Experimental models for evaluating antithrombotic therapies in replantation microsurgery

Breast Reconstruction Free Flap Failure: Does Platelet Count Matter?

BACKGROUND

Microvascular free tissue transfer is an increasingly popular modality for autologous tissue breast reconstruction. However, flap failure remains an ominous risk that continues to plague surgeons and patients even in the setting of meticulous surgical technique and monitoring. Venous and arterial thromboses are the leading causes of free flap failure. The purpose of this study was to determine whether thrombocytosis is associated with breast free flap failure.

METHODS

A retrospective study was conducted of breast reconstruction with free flaps in North America between 2015 and 2020 using the National Surgical Quality Improvement Program database. Patient comorbidities and preoperative laboratory tests were used to determine risk factors for free flap failure.

RESULTS

During the study interval, 7522 female patients underwent breast reconstruction with free flaps, and flap failure occurred in 2.7% patients (n = 203). In multivariate regression analysis, breast free flap failure was significantly higher in patients smoking cigarettes within the past year (P = 0.030; AOR, 1.7) and dyspnea on moderate exertion or at rest (P = 0.025; AOR, 2.6). Furthermore, each 50 K/mcL elevation in platelet count was independently associated with an increased odds of flap failure (P < 0.001; AOR, 1.2). Patients experienced significantly higher rates of flap failure with platelet counts greater than 250 K/mcL (P = 0.004), which remained significant through progressively increasing thresholds up to 450 K/mcL.

CONCLUSIONS

Platelet count greater than 250 K/mcL is associated with progressively increasing risk of free flap failure in breast reconstruction. Future studies of personalized patient anticoagulation protocols based on hemostatic metrics may improve free flap survival after autologous tissue breast reconstruction.

Management of complications with flap procedures and replantation

Replantation and flap procedures employ microvascular techniques to salvage or reconstruct a severely damaged limb or digit. The most devastating complications include complete or partial flap loss, or replantation failure due to vascular complications. Often, these complications can be prevented by appropriate patient selection, careful surgical planning, meticulous technique, and proper postoperative management. This article discusses complications related to replantation and flap procedures in the upper limb, focusing on preventing and managing these complications.

Murine arterial thrombus induction mechanism influences subsequent thrombodynamics

BACKGROUND

The mechanism of thrombotic induction in experimental models can vary greatly, as can the applied evaluative measures, making comparisons among models difficult.

OBJECTIVES

This study comparatively evaluated the arterial thrombodynamic response among injury mechanisms.

METHODS

Thrombotic responses were induced in mouse carotid arteries, with subsequent intravital imaging using rhodamine-6G-labeled platelets to quantitate platelet accumulation over 30minutes. Nine induction methods were evaluated: brief pinch, temporary hard ligation, cautery/heat, needle puncture, intralumenal wire (scratch), intralumenal adventitia/collagen (2 different models), and brief exposures to either iron-based surface electrolytic injury or ferric chloride.

RESULTS

The accumulation of platelets was variable among induction methods, with a greater response to more severe injury mechanisms, free radical injury, and exposed collagen. Temporal profiles were generated by normalizing data to peak platelet accumulation for each run; rapid platelet development and subsequent detachment were found for mechanical injuries that maintained vessel integrity (pinch and ligation injuries), with more sustained growth for more severe mechanical (wire) injury or breach of the vessel (needle puncture or intralumenal collagen). A delayed but extended temporal response was seen with free radical injury (both electrolytic and ferric chloride).

CONCLUSIONS

These findings demonstrate a dependence of platelet thrombodynamics on the method of induction, with collagen exposure causing greater, more prolonged activity, while free-radical injury effected a delayed but sustained platelet thrombus formation with slower resolution. A better understanding of how these various injury models relate to clinical causes of arterial thrombosis is needed for optimal translational interpretation of murine models of thrombosis.

Perioperative management of antithrombotic medication in head and neck reconstruction-a retrospective analysis of 137 patients

PURPOSE

Various protocols exist to prevent thrombosis after free flap surgery in the head and neck. This study reviews the outcome and incidence of perioperative complications in patients undergoing head and neck reconstruction, simply using subcutaneous low-molecular-weight heparin.

