Perioperative low molecular weight heparin for infrageniculate bypass

Fondaparınux versus nadroparın for preventıon of venous thromboembolısm after electıve hıp and knee arthroplasty

OBJECTIVE

To evaluate the efficacy and safety of fondaparinux compared with nadroparin for prevention of venous thromboembolism after arthroplasty.

PATIENTS AND METHODS

One hundred fifteen patients were randomized into 2 treatment groups. Patients were given fondaparinux in Group I and nadroparin in Group II. Measurements were performed on Days 1, 5, and 21. The wound area was assessed with a subjective visual analog scale.

RESULTS

The blood counts, clinical biochemical tests, and coagulation tests (ie, thrombin time, partial thromboplastin time, activated partial thromboplastin time, fibrinogen, prothrombin time-International Normalized Ratio, and antithrombin III activity) did not show statistically significant differences between Group I and Group II. In both study groups, anti-factor Xa activities increased significantly on the fifth and 21st day. The scores of the subjective visual analog scale showed significance on Day 21.

CONCLUSIONS

Our results confirm the safety and efficacy of both fondaparinux and nadroparin for prophylaxis after major orthopedic surgery.

Antithrombotic agents for preventing thrombosis after infrainguinal arterial bypass surgery

BACKGROUND

Peripheral arterial disease (PAD) is frequently treated by either an infrainguinal autologous (using the patient's own veins) or synthetic graft bypass. The rate of occlusion of the graft after one year is between 12% and 60%. To prevent occlusion, patients are treated with an antiplatelet or antithrombotic drug, or a combination of both. Little is known about which drug is optimal to prevent infrainguinal graft occlusion. This is an update of a Cochrane review first published in 2003.

OBJECTIVES

To evaluate whether antithrombotic treatment improves graft patency, limb salvage and survival in patients with chronic PAD undergoing infrainguinal bypass surgery.

SEARCH STRATEGY

The Cochrane Peripheral Vascular Diseases Group searched their Specialised Register (last searched August 2010) and the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2010, Issue 3).

SELECTION CRITERIA

Randomised, controlled trials; two review authors independently assessed the methodological quality of each trial using a standardised checklist.

DATA COLLECTION AND ANALYSIS

Data collected included patient details, inclusion and exclusion criteria, type of graft, antithrombotic therapy, outcomes, and side effects.

MAIN RESULTS

A total of 14 trials were included in this review; 4970 patient results were analysed. Four trials evaluating vitamin K antagonists (VKA) versus no VKA suggested that oral anticoagulation may favour autologous venous, but not artificial, graft patency as well as limb salvage and survival. Two other studies comparing VKA with aspirin (ASA) or aspirin and dipyridamole provided evidence to support a positive effect of VKA on the patency of venous but not artificial grafts. Three trials comparing low molecular weight heparin (LMWH) to unfractionated heparin (UFH) failed to demonstrate a significant difference on patency. One trial comparing LMWH with placebo found no significant improvement in graft patency over the first postoperative year in a population receiving aspirin. One trial showed an advantage for LMWH versus aspirin and dipyridamol at one year for patients undergoing limb salvage procedures. Perioperative administration of ancrod showed no greater benefit when compared to unfractionated heparin. Dextran 70 showed similar graft patency rates to LMWH but a significantly higher proportion of patients developed heart failure with dextran.

AUTHORS' CONCLUSIONS

Patients undergoing infrainguinal venous graft are more likely to benefit from treatment with VKA than platelet inhibitors. Patients receiving an artificial graft benefit from platelet inhibitors (aspirin). However, the evidence is not conclusive. Randomised controlled trials with larger patient numbers are needed in the future to compare antithrombotic therapies with either placebo or antiplatelet therapies.

The effect of nadroparine on coagulation mechanisms: ultrastructural analysis

Low molecular weight heparins are widely used in the prophylaxis and treatment of thrombotic disorders. The effect of low molecular weight heparins on coagulation was examined ultrastructurally in an animal model. A test and a control group was formed, each consisting of five rabbits. Nadroparine (225 Institute of Chaoy Unit/kg twice daily) was applied to the test group for 10 days. The control group received 1 ml saline solution subcutaneously. Blood and vascular tissue samples collected at the end of the 10th day were evaluated under a JEM 100 B electron microscope. Platelet degranulation and agglutination was observed in the control group. Fibrin materials were detected in the cytoplasms and surroundings of degranulated platelets. Erythrocyte accumulation was remarkable on the vascular endothelium with intact coagulation periods. In the test group, outer membranes of platelets, hyalomere, and granular structures in the granulomeres were detected to be nearly intact. There were rare erythrocytes in the large vascular lumens. The aggregation phase had occurred but no agglutination was detected. Nadroparine seems to preserve consistency of lipoprotein membranes of platelets and granular structures containing enzymes, which contribute to the coagulation mechanisms.

