Haematological Effects of Intermittent Pneumatic Compression for Deep Vein Thrombosis Prophylaxis.

Intermittent pneumatic compression (IPC) is a widely used and recommended method to prevent deep vein thrombosis. While the haemodynamic effects of IPC are well understood, the objective of this systematic review was to analyse the evidence for additional haematological changes. Forty-eight studies were identified where the haematological effects of IPC were measured. The many differences between the studies prevented meta-analysis, but there was a significant amount of evidence that global fibrinolytic activity was increased by IPC, and that levels of D-dimer and tissue factor pathway inhibitor in the blood also increased. There was less consistent evidence for changes in tissue plasminogen activator, plasminogen activator inhibitor and other fibrinolytic parameters. The evidence for changes in pro-coagulant factors and many measures of platelet activation was weak, but there was evidence for increases in prostacyclin. There is sufficient evidence to conclude that IPC does produce haematological changes, but not enough data to clarify the detail of those changes or to determine if it is mediated more by direct compression of the blood vessels, or by the flow changes.

Research quality in the study of mechanical methods of deep vein thrombosis prophylaxis.

There is a lack of good-quality recent clinical data to support the use of mechanical methods to prevent deep vein thrombosis. Recommendations and meta-analyses have to rely on old data from evaluations of devices that are no longer available, with diagnostic methods that are obsolete. The aim of this narrative review is to examine the reasons why better recent evidence is not available, and how this will affect innovation in mechanical deep vein thrombosis prophylaxis. Analysis of recent published trials shows great variability in techniques and technologies, which complicates evaluation of the effectiveness of properties of intermittent pneumatic compression, graduated compression stockings, and electrical stimulation devices. Negative controlled trials have become difficult to conduct, and low rates of deep vein thrombosis have left many comparative trials of devices underpowered. There is a risk that if new approaches to enable clinical research are not developed that technological advancement of mechanical prophylaxis will be inhibited.

Intermittent pneumatic compression or graduated compression stockings for deep vein thrombosis prophylaxis? A systematic review of direct clinical comparisons.

OBJECTIVE: To review the relative efficacy of intermittent pneumatic compression (IPC) and graduated compression stockings (GCS) stated in direct clinical comparisons. SUMMARY BACKGROUND DATA: Both IPC and GCS are recommended for deep vein thrombosis (DVT) prophylaxis in surgical patients. Although both are known to be effective, guidance is less clear on the clinical grounds for choosing between the 2 devices. METHODS: Major medical databases were searched for trial reports published between January 1970 and August 2008. All trials comprising a direct clinical comparison between IPC and GCS were reviewed. RESULTS: Ten direct comparisons were found, 9 of which were with surgical patients. The difference in DVT outcome only reached statistic significance in 3, all of which showed IPC to have the lower DVT rate. Five of the trials that did not produce statistic significance included fewer than 40 patients in each study group. The crude cumulated DVT rate for all the trials was 5.9% for GCS and 2.8% for IPC. CONCLUSION: There is only weak evidence to show a difference in performance between the devices, however, given the many influential factors, caution should be taken in assuming equivalence.

Influence of intermittent compression cuff design on calf deformation: computational results.

The intermittent compression of the calf with an external pressure cuff for the prevention of deep vein thrombosis (DVT) is a well established treatment for surgical patients. The exact mechanisms by which DVT is prevented are poorly understood. This study presents a finite element model of calf cross section, based on MR images of calf geometry, to examine the variation in calf deformation during compression with four different cuff types. Cuff pressure distribution is modelled using interface pressures obtained in a volunteer study. The model has been validated against gross calf deformation obtained from MR images of the compressed calf. This validation has illustrated the importance of out-of-plane boundary conditions, material properties and the variation in cuff loading in the axial direction. In the future this model may have merit in determining optimum pressure loading regimes for Intermittent Pneumatic Compression (IPC) cuff design.

Influence of intermittent compression cuff design on interface pressure and calf deformation: experimental results.

Intermittent pneumatic compression (IPC) is widely used for deep vein thrombosis (DVT) prophylaxis. The technique involves periodic inflation of a compression cuff around a limb, which acts to simulate the muscle pump mechanism, encouraging venous blood flow. However, there is uncertainty regarding the relationship between compression, vascular effects and clinical outcomes. This study investigates calf compression provided by four IPC cuffs with different air bladder configurations. Interface pressure between the cuff and the skin surface is measured and magnetic resonance (MR) images are obtained showing the calf cross section before and during compression. The data will be used to inform numerical simulations of IPC, leading to increased understanding of the implications of cuff design in relation to IPC and DVT prophylaxis.

The influence of inflation rate on the hematologic and hemodynamic effects of intermittent pneumatic calf compression for deep vein thrombosis prophylaxis.

OBJECTIVE: The study was conducted to determine whether the different inflation rates of intermittent pneumatic compression systems used in deep vein thrombosis prophylaxis influence their hematologic and hemodynamic effects. METHODS: A rapidly inflating intermittent calf compression system and a more gently inflating equivalent were applied to 20 healthy male volunteers for 2 hours each. Venous blood samples were taken for analysis of blood coagulation and fibrinolytic potential. Blood flow velocity was measured in the femoral vein with Doppler ultrasound. RESULTS: Tissue factor pathway inhibitor significantly increased after the 2 hours of compression for both pumps (78.0 to 85.0 ng/mL rapid, P = .004; 76.5 to 78.0 ng/mL gentle, P = .5), as did plasminogen activator activity (0.85 to 1.05 IU/mL rapid, P = .006; 0.85 to 1.5 IU/mL gentle, P = 0.5). Plasminogen activator inhibitor 1 activity was reduced, although only approaching significance for the gentle system (16.5 to 14.3 AU/mL, P = .06). A D-dimer test for global fibrinolysis showed significant increases for the gently inflating system (97 to 411 ng/mL P < .001) but not for the rapidly inflating system (276 to 350 ng/mL P = .9). The rapidly inflating system produced significantly higher venous peak velocities and augmentations as expected. CONCLUSIONS: Although the data confirm that both types of intermittent compression suppress procoagulant activation, rapid inflation clearly produced no extra benefit in increasing global fibrinolysis, and may be less hematologically effective.

