Abstract
Background
The optimal strategy for postoperative deep venous thrombosis (DVT) prophylaxis remains among the most controversial topics in hip and knee arthroplasty. Warfarin, the most commonly used chemical anticoagulant, initially causes transient hypercoagulability; however the optimal timing of treatment with respect to surgery remains unclear. Our purpose was to evaluate the effects of pre- versus postoperative initiation of warfarin therapy with a primary endpoint of perioperative change in hemoglobin (pre- minus post-operative level), with secondary endpoints of postoperative International Normalized Ratio (INR), drain output, and bleeding/thrombotic events.
Methods
A quasi-experimental study design was employed, under which patients were assigned to begin taking warfarin the night prior to surgery or the night following surgery based on day of the week seen in clinic. An a priori power analysis was conducted in order to ensure appropriate enrollment to detect a 0.5 g/dL difference in perioperative change in hemoglobin between groups, given an alpha level of 0.05 and beta of 0.80. Based on the results, the study included all primary, elective total hip and knee arthroplasties performed by a single surgeon over a 12 month period. Fifteen patients were excluded (7 chronic anticoagulation, 3 hip fractures, 2 medical contraindications, 3 simultaneous procedures), leaving 165 cases (108 hips, 57 knees) available for study. Of these, 73 received warfarin preoperatively (49 hips, 24 knees) and 92 postoperatively (59 hips, 33 knees). Warfarin was dosed according to a standard nomogram in both groups. INR (on postoperative days 1 and 2), perioperative decrease in hemoglobin (difference between level preoperatively and on postoperative days 1 and 2), and drain outputs were compared between groups using a student t test. Adverse events (transfusions, hematomas, epidural complications, and pulmonary embolus) were compared using two-tailed Fischer's exact test.
Results
No statistically significant difference in perioperative hemoglobin change was observed between treatment groups on either postoperative day 1 (mean 3.279 versus 3.377, p=0.6824) or 2 (mean 4.0 versus 4.12, p=0.6831). As expected, the preoperative warfarin group demonstrated higher INRs on both postoperative days 1 (mean 1.18 versus 1.12, p=0.0023) and 2 (mean 1.46 versus 1.31, p=0.0006). Of note, preoperative warfarin dosing was also associated with significantly lower drain outputs (mean 185.4 versus 268.7, p=0.0025). 9 transfusions (4 preoperative dosing, 5 postoperative dosing), 3 hematomas (1 preoperative dosing, 2 postoperative dosing), and 1 pulmonary embolus (preoperative dosing) occurred, but no significant difference could be detected given the numbers available for study.
Conclusions
Initiation of warfarin pre- rather than postoperatively was not associated with a significant difference in perioperative hemoglobin change, although a significant reduction in drain output was observed. Larger studies are needed to determine whether the risk of adverse events is increased with either dosing strategy.
