BJA Advance Access published online on May 30, 2008
British Journal of Anaesthesia, doi:10.1093/bja/aen132
International normalized ratio and prothrombin time values before the removal of a lumbar plexus catheter in patients receiving warfarin after total hip replacement
Department of Anesthesiology, University of Pittsburgh Medical Center, UPMC Shadyside Hospital, Suite M104 (Posner Pain Center), 5230 Centre Avenue, Pittsburgh, PA 15232, USA
* Corresponding author. E-mail: chelje{at}anes.upmc.edu
Accepted for publication February 26, 2008.
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Abstract |
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Background: There is a paucity of data regarding the coagulation status when discontinuing perineural catheters in patients receiving anticoagulant after operation. This retrospective study was designed to establish international normalized ratio (INR) and prothrombin time (PT) at the time of removal of lumbar plexus perineural catheters in patients receiving warfarin after total hip replacement.
Methods: Patients who received a continuous lumbar plexus nerve block for postoperative analgesia and received warfarin after total hip surgery between August 2002 and June 2007 were included in this retrospective study. PT and INRs were recorded before surgery and every day after operation along with any post-surgical nerve injury and bleeding related to the removal of the perineural catheter.
Results: Six hundred and seventy patients met the inclusion criteria. Almost all lumbar plexus catheters (89%) were removed on postoperative day 2. At the time of the perineural catheter removal, 36.2% of patients had an INR >1.4 (range: 1.5–3.9). One case of local bleeding was recorded at the time of the catheter removal with an INR of 3.0. This was managed with a direct pressure at the site.
Conclusions: Although in this retrospective analysis, we demonstrated that lumbar plexus catheters were removed with an INR 
1.5, additional data are required to confirm the safety of such an approach.
Keywords: anaesthetic techniques, regional, lumbar plexus; analgesia techniques, regional, i.a.; blood, coagulation; pain, acute
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Introduction |
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Guidelines on anti-coagulation and regional anaesthesia have mainly focused on neuraxial block and do not address the safety of anticoagulation and peripheral nerve blocks.1 2 It is recognized that, in patients receiving thromboprophylaxis, the removal of a deep perineural catheter raises the most bleeding concerns. Recently, Buckenmaier and colleagues3 and Chelly and Schilling4 reported on outcomes from continuous nerve blocks in anticoagulated trauma and surgical patients. Apart from anecdotal case reports of bleeding complications,5–7 these are the first reports on patients with such a combination.3 4
The most recent guidelines on the use of anticoagulants for the prevention of deep venous thrombosis (DVT) and pulmonary embolism (PE) recommend the use of warfarin or low molecular weight heparins (LMWHs) as perioperative prophylaxis for joint replacement.8 LMWHs do not affect the international normalized ratio (INR) and prothrombin time (PT). In contrast, warfarin dosing can be titrated using the INR. Presently, recommendations are to maintain the INR at 2.5 (range 2.0–3.0) which is well above the recommended values for the safe conduct of neuraxial block.1 Therefore, the use of warfarin in patients receiving continuous nerve block for postoperative analgesia represents an interesting setting to determine the coagulation status at the time of the removal of a deep perineural catheter.
This study was designed to establish the coagulation status using INR and PT at the time of removal of lumbar plexus perineural catheters in patients receiving warfarin after total hip replacement.
