Continuous renal replacement therapy in neonates and young infants during extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) is a therapy that ensures adequate tissue oxygen delivery in patients suffering cardiac and/or respiratory failure that are unresponsive to conventional therapy. During ECMO, it is common to see a decrease in urine output that may be associated with acute renal failure. In this context, continuous renal replacement therapy (CRRT) should be considered. Our aim is to evaluate a pioneer experience in Latin America, related to the use of CRRT in a group of neonatal-pediatric patients during ECMO. We conducted a retrospective review of patients treated with ECMO at our institution between May 2003 and May 2005. Twelve infants were treated with ECMO, six of them also underwent CRRT. The main reasons for CRRT initiation were fluid overload and progressive azotemia. Observed complications were clots in the filter and excessive ultrafiltration. CRRT was successful in fluid management and solute clearance in all patients. Discharge survival rate was 83%, all of them with normal renal function. Concurrent CRRT with ECMO is technically feasible and efficacious in the management of fluid overload and solute clearance. We report the first experience with these therapies in a Latin American neonatal-pediatric ECMO program associated with the Extracorporeal Life Support Organization.     

Indications for continuous renal function replacement therapy

One of the most important achievements in the contemporary intensive care management is introduction of continuous renal replacement therapy (CRRT). The most common indications for CRRT are acute renal failure complicated with heart failure, volume overload, hypercatabolism, acute or chronic liver failure, and/or brain swelling. Less common indications include systemic inflammatory response (SIRS), sepsis, multiorgan failure (MOF), adult respiratory distress syndrome, crush syndrome, tumor lysis syndrome, lactacidosis, and chronic heart failure. Methods of CRRT could be used during or after open heart operations, heart, lung or/and liver transplantation in adults and children. Modern approach to treatment of acute renal failure introduces dialysis early in the course of disease in order to avoid complications on other organs. Sepsis, SIRS and septic shock are still major therapeutic problems in intensive care units with a mortality rate over 50%. Numerous uncontrolled and several controlled clinical studies have demonstrated that CRRT could remove inflammatory substances including cytokines, activated components of the complement, and derivatives of the arachidonic acid. Hemodynamic stability and gas exchange in the lungs were significantly improved. These is due not only to removal of inflammatory substances but also to other nonspecific hemodynamic effects (control of body temperature, fluid and metabolic balance). Besides the convection, cytokines could be removed from the plasma with adsorption on the membrane of dialyzer or hemofilter. Prophylactic use of CCRT in patients with normal renal function, without disturbances in fluid excretion and with normal hemodynamics is still controversial, while the possible benefit is not higher than the risks of invasive therapeutic method, and there is no evidence that prophylactic CCRT could prevent development of acute renal failure in these patients. However, current knowledge of MOF pathophysiology justifies the use of CRRT in patients with signs of heart failure, disturbances in metabolic and fluid homeostasis and sepsis, and in patients with the risk of developing acute respiratory failure or MOF, despite the mild impairment of renal function according to laboratory results.     

Extended daily dialysis vs. continuous hemodialysis for ICU patients with acute renal failure: a two-year single center report

Extended daily dialysis (EDD) is an easily implemented alternative to continuous renal replacement therapy (CRRT) in the intensive care unit (ICU). Since EDD offers most of the advantages of CRRT, we sought to compare the effectiveness of these two modalities. In this 2-year study, 54 ICU patients with ARF were treated with either continuous hemodialysis (CHD) or EDD. Oliguria was present in 64% of patients who received CHD vs. 73% of EDD patients (p=NS) while 93% of CHD and 81% of EDD patients required mechanical ventilation (p=NS). Patients treated with EDD were younger than those who received CHD (47.0 +/- 12.6 vs. 56.7 +/- 13.7, p=0.009), but there were no significant differences in gender or mean APACHE II scores at the time of randomization. Mean arterial blood pressures measured during treatment were maintained between 70 and 80 mmHg for both EDD and CHD and average daily serum electrolyte levels fell within normal ranges for EDD and CHD. Average daily fluid input and output were 5.8 +/- 3.3 L and 6.0 +/- 3.2 L for CHD vs. 3.3 +/- 2.6 and 3.0 +/- 1.7 L for EDD after exclusion of data from 2 burn patients. Hourly heparin anticoagulation rates were 1080 U/hour for CHD and 643 U/hour for EDD, p=0.02. Anticoagulation-free treatments were performed during 43% of all EDD treatments vs. 21% of all CHD treatments, p<0.001. Clotting of the dialyzer or circuit occurred at least once during 51% of all CHD treatment days vs. 22% of EDD treatments (p<0.001). We conclude that EDD is a safe, effective alternative to CRRT that offers comparable hemodynamic stability and excellent small solute control.     

