Experience with prostacyclin in cardiopulmonary bypass in dog and man

The activation and disruption of platelets resulting from contact with bypass equipment is responsible for bleeding problems after open-heart surgery and for vascular injury leading to cerebral damage. This paper presents experimental and clinical evidence for the benefits of the preservation of platelets by prostacyclin (PGI2) during cardiopulmonary bypass operations. Work with dogs showed that PGI2 was more effective than heparin in maintaining the numbers and aggregability of the platelet population, but by far the most effective was a combination of the two agents. A subsequent double-blind clinical trial on 24 patients undergoing coronary vein grafts, in which the combination was compared with heparin alone, confirmed these findings in man. In the presence of PGI2, platelet numbers and aggregability were preserved, with a consequent reduction in blood loss. Significantly fewer reinforcing doses of heparin were required by the PGI2 group. The integrity of platelets in the presence of PGI2 was reflected by the lack of micro-aggregates and fibrin deposits on arterial line filters. In both the human and dog studies, PGI2 was shown, by the cultured foetal mouse heart test, to prevent the release of circulating cardiotoxic factors during bypass. The known vasodilator effect of PGI2 was observed but caused no clinical problems. An unexpected feature was the maintenance of perfusion pressure without the need for additional fluid. This may indicate that PGI2 reduces capillary permeability.