Simple and accurate quantification of dialysis in acute renal failure patients during either urea non-steady state or treatment with irregular or continuous schedules

Archetypal sustained low-efficiency daily diafiltration (SLEDD-f) for critically ill patients requiring kidney replacement therapy: towards an adequate therapy

Sustained low-efficiency dialysis is a hybrid form of kidney replacement therapy that has gained increasing popularity as an alternative to continuous forms of kidney replacement therapy in intensive care unit settings. During the COVID-19 pandemic, the shortage of continuous kidney replacement therapy equipment led to increasing usage of sustained low-efficiency dialysis as an alternative treatment for acute kidney injury. Sustained low-efficiency dialysis is an efficient method for treating hemodynamically unstable patients and is quite widely available, making it especially useful in resource-limited settings. In this review, we aim to discuss the various attributes of sustained low-efficiency dialysis and how it is comparable to continuous kidney replacement therapy in efficacy, in terms of solute kinetics and urea clearance, and the various formulae used to compare intermittent and continuous forms of kidney replacement therapy, along with hemodynamic stability. During the COVID-19 pandemic, there was increased clotting of continuous kidney replacement therapy circuits, which led to increased use of sustained low-efficiency dialysis alone or together with extra corporeal membrane oxygenation circuits. Although sustained low-efficiency dialysis can be delivered with continuous kidney replacement therapy machines, most centers use standard hemodialysis machines or batch dialysis systems. Even though antibiotic dosing differs between continuous kidney replacement therapy and sustained low-efficiency dialysis, reports of patient survival and renal recovery are similar for continuous kidney replacement therapy and sustained low-efficiency dialysis. Health care studies indicate that sustained low-efficiency dialysis has emerged as a cost-effective alternative to continuous kidney replacement therapy. Although there is considerable data to support sustained low-efficiency dialysis treatments for critically ill adult patients with acute kidney injury, there are fewer pediatric data, even so, currently available studies support the use of sustained low-efficiency dialysis for pediatric patients, particularly in resource-limited settings.

Toxicosis with grapes or raisins causing acute kidney injury and neurological signs in dogs

Background

The ingestion of grapes or raisins has been reported to cause acute kidney injury (AKI) in dogs, with a clinical picture dominated by early gastrointestinal signs and rapidly developing uremia. Ataxia is mentioned in a few reports, but not further characterized.

Objectives

To evaluate the clinical, laboratory, and pathological features of dogs diagnosed with grape or raisin toxicosis (GRT) with emphasis on renal and neurological manifestations, compared to a control group of dogs with AKI from other causes.

Animals

Fifteen client‐owned dogs with GRT and 74 control dogs.

Methods

Retrospective study over 17 months.

Results

All dogs with GRT were presented with severe AKI (grade 4, n = 5; grade 5, n = 10). Eleven dogs (73%) had marked forebrain, cerebellar, or vestibular signs. These manifestations dominated the clinical picture in some dogs, but were not associated with the severity of azotemia or the presence of systemic hypertension. Eight dogs (53%) survived, and 5 dogs experienced a complete neurological recovery. Causes of death were unrelated to the neurological manifestations. Neuropathological examination of 4 dogs did not identify any structural central nervous system abnormality. Only 2 control dogs (3%) displayed neurological signs with seizures unrelated to the AKI; 42 control dogs (57%) survived.

Conclusions and Clinical Importance

Severe forebrain, cerebellar, or vestibular signs may be an important feature of GRT and dominate the early clinical picture. The described features suggest a reversible functional brain injury specific to GRT and unrelated to uremia.

Evaluation of a novel non-surgical post-pyloric feeding technique in dogs with severe acute kidney injury

OBJECTIVES

To evaluate the placement and the performance of a new post-pyloric feeding (PPF) system, and compare it to esophageal (E) feeding in dogs with severe acute kidney injury (AKI).

DESIGN

Prospective study.

SETTING

University teaching hospital.

ANIMALS

Twenty client-owned dogs with severe AKI treated with hemodialysis.

