Solute Removal Index Research Articles

The Clear Space Index.

Kt/V for urea (Kt/V) is a dimensionless clinical index of dialysis dose; however, it does not directly reflect the removal capacity of the solute. Since the total amount of solute removal, M, is directly proportional to the initial solute concentration CB(0), it is reasonable to introduce an index by dividing M by CB(0). This index was termed 'clear space' (CS) because it was later found that it reflects the body fluid volume, the concentration of which becomes zero by the treatment. Although CS originally requires measurement of M, storing all the effluent of dialysis fluid, it may be more easily calculated by measuring concentrations in blood, using a simpler formula without storing any effluent of dialysis fluid. Moreover, this technique is applied not only for urea, but also for much larger solutes. The concept of CS is also applied to peritoneal dialysis, identifying the maximum CS relative to the total effluent volume of the dialysis fluid. It was shown by CS analysis that the 1-compartment model may not work well, even for small solutes like urea, under higher levels of solute removal. It was also shown that divergence from the 1-compartment model was greater in patients with regenerated cellulose membranes than in those with synthetic polymeric membranes. Key Messages:CS is a simple yet useful solute removal index that avoids the effect of CB(0) and may be used for comparison of dose among two or more treatment modalities. Unlike Kt/V, CS can be measured for all kinds of solute, giving the average for two or more compartments in which the concentration of solute of interest becomes zero.

Are Dialysis Adequacy Indices Independent of Solute Generation Rate?

KT/V is by definition independent of solute generation rate. Alternative dialysis adequacy indices (DAIs) such as equivalent renal clearance (EKR), standard KT/V (stdKT/V), and solute removal index (SRI) are estimated as the ratio of solute mass removed to an average solute mass in the body or solute concentration in blood; both nominator and denominator in these formulas depend on the solute generation rate. Our objective was to investigate whether and under which conditions the alternative DAIs are independent of solute generation rate. By using general compartment modeling, we show that for the metabolically stable patient (in whom the solute generated during the dialysis cycle, typically, 1 week, is equal to the solute removed from the body), DAIs estimated for the dialysis cycle are in general independent of the average solute generation rate (although they may depend on the pattern of oscillations in the generation rate). However, the alternative adequacy parameters (such as EKR, stdKT/V, and SRI) may depend on solute generation rate for metabolically unstable patients.

Renal Replacement Therapy in Acute Renal Failure: Which Index is Best for Dialysis dose Quantification?

The "delivered dose" of dialysis may significantly affect the outcome of acute renal failure (ARF) patients requiring dialysis. Our study aimed to elucidate which dose quantification method offers an appropriate parameter to compare different treatments in ARF patients. Six sustained low-efficiency daily dialysis (SLEDD), and 7 continuous venovenous hemofiltration (CVVH) patients with a prescribed Kt/V of 1.0 were studied during a single treatment. CVVH was studied over the first 24 hours after initiation. SLEDD was performed for 6-12 h. Solute clearance (K) was determined by direct dialysate quantification (DDQ). The single-pool Kt/V (spKt/V), equilibrated Kt/V (eqKt/V), equivalent renal urea clearance (EKRc), and solute removal index (SRI) were calculated. There were no significant differences at enrollment between the SLEDD and the CVVH groups in any patient characteristics except for the serum creatinine levels. The prescribed Kt/V of both groups was similar (SLEDD, 0.9+/-0.22; CVVH, 1.10+/-0.12, p=NS). The EKRc, which is used to verify kinetic equivalence among patients treated with differing renal replacement therapies (RRT), was higher in CVVH (15.7 in SLEDD; 27.4 in CVVH, p<0.0001), despite the fact that there was no difference between the delivered spKt/V for the SLEDD (1.05+/-0.40) and the CVVH (1.10+/-0.11) groups. The values for SRIurea (0.61 in SLEDD; 1.04 in CVVH, p=0.001), SRIcreatinine (0.55 in SLED; 1.02 in CVVH, p<0.0001), and SRIphosphate (1.81 in SLED; 3.60 in CVVH, p=0.03) were higher in CVVH. The EKRc is calculated assuming a steady state, which is an incorrect assumption in ARF patients with hypercatabolism. The SRI calculated using direct dialysate effluent quantification appears to be more reliable as an index of the dialysis dose compared to other methods in ARF patients. However, the use of the dialysate-side SRI is limited by the difficulty of dialysate effluent collection.