Intermittent venous compression, and the duration of hyperaemia in the common femoral artery.

External compression of limbs to below-diastolic pressure (venous compression) has been shown to produce a short-lived hyperaemia in supply arteries. Intermittent pneumatic compression is currently under investigation therefore as a treatment for peripheral arterial disease. The optimal timing of the compression will depend on the duration of hyperaemia produced by a particular duration of compression, and the purpose of this work was to test that link. Nineteen healthy volunteers underwent intermittent compression of one leg with two compression cycles - one compressing for 10 s each time, the other for 1 min. Blood flow velocities in the common femoral artery was shown to increase on release of the compression by 38% (inter-quartile range 27-56%) for the sequence with short duration compression, and by 57% (inter-quartile range 37-87%) for the longer sequence (difference, P = 0.005, Wilcoxon). The hyperaemia duration above the baseline level was 37 s (inter-quartile range 32-49 s) for the short sequence, and 54 s (inter-quartile range 37-76 s) for the longer sequence (difference, P = 0.001, Wilcoxon). The magnitude of the change in the compression duration was not equalled by the difference in hyperaemia duration, suggesting that the physiological mechanism behind the hyperaemia is unlikely to be due solely to simple accumulation of metabolites, and a myogenic mechanism remains possible. Therapies for peripheral arterial disease need not employ long duration compression, as a greater percentage of time will be spent in hyperaemia with short duration intermittent compression.

Evidence-based compression: prevention of stasis and deep vein thrombosis.

OBJECTIVE: To summarize the currently published scientific evidence for the venous flow effects of mechanical devices, particularly intermittent pneumatic compression, and the relation to prevention of deep vein thrombosis (DVT). SUMMARY BACKGROUND DATA: While intermittent pneumatic compression is an established method of DVT prophylaxis, the variety of systems that are available can use very different compression techniques and sequences. In order for appropriate choices to be made to provide the optimum protection for patients, the general performance of systems, and physiological effects of particular properties, must be analyzed objectively. METHODS: Medline was searched from 1970 to 2002, and all relevant papers were searched for further appropriate references. Papers were selected for inclusion when they addressed specifically the questions posed in this review. RESULTS: All the major types of intermittent compression systems are successful in emptying deep veins of the lower limb and preventing stasis in a variety of subject groups. Compression stockings appear to function more by preventing distension of veins. Rapid inflation, high pressures, and graded sequential intermittent compression systems will have particular augmentation profiles, but there is no evidence that such features improve the prophylactic ability of the system. CONCLUSIONS: The most important factors in selecting a mechanical prophylactic system, particularly during and after surgery, are patient compliance and the appropriateness of the site of compression. There is no evidence that the peak venous velocity produced by a system is a valid measure of medical performance.

Spatial-temporal display of colour-flow ultrasound for the assessment of the effects of intermittent pneumatic compression in limbs.

Colour-flow M-mode ultrasonography in three dimensions (two spatial, one temporal) was used to assess the effects of intermittent pneumatic compression on the blood flow velocities in the common femoral vein and artery. The linear array of a standard 3-D system was held in place over the vessels, to record while a calf and thigh cuff compressed to 60 mmHg. The data was reconstructed in 3-D and, subsequently, sliced in different planes. The technique effectively demonstrated the emptying of distal veins during compression, and hyperaemia in the artery on deflation, in the coronal and sagittal planes. Reconstructions of this type may be of use in visualising the distribution of flow changes within blood vessels.

Effects of supine intermittent compression on arterial inflow to the lower limb.

HYPOTHESIS: Intermittent pneumatic compression will affect the arterial blood flow in the lower limb at moderate pressure, without requiring dependency. DESIGN: Before-after trial. SETTING: Vascular ultrasound unit of a university hospital. PATIENTS: A volunteer sample of 19 healthy subjects without symptoms or history of vascular disease and 17 patients with peripheral arterial disease were studied. Six patients and 1 healthy volunteer were not included in the study group because of measurement difficulties or refusal when approached. INTERVENTIONS: Common femoral artery blood flow velocities were measured with Doppler ultrasound during 10 minutes of intermittent compression of the calf and thigh at 60 mm Hg, while the subject was supine. The data were collected every 5 seconds from 4 minutes before to 4 minutes after the therapy period, and toe temperatures were also measured with an infrared radiometer. MAIN OUTCOME MEASURES: Resting to postcompression percentage increases in flow velocity were measured, along with more representative measures of the total flow change during the intermittent compression period. RESULTS: On compression, the blood flow velocity decreased slightly (15% in healthy subjects and 6% in patients) and increased on release (21% and 29%, respectively). Overall, blood flow did not decrease during therapy as expected (increases of 1% and 2%, respectively), and the toes of the patients warmed (by 2.2 degrees C). CONCLUSIONS: This work confirms the initial hypothesis in both subject groups. There appears to be physiological justification for investigating intermittent compression as a therapy for patients with intermittent claudication and rest pain in the supine position as well as seated.