Implantation Of Vascular Grafts Research Articles

Purpura localisé révélateur d’une infection tardive de prothèse vasculaire

Prosthetic graft infection after vascular reconstruction is a rare but serious complication. We report a case of infection occurring late after implantation of an iliofemoral prosthetic vascular graft. The Staphylococcus aureus infection was revealed by vascular purpura localized on the right leg 7 years after implantation of a vascular prosthesis. This case illustrates an uncommonly late clinical manifestation presenting as an acute infection 7 years after the primary operation. In this situation, the presentation differs from early infection, which generally occurs within the first four postoperative months. Diagnosis and treatment remain a difficult challenge because prosthetic graft infection is a potentially life-threatening complication. Morbidity and mortality rates are high. Here we detail specific aspects of the clinical and radiological presentation.

Cutaneous Septic Embolism Presenting as Erythematous Plaques

Dear Editor: Intravascular devices such as prosthetic vascular grafts are therapeutic tools of fundamental importance for patients with several vascular diseases. Due to the expanding usages of these devices, incidences of infectious complications are also increasing. The skin can be one of the first sites where signs of sepsis can appear. It is important to be aware of the different clinical features of septic emboli in order to detect them early. An 'erythematous plaque' eruption due to septic embolism from an infected prosthetic aortic graft is being reported. A 62-year-old man was being admitted to the emergency room with a 5-day history of fever and an erythematous plaque on his right thigh. The patient was an ex-smoker and had a history of arterial hypertension, chronic renal failure and ischemic heart disease. Five years ago, he required an amputation below his right knee and implantation of prosthetic vascular grafts due to severe peripheral vascular diseases. Physical examinations revealed painless, warm, erythematous and edematous plaques with poorly defined borders on the right thigh (Fig. 1). Fig. 1 Erythematous and edematous plaques with poorly defined borders affecting the right leg of the patient. Blood tests showed increased plasma creatinine (3.2 mg/dl; reference: 0.3~1.3 mg/dl) and C-reactive protein (26.76 mg/dl; reference: <1 mg/dl) with 89% neutrophilia. Chest X-rays and urine sediments were normal. A skin biopsy was performed showing intraluminal neutrophil thrombi in the deep dermis vessels, suggesting cutaneous septic embolism (Fig. 2). Fig. 2 (A) Skin biopsy showing deep dermis vessels with luminal occlusion due to the presence of neutrophils and fibrinoid material (H&E, ×20). (B) Detail at high magnification showing an intraluminal neutrophil thrombus in the deep dermis vessels ... Blood and skin cultures were negative. Transthoracic echocardiography showed no signs of infective endocarditis. computed tomography angiography, positron emission tomography scan and leukocyte scintigraphy showed collections in the inguinal and abdominal perivascular prosthetic grafts. Piperacillin/tazobactam plus vancomycin were prescribed with good initial responses. He also underwent surgical replacement of the vascular prosthesis, but died of dehiscence due to the new prosthesis two days after the surgery. The culture of the infected vascular graft was positive for Streptococcus viridans. Bacterial endocarditis, infected pseudoaneurysm after endovascular procedures and infected endovascular devices are the most frequent sources of infected emboli, which can lodge to distal vascular trees causing skin lesions. Clinical findings of cutaneous septic embolism are variable: palpable purpura, petechiae, hemorrhagic plaques, pustules, nodules, digital cyanosis and livedo reticularis have been described. Osler nodes and Janeway lesions are special forms of septic emboli presentations, commonly associated with bacterial endocarditis1. On the other hand, erythematous plaques have been poorly described in the literature2. Cutaneous septic embolism biopsy determines the presence of thrombus of neutrophil in dermal blood vessels, although bacteria are usually not detected3. Once the diagnosis of infected emboli in patients carrying vascular devices is made, empiric broad-spectrum antibiotic therapy should start immediately4. Imaging studies should be performed to locate the infected focus for optimal surgery. Our patient presented erythematous plaques due to infectious emboli with no evident of clinical signs of sepsis. Histopathology aids us to establish a diagnosis. Unfortunately, the patient died after the surgery. Erythematous plaques eruption should be taken into account as a clinical form of cutaneous septic emboli.