Hemodialysis: Techniques and Prescription

Hemodialysis: Techniques and Prescription

Modified urea reduction ratio (mURR) is a good estimate of solute removal index (SRI) for urea

Modified urea reduction ratio (mURR) is a good estimate of solute removal index (SRI) for urea

Solute removal index correlates more with equilibrated Kt/V than with single pool Kt/V in haemodialysis patients.

Solute removal index (SRI) is an adequacy index that estimates haemodialysis dose based on urea removal in the spent dialysate. We examined the SRI, single pool Kt/V (spKt/V) and equilibrated Kt/V (eKt/V) in two groups of chronic haemodialysis patients; group A, 25 patients received haemodialysis twice weekly and group B, 11 patients received haemodialysis thrice weekly. The Ing's partial dialysate collection method was used for spent dialysate collection. The SRI values of the first and second dialysis sessions in a week in group A were 68.7 +/- 4.7 and 69.7 +/- 4.1%, respectively, while that of the first, mid-week and third dialysis sessions in a week in group B were 56.5 +/- 5.3, 55.8 +/- 5.4 and 57.5 +/- 6.2%, respectively. The correlation coefficients (r) between SRI and spKt/V in the first and second dialysis sessions in a week in group A were 0.90 (P < 0.01) and 0.95 (P < 0.01), respectively, and that in the first, mid-week and third sessions for group B were 0.96 (P < 0.01), 0.94 (P < 0.01) and 0.91 (P < 0.01), respectively. The r values between SRI and eKt/V in the first and second sessions for group A were 0.97 (P < 0.01) and 0.99 (P < 0.01), respectively, and that in the first, mid-week and third sessions for group B were 0.98 (P < 0.01), 0.97 (P < 0.01) and 0.98 (P < 0.01), respectively. Therefore, the correlation between SRI and eKt/V (r values approaching one) was better than that between SRI and spKt/V in all dialysis sessions in a week for both group A and B patients. We conclude that the SRI, an index based on dialysate urea removal, correlates more with equilibrated Kt/V (an index that accounted for postdialysis urea rebound) than with single pool 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 &lt; 0.001). Also there was statistically significant correlation between solute removal index (SRI), Kt/V Daugirdas (r = 0.81, p &lt; 0.001) and Kt/V online (r = 0.92, p &lt; 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 &lt; 0.03), and Kt/V online (r = −0.17, p &lt; 0.03) although the nPCR (normalized PCR) had marginal positive correlation (r = 0.35, p &lt; 0.05) (r = 0.42, p &lt; 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.

