Heparin dosage is adjusted to maintain activated partial thromboplastin time (APTT) levels at a therapeutic level 1.5 to 2.5 times the control value. Initial APTT should be measured after 6 hours of heparin administration and the dose adjusted as necessary. Patients having sub-therapeutic APTT levels in the first 24 hours have a 15-fold increased risk of recurrent VTE when compared to patients who are adequately anticoagulated. Patients should be managed aggressively using intravenous heparin to achieve prompt anticoagulation. A weight-based nomogram is helpful in achieving a therapeutic APTT level (Table 22.12) (147). Oral anticoagulant (warfarin) administration may be started on the first day of heparin infusion. The international normalized ration (INR) should be monitored daily until a therapeutic level is achieved (2.0 to 3.0 times normal value). The change in the INR resulting from warfarin administration often precedes the anticoagulant effect by approximately 2 days, during which time low protein C levels are associated with a transient hypercoagulable state. Therefore, heparin should be administered until the INR was maintained in a therapeutic range for at least 2 days, confirming proper warfarin dose. Intravenous heparin may be discontinued in 5 days if an adequate IRN level is established.
Low-Molecular-Weight Heparin Two LMWH preparations (enoxaparin and dalteparin) were effective in the treatment of venous thromboembolism and have a cost-effective advantage over intravenous heparin in that they may be administered in the outpatient setting.
The dosages used in treatment of thromboembolism are unique and weight adjusted according to each LMWH preparation. Because LMWH has a minimal effect on APPT, serial laboratory monitoring of these levels is not necessary. Similarly, monitoring of anti-Xa activity (except in difficult cases or those with renal impairment) is not of significant benefit in a dose adjustment of LMWH. The increased bioavailability associated with LMWH allows for twice-a-day dosing, potentially making outpatient management an option for a subset of patients. A meta-analysis involving more than 4,000 patients from 22 trials suggests that LMWH is more effective, safer, and less costly when compared with unfractionated heparin in preventing recurrent thromboembolism (148).
Many of the signs and symptoms of pulmonary embolism are associated with other, more commonly occurring pulmonary complications following surgery. The classic findings of pleuritic chest pain, hemoptysis, shortness of breath, tachycardia, and tachypnea should alert the physician to the possibility of a pulmonary embolism. Many times the signs are subtle and may be demonstrated only by a persistent tachycardia or a slight elevation in the respiratory rate. Patients suspected of pulmonary embolism should be evaluated initially by chest x-ray, electrocardiography, and arterial blood gas assessment. Any evidence of abnormality should be further evaluated by a spiral CT scan of the chest or a ventilation-perfusion lung scan. A high percentage of lung scans may be interpreted as “indeterminate.” In this setting, careful clinical evaluation and judgment are required to decide whether pulmonary arteriography should be performed to document or exclude the presence of a pulmonary embolism.
The treatment of pulmonary embolism is as follows: 1.
Immediate anticoagulant therapy, identical to that outlined for the treatment of DVT, should be initiated.
2.
Respiratory support, including oxygen and bronchodilators and an intensive care setting, if necessary.
3.
Although massive pulmonary emboli are usually quickly fatal, rarely pulmonary embolectomy is successful.
4.
Pulmonary artery catheterization with the administration of thrombolytic agents bears further evaluation and may be important in patients with massive pulmonary embolism.
5.