MATERIALS AND METHODS

A total of 137 free tissue transfers performed between 2007 and 2010 were reviewed. All patients received a general thrombosis prophylaxis with subcutaneous low-molecular-weight enoxaparin. No aspirin, dextran, or additional antithrombotic medication was administered.

RESULTS

Overall flap survival was 97.1%. A total of 3 complete and 1 partial flap loss occurred, all due to venous thrombosis. Five cases of venous congestion were successfully revised.

CONCLUSION

The free flap survival rate using simple subcutaneous heparin seems to be equivalent to other management regimens. Therefore, we suggest that no additional antithrombotic treatment is needed for patients who undergo head and neck reconstruction with free tissue transfer.

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.

Thrombosis and altered expression of intercellular adhesion molecule-1 (ICAM-1) after avulsion injury in rat vessels

This study was undertaken to characterize the relative degrees of arterial and venous trauma after graded avulsion injuries. Rat femoral arteries and veins were subjected to reproducible avulsion injuries using forces of between 60 and 220g. Thrombotic occlusion occurred at lower avulsion forces in veins than in arteries. Histologic and scanning electron microscopic analysis indicated increased endothelial disruption and exposed elastic lamina with increasing avulsion force in both vessels, but more prominently in arteries. Intercellular adhesion molecule-1 (ICAM-1) mRNA expression was evident at 3 and 6 hours after avulsion injury in veins, but only with higher avulsion-force injuries in arteries. ICAM-1 mRNA expression was not found in either vessel before or after this 3 to 6 hour post-injury interval. These results indicate that the amount of avulsion force to which traumatized extremity vessels are subjected has a direct effect on the degree of intimal injury and subsequent thrombosis.

Salvage of free flaps after venous thrombosis: Case report

Venous thrombosis of a free flap is a serious complication in microsurgery. Several agents with the ability to dissolve an occluding thrombus exist. Recombinant tissue plasminogen activator (rt-PA) seems the most effective. We present our experience with a procedure that was successful in elimination of the occluding thrombus in two patients.

Catecholamine sensitivity in the rat femoral artery after microvascular anastomosis

Tissue can demonstrate vasospastic instability after microvascular anastomosis. This study investigates the in vitro effect of increasing concentrations of phenylephrine on the rat femoral artery after microvascular anastomosis. Bilateral groin flaps based on the inferior epigastric artery were raised on 55 Wistar male rats. On the test side, a microvascular anastomosis was performed, but not on the control side. On days 2-12 postoperatively, the rats were sacrificed and the femoral arteries harvested and suspended in increasing concentrations of phenylephrine. The vascular tone on the test and control sides were recorded and compared. Increased sensitivity was found on the test side as compared with the control side (P = 0.000). This supersensitivity to phenylephrine was blocked by the addition of phentolamine and it is believed to be the result of sympathetic denervation, which occurs when the sympathetic fibers are cut during the harvesting of the flap. The resulting vascular instability is believed to contribute to flap failure.

Comparison of arterial and venous patency in a rat model of subendothelium-stimulated thrombosis

The effectiveness of anticoagulants and platelet aggregation inhibitors was compared using comparable rat models of arterial and venous thrombosis. A mechanical endothelium-denuding injury was created on the lumenal surface of donor Lewis rat carotid arteries. These were cut into 4-5 mm lengths and grafted into femoral veins and arteries of recipient syngeneic rats using microvascular anastomotic techniques. Recipients received either systemic heparin, or aspirin with dipyridamole, or saline (control). In the arteries, the 1-day patency rate was 94% in the heparin-treated rats, but only 50% in the aspirin/dipyridamole group and 44% in the control group. The venous patency rate was 56% in the heparin group, 31% in the aspirin/dipyridamole group, and 0% in the control group. This unique model for comparing thrombosis in arteries and veins shows that anticoagulation is more effective than inhibition of platelet aggregation in the rat arterial system, with less of a differential effect in the venous system.

In vitro platelet aggregation studies in microvascular surgery research: a method in the rat model

There is now a growing awareness of the central role of platelet function in microvascular thrombosis. Platelet aggregation studies remain one of the most useful ways of studying platelet function and response to different stimuli. This brief communication highlights some of the main variables that can affect platelet aggregation in rats and emphasizes the existence of important differences in these variables compared with human platelet aggregation.

