Heparin-coated versus non-coated surfaces for extracorporeal circulation.

Studies were made to compare completely heparin-bonded (HBS) and conventional extracorporeal circulation surfaces using capillary membrane oxygenators (CMO) in sheep and dogs for up to five days. The aims were: to investigate the need for systemic heparinization in the case of heparin-coated surfaces, to assess blood compatibility and gas exchange performance of both systems and the extent of complement activation, and to find solutions for plasma leakage by the use of CMO. All studies were performed under standardized conditions, such as drugs, surgery, priming, blood flow rate etc. For heparin-coated surface studies all blood interfaces (CMO, catheters, tubes, etc) were coated. It was possible to eliminate systemic heparinization totally when HBS were used. During the five-day non-heparin application period blood coagulation parameters were almost unchanged and in the physiological range, platelets did not drop below 80%, hemolysis was negligible and gas exchange performance was unaffected. Less complement activation occurred with HBS than with non-coated surfaces.

Heparin free long-term extracorporeal circulation using bioactive surfaces.

As already shown, a single bolus injection of heparin is sufficient to perform extracorporeal circulation (ECC) for long-term lung support if bioactive surfaces (HBS) are used. In the present study whether complete avoidance of systemic heparinization using HBS is possible was studied. Seven conscious sheep (50-60 kg) underwent venovenous bypass under standardized conditions using a Maxima capillary membrane oxygenator. Drug administration, surgery, and other conditions, such as priming volume and blood flow rates, were identical in all experiments. All blood contacting surfaces (oxygenator, catheters, etc.) were HBS. The ECC periods were set for 24 hr (n = 3) and 5 days (n = 4). At no time was heparin administered. No complications occurred in any experiment. Partial thromboplastin time, activated clotting time, and other coagulation parameters remained within physiologic ranges. Platelets did not drop below 80% of baseline values, and hemolysis rates were negligible. Blood gas data and other vital parameters were normal during the entire ECC period. Results show that HBS can be applied to long-term ECC, without the necessity for heparin administration.

Application of surfaces with end point attached heparin to extracorporeal circulation with membrane lungs.

Application of heparin bonded surfaces (HBS) in the extracorporeal circuit (ECC) might avoid or at least reduce conventional heparin administration and would be of great benefit, especially in long-term perfusion. In this study, six sheep had a veno-venous bypass using membrane oxygenators with either total HBS or, in a control group, with untreated surfaces. Under strictly standardized conditions (body weight, drugs, geometry of tube, catheters, etc.), the animals in both groups received 300 IU/kg heparin before the catheterization as a bolus injection. In both groups, the measured heparin level decreased within 6 hours to zero, accompanied by a fall of other coagulation parameters (ACT, PTT etc.) to normal. In the control group, the ECC failed at this point because of clots in the oxygenators, whereas perfusions using HBS continued without further changes in clotting parameters until 12, 22, and 53 hours when the experiments were stopped intentionally. During the first 6 hours platelets showed a similar decrease in number in both groups and were comparable with conventional heparin treatment during further ECC periods. Other parameters, such as AT III, FXa, fibrinogen, and leukocytes were normal in both groups. The plasma hemoglobin increased markedly at the end of perfusion time in the control group but remained low even after 53 hours of ECC with HBS. The results indicate that the use of such completely heparin bonded systems can lead to a drastic reduction in systemic heparin administration.