Preoperative blood samples from 17 patients undergoing major abdominal surgery were examined by the thrombelasto-graph saline dilution test, which has previously been shown to be a predictor of the risk of early postoperative deep vein thrombosis (DVT)(Heather et al 1980). By this test 8 patients were predicted to be at low risk of developing a DVT and received no special prophylaxis. 9 patients were considered to be at risk and were treated with a subcutaneous dose of 1000 units of heparin with the premedication together with a low dose of intravenous heparin infusion from the induction of anaesthesia until 2 hours after operation. Plasma antithrombin III (ATIII) concentration and anti-factor Xa activity were measured preoperatively, on day 1 and on day 3. No early DVT occurred, as assessed by I125 fibrinogen scanning, in either the untreated low risk patients or in the high risk patients receiving heparin infusion. The high risk patients had lower levels of ATIII before operation than the low risk patients (75±9%; 98±39%) and significantly lower levels on day 3 (64±25%; 106±34% p<0.02). However, these lowered levels of ATIII appeared in the high risk group to be augmented by the significant increase in anti-factor Xa activity 127±64%. before operation, 217±89%, on day 1 (p<0.02). Furthermore, on day 3 the high risk patients had significantly greater activity than those patients in the low risk group (212±76%; 106±34% p<0.02).These results show that those patients at risk of developing a postoperative DVT had a significantly enhanced activation of anti-factor Xa, as a result of intravenous low dose heparin with the subsequent abolition of early venous thrombosis.
Oxygen delivery optimization using lithium indicator dilution and pulse power analysis during major surgery in high-risk patients