INTERVENTIONS

Dogs were randomly assigned to 2 feeding techniques, PPF or E feeding; for PPF, an 8-Fr jejunal (J) tube was introduced through a standard 18-Fr E-tube and advanced endoscopically through the pylorus. A commercial liquid diet was administered at a continuous rate for at least 5 days. After the removal of the internal J-tube, feeding was continued through the E-tube. Control dogs were fed blended food 5 times daily through an E-tube. Placement technique, nutritional efficiency, and metabolic response to nutritional support were compared between the groups.

MEASUREMENTS AND MAIN RESULTS

Feeding tubes were placed a medium of 1 day (interquartile range, 0.8 d) after presentation. Median procedure-time in the group PPF was 26.5 min (11.5 min), including 8.5 min (2.7 min) for the E-tube and 17.5 min (5.0 min) for the J-tube. J-tubes were used for 5 days (1.5 d) with oral displacement observed in 3/10 dogs. The goal to administer 130% resting energy requirement within 3 days was reached in 13/20 dogs (8/10 PPF, 5/10 E). Despite nutritional support, dogs lost 1.2% body weight per day (1.1%), with no difference between the groups. The metabolic improvement was comparable between the groups, despite marked differences in the diet composition.

CONCLUSIONS

This new feeding technique can be recommended as an efficient method for early nutritional support in dogs with severe AKI. The protein-energy wasting observed despite active nutritional support suggests, however, the necessity for increased feeding targets or qualitative changes in diet composition for dogs with AKI.

Usefulness of prolonged renal replacement therapy in patients with acute kidney injury requiring dialysis

Acute kidney injury (AKI) requiring dialysis is becoming more common. Several types of renal replacement therapies have been used, including continuous, intermittent, and prolonged intermittent renal replacement therapy (PIRRT). There is no clear difference between those therapies in terms of patient survival. The aim of this study was to describe a form of PIRRT (shift continuous veno-venous hemodialysis [CVVHD]) and the results of this technique in a population of patients with AKI requiring dialysis in a tertiary care center. We studied 302 patients with AKI requiring dialysis over a 3-year period. All patients were treated in the intensive care unit. There were 1709 treatments in the study. Shift CVVHD was done for 8 h daily using NxStage machines, with a bicarbonate base dialysate at a rate of 5 L/h. Demographics and laboratory data were obtained from the electronic medical record. Dialysis data were obtained from the dialysis run sheets. Patient mortality was 51.3%.The dialysis time was close to 8 h and the blood flow was 310 (± 43) mL/min. The mean arterial pressure was stable before and after the dialysis. The total ultrafiltration averaged 2934 mL per treatment; the ultrafiltration rate was 4.1 (± 3.1) mL/kg/h, and the ultrafiltration per hour was 359 (± 257.8) mL/h. The average dialysate potassium used was 2.9 mEq/L. The dose of dialysis was 57 (± 19) mL/kg/h. The urea reduction ratio was 48% (± 15%), the standardized KT/V (a measure of dialysis dose obtained by urea kinetic modeling) was 3.5 (± 0.9), and the equivalent renal urea clearance (EKR) was 9.8 (± 4.1) mL/min. The method produced a consistent reduction in the levels of blood urea nitrogen, creatinine, potassium, and phosphorous. The delivered dose of dialysis was stable during the observation period. In conclusion, shift CVVHD is effective in treating patients with AKI requiring dialysis and has a survival similar to that of continuous therapies with less intensive use of resources.

Prediction equation for calculating residual kidney urea clearance using urine collections for different hemodialysis treatment frequencies and interdialytic intervals

Background

The purpose of the study was to explore the precision of an equation designed to estimate residual kidney urea clearance (KRU) from interdialytic urine collection data and pre-hemodialysis (HD) serum urea nitrogen (SUN) in different hemodialysis treatment schedules.

Methods

The generalizability of the proposed equation was tested in 32 731 HD treatments where urine was collected prior to a dialysis session, mostly for 24 h but sometimes longer, in patients being dialyzed 1-4 times/week.

Results

The residual kidney urea clearance estimating equation predicted a KRU that matched the one computed by formal modeling within 5% in >98% of sessions analyzed. The errors in estimated versus modeled KRU for interdialytic intervals (IDIs) of 2, 3, 4 and 7 days, were 1.6 ± 1.5%, -0.4 ± 1.6%, 0.9 ± 1.6%, and 1.5 ± 1.2%, respectively. Percent errors were similar for schedules of 1-4/week with the exception of urine collection during the 2-day interval of a 2:5-day twice-weekly schedule; here error averaged 5.0 ± 1.2%. Use of the average of the SUN values at the start and end of the collection period overestimated modeled KRU by 11.3 ± 4.5%, whereas an equation suggested by others underestimated modeled KRU by -9.9 ± 3.4%.