Management of fluid balance in continuous renal replacement therapy: technical evaluation in the pediatric setting

Fluid overload control and fluid balance management represent very important factors in critically ill children requiring renal replacement therapy. A relatively high fluid volume administration in children and neonates is often necessary to deliver adequate amounts of blood derivatives, vasopressors, antibiotics, and parenteral nutrition. Fluid balance errors during pediatric continuous renal replacement therapy (CRRT) might significantly impact therapy delivery and have been described as potentially lethal. The aim of this study was to evaluate the accuracy of delivered vs. prescribed net ultrafiltration (UF) during CRRT applied to 2 neonates and 2 small children, either as dialytic treatment alone or during extracorporeal membrane oxygenation (ECMO). In accordance with an Acute Dialysis Quality Initiative workgroup statement, net UF was defined as the "overall amount of fluid extracted from the patient in a given time". Mean prescribed net UF was 18.5 ml/h (SD=6.7) during neonatal treatments and 70.3 ml/h (SD=22.5) during CRRT in small children. Daily net UF ranged from 200 mL to about 600 mL in the 2 neonates and from 1,200 to 1800 mL in the 2 children. The percentage error of delivered net UF ranged from -1.6% to 5.8% of the prescribed level. The mean error of the ECMO/CRRT patients was 3.024 ml/h vs. 0.45 m/h for the CRRT patients (p<0.001). The same difference was not evident when the 2 neonates were compared with the 2 small children (without considering the presence of ECMO). CRRT and net UF delivery appeared to be accurate, safe, and effective in this small cohort of high-risk pediatric patients.     

Hepatorenal syndrome: resolution of ascites by continuous renal replacement therapy in an alcoholic coinfected with hepatitis B, C, and human immunodeficiency viruses

A 39-yr-old male with hepatorenal syndrome type 1 and refractory ascites was treated with continuous renal replacement therapy (CRRT) resulting in clinical improvement. He was positive for antibodies to hepatitis B, C, and human immunodeficiency viruses, and had a history of chronic alcohol and iv drug abuse. The patient had 4 hospital admissions during a 12-wk period. He first presented with advanced liver disease including pedal edema and a serum ammonia level of 56 micromol/L (reference range: 11 - 35 micromol/L). In subsequent admissions, he had asterixis, nausea, vomiting, jaundice, and worsening pedal edema. On his 4th admission, there was lethargy, tense ascites, decreased urinary output, bilateral edema of the lower extremities and scrotum, serum creatinine of 6.2 mg/dl (reference range: 0.6 - 1.5 mg/dl), and weight gain of 16 kg during the prior 8 wk. During the first 3 hospitalizations, he was treated with lactulose with slight improvement. On the 4th admission, he was started on low-dose dopamine (3 microg/kg/min) and 25% salt-poor albumin without clinical improvement. A pulmonary artery catheter was placed and hemofiltration by CRRT was performed for 5 days, with removal of 26.7 L of fluid and a net reduction of 11 kg of body weight. Serum creatinine decreased to 4.2 mg/dl during CRRT and was 2.2 mg/dl at hospital discharge 2 weeks later. His PaO(2) improved from 66 to 78 mmHg and his systemic vascular resistance increased from 571 to 799 dyne.sec/cm(5). CRRT was effective in relieving severe fluid retention and producing marked clinical improvement. We suggest that CRRT should be considered for the treatment of refractory ascites including that caused by hepatorenal syndrome.     

