Deep venous thrombosis (DVT) is a venous return disorder caused by abnormal coagulation of blood in the deep venous system and is a common complication after surgery. The main hazard of DVT is acute stage thrombus shedding, which can cause a pulmonary embolism (PE) and acute respiratory distress syndrome when the blood flow blocks the pulmonary artery
An average incidence of DVT of 24 percent was found among 474 untreated control neurosurgical patients 1).
However, based on the current literature, the incidence of DVT varies in patients with different diseases. For example, the incidence of DVT is 1.5–18% and 32% in patients with a subarachnoid hemorrhage and in patients with a brain tumor, respectively 2) 3).
In addition, the incidence of DVT after craniotomy has been reported to be as high as 50%, and using a threshold of 2 mg/L, D-dimer levels indicate venous thromboembolism with a high degree of sensitivity and specificity in patients who have undergone craniotomy 4).
In a study lower extremity DVT was a common complication following craniotomy in the enrolled Chinese neurosurgical patients. Multiple factors were identified as predictive of DVT in neurosurgical patients, including the presence of a tumor, an age greater than 50 years, hypertension, and immobility 5).
The rate of lower extremity DVT after neurosurgery was 31.1% in the series of Guo et al 9).
Despite the uniform application of mechanical DVT prophylaxis and the use of chemoprophylaxis in a majority of patients, Dermody et al found a 23% incidence of DVT in hospitalized, nonambulatory, neurosurgical patients. No patients with isolated calf DVT had an embolic complication but 13.3% progressed proximally in short-term follow-up. While chemical prophylaxis significantly reduced DVT risk, no factor was sufficiently predictive to exclude patients from screening. These data substantiate the importance of full leg venous duplex ultrasound (VDUS) screening and maximizing DVT prophylaxis in this high risk population 10).
Currently, color flow duplex scanning performed by skilled operators provides the most practical and cost-effective method for assessing DVT of the proximal and distal lower extremity veins.
Unfortunately, most duplex ultrasound-based algorithms for the diagnosis of DVT, and some vascular laboratories, still do not include an initial ultrasound evaluation of the calf veins as part of their routine evaluation for DVT, even in symptomatic patients. This is largely the result of outdated perceptions of the inaccuracy of ultrasound evaluation of DVT isolated to the calf veins. Failure to perform a complete initial examination necessitates serial ultrasound examinations or alternative strategies to detect possible extension of venous thrombi initially isolated to the calf veins. Such strategies are inefficient, and unlikely to be cost effective, compared with the modern practice of a single stand-alone color flow duplex study of the proximal and distal lower extremity veins in patients with suspected DVT.
According to the Diagnosis and Treatment Guide of DVT created previously 11) 12) The diagnosis of DVT should be confirmed through auxiliary examinations, including Doppler ultrasound, plasma D-dimer, confidential interval venography, magnetic resonance imaging venography and angiography, etc.
The Doppler ultrasound diagnostic points of DVT are as follows: (1) The probe pressurized venous lumen is not completely closed; (2) the diameter of the embolization segment vein widens obviously, and the thrombosis echo within the lumen has varying degrees of intensity; (3) color Doppler ultrasound provides color flow imaging during embolization that indicates that the vein is thinned or that there is no blood flow; (4) pulse Doppler shows no blood spectrum in the thrombus segment, and the blood spectrum of the distal thrombus does not change with respiration; and (5) Valsalva test is abnormal.
Treatment is recommended for both proximal and symptomatic distal (isolated calf) DVT. If anticoagulation cannot be administered or is contraindicated for calf DVT, then the recommendations are for serial noninvasive studies over the next 10 to 14 days to assess for proximal progression of the thrombus 13).
Non-specific signs may include pain, swelling, redness, warmness, and engorged superficial veins. Pulmonary embolism, a potentially life-threatening complication, is caused by the detachment (embolization) of a clot that travels to the lungs.
Together, DVT and pulmonary embolism constitute a single disease process known as venous thromboembolism. Post-thrombotic syndrome, another complication, significantly contributes to the health-care cost of DVT. Prevention options for at-risk individuals include early and frequent walking, calf exercises, anticoagulants, aspirin, graduated compression stockings, and intermittent pneumatic compression.
In 1856, German pathologist Rudolf Virchow postulated the interplay of three processes resulting in venous thrombosis, now known as Virchow's triad: a decreased blood flow rate (venous stasis), increased tendency to clot (hypercoagulability), and changes to the blood vessel wall. DVT formation typically begins inside the valves of the calf veins, where the blood is relatively oxygen deprived, which activates certain biochemical pathways. Several medical conditions increase the risk for DVT, including cancer, trauma, and antiphospholipid syndrome. Other risk factors include older age, surgery, immobilization (as with bed rest, orthopedic casts, and sitting on long flights), combined oral contraceptives, pregnancy, the postnatal period, and genetic factors such as a non-O blood type. The frequency of occurrence (incidence) increases dramatically from childhood to old age; in adulthood, about 1 in 1000 adults develops DVT annually.