Middle molecule and small protein removal in children on peritoneal dialysis

Dialysis efficiency has a great influence on the outcome of patients. Few data are available on the removal of solutes with molecular weights higher than urea and creatinine. The aim of our study was to assess the transport and the removal of substances with molecular weights up to 15 kD and to evaluate the contribution of residual renal function in peritoneal dialysis (PD) children. Seventeen patients of 12 +/- 4 years undergoing automated PD were studied. Ten patients had 563 +/- 355 mL/day of urine output, and 7 were anuric. During a standardized nightly intermittent PD (NIPD) session, a single-injection inulin clearance was performed. Urea, creatinine, inulin (measured by HPLC), cystatin C and beta2-microglobulin (beta2m) were measured in blood, urine and dialysate. Clearances (L/week/1.73 m2) and weekly solute removal index (SRI) were calculated for all the solutes; weekly Kt/V was calculated for urea. In non-anuric versus anuric patients the total clearances were: urea 82.6 +/- 18.3 versus 71.3 +/- 26.4; creatinine 82.7 +/- 28.6 versus 47.8 +/- 18.8; inulin 42.8 +/- 11.3 versus 32.8 +/- 20.4; beta2m 14.2 +/- 13.8 versus 9.2 +/- 8.3; cystatin C 20.2 +/- 9.4 versus 9.7 +/- 4.8. In the patients with residual diuresis, the urea was removed mainly by PD (69.2%), while inulin, beta2m and cystatin C were removed by renal clearance (64.0%, 79.5% and 62.8%, respectively). Total, peritoneal and renal weekly Kt/V values in the subjects with residual renal function, were 2.86 +/- 0.70, 1.99 +/- 0.40 and 0.87 +/- 0.43, respectively. Peritoneal weekly Kt/V in the anuric patients was 2.36 +/- 0.85; total weekly Kt/V in the total group was 2.65 +/- 0.78. Weekly SRIs in non-anuric versus anuric patients were: urea 2.56 +/- 0.58 versus 2.09 +/- 0.74; creatinine 2.66 +/- 0.73 versus 1.46 +/- 0.56; inulin 2.36 +/- 0.92 versus 1.64 +/- 1.60; beta2m 1.26 +/- 1.10 versus 1.20 +/- 1.90; cystatin C 1.72 +/- 0.83 versus 1.58 +/- 1.62. Solutes removed during PD tend to decrease following an increase in molecular weight of the substance. Since anuric patients are at higher risk of middle molecule and small protein accumulation, more attention should be paid to the removal of middle molecules. Further studies should be undertaken to evaluate whether removing them has a clinical impact and to determine their threshold levels.

Artificial intelligence: A new approach for prescription and monitoring of hemodialysis therapy

The effect of dialysis on patients is conventionally predicted using a formal mathematical model. This approach requires many assumptions of the processes involved, and validation of these may be difficult. The validity of dialysis urea modeling using a formal mathematical model has been challenged. Artificial intelligence using neural networks (NNs) has been used to solve complex problems without needing a mathematical model or an understanding of the mechanisms involved. In this study, we applied an NN model to study and predict concentrations of urea during a hemodialysis session. We measured blood concentrations of urea, patient weight, and total urea removal by direct dialysate quantification (DDQ) at 30-minute intervals during the session (in 15 chronic hemodialysis patients). The NN model was trained to recognize the evolution of measured urea concentrations and was subsequently able to predict hemodialysis session time needed to reach a target solute removal index (SRI) in patients not previously studied by the NN model (in another 15 chronic hemodialysis patients). Comparing results of the NN model with the DDQ model, the prediction error was 10.9%, with a not significant difference between predicted total urea nitrogen (UN) removal and measured UN removal by DDQ. NN model predictions of time showed a not significant difference with actual intervals needed to reach the same SRI level at the same patient conditions, except for the prediction of SRI at the first 30-minute interval, which showed a significant difference (P = 0.001). This indicates the sensitivity of the NN model to what is called patient clearance time; the prediction error was 8.3%. From our results, we conclude that artificial intelligence applications in urea kinetics can give an idea of intradialysis profiling according to individual clinical needs. In theory, this approach can be extended easily to other solutes, making the NN model a step forward to achieving artificial-intelligent dialysis control. © 2001 by the National Kidney Foundation, Inc.

Relationship between increased interdialytic body weight and left ventricular hypertrophy in maintenance dialysis patients

