| Abstract|| |
The blood urea concentration is artificially low immediately following highefficiency dialysis. Post-dialysis urea rebound correlates with hemodialysis efficiency, and is inversely correlated with dialysis treatment time. We evaluated the effect of variation in the length of hemodialysis treatment on urea, creatinine and other solutes rebound. We used two protocols for hemodialysis, using 500-ml dialysate/min and similar dialyzed blood volume. Protocol A: hemodialysis with blood flow of 300 ml/min for four hours; protocol B: hemodialysis with blood flow of 400 ml/min for three hours. Fifteen stable anuric patients with end- stage renal disease (ESRD) were hemodialysed using each protocol, three sessions a week, for a period of two weeks. The mean dialyzed blood volume in protocol A and B was 66 ± 4 and 67 ± 4.8 liters/session, respectively. The mean blood flow in protocol A was 286 ± 22 ml/min, and in protocol B was 395.3 ± 13 ml/min. The mean urea pre and immediately post dialysis in patient using protocol A was 20.5 ± 5.4 and 5.55 ± 2.2 mmol/L, respectively. While in protocol B it was 19.8 ± 4.6 and 6 ± 1.68 mmol/L. The mean urea, one hour post dialysis, in protocol A was 6.51 ± 1.9 Vs 8.04 ± 2.6 mmol/L in protocol B (P value < 0.003). The percent rebound of mean blood urea concentration in protocol A and B one hour post dialysis was 17.3% vs 34%, respectively. Predialysis creatinine in protocol A and B was 894 ± 156.8 vs 907.9 ± 163 umol/L, respectively (P= 0.4). The immediately post-dialysis creatinine in protocol A and B, was 317± 98.4 vs 331 ± 72.0 µmol/L (P = 0.4), while one hour later it was 398.6 ± 104.0 vs 442.6 ± 107.2 µmol/L, respectively (P value < 0.007). The percent rebound of creatinine was 25.6% in protocol A vs 33.5% in protocol B. These results show significant difference between the two protocols, and confirm increased rebound of urea and creatinine one hour post dialysis with shorter time of dialysis treatment.
|How to cite this article:|
Al-Wakeel JS. Post-dialysis Solutes Rebound: Comparison of Two Protocols for Hemodialysis. Saudi J Kidney Dis Transpl 1998;9:139-43
|How to cite this URL:|
Al-Wakeel JS. Post-dialysis Solutes Rebound: Comparison of Two Protocols for Hemodialysis. Saudi J Kidney Dis Transpl [serial online] 1998 [cited 2020 Sep 26];9:139-43. Available from: http://www.sjkdt.org/text.asp?1998/9/2/139/39286
| Introduction|| |
During hemodialysis, reduction in the urea concentration in the intracellular fluid (ICF) compartment will lag behind that in the extra cellular fluid (ECF) compartment, and following the end of dialysis, a "rebound" in the blood level of urea will occur where it continues to rise due to diffusion of urea from the ICF to ECF to establish an equilibrium state  .
The eventual equilibrium of urea level, typically achieved 60 minutes post-dialysis, may be up to 20% more than the immediate post dialysis concentration ,, . Urea generation and catabolism, during and in the early post dialysis period, seem to play fewer roles in post dialysis urea rebound (PDUR), at least in chronic stable hemodialysis patients , .
Post-dialysis urea rebound varies among patients, but should remain relatively constant in a given patient with stable hemodynamic parameters , . PDUR correlates with hemodialysis efficiency and inversely correlates with dialysis treatment time  . Women as well as patients with high access recirculation have high PDUR  .
In theory, PDUR should be increased with shorter dialysis session, higher blood flow rate, and higher pre-dialysis urea  . Furthermore, there is a tendency for patients with a longer hemodialysis session to have a lower PDUR  .
There has been no published data to show whether creatinine rebound phenomenon is also present post dialysis with different blood flow rates. We conducted this study to compare the degree of rebound of urea and creatinine in two hemodialysis protocols identical in dialyzed blood volume, with variation in the length of treatment.
| Materials and Methods|| |
Fifteen anuric patients with end- stage renal disease, due to variable etiology were enrolled in this study after informed consent. They were five males and ten females. The age was 46 ± 17 years (range, 21-74). All patients received hemodialysis for more than six months using Gambro AK 100 dialysis machines and cellulose hollow fiber dialysis filters (Terumo M-101 or M-121). Their underlying etiologies of ESRD are as shown in [Table - 1].
All patients had good access blood flow (fistula or graft) with access recirculation of less than 10% at the time of enrollment in this study. All patients were dialyzed according to one of two protocols: In protocol "A", patients had dialysis with blood flow of 300 ml/min for four hours per session for two weeks. In protocol "B", patients had dialysis with blood flow of 400 ml/min for three hours per session for two weeks. The same patients had both protocols for three sessions of dialysis per week. The dialysate flow was constant in the two protocols at a rate of 500 ml/min. At the last dialysis session of the study period, blood samples were obtained from a peripheral vein (without tourniquet), pre-dialysis, immediately at the end of, and one hour post dialysis for measurement of urea, creatinine, Na+, K+, HCO3; C1-, Ca++, PO4., Mg++ glucose, white blood count (WBC), hemoglobin (Hb), hematocrit (HCT), and platelets. All patients were kept fasting from the beginning of the dialysis session till all blood samples were obtained. All the patients had their weights measured pre- and post-dialysis each time in both protocols.
