Comparison of the influence of intralumenal irrigation solutions on free flap survival

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.

Technical tips for safe perforator vessel dissection applicable to all perforator flaps

The introduction of perforator flaps by Koshima and Soeda in 1989 was met with much animosity in the surgical community. The flaps challenged conventional teaching and were often branded as being unsafe. Surgeries using perforator flaps are now routinely practiced all over the world, with increasing emphasis on minimizing donor site morbidity, and perforator flaps are becoming the current gold standard. The simple principles and techniques of perforator dissection can be applied to all perforator flaps, provided the surgeon has an intimate knowledge of the regional anatomy. Thus, virtually any piece of skin can be harvested as long as it incorporates a feeding vessel. This article highlights the essential techniques in planning and raising perforator flaps and the common pitfalls to be avoided.

[Evidence-based medicine and prevention of thrombosis in microsurgery. Critical review]

Prevention of thrombosis in microsurgery was the point of numerous publications without any referenced protocol. The question of this article was to know if it existed, for a patient who needed a microsurgical procedure, any medical treatment used, proved to lower the thrombotic risk. Using principles of evidence-based medicine, we observed that none of the medical treatments proved efficiency on preventing vascular thrombosis, arterial or venous. The low molecular weight heparins (LMWH) could be used on postoperatives to prevent the deep venous thrombosis of lower limbs but not to lower specially the microvascular thrombosis rate. Aspirin did not improve the positive rates and its adjunction to LMWH increased the bleeding. The evidence-based medicine, as we used it here, permits to conclude that the microsurgeon should not wait any miracle of the medical treatments. Until scientific studies prove efficacity of a treatment, the surgeon has to make a personal choice: keeping habits or following evidence-based medicine. The experience of the surgeon, of the anesthetist and of the paramedical team seem to be the main point to decrease the thrombotic risk during the multidisciplinary healing care of the patient.

Ischemia and reperfusion in skin flaps: effects of mannitol and vitamin C in reducing necrosis area in a rat experimental model

PURPOSE: The aim of the present study was to develop an experimental model of ischemia-reperfusion injury in rat skin flap and to verify the effect of mannitol and vitamin C on reducing necrosis area. METHODS: A 6-x 3-cm groin skin flap was raised and submitted to 8 hours of ischemia by clamping the vascular pedicle and to 7 days of reperfusion. The animals were divided in four groups: S1 and S2 (10 animals each) and C and T (14 animals each). In groups S1 and S2 skin flaps were not submitted to ischemia and animals received lactated Ringer's solution (S1) and antioxidant solution (S2 ). In groups C and T, flaps were subjected to 8 hours of warm ischemia and animals received Lactated Ringer's solution (Group C) and antioxidant solution immediately before reperfusion, (Group T). Flap survival was evaluated on the seventh day using a paper template technique and computer-assistant imaging analysis of necrotic and normal areas. RESULTS: Statistical analysis showed no area differences between groups C and T. CONCLUSION: The experimental model provided consistent necrotic area in control groups and drugs used were not effective in improving skin flap survival.

Pharmacologic optimization of microsurgery in the new millennium

LEARNING OBJECTIVES

After studying this article, the participant should be able to: 1. Understand the mechanisms by which the three most common antithrombotic agents work. 2. Be familiar with accepted dosing levels for the three agents. 3. Understand the rationale for their use and formulate an algorithmic approach to microvascular thrombosis. Microsurgical anastomoses are largely technically dependent; however, there exists a finite rate of failure, with often devastating consequences. Pharmacologic prophylaxis and intervention are used extensively in microsurgical cases, yet a unified algorithm does not exist among the various basic science and clinical studies in the literature. This results in a confusing and nonstandardized practice based on anecdotal experiences. The purpose of this article is to review the literature on this topic and synthesize a practical clinical management algorithm for pharmacologic therapy in microsurgery.