Slow continuous renal replacement therapies: an update

Continuous renal replacement therapies (CRRT) are now being used by nephrologists, intensivists, and anesthesiologists. The various CRRT modalities differ in the kind of vascular access, the application of diffusive or convective clearances (or a combination of both), and in the location where the replacement fluid enters the circuit. CRRTs have certainly made the management of critically ill patients with acute renal failure (ARF) combined with cardiovascular instability, severe fluid overload, hypercatabolism, cerebral edema, adult respiratory distress syndrome, lactic acidosis, sepsis or other inflammatory syndromes, crush syndrome, congestive heart failure, and cardiopulmonary bypass easier. Continuous therapies incorporate several advantages including improved hemodynamic stability, optimal fluid balance, gradual urea removal, elimination of septic mediators, and the possibility of unlimited parenteral nutrition. Major difficulties and unsolved problems of CRRT are the ongoing necessity of continuous anticoagulation, considerable loss of amino acids, vitamins, trace elements, potassium, phosphate, and some drugs, as well as immobilization of the patient. The advantages of CRRT should theoretically translate into improved outcomes of critically ill ARF patients, but the superiority of continuous modalities in terms of outcome is still controversial, despite encouraging results in some clinical trials. Currently used CRRT with sophisticated treatment devices has become more expensive than hemodialysis, but the cost cannot be used as an argument against the continuous treatment modalities.     

Continuous renal replacement therapy with a polymethyl methacrylate membrane hemofilter suppresses inflammation in patients after open-heart surgery with cardiopulmonary bypass

Cardiopulmonary bypass (CPB) induces a complex inflammatory response involving an increase in inflammatory cytokines, called postperfusion syndrome. Previous studies demonstrated that adsorption of the serum cytokines can reduce acute inflammation and improve clinical outcomes. In this study, patients were placed on continuous renal replacement therapy (CRRT) with a polymethyl methacrylate (PMMA) membrane hemofilter immediately after the start of an open-heart surgery with CPB and throughout the postoperative course to prevent postperfusion syndrome. The aim of this study was to assess whether continuous CRRT using a PMMA filter (PMMA–CRRT) could affect cytokine expression and improve perioperative outcomes. We designed a randomized controlled trial, which included 19 consecutive adult patients on maintenance dialysis and 7 consecutive adult patients who were not on maintenance dialysis (NHD group). Patients on maintenance dialysis were randomly divided into two groups: Ten patients who received CRRT with a polysulfone membrane hemofilter (PS group) and nine patients who received CRRT with a PMMA membrane (PMMA group). Blood samples were collected from the radial or brachial artery at five different time points. Comparisons between the PS, PMMA, and NHD groups revealed a significant main effect of time on changes in serum IL-6 and IL-8 concentrations (p?<?0.01) and an interaction (p?<?0.05) between time and group. Plasma IL-6 and IL-8 levels after surgery were significantly lower in the PMMA group than in the PS group, while other cytokines measured in this study were not significantly different. In addition, clinical outcomes were not significantly different between the groups. The continuous use of PMMA-CRRT throughout the perioperative period suppressed serum IL-6 and IL-8 concentrations, although there were no differences in clinical outcomes.     

Predicting the outcome of renal replacement therapy in severe acute renal failure

Continuous renal replacement therapy (CRRT), such as continuous venovenous hemofiltration, has theoretical advantages over intermittent hemodialysis (IHD) that are related to cardiorespiratory stability, metabolic control, and fluid balance allowing nutritional supplementation. However, retrospective and controlled studies fail to show these advantages because of comorbidity associated with triage to CRRT. To compare outcomes using IHD versus CRRT, we applied published risk stratification models (Cleveland Clinic Foundation, Lohr index, and APACHE II) to the 349 patients with acute renal failure requiring renal replacement therapy at University of Michigan over the 2 year period including 1995 and 1996. The Cleveland Clinic Foundation model best predicted overall mortality, but our CRRT patients had excess, unpredicted mortality that was particularly prominent in the lower risk categories. The Lohr clinical score predicted mortality less accurately but also was associated with higher, unpredicted mortality at lower risk scores among the CRRT patients. APACHE II scores did not predict mortality very well among IHD, CRRT, or the combined group of patients. We conclude that the need for CRRT itself predicts mortality over and above that included in published risk models. Either CRRT is associated with some unidentified morbidity (e.g., treatment associated infection) or, more likely, triage to CRRT is associated with as yet unspecified comorbidity not detected in existing risk stratification schemes. It will be important to address these issues in any future studies evaluating outcome or comparing renal replacement therapy modalities among patients with severe acute renal failure.     

