[Major thrombopenia induced by heparin. Practical approach to cardiac surgery under extracorporeal circulation].

Major heparin-induced thrombocytopaenia (HIT) is a condition which is feared more for its thrombotic complications than for the risk of haemorrhage. The platelet count is part of routine surveillance of patients receiving this treatment which must be withdrawn if HIT occurs. The use of heparin remains essential for cardio-pulmonary bypass surgery. There are two possible scenarios: The thrombocytopaenia occurs in the postoperative period: the standard heparin may be relayed by oral anti-vitamin K anticoagulants, platelet antiaggregant drugs or by low molecular weight heparin (LMWH). The diagnosis of HIT is made before surgery: three therapeutic attitudes are discussed with respect to the urgency of surgery: surgery is deferred for 6 to 8 weeks to allow the platelet count to return to normal and the responsible circulating antibody to disappear; the use of LMWH providing the tests of platelet aggregation are negative with this product; in addition, there are other problems specific to their use in cardiopulmonary bypass to be considered; blood exchange at the beginning of cardiopulmonary bypass to eliminate the circulating factor responsible and so allow the use of standard heparin during and after the operation: this is the only possible solution in cases with in vitro aggregant activity of LMWH.