A phase II trial of intraluminal irrigation with recombinant human tissue factor pathway inhibitor to prevent thrombosis in free flap surgery

A multicenter, multinational, blinded, randomized, parallel-group, phase II study was conducted to investigate the use of recombinant human tissue factor pathway inhibitor (rhTFPI; SC-59735) as an antithrombotic additive to the intraluminal irrigating solution during microvascular anastomosis in free flap reconstructive surgery. A total of 622 patients undergoing free flap reconstruction were randomly assigned to three groups. For each group, a different intraluminal irrigating solution was administered at completion of the microvascular arterial and venous anastomoses and before blood flow to the flap was reestablished: rhTFPI at a concentration of 0.05 or 0.15 mg/ml (low-dose or high-dose group, respectively) or heparin at a concentration of 100 U/ml (current-standard-of-practice group). There were no other differences in treatment among the groups. Patient characteristics, risk factors, and surgical techniques used were similar among all three groups. Flap failure was lower (2 percent) in the low-dose rhTFPI group than in the high-dose rhTFPI (6 percent) and heparin (5 percent) groups, but this difference was not statistically significant (p = 0.069). There were no significant differences in the rate of intraoperative revisions of vessel anastomoses (11 percent, 12 percent, and 13 percent) or postoperative thrombosis (8 percent, 8 percent, and 7 percent) among the low-dose rhTFPI, high-dose rhTFPI, and heparin groups, respectively. The rate of postoperative wound hematoma was significantly lower in the low-dose rhTFPI group (3 percent) than in the high-dose rhTFPI (8 percent) and heparin (9 percent) groups (p = 0.040). There were no differences in blood chemistry or coagulation values among the three study groups. Other than hematomas, there were no differences in the incidence or severity of adverse reactions among the three groups. It is concluded that use of rhTFPI as an intraluminal irrigant during free flap reconstruction is safe, well tolerated, and as efficacious as use of heparin for preventing thrombotic complications during and after the operation. Furthermore, the lower dose of rhTFPI (0.05 mg/ml) may reduce the occurrence of postoperative hematoma and help prevent flap failure.

Effect of clamp versus anastomotic-induced ischemia on critical ischemic time and survival of rat epigastric fasciocutaneous flap

BACKGROUND

There are many models used to explore ischemic-related phenomena. The rat epigastric fasciocutaneous flap model is the one most commonly used. Critical ischemic time is the maximum ischemic insult that tissue can undergo and still remain viable. Experimentally, ischemia is induced either by clamping the vascular pedicle or by dividing the pedicle then performing microvascular arterial and venous anastomosis. We sought to determine what effect the different methods of inducing ischemia have on the critical primary ischemic time and, thus, flap survival.

METHODS

A right 3 cm x 6 cm groin flap based on the inferior epigastric vessels was raised in each rat. Ischemic times of 4, 6, 8, or 10 hours were induced either by placing temporary occlusion clamps on each vessel of the vascular pedicle (island pedicle group) or by ligation and division of the pedicle with subsequent microvascular anastomosis (free flap group). Survival was assessed at 7 days.

RESULTS

The primary ischemic time at which one half of free flaps are predicted to die was calculated to be 7.60 hours, compared with 6.09 hours for the island pedicle flaps (p<.05).

CONCLUSIONS

Fasciocutaneous flaps undergoing ligation and anastomosis are more resistant to ischemia than are those undergoing clamping of the pedicle. Possible etiologic factors responsible for this experimental finding are discussed.

1457 years of microsurgical experience

Microsurgery is a relatively new field of surgery involving various methods and practices that are currently evolving. Our goal was to register the current practices employed by the members of the American Society for Reconstructive Microsurgery. A survey was mailed to the 319 members of the society, resulting in a response rate of 33 percent (106 of 319). The data reflect the combined experience of 10,839 free-tissue transfers and 3487 digital and upper and lower extremity replants over a 4-year period between 1990 and 1994. Practices employed, such as pharmacologic adjuvant therapy, monitoring techniques, flap types, and success rates reported by the members of the American Society for Reconstructive Microsurgery, were analyzed.

Topical application of low molecular weight heparin in a rabbit traumatic anastomosis model

Low molecular weight heparins (LMWHs) are antithrombotic drugs composed of lower molecular weight components of heparin with an apparent molecular weight in the range of 4.0-8.0 KDA. These agents have been used clinically for several years. They have different mechanisms of action compared to heparin, a longer half-life and much higher bioavailability. Anticoagulant drugs such as heparin have been used topically in our previous studies to avoid bleeding complications observed with systemic administration. In this study, low molecular weight heparin (Certoparin, Sandoz) was topically administered in a rabbit ear arterial crush-avulsion thrombosis model and compared with heparin. The animals were divided into three groups: LMWH, heparin and saline control groups. In the LMWH group, the patency rate was 71% (10 of 14) at both 1 and 7 days. The patency rate in the heparin group was 95% (19 of 20) at 24 hrs and 80% (16 of 20) at 7 days. In the saline control group, the vessel patency rate was 17% at 24 hrs and 13% at 7 days. Clotting times such as ACT, PT and APTT performed on samples drawn one hour after drug administration were within the normal ranges for both the control and the treatment groups. The results suggest that topical administration of LMWH prevents the occurrence of thrombosis at the traumatic anastomosis site to a similar degree as heparin.

