Anticoagulation for continuous renal replacement therapy

Effects of hydrophilic polymer-embedded membrane on permeability and cell adhesion during continuous hemofiltration

Background and Aims

Clotting within the membrane and/or venous ‘air trap’ chamber is common problems during continuous blood purification therapy. Frequent clotting during continuous blood purification therapy leads to inadequate solute removal, an increased circuit and filter cost, and an increased burden for the medical staff. Improvements in filter membrane materials may reduce the extent of clotting and prolong the filter life. The purpose of the present study was to clarify the characteristics of an NV polymer-embedded membrane (NV-PS) after long-term use, especially the adhesiveness of blood cells and changes in the solute removal performance.

Methods

Continuous hemofiltration (CHF) experiments using a permeate recycle mode were performed for 24 h using the same porcine whole blood divided into two portions to compare the NV-PS with a conventional polysulfone membrane (PS). The activated clotting time was adjusted to within a range of 300–400 s. The change in the dextran sieving coefficient (SC) of the membrane and the residual blood clots in the filters were evaluated after the completion of the CHF experiment.

Results

The increase in the transmembrane pressure and the pressure drop of the hemofilter were significantly smaller using the NV-PS than with the PS. For larger molecules (SC $$ \leqq $$ ≦ 0.4), the reduction in SC after blood contact was significantly smaller for the NV-PS. Fewer blood cells remained in the residual blood clots when the NV-PS was used.

Conclusion

NV-PS has the advantages of showing a lower degree of reduction of the solute removal performance and also a lower degree of clogging of the hollow fibers during prolonged circulation. These characteristics may be expected to be advantageous when this membrane is used for continuous blood purification therapy in acute-phase patients.

Filter lifetimes of different hemodiafiltration membrane materials in dogs: reevaluation of the optimal anticoagulant dosage

Background

In continuous renal replacement therapy (CRRT), administration of anticoagulants is necessary for achieving a certain level of filter lifetime. Generally, anticoagulant doses are controlled to keep activated partial thromboplastin time and other indicators within a certain target range, regardless of the membrane materials used for the filter. However, in actual clinical practice, the filter lifetime varies significantly depending on the membrane material used. The objective of this study was to demonstrate that the minimum anticoagulant dose necessary for prolonging the filter lifetime while reducing the risk of hemorrhagic complications varies depending on the type of membrane.

Methods

In three beagles, hemodiafiltration was performed with hemofilters using polysulfone (PS), polymethylmethacrylate (PMMA), and AN69ST membranes separately. The minimum dose of nafamostat mesylate (NM) that would allow for 6 h of hemodiafiltration (required dose) was investigated for each membrane material.

Results

The NM doses required for 6 h of hemodiafiltration were 2 mg/kg/h for the PS membrane, 6 mg/kg/h for the PMMA membrane, and 6 mg/kg/h for the AN69ST membrane.

Conclusion

For hemodiafiltration performed in beagles, the required NM dose varied for each filter membrane material. Using the optimal anticoagulant dose for each membrane material would allow for safer CRRT performance.

Metabolic and Nutritional Aspects of Acute Renal Failure in Critically Ill Patients Requiring Continuous Renal Replacement Therapy

Acute renal failure (ARF) is rarely an isolated process but is often a complication of underlying conditions such as sepsis, trauma, and multiple-organ failure in critically ill patients. As such, concomitant clinical conditions significantly affect patient outcome. Poor nutritional status is a major factor in increasing patients' morbidity and mortality. Malnutrition in ARF patients is caused by hypercatabolism and hypermetabolism that parallel the severity of illness. When dialytic intervention is indicated, continuous renal replacement therapy (CRRT) is a commonly used alternative to intermittent hemodialysis because it is well tolerated by hemodynamically unstable patients. This paper reviews the metabolic and nutritional alterations associated with ARF and provides recommendations regarding the nutritional, fluid, electrolyte, micronutrient, and acid-base management of these patients. The basic principles of CRRT are addressed, along with their nutritional implications in critically ill patients. A patient case is presented to illustrate the clinical application of topics covered within the paper.

