Lester R. Amiss

Acute Thrombogenic Effects of Fibrin Sealant on Microvascular Anastomoses in a Rat Model

Topically applied bioadhesives and hemostatic agents have gained wide acceptance in various surgical endeavors. However, the effect of thrombin-based fibrin sealant (fibrin glue) when applied to microvascular anastomoses has not been evaluated thoroughly. Although fibrin sealant has been used directly on vascular anastomoses in macrovascular surgery, there has been little exploration into the utility and potential complications when used in the microsurgical setting. This study explored the influence of fibrin sealant containing increasing concentrations of bovine thrombin on microvascular anastomoses in a rat epigastric free flap model. The survival of the free flap in this model appeared to be inversely proportional to the concentration of thrombin in the fibrin sealant. When thrombin alone was applied to the anastomoses, the rate of thrombosis was the highest. Venous anastomosis was the most sensitive to the deleterious effects of topically applied thrombin.

Seroma prevention in a rat mastectomy model: use of a light-activated fibrin sealant.

Seroma formation following mastectomy and axillary dissection remains a common and significant problem contributing to patient morbidity and health-care costs. Previous data have suggested that fibrin sealant (FS), a biological adhesive, is capable of controlling lymphatic leakage and assisting with skin graft adhesion. In this study, the use of an experimental, light-activated FS under development by CryoLife (CFS) was evaluated in a rat mastectomy model in order to reduce seroma formation. CFS is a premixed form of FS, containing an inactivator that is reversed in the presence of light, causing sealant to form. In this model, rats underwent mastectomy and extensive dissection of the axillary lymphovasculature. Next, 1 ml of saline or FS was applied to the operative site and the wound was closed. Three groups of animals were evaluated 5 days postoperatively by measuring the volume (in milliliters) of seroma able to be aspirated from the surgical site. The saline control group (N = 20) had a seroma volume (mean ± standard deviation [SD]) of 4.2 ± 2.9 ml, while a form of CFS containing human fibrinogen (80 to 100 mg per milliliter) and human thrombin (20 U per milliliter) (N = 20) had a significantly smaller seroma volume of 1.1 ± 1.6 ml (p < 0.001 analysis of variance). University of Virginia (UVA) FS, containing human fibrinogen (20 mg per milliliter) and bovine thrombin (500 U per milliliter) (N = 20), had a serorna volume of 2.0 ± 1.6 ml (p < 0.01, compared to control; p > 0.2, compared to CFS). Thus, this form of CFS significantly reduced seroma formation compared to saline control and also appeared to result in a smaller fluid accumulation than with UVA FS, although this trend was not statistically significant. These data suggest that the use of CFS may help to reduce seroma formation in humans.

Secondary ischemic tolerance improved by administration of L‐NAME in rat flaps

Nitric oxide (NO) under basal conditions is an important regulator of vascular tone. Under ischemic conditions, however, NO can combine with superoxide anion to produce the damaging hydroxyl free radical. The current project observes the effect of inhibiting NO production (L‐Nitro‐amino‐methyl‐arginine, L‐NAME) on flaps rendered ischemic by secondary (2°) venous obstruction.

Thrombogenic effects of a nonthrombin-based fibrin sealant compared with thrombin-based fibrin sealant on microvenous anastomoses in a rat model.

&NA; The efficacy and safety of tissue adhesives needs to be clearly defined. A thrombin‐based preparation of fibrin sealant has recently been shown to have deleterious effects on microvascular anastomoses in an animal model. The authors found that fibrin sealant constructed with a high concentration of bovine thrombin (1,000 IU per milliliter) was detrimental to microvascular patency when applied to the anastomosis in a rat free flap model. The microvenous anastomosis had the highest rate of thrombosis and failure in this model. A nonthrombin‐based fibrin sealant has recently become available for experimental investigation. This study examined the thrombogenic effect of this nonthrombinbased fibrin sealant on microvenous anastomoses in a rat free flap model compared with the effect of traditionally prepared fibrin sealant with varying concentrations of thrombin. The conclusions reveal that flap survival with application of the nonthrombin‐based fibrin sealant to the anastomosis was comparable with flap survival of the control animals. Flap survival with application of the traditionally prepared thrombin‐based fibrin sealant was also comparable with flap survival of the control animals when a concentration of 500 IU per milliliter of thrombin was used. However, flap survival decreased significantly (p <0.005) when a concentration of 1,000 IU per milliliter of thrombin was used in the construct of the fibrin adhesive. These results support the previous findings of the harmful effects of thrombin when used in high concentrations and applied to the microvenous anastomosis of this free flap model. Moreover, this initial investigation with a nonthrombin‐based fibrin sealant did not show any deleterious effects on the microvenous anastomosis compared with control animals. Drake DB, Faulkner BC, Amiss Jr LR, Spotnitz WD, Morgan RF. Thrombogenic effects of a nonthrombin‐based fibrin sealant compared with thrombin‐based fibrin sealant on microvenous anastomoses in a rat model. Ann Plast Surg 2000;45:520‐524

Amelioration of secondary ischaemic injury by perfusion with University of Wisconsin (UW) solution in rat skin flaps.

This study was designed to observe the effect of perfusion with University of Wisconsin (UW) preservation solution on skin flap survival following secondary ischaemia caused by venous obstruction in rats. An epigastric flap model was used. Saline-perfused flaps exhibited no significant improvement in survival compared to untreated animals (NS). Skin flaps perfused with UW solution, however, had a significant increase in survival to 40% (8/20) (p < 0.01) when perfused before the onset of primary ischaemia and 30% (p < 0.05) when given before the onset of secondary ischaemia. These results show that UW solution improves skin flap survival, presumably through preservation of the microvasculature.

The Dorsal Rat Flap: A Discussion of the Model and the Salutary Effect of Cimetidine on Flap Survival

Failure of skin flaps remains a significant clinical problem. The dorsal rat flap, a reliable experimental model, was used to test the efficacy of cimetidine in treating a falling flap. Flaps were elevated in 45 rats divided into three equal groups. Group 1 was a saline control group. Group 2 received cimetidine 250 mg/kg three time a day for 7 days postoperatively, and Group 3 received cimetidine for 1 day before surgery, and then as in Group 2. Necrosis was assessed on the seventh postoperative day. Group 2 had 31.1 ± 1.3 (mean % ± SEM) necrosis, significantly better than saline control animals (p < 0.01) and pretreated animals (p < 0.05). These results suggest the usefulness of cimetidine in ischemic flap surgery.