Jeong Chul Kim

RIFLE-Based Data Collection/Management System Applied to a Prospective Cohort Multicenter Italian Study on the Epidemiology of Acute Kidney Injury in the Intensive Care Unit

The epidemiology of acute kidney injury (AKI) has been difficult to explore in the past, due to different definitions across various studies. Nevertheless, this is a very important topic today in light of the high morbidity and mortality of critically ill patients presenting renal dysfunction during their stay in the intensive care unit (ICU). The case mix has changed over the years, and AKI is a common problem in critically ill patients often requiring renal replacement therapy (RRT). The RIFLE and AKIN initiatives have provided a unifying definition for AKI, making possible large retrospective studies in different countries. The present study aims at validating a unified web-based data collection and data management tool based on the most recent AKI definition/classification system. The interactive database is designed to elucidate the epidemiology of AKI in a critically ill population. As a test, we performed a prospective observational multicenter study designed to prospectively evaluate all incident admissions in ten ICUs in Italy and the relevant epidemiology of AKI. Thus, a simple user-friendly web-based data collection tool was created with the scope to serve for this study and to facilitate future multicenter collaborative efforts. We enrolled 601 consecutive incident patients into the study; 25 patients with end-stage renal disease were excluded, leaving 576 patients for analysis. The median age was 66 (IQR 53–76) years, 59.4% were male, while median Simplified Acute Physiology Score II and Acute Physiology and Chronic Health Evaluation II scores were 43 (IQR 35–54) and 18 (IQR 13–24), respectively. The most common diagnostic categories for ICU admission were: respiratory (27.4%), followed by neurologic (17%), trauma (14.4%), and cardiovascular (12.1%). Crude ICU and hospital mortality were 21.7% and median ICU length of stay was 5 (IQR 3–14) days. Of 576 patients, 246 patients (42.7%) had AKI within 24 h of ICU admission, while 133 developed new AKI later during their ICU stay. RIFLE-initial class was Risk in 205 patients (54.1%), Injury in 99 (26.1%) and Failure in 75 (19.8%). Progression of AKI to a worse RIFLE class was seen in 114 patients (30.8% of AKI patients). AKI patients were older, with higher frequency of common risk factors. 116 AKI patients (30.6%) fulfilled criteria for sepsis during their ICU stay, compared to 33 (16.7%) of non-AKI patients (p < 0.001). 48 patients (8.3%) were treated with RRT in the ICU. Patients were started on RRT a median of 2 (IQR 0–6) days after ICU admission. AKI patients were started on RRT a median of 1 (IQR 0–4) day after fulfilling criteria for AKI. Median duration of RRT was 5 (IQR 2–10) days. AKI patients had a higher crude ICU mortality (28.8 vs. 8.1%, non-AKI; p < 0.001) and longer ICU length of stay (median 7 vs. 3 days, non-AKI; p < 0.001). Crude ICU mortality and ICU length of stay increased with greater severity of AKI. 225 (59.4% of AKI patients) had complete recovery of renal function, with a serum creatinine at time of ICU discharge which was ≤120% of baseline; an additional 51 AKI patients (13.5%) had partial renal recovery, while 103 (27.2%) had not recovered renal function at the time of death or ICU discharge. The study supports the use of RIFLE as an optimal classification system to stage AKI severity. AKI is indeed a deadly complication for ICU patients, where the level of severity is correlated with mortality and length of stay. The tool developed for data collection was user-friendly and easy to implement. Some of its features, including a RIFLE class alert system, may help the treating physician to systematically collect AKI data in the ICU and possibly may guide specific decisions on the institution of RRT.

A wearable artificial kidney: technical requirements and potential solutions

Recently, new approaches for miniaturization and transportability of medical devices have been developed, paving the way for wearability and the possibility of implantation, for renal replacement therapies. A wearable artificial kidney (WAK) is a medical device that supports renal function during ambulation or social activities out of hospital. With the aim of improving dialysis patients’ quality of life, WAK systems have been developed for several decades. However, at present there are a lot of technical issues confronting the attempt to apply WAK systems in clinical practice. This article focuses on technical requirements and potential solutions for WAKs and reviews up-to-date approaches related to dialysis membrane, dialysate regeneration, vascular access, patient-monitoring systems and power sources for WAKs.

