Summary
The activated clotting time (ACT) as a control of heparinization has been analysed
in 30 consecutive adult patients during extracorporeal circulation (ECC).
Among 26 patients without preoperative anticoagulation preoperative coagulation studies
revealed only minor abnormalities. In 4 patients, who were anticoagulated with coumarins
preoperatively, the results of the preoperative coagulation studies revealed abnormalities,
typical of this medication. The changes in these patients did not affect the ACT.
A dose-response curve was constructed before ECC was established. This curve showed
considerable individual Variation. The average heparin dose required to obtain an
ACT of 480 seconds was 394 units/kg body weight with a range of 200 to 700 units/kg.
From these dose-response curves it could be calculated, that a standard protocol for
heparin would imply administration of 800 units/kg, if all patients were to obtain
an ACT of 480 seconds or more. If only 300 units/kg were given, only 30% of the patients
would receive proper heparinization.
The Protamine dosage after ECC can be evaluated from the dose-response curve. Thus
complete neutralization of heparin was obtained in 28 patients with a single dose
of protamine whereas 2 patients required a further dose.
A good correlation was established between the ACT and the whole blood clotting time.
The ACT obtained 4 hours after neutralization of heparin showed a mean value similar
to that obtained immediately after neutralization.
The postoperative blood loss in this group of patients was considerably reduced when
compared to a preceding series, in which heparin was administered and neutralized
according to a fixed protocol.
In conclusion ACT controlled heparinization carrres the advantage of an individualized,
readily adjusted, and accurately neutralized dose of heparin by the use of a simple
technique which does not require the help of expert laboratory personnel.
Key words
Activated clotting time (ACT) - Extracorporeal circulation - Heparinization
