[Heparin level determination during extracorporeal circulation in open heart surgery]

Because of the high dosages which have to be given during extracorporal circulation it is often impossible to measure the end point of coagulation for both thrombin time and aPTT. A correct determination of the heparin level has become possible with synthetic substrates with the help of the "Protopath proteolytic enzyme detection system" (AHS, Munich). With a fluorogenic synthetic substrate in a one-way cuvette and calibrated fluorometer the heparin and AT III levels can easily be measured. Very high levels of heparin which averaged 6,9 U/ml +/- 1,0 10 minutes after heparinization and 4,4 U/ml +/- 1,0 60 minutes later were found in ten patients with open heart surgery during extracorporal circulation. AT III decreased to less than 50% possibly due to dilutional effects. Ten minutes after protamine neutralization heparin levels were less than 0,1 U/ml. After two hours AT III levels returned to 70%. Measurement of heparin blood levels adds to the quality of anticoagulant control in situations where high dosages of heparin are given.