A Computational Analysis of an In Vitro Vessel Wall Injury Model

Implantation of vascular grafts or stents causes significant injury to the vessel wall. Activated coagulation factors, such as FXa are generated at the injury site. The size of the injury and the flow conditions influence the transport of these activated factors. A simulation model has been developed to evaluate surface bound coagulation inhibitors on medical devices. Tissue factor pathway inhibitor (TFPI) isa potent inhibitor of FXa in vivo. This physiologically relevant in vitro model studies the mechanism by which immobilized rTFPI effectively inhibits TF initiated thrombosis.Computational fluid dynamics was used to develop the model and validated by experiments performed in a parallel plate flow chamber. The lower plate was divided into two zones. The first zone represents fibroblasts that catalyze FXto FXa by TF-FVIIa. The second represents passively absorbed surface bound rTFPI. The efficacy of rTFPI in inhibiting FXa from the injury site was studied under both venous and moderate arterial shear rates. This model extends a previous model to include a more physiologic model of vessel wall injury in which FXa generation by TF:VIIa occurs at the wall upstream of the TFPI coated surface. The previous model estimated a uniform inlet FXa concentration of 20 nM (20% conversion of the approximate physiologic concentration of 100 nM) to the parallel plate chamber.

Sensor and biosensor to detect vascular graft infection: diagnosis and challenges

Vascular graft implantation is a very common practice in clinics; however, one of the major limitations of synthetic vascular grafts is that they are prone to infection, which has drastic implications. In severe stages of infection, this requires removal of the graft, if left untreated the mortality is almost definite. Therefore, it is important to detect the graft infection early in the disease process to manage and eliminate the graft infection with appropriate drug delivery. However, current infection detection methods are time consuming, not reliable and expensive. Therefore, researchers recently geared their effort toward developing sensor/biosensor technology to detect infection. In recent years, biochemical sensors and biosensors have emerged as a dynamic technique to perform qualitative and quantitative analysis of various analytes in the clinical environment. The need for a low cost, reliable, sensitive and biocompatible sensor device is crucial in the complex biological environment. In this review, we examine the different types of vascular graft infections and the major cause of such infections associated with implantation. Routine detection methods along with their limitations are also discussed. With the growing number of vascular graft infections being diagnosed worldwide and the increased number of fatalities due to late detection, there is a need to have such a device that can ensure in vivo continuous monitoring. As point-of-care diagnostic devices present a viable option for the rapid and sensitive detection and analysis, it is another option in the early diagnosis of prosthetic vascular graft infections (PVGIs), to use a reliable and cost effective sensor. For this reason, specific biomarkers to detect graft infection along with their detection using sensor or biosensor is the main focus of this review. This review provides an overview of the in vivo implantable devices available today, areas which are currently being developed and researched for in vivo implantation and a consideration of future prospects of the technology with their challenges.

Improvement of adhesion of fucoidan on polyethylene terephthalate surface using gas plasma treatments

Attachment of polysaccharide fucoidan to the polyethylene terephthalate (PET) polymer surface was studied by X-ray photoelectron spectroscopy (XPS). Fucoidan has antithrombogenic and anticoagulant properties and is therefore a promising coating for vascular graft implants for improving their hemocompatibility. Samples of PET polymer were first modified by nitrogen plasma treatment in order to change the surface wettability and to introduce amino groups to the surface, which act as a linker for further binding of fucoidan. Plasma treated samples were then incubated for 30 min in fucoidan solution. The presence of fucoidan layer on the polymer surface was demonstrated by appearance of S2p signal in the XPS spectra of the coated PET samples. The procedure for immobilization of fucoidan on PET surface was optimized by varying pH value of fucoidan solution from 5 to 7.4. The best results were obtained when using lower pH value pH = 5. At these conditions the thickness of the fucoidan coating was estimated to about 7 nm.

