Evaluation of the effect of pharmacologic agents on crush-avulsion arterial injuries: a scanning electron microscopy study

Low-molecular-weight heparin salvage in pedicled flap reconstruction in head and neck: a prospective cohort study

OBJECTIVE

To determine if systemic administration of low-molecular-weight heparin impacts venous compromise in loco-regional flap reconstruction for head and neck subsites.

METHODS

This prospective study was conducted on patients who had developed features of venous compromise of the flap. The case group received low-molecular-weight heparin (dalteparin).

RESULTS

Of the 73 patients who developed venous congestion, low-molecular-weight heparin was administered in 47 patients. In the low-molecular-weight heparin subset, 23 patients had either reversal or non-progression of venous compromise (48.9 per cent). Of the patients who had no response to low-molecular-weight heparin rescue, complete necrosis was seen in 4 and partial flap necrosis was observed in 19. The corresponding numbers in the control group were 13 and 12, respectively (odds ratio 23.9, p = 0.002). Additionally, the low-molecular-weight heparin arm had a lower incidence of partial or complete flap necrosis (p = 0.002).

CONCLUSION

Low-molecular-weight heparin salvage, when instituted early, is likely to result in a significant reduction in flap-related morbidity.

Use of electron microscopy to study platelets and thrombi

Electron microscopy has been a valuable tool for the study of platelet biology and thrombosis for more than 70 years. Early studies using conventional transmission and scanning electron microscopy (EM) provided a foundation for our initial understanding of platelet structure and how it changes upon platelet activation. EM approaches have since been utilized to study platelets and thrombi in the context of basic, translational and clinical research, and they are instrumental in the diagnosis of multiple platelet function disorders. In this brief review, we provide a sampling of the many contributions EM based studies have made to the field, including both historical highlights and contemporary applications. We will also discuss exciting new imaging modalities based on EM and their utility for the study of platelets, hemostasis and thrombosis into the future.

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.

The outcome of prostaglandin-E1 and dextran-40 compared to no antithrombotic therapy in head and neck free tissue transfer: analysis of 1,351 cases in a single center

Free tissue transfer has become a popular technique for soft tissue defect reconstruction in head and neck cancer ablation. Although high success rates and good reliability of free flaps are proven, microvascular thrombosis is still the most critical issue for microsurgeons. Pharmacological antithrombotic agents are widely used but their efficacy is still debated. In this study, we analyzed whether prostaglandin-E1 (PGE1) and dextran-40 can improve the outcomes compared to no antithrombotic therapy at all. We retrospectively reviewed 1,351 free flaps performed for head and neck reconstruction after cancer ablation. Three groups defined were 232 flaps received PGE1, 283 flaps received dextran-40, and 836 received no antithrombotic therapy. The demographics of these three groups indicated no statistical differences. The results showed that flap survival revealed no significant difference among PGE1, dextran-40, and control group (P = 0.734). There was a tendency to hematomas in PGE1 group (P = 0.056) when compared with other two groups. Dextran-40 significantly increased flap failure rate in high-risk patients with diabetes mellitus (P = 0.006) or hypertension (P = 0.003), when compared with PGE1 and control group. These results revealed antithrombotic therapy with PGE1 and dextran-40 do not determine a significant improvement in flap survival.

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.

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.

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.

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.

Effects of enoxaparin, standard heparin, and streptokinase on the patency of anastomoses in severely crushed arteries

The effects of topical irrigation with three antithrombotic agents on the patency of anastomosed arteries following crush injury were examined. Following an impact crush injury with a 25 kg crush load, the femoral arteries of rats were divided and then anastomosed. During anastomoses, the vessel lumina were topically irrigated with saline, streptokinase, standard heparin, or enoxaparin (a low molecular weight heparin). The results were evaluated by patency test and histology up to day 56. The thrombosis rate at days 1 and 7 was statistically lower (P < 0.05) in the standard heparin and the enoxaparin groups than in the other two groups. The difference between the standard heparin and the enoxaparin groups was not statistically significant. Histology at day 1 showed that thrombus in the occluded vessels adhered to the exposed adventitia in the crushed area or the adventitia was covered by fibrin, red blood cells, and platelet mesh in the patent vessels. The results showed that 1) topical irrigation with standard heparin or enoxaparin solution significantly reduced the thrombosis rate at the anastomosis site of the crushed arteries; and 2) enoxaparin was as effective an antithrombotic agent as standard heparin when topically applied during microvascular anastomoses.