Estudo experimental do uso de um antagonista do receptor da glicoproteína IIb/IIIa das placentas na prevenção de tromboses em microanastomoses vasculares

O autor comparou, experimentalmente, a eficácia da droga abciximab, um antagonista do receptor da glicoproteína IIb/IIIa das plaquetas, na prevenção da trombose nas microanastomoses arteriais em ratos Wistar. Utilizou 20 animais, dos quais 10, do grupo controle, receberam solução salina e 10 receberam abciximab, na concentração de 0,8mg/kg, injetados na veia femoral. Trinta minutos após a administração da solução salina ou abciximab, todos os animais foram submetidos ao mecanismo provocador de trombose vascular da artéria femoral do lado oposto ao utilizado para administração da droga, por meio de um trauma externo promovido por aparelho IMPACTOR, desenvolvido pela New York University para padronização de lesão da medula nervosa, o que padronizou a lesão arterial. Todos os animais foram submetidos à microanastomose vascular com mononáilon 10-0, em pontos separados, no local do trauma externo. Foram realizados testes para analisar a perviabilidade vascular da artéria femoral no período de 10, 20 e 30 minutos após o término da anastomose. Após este período, todas as artérias femorais submetidas às microanastomoses foram ressecadas e analisadas em microscopia óptica para avaliar a presença de formação de trombos. Após a análise estatística dos dados, o autor concluiu que o uso do antagonista do receptor da glicoproteína IIb/IIIa das plaquetas diminuiu a incidência de tromboses nas microanastomoses vasculares.

Antithrombotic potencies of enoxaparin in microvascular surgery: influence of dose and administration methods on patency rate of crushed arterial anastomoses

This study evaluated the influence of the dose and administration methods of enoxaparin, a low-molecular-weight heparin, on the patency rate of crushed rat femoral arteries following anastomosis. An impact crush with a 25-kg magnitude was applied to a 2-mm segment of 100 rat femoral arteries, followed by anastomosis. The arteries were divided into five groups: group 1 received systemic enoxaparin alone with a relatively high dose (45 IU) twice a day for 3 days; groups 2 and 3 received topical irrigation with a lower (15 IU/mL) concentration and a higher (45 IU/mL) concentration, respectively; group 4 received systemic and topical application at a lower (15 IU) dose and concentration (15 IU/mL); and group 5 received systemic and topical application at a higher (45 IU) dose and concentration (45 IU/mL). The results of this study demonstrate the following: (1) topical irrigation with enoxaparin at a concentration of 45 IU/mL-three times higher than that recommended for clinical use adjusted by body weight (15 IU/mL)-is effective for antithrombotic action; (2) a combination of systemic and local application does not offer additional benefit in the patency rate when compared to local irrigation alone; (3) systemic administration alone does not prevent thrombus formation; and (4) enoxaparin is potentially useful to enhance the patency rate in compromised microvessels.

Comparison of the antithrombotic effect of the new recombinant hirudin HBW 023 and heparin in small arteries and veins

The study was composed of two parts, arterial and venous; the 24 rabbits in each arm were divided into three equal groups and treated with either saline (control) or 1 mg/kg body weight (bw) of a new recombinant hirudin HBW 023 given as a single dose or standard heparin 1 mg/kg bw followed by quarter doses of heparin every half hour. Both arms included a control group given equal volumes of saline. The study continued for 2 hours. The following parameters were evaluated: bleeding times from arteriotomy/venotomy, patency rates, and the weights of thrombotic materials. Plasma samples were taken for evaluation of anti-factor lla (anti-Flla), anti-factor Xa (anti-Fxa), and activated partial thromboplastin time (APTT). The bleeding times were significantly prolonged but were still within clinically acceptable levels, following both HBW 023 and heparin treatment. Patency rates were significantly improved in both the arterial and venous arms following HBW 023 and heparin treatment. A corresponding reduction in thrombotic materials was simultaneously registered in the arterial and venous arms following HBW 023 and heparin treatment. Hirudin (HBW 023) significantly improved the reduction compared with the heparin group in the venous study. Heparin treatment caused expected high levels of anti-FXa and prolonged APTT, but hirudin, being at least as effective in antithrombotic potency, changed the pre-treatment levels only slightly. Anti-Flla levels were immediately increased by both heparin and hirudin (the highest levels) but reached low levels after 2 hours of single-dose hirudin treatment, despite a simultaneously excellent antithrombotic effect. We conclude that the new recombinant hirudin HBW 023, like standard heparin, is a highly efficient antithrombotic agent in both small arteries and veins following severe vessel wall trauma. The bleeding times were simultaneously prolonged significantly (still within acceptable limits) following both heparin and HBW 023 treatment in the arterial arm but were only prolonged following heparin treatment in the venous arm. The advantage of r-hirudin HBW 023 was furthermore the single dose administration.