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Methods |
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This was a retrospective study approved initially by the University of Pittsburgh Medical Center (UPMC) quality assurance committee and secondarily by the Institutional Review Board (IRB). We collected data on INR and PT, bleeding, and nerve injury complications from patients undergoing total hip replacement between August 2002 and June 2007 who received warfarin thromboprophylaxis and in whom continuous lumbar plexus nerve block was performed to provide postoperative analgesia. In the USA, the orthopaedic surgeon chooses the anticoagulant used for thromboprophylaxis. All patients were operated on by the same surgeon who exclusively uses warfarin for thromboprophylaxis. According to this orthopaedic clinical pathway, INR and PTs (normal range for UPMC Shadyside Hospital: 0.9–1.1 and 11.6–14.3 s, respectively) were measured before surgery and daily after operation until the discharge of the patient. The dose of warfarin administered was varied (2.5, 5, 7.5, or 10 mg) according to the patient's weight and prior history of thromboembolism and was administered on the day of surgery. The lumbar plexus catheter was placed before surgery as laid down in our acute interventional perioperative pain protocol. The removal of each lumbar plexus catheter was scheduled on postoperative day 2 without any consideration of the INR value. It was performed by the nurse assigned to care for the patient 2 h after the pump infusing local anaesthetics was stopped at 6 a.m. After the removal of the perineural catheter, the nurse was instructed to monitor the patient for clinical evidence of perineural haematoma (pain at the site, morphologic changes) and neurological deficits. A computed tomography (CT) scan was performed if necessary. Before discharge, each patient underwent a lower extremity ultrasound to possibly detect the presence of a DVT. Patients with suspected PE underwent a diagnostic CT scan.
Statistical analysis
The distributions of both INR and PT were analysed for skewness and kurtosis.9 Since, both INR and PT distributions had significant skewness and kurtosis (P<0.05 for each) and given that the application of Tukey's ladder of transformations established that both distributions were not transformable to normality; therefore, data are presented as median (range) and compared using quantile regression,10 with the exception of patient characteristics (Table 1) where data are presented as median (range) and mean (SD).
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Results |
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Six hundred and seventy patients were included in this study. The patient characteristics are presented in Table 1. Four hundred and eighty-six patients underwent primary hip arthroplasty and 154 patients had a revision of a total hip arthroplasty. In addition, 18 patients underwent removal of an infected hip prosthesis and three had an open reduction and internal fixation of a femur fracture. Four patients underwent a hip hemiarthroplasty and five underwent a Girdlestone procedure. Most lumbar plexus catheters (89%) were removed on postoperative day 2. Two catheters were removed on postoperative day 0 (day of surgery) and 31 catheters were removed on postoperative day 1 at the request of the patient or because of catheter dislodgement (4.6%). In addition, 33 catheters were removed on day 3 and five catheters removed on postoperative day 4 for better pain control.
The median (range) dose of warfarin was 7.5 (0–10) mg on the day of surgery, 1 (0–12.5) mg on postoperative day 1, and 3 (0–10) mg on the day when the lumbar plexus catheter was removed. The distribution of the warfarin doses on the day of surgery (POD0), on postoperative day 1 (POD1), and on the day of the lumbar plexus removal (LPDC) are presented in Table 2. INR and PT increased significantly between the values obtained before surgery and postoperative day 1 (P<0.0001 for each). In addition, INR (P<0.0001) and PT (P<0.006) increased significantly between postoperative day 1 and the day of the lumbar plexus catheter removal. The distribution of each INR and PT value obtained before surgery, on postoperative day 1 and on the day of the catheter removal, is presented in Figure 1. The distribution of INR of patients receiving warfarin for thromboprophylaxis after a total hip replacement at the time of the lumbar plexus catheter removal is presented according to the thromboprophylaxis guidelines:1 8 0.9–1.4 (normal), 1.5–1.9 (sub-therapeutic), 2.0–3.0 (therapeutic), and 3.1–3.9 (over the therapeutic range) in Figure 2. As indicated in this figure, 36% of the lumbar plexus catheters were removed with an INR above normal (1.5), including 24% with an INR between 1.5 and 1.9 and 12% with an INR above 2.0.
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P<0.05).
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The only reported bleeding complication was that of bleeding at the catheter site after removal, where the INR was 3.0 at the time of removal. This was managed with direct pressure on the site and resolved without any haematoma formation or neurological compromise. The patient received vitamin K on the following day when the INR was 4.0, after which was continued on warfarin upon being discharged from the hospital.