Effects of increased surface coverage of polyvinylpyrrolidone over a polysulfone hemofilter membrane on permeability and cell adhesion during continuous hemofiltration

The purpose of the present study was to evaluate the adhesiveness of blood cells and the solute removal performance change of modified polysulfone membranes which have increased polyvinylpyrrolidone (PVP) coverage over their surface. Continuous hemofiltration (CHF) experiments for 24 h were carried out using an ex vivo hemofilter evaluation system to compare a modified polysulfone hemofilter (SHG) with the conventional polysulfone hemofilter (SH). The 25 and 50 % cutoff values of the sieving coefficient of dextran after CHF and the protein concentration in the filtrate was higher in SHG, indicating that less fouling occurred in the SHG membrane. Adhesion of blood cells after 24 h of CHF was significantly higher in the case of SH than in the case of SHG. Blood cell adhesion and membrane fouling were reduced with the use of a polysulfone membrane modified with increased PVP coverage over the surface.

Nafamostat mesilate: can it be used as a conduit preserving agent in coronary artery bypass surgery?

Background

Graft vessel preservation solution in coronary artery bypass surgery is used to maintain the graft conduit in optimal condition during the perioperative period. Nafamostat mesilate (NM) has anticoagulation and anti-inflammatory properties. Therefore, we investigated NM as a conduit preservative agent and compared it to papaverine.

Methods

Sprague-Dawley (SD) rat thoracic aortas were examined for their contraction-relaxation ability using phenylephrine (PE) and acetylcholine (ACh) following preincubation with papaverine and NM in standard classical organ baths. Human umbilical vein endothelial cells (HUVECs) were cultured to check for the endothelial cell viability. Histopathological examination and terminal deoxynucleotidyl transferase dUTP nick end labeling assay were performed on the thoracic aortas of SD rats.

Results

The anti-contraction effects of papaverine were superior to those of NM at PE (p<0.05). The relaxation effect of NM on ACh-induced vasodilatation was not statistically different from that of papaverine. Viability assays using HUVECs showed endothelial cell survival rates of >90% in various concentrations of both NM and papaverine. A histopathological study showed a protective effect against necrosis and apoptosis (p<0.05) in the NM group.

Conclusion

NM exhibited good vascular relaxation and a reasonable anti-vasocontraction effect with a better cell protecting effect than papaverine; therefore, we concluded that NM is a good potential conduit preserving agent.

Renal replacement therapy in the intensive care unit

Acute renal failure is a frequent complication in critically ill patients that carries with it considerable morbidity and mortality. The management of renal failure in patients with multi-organ failure is different from that of renal failure that presents as a single organ failure. Intermittent haemodialysis, done in the conventional manner may not be tolerated by most critically ill patients. Continuous renal replacement therapy is physiologically superior; however, there is lack of strong evidence to prove a clinical benefit. Hybrid therapies that combine the benefits of intermittent haemodialysis and continuous therapies have emerged in the past few years. These are simpler to carry out, provide more flexibility and may be cost effective and need to be studied in a systematic manner.

A randomized comparative crossover study to assess the affect on circuit life of varying pre-dilution volume associated with CVVH and CVVHDF

OBJECTIVE

To determine if circuit life is influenced by a higher pre-dilution volume used in CVVH when compared with a lower pre-dilution volume approach in CVVHDF.

DESIGN

A comparative crossover study. Cases were randomized to receive either CVVH or CVVHDF followed by the alternative treatment.

SUBJECTS

All patients >or= 18 yrs of age who required CRRT while in ICU were eligible to participate, but excluded if coagulopathic, thrombocytopenic or unable to receive heparin. Based on an intention-to-treat, 45 patients were randomized to receive either CVVH or CVVHDF followed by the alternative treatment.

SETTING

A 24-bed, tertiary, medical and surgical adult intensive care unit (ICU).

INTERVENTION

Blood flow rate, vascular access device and insertion site, hemofilter, anticoagulation and machine hardware were standardized. An ultrafiltrate dose of 35 ml/ kg/h delivered pre-filter was used for CVVH. A fixed pre-dilution volume of 600 mls/h with a dialysate dose of 1 L was used for CVVHDF.

