (volume of distribution of urea or total body water) to be determined, hence an accurate Kt/V. In continuous dialysis this approach cannot be used due to the steady-state nature of blood urea levels. Instead, V is estimated, generally from the Watson equations. This estimate has sufficient inaccuracy to result in substantial unrecognized underdialysis in many patients.     

Daily Hemodialysis versus Standard Hemodialysis: TAC,TAD, Weekly eKt/V,std(Kt/V), and PCRn

Seven patients, mean age 42.57 ± 15.69 years (range 21 – 67 years), on standard hemodialysis (SHD), 4 – 5 hours, three times per week for 11.0 ± 6.63 years (range 1 – 18 years), were switched to daily hemodialysis (DHD), 2 – 2.5 hours, six times per week. For each type of treatment similar parameters were applied, and the total weekly time was the same. Mean duration of DHD was 15.4 ± 4.98 months (range 7 – 20 months). We report here our results of quantification in each method, including time-averaged concentration (TAC), normalized protein catabolic rate (PCRn), equilibrated Kt/V (eKt/V), equivalent normalized continuous standard clearance [std(Kt/V)], equivalent renal urea clearance (eKRn), and time-averaged deviation (TAD). With DHD, urea TAC was reduced from 19.09 ± 3.47 to 15.16 ± 3.21 mmol/L (p = 0.026), urea TAD diminished from 4.76 ± 1.04 to 2.52 ± 0.57 mmol/L (p = 0.000 53), PCRn increased from 1.11 ± 0.23 to 1.42 ± 0.24 g/kg/day (p = 0.001), weekly eKt/V increased from 4.11 ± 0.31 to 4.74 ± 0.43 (p = 0.000 25), std(Kt/V) rose from 2.17 ± 0.06 to 4.02 ± 0.25 (p = 0.0001), and eKRn increased from 12.96 ± 0.60 to 21.7 ± 3.09 mL/min (p = 0.000 45). On DHD the most important quantitative variation is the decrease of urea TAD (closer to that of a healthy kidney), due to the increased frequency of dialysis; std(Kt/V) practically doubled and represents 30% of that of normal renal function. These changes are probably the main explanation for the clinical improvements, but it is difficult to dissociate the effects of increased dialysis dose from the effects of decreased TAD.     

Kinetic Studies on Urea Extraction with Hemodialysis in Adolescents by On‐line Monitoring of Dialysate Urea

Kinetics of urea extraction during a single dialysis session in children are unknown, because analysis of solutes in dialysate is difficult due to their extreme dilution. >Objective: A novel urea monitor of the Gambro Company might be of help in studying urea kinetics also in children. Methods: We studied 107 urea kinetics in 5 adolescents aged 13–19 years, weighing 26–58 kg, and looked for influences of membrane size, blood flow, and duration of one dialysis session. Urea measurement applies to the change of electric dialysate conductivity due to ionization because of urea splitting by urease. Bicarbonate dialysis regimen was 4–5 h each, 3 times a week, using polysulfone high‐flux dialyzers (Fresenius F60 or F80, depending on body size). Results: Average 4‐h urea Kt/V values for F60 (n = 85) were 1.69±0.53 and for F80 (n = 21) 1.63±0.25, extracted urea mass was 16.0±5.4 g and 32.5±5.4 g, respectively (p < 0.05); Kt/V urea results for blood flows of 180–220 mL/min were 1.36±0.52 and for <180 mL/min 1.10±0.43; extracted urea mass was 17.3±8.0 and 11.7±4.9 g, respectively (p < 0.05). Total average urea extraction ratio after 2 h of dialysis (n = 107) was 64.8±5.6%. Extraction ratio during the 4^th h of dialysis was only 15.3±4.1% and during the 5^th h not more than 9.0±3.6% of total urea extraction. Conclusion: Kinetics of urea extraction helps understanding dialysis processes in children. Adapting the size of the dialyzer according to body size raises urea extraction and maintains urea clearance Kt/V at the desired quality level. An inadequate blood flow lowers both urea extraction and urea clearance Kt/V. Prolonging dialysis beyond 4 h is, at least in concern of urea kinetic modelling, a rather ineffective means. We speculate that children with blood flow problems should be dialysed more often.     

Use of Systemic Blood Urea Nitrogen Levels Obtained 30 Minutes before the End of Hemodialysis to Portray Equilibrated,Postdialysis Blood Urea Nitrogen Values

Blood urea nitrogen (BUN) levels obtained at 30 minutes before the end of dialysis were found to be closely similar to equilibrated, postdialysis BUN values obtained 30 minutes after the end of dialysis. Because of this similarity, the former BUN values can be used to derive equilibrated urea reduction ratio, or equilibrated Kt/V instead.     

