The use of biological glue in aortic surgery

In vivo degradability of hydrogels prepared from different gelatins by various cross-linking methods

This study is an investigation to evaluate the in vivo degradation of gelatin hydrogels in terms of their number of cross-links. Various hydrogels were prepared from acidic gelatin, extracted from bovine bone, porcine skin or fish scale, and basic gelatin, extracted from porcine skin, through four types of cross-linking methods, i.e., glutaraldehyde (GA) or dehydrothermal treatment and ultraviolet (UV) or electron beam irradiation. The water content of hydrogels and their number of cross-links, calculated from the tensile modulus of hydrogels, were evaluated as the measure of hydrogel cross-linking extent. Following subcutaneous implantation of 125I-labeled gelatin hydrogels into mice, the radioactivity remaining was measured at different time intervals to assess the in vivo degradability of hydrogels. Irrespective of the gelatin type and cross-linking method, a good correlation was found between the in vivo degradability of hydrogels and their number of cross-links, which is different from the correlation to their water content. This finding indicates that the degradability of hydrogels is governed by their number of cross-links.

Isocyanate-functional adhesives for biomedical applications. Biocompatibility and feasibility study for vascular closure applications

Biodegradable isocyanate-functional adhesives based on poly(ethylene glycol)-adipic acid esters were synthesized, characterized, and evaluated in vitro and in vivo. Two types of formulations, P2TT and P2MT, were developed by functionalization with 2,4-tolylene diisocyanate (TDI) or 4,4'-methylene-bis(phenyl isocyanate) (MDI), respectively, and branching with 1,1,1-trimethylolpropane (TMP). The biocompatibility of the synthesized adhesive formulations was evaluated as per ISO 10993. Cytotoxicity, systemic toxicity, pyrogenicity, genotoxicity (reverse mutation of Salmonella typhimurium and Escherichia coli), hemolysis, intracutaneous reactivity, and delayed-type hypersensitivity were evaluated. All formulations met the requirements of the conducted standard tests. The biological behavior and ability of the adhesive formulations to close an arteriotomy and withstand arterial pressure following partial approximation with a single suture were evaluated in a rat abdominal aorta model. Animals were evaluated at 1, 2, 3, and 4 weeks after surgery. Macroscopic and histopathologic evaluation of explanted arteries suggested that the P2TT formulation had better in vivo performance than the P2MT formulation. Additionally, the P2TT formulation resulted in less tissue reaction than P2MT formulation. To our knowledge, this is the first study demonstrating the potential of this new class of isocyanate-functional degradable adhesives for vascular applications.

Perioperative blood transfusion and blood conservation in cardiac surgery: the Society of Thoracic Surgeons and The Society of Cardiovascular Anesthesiologists clinical practice guideline

BACKGROUND

A minority of patients having cardiac procedures (15% to 20%) consume more than 80% of the blood products transfused at operation. Blood must be viewed as a scarce resource that carries risks and benefits. A careful review of available evidence can provide guidelines to allocate this valuable resource and improve patient outcomes.

METHODS

We reviewed all available published evidence related to blood conservation during cardiac operations, including randomized controlled trials, published observational information, and case reports. Conventional methods identified the level of evidence available for each of the blood conservation interventions. After considering the level of evidence, recommendations were made regarding each intervention using the American Heart Association/American College of Cardiology classification scheme.

RESULTS

Review of published reports identified a high-risk profile associated with increased postoperative blood transfusion. Six variables stand out as important indicators of risk: (1) advanced age, (2) low preoperative red blood cell volume (preoperative anemia or small body size), (3) preoperative antiplatelet or antithrombotic drugs, (4) reoperative or complex procedures, (5) emergency operations, and (6) noncardiac patient comorbidities. Careful review revealed preoperative and perioperative interventions that are likely to reduce bleeding and postoperative blood transfusion. Preoperative interventions that are likely to reduce blood transfusion include identification of high-risk patients who should receive all available preoperative and perioperative blood conservation interventions and limitation of antithrombotic drugs. Perioperative blood conservation interventions include use of antifibrinolytic drugs, selective use of off-pump coronary artery bypass graft surgery, routine use of a cell-saving device, and implementation of appropriate transfusion indications. An important intervention is application of a multimodality blood conservation program that is institution based, accepted by all health care providers, and that involves well thought out transfusion algorithms to guide transfusion decisions.