Late-term results of tissue-engineered vascular grafts in humans

The development of a tissue-engineered vascular graft with the ability to grow and remodel holds promise for advancing cardiac surgery. In 2001, we began a human trial evaluating these grafts in patients with single ventricle physiology. We report the late clinical and radiologic surveillance of a patient cohort that underwent implantation of tissue-engineered vascular grafts as extracardiac cavopulmonary conduits. Autologous bone marrow was obtained and the mononuclear cell component was collected. Mononuclear cells were seeded onto a biodegradable scaffold composed of polyglycolic acid and epsilon-caprolactone/L-lactide and implanted as extracardiac cavopulmonary conduits in patients with single ventricle physiology. Patients were followed up by postoperative clinic visits and by telephone. Additionally, ultrasonography, angiography, computed tomography, and magnetic resonance imaging were used for postoperative graft surveillance. Twenty-five grafts were implanted (median patient age, 5.5 years). There was no graft-related mortality (mean follow-up, 5.8 years). There was no evidence of aneurysm formation, graft rupture, graft infection, or ectopic calcification. One patient had a partial mural thrombosis that was successfully treated with warfarin. Four patients had graft stenosis and underwent successful percutaneous angioplasty. Tissue-engineered vascular grafts can be used as conduits in patients with single ventricle physiology. Graft stenosis is the primary mode of graft failure. Further follow-up and investigation for the mechanism of stenosis are warranted.

Extracardiac Fontan with T-shape conduit in non-confluent pulmonary arteries

A 34 months-old male patient with double inlet right ventricle with nonconfluent pulmonary arteries who underwent successful extracardiac fenestarated Fontan procedure using pre-designed T-shaped PTFE vascular graft after multi-step rehabilitation of the diminutive hilar pulmonary arteries. At first we performed 6 mm confluent pulmonary artery vascular graft implantation with 4 mm BT shunt at patient's 4 weeks old. At 9 months of patient, we upsized the confluent pulmonary arterial graft to 8 mm with bidirectional cavopulmonary connection, and, at 34 months, we performed extracardiac conduit Fontan procedure with pre-designed T-shape conduit including the confluent pulmonary arterial portion at last. Patient shows excellent functional status and development.

Evaluation of the biocompatibility of a new vascular prosthesis coating by detection of prosthesis-specific antibodies

In recent experimental studies, we could demonstrate the occurrence of antibodies against the prosthesis matrix and coating following implantation of polyester-based vascular grafts. Therefore, this study aimed at evaluating the biocompatibility of a new absorbable polymer coating by detection of antibodies against the coating and the polyester matrix. Two polyester vascular prostheses coated either with the polymer (PP-prosthesis) or with gelatine (PG-prosthesis) were functionally implanted into sheep (n = 22 per group). Blood was drawn on days 1 (pre-OP) and 7, 14, 28, 56, 84, 140 (post-OP). Homogenates from both prostheses (PP-target or PG-target) or from an uncoated prosthesis (P-target) were used as assay targets in a particle-based immunoassay. The antibody binding against the P-target was significantly higher in the PP-group than in the PG-group on days 7-56, but not on days 84 and 140. Within both groups, no significant differences but a significant correlation between the binding against the P-target and the coated target was found. Therefore, the absorbable polymer did not induce a specific humoral immune response. In conclusion, the overall immunogenicity of the polymer-coated graft was comparable to the gelatine-coated graft. The detection of prosthesis-specific antibodies seems to be useful for in vivo biocompatibility testing.

Local tissue reaction and differentiation of the prosthesis‐specific antibody response following functional implantation of vascular grafts in pigs

The study was aimed at investigating the local tissue reactions through a histological examination of beta-1-integrin expression and neointima formation, and humoral immune responses by detection of prosthesis-specific antibodies, after functional implantation of vascular prostheses. In three groups of pigs, the infrarenal aorta was replaced with segments of collagen-impregnated Dacron-prostheses: M-prosthesis--medium primary porosity, double velour layer, crimping; C-prosthesis--low primary porosity, no velour, crimping; T-prosthesis--high primary porosity, no velour, no crimping. For each prosthesis type, one series with four animals was used for examining the tissue reactions, and a second series with eight animals was used to study the antibody response, both until 116 days postoperative. In the first three weeks, the M-prosthesis caused the highest tissue reactions and the highest antipolyester antibodies, but the lowest anticollagen antibodies, whereas the T-prosthesis caused the highest anticollagen antibodies, but the least tissue response and antipolyester antibodies in the early phase. On day 116, the C-prosthesis caused the highest tissue reactions and highest polyester-specific antibodies. These results indicate a possible association between local inflammatory reactions and humoral immune responses, influenced by properties of vascular grafts.