Conclusions

The equation tested predicts values for KRU that are similar to those obtained from formal urea kinetic modeling, with percent errors that only rarely exceed 5%. It gives relatively precise results for a wide range of HD treatment schedules, IDIs and urine collection periods.

Keywords

chronic hemodialysis, clearance, guidelines, hemodialysis, predialysis.

A swan song for Kt/Vurea

Dialyzer clearance of urea multiplied by dialysis time and normalized for urea distribution volume (Kt/V_urea or simply Kt/V) has been used as an index of dialysis adequacy since more than 30 years. This article reviews the flaws of Kt/V, starting with a lack of proof of concept in three randomized controlled hard outcome trials (RCTs), and continuing with a long list of conditions where the concept of Kt/V was shown to be flawed. This information leaves little room for any conclusion other than that Kt/V, as an indicator of dialysis adequacy, is obsolete. The dialysis patient might benefit more if, instead, the nephrology community concentrates in the future on pursuing the optimal dialysis dose that conforms with adequate quality of life and on factors that are likely to affect outcomes more than Kt/V. These include residual renal function, volume status, dialysis length, ultrafiltration rate, the number of intra-dialytic hypotensive episodes, interdialytic blood pressure, serum potassium and phosphate, serum albumin, and C reactive protein.

A Pilot Randomized Controlled Trial of Comparison between Extended Daily Hemodialysis and Continuous Veno-venous Hemodialysis in Patients of Acute Kidney Injury with Septic Shock

AIM OF STUDY

Acute kidney injury (AKI) is common in patients of septic shock. There is sparse data comparing sustained low-efficiency dialysis (SLED) and continuous renal replacement therapy (CRRT) in patients with septic shock.

MATERIALS AND METHODS

This is a prospective randomized study in a 12-bedded medical intensive care unit. After clearance from institute's ethics committee and obtaining informed consent from the relatives, sixty adult patients with septic shock who were to undergo dialysis for AKI were included in the study. They were randomly assigned to SLED or CRRT group. Hemodynamic instability was defined as in terms of vasopressor dependency (VD). The worst value of VD during the dialysis session was taken into consideration. The primary objective was look at hemodynamic changes and secondarily into the efficacy.

RESULTS

The demographic data were comparable between the sixty patients randomized to thirty in each group. Delta VD and delta vasopressor index (DVI) were similar in SLED group compared to the CRRT group. CRRT group had better efficacy in terms of both equivalent renal urea clearance though fluid balance was not significantly better in CRRT group.

CONCLUSION

SLED is a viable modality of renal replacement therapy in patients with septic shock as the hemodynamic effects are similar to CRRT.

Preservation of residual kidney function in hemodialysis patients: reviving an old concept

Residual kidney function (RKF) may confer a variety of benefits to patients on maintenance dialysis. RKF provides continuous clearance of middle molecules and protein-bound solutes. Whereas the definition of RKF varies across studies, interdialytic urine volume may emerge as a pragmatic alternative to more cumbersome calculations. RKF preservation is associated with better patient outcomes including survival and quality of life and is a clinical parameter and research focus in peritoneal dialysis. We propose the following practical considerations to preserve RKF, especially in newly transitioned (incident) hemodialysis patients: (1) periodic monitoring of RKF in hemodialysis patients through urine volume and including residual urea clearance with dialysis adequacy and outcome markers such as anemia, fluid gains, minerals and electrolytes, nutritional, status and quality of life; (2) avoidance of nephrotoxic agents such as radiocontrast dye, nonsteroidal anti-inflammatory drugs, and aminoglycosides; (3) more rigorous hypertension control and minimizing intradialytic hypotensive episodes; (4) individualizing the initial dialysis prescription with consideration of an incremental/infrequent approach to hemodialysis initiation (e.g., twice weekly) or peritoneal dialysis; and (5) considering a lower protein diet, especially on nondialysis days. Because RKF appears to be associated with better patient outcomes, it requires more clinical and research focus in the care of hemodialysis and peritoneal dialysis patients.

