Blood Urea Nitrogen Stability: A Feasibility Study for Home Hemodialysis Adequacy Testing Through Mail

Urea kinetic modeling measures the delivered dose of hemodialysis and is used to monitor dialysis adequacy. Obtaining samples for adequacy calculations is a challenge for home hemodialysis (HHD) patients. Ideally, the urea reduction ratio (URR) should be measured at a typical dialysis session; therefore, for HHD patients test specimens should be drawn at home and transferred to a clinical laboratory. Would blood urea nitrogen (BUN) remain stable if samples were mailed to the laboratory? To answer this question, BUN was measured in pre- and postdialysis samples from 20 patients over 8 days of laboratory storage. While BUN values varied among the patient population, neither pre- nor postdialysis values showed any significant variation during the 8-day storage time. These results suggest that BUN values are sufficiently stable for specimens to be drawn at home and mailed to a testing laboratory.     

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.     

Urea standard Kt/Vurea for assessing dialysis treatment adequacy

Urea standard Kt/V_urea (stdKt/V_urea) has been proposed as a dose measure to assess the adequacy of dialysis treatments of arbitrary length and frequency. It is based on two fundamental assumptions: 1) that clinical outcomes for hemodialysis and peritoneal dialysis patients are equivalent and 2) that the equivalency of such clinical outcomes is achieved when the mean predialysis blood urea nitrogen or urea concentration is identical for both therapies. The relationships among urea stdKt/V_urea, equilibrated Kt/V_urea, and single‐pool Kt/V_urea are reviewed, and the assumptions required for the validity of urea stdKt/V_urea as a universal dose measure to describe dialysis treatment adequacy are discussed. It is proposed that urea stdKt/V_urea is a dose measure for both water‐soluble and protein‐bound toxin clearances; therefore, this parameter may be a practical dose measure for assessing the adequacy of dialysis during treatments of arbitrary length and frequency.     

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.     

Erythrocyte Toxicities of Imidazolidinyl Urea and Diazolidinyl Urea

The addition of antimicrobial preservatives to pharmaceutical and cosmetic products is necessary to prevent microbial growth. However, the use of preservatives can also produce other undesirable effects. For several years, researchers have been investigating the use of alternative methods in safety assessment of cosmetic ingredients and formulations by means of variety methods. The aim of this study was to evaluate the erythrocyte toxicities of two commercial preservatives： imidazolidinyl urea and diazolidinyl urea. Relatively few studies about the cytotoxicity of these preservative are available. The determination of their cytotoxicity is an essential step to warrant their safe use. Erythrocyte toxicities were evaluated by assessment of the amount of hemoglobin released by red blood cells after their lysis. In this study, both imidazolidinyl urea and diazolidinyl urea showed cytotoxic activity against red blood cells. The imidazolidinyl urea induce a small release of hemoglobin after 120 min of incubation. But, the diazolidinyl urea induce a massive release of hemoglobin from the imidazolidinyl urea （a rate of 83% at concentrations of 6.25 mg/mL and 12.5 mg/mL）.     

Effect of Low Dialysate Flow Rate on Hemodialyzer Mass Transfer Area Coefficients for Urea and Creatinine

Recent work has shown that the dialyzer mass transfer area coefficient (K_oA) for urea increases when the dialysate flow rate is increased from 500 to 800 mL/min. In this study we determined urea and creatinine clearances for two commercial dialyzers containing polysulfone hollow fibers in vitro at 37°C, a nominal blood flow rate of 300 mL/ min, and dialysate flow rates (Q_d) ranging from 100 to 800 mL/min. A standard bicarbonate dialysis solution was used in both the blood and dialysate flow pathways, and clearances were calculated from solute concentrations in the input and output flows on both the blood and dialysate sides. Urea and creatinine K_oA values, calculated from the mean of the blood and dialysate side clearances, increased (p < 0.01) with increasing Q_d over the entire range studied. The increase in both urea and creatinine K_oA with increasing Q_d was proportional to the K_oA value. These data show that changes in Q_d alter small solute clearances greater than predicted assuming a constant K_oA.     

