By Lexa W. Lee
NEW ORLEANS -- October 19, 2009 -- Thromboembolic prophylaxis after cardiac surgery is important because the capacity for thrombin generation increases postoperatively, as reported in the results of a new study at the 2009 Annual Meeting of the American Society of Anesthesologists (ASA).
There are only limited data about haemostatic changes that occur after open-heart surgery; most of the literature concerns perioperative bleeding and intraoperative haemostasis. Postoperatively, however, thrombotic events in cardiac surgery patients may be due to systemic thrombin generation, noted lead investigator Susanne Lison MD, Ludwig Maximilians University of Munich, Munich, Germany, presenting her study here on October 17.
The purpose of this study was to evaluate postoperative thrombin generation by measuring prothrombin fragment 1+2 (F1+2), an indicator of ongoing thrombin generation in plasma. The thrombin dynamics test (TDT) was used to quantify the enzymatic thrombin activity that can potentially be activated in plasma.
The researchers prospectively enrolled 220 first-time cardiac-surgery patients. Of these, 134 had coronary-artery bypass grafts (CABG) and 86 had aortic-valve replacement (AVR). Standard perioperative procedures were followed. Blood samples were taken preoperatively, at the end of operation, 4 hours after the end of operation, and the morning of postoperative days 1, 3, and 5. TDT, thrombin onset time, and levels of F1+2, fibrinogen, and a fibrin degradation product known as D-dimer were recorded.
TDT was significantly reduced at the end of operation (83%, P < .05) relative to preoperative values (97%). On postoperative day 1, TDT was significantly elevated (100%, P < .05). Levels returned to near-preoperative values on postoperative day 3 (98%).
After coumadin treatment in the AVR group, TDT was significantly reduced on postoperative day 3 and 5 (P < .05). In the CABG group (which did not receive coumadin), TDT remained significantly elevated.
All patients showed a peak of F1+2 immediately at the end of operation (922 pmol/L) relative to preoperatively (160 pmol/L). Levels remained significantly elevated (222 pmol/L, postoperative day 1; 246 pmol/L, postoperative day 3; 256 pmol/L, postoperative day 5, P < .05). Fibrinogen levels were significantly decreased at the end of operation and 4 hours after the end of operation, but increased significantly above preoperative levels on postoperative day 1, and further increased during the 4 remaining days.
D-dimer showed increased fibrinogen levels at the end of operation and further increased during the remaining days.
Mortality within 30 days was 1.4%.
The researchers concluded that there is an elevated thrombin-generating capacity or "procoagulant milieu," accompanied by ongoing thrombin generation (represented by F1+2), which can raise the postoperative risk of thromboembolic complications in patients who have undergone major cardiac surgery.
The investigators believed the initial drop in TDT values at the end of operation to have been partly independent of cardiopulmonary bypass, and are related instead to surgical stress with systemic inflammation.
Coumadin treatment in the AVR patients reduced TDT significantly, which might help reduce thrombotic complications postoperatively despite ongoing thrombin generation.
No association between TDT and adverse events was found. This lack of association was thought to be due to small sample size and the low incidence of complications. Nonetheless, it is the opinion of the researchers that proper attention be given to postoperative thromboembolic prophylaxis in cardiac surgery.
[Presentation title: Thrombin Generation in the Postoperative Period After Cardiac Surgery. Abstract A49]
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