Prevention of Venous Thromboembolism

A global assessment of hemostatic function of healthy allogeneic stem cell donors undergoing apheresis by rotational thromboelastometry

INTRODUCTION

Peripheral blood stem cell (PBSC) collection via apheresis requires the administration of granulocyte colony-stimulating factor (filgrastim) to stem cell donors. Several reports have shown that filgrastim administration and apheresis procedure induce a hypercoagulable state across PBSC collection, which might predispose certain donors to thrombotic complications.

METHODS

We evaluated the hemostatic functions of healthy allogeneic stem cell donors by rotational thromboelastometry (ROTEM). Blood samples from healthy donors (n = 30) were collected at defined time points: before filgrastim (baseline), on the day of apheresis before and after the procedure, and 1 week after apheresis.

RESULTS

The results indicated that hemostatic changes are temporary since all parameters in both EXTEM and INTEM assays are restored to their initial values 1 week after the apheresis.

CONCLUSION

We concluded that stem cell apheresis does not induce a hypercoagulable state in healthy donors. This is the first study evaluating the hemostatic functions of stem cell donors by ROTEM.

The Double Hazard of Bleeding and Thrombosis in Hemostasis From a Clinical Point of View: A Global Assessment by Rotational Thromboelastometry (ROTEM)

Hemostasis is a complex dynamic process involving bleeding and thrombosis as two end-points. Conventional coagulation tests which are measured in plasma examine only isolated portions of the coagulation cascade, thereby giving no information on important interactions essential to the clinical evaluation of hemostatic function. Thromboelastography (TEG), originally described in 1948 has improved over the decades and become a valuable tool of coagulation testing because of the limitations of standard coagulation tests. TEG is a technique that provides data about the entire coagulation system, from the beginning of clot formation to fibrinolysis, involving both cellular and plasma components of hemostasis. Rotational thromboelastometry (ROTEM) which evolved from TEG technology overcome several limitations of classical TEG while maintaining a good correlation with conventional TEG determination. ROTEM analyses are useful for rapid assessment of global clotting function in various clinical situations including liver transplantation, cardiac surgery, obstetrics, trauma, hemophilia and idiopathic thrombocytopenic purpura. ROTEM has been also reported to be useful in identifying various hypercoagulable conditions including major surgery, malignancy, Behcet’s disease and apheresis. Further developments in ROTEM based transfusion strategies may also reduce transfusion requirements and improve clinical outcomes by optimizing the administration of blood components. This is a literature review of ROTEM including its technique, interpretation and specially clinical applications in different scenarios of bleeding and thrombotic disorders.

Postoperative complications after lower extremity arterial bypass increase the risk of new deep venous thrombosis

Background Deep venous thrombosis after any surgical operations is considered a preventable complication. Lower extremity bypass surgery is a commonly performed operation to improve blood flow to lower extremities in patients with severe peripheral arterial disease. Despite advances in endovascular surgery, lower extremity arterial bypass remains the gold standard treatment for severe, symptomatic peripheral arterial disease. The purpose of this study is to identify the clinical risk factors associated with development of deep venous thrombosis after lower extremity bypass surgery. Methods The American College of Surgeons' NSQIP database was utilized and all lower extremity bypass procedures performed in 2013 were examined. Patient and procedural characteristics were evaluated. Univariate and multivariate logistic regression analysis was used to determine independent risk factors for the development of postoperative deep venous thrombosis. Results A total of 2646 patients (65% males and 35% females) underwent lower extremity open revascularization during the year 2013. The following factors were found to be significantly associated with postoperative deep venous thrombosis: transfusion >4 units of packed red blood cells (odds ratio (OR) = 5.21, confidence interval (CI) = 1.29-22.81, p = 0.03), postoperative urinary tract infection (OR = 12.59, CI = 4.12-38.48, p < 0.01), length of hospital stay >28 days (OR = 9.30, CI = 2.79-30.92, p < 0.01), bleeding (OR = 2.93, CI = 1.27-6.73, p = 0.01), deep wound infection (OR = 3.21, CI = 1.37-7.56, p < 0.01), and unplanned reoperation (OR = 4.57, CI = 2.03-10.26, p < 0.01). Of these, multivariable analysis identified the factors independently associated with development of deep venous thrombosis after lower extremity bypass surgery to be unplanned reoperation (OR = 3.57, CI = 1.54-8.30, p < 0.01), reintubation (OR = 8.93, CI = 2.66-29.97, p < 0.01), and urinary tract infection (OR = 7.64, CI = 2.27-25.73, p < 0.01). Presence of all three factors was associated with a 54% incidence of deep venous thrombosis. Conclusions Development of deep venous thrombosis after lower extremity bypass is a serious but infrequent complication. Patients who require unplanned return to the operating room, reintubation, or develop a postoperative urinary tract are at high risk for developing postoperative deep venous thrombosis. Increased monitoring of these patients and ensuring adequate deep venous thrombosis prophylaxis for such patients is suggested.

