Efficacy of perioperative thromboprophylactic agents in the maintenance of anastamotic patency and survival of rat microvascular free groin flaps

Evidence-Based Approaches to Anticoagulation in Reconstructive Microsurgery-A Systematic Literature Review

This systematic review addresses the crucial role of anticoagulation in microsurgical procedures, focusing on free flap reconstruction and replantation surgeries. The objective was to balance the prevention of thrombotic complications commonly leading to flap failure, with the risk of increased bleeding complications associated with anticoagulant use. A meticulous PubMed literature search following Evidence-Based-Practice principles yielded 79 relevant articles, including both clinical and animal studies. The full-texts were carefully reviewed and evaluated by the modified Coleman methodology score. Clinical studies revealed diverse perioperative regimens, primarily based on aspirin, heparin, and dextran. Meta-analyses demonstrated similar flap loss rates with heparin or aspirin. High doses of dalteparin or heparin, however, correlated with higher flap loss rates than low dose administration. Use of dextran is not recommended due to severe systemic complications. In animal studies, systemic heparin administration showed predominantly favorable results, while topical application and intraluminal irrigation consistently exhibited significant benefits in flap survival. The insights from this conducted systematic review serve as a foundational pillar towards the establishment of evidence-based guidelines for anticoagulation in microsurgery. An average Coleman score of 55 (maximum 103), indicating low overall study quality, however, emphasizes the need for large multi-institutional, randomized-clinical trials as the next vital step.

Promoting endogenous repair of skeletal muscle using regenerative biomaterials

Skeletal muscles normally have a remarkable ability to repair themselves; however, large muscle injuries and several myopathies diminish this ability leading to permanent loss of function. No clinical therapy yet exists that reliably restores muscle integrity and function following severe injury. Consequently, numerous tissue engineering techniques, both acellular and with cells, are being investigated to enhance muscle regeneration. Biomaterials are an essential part of these techniques as they can present physical and biochemical signals that augment the repair process. Successful tissue engineering strategies require regenerative biomaterials that either actively promote endogenous muscle repair or create an environment supportive of regeneration. This review will discuss several acellular biomaterial strategies for skeletal muscle regeneration with a focus on those under investigation in vivo. This includes materials that release bioactive molecules, biomimetic materials and immunomodulatory materials.

Effects of Bemiparin Sodium Versus Dabigatran Etexilate After Anastomosis in Rat Carotid Arteries on the Development of Neointima and Thrombolytic Efficacy

BACKGROUND

Revascularization before infarct development after cerebral ischemia may affect morbidity. The success of revascularization can be less than expected because of spontaneous thrombosis or restenosis with intimal hyperplasia. The aim of this study was to compare dabigatran etexilate, a direct thrombin inhibitor, with bemiparin sodium, a second-generation low-molecular-weight heparin, after carotid artery anastomosis.

METHODS

This study used 24 randomly selected Sprague-Dawley rats. The rats were separated into 3 equal groups: group 1 (control group); group 2 (dabigatran group), in which dabigatran 10 mg/kg was orally administered for 7 days; and group 3 (bemiparin group), in which bemiparin 250 IU/kg was subcutaneously administered for 7 days. The right-side carotid artery of rats was used for anastomosis and the left-side carotid artery was used for the control. The carotid artery was explored and transected. Anastomosis was applied using 10/0 polypropylene sutures. After 7 days of treatment, the right and left carotid arteries were removed. Lumen diameter, lumen area, tunica media thickness, edema, vessel wall injury, intimal hyperplasia, thrombus, and inflammation were evaluated in tissue biopsy specimens.

RESULTS

Bemiparin used after anastomosis caused less thickening of tunica media and reduced intimal hyperplasia but did not decrease lumen diameter and area. Dabigatran increased edema and inflammation but did not prevent intimal hyperplasia.

CONCLUSIONS

Bemiparin reduced intimal hyperplasia and prevented thrombosis angiogenesis, but dabigatran did not prevent intimal hyperplasia, and its anticoagulation effect was more than the antithrombotic effect.

Towards standardization of training and practice of reconstructive microsurgery: an evidence-based recommendation for anastomosis thrombosis prophylaxis

BACKGROUND

Despite significant improvements in survival rates, free flap failures still occur even in experienced hands and are most commonly due to arterial or venous thrombosis. In the absence of an evidence-based guideline on the prevention of thrombosis, we reviewed the literature to assess the evidence base for commonly used interventions aimed at its prevention.

METHODS

A comprehensive literature search was performed using the following keywords "free flap" and microsurgery with "pre-operative screening," "prevention of thrombosis," "ketorolac," "heparin," "low molecular weight heparin," "aspirin," "dextran," and "statins."