CONCLUSIONS

Based on available evidence, institution-specific protocols should screen for high-risk patients, as blood conservation interventions are likely to be most productive for this high-risk subset. Available evidence-based blood conservation techniques include (1) drugs that increase preoperative blood volume (eg, erythropoietin) or decrease postoperative bleeding (eg, antifibrinolytics), (2) devices that conserve blood (eg, intraoperative blood salvage and blood sparing interventions), (3) interventions that protect the patient's own blood from the stress of operation (eg, autologous predonation and normovolemic hemodilution), (4) consensus, institution-specific blood transfusion algorithms supplemented with point-of-care testing, and most importantly, (5) a multimodality approach to blood conservation combining all of the above.

The effect of autologous fibrin tissue adhesive on postoperative cerebrospinal fluid leak in spinal cord surgery: a randomized controlled trial

STUDY DESIGN

A prospective randomized study evaluating the efficacy of autologous fibrin tissue adhesive for decreasing postoperative cerebrospinal fluid (CSF) leak in spinal cord surgery.

OBJECTIVE

To compare postoperative CSF leak in 3 groups (i.e., autologous fibrin tissue adhesive used, commercial fibrin glue used, and no fibrin tissue adhesive used) of patients undergoing spinal surgery who needed dural incision.

SUMMARY OF BACKGROUND DATA

Spinal cord operations, particularly when dural incision is inevitable, sometimes involve postoperative CSF leak. Because CSF leak is a serious complication, countermeasure is necessary to prevent it after dural suture. Commercial fibrin tissue adhesive was formerly used. Because the possibility of prion infection was widely noticed, commercial fibrin tissue adhesive containing animal components has been used less often.

METHODS

In 13 of 39 cases in which dural incision would be made, 400 mL whole blood was drawn, and autologous fibrin tissue adhesive was made of plasma. Cases were divided into 3 groups: (1) dural closure alone, (2) use of autologous fibrin tissue adhesive after dural closure, and (3) use of commercial fibrin tissue adhesive after dural closure. The primary outcome measure was determined as postoperative (3 days) volume of drainage fluid, and results were analyzed using the analysis of variance. The secondary outcome measure was general blood test, coagulation assay, and plasma fibrinogen, and these were analyzed also using the analysis of variance.

RESULTS

There was a significant difference in the primary outcome between the autologous and control groups. No complications such as infection or continuous CSF leak were observed in any case. The mean volume of drainage fluid was 586.2 mL in the group with autologous fibrin tissue adhesive and 1026.1 mL in the group without fibrin tissue adhesive. The volume of drainage fluid was significantly lower in the former group than that in the latter group. There was no statistical difference between the volumes of the group with autologous adhesive and with commercial adhesive (639.2 mL).

CONCLUSIONS

We used autologous fibrin tissue adhesive as a new sealant after dural closure instead of commercial fibrin tissue adhesive. No definitive CSF leak was observed, and the volume of drainage fluid was significantly lower in the group with autologous fibrin tissue adhesive than that in the group without fibrin tissue adhesive. The use of autologous fibrin tissue adhesive was superior to that of commercial fibrin tissue adhesive in cost.

Late aortic root redissection following surgical treatment for acute type A aortic dissection using Gelatin-Resorcin-Formalin glue

OBJECTIVES

Although Gelatin-Resorcin-Formalin (GRF) glue is widely used in surgery for acute aortic dissection, late complications possibly due to the glue, such as late aortic root redissection, have also been reported. We have experienced similar complications, some of which required redo surgeries, and these cases are reviewed.

METHODS

Twenty-six consecutive patients who underwent surgery for acute type A aortic dissection using GRF glue, from December 1996 to February 2001, were retrospectively studied, with a special focus on any late complications and any reoperation.

RESULTS

Of the 21 patients who survived and were followed as outpatients, false aneurysms were found in 5 patients (21%) at 24-42 (mean 34) months following the initial surgery. Of these, 2 patients required resternotomy because of the increasing aneurysm diameter. In both cases, the aortic root was redissected at the site of the GRF glue use where the anastomosis between the aortic root and the prosthesis had widely opened and had become the aneurysm entry point. Significant aortic regurgitation was noticed in 3 patients (14%, 1 of whom showed a false aneurysm), and 2 of these underwent reoperation for aortic root redissection.

CONCLUSIONS

A high incidence of aortic root redissection with false aneurysm and/or aortic insufficiency was found following the surgery for acute aortic dissection using GRF glue. These patients should be carefully followed for years after surgery.

Development of an animal model for assessment of the hemostatic efficacy of fibrin sealant in vascular surgery

PURPOSE

Sustained hemostatic function of fibrin sealant (FS) is crucial when it is used in cardiovascular surgery. The purpose of this study was to develop a model that can determine the long-term hemostatic efficacy of tissue sealants in a vascular surgery.