In this series, we recorded one femoral nerve injury that resolved within 7 months. Finally, we also recorded six DVTs of which three of the patients were clinically symptomatic for PEs.
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Discussion |
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This study provides original data concerning the INR at the time of the removal of the lumbar plexus catheter after total hip replacement or hip fracture fixation. Our data indicate that at the time of the removal of the lumbar plexus catheter, more than one-third of the patients had an INR >1.4 which represents the highest recommended limit for performing a regional block according to the most recent consensus.1 2 They also demonstrate that 12% of patients had an INR of 2.0 and above when the lumbar plexus catheter was removed and that in this group of patients no major bleeding was observed resulting from the removal of the perineural catheter. This constitutes a preliminary finding that suggests the removal of a deep perineural catheter may be safely performed with an INR >1.4 in patients receiving warfarin for the thromboprophylaxis.
In the absence of data regarding the relative risk of bleeding complications at the time of the removal of deep perineural catheter in patients receiving thromboprophylaxis, several authors have recommended the same guidelines for the removal of lumbar plexus catheters than those proposed for epidurals. The data reported by Buckenmaier and colleagues3 and Chelly and Schilling4 seem to support the previously proposed concept that it is safe to remove a perineural catheter in patients benefiting from thromboprophylaxis with a variety of anticoagulants and receiving a variety of continuous nerve block techniques.11
For hip arthroplasty and hip fracture, current guidance on the use of an adjusted-dose vitamin K antagonist recommends maintaining the INR at 2.5 (range 2.0–3.0).8 Our data indicate that only 12% achieved the recommended therapeutic end-point 2 days after surgery at the time of the removal of the lumbar plexus catheter. This calls into question the effectiveness of warfarin. Thus, it is well established that an increased coagulability is observed immediately after joint replacement.12 Our data suggest that little protection was provided in most patients with the present warfarin dosing protocol.
Postoperative pain after primary total hip arthroplasty is considered to be mild to moderate at rest, but the required mobilization of the joint is usually associated with an increased level of pain and an increased need for opioids. To reduce the use of i.v. opioids, which are associated with significant side-effects, several regional techniques have been proposed for postoperative pain management after hip replacement including the use of epidurals, either single femoral or lumbar plexus blocks, and even continuous femoral nerve blocks. Epidural analgesia has been shown to be an effective alternative to PCA opioid,13 but the increased risks of epidural haematoma in patients receiving anticoagulation have limited its use beyond the recovery period. Single femoral or lumbar plexus blocks have been used, but have shown to provide short-lasting postoperative analgesia.14 The use of continuous femoral block performed either before or after surgery has also been advocated.13 Because the femoral catheter may lay in the surgical field, preoperative placement of a femoral catheter may not always be possible. This is the case in our practice. Recently, the comparison of continuous femoral and continuous lumbar plexus blocks demonstrated that the use of a continuous lumbar plexus technique provided better analgesia and less motor block than a continuous femoral block.15 However, the performance of a lumbar plexus block requires expertise as it may lead to serious complications.16
Although our data were similar to those reported recently by other authors17 18 using similar detection techniques, the frequency of clinically symptomatic DVTs and PEs was very low in this series. On the basis of a radiological approach and in the absence of treatment, the frequency of DVTs has been estimated around 45% in patients undergoing hip arthroplasty.19 There is no doubt that our data and those of others using a similar approach17 18 underestimate the true frequency of these complications and that the use of venous thrombogram, which is considered the gold standard, is a much more accurate technique in detecting DVTs that are not clinically symptomatic. However, ultrasound and clinical symptoms represent the approaches most commonly used to establish DVT.
In this study, a number of lumbar plexus catheters were removed with an INR 1.5 without any serious adverse outcomes in patients receiving warfarin after operation. However, additional data are required to confirm the safety of such an approach.
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Research sponsored by the Department of Anesthesiology, University of Pittsburgh Medical Center, Pittsburgh, PA, USA.
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