Oxygen delivery to the blood stream by the dialysis fluid during continuous renal replacement therapy ex vivo

Journal of Artificial Organs - Continuous renal replacement therapy (CRRT) maintains a balance in body water and electrolytes. CRRT supplies a higher quantity of fluid than intravenous fluid...     

Solute removal characteristics of continuous recirculating peritoneal dialysis in experimental and clinical studies

Continuous recirculating peritoneal dialysis (CRPD) was introduced to enhance solute removal efficiency in conventional peritoneal dialysis (PD) therapies such as continuous ambulatory peritoneal dialysis (CAPD). In CRPD, a portion of the dwell dialysate in the patient's peritoneal cavity is drained through a double-lumen catheter and purified by an extracorporeal dialyzer. In this study, solute removal characteristics and safety of CRPD are examined in ex vivo and clinical studies. Recirculation dialysis experiments using nine dogs (13.6 +/- 2.5 kg of body weight) were carried out for 240 min in the ex vivo study, whereas another seven dogs (12.1 +/- 2.8 kg) received conventional peritoneal dialysis (CPD) (120 min dwelling x 2) and six additional dogs (11.9 +/- 2.7 kg) received a Tidal PD (20 min dwelling x 12; 50% of tidal volume ratio) as controls. The ex vivo study revealed that CRPD has a higher efficiency for solute removal than CPD and is equivalent to Tidal PD. In the BUN reduction rate, the 19.4 +/- 5.5% in 240 min CRPD (n = 9) was significantly higher (p < 0.05) than the 3.5 +/- 3.6% in 240 min CPD (n = 7) and equivalent to the 17.3 +/- 4.7% in 240 min Tidal PD (n = 6). Continuous recirculating peritoneal dialysis maintained a low UN level in the peritoneal cavity due to dialysis with an extracorporeal dialyzer. This tendency was also seen in creatinine removal. In the clinical study, CRPD (n = 10) and CPD (n = 5) treatments were used in three renal failure patients. Higher solute removal efficiency was shown in CRPD than in CPD treatments, and the urea peritoneal clearance was 14.1 +/- 4.4 ml/min in CRPD (n = 10), significantly higher (p < 0.05) than the 7.3 +/- 2.1 ml/min in CPD (n = 5). No fibrin formation occurred during CRPD treatments.     

Fluid balance error in continuous renal replacement therapy: a technical note

BACKGROUND: The reliability and safety of continuous renal replacement therapy (CRRT) machines have improved, yet there still remains the potential for fluid balance errors to occur during treatment. METHODS: In vitro testing of two Kimal Hygieia CRRT machines (Plus and Ultima) was performed. Normal saline to simulate the blood circuit and standard bicarbonate-based fluid for replacement were used. All tests were performed in CVVH mode at four ultrafiltration (UF) rates. The testing was based on creation of a voluntary fluid balance error by clamping the line that fills the replacement fluid chamber to stop flow to the (simulated) patient. The time to alarms and fluid balance errors were recorded. The alarms were overridden and the accumulated fluid balance error allowed by the machine was determined. RESULTS: The alarm occurred approximately 1 minute after the replacement fluid line was clamped at all UF rates. There was no limit to the number of times the alarm could be overridden and the accumulated negative fluid balance was proportional to the prescribed UF rate. After the replacement fluid chamber was allowed to re-fill, the machine attempted to correct the fluid deficit and consistently delivered excess fluid to generate a positive fluid balance error. CONCLUSIONS: The Hygieia machines appear designed with appropriate alarm and safety features. However, simulated fluid balance errors raise caution for operators. Clinicians and nurses need to understand the clinical implications of alarm overrides. Fluid balance errors caused by failure to acknowledge and correct replacement fluid failure alarms may cause harm to patients.     

Patient and kidney survival by dialysis modality in critically ill patients with acute kidney injury