Comparative study on the use of anticoagulants heparin and recombinant hirudin in a rabbit traumatic anastomosis model

Antithrombotic drugs, such as heparin, have been used in the clinics for a long time. Heparin acts by binding with antithrombin III to form a complex thereby enhancing the activity of antithrombin III to inactivate coagulation factors IIa, IXa, Xa, XIa and XIIa. Hirudin is a new antithrombotic agent and is reported to be much more powerful than heparin on a gravimetric basis. When both are administered systemically, one of the common complications seen is bleeding. Some previous studies have shown that local vascular endothelial concentrations of heparin are 30 to 7500 times greater than those found in the circulating blood. In order to avoid such complications, topical administration of antithrombotic drugs may be an ideal route of administration. The rabbit ear arterial crush-avulsion thrombosis model was used in this study. The animals were divided into five groups: one control group and four treatment groups which received varying concentrations of heparin and hirudin. In the saline control group, the patency rate was 19.23% at 24 hrs and 15.38% at 7 days. A higher patency rate at 7 days was obtained in groups treated with high concentration of heparin and hirudin. ACT, PT and APTT performed on samples drawn one hour after drug administration were within the normal range in both the control and the treatment groups. Scanning electron microscopy revealed the different extent of the clots on the injured intimal surfaces of the vessels in different groups. The results indicate that high concentrations of topically administered heparin or hirudin minimize the systemic complications and maximize the antithrombotic effects.

Comparative study of intraarterial and intravenous anticoagulants in microvascular anastomoses

Using a rat femoral artery crush-avulsion model previously described by the authors (Rooks et al.: Microsurgery 14: 130-134, 1993), we analyzed the relative efficacy of intraarterially delivered anticoagulants against similar systemically administered intravenous anticoagulants with double blinded experimentation. The model uses a standardized crush of approximately 0.3 J and a standardized avulsion. This is followed by vascular stasis for 90 seconds after vessel repair. All rats were limited to 175 to 225 gm in weight to control vessel size. Urokinase, heparin sodium, and dextran (40,000 Dalton) were evaluated in this study. A statistically significant (p-value = 0.02) increase in urokinase efficacy was found with intraarterial delivery. (Patency rate increased from 40% to 100%). No advantage to intraarterial delivery was evident with either dextran or heparin. There was a dose related improvement in patency with heparin that was unaffected by delivery route. (Patency increased from 30% to 80% with a statistical p-value of 0.018.)

Refinement of the rat crush-avulsion femoral artery injury model

A model for studying arterial crush-avulsion injuries in the rat is described. The model uses a standardized crush of approximately 0.3 joules and a standardized avulsion. The crush is accomplished by gravity acceleration of a 400 g weight over a distance of 7.5 cm. The weight impacts an anvil over the artery distributing the force of the impact over a 10 mm length of the vessel. The avulsion is accomplished by a hemostat attached to a second, 120g weight. Vascular stasis for 90 sec after vessel repair in a 175-225 g rat will consistently result in an 80% anastomotic failure. The model allows evaluation of anticoagulant effects singly or in combination. Agents may be given either systemically by intravenous route or locally by intraarterial route.

Development of a mouse intestinal transplantation model

We have recently developed a mouse intestinal transplantation model. The proximal segment of donor jejunum is transplanted into the recipient in a heterotopic position. End-to-side anastomoses are performed between donor aorta and recipient aorta and between donor portal vein and recipient inferior vena cava. Mortality rates were initially high due to shock, arterial thrombosis, and postoperative sepsis. Refinements in surgical techniques reduced these complications, resulting in a high rate of success. Important technical factors included (1) minimizing ischemic injuries to the graft in both the donor and the recipient, (2) using an aortic patch and elliptical aortotomy for anastomosis, (3) administering large volumes of crystalloid to maintain normal blood pressure during the donor and recipient surgeries, and (4) using broad-spectrum antibiotics as postoperative prophylaxis. The mice with isografts had normal intestinal function and histology when they were sacrificed 1 month after surgery. This new model of small bowel transplantation will be a useful tool to study the immunology of intestinal grafting at the molecular level.

