Biomaterials in cardiopulmonary bypass

S-Nitroso-N-acetylpenicillamine impregnated endotracheal tubes for prevention of ventilator-associated pneumonia

The chances of ventilator-associated pneumonia (VAP) increases 6-20 folds when an endotracheal tube (ETT) is placed in a patient. VAP is one of the most common hospital-acquired infections and comprises 86% of the nosocomial pneumonia cases. This study introduces the idea of nitric oxide-releasing ETTs (NORel-ETTs) fabricated by the incorporation of the nitric oxide (NO) donor S-nitroso-N-acetylpenicillamine (SNAP) into commercially available ETTs via solvent swelling. The impregnation of SNAP provides NO release over a 7-day period without altering the mechanical properties of the ETT. The NORel-ETTs successfully reduced the bacterial infection from a commonly found pathogen in VAP, Pseudomonas aeruginosa, by 92.72 ± 0.97% when compared with the control ETTs. Overall, this study presents the incorporation of the active release of a bactericidal agent in ETTs as an efficient strategy to prevent the risk of VAP.

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.

Levels of inflammatory markers in the blood processed by autotransfusion devices during cardiac surgery associated with cardiopulmonary bypass circuit

Intraoperative blood salvage devices allowing a reinfusion of red blood cells (RBCs) after processing of shed blood and stagnant blood in the mediastinal cavity are more and more used to reduce homologous blood requirements in cardiac surgery with cardiopulmonary bypass (CPB). As the proinflammatory activity of the shed blood also contributes to morbidity during CPB, we conducted a prospective study in order to examine the quality of autologous blood before and after processing with five different devices [BRAT2, Sequestra, Compact Advanced, Cell Saver 5 (CS5), Continuous Autologous Transfusion System (CATS)]. All systems resulted in an excellent haemoconcentration, ranging from 53.7% (Compact) to 68.9% (CATS). The concentrations and elimination rates of several inflammatory markers [IL-1beta, IL-2, IL-8, TNFalpha, myeloperoxidase (MPO), elastase] were examined. Except for the Sequestra, an important increase in concentration of IL-1beta (between 30% and 220%) has been observed after processing with each device. In contrast, the attenuation rate of IL-6 and TNFalpha (95%) was optimal for all investigated blood salvages systems. Regarding IL-8, only the CATS and CS5 systems were able to attenuate this biological parameter with an excellent efficacy. The rate of attenuation in MPO and elastase, as markers of leukocyte activation, was higher than 80% for all devices. In conclusion, the different RBC washing systems tested in this study resulted in a significant attenuation of the inflammatory response. Increased levels of IL-1beta after processing remained, however, unclear. According to the type of protocol, based on inlet haematocrit, fill and wash speeds, and wash volumes, small variations in reducing the inflammatory response have been observed from one device to another.

Low heparinization with heparin-bonded bypass circuits: is it a safe strategy?

BACKGROUND

The use of heparin-bonded cardiopulmonary bypass circuits with reduced doses of heparin sodium has been shown to give hemostatic benefits to the patient. However, fears persist that the use of less heparin may put the patient at risk for thrombotic events. This work tested the hypothesis that heparin-bonded circuits per se are effective in preserving cells and reducing thrombin generation when a reduced dose of heparin is used in vitro.

METHODS

Simulated extracorporeal circulation was carried out using the same unit of fresh heparinized (1.1 U/mL) human blood to simultaneously perfuse a heparin-bonded circuit and a nonbonded circuit. Samples were taken at 30, 60, 120, and 360 minutes and analyzed for markers of cell activation and thrombin generation.

RESULTS

The concentrations of platelet and white blood cell activation markers were found to be significantly lower in the heparin-bonded circuits compared with the nonbonded circuits. In addition, markers of thrombin generation were significantly lower in bonded circuits. Scanning electron microscopy revealed fewer adherent cells and less debris on the bonded surface compared with the nonbonded surface.

CONCLUSIONS

Cell activation and thrombin generation were significantly reduced as a result of the presence of immobilized heparin in a system of cardiopulmonary bypass with reduced plasma heparin. However, evidence of contact activation in the bonded circuits was found after 120 minutes, indicating that anticoagulation in the system was not adequate. This becomes more important clinically where the extrinsic pathway of coagulation is also involved.

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.

Review on the multifactorial aspects of bioincompatibility in CPB

Over the last few years, a great emphasis has been placed on the bioincompatibility of foreign, nonphysiological materials used during CPB. It is only recently that bioincompatibility has objectively been recognized to be multifactorial, with the dominant implicated sources being cardiotomy blood suction, shear stresses or flow dynamics and, to a lesser degree, the blood/artificial surface interactions, the heparin/protamine complex and the various forms of emboli or debris. In summary, in CPB, the reduction of postoperative complications, such as whole body inflammatory reactions, bleeding and organ dysfunctions, can only be impacted if the primary, dominant sources of bioincompatibility are reduced or eliminated.

Neutrophil activation during cardiopulmonary bypass in paediatric and adult patients

It has been reported that the 'systemic inflammatory' response occurring during cardiopulmonary bypass (CPB) may be responsible for postoperative complications. This inflammatory response is triggered by the platelet coagulation system, complement activation, resulting in neutrophil activation and degranulation. The aim of this study was to quantify the specific markers of neutrophil activation in the adult and paediatric patient during CPB. We report that neutrophil myeloperoxidase (MPO) and human neutrophil elastase (HNE) are significantly increased in both the paediatric and adult patients. This study utilized enzymatic assays that quantified the enzymatic activity in the blood circulation rather than measurement of the enzyme protein complex. Increased concentrations of MPO were, in part, related to the blood prime with the paediatric patients and the HNE concentrations were related to time on CPB in both the paediatric and adult patient. This study demonstrated that there are significantly elevated neutrophil enzyme activities in the CPB patient and underscores the pivotal role of the neutrophil in the pathophysiology of CPB.

Comparison of the performance characteristics of three generations of membrane oxygenators: Univoxregistered, Univoxreqistered Goldtrademark and SpiralGoldtrademark

With continuous enhancement in oxygenator design, the question is raised as to how these changes actually impact the performance of the oxygenator. The recent addition of two new oxygenators by the Bentley Division of Baxter Healthcare Corporation provided us with a unique opportunity to compare the performance of each device and isolate the impact of each design change on performance. While the basic design and flow patterns have remained the same, application of the Duraflo II treatment has produced the Univox Gold and a change in the fibre-winding technique has produced the SpiralGold. This study compared the effects of heparin coating (Univox to Univox Gold) and fibre-winding (Univox Gold to SpiralGold) on gas and heat transfer and resistance to blood flow (pressure drop). Six oxygenators of each model were evaluated utilizing an in vitro single pass circuit, which first conditioned bovine blood to the Association for the Advancement of Medical Instrumentation (AAMI) venous standards. Blood flows of 4.0, 5.0, 6.0 and 7.0 l/min, FiO2 values of 1.0, 0.8 and 0.6, and gas-to-blood flow ratios of 0.5, 1.0 and 1.5 were chosen as test variables. Data generated included oxygen transfer, carbon dioxide transfer, arterial pO2, resistance to blood flow, and coefficient of heat exchange. The results indicate that the Duraflo II treatment does not have a significant effect on gas and heat transfer or resistance to blood flow. The fibre-winding technique employed with the new SpiralGold, however, has improved significantly gas exchange and arterial pO2 when compared with the previous Univox models. Resistance to blood flow and coefficient of heat exchange were not affected significantly by the winding technique.