SUMMARY: Interdialytic weight gain (IDWG) has been reported to contribute to cardiovascular mortality in haemodialysis patients. In order to determine the relationship of IDWG to the pre‐dialysis blood pressure and left ventricular hypertrophy, 168 patients on maintenance haemodialysis were initially evaluated. The IDWG was estimated as the current pre‐dialysis weight minus the preceding post‐dialytic weight and expressed as a proportion (%) of the current dry weight. Patients were divided into two groups: group I consisted of patients with a mean IDWG &gt; 5% each month for 6 months and group II consisted of patients with a mean IDWG &lt; 5% each month for 6 months. As 51 patients had increased IDWG &gt; 5% on more than one occasion, but fewer than six times, they were not included in the above two groups. Thus, 117 patients (33 men, 84 women) were enrolled in this study. All patients received haemodialysis three times a week, with a duration of 4.6 ± 0.5 h per dialysis session. Pre‐dialysis systolic and diastolic blood pressure (SBP, DBP) and left ventricular mass index (LVMI), as determined by echocardiography, were studied regularly. The results demonstrated that the IDWG correlated significantly with age (r = −0.209, P = 0.024) and solute removal index (Kt/V) (r = 0.254, P = 0.006), but did not correlate with pre‐dialysis systolic or diastolic blood pressure. In contrast, LVMI correlated with SBP (r = 0.816, P &lt; 0.001), DBP (r = 0.377, P &lt; 0.001) and age (r = 0.458, P &lt; 0.001). Left ventricular hypertrophy presented in 18 group I subjects (81%) and 68 group II subjects (72%) respectively (P &lt; 0.001). In conclusion, this study shows that excessive IDWG in patients maintained on haemodialysis does not correlate with pre‐dialysis blood pressure, emphasizing that additional factors other than fluid volume may play a role in the control of blood pressure in uraemic patients.

Measurement of the delivery of dialysis in acute renal failure

Recent studies in patients with acute renal failure (ARF) have shown a relationship between the delivered dose of dialysis and patient survival. However, there is currently no consensus on the appropriate method to measure the dose of dialysis in ARF patients. In this study, the dose of dialysis was measured by blood- and dialysate-based kinetic methods in a group of ARF patients who required intermittent hemodialysis. Treatments were performed using a Fresenius 2008E volumetric hemodialysis machine with the ability to fractionally collect the spent dialysate. Single-, double-pool, and equilibrated Kt/V were determined from the pre-, immediate post-, and 30-minute post-blood urea nitrogen (BUN) measurements. The solute reduction index was determined from the collected dialysate, as well as the single- and double-pool Kt/V. Forty-six treatments in 28 consecutive patients were analyzed. The mean prescribed Kt/V (1.11 +/- 0.32) was significantly greater than the delivered dose estimated by single-pool (0.96 +/- 0.33), equilibrated (0.84 +/- 0.28), and double-pool (0.84 +/- 0.30) Kt/V (compared with prescribed, each P < 0.001). There was no statistical difference between the equilibrated and double-pool Kt/V (P = NS). The solute removal index, as determined from the dialysate, corresponded to a Kt/V of 0.56 +/- 0.27 and was significantly lower than the single-pool and double-pool Kt/V (each P < 0.001). Blood-based kinetics used to estimate the dose of dialysis in ARF patients on intermittent hemodialysis provide internally consistent results. However, when compared with dialysate-side kinetics, blood-based kinetics substantially overestimated the amount of solute (urea) removal.

Imprecision of the hemodialysis dose when measured directly from urea removal

The postdialysis blood urea nitrogen (BUN; Ct) is a pivotal parameter for assessing hemodialysis adequacy by conventional blood-side methods, but Ct is relatively unstable because of hemodialysis-induced disequilibrium. The uncertainty associated with this method is potentially reduced or eliminated by measuring urea removed on the dialysate side, a more direct approach that can determine adequacy from the fraction of urea removed and by substituting an estimate of the equilibrated postdialysis BUN (Ceq) for Ct. For a patient with a known urea volume (V), Ceq, the equilibrated Kt/V (eKt/V), and the solute removal index (SRI) can be calculated from the predialysis BUN (C0), total urea nitrogen removed (A), and V from simple mass balance calculations (dialysate/volume method). However, a theoretical error analysis showed that relatively small errors in A, C0, or V are magnified when SRI or eKt/V is calculated using this method, especially at higher eKt/V values (for example, if eKt/V = 1.4 per dialysis, a 7% dialysate collection error causes a 20% error in eKt/V). During three to four baseline dialyses in each of 39 patients enrolled in the pilot phase of the HEMO Study, "A" was measured using an instrument that sampled dialysate frequently (Biostat), and V was calculated from A, C0, and Ceq (median CV for V = 5.6%). The mean V was then applied to the dialysate/volume method to estimate eKt/V and SRI during two to five subsequent dialyses per patient (comparison dialyses). The accuracy and precision of these estimates were assessed by comparing them with eKt/V and SRI derived from a direct measurement of Ceq drawn 30 minutes after dialysis (reference method), from mathematical curve-fitting of sequential dialysate urea concentrations (dialysate curve-fit method), and from another blood-side method that estimates eKt/V from single pool Kt/V and the fractional rate of solute removal (rate method): eKt/V = spKt/V - 0.6.K/V + 0.03. During 128 comparison dialyses, median absolute errors for calculated eKt/V compared with the reference method were 0.169, 0.061, and 0.071 for the dialysate/volume method, the rate method, and the dialysate curve-fitting method, respectively. The corresponding correlation coefficients were 0.47, 0.88, and 0.81. For SRI, median absolute errors were 0.044, 0.018, and 0.027, and the correlation coefficients were 0.54, 0.85, and 0.74 for the three methods. The precision of eKt/V and SRI measurements was significantly lower for the dialysate/volume method compared with the blood-side methods. Inclusion of the dialysate curve analysis provided by the Biostat restored precision to the dialysate method to a level comparable to that of the blood-side methods. New techniques employing dialysate urea analysis should include a concentration profile to avoid these inherent methodological errors and assure the accuracy of eKt/V and SRI.

