Monitoring of the blood response in blood purification

Ex Vivo Testing of Heparin-Coated Extracorporeal Circuits: Bovine Experiments

In this study the intrinsic thrombogenicity of the extracorporeal circuits and the benefit of heparin-bonded circuits in an extracorporeal life support system without full systemic heparinization and with minimal interference of the so called material-independent factors was tested in four calves. In two circuits (group A) all blood-contacting surfaces were coated with end-point-attached heparin and the other two were non-coated (group B). Under standardized conditions the calves were perfused at a blood flow rate of 2 L/min. After only one bolus injection of heparin (250 IU/kg body weight) before cannulation, plasma heparin activity rapidly decreased in both groups: half life of about 55 minutes. This decrease of the heparin activity was accompanied by a fall of the activated clotting time (ACT) level to baseline values. The experiments using a heparin-coated circuit, had a runtime of more than 360 minutes, whereas the experiments using a non-coated circuit had to be terminated after a runtime of 255 minutes, because massive fibrin formation was noticed in the circuit. This formation was accompanied by a rapid increase in the line pressure, measured just before the inlet of the oxygenator. The macroscopic inspections after terminating the experiments and rinsing the circuit showed a clean circuit in group A. The fibrinopeptide A (FPA) level increased faster during perfusion with the non-coated circuit than in the heparin coated circuit. Lung histopathological examinations of the lungs of the animals in group A showed no fibrin deposition, whereas most of the blood vessels of the lung preparations of the animals in group B were partially or completely occluded with fibrin. These results suggest that heparin-bonding greatly reduces the thrombogenicity of the extracorporeal circuit, and therefore it can reduce the need for systemic heparinization in an extracorporeal life support system.

In vitro Blood Compatibility Evaluation of Hollow Fibre Membrane Using a Controlled Flow System: A Comparative Study

A procedure has been established for the in vitro assessment of hollow fibre haemodialysis membranes. A 30 ml syringe containing 20 ml of fresh non-anticoagulated blood was mounted onto a non-pulsatile syringe pump and blood was perfused through minimodules constructed from 80 fibres retrieved from Cuprophan (Baxter ST15), cellulose acetate (M57-12, JMS Co Ltd, Hiroshima, Japan), and AN69HF (Filtral 20, Hospal, France) dialysers. Samples were collected before perfusion, 3, 6, 9 and 12 minutes. The modules were clamped vertically to minimise the effect of red cell pooling and the dialysate compartment was filled with 0.9% saline to minimise ultrafiltration. After sample processing, complement C3a, thrombin-antithrombin III complexes, prothrombin F1 + 2, and factor XII-like activity were evaluated. The results indicated that the system could discriminate between the membranes evaluated and therefore was a relevant procedure for the assessment of hollow fibre haemodialysis membranes.

The influence of biomaterials on inflammatory responses to cardiopulmonary bypass

The nature of cardiopulmonary bypass and the complexity of the inflammatory response make the detection and interpretation of a biomaterial influence difficult. However, if mediation of the inflammatory response is considered to be an appropriate clinical goal, alteration to the biomaterial influence merits further investigation.

Blood-contacting biomaterials: bioengineering viewpoints

The investigation of blood-contacting biomaterials is an important challenge and is relevant for an improvement in the clinical application of biomaterials. With the purpose of improved clinical treatment, bioengineering viewpoints of blood-contacting biomaterials cover the material options and selection, the utilization of materials, the development of materials with better properties, and processing characteristics, and the design of relevant evaluation procedures. The bioengineering objective remains that of achieving an enhanced understanding of the relationship between a biomaterial and the biological response.

Biomaterials for blood-contacting applications

Consideration of biomaterials for blood-contacting applications should take into account blood-biomaterial interactions, factors influencing the blood response and evaluation procedures. Examination of blood-biomaterial interactions indicates that relevant features are protein adsorption, platelet reactions, intrinsic coagulation, fibrinolytic activity, erythrocytes, leucocytes and complement activation. Factors influencing the blood response to a biomaterial in clinical application are the biomaterial structure, the presence of an antithrombotic agent, the patient status as determined by the disease and drug therapy, and the nature of the application. Evaluation options for biomaterials are clinical, in vivo, ex vivo and in vitro, with ex vivo and in vitro procedures relevant for biomaterial development.

Biomaterials in cardiopulmonary bypass

The improved utilization of biomaterials in cardiopulmonary bypass is dependent on polymer science and technology, procedures for blood compatibility assessment, optimization of biomaterial/antithrombotic agent combinations and the interpretation of clinical data.