Results of Kidney Transplantation With Simultaneous Implantation of Vascular Graft

Background Arteriosclerosis and calcification of iliac arteries are common in patients on dialysis. This study sought to evaluate the outcome after kidney transplantation and simultaneous implantation of vascular grafts. Patients and Methods In a single center study we evaluated donor and recipient data among 443 kidney transplantations in adults performed between January 2002 and October 2006. In 11 recipients (2.5%) a vascular graft (Gore-Tex) was implanted due to severe arterioscleroses of the iliac vessels. Results Reconstruction of the lower limb blood supply was performed with an ileofemoral Gore-Tex-Bypass in 9 of 11 patients, with an aortofemoral bypass in 1 patient, and with a femoroiliac crossover bypass in 1 patient. Overall, 8 of 11 patients (73%) had an uneventful postoperative course. Six of 11 patients had primary graft function. Conclusions This analysis demonstrated that vascular reconstruction during kidney transplantation has to be performed rarely but has a strong impact on further life and kidney function. In 8 of 11 patients, kidney function at 6 months was good. Severe arteriosclerosis is usually not a contraindication for kidney transplantation. However, training in vascular surgery seems to be important to achieve satisfying results. In this series, simultaneous implantation of vascular prosthetic grafts was safe since there were no infectious complications of the graft itself.

Shear stress contributes to t-PA mRNA expression in human endothelial progenitor cells and nonthrombogenic potential of small diameter artificial vessels

Seeding endothelial progenitor cells (EPCs) onto the surface of vascular grafts has been proved to be a promising strategy to improve nonthrombogenic potentials of small diameter artificial vessels. Here, we investigated whether in vitro shear stress modulates the tissue-type plasminogen activator (t-PA) secretion and mRNA expression in human EPCs and improves patency of the EPC-seeded polyurethane small diameter vascular grafts implanted in the canine carotid artery in vivo. In vitro shear stress, in a dose-dependent manner, increased t-PA secretion and mRNA expression of human EPCs. The in vivo implantation of EPC-seeded vascular grafts remained highly patent in shear stress pretreatment compared with stationary condition. The present findings demonstrate for the first time that in vitro shear stress can enhance t-PA secretion and gene expression in human EPCs, which contributes to improvement in nonthrombogenic potentials of EPC-seeded small diameter artificial vessels with maintenance of in vivo highly patency rate.

Elastin Calcification in the Rat Subdermal Model Is Accompanied by Up-Regulation of Degradative and Osteogenic Cellular Responses

Calcification of vascular elastin occurs in patients with arteriosclerosis, renal failure, diabetes, and vascular graft implants. We hypothesized that pathological elastin calcification is related to degenerative and osteogenic mechanisms. To test this hypothesis, the temporal expression of genes and proteins associated with elastin degradation and osteogenesis was examined in the rat subdermal calcification model by quantitative real-time reverse transcription-polymerase chain reaction and specific protein assays. Purified elastin implanted subdermally in juvenile rats exhibited progressive calcification in a time-dependent manner along with fibroblast and macrophage infiltration. Reverse transcription-polymerase chain reaction analysis showed that relative gene expression levels of matrix metalloproteinases (MMP-2 and MMP-9) and transforming growth factor-beta1 were increased in parallel with calcification. Gelatin zymography showed strong MMP activities at early time points, which were associated with high levels of soluble elastin peptides. Gene expression of core binding factor alpha-1, an osteoblast-specific transcription factor, increased in parallel with elastin calcification and attained approximately 9.5-fold higher expression at 21 days compared to 3 days after implantation. Similarly, mRNA levels of the bone markers osteopontin and alkaline phosphatase also increased progressively, but osteocalcin levels remained unchanged. We conclude that degenerative and osteogenic processes may be involved in elastin calcification.

