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Biomedical subjects

J B Towne

Publications and source records attributed to J B Towne.

At least 73 records · Page 4Linked to original sources
PubMed1991

Antibiotic-bonded PTFE vascular grafts: the effect of silver antibiotic on bioactivity following implantation.

Use of an infection-resistant vascular prosthesis has appeal for grafting in sites of potential contamination or to replace graft segments involved in low-grade infections caused by coagulase-negative staphylococci (CNS). In this study, antibiotic retention on polytetrafluoroethylene (PTFE) grafts prepared using three antibiotic-bonding methods was compared following implantation into the arterial circulation. Ciprofloxacin or silver-ciprofloxacin was bonded to PTFE surfaces by surfactant-mediated or direct bonding methods. Antibiotic-bonded grafts of each type (n = 8) or control grafts (n = 2) were used to replace the carotid or femoral arteries of 10 dogs. Duplicate grafts segments (0.5 x 0.5 cm) were explanted at various time intervals ranging from 1 hr to 14 days later and imprinted onto culture plates of Klebsiella pneumonia. Antibiotic retention (micrograms/ml) was determined by measuring zones of inhibition and correlated with known disc concentrations of ciprofloxacin. Antibacterial bioactivity of grafts bonded with silver-antibiotic complexes was superior (P less than 0.02) to bonding of antibiotic alone at 3 and 24 hr following implantation. Ciprofloxacin retention in excess of the minimum bactericidal concentration (0.5 microgram/ml) of Staphylococcus epidermidis was demonstrated on all silver-antibiotic-bonded grafts after 14 days of implantation. At 7 and 14 days following implantation, the bioactivity of all antibiotic-bonded grafts exceeded 0.125 micrograms/ml of ciprofloxacin, the minimum inhibitory concentration of S. epidermidis. Bonding of silver-ciprofloxacin on PTFE grafts provided an effective source of local antibiotic release at levels which may be useful for bypass grafting in contaminated wounds or for in situ replacement of grafts infected by CNS.

Animals↗
PubMed1991

Experience with in situ saphenous vein bypasses during 1981 to 1989: determinant factors of long-term patency.

From 1981 to 1989, 361 consecutive in situ saphenous vein bypasses were performed. Indications for revascularization were critical limb ischemia (n = 335, 93%), popliteal aneurysm (n = 15, 4%), and claudication (n = 11, 3%). Outflow tract was the popliteal artery in 116 (32%) and tibial artery in 245 (68%) of bypasses. At 6 years primary patency was 63% and secondary patency was 81%. During the performance of the in situ bypass procedure, 86 (24%) venous conduits were modified because of a technical failure (n = 49, 13%) or an inadequate vein segment (n = 37, 10%). Secondary patency at 4 years for bypasses requiring modification was 72% compared to 84% for bypasses not modified (p less than 0.05). Atherosclerotic disease of the inflow artery necessitating endarterectomy, patch angioplasty, or replacement lowered primary patency at 3 years (69%) compared to the inflow artery not requiring reconstruction (46%, p less than 0.02). In the follow-up period, 95 (26%) bypasses were revised because of thrombosis or hemodynamic failure. Bypasses requiring revision had a 4-year secondary patency of 68% compared to 88% for bypasses not revised (p less than 0.02). The first 179 cases (1981 to 1985) were compared to the subsequent 182 cases (1986 to 1989). The secondary patency at 3 years for the latter half (92%) compared to the first half (80%) of the experience was significantly improved (p less than 0.02). The secondary patency for bypasses not requiring revision was significantly improved (p less than 0.02) for the latter half (n = 142, 97%) compared to the first half (n = 124, 83%) of the series. Long-term patency with the in situ saphenous vein bypass is dependent on surgical experience, quality of the venous conduit, and atherosclerotic disease of the inflow artery that necessitates reconstruction. Meticulous surgical technique and compulsive bypass surveillance results in superior long-term patency.

Anastomosis, Surgical↗
PubMed1991

Durability of vein graft revision: the outcome of secondary procedures.