Periadventitial delivery of heparin in the prevention of microvenous thrombosis

PURPOSE

In spite of advances in technique and instrumentation, microvascular free tissue transfer remains associated with a persistent risk of flap failure. The use of systemic anticoagulants to overcome the formation of vasoocclusive thrombi at reactive anastomotic sites is associated with a high rate of flap hematoma and is ill advised in the operative setting. The purpose of this study was to investigate the use of a biodegradable, nontoxic polymer gel (polyvinyl alcohol, PVA) to effect a sustained localized release of perivascular heparin around thrombogenic venous anastomoses.

MATERIALS AND METHODS

A modified adventitial inclusion model was created in the femoral vein of 64 adult female Sprague-Dawley rats. Animals were divided into four experimental groups: 1) no treatment (controls), 2) periadventitial PVA gel contained in a vicryl chamber, 3) periadventitial PVA gel mixed with heparin, and 4) systemic heparin (intravenous pump). Patency rates in the femoral vein were checked at 10 minutes, 1 hour, 1 day, and 4 days after surgery. Systemic coagulation parameters and histology (scanning electron microscopy, SEM) were assessed in representative animals from all groups.

RESULTS

Patency rates for experimental groups showed a significant improvement in animals treated with PVA/heparin and systemic heparin over controls. Wound hematomas occurred in 7 of 16 animals in group 3, and in 4 of 16 animals in group 4. Activated partial thromboplastin times were elevated in group 4 only (> 150 seconds).

CONCLUSIONS

Continuous release of periadventitial heparin using a polymeric delivery system may represent an efficient means of attenuating the reactivity of microvenous anastomoses without affecting systemic coagulation parameters. In this model, however, its use was associated with a high rate of local wound hematoma.

Modified crush-avulsion anastomosis model on the rat femoral vein

A crush-avulsion anastomosis model was established on the rat femoral vein. Saline or heparin was used as a luminal topical agent and was allowed to contact the damaged endothelium for 10 min. Patency and coagulation parameters were investigated for 1 week. The heparin treated group had a patency rate of 93% at 1 hr vs. 13% for the saline treated group (P < 0.001). At 7 days, the heparin treated group had an 87% patency vs. 7% for the saline-treated group (P < 0.001). Scanning electron micrography (SEM) provided evidence of the deposition of the components of early thrombosis in the crushed venous wall. In contrast, the SEM of the heparin treated group shows a paucity of any evidence of thrombus. These results indicate that the rat vein crush-avulsion model is a reliable and reproducible thrombosis model with low patency. The methods used with the topical agent may improve the patency rate in crush avulsion injuries.

Effect of phosphate concentration in buffered irrigating solutions on arterial thrombosis

The concentration of phosphate in buffered saline irrigation solutions was evaluated for its effect upon the incidence of arterial thrombosis. A rabbit thrombosis model of combined intimal abrasion and twisted pedicle in the rabbit central ear artery was used. Higher concentrations of phosphate (20 mM) in normal saline yielded a lower thrombosis rate at 7 days postoperatively (50%) in comparison to 5 mM phosphate (89% thrombosis rate; P < 0.05). A standard phosphate-buffered salt solution (Dulbecco's; 9.5 mM phosphate with potassium, calcium, and magnesium salts) also had a high thrombosis rate (91%). This study demonstrates that subtle variations in the irrigation solution can have profound effects upon arterial thrombosis.

Current status of topical antithrombotic agents in microvascular surgery

Several technical advances over the years have allowed microsurgery to be successful. However, thrombosis, particularly at the anastomosis site, remains a complication of microvascular surgery. Various preventive measures, including drugs, have been used to improve microvascular surgical anastomotic patency rates. The purpose of this article is to review the literature and the current status of topical antithrombotic agents. From this review along with laboratory investigations it is concluded that a combination of topical as well as systemic agents offers the best patency rates. However, the "ideal" antithrombotic agent is yet to be discovered and investigations need to be continued in order to improve or eliminate the complication of microvascular thrombosis. But the importance of atraumatic technique cannot be overemphasized.

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.