RESULTS

Thirteen clinical studies were included in this review. No high-level evidence is available to support any perioperative or postoperative interventions aimed at reducing the risk of flap thrombosis.

CONCLUSIONS

Higher level studies are needed to investigate the clinical use of antithrombotic medications in microsurgery; however, given the small failure rates in modern practice, these will need to be large multicenter trials in order to reach sufficient power.Level of Evidence: Level III, risk/prognostic study.

Impact of different antithrombotics on the microcirculation and viability of perforator-based ischaemic skin flaps in a small animal model

The effects of antithrombotic drugs on random and free flap survival have been investigated in the past, but the experimental and clinical results are not in agreement. A perforator-based critical ischaemia model was used to evaluate the effects of different perioperatively administered pharmaceutical agents on tissue ischaemia and to assess the potential additional haemorheological or vasodilative effects of antithrombotics on flap microcirculation. Combined laser Doppler flowmetry and remission spectroscopy revealed an increase in certain microcirculation parameters in most groups in comparison with saline controls, and these changes correlated with flap survival. Clopidogrel and hirudin significantly improved the amount of viable flap tissue in comparison with controls, while unfractioned heparin had a negative effect on flap survival. Low molecular weight heparin, aspirin, pentoxifylline, and hydroxyethyl starch had no impact on the amount of viable flap tissue. A higher complication rate was observed in all experimental groups, but only clopidogrel had a negative impact on the flap viability. Our results add to the body of evidence supporting the conclusion that perioperative antithrombotic treatment improves flap survival. Clopidogrel and hirudin are effective pharmacological agents that significantly increased the viability of perforator-based skin flaps in rats, but at a higher risk of postoperative bleeding.

Effect of Postoperative Aspirin on Outcomes in Microvascular Free Tissue Transfer Surgery

Objective

Examine if outcomes and complication rates for free flaps vary when postoperative aspirin is used as pharmacologic thromboprophylaxis compared with no anticoagulation.

Study Design

Case series with chart review.

Setting

Oregon Health and Science University, an academic medical center.

Subjects and Methods

A case series with chart review was performed using a prospectively maintained microvascular reconstructive database to identify cases of free tissue transfer between February 2006 and April 2010. Outcome variables included complications, flap failure, reexploration, and salvage. Chi-square analysis was performed to identify differences based on type of postoperative antithrombotic therapy.

Results

A total of 390 consecutive free tissue transfer procedures were performed; 184 received no postoperative thromboprophylaxis, 142 received aspirin, 48 received low molecular weight heparin or a combination of agents, and 16 received a heparin drip. The overall complication rate was 38%, with significantly more complications in the aspirin group compared with no prophylaxis ( P = .002). There was no significant difference in bleeding complications ( P = .192) or flap failure ( P = .839) between aspirin and no anticoagulation. There were more postoperative revisions in the aspirin group ( P = .039).

Conclusion

Postoperative thromboprophylaxis with aspirin after microvascular free tissue transfer does not provide an improvement in free flap survival and may be associated with a higher complication rate. Prospective, randomized studies are required to elucidate the role of postoperative pharmacotherapy for prophylaxis against microvascular thrombosis.

Anticoagulative strategies in reconstructive surgery--clinical significance and applicability

Advanced strategies in reconstructive microsurgery and especially free tissue transfer with advanced microvascular techniques have been routinely applied and continously refined for more than three decades in day-to-day clinical work. Bearing in mind the success rates of more than 95%, the value of these techniques in patient care and comfort (one-step reconstruction of even the most complex tissue defects) cannot be underestimated.

However, anticoagulative protocols and practices are far from general acceptance and – most importantly – lack the benchmark of evidence basis while the reconstructive and microsurgical methods are mostly standardized.

Therefore, the aim of our work was to review the actual literature and synoptically lay out the mechanisms of action of the plethora of anticoagulative substances.

The pharmacologic prevention and the surgical intervention of thrombembolic events represent an established and essential part of microsurgery. The high success rates of microvascular free tissue transfer as of today are due to treatment of patients in reconstructive centers where proper patient selection, excellent microsurgical technique, tissue transfer to adequate recipient vessels, and early anastomotic revision in case of thrombosis is provided. Whether the choice of antithrombotic agents is a factor of success remains still unclear. Undoubtedly however the lack of microsurgical experience and bad technique can never be compensated by any regimen of antithrombotic therapy. All the more, the development of consistent standards and algorithms in reconstructive microsurgery is absolutely essential to optimize clinical outcomes and increase multicentric and international comparability of postoperative results and complications.

