Lower limb immobility and venous thromboembolism risk: Investigating preventive measures

Prolonged work-related seated immobility and lower limb immobilisation (LLI) are two situations in which the risk of venous thromboembolism (VTE) is poorly understood, and no evidence-based guidelines for the reduction of risk exist. The aim of this research was to investigate the role of prolonged work-related immobility and LLI as risk factors for VTE and to assess the haemodynamic effects and feasibility of two possible preventive measures; the Legflow device during prolonged work-related immobility and an intermittent pneumatic compression device (IPC) during LLI. Four studies of work-related immobility were conducted: a case-control study to assess the risk of prolonged seated immobility and VTE; a meta-analysis of two case-control studies to assess the risk of VTE in sedentary workers; a study of popliteal vein haemodynamics in ten adults using the Legflow device while seated and a feasibility study of the Legflow device in 96 sedentary office workers in their working environment. Four studies of LLI were completed: a meta-analysis of two case-control studies to assess the association between LLI and VTE risk; an audit of VTE rates in patients with Achilles tendon injury undergoing LLI prescribed prophylactic aspirin; a study of the effect of an IPC device beneath a fibreglass cast on popliteal vein haemodynamics in 24 adults and a feasibility study of the IPC device in patients undergoing LLI at the Fracture Clinic at Wellington Regional Hospital. There was no association between prolonged seated immobility and VTE (odds ratio (OR) 1.18, 95%CI 0.56 to 2.48, P=0.67). Each additional hour seated in a 24 hour period was associated with VTE (OR 1.08, 95%CI 1.01 to 1.6, P=0.02). There was an association between sedentary occupations and VTE (OR 1.79, 95%CI 1.22 to 2.63, P=0.003). The Legflow device increased popliteal vein peak systolic velocity (PVPSV) (difference between the Legflow-mobilised and immobile limb adjusted for baseline 60.0 cm/s, (95%CI 44.6 to 75.3 P<0.001). In the working environment 50% (95%CI 40 to 60%) of sedentary office workers were adherent (use ≥ four times per day) with the Legflow device. LLI was associated with VTE (OR 73.1, 95%CI 10.1 to 530, P<0.001). A total of 14/218 (6.4%, 95%CI 3.6% to 10.5%) Achilles tendon patients prescribed aspirin developed VTE, an incidence similar to the 6.3% identified in a previous patient group not routinely prescribed VTE prophylaxis. The haemodynamic effect of the IPC device was not impaired by its placement within a fibreglass leg cast (difference in PVPSV between IPC in-cast and IPC outside-cast -0.8 cm/s, 95%CI -6.5 to 4.9, P=0.78). Only 7/142 (5%, 95%CI 2.0 to 9.9%) of potentially eligible patients utilised the IPC device in the feasibility study. Prolonged work- and computer-related seated immobility and sedentary professions are associated with VTE. The Legflow increases venous blood flow in seated adults and is a feasible device for use in the office environment. The introduction of aspirin for VTE prophylaxis of VTE during LLI did not influence VTE rates. The haemodynamic effect of the IPC is not impaired in a fibreglass cast, but its use is not a feasible option in the clinical setting of LLI.