Quantification of Dialytic Removal and Extracellular Calcium Mass Balance during a Weekly Cycle of Hemodialysis

Objectives

The removal of calcium during hemodialysis with low calcium concentration in dialysis fluid is generally slow, and the net absorption of calcium from dialysis fluid is often reported. The details of the calcium transport process during dialysis and calcium mass balance in the extracellular fluid, however, have not been fully studied.

Methods

Weekly cycle of three dialysis sessions with interdialytic breaks of 2-2-3 days was monitored in 25 stable patients on maintenance hemodialysis with calcium concentration in dialysis fluid of 1.35 mmol/L. Total and ionic calcium were frequently measured in blood and dialysate. The volume of fluid compartments was measured by bioimpedance.

Results

Weekly dialytic removal of 12.79 ± 8.71 mmol calcium was found in 17 patients, whereas 9.48 ± 8.07 mmol calcium was absorbed per week from dialysis fluid in 8 patients. Ionic calcium was generally absorbed from dialysis fluid, whereas complexed calcium (the difference of total and ionic calcium in dialysis fluid) was removed from the body. The concentration of total calcium in plasma increased slightly during dialysis. The mass of total and ionic calcium in extracellular fluid decreased during dialysis in patients with the dialytic removal of calcium from the body and did not change in patients with the absorption of calcium from dialysis fluid.

Conclusions

We conclude that about one third of patients on dialysis with calcium 1.35 mmol/L in dialysis fluid may absorb calcium from dialysis fluid and therefore individual prescriptions of calcium concentration in dialysis fluid should be considered for such patients.

The Saga of Two Centuries of Urea: Nontoxic Toxin or Vice Versa?

In the early 1700s, a substance ultimately identified as urea was reported for the first time in urine. About a century later, in 1828, synthesis of this organic compound was achieved, thus giving rise to modern organic chemistry. In parallel, physicians showed that urine comes from the kidneys and contains large amounts of urea, which is produced outside of the kidneys, establishing the humoral approach of renal physiology. Urea was the first uremic retention solute to be identified and it has been used as a marker of renal disease ever since. However, progress in the knowledge of urea metabolism has shown that it is susceptible to many extrarenal variations and, therefore, it cannot be a reliable marker of renal function. It reflects protein intake in the stable patient and has been used to assess nutrition and dialysis efficacy in renal patients. Although it has been studied for almost 200 years, its toxicity has been largely debated. An indirect toxicity occurring through carbamylation of lysine residues is now well established and some evidence from recent work also supports direct toxicity of urea, offering additional rationale for interventional prevention of uremic complications.

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.

The hemodynamic effects during sustained low-efficiency dialysis versus continuous veno-venous hemofiltration for uremic patients with brain hemorrhage: a crossover study

OBJECT

Hemodynamic instability occurs frequently during dialysis treatment and remains a significant cause of patient morbidity and mortality, especially in patients with brain hemorrhage. This study aims to compare the effects of hemodynamic parameters and intracranial pressure (ICP) between sustained low-efficiency dialysis (SLED) and continuous veno-venous hemofiltration (CVVH) in dialysis patients with brain hemorrhage.

METHODS

End-stage renal disease (ESRD) patients with brain hemorrhage undergoing ICP monitoring were enrolled. Patients were randomized to receive CVVH or SLED on the 1st day and were changed to the other modality on the 2nd day. The ultrafiltration rate was set at between 1.0 kg/8 hrs and 1.5 kg/8 hrs according to the patient's fluid status. The primary study end point was the change in hemodynamics and ICP during the dialytic periods. The secondary end point was the difference between cardiovascular peptides and oxidative and inflammatory assays.

RESULTS

Ten patients (6 women; mean age 59.9 ± 3.6 years) were analyzed. The stroke volume variation was higher with SLED than CVVH (generalized estimating equations method, p = 0.031). The ICP level increased after both SLED and CVVH (time effect, p = 0.003) without significant difference between modalities. The dialysis dose quantification after 8-hour dialysis was higher in SLED than CVVH (equivalent urea clearance by convection, 62.7 ± 4.4 vs 50.2 ± 3.9 ml/min; p = 0.002). Additionally, the endothelin-1 level increased after CVVH treatment (p = 0.019) but not SLED therapy.