Evaluation of Pre- and Postdilutional On-Line Hemodiafiltration Adequacy by Partial Dialysate Quantification and On-Line Urea Monitor

On-line highflux hemodiafiltration (HDF) is a clinically interesting and effective mode of renal replacement therapy, which offers the possibility to obtain an increased removal of both small and large solutes. The fundamental role of urea kinetic monitoring to assess dialysis adequacy in conventional hemodialysis has been widely studied. Both direct measurement of the urea removed by the modified direct dialysate quantitation (mDDQ) based on partial dialysate collection (PDC) and dialysate-based urea kinetic modeling (DUKM) using urea monitor have been advocated. The validity of this assessment tool in the patients with on-line HDF remained unclear. The aims of this investigation were (1) to compare the delivered Kt/V, urea mass removal (UMR), solute removal index (SRI) and normalized protein catabolic rate (nPCR) between pre- and postdilutional high-flux HDF; (2) to verify and compare the efficiency of pre- and postdilutional HDF using DUKM with on-line dialysate urea sensor, and mDDQ with partial dialysate collection. During both mode of HDF, the paired analysis urea removed and Kt/V showed no significant difference. Using mDDQ, mean values for predilutional mode were as follows: Kt/V 1.53 ± 0.01 UMR, 16.8 ± 0.3 g/session; urea clearance 178 ± 18 ml/min; SRI 75.5 ± 7.7%; urea distribution volume (V) 28.3 ± 1.2 liters; nPCR 1.34 ± 0.18 g/kg/day; on the other hand, mean values for postdilutional mode were Kt/V 1.58 ± 0.01; UMR 17.10 ± 0.28 g/session; urea clearance 184 ± 21 ml/min; SRI 77.2 ± 3.5%; urea distribution volume, 27.8 ± 1.5 liters; nPCR 1.34 ± 0.19 g/kg/day. The mean value of urea generation rate was 5.82 ± 1.12 mg/min during HDF. Our results showed that dialysis adequacy was achieved with both high-volume predilutional HDF and postdilutional HDF. These two modes of HDF provided similar and adequate small solute clearance. In addition, we found that on-line analysis of urea kinetics is a reliable tool for quantifying and assuring delivery of adequate dialysis.

Chronic renal replacement therapy in children: Which index is best for adequacy?

