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Deep Venous Thrombosis Prophylaxis In Orthopedic Surgery

Thrombosis is a naturally occurring physiologic process. Under normal circumstances, a physiologic balance is present between factors that promote and retard coagulation. A disturbance in this equilibrium may result in the coagulation process occurring at an inopportune time or location or in an excessive manor. Alternatively, failure of the normal

coagulation mechanisms may lead to hemorrhage

Thrombosis is a naturally occurring physiologic process. Under normal circumstances, a physiologic balance is present between factors that promote and retard coagulation. A disturbance in this equilibrium may result in the coagulation process occurring at an inopportune time or location or in an excessive manor. Alternatively, failure of the normal coagulation mechanisms may lead to hemorrhage

Venous stasis

More time for clotting

Small clots not washed away

Increased blood viscosity

Vessel wall damage

Accidental trauma

Surgical trauma

Blood coagulability increase

Increase in tissue factor

Presence of activated factors

Decrease in coagulation inhibitors (antithrombin III [ATIII])

Venous thrombi generally form in regions of stasis composed of red blood cells embedded in a mesh of fibrin strands and platelets,

The nature of orthopedic illnesses and diseases, trauma, and surgical repair or replacement of hip and knee joints

predisposes patients to the occurrence of venous thromboembolic (VTE) disease. These complications are predictable and are the result of alterations of the natural equilibrium mechanisms in various disease states

The risk factor assessment guidelines include the following list of factors that increase the risk of development of DVT:

Aged older than 40 years

Prolonged immobility of paralysis

Prior DVT

Cancer

Major surgery (abdomen, pelvis, lower extremity)

Obesity

Varicose veins

Heart failure

Myocardial infarction

Stroke

Pelvis, hip, or leg fracture

High-dose estrogen (questionable)

Indwelling central venous catheter

Nephrotic syndrome

Inflammatory bowel disease

Pregnancy

Congential or acquired thrombophilic disorder or hypercoagulable state

These factors include those that diminish venous flow or return, increase viscosity, or alter mobility. Age is one of the most easily definable factors. The risk of DVT increases in exponential fashion with increasing age (

Orthopedic patients were divided into 4 risk groups, ranging from low to very high.

Low-risk patients were younger than 40 years, with surgical procedures lasting less than 30 minutes, and small fractures.

 Moderate-risk patients were aged 40-60 years. Other factors included surgery that required a tourniquet (eg, arthroscopy), lower extremity

fractures, cast immobilization, or spine surgery.

High-risk patients were older than 60 years, with open lower leg fractures, 4 days or more of immobilization, or additional risk factors.

The highest risk group was patients with hip or knee replacement surgery, hip fracture, open lower leg fracture, multiple trauma, or spinal cord injury (SCI).

Mechanical methods of DVT prophylaxis have included the use of elastic compression stockings, early ambulation, continuous passive motion, and IPC devices.

Pharmacologic methods:

Many pharmacologic agents are currently available to prevent thrombosis. Agents that retard or inhibit the process belong under the general heading of anticoagulants. Agents that prevent the growth or formation of thrombi are properly termed antithrombotics and include anticoagulants and antiplatelet drugs, whereas thrombolytic drugs lyse existing thrombi.

 RPlatelet active drugs

Platelet-active drugs such as aspirin or cyclooxygenase-1 (COX-1) inhibitors have been used to prevent thrombosis. Aspirin is effective as a platelet inhibitor at very low doses (50-100 mg/d). This dose is significantly less than that necessary to produce an anti-inflammatory effect. A meta-analysis of the effect of aspirin following THR completed in 1994 had equivocal results.