CONCLUSIONS

With this controlled crossover study, the authors provide the pilot evidence that both SLED and CVVH display identical acute hemodynamic effects and increased ICP after dialysis in brain hemorrhage patients. CLINICAL TRIAL REGISTRATION NO.: NCT01781585 (ClinicalTrials.gov).

Toward the optimal dose metric in continuous renal replacement therapy

PURPOSE

There is no consensus on the optimal method to measure delivered dialysis dose in patients with acute kidney injury (AKI). The use of direct dialysate-side quantification of dose in preference to the use of formal blood-based urea kinetic modeling and simplified blood urea nitrogen (BUN) methods has been recommended for dose assessment in critically-ill patients with AKI. We evaluate six different blood-side and dialysate-side methods for dose quantification.

METHODS

We examined data from 52 critically-ill patients with AKI requiring dialysis. All patients were treated with pre-dilution CVVHDF and regional citrate anticoagulation. Delivered dose was calculated using blood-side and dialysis-side kinetics. Filter function was assessed during the entire course of therapy by calculating BUN to dialysis fluid urea nitrogen (FUN) ratios q/12 hours.

RESULTS

Median daily treatment time was 1,413 min (1,260-1,440). The median observed effluent volume per treatment was 2,355 mL/h (2,060-2,863) (p<0.001). Urea mass removal rate was 13.0 ± 7.6 mg/min. Both EKR (r²=0.250; p<0.001) and KD (r²=0.409; p<0.001) showed a good correlation with actual solute removal. EKR and KD presented a decline in their values that was related to the decrease in filter function assessed by the FUN/BUN ratio.

CONCLUSIONS

Effluent rate (mL/kg/h) can only empirically provide an estimated of dose in CRRT. For clinical practice, we recommend that the delivered dose should be measured and expressed as KD. EKR also constitutes a good method for dose comparisons over time and across modalities.

Assessing and delivering dialysis dose in acute kidney injury

Assessing and delivering dialysis dose in acute kidney injury (AKI) has emerged as an important issue in the management of critically ill patients. There is ongoing debate on how dose of dialysis should be expressed and measured. Most studies have focused on clearance of small molecules (blood urea nitrogen) as a marker of delivered dose and for establishing dose-outcome relationships. Recent evidence has shown that other markers may also be important to consider, as acid-base balance and fluid overload have emerged as important factors contributing to outcomes. In this review, we provide an evaluation of current approaches to prescribing and delivering dialysis dose in AKI, identify gaps in practice and propose an integrated approach to optimize dose delivery in dialysis with a goal to improve outcomes.

Urea kinetics and intermittent dialysis prescription in small animals

Hemodialysis improves survival for animals with acute kidney injury beyond what would be expected with conventional management of the same animals. Clinical evidence and experience in human patients suggest a role for earlier intervention with renal replacement to avoid the morbidity of uremia and to promote better metabolic stability and recovery. For a large population of animal patients, it is the advanced standard for the management of acute and chronic uremia, life-threatening poisoning, and fluid overload for which there is no alternative therapy.

Dosing of renal replacement therapy in acute kidney injury: lessons learned from clinical trials

Prescribing dialysis to manage acute kidney injury (AKI) is common and recently has become a controversial area for physicians. The concept of dialysis "dose" initially was developed for end-stage renal disease and has been extended to AKI in the last decade. Urea kinetic modeling has been the mainstay of dose quantification in end-stage renal disease. Extrapolation of these techniques to critically ill patients with AKI is difficult because of a non-steady state leading to a variable increase in urea generation rate, alterations in total-body water and its compartmental distribution, and changing renal excretory capacity. Additional challenges are imposed when dose is considered for different modalities of dialysis that vary in operational characteristics (diffusion, convection, and adsorption), duration (intermittent and continuous), and frequency. The purpose of this article is to review the concept of dialysis dose, perform a critical assessment of the most important clinical trials of dialysis dose in AKI, summarize clinical evidence from these trials, and define key research issues that should be addressed in the future.

Renal replacement therapy in acute kidney injury: intermittent versus continuous? How much is enough?