Antithrombotic agents for preventing thrombosis after infrainguinal arterial bypass surgery

BACKGROUND

Chronic peripheral arterial disease (PAD) is frequently treated by implantation of either an infrainguinal autologous venous or artificial graft. One-year occlusion rates for infrainguinal bypasses vary between 15 and 75%, depending on the site of distal anastomosis, length, quality, and material of the graft, but also on other factors such as proximal inflow and distal outflow conditions. To prevent graft occlusion, patients are usually treated with either an antiplatelet or antithrombotic drug, or a combination of both. Little is known about which drug is optimal to prevent infrainguinal graft occlusion.

OBJECTIVES

To evaluate whether antithrombotic treatment in patients with chronic PAD undergoing infrainguinal bypass surgery improves graft patency, limb salvage and survival by performing a meta-analysis of performed RCTs.

SEARCH STRATEGY

The search strategy was that adopted by the Cochrane Review Group on Peripheral Vascular Diseases. Additional data bases were reviewed (Reference lists of papers resulting from this search, MEDLINE from 1966-onwards and EMBASE from 1980-onwards using the terms 'anticoagulant' and 'arterial surgery'.

SELECTION CRITERIA

The methodological quality of each trial was assessed independently by at least two reviewers using the checklist provided by the Peripheral Vascular Diseases Collaborative Review Group, with emphasis on concealment of randomisation. Each trial was given an allocation score of A (clearly concealed), B (unclear if concealed), or C (clearly not concealed) and a summary score of A (low risk of bias), B (moderate risk), or C (high risk). Trials scoring A were included and those scoring C were excluded. For a trial scoring B, an attempt was made to obtain more information by contacting the author.

DATA COLLECTION AND ANALYSIS

For each trial, the number of patients originally allocated to each treatment group was extracted from the data and an 'intention to treat' analysis performed. Data collection on each trial included inclusion and exclusion criteria, patient details, type of graft, type and dose of antithrombotic therapy used, outcome, and side effects. The treatment and control groups were compared for important prognostic factors and differences described. If any of the above data was not available, further information was sought from the author. However, the heterogeneity between trials could not be tested due to inaccessible data. Data were synthesized by comparing group results.

MAIN RESULTS

The analysis including four trials which evaluated vitamin K antagonists (VKA) versus no VKA indicate, that oral anticoagulation tendentially favours venous but not artificial graft patency as well as limb salvage and survival. Two other studies comparing VKA with aspirin or aspirin/dipyridamole supported evidence for a positive effect of VKA on the patency of venous but not artificial grafts. Subgroup analysis for artificial grafts as performed in one trial showed a favourable effect of antiplatelet agents on synthetic bypasses. In two trials with a relatively small number of patients low molecular weight heparin treatment was associated with a lower incidence of early postoperative graft thrombosis compared to treatment with unfractionated heparin. In one trial infusion of antithrombin concentrate was reported to have a negative effect on intraoperative graft thrombosis necessitating the study to be stopped before termination. Perioperative administration of ancrod was compared to unfractionated heparin showing no benefit of one drug compared to the other.

REVIEWER'S CONCLUSIONS

Patients operated for an infrainguinal venous graft might benefit from treatment with VKA, whereas patients receiving an artificial graft might profit more from platelet inhibitors (aspirin). However, the evidence is not conclusive. Randomised controlled trials with larger patient numbers comparing antithrombotic therapies with either placebo or antiplatelet therapies are called for in the future.

Low-molecular-weight heparin in arterial reconstructive surgery: a double-blind, randomized dose-finding trial

Periprocedural and postprocedural anticoagulation during arterial reconstructive surgery (ARS) with intravenous heparin is standard of care. The general use and correct dosage of low-molecular-weight heparin, however, are still under debate. A prospective, randomized, double-blind trial was performed with a parallel group comparison of four dose regimen of a low-molecular-weight heparin, reviparin sodium, in patients undergoing major ARS. Sixty-five patients were randomly allocated to receive twice-daily subcutaneous injections of reviparin, 3500 (group A, n=17), 4200 (group B, n=16), 5950 (group C, n=16), and 7000 (group D, n=16) anti-Xa IU per day. Patients were eligible for the trial if they had angiographically proven peripheral arterial obstructive disease with a planned arterial reconstruction of the infrarenal aorta, iliaca artery, or femoralis artery. Fifty-nine patients completed the trial. The goal was to determine the optimal dose of the low-molecular-weight heparin to achieve a minimum of early vascular events (less than 12%) with a minimum of major bleeding events (less than 10%) during a short-term follow-up of up to 8 postoperative days. There was no reocclusion in the entire population. Patients randomized into the two lower dose groups (A and B), however, experienced a relatively high incidence of restenosis, whereas patients enrolled in group D, receiving the highest dose of reviparin, experienced an unacceptably high rate of bleeding events (all bleeds, 43%; major bleeding, 14.3%). Thus, the optimal dose of reviparin sodium to be administered in patients undergoing major ARS is half the therapeutic dose: 5950 to 6300 anti Xa IU (75-85 anti Xa IU/kg body weight per day). Patients included in group C had no major bleeding event (95% confidence interval, 0% to 6.6%), a significant improvement of the doppler ankle-brachial systolic pressure index (difference of 0.46 +/- 0.29, P=.017), and a higher rate of responders with regard to the puls status measured at the tibialis posterior arteries (66.7%) compared to groups A and B (46.7% and 54.5%, respectively, P=.086). The efficacy and safety of this dosage regimen in comparison to standard of care should be further substantiated in larger trials.

