Efficacy of Mechanical Prophylaxis for Venous Thromboembolism in Patients With Brain Tumors

Kurtis I. Auguste, M.D.; Alfredo Quiñones-Hinojosa, M.D.; Mitchel S. Berger, M.D.


Neurosurg Focus. 2004;17(4) 

In This Article

Pneumatic Compression Devices

External pneumatic compression devices have been shown to prevent the formation of DVTs in neurosurgical patients.[47,50,51] Modern devices evacuate blood from lower-extremity vessels in an automated fashion. In brief, a microprocessor directs pressurized air (for example, at 45 mm Hg) into segmental diaphragms secured around the leg for a fixed period of time (for example, for 11 seconds).[30] The compression is delivered in a sequential manner up the leg, producing a wavelike milking effect to evacuate leg veins. Sequential devices have been proven to be more effective than single-chamber, evenly distributed pressure in preventing DVTs.[37] The compression is set to cycle regularly (for example, every 60 seconds). Devices are available for feet, calves, and/or thighs. Published contraindications for the use of these devices are listed in Table 1 .

Pneumatic compression may exert its protective effect against thrombus formation in part by limiting venous stasis. Calnan, et al.,[11] were one of the first groups to illustrate that intermittent, rhythmic compression of the lower extremity mimics the normal pumping of calf muscles. Soon after, Sabri, et al.,[42] demonstrated a 400% increase in femoral vein pulsatility and a 250% increase in peak femoral venous blood flow when the devices were applied to the lower limbs of greyhound dogs. Comparable results were found in the lower extremities of humans who received pneumatic compression.[41] In more modern studies investigators have shown increased blood flow velocities in the popliteal and common femoral veins by applying intermittent pneumatic compression to the foot alone.[31] Mittel man, et al.,[36] compared the use of calf and thigh compression with calf compression alone and found an enhanced effect of blood clearance with sequential compressions of the calf and thigh. Similarly, Delis, et al.,[16] found greater outflow during foot plus calf compression when comparing it with foot compression alone. Current prophylactic devices most frequently compress at least two regions of the lower extremity, although more limited devices have retained some popularity.

Mechanical compression devices appear to exert part of their prophylactic effect through enhanced fibrinolysis.[14,25,49] Early studies in which euglobulin clotting times were analyzed as a marker for systemic fibrinolysis activity in postoperative patients demonstrated that calf compression augments clot breakdown.[3,33,43] Weitz, et al.,[55] showed that intermittent pneumatic calf compression, by preserving the normal thrombin/plasmin ratio in blood samples obtained in patients who receive this therapy when compared with those not receiving pneumatic compression, averts the hypercoagulable state noted by Owen, et al.[39] Intermittent pneumatic compression has been shown to increase the amount of tPA release and to de crease levels of plasminogen activator inhibitor.[25] This benefit may be short-lived, however; diminished fibrinolytic activity is seen from several minutes[25] to 18 hours[33] after discontinuation of pneumatic compression.

Various permutations of both upper- and lower-extremity compression have been tested to increase blood clearance and ultimately prevent VTEs. Nearly 30 years ago, Knight and Dawson[33] conducted a study in which they applied intermittent compression to the upper extremities of patients who had undergone surgery, and noted a reduced incidence of DVTs in the legs and increased serum fibrinolytic activity. Tarnay, et al.,[49] also showed increased fibrinolysis in patients receiving compression in the arms, although this difference was not statistically significant. Another interesting finding of this study was the increased fibrinolysis detected in serum samples obtained in the patient's arm after administration of pneumatic compression to the legs. This effect appeared to be proportional to the volume of tissue compressed; increased fibrinolysis was detected in patients who wore long compression boots when compared with those given shorter boots. The results of these studies indicate that the fibrinolytic activity promoted by mechanical prophylaxis has both local and systemic effects in protecting against clot formation.


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