Synthetic smooth muscle cell phenotype is associated with increased nicotinamide adenine dinucleotide phosphate oxidase activity: Effect on collagen secretion

Smooth muscle cells (SMCs) from prosthetic vascular grafts secrete higher levels of collagen than aortic SMCs under basal conditions and during incubation with oxidized low-density lipoprotein. We postulated that reactive oxygen species (ROS) contributed to the observed difference. The objective of this study was to assess the effect of ROS on collagen secretion by aortic and graft SMCs and explore the mechanism involved. SMCs isolated from canine aorta or Dacron thoracoabdominal grafts were incubated with 6-anilinoquinoline-5,8-quinone (LY83583), an agent that induces superoxide production. Type I collagen in the conditioned medium was measured by enzyme-linked immunosorbent assay, and superoxide anion production was measured by lucigenin assay. LY83583 stimulated a rapid increase in collagen production by graft SMCs that paralleled the LY83583-induced increase in superoxide production. The increase in both collagen and superoxide was greater in graft SMCs than aortic SMCs. Collagen and superoxide production were inhibited by superoxide scavengers. Nicotinamide adenine dinucleotide phosphate (NADPH) induced significantly more superoxide production by graft SMCs than aortic SMCs, suggesting that the NADPH oxidase system was more active in graft SMCs. NADPH oxidase inhibitors blocked the superoxide and collagen production induced by LY83583. In SMCs, the synthetic phenotype is associated with increased NADPH oxidase activity and elevated superoxide production in response to an oxidative stress. Superoxide, in turn, leads to increased collagen production. The inflammatory process after prosthetic vascular graft implantation causes oxidative stress that can stimulate collagen production by graft SMCs, contributing to the progression of intimal hyperplasia. The exaggerated response of graft SMCs to oxidative stress offers a potential target for therapeutic interventions.

Efficacy of the Direct Thrombin Inhibitor Ximelagatran in Maintaining Small-Diameter Vascular Graft Patency.

Objective: A clinically successful small-diameter prosthetic vascular graft has yet to be developed. Improved performance outcomes are also needed with larger-diameter prosthetic vascular grafts for arterial bypass. Ximelagatran (ExantaTM), a fixed-dose, oral direct thrombin inhibitor, is under investigation for thromboprophylaxis in various clinical settings. We hypothesized that ximelagatran could be successful in promoting patencies of small-diameter prosthetic vascular bypass grafts. We hypothesized that ximelagatran could be successful in promoting patencies of small-diameter prosthetic vascular bypass grafts. This 6-month study compared the performances of grafts implanted in carotid arteries in dogs treated with ximelagatran, aspirin, or ximelagatran + aspirin vs non-treated controls.Methods: Dogs (n=6 per group) received bilateral 6-cm long surgical implants of 4 mm internal diameter standard-walled ePTFE vascular grafts. Grafts were interpolated with end-to-end anastomoses as interposition grafts into the common carotid arteries. Ximelagatran administration (200 mg BID p.o.) began 4 hours post graft-implantation. Aspirin (325 mg QD p.o.) was initiated 3 days pre surgery. Medications were continued until study end point. Vascular graft patencies were assessed by non-invasive ultrasound studies 2 weeks post graft-implantation, then monthly. Study end points were bilateral graft failure or 6 months of implantation, whichever was first. A pathologist performed blinded evaluations of the retrieved grafts through calculations of thrombus-free surface areas (TFSA) and histological analyses of healing.Results: One ximelagatran- and one aspirin-treated dog were excluded from the study owing to surgical complications. Ximelagatran was well tolerated. There were no deviations from canine blood norms other than expected elevated PTs and APTTs in ximelagatran-treated animals. Graft Patency: At 6 months, mean graft patencies were similar for the ximelegatran and the ximelagatran + aspirin groups, but both groups were significantly different compared to the aspirin alone and control groups.1TFSA: Mean TFSA of grafts from both the ximelagatran and ximelagatran + aspirin groups were similar but were significantly different from the aspirin alone group.2Intimal Hyperplasia: Statistical differences between groups were not evident between specific locations. However, grafts from the control and aspirin alone groups had more intimal hyperplasia overall than the ximelagatran and ximelagatran + aspirin groups.Conclusions: Ximelagatran-treated dogs had small-diameter vascular graft implants with higher patencies, greater TFSAs and a trend toward less intimal hyperplasia compared with dogs medicated with aspirin alone or controls. We believe that further investigation is warranted in defining the potential use of ximelagatran in maintaining small-diameter vascular graft patencies.Study GroupDrug Dose(s)Patency*TFSA %1 Month3 Months6 MonthsXimelagatran200 mg BID100% (10/10)100% (10/10)88%1 (7/8)63.4%2Aspirin325 mg QD70% (7/10)40% (4/10)30% (3/10)22.4Ximelagatran + Aspirin200 mg BID + 325 mg QD83% (10/12)66% (8/12)66%1 (8/12)55.0%2Control-17% (2/12)0 (0/12)0 (0/12)0*ratio of number of grafts open to the flow of blood to the total number of evaluable grafts at each time period