Approximately 4% of all critically ill patients will require renal replacement therapy (RRT). Despite its potential reversibility, acute kidney injury has a significant impact on morbidity and mortality. Numerous studies have addressed the questions of modality choice and dose of RRT in the intensive care unit setting. There is no clear evidence that one renal replacement modality is superior to another. Two multicenter trials focusing on dialysis dose will probably be published in the next year, either confirming or invalidating the benefit of higher effluent rates. Another key aspect in the treatment of acute kidney injury is the consequence of RRT on long-term renal function. Although cohort studies have shown that continuous RRT shortens dialysis-dependence compared with intermittent hemodialysis, randomized trials and meta-analyses do not support these findings. Several unanswered questions, such as the timing of initiation and cessation of RRT, the modification of dialysis parameters over the course of acute kidney injury and the influence of fluid status need to be addressed in future trials in order to improve outcomes related to this condition.

Bimodal dialysis: theoretical and computational investigations of adequacy indices for combined use of peritoneal dialysis and hemodialysis

A theoretically correct method for evaluating the adequacy of bimodal dialysis (BMD), a combination of peritoneal dialysis (PD) and hemodialysis (HD) in the same patient, is lacking. We therefore performed computer simulations using a variable-volume, two-compartment urea kinetic model for 1-week treatments with 1) HD with three sessions, HD3, 2) continuous ambulatory PD, CAPD, 3) 6 days of CAPD and 1 day with HD session, and 4) 5 days of CAPD and 2 days with HD. Four dialysis adequacy indices (KT/V, stdKT/V, fractional solute removal, FSR, and equivalent clearance, EKR) were analyzed using four different reference methods for normalization of urea amount and concentration: 1) peak value, 2) peak average value, 3) time average value, and 4) treatment time average value. The analyses show that a proposed simplified rule of adding one third of weekly FSR for HD3 for each dialysis session and one seventh of weekly FSR for CAPD for each PD day for prediction of weekly FSR for BMD provides a fair prediction, although some corrections may be necessary, depending on the chosen reference method. In particular, KT/V may be added using this rule. We conclude that theoretically correct adequacy indices for BMD may be defined and calculated by using numerical simulations.

Renal replacement therapy in acute renal failure: which index is best for dialysis dose quantification?

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

An integrative description of dialysis adequacy indices for different treatment modalities and schedules of dialysis

Dialysis adequacy indices that are applied for the evaluation of the efficiency of urea removal include fractional water volume cleared from urea during dialysis (KT T/V), fractional solute removal (FSR), and equivalent urea clearance (EKR). Using a constant-volume, one-compartment urea kinetic model for an anuric patient, the FSR and EKR are shown to depend on only three nondimensional parameters: (i) KT/V, where K is the dialyzer clearance for hemodialysis (HD) or peritoneal mass transport coefficient for peritoneal dialysis (PD), T is the time period of dialysis, and V is urea distribution volume; (ii) T/Tc, where Tc is the length of treatment cycle; and (iii) VD/V, where VD is the volume of dialysis fluid applied. In particular, analytical formulas for FSR and EKR, valid for HD as well as for PD, were derived as functions of these three parameters. Numerical simulations, performed using a two-compartment urea kinetic model, showed that the analytical formulas are valid also for the two-compartment model, except for short, highly effective HD, where the overestimation of FSR and EKR using the analytical formulas is however, not higher than 20 and 16%, respectively. KT T/V is equal to KT/V for HD and FSR for PD. Thus, our formulas provide an integrative description of the relationships between dialysis efficiency indices and operational dialysis parameters that is valid for all modalities and schedules of dialysis. They may be applied not only for standard HD and continuous ambulatory PD, but also for HD with circulating dialysis fluid or intermittent forms of PD.

Current status of dosing and quantification of acute renal replacement therapy. Part 2: dosing paradigms and clinical implementation

The dosing and quantification of acute renal replacement therapy has emerged as one of the most pressing issues in the management of critically-ill patients with acute kidney injury. Although there is ongoing debate as to the best marker of uraemic injury in this setting, several landmark studies have identified clearance-related expressions of acute renal replacement therapy dose as important determinants of survival. Part 1 of this review examined the factors affecting the delivery of prescribed acute renal replacement therapy dose. Part 2 summarises and contextualises findings from recent dose-outcome studies, and reviews clinical tools to assist in the prescription and quantification of acute renal replacement therapy dose.