Effects of pentoxyfilline and heparin on reperfusion injury island skin flaps in rats exposed to tobacco

BACKGROUND

Ischemia-reperfusion injury is believed to be a major cause of transferred skin flap failure. Cigarette smoking is known to be associated with endogenous antioxidant depletion, hypercoagulability, and cutaneous vasoconstriction. This investigation was carried out to study possible effects of pentoxyfilline or heparin on rat skin reperfusion injury under tobacco exposure.

MATERIALS AND METHODS

Thirty-six rats were randomized into two major groups: 18 were exposed to cigarette smoke during a 4 wk period prior to surgery; the remaining 18 underwent a sham smoking procedure. Each group was further divided into three equal subgroups: heparin, pentoxyfilline, and saline solution. One identical skin flap was raised in each animal. The vasculature of the flap was clamped for 3 h and reperfused for 5 min. A venous blood sample was obtained from the flap after reperfusion for serum malondialdehyde (MDA) and myeloperoxidase (MPO) analysis. Flap survival was assessed 7 d after the procedure.

RESULTS

The lipid peroxidation levels and flap necrosis were significantly higher in the cigarette-smoking group skin flaps. There was also a decrease of MPO activity in this group compared with the non-smoking group. Heparin-treated rats had significantly lower MDA levels and showed the most viable percent area among smoking rats.

CONCLUSIONS

These data suggest that heparin had a significant beneficial effect both on flap survival and on the lipid peroxidation reduction after smoke exposure in the rat axial-pattern skin flap subjected to ischemia and reperfusion injury. Pharmacologic therapy may represent an alternative way to counteract tobacco effects in flap surgery in emergency situations.

Desirudin reduces the rate of microvenous thrombosis in a rat model

OBJECTIVES

In an effort to evaluate pharmacologic agents for optimal anticoagulant prophylaxis in patients undergoing free tissue transfer, we evaluated the efficacy of desirudin (Canyon Pharmaceuticals, Hunt Valley, MD), a recombinant hirudin that acts as a direct thrombin inhibitor, using a rat model of microvenous thrombosis.

STUDY DESIGN

Randomized, blinded study using an in vivo rat model of microvenous failure.

METHODS

Thirty-two rats received either desirudin or saline in a randomized, blinded fashion 30 minutes prior to performance of a standardized thrombogenic procedure on rat femoral veins. Bleeding time, vessel patency, and presence of clot within the anastomosis were subsequently assessed. Appropriate statistical analyses were then performed.

RESULTS

There was a significant increase in vessel patency in rats treated preoperatively with desirudin compared to controls receiving saline (96.9% vs. 53.1%, P < .001). In evaluating patent vessels for non-occluding clot, 41.2% of control rats had non-obstructive clot at the site of anastomosis, versus 3.2% of rats treated with desirudin (P = .002). Bleeding times were longer in desirudin-treated rats than those that received saline (7.17 +/- 3 minutes vs. 5.15 +/- 1.2 minutes, P = .027).

CONCLUSIONS

The use of preoperative desirudin increases the rate of microvascular anastomotic patency, decreases the occurrence of non-occluding clot, and increases bleeding time in an in vivo rat model, indicating potential efficacy in patients undergoing microvascular free tissue transfer.

Head and neck reconstruction with free flaps: a report on 213 cases

The aim of this retrospective study is to review the experience of our institution in performing microvascular head and neck reconstruction between 2000 and 2004. During this period, 213 free flaps, including 146 radial forearm free flaps, 60 fibular flaps and 7 scapular flaps, were performed. Free flap success rate and complications were reported. The pre-treatment factors influencing these results were subsequently analyzed. Functional and aesthetic outcomes were evaluated by the same clinician. There were 14 free flap failures, giving an overall free flap success rate of 93.4%. Salvage surgery for recurrent cancer was the only factor correlated with a higher risk of free flap failure (P = 0.0004). The local complication rate was 20.9%. High level of comorbidity (P = 0.009), salvage surgery for recurrent cancer (P = 0.03) and hypopharyngeal surgery (P = 0.002) were associated with a higher risk of local complications. An unrestricted oral diet and an intelligible speech were recovered by respectively 76 and 88% of the patients. Microvascular free flaps represent an essential and reliable technique for head neck reconstruction and allow satisfactory functional results.