Extracorporeal Carbon Dioxide Removal: The Future of Lung Support Lies in the History

Extracorporeal organ support in patients with dysfunction of vital organs like the kidney, heart, and liver has proven helpful in bridging the patients to recovery or more definitive therapy. Mechanical ventilation in patients with respiratory failure, although indispensable, has been associated with worsening injury to the lungs, termed ventilator-induced lung injury. Application of lung-protective ventilation strategies are limited by inevitable hypercapnia and hypercapnic acidosis. Various alternative extracorporeal strategies, proposed more than 30 years ago, to combat hypercapnia are now more readily available. In particular, the venovenous approach to effective carbon dioxide removal, which involves minimal invasiveness comparable to renal replacement therapy, appears to be very promising. The clinical applications of these extracorporeal carbon dioxide removal therapies may extend beyond just lung protection in ventilated patients. This article summarizes the rationale, technology and clinical application of various extracorporeal lung assist techniques available for clinical use, and some of the future perspectives in the field.

Enhancement of solute removal in a hollow-fiber hemodialyzer by mechanical vibration.

Better solute clearance, particularly of middle-molecular-weight solutes, has been associated with improved patient outcomes. However, blood-membrane interaction during dialysis results in the development of secondary mass transfer resistances on the dialyzer membrane surface. We discuss the potential effects of mechanical vibration on the diffusion, convection and adsorption of uremic solutes during dialysis. For sinusoidal and triangular vibratory motions, we conceptualized the hemodynamic changes inside the membrane and consequent effects on membrane morphology. Longitudinal vibration generates reverse flow by relative membrane motion, and transverse vibration generates a symmetric swirling flow inside the hollow fiber, which enhances wall shear stress and flow mixing. Moreover, the impulse induced by triangle wave vibration could provide higher absorption capacity to middle-molecular-weight solutes. Mechanical vibration could enhance solute removal by minimizing membrane morphology changes resulting from blood-membrane interaction during hemodialysis. These effects of mechanical vibration can be helpful in extracorporeal blood purification therapies including continuous, portable and wearable systems.

Implantable Left Ventricular Assist Devices and the Kidney

The use of left ventricular assist devices (LVADs) in treating patients with advanced heart failure restores cardiac output resulting in improved perfusion to multiple organ systems with important clinical benefits. Renal pathophysiology during LVAD support remains an evolving, poorly understood, and potentially dynamic problem. Changes in renal function after LVAD placement have been investigated in multiple studies with contradictory results. Renal dysfunction is common prior to LVAD placement, which complicates postoperative clinical outcomes. The purpose of this review is to assess the latest information regarding the effects of LVADs on renal function with regard to hemodynamics, physiology, pathology and clinical issues prior to and after placement of the devices. The review should then aid in identifying patients best suited to benefit from this technology and to refine the therapy to reduce associated risks.

Backfiltration: Past, Present and Future

Backfiltration has been recognized to be present in most diffusive-convective therapies. Although initially considered an inconvenience due to its implications in transport of contaminants in dialysate to the blood compartment, the availability of ultrapure dialysate has prompted a fresh look at the phenomenon of backfiltration with the possibility of exploiting it to further enhance the convective clearance of middle and large molecules. This review discusses the historical aspects of backfiltration, its mechanisms and influencing factors, and subsequently the different hemodialysis techniques in relation to increasing or diminishing this phenomenon.

Effects of arterial port design on blood flow distribution in hemodialyzers.

Background/Aims: Blood flow profiles in fiber bundles depend on the design of the arterial port and affects the biocompatibility of the hemodialyzer. We analyzed the effects of arterial port design on blood flow distribution in fiber bundles using nonintrusive imaging techniques. Methods: The velocity fields in arterial ports and the hemodynamics in fiber bundles were analyzed for hemodialyzers with different configurations using particle image velocimetry and perfusion computed tomography. Results: In a hemodialyzer with standard arterial ports, high blood flow profiles in the central and peripheral regions and low blood profiles in the middle region were developed due to jet flow and vortices around the jet. In a hemodialyzer with spiral arterial ports, higher flow profiles were developed due to the central vortices that decrease perfusion into the fiber bundles. Conclusion: The arterial port design of hemodialyzers should be optimized such that jet flow and vortices do not impair dialysis efficiency and biocompatibility.