| Statistical Analysis|| |
For the statistical analysis we used gold statpac version 3.2 using simple analysis to differentiate between variables and using student's t test for comparisons where appropriate.
| Results|| |
The mean pre-dialysis weight of patients in protocol A was 50.8 ± 9.14 kg (range 34-74 kg) with post-dialysis weight of 48.4±8.4 (range 33-70.2) kg, while in protocol B, the mean weight pre- and post-dialysis was 51 ± 8.8 (range 34.3-72) kg and 48.2 ± 9.8 (range 33.1-70.6) kg, respectively. The mean dialyzed blood volume in protocol A and B was 66 ± 4 (range 60-77) liters per-session and 67 ± 4.8 (range 54-70) liters per-session, respectively. The mean blood flow in protocol A and B was 286.6 ± 22 ml/min (range 250-300) and 395.3 ± 13 ml/min (range 350-400), respectively. [Table - 2],[Table - 3] show the results of blood analysis obtained in the two protocols with values of immediate and one hour post dialysis urea, creatinine, Na+, K+ HCO3, Cl-, Ca++,PO4---, Mg++, glucose, and their statistical analysis.
The percent of mean rebound one hour post dialysis for the concentrations of urea, creatinine, calcium, phosphorus, bicarbonate, potassium, chloride, sodium, magnesium and glucose is shown in [Figure - 1]. The mean urea pre and immediately post dialysis in patient using protocol A was 20.5 ± 5.4 and 5.55 ± 2.2 mmol/L, respectively. While in protocol B it was 19.8 ± 4.6 and 6 ± 1.68 mmol/L. The mean urea, one hour post dialysis, in protocol A was 6.51 ± 1.9 Vs 8.04 ±2.6 mmol/L in protocol B (P value < 0.003). The percent rebound of mean blood urea concentration in protocol A and B one hour post dialysis was 17.3% vs 34%, respectively. There was a post-dialysis rebound in the concentration of creatinine reaching 25.6% in protocol A versus 33.5% in protocol B. The rebounds for the concentration of calcium, potassium, phosphorus, and glucose were 2.26%, 11.9%, 13.2%, and 20.2% in protocol A versus 2.86%, 13.7%, 29.1% and 18.7% in protocol B respectively.
| Discussion|| |
This study demonstrates that the higher percentage of solute rebound, and hence reduction in actual clearance, is correlated with short-dialysis treatment time. Post-dialysis urea rebound has been reported to be considerable after short-high-flux hemodialysis sessions, reaching more than 20%  .
Furthermore, previous work has demonstrated that PDUR can still be substantial, nearly 10%, after a hemodialysis session length of 3.5 to 4.5 hours  . There has been no published data to confirm post dialysis rebound in the concentration of creatinine in various blood flow rates. In our study, we observed similar results with increasing post-dialysis urea rebound in response to increments of blood flow rates and/or decrements of dialysis treatment time. Our results confirm that PDUR is clinically important phenomenon and should be considered in the evaluation of dialysis efficiency and clearance. Furthermore, immediate post dialysis urea does not, in fact, reflect the actual concentration of urea in the body and may overestimate dialysis efficiency and clearance.
Similarly, we observed a post-dialysis rebound in concentration of other solutes including creatinine and potassium. This latter may raise a clinical concern especially when dealing with patients who have tendency for hyperkalemia.
Post-dialysis rebound in solute concentration is due to slow movement of solute from tissues during hemodialysis which creates solute gradients or disequilibrium among tissue compartments that dissipate after dialysis ceases ,, . The equilibrium and postdialysis rebound depend on the diffusibility of the solute, diffusion barriers, and tissue perfusion  . Furthermore, the pre-dialysis concentrations of solutes dictate the magnitude of disequilibrium and post-dialysis rebound.
In our study, we found an increase of calcium concentration measured immediately after dialysis with a slight decrease (negative rebound) as measured one-hour after dialysis, in both protocols. This transient hypercalcemia might reach toxic levels in some critically ill patients. It seems that the underlying mechanisms that would explain post-dialysis hypercalcemia are related to high concentration of Ca+T in dialysate fluid, and attempt to correct secondary hyperparathyroidism with vitamin D3. Further work is required to evaluate the effect of reduction in the oncentration of calcium in dialysate fluid on post-dialysis hypercalcemia. The positive rebound of posphorus in shorter dialysis, as observed in our study, may add to the deleterious effect of the hypercalcemia.
In summary, post-dialysis urea, creatinine and phosphorus rebound is higher in hemodialysis with a blood flow of 400 ml/min for three hours than in hemodialyis with a blood flow of 300 ml/min for four hours. This indicates lower clearance and increased rebound with shorter dialysis treatment time. Moreover, the actual concentrations for urea, creatinine, potassium, and phosphorus should be obtained from analysis of blood samples drawn one hour post dialysis. For practical purposes one should consider a post dialysis rebound of 10-20% when interpreting results of blood samples obtained immediately post-dialysis.
| Acknowledgment|| |
Thanks to Mr. Amir S. Marzouk for preparing the statistical analysis and to Ms. Miriam Gozo Culanding who gave excellent secretarial assistance in preparing this manuscript.
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Jamal S Al-Wakeel
Department of Medicine, P.O. Box 2925, Riyadh 11461
[Figure - 1]
[Table - 1], [Table - 2], [Table - 3]