Using a large, international cohort, we sought to determine the effect of initial technique of renal replacement therapy (RRT) on the outcome of acute renal failure (ARF) in the intensive care unit (ICU). We enrolled 1218 patients treated with continuous RRT (CRRT) or intermittent RRT (IRRT) for ARF in 54 ICUs in 23 countries. We obtained demographic, biochemical and clinical data and followed patients to either death or hospital discharge. Information was analyzed to assess the independent impact of treatment choice on survival and renal recovery. Patients treated first with CRRT (N=1006, 82.6%) required vasopressor drugs and mechanical ventilation more frequently compared to those receiving IRRT (N=212, 17.4%), (p<0.0001). Unadjusted hospital survival was lower (35.8% vs. 51.9%, p<0.0001). However, unadjusted dialysis-independence at hospital discharge was higher after CRRT (85.5% vs. 66.2%, p<0.0001). Multivariable logistic regression showed that choice of CRRT was not an independent predictor of hospital survival or dialysis-free hospital survival. However, the choice of CRRT was a predictor of dialysis independence at hospital discharge among survivors (OR: 3.333, 95% CI: 1.845 - 6.024, p<0.0001). Further adjustment using a propensity score did not significantly change these results. We conclude that worldwide, the choice of CRRT as initial therapy is not a predictor of hospital survival or dialysis-free hospital survival but is an independent predictor of renal recovery among survivors.     

持续低效血液透析与连续性肾脏替代治疗在感染性休克急性肾损伤患者的疗效对比

目的对比研究持续低效血液透析(SLED)与连续性肾脏替代治疗(CRRT)在感染性休克急性肾损伤(AKI)患者中治疗效果。方法选择60例感染性休克AKI的患者,其中男性36例,女性24例;年龄28~71岁,平均年龄49.56岁。随机分为SLED组(30例)和CRRT组(30例)。两组患者均按《2016国际严重脓毒症及脓毒症休克诊疗指南》治疗,在此基础上分别予以SLED(每次治疗8~10 h,24 h后重复治疗,每例患者至少进行3次以上)和CRRT[模式为连续性静脉-静脉血液滤过,治疗剂量35~40 mL/(kg·h),初始24 h持续治疗,然后根据病情调整治疗时间]。分别观察两组患者治疗前后的血肌酐、pH、钾离子、每天液体平衡、急性生理与慢性健康评价Ⅱ(APACHEⅡ)评分及治疗期间血流动力学稳定性的变化。并比较两组患者的重症监护病房(ICU)住院时间、90 d病死率。结果与CRRT组比较,SLED组治疗后12 h和治疗后5 d的血肌酐、钾离子水平均显著低于CRRT组(P<0.05)。与CRRT组APACHEⅡ评分[(14.78±3.79)分]比较,SLED组治疗后5 d的APACHEⅡ评分[(10.45±3.02)分]明显低于CRRT组(P<0.05)。两组患者治疗期间,SLED组具有与CRRT组相近的血流动力学稳定性(P>0.05)。其中,SLED组血管加压药指数(VI)为20.32±5.18,血管加压药依赖性(VD)为(22.08±4.41)%;CRRT组VI为21.05±5.63,VD为(22.67±4.95)%。SLED组患者ICU住院时间[(15.32±3.65)d]显著短于CRRT组[(19.76±4.18)d],差异有统计学意义(P<0.05)。但两组患者90 d病死率差异无统计学意义(33.33%vs 36.67%;P>0.05)。结论SLED治疗感染性休克AKI患者的疗效确切,且在治疗期间血流动力学稳定性方面并不亚于CRRT。     

Impact of dialysis practice patterns on outcomes in acute kidney injury in Intensive Care Unit

Aim:Recent advances in dialysis therapy have made an impact on the clinical practice of renal replacement therapy (RRT) in acute kidney injury (AKI) in Intensive Care Unit (ICU). We studied the impact of RRT practice changes on outcomes in AKI in ICU over a period of 8 years.Results:The mean age was 53.8 ± 16.1 years and 72.6% were male. Introduction of PIRRT resulted in 37% reduction in utilization of CRRT during period-2 (from 85.5% to 53.7%). The overall mortality was high (68%) but was significantly reduced during period-2 compared to period-1 (59% vs. 79.7%, P = 0.006). Metabolic acidosis but not the mode of RRT, was the significant factor which influenced mortality.Conclusions:Adaption of PIRRT resulted in 37% reduction of utilization of CRRT. The mortality rate was significantly reduced during the period of adaption of PIRRT, possibly due to early initiation of RRT in the latter period for indications such as anuria and metabolic acidosis.     

Changing acute renal failure treatment from intermittent hemodialysis to continuous hemofiltration: impact on azotemic control.

