Definition of immobility in studies of thromboprophylaxis in hospitalized medical patients: a systematic review

Background: Venous thromboembolism (VTE) is a common, serious and preventable complication in hospitalized patients. Thromboprophylaxis in medical patients is safe, effective, and cost saving, but remains underutilized. Although immobility plays an important role in determining VTE risk in medical patients, no clear criteria exist to guide clinicians in assessing immobility when making decisions about thromboprophylaxis.

Objectives: A systematic review was conducted to determine how immobility is defined and operationalized in randomized controlled trials (RCTs) of thromboprophylaxis in medical inpatients.

Methods: PubMed database was searched until September 2008 for RCTs of thromboprophylaxis in medical patients. Articles retrieved were further hand-searched to identify additional RCTs. Definitions of "immobility" were assessed.

Results: Twenty-one RCTs were retrieved, 18 were retained and 17 of these defined, to varying degrees, "immobility." Studies used several definition criteria, including the patient's degree of activity (14 studies), time spent immobile or mobile (13 studies), distance walked (4 studies) and underlying reason for immobility (4 studies); 14 studies used a combination of criteria. Definitions were clearly operationalized in 15 studies. The concept of "immobility" was utilized in study introductions (4 studies), inclusion/exclusion criteria (16 studies), as a stratification variable before randomization (1 study), in ongoing patient assessment (1 study), in treatment decisions (5 studies), as part of the study intervention (2 studies), as standard of care (2 studies), and in the results, discussion or conclusions (12 studies).

Conclusions: There is a marked lack of consistency in how the concept of immobility is defined and utilized in RCTs of thromboprophylaxis in medical inpatients. This circumstance may contribute to the underutilization of thromboprophylaxis in clinical practice with medical inpatients.