RESULTS

Thirty-one patients received CVVH or CVVHDF out of 45 participants followed by the alternative technique. There was a significant increase in circuit life in favor of CVVHDF (median=16 h 5 min, range=40 h 23 min) compared with CVVH (median=6 h 35 min, range=30 h 45 min). A Mann-Whitney U test was performed to compare circuit life between the two different CRRT modes (Z=-3.478, p<0.001). Measurements of circuit life on the 93 circuits which survived to clotting (50 CVVH and 43 CVVHDF) were log transformed prior to under taking a standard multiple regression analysis. None of the independent variables - activated prothrombin time (aPTT), platelet count, heparin dose, patient hematocrit or urea - had a coefficient partial correlation >0.09 (coefficient of the determination=0.117) or a linear relationship which could be associated with circuit life (p=0.228).

CONCLUSION

Pre-diluted CVVHDF appeared to have a longer circuit life when compared to high volume pre-diluted CVVH. The choice of CRRT mode may be an important independent determinant of circuit life.

Maintaining the CRRT circuit: non-anticoagulant alternatives

Prevention of clotting is an important factor in continuous renal replacement therapy (CRRT) to ensure that solute clearance, electrolytes and acid base and fluid balance are controlled. This article will focus attention on the components and design of the CRRT circuit, identifying strategies in the literature which may promote circuit life. It is important that the CRRT circuit incorporates biocompatible materials and is designed in a way which limits turbulent blood flow. Premature clotting is also more likely to occur when blood flow through the circuit is interrupted or sluggish as a result of poor vascular access, or when there is increased resistance or obstruction in the circuit. The pre-dilution method of fluid replacement reduces blood viscosity inside the haemofilter and assists in delaying the onset of blood clots by limiting the potential for haemoconcentration. The monitoring and adjustment of the blood level inside the venous bubble or air trap can lessen the effect of blood-air contact and protect the site from excessive clotting. A number of other factors are also considered important as predictors of circuit life in the operation and management of the circuit. They include the choice of access site and design configuration of the catheter device, and the level of competency of nursing staff preparing and monitoring circuit function. Whilst the value of intermittent saline flushing has not been proven to be of benefit in promoting circuit life, it remains to be determined whether the choice in the CRRT mode affects circuit life differently. In conclusion, specific measures in the application of CRRT besides anticoagulation therapy can influence the development of blood clots and the duration of circuit life. This requires the development of evidence-based practice guidelines which include strategies that are known to promote circuit life.

Anticoagulation in CRRT: Agents and strategies in Australian ICUs

BACKGROUND

Continuous Renal Replacement Therapy (CRRT) should ideally operate with as little interruption as possible. The majority of circuit terminations occur due to clotting. The Longevity of CRRT is able to be improved when the extracorporeal circuit is anticoagulated.

AIMS

This article willt focus attention on anticoagulant agents used in Australian intensive care units (ICU) to prevent clotting in the CRRT circuit.

DISCUSSION

Anticoagulants reviewed include unfractionated or standard heparin, regional heparinisation, low-molecular weight heparins and heparinoids, regional citrate, platelet-inhibiting agents (prostacyclin), thrombin antagonists (recombinant hirudin) and therapy with no anticoagulant use. Each type of anticoagulant was reviewed for mode of action, the method of delivery and how the effect is monitored. Circuit life and the incidence of bleeding were considered as the principle end points in selecting therapy, as well as side-effects with administration such as metabolic disturbances, contraindications to use including allergy and ease of use in the clinical environment.

CONCLUSION

No approach to anticoagulation has yet been reported to be as successful in extending circuit life, whilst remaining inexpensive, easy to manage and easy to reverse, as unfractionated heparin. Certain patient conditions may preclude the use of heparin, such as heparin-induced thrombocytopenia (HIT); then heparinoids, thrombin antagonists and sodium citrate are suggested as alternatives. Regional citrate reduces haemorrhagic complications in patients who have coagulation disorders or are at risk of bleeding. Clinical experience with various agents and strategies should also influence choice. The option of no anticoagulant may be appropriate in selected patients rather than more expensive and less familiar drugs.