METHODS

To determine the ability of the model to detect differences in FS performance, various concentrations of FS were prepared and tested. Tensile strength of FS clots was determined in vitro using a tensiometer. Laparotomy was performed on 49 anesthetized rabbits, and a segment of the aorta was occluded, transected, and then sutured in an end-to-end fashion with four or eight interrupted 9-O sutures. The four-suture repair was covered with FS or placebo, and blood flow restored. Spilled blood was absorbed with gauze and weighed to estimate blood loss. Four weeks after surgery the animals were euthanized and the vessels recovered for histology.

RESULTS

Average tensile strength of FS clots at 120, 90, and 60 mg/ml topical fibrinogen complex (TFC) concentration was 0.42 +/- 0.07 N, with no significant difference among them. The lowest TFC concentration, 30 mg/ml, produced weaker clots than either 120 or 90 mg/ml (P < 0.05). All rabbits with four-suture anastomoses that were treated with placebo bled to death after the vessel was unclamped (n = 6). Treatment of suture line with standard FS concentration (120 mg/ml TFC, n = 8) sealed the anastomosis and prevented blood loss. Hemostasis was sustained for 4 weeks, allowing vascular healing. All rabbits with the eight-suture anastomosis survived the operation but lost 42 +/- 9.2 ml blood (n = 5). Hemostatic efficacy of FS was unchanged when TFC was diluted to 90 mg/ml (n = 6) but further dilution to 60 mg/ml with water (n = 8) produced significantly less effective clots, with an average blood loss of 5.5 +/- 7.6 ml (P < 0.05) and two fatal clot failures postoperatively. When FS was diluted to 60 mg/ml TFC with a buffer, it maintained its hemostatic strength (n = 6). Further TFC dilution to 30 mg/ml led to consistent bleeding with an average blood loss of 35.3 +/- 10.3 ml (P < 0.001, n = 6).

CONCLUSIONS

The four-suture anastomosis of rabbit aorta offers a consistent and reliable method for evaluating the short- and long-term hemostatic efficacy of FS products. This model is not only able to determine the functional differences in various concentrations of FS, but it is also sensitive to detect the subtle changes in FS preparation (e.g., medium composition) that is not detected by in vitro testing.

The role of fibrin sealants in hemostasis

Hemostasis is a prerequisite for wound healing, and under normal physiologic conditions, it is achieved by means of the coagulation cascade. However, there are a number of surgical procedures where there may be considerable benefits to the patient, surgeon, or health-care costs if hemostasis can be achieved more efficiently. The rapid and effective control of bleeding during and after surgery reduces blood loss and can help reduce postoperative complications. These improved outcomes can reduce the need for transfusion, with the associated risk of viral transmission, and have a positive impact on operative and hospital stay times. Fibrin sealants are surgical hemostatic agents derived from human plasma that reproduce the final steps in the coagulation pathway and form a stable fibrin clot. Fibrin sealants are used in a broad range of surgical procedures to assist hemostasis, including cardiovascular, hepatic, and splenic surgery, gastrointestinal hemorrhage, skin grafting, and dental extractions in anticoagulated patients. Patients with coagulopathies are at high risk of prolonged or excessive bleeding during or after invasive surgery, and these patients may also benefit from the use of fibrin sealants. This article reviews the role of fibrin sealants in hemostasis, citing a number of key clinical studies that report a significant reduction in blood loss or chest drain output after surgery with fibrin sealant compared with controls.

Tissue sealing

The tissue adhesive property of fibrinogen was first described 60 years ago. However, it was not until the availability of concentrated plasma fibrinogen and bovine thrombin that the use of fibrin sealants in surgical practice became widespread. Today, fibrin sealants are used for tissue sealing across a range of surgical procedures, including cardiothoracic, gastrointestinal, neurosurgery, and vascular surgery. Tissue sealing with fibrin sealant reduces perioperative hemorrhage and controls blood loss from cut surfaces of tissues that are difficult to suture. The use of fibrin sealants can also reduce perioperative and postoperative complications by reducing fluid leakage, air leakage, and by preventing fistulae formation. Fibrin sealants have a unique physiologic action, and the resulting fibrin clot is fully degraded by the body's natural wound healing process. The range of surgeries and types of procedure that incorporate the use of fibrin sealants in tissue sealing is expanding. As commercially prepared fibrin sealants become more widely available, the number of patients and surgeons benefiting from improved surgical outcomes is also set to increase. This article reviews the areas of surgery within which fibrin sealants are currently used to assist tissue sealing and highlights the improved surgical outcomes, such as reduced blood loss, operative time, and postoperative complications.