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Biomedical subjects

C Ronco

Publications and source records attributed to C Ronco.

At least 127 records · Page 7Linked to original sources
PubMed2000

Impact of biofeedback-induced cardiovascular stability on hemodialysis tolerance and efficiency.

BACKGROUND: Hypotension is caused by a drop in blood volume during ultrafiltration, followed by vasoconstriction and reduced perfusion in some regions of the body. METHODS: We carried out a prospective controlled crossover study on 12 hypotension-prone patients with two different modalities: (A) acetate-free hemodiafiltration with standard ultrafiltration control, and (B) acetate-free hemodiafiltration with monitoring of blood volume and automatic biofeedback with machine-driven adjustments on ultrafiltration and dialysate conductivity. We measured urea Kt/V and equilibrated Kt/V (eKt/V), urea rebound, and urea removal. Hypotensive episodes and interventions were recorded. RESULTS: In group B, fewer hypotensive episodes were recorded (24 out of 72 in group B vs. 59 out of 72 in group A). Saline infusion was required in 57 cases in group A and 15 cases in group B. Urea Kt/V was 1.34 +/- 0.08 in group A and was 1.26 +/- 0.06 in group B; eKt/V was much higher in group B (1.12 +/- 0.05) than in group A (1.03 +/- 008). A significantly higher rebound was observed in group A (14.2 +/- 2.7%) compared with group B (6.4 +/- 2.3%). Discussion. A greater solute sequestration seems to occur during hemodialysis with hypotension. This results in lower eKt/V, enhanced postdialytic rebound, and lower solute removal. Higher efficiency can be observed when dialysis is carried out smoothly and cardiovascular stability is maintained. We conclude that new systems for blood volume monitoring and automatic biofeedback may not only reduce the number of hypotensive episodes during dialysis, but may also contribute to significantly increase the efficacy of the treatment.

Adult↗
PubMed2000

Effects of a reduced inner diameter of hollow fibers in hemodialyzers.

BACKGROUND: The clearance of middle molecules in high-flux hemodialyzers is due to the higher contribution of convection in the overall solute transport. Although net filtration can be maintained low by the machine control, internal filtration in the proximal part of the dialyzer remains high. The final fluid balance is achieved by significant amounts of backfiltration in the distal part of the dialyzer. To increase further middle molecule clearance (MMK), hemodiafiltration has been used. This technique, however, requires complex machines and large amounts of substitution fluid. We present a novel solution to increase the convective transport of middle molecules in high flux dialyzers without the need for substitution fluids. In particular, high-flux dialyzers with a reduced hollow fiber diameter are compared with standard dialyzers in terms of internal filtration and solute clearances. METHODS: Hemodialyzers with 175 micro inner diameter polysulfone fibers were compared with standard 200 micro polysulfone hollow fiber dialyzers. The study was carried out in vitro using a previously published method to measure internal filtration and backfiltration rates. The method is based on the detection by a gamma camera of segmental variations in concentration along the length of the dialyzer of a nondiffusable Tc99-labeled marker molecule injected in the blood in vitro circuit. At the same time, pressures were detected in the blood and dialysate compartment. The system was operated at zero net filtration maintaining volumetrically constant both dialysate and blood circuits. In vivo clearances were also measured for solutes with different molecular weight. RESULTS: The pressure drop in the blood compartment at 300 mL/min of blood flow passed from 112 to 159 mm Hg. At the same blood flow, the internal filtration-backfiltration rates increased from 23. 1 to 48.2 mL/min. This resulted in a significant increase of in vivo in clearances of vitamin B12 and inulin of more than 30%. Urea, creatinine, and phosphate clearance did not display any change. CONCLUSIONS: A reduction of the inner diameter of the hollow fibers in high-flux dialyzers may result in a significant increase of the blood compartment resistance. In turn, this results in increased rates of internal filtration and backfiltration. The practical effect in clinical dialysis is demonstrated on middle molecules. While, in fact, the clearances for small solutes such as urea and creatinine are not affected, the clearances of larger solutes such as vitamin B12 or inulin increase significantly (P < 0.01).

Biocompatible Materials↗
PubMed2000

Hemodiafiltration with online regeneration of the ultrafiltrate.