Modeling the Dose of Home Dialysis

The growing interest in daily dialysis and combined continuous and intermittent dialysis treatments has created the need for a dialysis dosing model that is valid over a wide range of dosing frequency and intensity. Three models have been described for this purpose and are reviewed here. They have in common the concept of a continuous clearance value which is equivalent to the summed intermittent dialysis prescribed. The continuous clearance models all define a point on the saw-toothed blood urea nitrogen (BUN) concentration profile and calculate the continuous clearance required to achieve this at the same urea generation rate. The points modeled are the peak predialysis concentration (pkKt/V), the average Co (standard Kt/V, stdKt/V), and time-averaged urea concentration (TAC), which is termed equivalent renal clearance (EKRt/V). At the present time the only data for evaluation of clinical relevance of the three models is continuous ambulatory peritoneal dialysis (CAPD) outcome. The stdKt/V predicts that optimal CAPD outcome requires weekly stdKt/V 2.0, while the pkKt/V and EKRt/V models predict optimal doses of 1.8 and 3.0. These results suggest that the stdKt/V is the most realistic model, but data over much higher levels of therapy are not yet available to judge generalizability. The stdKt/V model was used to assess dose in two hemodialysis studies with 5 to 6 dialyses per week and showed that in one study the stdKt/V was only 2.0, while in the second study it was 5.6. These results show that dose can vary widely with a similar number of dialyses per week and point to the need for a generalized dosing model to guide and compare studies of daily home dialysis.     

Gender,low Kt/V,and mortality in Japanese hemodialysis patients: Opportunities for improvement through modifiable practices

Guidelines have recommended single pool Kt/V > 1.2 as the minimum dose for chronic hemodialysis (HD) patients on thrice weekly HD. The Dialysis Outcomes and Practice Patterns Study (DOPPS) has shown that “low Kt/V” (<1.2) is more prevalent in Japan than many other countries, though survival is longer in Japan. We examined trends in low Kt/V, dialysis practices associated with low Kt/V, and associations between Kt/V and mortality overall and by gender in Japanese dialysis patients. We analyzed 5784 HD patients from Japan DOPPS (1999–2011), restricted to patients dialyzing for >1 year and receiving thrice weekly dialysis. Logistic regression models estimated the relationships of patient characteristics with Kt/V. Logistic models also were used to estimate the proportion of low Kt/V cases attributable to various treatment practices. Multivariable Cox regression was used to estimate the associations of low Kt/V, blood flow rate (BFR), and treatment time (TT), with all‐cause mortality. From 1999 to 2009, the prevalence of low Kt/V declined in men (37–27%) and women (15–10%). BFR <200 mL/min, TT <240 minutes, and dialyzate flow rate (DFR) < 500 mL/min were common (35, 13, and 19% of patients, respectively) and strongly associated with low Kt/V. Fifteen percent of low Kt/V cases were attributable to BFR <200 and 13% to TT <240, compared to only 3% for DFR <500. Lower Kt/V was associated with elevated mortality, more so among women (hazard ratio [HR] = 1.13 per 0.1 lower Kt/V, 95% CI: 1.07–1.20) than among men (HR = 1.06 per 0.1 lower Kt/V, 95% CI: 1.00–1.12). The relatively large proportion of low Kt/V cases in Japanese facilities may potentially be reduced 30% by increasing BFR to 200 mL/min and TT to 4 hours thrice weekly in HD patients. Associations of low Kt/V with elevated mortality suggest that modification of these practices may further improve survival for Japanese HD patients.     

State equation of liquid helium-4 from 0.8 to 2.5 K

A state equation for liquid helium is constructed in the range from 0.8 K to about 2.5 K, based on density and temperature as independent parameters. The equation has been fitted to experimental PVT, specific heat,(P/T) _v, sound velocity, and lambda line properties from 14 different authors to an accuracy comparable with reasonable experimental errors in the measured quantities. Inclusion of logarithmic terms leads to agreement with experimental data as close as 100 µK from the lambda line. It is found that the logarithmic amplitude ratio is not constant as a function of distance along the lambda line. A new determination of lambda line density is also presented. The equation is available in computer form.     

Increased dialyzer reuse with citrate dialysate

Dialyzer reuse is limited by the clotting of blood, which blocks the fibers and reduces the membrane surface area. Clotting during treatment may also reduce dialysis efficiency and potentially decrease delivered dose, Kt/V(urea). A new dialysate containing citric acid, instead of the standard acetic acid, as the acidifying agent has become available and is associated with reduced clotting during acute dialysis treatments. The effect of citric acid dialysate on dialyzer reuse was evaluated in this prospective, controlled, multicenter study involving maintenance hemodialysis patients. A total of 105 patients from five dialysis units were switched to the new dialysate and new dialyzers. Reuse outcome on the new dialysate was compared with the reuse on the regular acetic acid containing bicarbonate dialysate (controls). The overall reuse with citrate dialysate increased significantly from 15.1 +/- 9.4 to 18 +/- 10.0 (mean +/- SD) on regular and citrate dialysate, respectively (p = 0.0003). The most significant increase was seen in those patients who had limited reuse before the switch to citrate dialysate; 51, 59, and 134% increases occurred in those with 10 to 15, 5 to 10, and < 5 reuses at controls, respectively. Interestingly, the 10 patients with 10 or fewer reuses had significantly lower Kt/V(urea) at baseline (before the switch to citric acid dialysate) than those with > 10 reuses (1.23 +/- 0.23 vs. 1.47 +/- 0.23, respectively, p = 0.009). The Kt/V(urea) increased to 1.41 +/- 0.31 after the switch in the low-reuse group but the increase did not reach statistical significance (p = 0.07). The results from this study show that citric acid-containing dialysate is associated with increase in dialyzer reuse and appears to be related to reduced clotting.