Quantitative Analysis of Pulsatile Flow Contribution to Ultrafiltration

We evaluated the quantitative contribution of pulsatile flow to ultrafiltration (UF) in terms of fluid power, membrane stretch, and reduction of membrane layering. An in vitro comparison of the UF rate using pulsatile and roller pumps was performed with distilled water and bovine whole blood. The mean transmembrane pressure (TMPm) and UF rate were higher with the pulsatile pump for the same mean flow rate: 6.6 mm Hg and 21.1 mL/min higher on average for distilled water and 34.2 mm Hg and 31.4 mL/min higher on average for blood. The average UF rate was 8.4 mL/min higher with the pulsatile pump for the same TMPm with bovine blood. However, the relationship between the UF rate and the TMPm was independent of the flow configuration for distilled water. We showed that the higher UF rate in the pulsatile pump is mainly due to greater fluid power and reduction of membrane layering, while the membrane stretch was not an important factor.

In vitro Cytotoxicity of Bisphenol A in Monocytes Cell Line

Background/Aim: Bisphenol A (BPA) is used in the production of many plastics, which are used to build biomaterials that sometimes are in direct contact with blood. It is believed that the release of BPA into bloodstream may give rise to cytotoxic events for blood components. The aim of the present study was to perform an in vitro investigation of the observable cytotoxic effect of BPA, at increasing concentrations, on the monocyte cell line. Methods: We incubated in vitro monocyte cells (U937) for 24 h in cell line medium samples (RPMI 1640) at different concentrations of BPA. We then generated curves to evaluate viability, necrosis and apoptosis of monocytes against increasing concentrations of BPA. Results: The percentage values of concentrations of BPA corresponding to 50% of the viability and necrosis of the monocytes were 1.39 and 1.48 ng/ml, respectively. Based on our observations, we reported an increasing cytotoxic effect for higher concentrations. The apoptotic effect reached the maximum value at BPA concentration of 1.5 ng/ml; at still higher concentrations, we observed a predominantly necrotic cell death. Conclusion: Viability, necrosis and apoptosis of monocytes are strongly and positively correlated with BPA concentration. A direct contact of such compound with biological components of blood may lead to high levels of cytotoxicity, and require us to evaluate additional factors while judging the bio-incompatibility of BPA.

Effects of dialysate flow configurations in continuous renal replacement therapy on solute removal: computational modeling.

Background/Aims: Continuous renal replacement therapy (CRRT) is commonly used for critically ill patients with acute kidney injury. During treatment, a slow dialysate flow rate can be applied to enhance diffusive solute removal. However, due to the lack of the rationale of the dialysate flow configuration (countercurrent or concurrent to blood flow), in clinical practice, the connection settings of a hemodiafilter are done depending on nurse preference or at random. Methods: In this study, we investigated the effects of flow configurations in a hemodiafilter during continuous venovenous hemodialysis on solute removal and fluid transport using computational fluid dynamic modeling. We solved the momentum equation coupling solute transport to predict quantitative diffusion and convection phenomena in a simplified hemodiafilter model. Results: Computational modeling results showed superior solute removal (clearance of urea: 67.8 vs. 45.1 ml/min) and convection (filtration volume: 29.0 vs. 25.7 ml/min) performances for the countercurrent flow configuration. Countercurrent flow configuration enhances convection and diffusion compared to concurrent flow configuration by increasing filtration volume and equilibrium concentration in the proximal part of a hemodiafilter and backfiltration of pure dialysate in the distal part. In clinical practice, the countercurrent dialysate flow configuration of a hemodiafilter could increase solute removal in CRRT. Nevertheless, while this configuration may become mandatory for high-efficiency treatments, the impact of differences in solute removal observed in slow continuous therapies may be less important. Under these circumstances, if continuous therapies are prescribed, some of the advantages of the concurrent configuration in terms of simpler circuit layout and simpler machine design may overcome the advantages in terms of solute clearance. Conclusion: Different dialysate flow configurations influence solute clearance and change major solute removal mechanisms in the proximal and distal parts of a hemodiafilter. Advantages of each configuration should be balanced against the overall performance of the treatment and its simplicity in terms of treatment delivery and circuit handling procedures.