The concept of regeneration of dialysis fluids and of ultrafiltrate in particular has been recently revisited. Hemodiafiltration with online regeneration of the ultrafiltrate allows the concomitant infusion of sodium, calcium, and bicarbonate. Here, we studied the adsorptive characteristics of an integrated two-step sorbent system relative to different solutes present in the ultrafiltrate: sodium, calcium, phosphate, bicarbonate, uric acid, creatinine, and beta2-microglobulin. In vitro studies were performed in order to differentiate the relative roles for each sorbent (mineral-activated charcoal or hydrophobic resin) in adsorbing a given solute. Ex vivo studies were performed in order to evaluate the presence of cytokines (interleukin-1 beta and tumor necrosis factor-alpha), of cytokine (interleukin-1 beta and tumor necrosis factor-alpha)-inducing activities, and of the cytokine release in response to exogenous bacterial lipopolysaccharide by normal whole blood incubated with ultrafiltrate samples obtained at 15, 120, and 240 minutes after the start of treatment. The results of the present studies show the presence of immunomodulatory substances in the ultrafiltrate and the significant (P < 0.01) increase in the lipopolysaccharide-induced release of both interleukin-1 beta and tumor necrosis factor-alpha. The biological relevance of the ultrafiltrate and the possible relevance of the online, endogenous reinfusion are discussed.

Adsorption↗
PubMed2000

Adsorption in sepsis.

The pathophysiology of sepsis offers a highly complicated scenario. In sepsis, endotoxin or other gram-positive-derived products induce a complex and dynamic cellular response, giving rise to several mediators known to be relevant in the pathogenesis of septic shock such as specific mediators, substances responsible for up- or down-regulation of cytokine receptors and cytokine antagonists, inactivators of translational or transductional pathways, and precursor molecules. In this review, we delve into some new concepts stemming up from the use of sorbents in continuous plasma filtration. Nonspecific simultaneous removal of several mediators of the inflammatory cascade have led to improved outcomes in animal models of septic shock and to improved hemodynamics in a pilot clinical study. It seems of great importance to explore all possible treatment techniques that may have a direct impact on circulating mediators of sepsis and that also may interfere with the imbalance between proinflammatory and anti-inflammatory substances in the critically ill patient with multiple organ failure. In this view, the application of sorbents appears to open new and interesting therapeutic options. The search for innovative treatments specifically targeted to the special needs of the critically ill patients seems therefore more important than the attempt to adjust concepts and technologies that are normally applied to patients with chronic renal failure.

Adsorption↗
PubMed2000

Blood flow distribution in sorbent beds: analysis of a new sorbent device for hemoperfusion.

A new polymer-based sorbent cartridge has been recently developed for enhancing middle molecule removal during hemodialysis. The cartridge (Betasorb, Renaltech, New York, USA) has been designed to be placed in series with the dialyzer in the blood circuit. It is therefore important to evaluate the distribution of flow into the blood compartment of the device in order to assess if the surface of the sorbent is utilized to the best. For this purpose, a special imaging technique was utilized. Cartridges were analyzed during a simulated in vitro circulation at 250 and 350 ml/min of blood flow and 25% and 40% hematocrit. Cartridges were placed in vertical position and a cross longitudinal section 1 cm thick was analyzed in sequence by a helical scanner. Dye was injected into the arterial inlet and the progressive distribution was evaluated by sequential densitometrical measures carried out automatically by the machine. The sequential images analyzed by the scanner demonstrated excellent distribution of the flow in the blood compartment with minimal difference between the central and the peripheral regions of the compartment. In particular the following flow velocity pattern could be observed under the different experimental conditions tested. We may conclude that the cartridge design is adequate and no channelling effects could be detected in the blood compartment. The flow distribution is slightly affected by changes in flow rate and hematocrit showing an optimal utilization of the available surface for molecule adsorption.

Adsorption↗
PubMed2000

Dialysate flow distribution in hollow fiber hemodialyzers with different dialysate pathway configurations.

