Response of fibrinolytic activity to venous occlusion

Blood Flow Restriction Resistance Exercise as a Rehabilitation Modality Following Orthopaedic Surgery: A Review of Venous Thromboembolism Risk

Synopsis Restoration of skeletal muscle mass and strength is critical to successful outcomes following orthopaedic surgery. Blood flow restriction (BFR) resistance exercise has emerged as a promising means of augmenting traditional low-intensity physical rehabilitation exercise and has yielded successful outcomes in a wide range of applications. Though BFR is well tolerated and safe for most individuals, patients who have undergone orthopaedic surgery may be an exception, due to their heightened risk for venous thromboembolism (VTE). While the pathogenesis of VTE is multifactorial and specific to the individual, it is commonly described as a combination of blood stasis, endothelial injury, and alterations in the constituents of the blood leading to hypercoagulability. The collective literature suggests that, given the pathogenic mechanisms of VTE, limited use of a wide, partially occluding cuff during resistance exercise should be low risk, and the likelihood that BFR would directly cause a VTE event is remote. Alternatively, it is plausible that BFR may enhance blood flow and promote fibrinolysis. Of greater concern is the individual with pre-existing asymptomatic VTE, which could be dislodged during BFR. However, it is unknown whether the direct risk associated with BFR is greater than the risk accompanying traditional exercise alone. Presently, there are no universally agreed-upon standards indicating which postsurgical orthopaedic patients may perform BFR safely. While excluding all these patients from BFR may be overly cautious, clinicians need to thoroughly screen for VTE signs and symptoms, be cognizant of each patient's risk factors, and use proper equipment and prescription methods prior to initiating BFR. J Orthop Sports Phys Ther 2019;49(1):17-27. Epub 12 Sep 2018. doi:10.2519/jospt.2019.8375.

Blood Flow Restriction Therapy After Knee Surgery: Indications, Safety Considerations, and Postoperative Protocol

Blood flow restriction (BFR) training involves occluding venous outflow while maintaining arterial inflow by the application of an extremity tourniquet after surgery. BFR ultimately reduces oxygen delivery to muscle cells, similar to an anaerobic environment, and allows patients to exercise with low resistance and stimulates muscle hypertrophy and strength using heavy resistance. Thus orthopaedic surgeons and physical therapists are incorporating this type of training into their postoperative rehabilitation protocols, particularly after injuries or surgical procedures about the knee joint. The purpose of this Technical Note is to describe a BFR clinical application technique and to report on the indications, safety considerations, and postoperative knee surgery rehabilitation protocols for BFR.

Relative safety of 4 weeks of blood flow-restricted resistance exercise in young, healthy adults

This study evaluated the effect of 4 weeks of low-load resistance exercise with blood flow restriction (BFRE) on increasing strength in comparison with high-load resistance exercise (HLE), and assessed changes in blood, vascular and neural function. Healthy adults performed leg extension BFRE or HLE 3 days/week at 30% and 80% of strength, respectively. During BFRE, a cuff on the upper leg was inflated to 30% above systolic blood pressure. Strength, pulse-wave velocity (PWV), ankle-brachial index (ABI), prothrombin time (PT) and nerve conduction (NC) were measured before and after training. Markers of coagulation (fibrinogen and D-dimer), fibrinolysis [tissue plasminogen activator (tPA)] and inflammation [high sensitivity C-reactive protein (hsCRP)] were measured in response to the first and last exercise bouts. Strength increased 8% with BFRE and 13% with HLE (P<0.01). No changes in PWV, ABI, PT or NC were observed following training for either group (P>0.05). tPA antigen increased 30-40% immediately following acute bouts of BFRE and HLE (P=0.01). No changes were observed in fibrinogen, D-dimer or hsCRP (P>0.05). These findings indicate that both protocols increase the strength without altering nerve or vascular function, and that a single bout of both protocols increases fibrinolytic activity without altering selected markers of coagulation or inflammation in healthy individuals.

Evaluation of euglobulin clot lysis time as a screening method for determination of blood plasma fibrinolytic activity after venous occlusion

Determination of the fibrinolytic activity should be performed in patients with recurrent thromboembolic disease. As a screening procedure we suggest the euglobulin clot lysis time test after venous occlusion. This test is sufficiently reliable and easier to perform than the fibrin plate method, especially outside coagulation laboratories.

Defective fibrinolysis: a risk factor in early femoropopliteal graft thrombosis

Resting plasma fibrinolytic activity and fibrinolytic activity after stimulation by 10 min of venous occlusion (fibrinolytic potential) were estimated in 51 patients before femoropopliteal reconstructive surgery. Twelve patients suffered a graft thrombosis in the first month. Resting plasma fibrinolytic activity was similar in patients with thrombosed grafts and those with functioning grafts. However reduced fibrinolytic potential was found to be a risk factor for graft thrombosis in the month after surgery (P = 0.01). Other risk factors were increasing age (P = 0.007) and the indication for surgery (P = 0.03). Thirty-four patients whose grafts were functioning after 1 month were followed up for a mean of 9 months. A further eight grafts thrombosed. Neither fibrinolytic activity nor fibrinolytic potential were found to be risk factors for late graft thrombosis. Fibrinolytic potential has been shown to be an independent risk factor for early graft thrombosis. Perioperative fibrinolytic stimulation might be a method of improving femoropopliteal graft patency.

The fibrinolytic effects of anaesthesia

The fibrinolytic effects of six different anaesthetic agents were studied in 36 patients undergoing abdominal hysterectomy. Fibrinolytic activity was measured by dilute whole blood and euglobulin clot lysis times. Concentrations of plasminogen, fibrinogen and fibrin degradation products were also determined. Significant enhancement of fibrinolytic activity, measured as a decrease in clot lysis time, was seen during anaesthesia and surgery with all agents studied. Halothane produced the least effect and the greatest increase in fibrinolytic activity was seen during trichloroethylene anaesthesia. Lumbar extradural anaesthesia also consistently produced enhancement of fibrinolysis. The reasons for these results and their clinical implications are discussed.

The euglobulin clot lysis time, a rapid and sensitive method for the assay of fibrinolytic activity after venous stasis

For the estimation of fibrinolytic activity in euglobulin precipitates after venous stasis, the euglobulin clot lysis time (ECLT) proved to be as reproducible and probably even more sensitive than the fibrin plate method (FP). Furthermore, when euglobulin precipitates from 55 healthy individuals and 36 patients with thromboembolic disease were examined, a good correlation between the two methods was observed. The present observations indicate that the ECLT is suitable for routine screening of fibrinolytic activity after venous stasis.

Changes in haemostatic system after application of a tourniquet

In 35 patients undergoing routine orthopaedic operations in which occlusive tourniquets were used there was a pronounced rise in fibrinolytic activity in the systemic circulation which lasted for at least 15 minutes after the release of the tourniquet; this response was seen after operations on both arms and legs. In contrast there was no increase in fibrinolytic activity in the systemic circulation associated with venous occlusion. Neither the application of a tourniquet nor venous occlusion resulted in changes in factors V or VIII, fibrinogen, or platelet-count. The application of a completely occlusive tourniquet might be a simple form of prophylaxis against deep-vein thrombosis and would avoid the disadvantages of using heparin.