BACKGROUND: Continuous renal replacement therapy is increasingly used in the management of acute renal failure in critically ill patients. The advantages of continuous renal replacement therapy (CRRT) over intermittent hemodialysis (IHD), however, are not yet fully documented. In particular, it is unknown whether continuous veno-venous hemodiafiltration (CVVHDF) provides better control of azotemia than IHD. OBJECTIVES: To study the effect on azotemic control of changing acute renal failure treatment from IHD to CVVHDF. SETTINGS: Tertiary intensive care unit. PATIENTS: Forty seven consecutive critically ill patients with multiorgan failure and acute renal failure treated with IHD and 47 similar patients treated with CVVHDF. METHODS: Analysis of daily morning urea and creatinine concentrations over the period of renal replacement therapy in the ICU. Statistical comparison of data. RESULTS: The two groups of patients were comparable for mean age (55 years for IHD vs. 60 years for CVVHDF; NS) and number of failing organs prior to therapy (mean of 4.2 for IHD vs. 3.7 for CVVHDF; NS). Severity of illness at admission as assessed by APACHE II score, however, was greater for patients receiving CVVHDF (29.4 vs 25.7; p<0.003). CVVHDF was associated with a significantly lower plasma urea (p < 0.0001) and serum creatinine (p < 0.01) level at 24 hours of treatment despite similar levels at the start of therapy Throughout the duration of therapy, mean urea levels (35.0 mmol/L for IHD vs 23.4 mmol/L for CVVHDF) and mean serum creatinine levels (513 micromoles/L for IHD and 263 micromoles/L for CVVHDF) showed significantly (p <0.0001) better control of uremia with CRRT. CONCLUSIONS: Changing the form of renal replacement therapy from intermittent hemodialysis to continuous hemofiltration is associated with improved control of azotemia. The superior adequacy of small solute clearance achieved during CVVHDF provides additional support for its preferential use in the management of acute renal failure in the ICU.     

Slow continuous ultrafiltration with bound solute dialysis

Bound solute dialysis (BSD), often referred to as "albumin dialysis" (practiced clinically as the molecular adsorbents recirculating system, MARS, or single-pass albumin dialysis, SPAD) or "sorbent dialysis" (practiced clinically as the charcoal-based Biologic-DT), is based upon the thermodynamic principle that the driving force for solute mass transfer across a dialysis membrane is the difference in free solute concentration across the membrane. The clinically relevant practice of slow continuous ultrafiltration (SCUF) for maintenance of patients with liver failure is analyzed in conjunction with BSD. The primary dimensionless operating parameters that describe SCUF-BSD include (1) beta, the dialysate/blood binder concentration ratio; (2) kappa, the dialyzer mass transfer/blood flow rate ratio; (3) alpha, the dialysate/blood flow rate ratio; and, (4) gamma, the ultrafiltration/blood flow rate ratio. Results from mathematical modeling of solute removal during a single pass through a dialyzer and solute removal from a one-compartment model indicate that solute removal is remarkably insensitive to gamma. Solute removal approaches an asymptote (improvement in theoretical clearance over that obtainable with no binder in the dialysate) with increasing beta that is dependent on kappa and independent of alpha. The amount of binder required to approach the asymptote decreases with increasing solute-binder equilibrium constant, i.e., more strongly bound solutes require less binder in the dialysate. The results of experimental observations over a range of blood flow rates, 100 to 180 mL/min, dialysate flow rates, 600 to 2150 mL/h, ultrafiltration rates, 0 to 220 mL/h, and dialysate/blood albumin concentration ratios, beta = 0.01 to 0.04, were independently predicted remarkably well by the one-compartment model (with no adjustable parameters) based on BSD principles.     

A new method to evaluate patient characteristic response to ultrafiltration during hemodialysis