The dialysis dose, Kt/V, and Solute Removal Index (SRI) have been proposed as tools to measure and compare adequacy of different renal replacement therapies in adults. The aim of our study was to elucidate whether the Kt/V and SRI could be appropriate parameters to compare different treatments and define adequacy targets in children. Twenty-two pediatric chronic dialysis patients (2 to 17 years) were prospectively studied. Six patients were on continuous ambulatory peritoneal dialysis (CAPD), 7 patients were on automatic nightly peritoneal dialysis (ANPD), and 9 were on hemodialysis (HD). Patients had no peritonitis and were not hospitalized during the previous two months and, as proved by growth and subjective well being, were in steady state condition at the initiation of the protocol. As a consequence, the treatment delivered was assumed to be adequate and the prospective analysis was carried out within one month. Urea levels in dialysate, plasma and urine were measured to determine urea kinetics and measure adequacy parameters. Instantaneous urea clearance was much higher when hemodialysis was used (124.67 +/- 32.04 ml/min) compared to CAPD (2.79 +/- 0.29 ml/min) and ANPD (6.60 +/- 1.42 ml/min), as expected. The Urea dialytic clearance per week was greater in HD (67320 +/- 17299 ml) than in CAPD(28144 +/- 2895 ml) and ANPD (29910 +/- 4234 ml). Residual renal function contributed to the overall weekly clearance by 47% in CAPD, while it was only by 19% in HD and 26% in ANPD. The overall weekly clearance was therefore 79,842 ml/week in HD, 53,340 ml/week in CAPD and 41,012 ml/week in ANPD. Weekly dialytic Kt/V results were much higher in HD (3.75) than in CAPD (1.78) and ANPD (2.37). To these values, the renal Kt/V was added, reaching the values of overall (dialytic + renal) weekly Kt/V of 4.53 in HD, 3.41 in CAPD and 3.41 in ANPD. Although higher Kt/V values were observed in HD, when the SRI % was considered, HD appeared to be less efficient compared with the other two techniques. Since postdialytic rebound in HD patients averaged 22.5%, we may speculate that hemodialysis in children is less efficient than continuous or daily peritoneal dialysis because of a remarkable cardipulmonary recirculation and solute sequestration. In the global evaluation, dialysis SRI% appears to be more reliable as an index of adequacy compared to Kt/V in children. At least an integration between the two indices is strongly recommended.

Chronic Hemodialysis: Kt/V or Solute Removal Index to Evaluate the Effective Delivered Dose?

A standard for quantifying the hemodialysis dose has not yet been defined. Many authors suggest the use of an alternative method to Kt/V: the solute removal index (SRI). We compared three methods based on blood-side urea determinations with the direct quantification method (DDQ) for estimating the delivered dialysis dose, expressed as SRI as well as Kt/V. Eight patients underwent three consecutive dialysis sessions, with the same dialytic efficiency. For each patient and each dialytic session the SRI and Kt/V were determined using the DDQ method and the single pool variable volume kinetic model, in its classical version (SPVV) as well by using the postdialysis urea value determined 30 min after the end of the session (eqSPVV). Double pool Kt/V was also estimated by the Daugirdas-Schneditz rate equation. Our results showed that the SPVV kinetic model significantly overestimated the delivered dialysis dose, the mean value of SRI and Kt/V were respectively 8.9% and 17% higher than those obtained by DDQ. The eqSPVV allowed the SRI to be estimated with a difference of -0.3% and Kt/V with a difference of -2% in comparison with DDQ. By using the Daugirdas-Schneditz rate of equation, which does not require blood samples to be drawn after the end of the session, the difference in Kt/V value was 3%. Therefore, both the eqSPVV kinetic model and the Daugirdas method allow quantification of the delivered dialysis dose with results similar to those determined by DDQ, which cannot be routinely applied. Kt/V seems the best marker for dialytic doses quantification.

Kt/V or solute removal index: problems in measuring and interpreting the results.

Kt/V or solute removal index: problems in measuring and interpreting the results.

Determination of the solute removal index for urea by using a partial spent dialysate collection method

In 22 hemodialysis patients, during a dialysis session, the solute removal index (SRI) for urea obtained from the use of a partial spent dialysate collection method was compared with that derived from the use of a total spent dialysate collection technique. The partial spent dialysate collection method was used to harvest a small representative sample of the total spent dialysate. The volumes of spent dialysate collected by the partial and the total spent dialysate collection methods were 1.7 +/- 0.4 L and 129.6 +/- 15.3 L, respectively. The total amount of urea nitrogen removed by dialysis as estimated by the partial spent dialysate collection method was similar to that determined by the total spent dialysate collection approach. As a result, the SRI value for urea obtained by the partial spent dialysate collection method (namely, 63% +/- 8%) correlated very well (r = 0.95, P < 0.001) with that derived by the total spent dialysate collection technique (namely, 62% +/- 8%). Our data suggest that it is feasible to use a simple partial spent dialysate collection method to obtain SRI results in patients treated with hemodialysis. (Am J Kidney Dis 1998 Jun;31(6):986-90)

The other side of the coin: interdialytic weight gain as an index of good nutrition.