Low-molecular-weight heparin exerts an early antithrombotic effect in small arteries and veins following severe trauma

Administration of low-molecular-weight heparin (LMWH) and standard heparin was studied by evaluating vessel bleeding, patency, and thrombotic material following severe vascular trauma. Arteriotomy and intimectomy or venotomy and intimectomy were performed on small rabbit arteries or veins in two separate blinded studies. All vessels were closed using a continuous microvascular suture. Patency and weight of thrombotic materials were evaluated 2 hr after reperfusion. In the arterial study, two groups of 23-24 arteries were treated with saline or LMWH systemically. Bleeding times were 89 +/- 15 sec in the control group and 103 +/- 27 sec in the LMWH group; there was no significant difference between the groups. Patency was significantly increased in the LMWH group (79%) compared to the control group (52%). The weight of thrombotic material in the LMWH group (1.39 +/- 0.20 mg per artery) was significantly different compared to the control group (2.19 +/- 0.22 mg per artery). In the venous study, 65 veins were divided into three groups (21-23 vessels/group) and treated with systemic saline, heparin, or LMWH. Bleeding times in the conventional heparin group (37 +/- 7 sec), the control group (23 +/- 3 sec), and LMWH group (22 +/- 4 sec) were not significantly different. The patency rates were significantly increased in the heparin (42%) and LMWH (39%) groups compared to the control group (0%). The weight of thrombotic material in each vein was significantly less in the LMWH (1.07 +/- 0.24 mg) and heparin (1.78 +/- 0.52 mg) groups than in the control group (3.78 +/- 0.29 mg).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of venous flow alterations upon patency of rat femoral vein anastomoses

The rat femoral vein has become a standard model for laboratory training in microvascular anastomotic technique as well as for research investigations into factors affecting venous patency. This study examined the short-term patency (1 and 7 days) of rat vein anastomoses. The influences upon patency of epigastric flap creation and distal femoral vessel ligation (epigastric flow only) were explored. In a separate experiment, blood flow from the femoral vein was determined through catheter collection of venous efflux; the influences of island epigastric flap creation and distal femoral ligation on flow rates were explored. It was found that 82% of basic femoral vein anastomoses were patent at one day, while 100% of anastomoses associated with an epigastric flap and ligated/transected distal femoral vessel circulation (creating a low-tension anastomosis) were patent (P less than 0.01). With distal femoral vessel ligation and no transection (normal tension at the repair), anastomoses were patent in 90% of the veins when an epigastric flap was also raised, and in 60% when a flap was not created. When a flap was raised without disturbing the distal femoral circulation, vein patency was 75% at one day. When the vein anastomosis was performed with distal femoral vein ligation, the patency rate was 50%. All veins patent at 1 day were also patent at 7 days post-op; 96% of veins clotted at 1 day were found to be patent at 7 days. The venous efflux was not found to vary significantly when an epigastric flap was raised.(ABSTRACT TRUNCATED AT 250 WORDS)

Rat femoral vein-to-vein grafts as a microvascular practice model: factors that influence patency

The rat femoral vein has become a standard model for microvascular anastomosis practice as well as for research investigations into various manipulative influences upon venous patency. Although vein grafts to the rat artery are the focus of many experimental studies, few reports have investigated vein-to-vein grafts. This study examines the short-term patency (1-3 days) of vein grafts interpositioned to the rat femoral vein. Several factors are studied for their ability to alter the patency rate. The results indicate that patency is difficult to achieve following the creation of a second serial anastomosis (construction of a vein-to-vein graft). Systemic heparin consistently improves patency rates, and trends toward increased patency are seen for reduction in longitudinal tension of the repaired vessel. It is also implied that a deeper understanding of venous hemodynamics and thrombotic events may lead to improved methodologies in the clinical applications of microvenous repairs. These results indicate that rat vein-to-vein grafts may provide a challenging microvascular training model, while introducing the novice microsurgeon to some of the complicating factors encountered with microvascular grafting.