Doppler Ultrasound B-mode duplex Doppler imaging is the most common technique for the diagnosis of symptomatic venous thrombosis, especially when it arises in the proximal lower extremity. With duplex Doppler imaging, the femoral vein can be visualized and clots may be seen directly (144). Compression of the vein with the ultrasound probe tip allows assessment of venous collapsibility; the presence of a thrombus diminishes vein wall collapsibility. Doppler imaging is less accurate when evaluating the calf and the pelvic veins.
Venography Although venography is the standard technique for diagnosis of DVT, other diagnostic studies are accurate when performed by a skilled technologist and, in nearly all patients, may replace the need for contrast venography. Venography is moderately uncomfortable, requires the injection of a contrast material that may cause allergic reaction or renal injury, and may result in phlebitis in approximately 5% of patients (145). If the results of noninvasive imaging are normal or inconclusive and the clinician remains concerned given clinical symptoms, venography should be performed to obtain a definitive answer.
Magnetic Resonance Venography In addition to having a sensitivity and specificity comparable to venography, magnetic resonance venography (MRV) may detect thrombi in pelvic veins that are not imaged by venography (146). The primary drawback to MRV is the time involved in examining the lower extremity and pelvis and the expense of this technology.
The treatment of postoperative DVT requires the immediate institution of anticoagulant therapy. Treatment may be with either unfractionated heparin or LMWH, followed by 6 months of oral anticoagulant therapy with warfarin (Coumadin).
Unfractionated Heparin After venous thromboembolism is diagnosed, unfractionated heparin should be initiated to prevent proximal propagation of the thrombus and allow physiological thrombolytic pathways to dissolve the clot. An initial bolus of 80 U per kilogram is given intravenously, followed by a continuous infusion of 1,000 to 2,000 U per hour (18 U/kg/hour).
Table 22.12 Heparin Administration for Treatment of Deep Venous Thrombosis or Pulmonary Embolism: Weight-Based Nomogram
Time of Administration Dose
Initial dose 80-U/kg bolus, then 18 U/kg/h
The APTT should be measured every 6 h and the heparin dose adjusted as follows:
APTT <35 seconds (<1.2 × control) 80-U/kg bolus, then 4 U/kg/h
APTT 35–45 seconds (1.2–1.5 × control) 40-U/kg bolus, then 2 U/kg/h
APTT 46–70 seconds (1.5–2.3 × control) No change
APTT 71–90 seconds (2.3–3 × control) Decrease infusion rate by 2 U/kg/h
APTT >90 seconds (>3 × control) Hold infusion for 1 h, then decrease infusion rate by 3 U/kg/h
APTT, activated partial thromboplastin time. Reprinted from Raschke RA, Reilly BM, Guidry JR, et al. The weight-based heparin dosing nomogram compared with a “standard care” nomogram. Ann Intern Med 1993;119:874–881, with permission.