Thromboprophylaxis, coagulation disorders, and regional anaesthesia

The surgery and trauma-induced modulation of the coagulation system includes a considerable risk of perioperative thromboembolic complications unless effective thromboprophylactic treatment is given. In the present survey the patient at risk of deep vein thrombosis (DVT) and pulmonary embolism (PE) is characterized and the documented efficacy of different currently used thromboprophylactic regimens is summarized. Systemic thromboprophylactic treatment may include a risk of an increased bleeding tendency which may lead to haemorrhagic complications. In patients with a coagulation abnormality or in patients receiving anticoagulants for perioperative thromboprophylaxis there is a fear among anaesthesiologists that the use of regional anaesthesia (spinal or epidural) may be associated with spinal haemorrhagic complications, i.e. with spinal haematoma formation leading to compression of the spinal cord and severe neurologic sequelae. Present aspects on the risk of spinal haematoma formation at the combined use of pharmacological thromboprophylactic regimens and spinal or epidural anaesthesia/ analgesia are therefore summarized. Pregnancy is associated with changes in the haemostatic system, which in the preeclamptic or eclamptic patient may be rather pronounced and constitute a clinical problem since regional anaesthetic techniques are often preferred for obstetric anaesthesia/analgesia. The specific problems to be considered prior to the choice of regional anaesthesia/analgesia for a parturient with a suspected coagulation disorder are therefore commented on in more detail. Finally, recommendations are given for safe spinal and epidural analgesic and anaesthetic routines in patients with potential haemostatic disturbances due to thromboprophylactic treatment with anticoagulants or bleeding disorders.

Low molecular weight heparin in prevention of perioperative thrombosis

OBJECTIVE

To determine whether prophylactic treatment with low molecular weight heparin reduces the incidence of thrombosis in patients who have had general or orthopaedic surgery.

DESIGN

Meta-analysis of results from 52 randomised, controlled clinical studies (29 in general surgery and 23 in orthopaedic surgery) in which low molecular weight heparin was compared with placebo, dextran, or unfractionated heparin.

SUBJECTS

Patients who had had general or orthopaedic surgery.

INTERVENTION

Once daily injection of a low molecular weight heparin compared with placebo, dextran, or unfractionated heparin.

MAIN OUTCOME MEASURES

Incidence of deep venous thrombosis, pulmonary embolism, major haemorrhages, and death.

RESULTS

The results confirm that low molecular weight heparins are more efficacious for the prophylactic treatment of deep venous thrombosis than placebo (common odds ratio 0.31, 95% confidence interval 0.22 to 0.43; p < 0.001) and dextran (0.44, 0.30 to 0.65; p < 0.001). The results suggest that low molecular weight heparins are also more efficacious than unfractionated heparin (0.85, 0.74 to 0.97; p = 0.02), with no significant difference in the incidence of major haemorrhages (1.06, 0.93 to 1.20; p = 0.62).

CONCLUSIONS

Low molecular weight heparins seem to have a higher benefit to risk ratio than unfractionated heparin in preventing perioperative thrombosis. However, it remains to be shown in a suitably powered clinical trial whether low molecular weight heparin reduces the risk of fatal pulmonary embolism compared with heparin.

Prophylaxis of venous thromboembolism

The objective of prophylaxis in venous thromboembolism is, first, to prevent fatal pulmonary embolism and, second, to reduce the morbidity associated with deep vein thrombosis (DVT) and the postphlebitic limb. This should now be standard practice for most patients over 40 years of age undergoing major surgery and for younger patients with a history of venous thromboembolism. Particularly high-risk groups include patients over 60 years of age undergoing major surgery, those with malignancy, and those requiring hip operations. Low-dose subcutaneous heparin 5,000 IU commencing 2 hours preoperatively and continuing 12 hourly until the patient is fully mobile is unequivocally effective in preventing DVT in medical and surgical patients and, most importantly, significantly reduces the incidence of fatal postoperative pulmonary embolism and total mortality. Such prophylaxis, in the presence of established DVT, also limits proximal clot propagation, which is the precursor of major pulmonary embolism. Low-dose heparin prophylaxis is associated with a small risk of bleeding complications, evidenced mostly by an increased frequency of wound hematoma rather than major clinical hemorrhage. Low molecular weight heparin fragments (e.g., Fragmin, Choay, Enoxaparine) are emerging as useful alternative agents, having the advantage of once daily administration and yet providing similar efficacy in the prevention of DVT. Mechanical methods of prevention which counteract venous stasis, such as graduated elastic compression stockings, are also useful in protecting against DVT but have not been shown to prevent fatal postoperative pulmonary embolism. They are recommended particularly for patients in whom heparin prophylaxis is best avoided (e.g., neurosurgery) and possibly in combination with heparin in very high-risk patients.