 OPoral anticoagulant drugs, which act as antagonists to vitamin K. The mechanism of action is to interfere with the interaction between vitamin K and coagulation factors II, VII, IX, and X. Vitamin K acts as a cofactor at these levels

HFor DVT prophylaxis, the optimal INR level is between 2 and 3. When used for DVT prophylaxis following THR, warfarin results in a reduction of total DVT by 60% and proximal DVT by 70%. Disadvantages of warfarin use include its long onset of action, the necessity to monitor INR values frequently to obtain stable dosage

Heparins

Standard unfractionated heparin (UHF) also is recognized as an acceptable anticoagulant modality

 Postoperative DVT prophylaxis with UHF usually is achieved by administering a bolus of 5000 units every 8 hours. This LDH regimen results in a 60-70% reduction of DVT and PE in low-risk or moderate-risk patients. However, this method is not as effective in patients who are at high risk for development of DVT or PE. In these patients, adjusted-dose heparin with aPTT monitoring is preferred to maintain

the desired anticoagulant level. Studies have demonstrated a high hemorrhagic complication rate of 8-15% when this method is used for postoperative DVT prophylaxis

Disadvantages of UFH therapy include variable pharmacokinetics, the requirement for aPTT monitoring for adjusted-dose regimens, short half-life and low bioavailability, and lack of oral dosage form (although an oral form is currently in clinical trials). In addition, a small percentage of patients (2-4%) are susceptible to the development of heparin-induced thrombocytopenia (HIT),

Low molecular weight heparins

LMWHs are manufactured when standard heparin is treated by a variety of enzymatic or chemical methods to select those lower molecular weight moieties that contain the active ATIII binding site

The pharmacologic effect of this transformation is to make the LMWH more bioavailable (approximately 90%, compared with 29% for UFH) and to lengthen its half-life to 4 hours from 1 hour for UFH. LMWH also increases the activity ratio of anti-Xa to anti-IIa, resulting in increased antithrombotic activity.

Compared to placebo, LMWHs produced a 70-80% risk reduction for DVT in numerous studies without an increase in major bleeding in high-risk orthopedic patients

Low-risk category - minor surgery            

Moderate-risk category -  major surgery, and patients older than 40 years with no additional risk factors

High-risk category - patients older than 40 years and major surgery, myocardial infarction, and additional risk factors

Very high-risk category -  major surgery in patients older than 40 years with any of the following:

History of VTE event

Hip fracture or THR or TKR surgery

Stroke or spinal cord injury

Visceral malignancy

Additional risk factors

Suggested regimens for each risk category are as follows:

Low-risk category - Early ambulation with or without ES

Moderate-risk category - LDH 5000 units every 8 hours or IPC plus ES

High-risk category - LDH 5000 units every 8 hours and 2 hours preoperatively, or IPC, or LMWH

Very high-risk category - LMWH or oral warfarin with INR 2-3, or IPC plus LMWH,

Table: Sixth American College of Chest Physicians (2001) Prevention Strategies

The ACCP provides recommendations for specific treatment of patients following THRs as follows:

Postoperative LMWH  4-6 hours after surgery at one half dose initially or preoperatively 12 hours before surgery

Warfarin preoperatively or immediately postoperatively with INR range of 2-3 (target 2.5)

Adjusted-dose heparin

Adjuvant prescription with ES or IPC

LDH, ASA, Dextran, IPC alone not recommended

The following are ACCP recommendations for specific treatment of patients following TKRs:

LWMH 12-24 hours postoperatively or adjusted-dose warfarin preoperatively or immediately postoperatively with INR range of 2-3 (target 2.5)

Optional use of IPC

LDH not recommended

ACCP recommendations for patients with hip fractures are as follows:

LWMH 12-24 hours postoperatively or adjusted-dose warfarin immediately postoperative with target INR 2.5 (range 2-3) if bleeding is controlled

LDH may be alternative (limited data)

ASA alone not recommended

Complications of anticoagulant treatment include major and minor bleeding, hematoma formation, compartment syndrome, and HIT. Major bleeding is defined as one that alters the clinical course of the patient's treatment or changes the clinical outcome. Major bleeding may prolong the hospital stay, necessitate a return to the operating room, or result in unexpected transfusion. DVT prophylaxis should be delayed or terminated in these cases. Rehabilitation or mobilization also may be delayed.

October 26, 2002