Post -hemodialytic urea rebound and its impact factors in maintenance hemodialysis patients / 中华肾脏病杂志

Objective To study the urea rebound after hemodialysis in maintenance hemodialysis (MHD) patients and its impact factors. Methods From 124 stable MHD patients, blood samples were collected at the beginning, immediate post-hemodialysis, 15 minutes and 30 minutes after hemodialysis. The urea rebound was quantified, and its effect on URR and spKt/V was investigated. The impact factors on urea rebound were analyzed. Results In this group of patients, average post-hemodialytic urea rebound was 13.6%, leading to over-estimation of URR and spKt/V of 0.04 and 0.14, respectively. Hemodialysis efficiency expressed as K/V determined urea rebound most significantly. Other impact factors included higher hemoglobin, higher relative ultrafiltration, arteriovenous access, and male patients. Conclusions Urea rebound is common after the hemodialysis. For specific patients and hemodialysis sessions, ignoring it would result in significant over-estimation of delivered hemodialysis dose.

Usefulness of Assessing Hemodialysis Adequacy Using the Stop Dialysate Flow (SDF) Method / 대한신장학회잡지

BACKGROUND: K/DOQI guidelines recommend the slow flow method as a standardized method of postdialysis blood sampling for measuring hemodialysis adequacy. However, it is not easy to adopt this method when working in busy renal units where it is often difficult to obtain repeated samples exactly at the specified time. The stop dialysis flow (SDF) method recommended by the Scottish Renal Association since 1998 has the advantage of involving 2 steps only: (1) switch off dialysate flow at the end of hemodialysis without altering the blood pump speed and (2) take a blood sample after 5 minutes from the arterial or venous port. However, there are some limitations to SDF mthod in that it does not allow for tissue rebound after the first 5 minutes postdialysis and cannot be used directly to calculate equilibrated Kt/V (Kt/Veq) using either a 30-minute postdialysis sample. We derived a formula that uses a 5-minute postdialysis BUN sample using the SDF method to estimate the BUN concentration at 30 minutes and investigated if it is useful to assess hemodialysis adequacy using this method. METHODS: A total of 51 patients who had been undergoing hemodialysis in Chonnam National University Hospital and had agreed in joining this study were involved. Patients were randomly selected to 2 groups. Blood samples were obtained immediately before dialysis and at 0, 5, and 30 minutes postdialysis. We calculated the linear relationship between the 5-minute and 30-minute postdialysis samples in group A patients (n=25) and validated this equation using the data from the other group B patients (n= 26). We predicted what the 30-minute BUN concentration would be using the measured value of BUN at 5 minutes and compared directly the value of our estimated 30-minute BUN with the measured 30- minute BUN. RESULTS: There was a tight linear correlation (R2=0.993, p<0.05), between measured 5-minute postdialysis BUN concentrations and measured 30-minute postdialysis BUN concentrations in group A patients. This relationship is described by the linear regression equation: 30-minute BUN concentration=1.05x(5-minute BUN concentraion)+1.04. We used this equation to estimate the 30-minute BUN concentration in group B patients based on the 5-minute postdialysis BUN sample from these patients. And there was a close correlation between estimated and measured 30-minute postdialysis BUN concentration (R2= 0.989, p<0.05). The sensitivity, specificity, positive, and negative predictive values of this equation were high when used to estimate 30-minute urea reduction ratio (URR) greater than 65% (88.9%, 100%, 100 %, and 94.4%, respectively) and 30-minute Kt/Vsp greater than 1.2 (100%, 100%, 100%, 100%, respectively). CONCLUSION: We could estimate 30-minute postdialysis BUN concentration, 30-minute Kt/V, and 30-minute URR exactly using SDF method and linear regression equation derived in this study. The advantage of involving 2 steps only makes SDF method a useful tool in assessing hemodialysis adequacy.

