Investigation Of The Relationship Between Preoperative Chromogenic Antithrombin III Assays And Hemorrhage Following Heart Surgery

The above study is part of an ongoing program to determine the mechanisms of hemorrhage in patients who have undergone extracorporeal circulation. Antithrombin III levels were measured in 850 patients (Quantichrom III) prior to undergoing cardiovascular surgery. Following surgery the maximum rate of blood loss was assessed by measuring chest tube drainage at hourly intervals. Patients whose blood loss exceeded 150 ml in any one hour were defined as “bleeders.” 257 patients had a maximum rate of blood loss exceeding 150 ml per hour, and this group is called the bleeder group. The bleeder group had a range of antithrombin III values of 16 to 148% and a mode 66% compared to a range of 24 to 170% and a mode 80% for the non-bleeder group. The means of two groups were 66% and 84% (p < 0.05) were statistically significantly different. 156 patients had an antithrombin III level of less than 60% of which 81 fell into bleeder group.

Possible mechanisms of this relationship are: (1) During massive surgical procedures disseminated proteolysis occurs and those patients with a lower level of proteolytic enzyme inhibitors such as antithrombin III have an impaired ability to control this process, which ultimately leads to hemorrhage. (2) During the massive surgery, an imbalance in protein metabolism occurs. Patients who are poor “protein producers” for pathological, genetic or nutritional reasons are less able to respond to this depletion and they respond less readily to the depletion of proteins such as the coagulation proteins with resultant bleeding. Antithrombin III may be an “indicator protein” for such patients. (3) Reduced levels of antithrombin III reduce the potency of heparin, and thus level of anticoagulation during surgery.