The Effect of Postoperative Anticoagulation on Microvascular Thrombosis

BACKGROUND

Numerous protocols exist to prevent thrombosis after free-tissue transfer. Many surgeons advocate using aspirin or other antiplatelet agents, but little objective evidence supports this practice. This study evaluates the rate of microvascular thrombosis in patients undergoing free-tissue transfer treated with or without antiplatelet agents.

METHODS

All consecutive free flaps from 2002-2005 at a single center were reviewed using a prospectively maintained database. Patients were in 2 groups based on postoperative anticoagulation administration. In group 1, 325 mg of aspirin was administered daily for 5 days postoperatively. In group 2, patients were treated with 5000 units of low-molecular-weight heparin (LMWH) per day until ambulating. Patient demographics, procedure type, diagnosis, adjuvant treatment, and procedure type were recorded. Outcome variables included microvascular thrombosis, partial or total flap loss, hematoma, bleeding, deep venous thrombosis (DVT), pulmonary embolism, and death.

RESULTS

Four hundred seventy patients underwent 505 microvascular free flaps to reconstruct oncologic defects. Two hundred sixty flaps (group A) received postoperative aspirin therapy; 245 flaps (group B) received LMWH therapy. Both groups were statistically similar in their composition. No statistically significant difference was noted between the 2 groups when comparing outcome variables including microvascular thrombosis, partial or total flap loss, hematoma, bleeding, DVT, pulmonary embolism, and death.

CONCLUSIONS

Postoperative anticoagulation choice has no statistically significant effect on the incidence of free flap complications, including bleeding, thromboembolism, and flap loss. We conclude that aspirin or LMWH therapy demonstrates equivalent outcomes when used as single-agent postoperative anticoagulation in oncologic free flap reconstruction.

Thrombospondin-1 limits ischemic tissue survival by inhibiting nitric oxide-mediated vascular smooth muscle relaxation

The nitric oxide (NO)/cGMP pathway, by relaxing vascular smooth muscle cells, is a major physiologic regulator of tissue perfusion. We now identify thrombospondin-1 as a potent antagonist of NO for regulating F-actin assembly and myosin light chain phosphorylation in vascular smooth muscle cells. Thrombospondin-1 prevents NO-mediated relaxation of precontracted vascular smooth muscle cells in a collagen matrix. Functional magnetic resonance imaging demonstrated that an NO-mediated increase in skeletal muscle perfusion was enhanced in thrombospondin-1-null relative to wild-type mice, implicating endogenous thrombospondin-1 as a physiologic antagonist of NO-mediated vasodilation. Using a random myocutaneous flap model for ischemic injury, tissue survival was significantly enhanced in thrombospondin-1-null mice. Improved flap survival correlated with increased recovery of oxygen levels in the ischemic tissue of thrombospondin-1-null mice as measured by electron paramagnetic resonance oximetry. These findings demonstrate an important antagonistic relation between NO/cGMP signaling and thrombospondin-1 in vascular smooth muscle cells to regulate vascular tone and tissue perfusion.

Anticoagulation therapy in microsurgery: a review

The advent of microsurgical tissue transfer including replantation greatly has expanded the scope of reconstructive surgery. There are few recent innovations in anticoagulation therapies for microsurgery, however, and anastomotic thrombosis remains an occasional cause of surgical failure. No consensus exists on the ideal anticoagulation protocol for microsurgery. This article reviews major pharmacologic modalities of anticoagulation, delineates the mechanism of action and study of efficacy of each agent, and compares the risks and benefits of popular anticoagulation therapies. Finally, it examines available human outcomes-based data and attempts to provide a glimpse of the future direction of microsurgical anticoagulation research.

The Effect of Fondaparinux Versus Enoxaparin in the Survival of a Congested Skin Flap in a Rabbit Model

BACKGROUND

The purpose of this study was to evaluate the effects of fondaparinux, a selective antithrombin III agonist, in comparison to the low-molecular-weight heparin enoxaparin in the survival of a congested skin flap.

MATERIALS AND METHODS

Eighteen axial-pattern auricular flaps were performed on rabbits using a well-described congested flap model. Animals were randomized into 2 treatment groups, enoxaparin (n = 6) and fondaparinux (n = 6), and a control group (n = 6) that received no treatment. Skin flap survival area was measured postoperatively at 7 and 14 days.

RESULTS

The groups that received fondaparinux and enoxaparin had similar mean flap survival areas and were not statistically different. However, both treatment groups significantly increased flap survival compared with controls (P < 0.014).

CONCLUSIONS

Fondaparinux, like enoxaparin, significantly improves survival of congested flaps in rabbits. Its use instead of enoxaparin may be warranted, given that it eliminates the risk of heparin-induced thrombocytopenia. Further study in humans is warranted.