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.     

Mathematical Concept of Dialysis Unphysiology

Although the unphysiology of the intermittently applied dialysis treatment was a concern of the dialysis pioneers, the development of any mathematical theory of treatment unphysiology and its quantification was not attempted until the end of the 1980s. This paper suggests that the conventional urea kinetic modeling (UKM) be complemented with a new parameter, the time-averaged deviation (TAD). TAD is the mean plasma urea concentration fluctuation around its mean value (time-averaged concentration, TAC). The value of TAD increases with a decreasing number of dialysis treatments per week, that is, with increasing dialysis unphysiology. Thus it can be used to quantify this until now only intuitively assessed treatment parameter. Status of a patient on any given treatment schedule can be characterized by a point on the TAC/TAD plot. Sensitivity analysis performed using the TAC/TAD plot offers insight into the influence of different patient- and treatment-related parameters on the point location and thus enables both retrospective as well as prospective assessment of different treatment schedules. Clinical correlates of TAD will have to be found and studied to establish the importance of the treatment schedule unphysiology for the overall treatment outcome.     

Designing Advanced Catalysts for Energy Conversion Based on Urea Oxidation Reaction

Urea oxidation reaction (UOR) is the underlying reaction that determines the performance of modern urea‐based energy conversion technologies. These technologies include electrocatalytic and photoelectrochemical urea splitting for hydrogen production and direct urea fuel cells as power engines. They have demonstrated great potentials as alternatives to current water splitting and hydrogen fuel cell systems with more favorable operating conditions and cost effectiveness. At the moment, UOR performance is mainly limited by the 6‐electron transfer process. In this case, various material design and synthesis strategies have recently been reported to produce highly efficient UOR catalysts. The performance of these advanced catalysts is optimized by the modification of their structural and chemical properties, including porosity development, heterostructure construction, defect engineering, surface functionalization, and electronic structure modulation. Considering the rich progress in this field, the recent advances in the design and synthesis of UOR catalysts for urea electrolysis, photoelectrochemical urea splitting, and direct urea fuel cells are reviewed here. Particular attention is paid to those design concepts, which specifically target the characteristics of urea molecules. Moreover, challenges and prospects for the future development of urea‐based energy conversion technologies and corresponding catalysts are also discussed.     

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.     

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.     

改性硝酸脲作工业炸药敏化剂的研究

根据改性硝酸脲的性质，提出由改性硝酸脲作工业炸药敏化剂较梯恩梯有许多优点，并测试了由改性硝酸脲作敏化剂生产的工业炸药的性能。结果认为该炸药具有摩擦感度和撞击感度低，威力与铵梯炸药相同，成本低的优点。     

环境友好型人造板用脲醛树脂胶粘剂合成研究

采用弱碱-弱酸-弱碱工艺,在传统一次加料反应的基础上,尿素与甲醛"分批加入,多点分段"控制反应过程,进行脲醛树脂游离甲醛含量减量化的实验.通过单因素实验,考察F/U摩尔比、羟甲基化温度、聚合反应温度、改性剂等对脲醛树脂胶粘剂游离甲醛含量和性能的影响.结果显示,当甲醛与尿素的摩尔比为1.3:1,羟甲基化反应温度为95～98℃,聚合反应时间30min时,可以合成游离甲醛含量在0.05%以下的脲醛树脂胶粘剂,最终使由脲醛树脂胶粘剂制得人造板的性能技术指标达到E_0级标准.     

Does Increasing Dialyzer Blood Flow Always Improve Dialysis Efficiency?