Deterioration of suture materials at prosthetic?host anastomoses

We experienced a case of polypropylene suture rupture at anastomosis 5 years after fabric vascular graft implantation. Under a scanning electron microscope, the removed suture had a tapering-off breakage at the end and tortoiseshell-like deep cracks near the end. The tapered stump indicated that the suture had been stretched out gradually and had finally fractured.

The challenges of imaging based computational fluid dynamics.

Image based Computational Fluid Dynamics (CFD) simulation of the cardiovascular system is increasingly becoming important and its application in everyday medical practice can already be envisaged. The goal of this workshop is to address all the factors involved in the development of a computational framework/software for modelling and analyses of the cardiovascular system and provide examples. The development of such framework, requires integration, management and interpretation of data from several technology areas such as a) feature detection and extraction of arterial geometry from imaging data, b) adaptive grid generation techniques for 3-D asymmetric geometries c) hemodynamic modelling, disparate length-scale model, and fluid-tissue interaction with high-performance computing, d) CFD data validation, e) feature extraction/detection and visualisation algorithms, f) graphical user interface to allow remote visualisation of post processed data. These computational tools are employed to study flow in specific problem sites in the vascular tree such as the carotid, femoral, coronary and abdominal arteries. Such studies provide understanding of the factors involved in the initialisation and evolution of arterial disease due to altered flow conditions (as a result of plaque formation) such as flow separation and reversal, and low and oscillatory wall shear stress. It is also used to study the effect of various clinical procedures such as the implantation of stents, vascular grafts, vascular prostheses and artificial valve implants on local and global hemodynamics. This workshop will address a new emerging paradigm in clinical practice known as predictive medicine for effective surgical planning and post surgical rehabilitation. The workshop will also address the difficulties in the implementation of some of the technology areas in this application with examples of carotid, femoral, and abdominal artery simulations.

Intraoperative Contamination of Synthetic Vascular Grafts. Effect of Glove Change Before Graft Implantation. A Prospective Randomised Study

Objectives: to investigate the incidence of intraoperative graft contamination, bacterial species and the influence of change of surgeon's gloves on contamination. Design: a prospective randomised study.Materials and methods : forty patients had implantation of synthetic vascular grafts. All patients received intraoperative cloxacillin (2.0 g) or clindamycin (0.6 g) intravenously. The procedures were randomised to two groups: Group 1 – surgeons changed the gloves before the first contact with the vascular prosthesis and Group 2 – operation without glove change. The growth of all bacterial species from graft segments and from the gloves was recorded. The susceptibility to antibiotics was tested.Results : the number of contaminated grafts was similar in the two groups. Growth of bacteria was recorded from 92.5% (37/40) of the graft segments and 33% (51/156) of glove imprints. Of the cultured species, 75% and 47%, respectively, were identified as coagulase-negative staphylococci (CNS). Twenty-eight per cent of CNS were resistant to cloxacillin, 15% to clindamycin, and 10% to cloxacillin and clindamycin. In all, 25% of the CNS strains were resistant to the prophylactic antibiotic used. In 50% of cases, the antibiogram of the CNS strain recovered from gloves agreed with that of the strain harvested from the graft. Conclusions: a high incidence of graft contamination was found which was not reduced by changing gloves. However, changing gloves did seem to reduce the number of bacterial species.

DREZ surgery on conus medullaris (after failed implantation of vascular omental graft) for treating chronic pain due to spine (gunshot) injuries.