UNLABELLED: The efficiency of a hemodialyzer is largely dependent on its ability to facilitate diffusion, since this is the main mechanism by which small solutes are removed. The diffusion process can be impaired if there is a mismatch between blood and dialysate flow distribution in the dialyzer. The objective of the paper was to study the impact of different dialysate compartment designs on dialysate flow distribution and urea clearances. Eighteen hollow fiber 1.3 m2 hemodialyzers were studied, 6 each of 3 designs: Type A--standard fiber bundle (PAN 65DX Asahi Medical, Tokyo, Japan); Type B--spacing filaments external to the fibers (PAN 65SF Asahi Medical, Tokyo, Japan); Type C--fibers waved to give Moiré structure (FB130 Nissho-Nipro, Osaka, Japan). IN VITRO STUDIES: 3 dialyzers of each type were studied following dye injection into the dialysate compartment. Dynamic sequential imaging of longitudinal sections of the dialyzer were undertaken, using a new generation helical CT scanner (X-Press/HS1 Toshiba Corporation, Tokyo, Japan). In vivo studies: 3 dialyzers of each type were studied, in randomized sequence, in 3 different patients under standardized dialysis conditions. Blood- and dialysate-side urea clearances were measured at 30 and 150 minutes of treatment. Macroscopic and densitometrical analysis revealed that flow distribution was most homogeneous in the dialyzer with Moiré structure (Type C) and least homogeneous in the standard dialyzer (Type A). Space yarns (Type B) gave an intermediate dialysate flow distribution. Significantly increased urea clearances (p<0.001) were seen with Types B and C, compared to the standard dialyzer. Type C (Moiré) had the highest clearances although these were not significantly greater than Type B (space yarns). In conclusion, more homogeneous dialysate flow distribution and improved small solute clearances can be achieved by use of spacing yarns or waved (Moiré structure) patterns of fiber packing in the dialyzer. These effects are achieved probably as a result of reduced dialysate channeling resulting in a lower degree of mismatch between blood and dialysate flows. The new radiological technique using the helical CT scanner allows detailed flow distribution analysis and has the potential for testing future modifications to dialyzer design.

Equipment Design↗
PubMed1999

Opinions regarding outcome differences in European and US haemodialysis patients.

UNLABELLED: STUDY GOAL AND DESIGN: The aim of this evaluation was to understand why outcomes seem to be different in different parts of the world. In an attempt to look at this question from a point of view other than that necessarily adopted by epidemiological studies, we decided to explore the personal opinion of a selected group of American (US) and European (EU) experts by means of a simple questionnaire. A 13-item questionnaire was sent to 14 internationally recognized opinion leaders in the field of haemodialysis: all seven Europeans and five of the seven Americans responded. The answers to each question were stratified in order to highlight the key differences between the experts in the different continents. RESULTS: Ten of the 12 respondents (six EU and four US) said that dialysis outcomes are better in Europe; nine (six EU and three US) confirmed their opinion after taking patient characteristics into account. When asked to suggest reasons for this difference, the highest score was given to the quality of procedures and medical training with no differences between EU and US physicians. This was followed by three other factors that received the same overall score (financial issues, doctor bedside time and quality of pre-dialysis care), but it is interesting to note that the Europeans attributed considerably greater importance to bedside time than their US counterparts. CONCLUSION: It seems that the reported difference in dialysis outcomes between Europe and the US is a widely accepted fact. Although directed towards few respondents, our questionnaire does suggest some differences in the approach towards dialysis and end-stage renal disease patients.

Education, Medical↗
PubMed1999

Trace element and vitamin concentrations and losses in critically ill patients treated with continuous venovenous hemofiltration.

OBJECTIVES: To measure the blood concentrations of a number of trace elements and vitamins in critically ill patients and examine their elimination by continuous venovenous hemofiltration (CVVH). SETTING: Intensive care unit of a tertiary institution. DESIGN: Prospective, controlled, clinical study. PATIENTS: Eight critically ill patients requiring renal replacement therapy, nine patients requiring intensive care treatment but not requiring renal replacement therapy, and nine healthy controls. INTERVENTIONS: Measurement of trace element and vitamin concentrations in blood and ultrafiltrate. MEASUREMENTS AND MAIN RESULTS: Compared with normal volunteers, critically ill patients requiring CVVH had significantly lower median blood concentrations of vitamin C, vitamin E, selenium, and zinc. During the first 24 hrs of CVVH, there were no changes in the trace element and vitamin concentrations in blood, nor were there differences between pre- and postfilter samples. Micronutrient losses in the ultrafiltrate were small or undetectable except for Vitamin C, chromium, and copper. Compared with normal volunteers, critically ill patients not requiring CVVH also had significantly lower median blood concentrations of vitamin C, vitamin E, selenium, and zinc. There were no differences between the two critically ill groups. CONCLUSIONS: The clinical significance of the reductions in blood concentrations of selenium, zinc, vitamin C, and vitamin E in critically ill patients and the ultrafiltrate losses of Vitamin C, copper, and chromium remains unclear.

Ascorbic Acid Deficiency↗