This symposium on managing the risk of venous thromboembolism provided useful information for those interested in an optimized risk assessment in orthopedic patients and new aspects of pharmacological prophylaxis.
Guy D. Paiement, MD, gave a broad overview of the rates of deep vein thrombosis (DVT) and fatal pulmonary embolism in unprotected orthopedic patient populations. It was emphasized that lower extremity orthopedic procedures carry a risk of venous thromboembolism which exceeds the risk associated with surgery itself. There are certain hazard factors which seem to be specific to these orthopedic procedures:
* Twisting of the common femoral vein due to dislocation of the hip during hip arthroplastic surgery, thereby distending and breaking endothelial intercellular bridges and exposing collagen and other procoagulant substances.
* Venous endothelial damage caused by retractors and surgical manipulations.
* Increased levels of thromboplastic material due to reaming and preparation of the bone.
* Possible venous endothelial ed during the polymerization of bone damage secondary to the heat generatcement.
The risk exposure associated with lower extremity surgery may be increased by additional predisposing risk factors such as age, thrombophilic states, and immobilization. Thus, it can be concluded that the modality and duration of prophylaxis should be determined by individual risk assessment and that an appropriate management plan should be implemented for each patient to address the problem.
Numerous clinical trials have provided evidence that the risk of DVT is significantly reduced by pharmacological prophylaxis with low-molecularweight heparins (LMWHs). A.G.G. Turpie, MD, elucidated the mode of action of this range of compounds and highlighted the improved pharmacological profile of LMWHs compared with unfractionated heparin. New data on the pharmacology of LMWHs provide evidence of an improved benefit:risk ratio, thereby facilitating their long-term administration. In particular, their mòre predictable dose response and a dose-dependent mechanism of clearance, along with a longer plasma half-life has made them attractive for both prophylactic and therapeutic use. Furthermore, safety aspects such as lower potential for heparininduced thrombocytopenia or osteoporosis will play a significant role in the preferred use of LMWHs. In 1991, the European Consensus Statement had a favorable impact on clinical acceptance of LMWHs by clinicians and physicians, and helped, in particular, to establish new standards required by several health authorities to use LMWH as a reference for future prophylaxis trials in high-risk patients. Finally, in 1995, the American College of Chest Physicians included LMWH as a prophylaxis of choice for all major orthopedic indications, and these compounds were the only pharmacological treatment recommended for total knee replacement.
In an overview of the management of the risk of DVT in the perioperative period with enoxaparin, Michael R. Lassen, MD, concluded that LMWH seems to be superior to unfractionated heparin or dextran in high-risk patients undergoing orthopedic surgery. The risk of venous thromboembolism is, however, not confined to the period of hospitalization, but it may persist beyond discharge. Therefore, the question arises when to discontinue the prophylaxis after major orthopedic procedures.
The articles of André Planes, MD, and Paul E. Nilsson, MD, address the problem of post-discharge venous thromboembolism after hip replacement and the possible need for prolonged prophylaxis. These problems were considered key questions in the European Consensus Statement on venous thromboembolism, and with the continued pressure for earlier discharge due to limited healthcare system resources, this issue has attracted the interest of all practicing surgeons. If the risk of DVT after hospital discharge was found to be high, another logical question would be whether it can be reduced. The aim of the study by Planes et al was to assess the incidence of late-occurring venous thromboembolic complications after hospital discharge in patients who had undergone total hip replacement and were free of DVT at the time of discharge. By virtue of the comprehensive study design, which required two bilateral Phlebographie investigations in all patients, the question of new onset of DVT during the 21 day timespan after hospital discharge could be answered. In fact, there was a 20% incidence of DVT that developed after discharge, and prophylactic treatment with enoxaparin significantly reduced the risk without causing any significant adverse reactions. The study reported by Dr Nilsson was performed without diagnostic intervention during the study period, ie, under the conditions of the typical clinical setting where asymptomatic patients do not undergo objective screening procedures at the time of discharge. Despite prophylaxis with LMWH prior to discharge in all patients, there was a 38% incidence of DVT in patients who received placebo instead of enoxaparin for 1 month post-surgery. This trial also provided evidence that prolonged prophylaxis with enoxaparin significantly reduced the risk of thromboembolism and that the incidence of proximal DVT could also be significantly lowered by enoxaparin.
The limited resources of healthcare systems requiring earlier patient discharge has led to the problem of an inverse relationship between the duration of hospitalization and the probability of thromboembolic complications post-discharge. The aim of this symposium was to address this problem by providing data on how to assess the individual patient's risk and how to manage the risk of late DVT. Based on the favorable results of two different studies that evaluated the post-discharge prophylactic management of the orthopedic patient with enoxaparin, it is concluded that the risk of late DVT can be significantly reduced by continuous prophylaxis beyond discharge.