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PREVENT trial

PREVENT trial to assess thromboprophylaxis with IPC

A new multi-centre, randomised controlled trial, which will recruit 2,000 critically ill patients from over 20 hospitals in three countries, will assess whether the adjunct use of intermittent pneumatic compression (IPC) with pharmacologic prophylaxis compared to pharmacologic prophylaxis alone in critically ill patients reduces the risk of venous thromboembolism (VTE). The primary outcomes of the Pneumatic compREssion for preventing VENous Thromboembolism (PREVENT trial) is the incidence of proximal lower extremity deep vein thrombosis (DVT) within 28 days after randomisation.

(Credit: Blausen.com staff. Blausen gallery 2014)

A new multi-centre, randomised controlled trial, which will recruit 2,000 critically ill patients from over 20 hospitals in three countries, will assess whether the adjunct use of intermittent pneumatic compression (IPC) with pharmacologic prophylaxis compared to pharmacologic prophylaxis alone in critically ill patients reduces the risk of venous thromboembolism (VTE). The primary outcomes of the Pneumatic compREssion for preventing VENous Thromboembolism (PREVENT trial) is the incidence of proximal lower extremity deep vein thrombosis (DVT) within 28 days after randomisation. Radiologists interpreting the scans are blinded to intervention allocation, whereas the patients and caregivers are unblinded. The trial has 80% power to detect a 3% absolute risk reduction in proximal DVT from 7 to 4%.

A paper, ‘Thromboprophylaxis using combined intermittent pneumatic compression and pharmacologic prophylaxis versus pharmacologic prophylaxis alone in critically ill patients: study protocol for a randomized controlled trial’, describing the trial design and outline has been published in the journal Trials. The researchers expect to complete recruitment by 2018.

The study authors note that the evidence regarding the effectiveness of mechanical prophylaxis including an IPC and graduated compression stockings (GCS) for thromboprophylaxis is less clear. The thromboprophylactic effect of IPC is thought to be related to enhancing venous blood flow in the lower extremities, increase in endogenous fibrinolysis, stimulation of vascular endothelial cells and a reduction in venous caliber. It is thought that IPC may have several hemodynamic effects; as it has been shown to augment venous return, increase central venous pressure and pulmonary arterial pressure and increase cardiac output in healthy volunteers.

The lack of clear evidence for IPC and GCS has been reflected in the wide variation in the use of these devices in surveys from Canada, France, Australia and Germany, and more importantly, in the current practice guidelines. The American College of Physicians (ACP) guidelines for non-surgical patients recommend against the use of GCS, and suggest IPC as an alternative to pharmacologic thromboprophylaxis if the patient has a contraindication; but make no recommendation about its adjunct use to pharmacologic thromboprophylaxis. In contrast, The American College of Chest Physicians’ (ACCP) 2012 guidelines recommend the use of GCS or IPC, although preference is given to IPC as an alternative but not as an adjunct to pharmacologic thromboprophylaxis in non-surgical critically ill patients.

The secondary objective of the PREVENT trial are:

  • To study the effect of adjunct use of IPC on the incidence of pulmonary embolism and of distal lower extremity DVT
  • To study the effect of the adjunct use of IPC on intensive care unit (ICU), hospital and 90-day mortality and hospital length of stay (LOS)
  • To study the effect of adjunct use of IPC on hemodynamic status in terms of the need for vasopressor therapy
  • To study the effect of adjunct use of IPC on patients with heart failure in terms of ventilator-free days
  • To study the effect of adjunct use of IPC on VTE in the following subgroups: trauma, patients with central venous catheters in the femoral veins, stroke, postoperative patients, heart failure and shock
  • To examine whether there are differences in the effect of IPC based on whether UFH or LMWH is used
  • To examine whether there are differences in the thromboprophylactic effect between sequential and non-sequential IPCs
  • To examine whether there are differences in below-knee and above-knee sleeves
  • To examine whether IPC applied to the lower extremities reduces non-lower extremity thrombosis
  • To examine if there is dose-effect relationship of the IPC duration and incident DVT risk
  • To examine whether IPC increases the risk of skin ulcers or lower extremity ischemia and affects mobilization practice

All patients admitted to the ICU will be screened for eligibility within the first 48h of ICU admission.

The intervention group will receive IPC in addition to pharmacologic prophylaxis ordered by the treating team; the control group will receive pharmacologic prophylaxis only. All IPC devices intended for DVT prophylaxis can be used in the study. Sequential devices (with multi-chamber cuffs) are preferred, but non-sequential (with single-chamber cuffs) are acceptable. The type of device will be documented.

The use of IPC will follow the manufacturer’s instructions and local policies. IPC will be applied to both legs and preferably with thigh-length sleeves, but knee-length sleeves are acceptable. Foot pumps may be used in addition to the thigh- or knee-length sleeves. The ability to use IPC on both legs is one of the inclusion criteria. However, if during the study period the IPC could not be used on one leg, it should be continued on the other side and the use of a foot pump on the contraindicated leg considered if available. The researchers aim to apply IPC continuously, both day and night for at least 18h per day. The IPC may be removed during washing, physiotherapy, or screening compression duplex ultrasound. Nursing staff will record the application of IPC on the patient chart or on a daily data collection form designed to track adherence.

The study interventions will continue for the duration of the ICU stay or up to 28 days after randomisation, after which the use of IPC will be at the discretion of treating team.

The ICU team will have full, independent control of patient management and as such, management other than IPC will not be influenced by the allocated intervention. The trial patients may have other risk factors that may modify the risk for development of DVT. Research coordinators will record all such risk factors. These may include drugs such as antiplatelet agents (aspirin, ticlopidine, clopidogrel) and anticoagulants that are started after randomization (warfarin, therapeutic-dose LMWH, therapeutic heparin administered intravenously, other anticoagulants). The use of these medications will be at the discretion of the clinical team. The use of GCS will not be permitted; if used the reason will be documented.

“To our knowledge, this is the first RCT that compares adjunct IPC and pharmacologic prophylaxis versus pharmacologic prophylaxis alone in critically ill patients...The results of this study will contribute to a better understanding of the effectiveness of IPC in critically ill adults,” the authors conclude. “In addition, the PREVENT trial will likely contribute to future clinical practice guidelines and patient safety initiatives by providing evidence that will inform practice regarding the best thromboprophylaxis for critically ill adult patients.”

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