Low dose dextran 40 in reconstructive hip surgery patients

Preoperative and postoperative bilateral lower extremity venography was used to evaluate the efficacy of low dose dextran 40 in prophylaxis of deep venous thrombosis in reconstructive hip surgery patients. Patients were given dextran 40 at 50 cc/hr, with 250 cc given perioperatively and 500 cc given on postoperative days two and four. Five of 227 patients had positive venograms preoperatively. Of these 227 patients, 179 met protocol requirements and had venography postoperatively. Venous thrombosis occurred in 33 (18%) of those studied postoperatively. Of these, 11 were calf clots without extension to the popliteal region. Therefore, there were 22 patients (12%) with femoral or popliteal involvement overall. There were two deaths, neither of which was secondary to pulmonary embolus or a complication of dextran. There were two wound complications. These results suggest that low dose dextran 40 administered as indicated is a safe and efficacious means of deep venous thrombosis prophylaxis in reconstructive hip surgery patients.

Blood rheology in general medicine and surgery

Traditionally, blood rheology tests have been used in diagnosis and monitoring of infection, rheumatic diseases and malignancy, and are still of clinical value in these conditions. In the last twenty years, clinical and epidemiological studies have shown that the haematological determinants of blood flow resistance (haematocrit, fibrinogen, white cell count and altered red and white cell rigidity) are also associated with nutritional, metabolic, endocrine and vascular disorders. Decreased red cell deformability may contribute to reduced red cell survival and anaemia in burns, malaria, liver disease and kidney failure. In trauma and inflammatory disease, overt hyperviscosity is usually prevented by vasodilatation and reduction in the haematocrit. However, low-flow states may arise systemically from haemoconcentration (contracted plasma volume, Chapter 3) in severe burns, inappropriate red cell transfusion, or dehydration due to illness; systemically in circulatory shock; and locally in venous thrombosis or arterial disease. In such circumstances, the intrinsic flow resistance of blood may perpetuate flow disturbance, ischaemia and thrombosis. Conversely, optimal levels of haematocrit, fibrinogen and white cell count may be lower than normal in low-flow states. Haemodilution by colloid infusion is beneficial in burns, shock, major surgery, prevention of postoperative venous thrombosis, chronic stable claudication and possibly in acute stroke and retinal vein thrombosis. Plasma exchange may be beneficial in severe Raynaud's phenomenon. Defibrination with ancrod is effective in prevention and treatment of venous thrombosis but its role in arterial disease is unproven. The benefits of streptokinase therapy in venous thrombo-embolism and acute myocardial infarction may be partly rheological, due to fibrinogen depletion. Drugs with rheological effects may be beneficial in intermittent claudication.

Graded compression Stockings with and without Heparin-Dihydroergotamine in the Prevention of Deep Venous Thrombosis following Elective Hip Alloplasty

Two hundred and five patients scheduled for total hip alloplasty were randomized to one of the following two regimes, in order to prevent postoperative thromboembolism. (1) Graded compression stockings and heparin 5000 iu/dihydroergotamine 0.5 mg twice a day subcutaneously. (2) Graded compression stockings and placebo twice a day subcutaneously. Screening for deep venous thrombosis (DVT) was carried out by 99mTc-plasmin scintimetry and whenever this was indicative for DVT, ascending phlebography was performed. The definitive criteria for DVT were intraluminal filling defects on phlebography. If DVT was diagnosed, pulmonary perfusion/ventilation scintigraphy was performed. In the group receiving heparin/dihydroergotamine 11 of 96 patients (11%) developed DVT and in the placebo group 25 of 109 patients (23%) developed DVT (P < 0.05). One patient in the combination treatment group and seven patients in the placebo group developed pulmonary embolism ( P < 0.05). It is concluded that the combination of graded compression stockings, low dose heparin and dihydroergotamine is superior to graded compression stockings alone in preventing thromboembolism following total hip alloplasty.

Heparin with and without graded compression stockings in the prevention of thromboembolic complications of major abdominal surgery: a randomized trial

One hundred and seventy-six patients scheduled for elective major abdominal surgery were randomized to two prophylactic regimens to prevent postoperative thromboembolism. All patients were screened with the 125I-labelled fibrinogen uptake test, and thromboembolism was verified by ascending phlebography and/or perfusion/ventilation lung scintigraphy. In the group of patients receiving low-dose heparin treatment (5000 units twice daily subcutaneously) 12 per cent developed thromboembolic complications. In the other group, where low-dose heparin treatment was supplemented with graded compression stockings only 2 per cent developed thromboembolism. It is concluded that the combination of low-dose heparin and the use of graded compression stockings is superior to heparin alone in preventing thromboembolism following major abdominal surgery.