When pulmonary embolism is suspected, a chest x-ray, electrocardiography, and arterial blood gas assessment are warranted. Any abnormality justifies further evaluation by ventilation-perfusion lung scan or a spiral computed tomography scan of the chest. Unfortunately, a high percentage of lung scans are interpreted as “indeterminate.” In such cases, careful clinical evaluation and judgment are needed to determine whether pulmonary arteriography is necessary to document or exclude pulmonary embolism.
Immediate, aggressive therapy is crucial
The treatment of postoperative DVT requires immediate anticoagulant therapy using either unfractionated heparin or LMWH, followed by 6 months of oral anticoagulant therapy with warfarin.
Treatment strategy: Unfractionated heparin
Once VTE is diagnosed, start unfractionated heparin to prevent proximal propagation of the thrombus and allow physiologic thrombolytic pathways to dissolve the clot. After an initial IV bolus of 5,000 U, give the patient a continuous infusion of 30,000 U daily, and adjust the dose to maintain APTT levels at a therapeutic level that is 1.5 to 2.5 times the control value.
Subtherapeutic APTT levels in the first 24 hours mean a risk of recurrent thromboembolism 15 times greater than the risk in patients with appropriate levels. Therefore, aggressive management is warranted to achieve prompt anticoagulation.
Start an oral anticoagulant (warfarin) on the first day of heparin infusion, and monitor the international normalized ratio (INR) daily until a therapeutic level is achieved. The change in the INR after warfarin administration often precedes the anticoagulant effect by about 2 days, during which time low protein C levels are associated with a transient hypercoagulable state. Therefore, it is important to continue the heparin until the INR has been maintained in a therapeutic range for at least 2 days to confirm the proper warfarin dose. Intravenous heparin can be discontinued after 5 days if an adequate INR level has been established.
Alternative strategy: LMWH
A meta-analysis involving more than 1,000 patients from 19 trials suggests that LMWH is more effective, safer, and less costly than unfractionated heparin in preventing recurrent thromboembolism.19 The lower cost derives from the ability to use the drugs in an outpatient setting.
Dosages are unique and weight-adjusted according to each LMWH preparation. Because LMWH has a minimal effect on APTT, serial laboratory monitoring of APTT levels is unnecessary. Nor is monitoring of anti-Xa activity of significant benefit in the dose adjustment of LMWH.
Basic treatment of pulmonary embolism
In most cases, immediate anticoagulant therapy identical to that outlined for DVT is sufficient to prevent repeat thrombosis and embolism and to allow the patient’s endogenous thrombolytic mechanisms to lyse the pulmonary embolus.
Other interventions include:
- Respiratory support, including oxygen, bronchodilators, and intensive care.
- Although massive pulmonary emboli are usually quickly fatal, pulmonary embolectomy has been successful on rare occasions.
- Pulmonary artery catheterization and administration of thrombolytic agents may be important in patients with massive pulmonary embolism.
- Vena cava interruption may be necessary when anticoagulant therapy does not prevent rethrombosis and the formation of emboli from the lower extremities or pelvis. A vena cava umbrella or filter may be inserted percutaneously above the level of the thrombosis and caudad to the renal veins.
Take-home points
- Identify risk factors preoperatively
- VTE prophylaxis is warranted for most gynecologic surgery patients and can reduce the incidence of VTE by at least 60% with appropriate use! Plan prophylaxis in women at moderate, high, and highest risk, and remember that individuals at high and highest risk require more intense prophylaxis to realize a benefit.
- Maintain a high level of suspicion in women with signs and symptoms of DVT or pulmonary embolism in the first postoperative month. It is better to over-evaluate than to miss a potentially fatal complication.
- Treat women with VTE immediately with heparin or LMWH.