BACKGROUND: Several factors are involved in the pathogenesis of dialysis discomfort interfering with optimal fluid removal and reducing the efficacy of the treatment; the most important one is a decrease in blood volume caused by an imbalance between ultrafiltration (UF) and plasmarefilling (PR) rates. OBJECTIVES: This study is aimed at devising a method to tailor the dialysis therapy to each individual patient, by analyzing the relationship between PR and UF during the sessions in stable patients and widening the knowledge of fluid exchanges during the treatment. METHODS: Thirty stable patients undergoing maintenance hemodialysis were enrolled. Three dialysis sessions were monitored for each patient; systemic pressure, blood composition, blood volume % variation, weight loss and conductivity were recorded repeatedly. A Plasma Refilling Index (PRI), defined and calculated by means of parameters measured throughout the dialysis, was introduced as a novel instrument to study plasma refilling phenomena. Results. The PRI provides understanding of patient response (in terms of plasma refilling) to the set UF. In the monitored sessions, the PRI trend is found to be characteristic of each patient; a PRI course that is at variance with the characteristic trend is a signal of inadequate or unusual dialysis scheduling. Moreover, statistical analysis highlights two different PRI trends during the first hour and during the rest of the treatment, suggesting the presence of different treatment phases. CONCLUSION: The main advantage of the PRI index is that it is non-invasive peculiar to each patient and easy to compute in a dialysis routine based on online data recorded by the monitor. A deviation from the characteristic trend may be a warning for the clinician. The analysis of the PRI trend also suggests how to modulate UF as a function of interstitial to intravascular fluid removal balance during dialysis.     

Outcome comparisons of intermittent and continuous therapies in acute kidney injury: what do they mean?

Despite the fact that no new clinical outcome studies comparing intermittent hemodialysis (IHD) and continuous renal replacement therapy (CRRT) for acute kidney injury (AKI) have been published in the past year, two meta-analyses addressing the topic (Bagshaw et al, Crit Care Med 2008; 36: 610-7, and Pannu et al, JAMA 2008; 299: 793-805) have been published recently. With respect to randomized controlled trials (RCTs), there was a substantial overlap between the studies considered in the analysis by Bagshaw et al and those considered in the analysis by Pannu et al. Although neither metaanalysis showed a benefit for either modality with respect to mortality or renal recovery, the two publications offered vastly different conclusions. Bagshaw et al concluded it is impossible to make any definitive recommendations about dialysis modality choice in AKI because previous studies were not adequately powered and failed to standardize for treatment dose. On the other hand, because the metaanalysis of Pannu et al demonstrated equivalent patient outcomes, and in light of the lower costs of IHD, they suggested that alternate-day hemodialysis should become the preferred therapy in many critically ill patients. As the clinical practice recommendations made by Pannu and colleagues have very important implications, we believe their analysis should be critically assessed. In this review, the weaknesses of the RCTs considered in the meta-analysis by Pannu et al are presented. Furthermore, the assumption by Pannu et al that IHD is associated with lower costs than CRRT is challenged, as they did not consider adequately both the short-term and long-term costs associated with the dialytic management of AKI patients. Based on our critical analysis, we believe the AKI dialytic treatment approach recommended by the JAMA investigators (Pannu et al) is not supported by the aggregate of the available clinical outcome data and, therefore, remains highly controversial. We would like to join with others in the AKI field by strongly recommending that investigators and other clinicians stop trying to make conclusive determinations about dialysis modalities when robust supportive data simply are not available. Instead of additional intermodality comparisons, the focus of future clinical research should be toward generating high-quality data on intramodality interventions, such as treatment dose and timing of treatment initiation. In this regard, at least for CRRT, we anxiously await the results of the ongoing RCTs evaluating the effect of CRRT dose on patient outcome.     

Transit Time, Residence Time, and the Rate of Approach to Steady State for Solute Transport During Peritoneal Dialysis

Mean transit time (MTT) and mean residence time (MRT) for solutes of low and middle molecular mass passing a system by convective–diffusive transport were calculated for the system of blood capillaries and lymphatic vessels within a tissue layer and dialysis fluid surrounding the tissue, i.e., the system with possible inflow and outflow of solutes through its surface and through the source/sink distributed within it. The general formulas were derived for MTT and MRT for various directions of the net solute flow (e.g., absorption of the solute from dialysis fluid to blood or removal of the solute from blood to dialysis fluid). MRT was calculated for diffusive transport of small and middle molecular weight solutes, and was 20 min for absorption of small molecules from dialysis fluid; however, for middle molecules MRT was increased up to 50 min. MRT for transport from blood to dialysis fluid was considerably shorter than in the opposite direction, especially for thin tissue layers. Furthermore, numerical simulations showed that the rates at which the system approaches the steady state were shorter than their theoretical estimations by MRT for absorption from dialysis fluid. The analysis was possible due to the application of the distributed model of peritoneal dialysis, which represents the real geometric characteristics of the transport system.