Recent clinical advances in the management of critically ill patients with acute renal failure

BACKGROUND

Significant progress has been made in the field of renal replacement therapy for critically ill patients with acute renal failure (ARF) over the past few years. This review highlights these developments.

METHODS

Recent studies assessing the clinical utility of the RIFLE classification system for the diagnosis of ARF were reviewed. Clinical outcome studies evaluating the effect of continuous renal replacement therapy (CRRT) dose and timing of initiation were assessed. The final review topic was the effect of dialysis modality on the recovery of renal function in ARF patients.

CONCLUSIONS

Based on recent clinical studies, the increasing use of the RIFLE criteria is justified, as this approach appears to be a robust method for both the diagnosis of and prognostication in ARF. A large randomized trial involving convective CRRT supports the commonly used prescription of 35 ml/ kg/h in clinical practice. Moreover, numerous recent outcome studies, also largely involving convective CRRT, provide a clinical rationale for the increasingly common clinical practice of earlier initiation. Finally, several recent studies suggest CRRT, relative to conventional hemodialysis, results in a greater rate of renal recovery in ARF patients.

Theoretical and Numerical Analysis of Different Adequacy Indices for Hemodialysis and Peritoneal Dialysis

BACKGROUND

Apart from KT/V, equivalent urea clearance (EKR) and fractional solute removal (FSR) can also be used to assess the dialysis adequacy. Our objective was to analyze the relationships between these indices for different dialysis modalities and schedules, using urea kinetic modeling.

METHODS

EKR and FSR were calculated for HD (three or six times per week), automatic nightly PD (ANPD) and CAPD using the following reference values of urea concentration and mass in the body: peak, peak average, time average and treatment time average.

RESULTS

The standard KT/V approach is related to the treatment time average, whereas the standard EKR is related to the time average reference values. In spite of KT/V = 3.5 (K meaning dialyzer clearance or peritoneal diffusive mass transport coefficient), EKR and FSR were lower for ANPD and CAPD than for HD. The ratio of EKR to FSR was essentially the same for the different treatment modalities (range 3.48-4.07 ml/min). This could be explained by the theoretical analysis which predicts the value of EKR/FSR = V/Tc, independent of the treatment modality and schedules (V is a solute distribution volume, Tc is the time of the full dialysis cycle).

CONCLUSION

Whereas the index KT/V in its standard form cannot be used to compare different dialysis regimens, EKR and FSR provide very similar evaluation of different dialysis modalities and schedules, and may be considered as equivalent measures for comparative studies of dialysis adequacy.

Sustained low-efficiency dialysis in the ICU: cost, anticoagulation, and solute removal

Hemodialysis (HD) for critically ill patients with acute renal failure has been provided as intermittent hemodialysis (IHD) or continuous renal replacement therapy (CRRT). IHD is often complicated by hypotension and inadequate fluid removal, and CRRT by high cost of solutions and problems with anticoagulation. Sustained low-efficiency daily dialysis (SLED) has been suggested as an alternative treatment. This is an observational, prospective pilot study describing the introduction of SLED at our institution. We compared SLED (23 patients, 165 treatments) with CRRT (11 patients, 209 days), focusing on cost, anticoagulation, and small solute removal. SLED consisted of 8 h of HD 6 days a week, with blood flow of 200 ml/min, dialysate flows of 350 ml/min, and hemofiltration with 1 l of saline/h. CRRT patients were anticoagulated with either heparin or citrate, and SLED patients with either heparin or saline flushes. The weekly costs to the hospital were $1431 for SLED, $2607 for CRRT with heparin, and $3089 for CRRT with citrate. Sixty-five percent of SLED treatments were heparin-free; filter clotting occurred in 18% of heparin treatments and 29% of heparin-free treatments (NS). Weekly Kt/V was significantly higher for SLED (8.4+/-1.8) and time-averaged serum creatinine was lower; equivalent renal clearance (EKRjc) was 29+/-6 ml/min for SLED, similar to that for CRRT. In summary, SLED may be routinely performed without anticoagulation; it provides solute removal equivalent to CRRT at significantly lower cost.