The Method to Predict Postdialysis Equilibrated Kt/V with Only Intradialytic Urea Samples / 대한신장학회잡지

PURPOSE: Postdialysis urea rebound(PDUR) causes the overestimation of actual amount of delivered dialysis in Kt/V from single pool urea kinetic. To correct PDUR and predict equilibrated Kt/V(eKt/V) some methods have suggested by Daugirdas, et al., Smye, et al. and Tattersall, et al. The purposes of this study were to determine the optimum intradialytic urea sample time that fits best with PDUR and to compare calculated Kt/V by this sample with the different other methods. METHODS: The subjects were 21 patients who were dialyzed at three times 4 hours weekly, using bicarbonate and cellulosynthetic membranes. Blood samples to measure BUN were obtained at initiation of dialysis session and then at 80, 120, 180, 200, 210, 220 minutes, and the end of dialysis session times and then at 45 minutes of postdialysis. We compared four different methods of eKt/V with the equilibrated 45-minute PDUR Kt/V(eKt/V PDUR) as the reference method. RESULTS: The mean PDUR was 17.2+/-%. spKt/V and eKt/V PDUR was 1.300+/-.24 and 1.120+/-.20 respectively, leading to overestimation of actual delivered Kt/V by 13.5+/-%. The best time for intradialytic sampling to fit with PDUR BUN was 40 minute before the end of session. eKt/V by Daugirdas formulae(eKt/V Dau=1.315+/-.21, r=0.972, p<0.001), Tattersal formulae(eKt/V Tat=1.134+/-.22, r= 0.972, p<0.972, p<0.001) and Smye formulae(eKt/V Smye=1.156+/-.24, r=0.900, p<0.001) showed good correlation with eKt/V PDUR. eKt/V calculated by the sample of 40 minute before end of session(eKt/V T-40=1.120+/-.20, r=0.984) had tendency of the best correlation with eKt/V PDUR. Among these different methods, eKt/V T-40 had the best degree of agreement with eKt/V PDUR by Bland-Altman analysis. CONCLUSION: Our results suggest that the use of spKt/V is not adequate to estimate the amount of delivered hemodialysis dose because of the existence of significant postdialysis urea rebound even conventional 4 hour dialysis. Intradialytic sampling method is a simple and accurate method to predict eKt/V for use in clinical practice.

Effects of Postdialysis Urea Rebound on Dialysis Adequacy in Hemodialysis Patients / 대한신장학회잡지

Urea reduction ratio (URR) and Kt/Vurea are objective parameters of dialysis delivery in hemodialysis patients and correlate with nutritional status and patient outcome. URR and Kt/Vurea depend on postdialysis blood urea nitrogen (BUN). In patients with severe postdialysis urea rebound (PDUR), these parameters do not accurately reflect dialysis adequacy. We measured PDUR 30 minutes after dialysis in 26 chronic stable hemodialysis patients. The impact of PDUR on dialysis delivery assessed by URR and Kt/Vurea and the independent factors affecting on PDUR were evaluated. All patients had been dialyzed for 4 hours thrice a week using hemophan membrane. 1) The mean age of patients was 48.6+/-14.8 years and sex ratio was 1:2.3. The mean duration of hemodialysis was 42.7+/-45.0 months. Primary renal diseases were chronic glomerulonephritis 11 (42.3%), diabetic nephropathy 7 (26.9%), and hypertension 4 (15.4%). 2) The mean blood flow was 209.2+/-17.4ml/min. URR, Kt/Vurea, and nPCR using immediate postdialysis BUN were 60+/-7%, 1.13+/-0.21, 1.09+/-0.28g/kg/ day, respectively. The mean recirculation rate was 4.4+/-2.3%. 3)The mean PDUR was 12.2+/-4.6% (range:6-22 %). URR, Kt/Vurea, and nPCR using BUN 30 minutes after dialysis were 55+/-7%, 0.99+/-0.18, and 1.02+/-0.25 g/kg/day, respectively and were significantly lower than those using immediate postdialysis BUN (P or = 12%), high PDUR group was significantly higher than low PDUR group in hematocrit (27.0+/-2.6 vs. 23.5+/-3.6%, P=0.008), URR (64.3+/-5.4 vs. 55.8+/-6.8%, P=0.002), Kt/Vurea (1.26+/-0.17 vs. 1.03+/-0.18, P=0.002), and total recirculation rate (5.6+/-2.7 vs. 3.6+/-1.7%, P=0.05). There were no differences in age, sex, postdialysis body weight, ultrafiltration rate, blood flow, serum albumin, predialysis BUN, creatinine, and nPCR. 5) In multiple regression analysis, the independent factors affecting on PDUR were Kt/Vurea (beta=0.546, P<0.001), recirculation rate (beta=0.422, P<0.001), and hematocrit (beta=0.366, P=0.0017). In conclusion, we think that PDUR should be considered in hemodialysis patients when estimating dialysis delivery, especially if they had high Kt/ Vurea, recirculation rate, and hematocrit.