The results of DREZlesioning procedure used for the treatment of chronic intractable pain due to deafferentation caused by gunshot injuries at the thoracolumbar (T10-L1) spine level are reported in six patients. The specificity of these cases arises from the fact that all the patients underwent, after decompressive laminectomy, an implantation of vascularized omental graft on the injured cord segments, 4-17 months after injury. Because of the failure of this method, which did not improve spinal function nor hinder the development of pain, surgery in the DREZ was performed 2-5 years after implantation. The results of the microsurgical DREZotomy procedure in those patients, 7-12 months after the surgery were: 4 patients with complete pain relief and 2 patients with pain relieved of 80%. All the patients with well-confined segmental pain were completely cured.

Antimicrobial Chemotherapy in the Control of Surgical Infectious Complications

In spite of the progress in surgical technique and antibiotic prophylaxis, postoperative infection still accounts for both the commonest surgical complication and one of the most frequent nosocomial infections, also causing an increase in duration and costs of hospital stay. The choice of treatment for post-surgical infections requires an understanding of the usual infecting flora, available antimicrobial agents, and susceptibility patterns. The most common organisms in simple wound infection are Gram-positive cocci and mainly Staphylococcus aureus. Staphylococcus epidermidis and S. aureus (quite often methicillin-resistant strains) are the organisms which predominate in the infectious complications following clean surgical procedures with implantation of vascular grafts or prosthetic devices. Mixed aerobic and anaerobic flora are mainly responsible for cases of intra-abdominal and intra-pelvic postoperative infections: the most common aerobes are Enterobacteriaceae (Escherichia coli, Proteus spp., and others) and enterococci, and among anaerobes Bacteroides fragilis group prevails. Adequate drainage and surgical control of the source of infection, when needed, and adjunctive effective antimicrobial therapy are important factors in successful treatment of postoperative infections. Semisynthetic penicillinase-resistant penicillins and glycopeptides (vancomycin and teicoplanin) are the drugs of choice for the treatment of infections caused by penicillin-resistant methicillin-sensitive, and methicillin-resistant, respectively, S. aureus and S. epidermidis. For the treatment of intra-abdominal and intra-pelvic infections, animal and human studies support the recommendation that treatment should be directed against both Gram-negative enteric and anaerobic bacteria. Combinations of aminoglycosides with clindamycin or metronidazole have been widely used with great success; however adverse reactions such as nephrotoxicity and ototoxicity have been a problem in some patients. In recent years monotherapy with either a carbapenem (imipenem/cilastatin or meropenem) or a penicillin/β-lactamase inhibitor combination has been proposed. Among these combination antimicrobials, piperacillin combined with tazobactam is a very well designed formulation. Indeed, piperacillin is active against a broad range of Gram-negative and Grampositive pathogens, and tazobactam is a potent β-lactamase inhibitor which acts on a variety of clinically important plasmid and chromosomal beta-lactamases. This combination seems particularly attractive for the treatment of mixed polymicrobial anaerobic-aerobic infections such as intra-abdominal and intra-pelvic postoperative infections.

Simulation of arterial hemodynamics after partial prosthetic replacement of the aorta

Background. Replacing parts of the aorta with a noncompliant vascular prosthesis results in marked alterations of the aortic input impedance and influences arterial hemodynamics. We propose a mathematical model of circulation that can predict hemodynamic changes after simulation of vascular grafting. Methods. A new mathematical model of the human arterial system was developed on a 75-MHz Pentium personal computer using Matlab software. The human arterial tree was delineated according to a 128-branch design encompassing bifurcations and physical properties of the arterial wall. A digitized aortic flow wave was chosen as the input signal to the system. After determination of the modules of elasticity of native vascular tissue and standard prostheses in technical experiments, replacement of any part of the aorta with a prosthesis was simulated by increasing the elasticity in the parts desired. Results. During control conditions, the model displayed a physiologic distribution of flow and pressure waves throughout the arterial system. Simulated replacement of the aorta resulted in an increase in pressure amplitude and a partial loss of the aortic “Windkessel” function. Calculation of the aortic input impedance showed an increase in the characteristic impedance, whereas the peripheral resistance remained unaltered. Conclusions. This mathematical model of the arterial circulation is useful for simulating hemodynamic changes after implantation of vascular grafts. The results of the model analysis are consistent with those in previous experimental work.