Excessive interdialytic weight gain (IDWG) is usually attributed to fluid and sodium overload. Abnormal thirst regulation, hormonal derangements, and social, cultural, and psychological habits may account for low compliance with fluid and salt restrictions. However, food intake is an important determinant of IDWG, and high IDWG may reflect the nutritional status of hemodialyzed patients, rather than their scanty compliance. The relationship between IDWG, efficacy of dialysis, and nutritional status was investigated in 38 patients (28 men and 10 women), in whom urea kinetics was studied by means of an on-line urea sensor (UM 1000, Baxter Healthcare, McGraw Park, IL), and Kt/V and protein catabolic rate (PCR) were calculated. Records from 161 dialysis sessions were analyzed and grouped according to their IDWG (group A, weight gain > 5% and group B, weight gain < 5% of dry body weight). In group A, Kt/V, solute removal index, urea reduction ratio, predialytic blood urea nitrogen (BUN), urea removed, and PCR were statistically higher than in group B (P < 0.05). Regression analysis showed a significant and positive correlation between IDWG and PCR. In 17 of 38 patients with steadily high IDWG, serum albumin levels, predialytic BUN, and PCR were significantly higher than in patients with low IDWG (P < 0.05). Sex and predialytic blood pressure did not correlate with IDWG; in contrast, age negatively affected both IDWG and PCR (age v IDWG and age v PCR, r = 0.22; P < 0.008 and P < 0.006, respectively). These results confirm that high IDWG is associated with better nutritional status.

Evaluation of high-flux hemodiafiltration efficiency using an on-line urea monitor

On-line urea monitoring of the effluent dialysate offers a real-time assessment of dialysis efficiency and metabolic/nutritional characteristics of hemodialysis patients. Quantitative parameters were evaluated by dialysate urea kinetic modeling (DUKM) with an on-line urea sensor in 23 patients treated by high-flux hemodiafiltration (HDF) (215 sessions of 210 to 240 minutes with a mean blood flow rate of 367 +/- 44 mL/min). Overall, the mean effective Kt/V was 1.52 +/- 0.29, the urea mass removed (22.8 +/- 5.5 g/session or 814 +/- 198 mmol/session), the solute removal index (SRI) 73% +/- 6.1%, and the mean normalized protein catabolic rate (nPCR), 1.15 +/- 0.31 g/kg/day. Blood urea kinetic modeling (BUKM), based on pre- and postsession urea concentrations, using equations from Daugirdas and Garred to calculate equilibrated Kt/V and nPCR, respectively, were in good agreement with DUKM, the differences observed appearing not clinically relevant. The variability of evaluated parameters was verified over consecutive sessions for a mean period of 3 weeks in the entire group. Mean variation in Kt/V was 8%; in urea mass removal, 18%; and in nPCR, 18%. When assessed over 1 week in a subgroup of 13 patients, Kt/V and PCR remained relatively stable, and urea mass removal per- and postsession declined from 23.5 +/- 8.0 g (840 +/- 285 mmol) to 18.7 +/- 6.3 g (667 +/- 225 mmol) from the first to the third session of the week, most likely as a consequence of interdialytic intervals. Predialysis urea concentrations followed the same trend. In the current study, DUKM with on-line urea sensor has confirmed that HDF is a highly efficient renal replacement modality; the variability observed in quantitative parameters supports a need for frequent adequacy monitoring. On-line urea monitoring of effluent dialysate is a simple device that provides the opportunity to tailor treatment to patient needs. (Am J Kidney Dis 1998 Jan;31(1):74-80)

SOLUTE REMOVAL INDEX (SRI)

SOLUTE REMOVAL INDEX (SRI)