As dialyzer blood flow is increased during hemodialysis, diminishing increments in clearance are inevitable. In addition, as clearance increases, diminishing increases in solute removal from the patient are inevitable. The causes of these equally self-defeating and additive effects are the fundamental self-limitation of the dialysis itself due to first-order kinetics, membrane-limited diffusion within the dialyzer, and disequilibrium within the patient. Access recirculation is a specialized cause of solute disequilibrium that is separately measurable and preventable. Cardiopulmonary recirculation (CPR) is a predictable form of solute disequilibrium that is found in all patients with peripheral arteriovenous shunts and is absent during vein-to-vein dialysis. Other forms of blood flow-dependent disequilibrium probably also play a role in diminishing the efficiency of hemodialysis. Sequestration of urea in muscle during hemodialysis is suggested by reduction in the magnitude of rebound when patients exercise (and increase muscle blood flow) during hemodialysis. This discussion is not intended to discourage attempts to increase solute removal by increasing blood flow, but rather to place this maneuver in a proper perspective. Other maneuvers such as increasing dialysis frequency may be more effective as a means of improving dialysis efficiency.     

Effect of Dehydration and Urea on Stability of Homosulfamine in Solid States

In the presence of urea in solid states, the stability of unpulverized homosulfamine hydrate (phase I; UHH) is significantly decreased whereas that of unpulverized homosulfamine anhydrate (UHA) is not. The stability of UHH is decreased slightly more by pulverization (PHH). The major objective of this study was to investigate the effects of urea, dehydration, and pulverization on the stability of homosulfamine in solid states. Binary mixtures of UHH and urea, PHH and urea, and UHA and urea in a ratio of 1:1 (wt/wt) were prepared as physical mixtures and were analyzed by scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), and Fourier transform infrared (FTIR) spectroscopy to study their appearance and structural changes before and after storage. PXRD analysis revealed that physical mixtures comprising UHH and urea and PHH and urea have the same diffraction pattern as that of the mixture of UHA and urea after preparation. The dehydration rate of the crystal water of UHH was accelerated by the presence of urea in addition to pulverization. Moreover, the PXRD patterns of the physical mixtures of UHH/urea and PHH/urea were significantly altered during storage, whereas that of UHA/urea was not, which was consistent with the SEM and FTIR results. The particle shape and appearance of UHH varied significantly as a result of pulverization. The stability of homosulfamine was influenced not only by the presence of urea and dehydration but also by the surface state and particle size of the crystalline form.     

新型尿素吸附剂——果胶铜凝胶球的吸附性能

用铜离子交联果胶制得果胶铜凝胶球,用红外光谱和扫描电镜初步表征其结构,并研究果胶铜凝胶球对尿素的吸附性能。分别考察了果胶浓度、铜离子浓度、吸附时间、温度和尿素浓度对吸附的影响。结果表明:303K时,果胶铜凝胶球对尿素的吸附反应在7h时达平衡,当果胶浓度为2.5%,氯化铜浓度为2.0%,尿素浓度为400mg/L时,吸附量为48.63mg/g。吸附等温线符合Freundlich方程,温度过高和过低对吸附均不利。     

尿素法制备纳米氮化锆粉体

利用尿素为固体氮源, 通过尿素分子与ZrCl₄、ZrOCl₂·8H₂O无机锆盐发生络合反应得到Z-U和ZO-U两种ZrN陶瓷的前驱体, 两种前驱体在较低温度下热裂解都可以得到ZrN陶瓷粉体。使用FT-IR对前驱体分子进行了结构分析, 采用TG-DTA跟踪了前驱体的热裂解过程, 并通过XRD和SEM对最终热裂解获得的ZrN产物进行了表征, 探讨了不同锆源制备前驱体的热裂解反应历程及其对产物ZrN的影响。结果显示: 结晶水的存在对络合反应有较大影响, 从而造成两种前驱体分子结构上存在较大差异; 尽管热裂解反应历程相似, 由于前驱体分子结构不同, 获得的ZrN粉体在纯度和形貌上存在较大差异; Z-U前驱体更容易得到纯度高的ZrN纳米粉体。     

复杂环境下64 m尿素造粒塔的爆破拆除

介绍了金陵石化64 m高尿素造粒塔的爆破拆除。该尿素造粒塔所处环境十分复杂，为保证其安全爆破拆除，不损伤四邻建筑，参考烟囱及冷却塔爆破方法，采用高切口定向爆破方案。同时，根据其自身的结构特点，采用了大切口的预处理措施。爆破结果表明：方案可行，拱形超大导向窗可用于类似工程。