Alterations of Blood Clotting With the Use of Sequential Compression Devices on the Lower Limbs

This study aims to assess possible alteration in coagulation (blood clotting) following treatment with sequential compression devices (SCD) plus low-molecular weight heparin (LMWH) as opposed to LMWH alone.

The investigators will examine coagulation in the early postoperative period of patients undergoing major abdominal surgery during their stay in our Intensive Care Unit.

In addition to common laboratory tests, the investigators will examine coagulation using TEG®, a device which allows a semi-quantitative examination of all phases of coagulation.

Low molecular weight heparins (LMWH) are routinely used in perioperative prophylaxis of thromboembolic complications \[(chiefly deep vein thrombosis (DVT)\]. LMWHs have been proved to be safe and equipotent or superior when compared with unfractionated heparin.

Sequential compressing devices (SCD) are relatively novel pneumatic stockings with several air chambers. A computerized pump applies a gradient of pressure which decreases from the foot cranially. Pressure is also applied intermittently according to predetermined schedules. This devices are being employed for DVT prophylaxis in patients for whom anticoagulation therapy is contraindicated, or in those who have a low risk of DVT. They have also been employed to complement anticoagulant therapy in patients at high risk of DVT, such as those undergoing orthopedic surgery (Fordyce, 1992; Handoll, 2002; Warwick, 2002; Pitto, 2004).

The mechanism of action of SCD seems to be primarily mechanical, through a displacement of a column of blood through the venous system and towards the heart; they act as a surrogate of the muscular pump in immobilized patients (Killewich, 1995).

There is also some evidence that SCD activity may influence the coagulation/fibrinolysis system towards hypocoagulability (Dai, 2000; Kohro, 2003); Kohro and colleagues have also hypothesized that the shear forces generated by SCD may alter platelet adhesion by a direct effect on platelets and/or by increasing the release of factors from the venous endothelium (Kohro, 2005).

The investigators aim to assess the effects on coagulation when SCD are applied to patients at high risk of DVT in addition to standard LMWH therapy.The investigators chose to study a population in whom SCD may be useful in reducing the incidence of DVT, such as patients undergoing postoperative monitoring in the intensive care unit (ICU) after major abdominal surgery for cancer.

In addition to standard laboratory tests, the investigators will use thrombelastography (TEG®) to assess all phases of coagulation. A TEG parameter, maximum amplitude (MA), has been linked to an increase of thrombotic complications in a postoperative population (McCrath, 2005).

Eligibility Criteria:
Inclusion Criteria:

* Elective major abdominal surgery for neoplasm
* Planned admission to postsurgical ICU due to the patient's meeting one or more of the following:

  * ASA Physical Status Class 4
  * Surgery of modified Johns-Hopkins class ≥IV
  * ASA 3 with modified Johns-Hopkins class 3 surgery
  * Expected duration of surgery ≥8 h

Exclusion Criteria:

* History of coagulation abnormalities, either congenital or acquired
* Ongoing treatment with anticoagulants/antiplatelet agents other than LMWH or hormones
* Massive edema of the legs
* Severe peripheral arteriopathy or neuropathy
* Malformations or recent surgery/trauma to the lower extremities