Original contribution
Coagulation Status Using Thromboelastography in Patients Receiving Warfarin Prophylaxis and Epidural Analgesia

https://doi.org/10.1016/S0952-8180(02)00373-2Get rights and content

Abstract

Study Objective

To determine the coagulation status of patients receiving postoperative warfarin and epidural analgesia using thromboelastography (TEG®).

Design

Prospective, observational, clinical study.

Setting

Orthopedic postoperative division at a university hospital.

Patients

52 ASA physical status II and III patients undergoing knee arthroplasty and receiving prophylactic warfarin and epidural analgesia.

Interventions

Patients’ preoperative and postoperative coagulation status was determined by TEG®. Daily TEG® parameters were obtained until the epidural catheter was removed. TEG® parameters include reaction time (R-time or time until the first significant levels of detectable clot formation), K-time (clot firmness), maximum amplitude (MA-clot strength), alpha angle (clot development), and coagulation index (overall coagulation). In addition, daily international normalized ratios (INRs) were obtained as per our routine practice.

Main Results

On the day of catheter removal reaction time was significantly increased compared with preoperative values (p < 0.0001), but it remained within normal ranges. There was no change in the coagulation index. However, INR was abnormal and significantly increased (INR = 1.48±0.3; p < 0.0001), compared with preoperative values, on the day when the epidural catheter was removed.

Conclusions

When the epidural catheters are removed, overall coagulation status, as measured by TEG®, and despite an elevated INR (mean INR <1.5), remained within normal limits in patients receiving low-dose warfarin prophylaxis.

Introduction

Fatal pulmonary embolism is one of the most catastrophic complications of knee replacement surgery, and occurs secondary to the development of deep venous thrombosis (DVT). Vessel wall damage, venous stasis, and a hypercoagulable state following total knee replacements contribute to the formation of DVTs.1 Prophylactic anticoagulation decreases the risks of these complications. Low-dose warfarin prophylaxis has been demonstrated to be as effective as higher doses for thromboprophylaxis, with a decreased incidence of bleeding complications.2

The epidural technique provides excellent intraoperative anesthesia and postoperative analgesia following knee replacement procedures, and allows patients to perform knee mobilization exercises in the postoperative period.3 Furthermore, epidural analgesia leads to a shorter duration in the rehabilitation center when compared with patient-controlled intravenous analgesia (IV PCA) with an opioid.3 However, there is cause for concern when providing epidural analgesia to patients who are also receiving anticoagulation therapy. The only two studies of oral anticoagulant therapy and epidural analgesia in the literature are retrospective reviews that demonstrate the safety of combining these two treatment modalities postoperatively, although no firm guidelines are given regarding the level of anticoagulation and epidural catheter removal.4, 5 It has been suggested that epidural catheter removal is potentially traumatic, and that the coagulation status should be normalized before catheter removal.6, 7, 8 The theory behind this approach is that approximately 50% of hematoma formation occurs after catheter removal.6 The American Society of Regional Anesthesia (ASRA) makes no definitive recommendation for removal of epidural catheters in patients with therapeutic levels of anticoagulation, but recommends longer neurologic testing if the international normalized ratio (INR) is greater than 1.5.9 Some anesthesiologists are reluctant to provide postoperative epidural analgesia in anticoagulated patients. It is our current practice to provide postoperative epidural analgesia to patients receiving low-dose warfarin and to remove the epidural catheter on postoperative Day 2 (POD 2) provided the INR is no greater than 2.

The purpose of this observational study was to determine a baseline and then follow the overall coagulation status, using thromboelastographic technique (TEG®), in patients receiving thromboprophylaxis. TEG® values were measured during the first two days of the postoperative period, or longer if the epidural catheter remained in situ. Dr. Hellmut Hartert pioneered the technology for the Thromboelastograph® at the University of Mainz in Heidelberg, Germany in 1948.10 TEG® is a sensitive test for the global assessment of coagulation, and can determine clot strength, rate of clot formation/strengthening and fibrinolysis. *,11, 12, 13 In addition, it is a test of platelet function, plasma factor activity, and activators and inhibitors of coagulation.*,11, 12, 13

Section snippets

Materials and Methods

After institutional review board approval from the Brigham and Women’s Hospital Human Research Committee and written informed consent were received, 52 ASA physical status II and III patients (mean age 69±2 yr) who were scheduled for knee arthroplasty, who had no prior bleeding or coagulation abnormalities, and who were to receive epidural anesthesia were enrolled in the study. Nonsteroidal antiinflammatory drugs and aspirin were held before surgery. Before epidural catheter placement, complete

Results

Two of the original 52 patients were excluded from the data analysis because they did not follow the protocol. From the remaining 50 study patients, 176 TEG® samples, INRs, and CBCs were obtained. One patient received preoperative warfarin but did not receive any further doses after it was found that he had a prior history of rectal bleeding. Another patient was withdrawn from the study after the epidural catheter was unintentionally removed on postoperative day 2, with an INR of 2.3. No

Discussion

The principal findings of our study were that the TEG® was normal in patients receiving warfarin prophylaxis when the average INR was 1.48±0.3 at the time of epidural catheter removal. Our results are in agreement with those of Horlocker et al.4 and Wu and Perkins.5 In fact, our average INR is almost identical to the one alluded in the ASRA guidelines, as well as the one used in the current medical and surgical guidelines of anticoagulated patients undergoing surgical procedures.16 An INR value

Acknowledgements

The authors appreciate all of the historical information on TEG® provided by Eli Cohen, PhD. The authors acknowledge the help provided by the members of the orthopedic anesthesia service, especially Jean Marie Carabuena, MD, in collecting the blood samples. The authors also wish to acknowledge the help provided by Idith Mariano and Jennie Moore in arranging for the collection of the blood samples by the phlebotomists. The authors thank Sanjay Datta, MD, for allowing us to use the TEG® machine.

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    *

    Instructor in Anaesthesia

    Associate Professor of Anaesthesia

    Assistant Professor of Anaesthesia

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