Comparison of the use of enoxaparin versus unfractionated heparin in patients undergoing lower extremity revascularization

Present available studies suggest that heparin prevents early vessel thrombosis in the immediate postoperative (POP) period after lower extremity bypass. Long-term anticoagulation with warfarin has also been used in these patients, based on its beneficial effect in preventing long-term graft failure. To compare the effectiveness between unfractionated heparin (UH) and low-molecular-weight heparin (enoxaparin) when used as transitional therapeutic POP anticoagulant therapy, a prospective study was performed. Seventy consecutive patients undergoing lower extremity bypass were studied. The initial 35 patients were started on a drip of UH 6 hours POP. The next 35 consecutive patients were treated with enoxaparin, the first dose starting 6 hours POP. All patients underwent subsequent anticoagulation with oral warfarin. There were no statistically significant differences between the two groups with regard to demographics, percentage of above/below the knee bypasses, type of conduit used, emergency operations, and overall complications. There was a significant difference in the length of stay (p = 0.05) in favor of the enoxaparin group, which also reflected a decreased overall cost in this group. In conclusion, POP anticoagulation with enoxaparin is as safe end effective as UH in patients undergoing lower extremity revascularization. Enoxaparin was associated with a decreased overall length of stay and hospital costs.

Low Molecular Weight Heparin: An Evaluation of Current and Potential Clinical Utility in Surgery

Heparin, a mixture of glycosaminoglycans of various sizes, is a potent natural anticoagulant. Low molecular weight heparins (LMWH) contain only the polymers of smaller size, which appear to possess most of the antithrombotic potential. Pharmacological differences between the two suggest a number of advantages with LMWH therapy. Our objective was to establish the utility of LMWHs in comparison to the current practice of anticoagulation in surgical patients. Articles were obtained through MEDLINE and CURRENT CONTENTS queries. The searches were limited to English and French-language articles and included published overviews containing relevant individual trials. We examined the current literature, consisting of 1,730 published reports from 1979-1998, regarding the biochemistry, pharmacology, physiology, and clinical applications of LMWH in comparison with current therapy. Studies were selected based on their relevance to LMWHs, the size and methods of trials, and their application to clinical care. Peer-reviewed published data were critically evaluated by independent extraction by several authors. Established rules for levels of evidence were used to objectively evaluate the strength of evidence supporting recommendations in each clinical area. LMWHs provide superior anticoagulation in the prophylaxis of DVT following orthopedic, general, and trauma surgery. Further studies should establish which other patients may benefit from such prophylaxis. Current evidence does not support the use of LMWHs in patients with mechanical heart valves or those on mechanical cardiac support devices; however, it may have a role in the maintenance of vascular graft patency. Further studies should examine the role of LMWHs in transplant atherosclerosis, and in patients requiring long-term anticoagulation at high risk for bleeding with warfarin therapy. The economic implications of LMWH administration remain unclear. On the basis of the information presented in this review, LMWHs are promising new agents in prophylaxis and treatment of both arterial and venous thrombosis. In the near future, LMWHs are likely to supplant UFH and perhaps warfarin in many applications.http://link.springer-ny.com/link/service/journals/00547/bibs/8n4p203.html</hea

Adjuvant medical therapy in peripheral bypass surgery

BACKGROUND

A review was conducted of published clinical trials of adjuvant medical therapy in infrainguinal bypass procedures to evaluate the strength of the evidence for the use of various agents.

METHODS

Trials were identified by literature search. The methods used were reviewed and the results with each agent tested were assessed taking into account the soundness of the study design.

RESULTS

Thirty-three studies were identified; fewer than half had a randomized and double-blind design. Most were single-centre studies including a mixture of different surgical procedures and patients with varying degrees of lower limb ischaemia. Clinical outcomes were seldom reported. The median sample size was 61. The median follow-up duration was 12 months, but was often not standardized for all patients in a trial. Only aspirin in prosthetic grafts and ticlopidine in vein grafts have been shown in well designed, double-blind, randomized, controlled trials to reduce the likelihood of occlusion in infrainguinal bypass grafts.

CONCLUSION

The majority of the trials reviewed had significant deficiencies in their design, reducing the reliance that can be placed on their results. Further studies are required to investigate adequately the effectiveness of existing medical therapies for the maintenance of infrainguinal bypass grafts.