Occlusive lesions that reduced graft blood flow and ankle systolic pressure were identified in 83 femorodistal saphenous vein bypasses by use of duplex scanning or arteriography. Sites of stenosis included vein conduit (n = 41), anastomoses (n = 20), outflow arteries (n = 15), or inflow (n = 9) arteries. One hundred three secondary procedures consisting of vein-patch angioplasty (n = 31), sequential (n = 21) or interposition (n = 17) graft placement, percutaneous transluminal balloon angioplasty (n = 17), or excision of the lesion and primary anastomosis (n = 16) were performed to correct primary (n = 85) or recurrent (n = 18) graft stenoses. Cumulative graft patency after reintervention was 96% at 1 year, and 85% at 5 years. Stenosis or occlusion of revision sites was less after excision (0 of 16) or replacement (1 of 17) of abnormal segments compared to vein-patch angioplasty (8 of 31) or balloon angioplasty (9 of 18). Sequential or jump grafts constructed to improve graft outflow impaired by either myointimal or atherosclerotic occlusive lesions were the least durable secondary procedures. Five of eight graft failures in this series resulted from sequential/jump graft occlusion. All categories of secondary procedures normalized graft and limb hemodynamics, although only one third of patients reported symptoms of limb ischemia before revision. Surveillance of infrainguinal vein bypasses for occlusive lesions is a valid concept to salvage patent but hemodynamically-failing grafts. Secondary procedures that excised the lesion, used autologous tissue reconstruction, and normalized hemodynamics at the revision site and in the vein bypass were associated with a low incidence of restenosis and prolonged graft patency.

Aged↗
PubMed1991

Percutaneous intraarterial thrombolysis in the treatment of thrombosis of lower extremity arterial reconstructions.

Vascular grafts may be salvaged with thrombolytic therapy after acute occlusion as an alternative to balloon catheter thrombectomy. From October 1987 to May 1990, 15 arterial bypasses to the lower extremity (infrainguinal saphenous vein [n = 7] or expanded polytetrafluoroethylene [n = 6], and Dacron aortofemoral bifurcation graft limbs [n = 2]) were treated for 30 occulsions with intraarterial urokinase (390,000 IU to 5,808,000 IU) infused from 3 to 40 hours. The origins of 15 graft occlusions were morphologic defects (intimal hyperplasia with anastomotic or conduit stricture), pseudoaneurysm, or progression of disease distal to the graft. Two occlusions were attributed to coagulation disorders. A cause could not be identified for 13 occlusions. Patency was initially restored to all grafts with use of thrombolytic therapy, however, adjunctive surgical thrombectomy to remove persistent thrombus from the graft or outflow vessels was required after six thrombolytic infusions. One graft in the series could not be salvaged leading to below-knee amputation. Graft defects were corrected by balloon angioplasty (n = 7) or surgical revision of the conduit (n = 8). Five significant hemorrhagic complications occurred from the catheter insertion site requiring four emergent surgical procedures and resulting in the death of a fifth patient from a myocardial infarction. This technique allows chemical thrombectomy of branch arteries distal to the graft and inaccessible to a balloon embolectomy catheter, and permits diagnosis of abnormal graft morphology that may be the cause of the graft occlusion. Graft reocclusion can be expected if technical defects in the arterial reconstruction are not revised or hypercoagulable states are not treated.

Angioplasty, Balloon↗
PubMed1991

Comparison of serum and tissue antibiotic levels in diabetes-related foot infections.

Parenteral antibiotics are used as an adjunct to amputation or operative debridement for patients with diabetes who require emergency surgery for a septic foot. In 26 patients with a diabetes-related foot infection, one dose of various intravenous antibiotic regimens (gentamicin and clindamycin, ticarcillin/clavulanate, ampicillin/sulbactam) was administered during the hour before the procedure, and assays were performed to measure the antibiotic serum and tissue levels at the time of surgical debridement. Aerobic and anaerobic cultures were performed on infected tissue. The 172 bacterial isolates, including 95 aerobes and 77 anaerobes, (6.6 isolates per patient) underwent antibiotic susceptibility testing. Antibiotic levels were calculated by biologic assay from serum and tissue biopsies from the viable margins of the surgical site, which subsequently healed primarily or supported a split-thickness skin graft. Sixteen of the patients achieved therapeutic serum levels, and therapeutic tissue levels were reached in six patients at the time of surgery. A significantly lower number of patients had therapeutic tissue levels compared to serum levels (p less than 0.01, chi square). Initial intravenous antibiotic administration provides inadequate tissue concentrations for treating foot infections in patients with diabetes. Adequate serum antibiotic levels do not reflect therapeutic tissue antibiotic levels at the surgical margins in this group of patients.

Anti-Bacterial Agents↗
PubMed1991

In situ replacement of vascular prostheses infected by bacterial biofilms.

Late prosthetic graft infections are commonly the result of coagulase-negative staphylococci that survive within a biofilm on prosthetic surfaces and provoke perigraft inflammation. The indolent nature and microbiologic characteristics of bacterial biofilm infections coupled with the morbidity of graft excision and extraanatomic bypass grafting prompted us to use in situ graft replacement in 15 patients admitted to the hospital with 17 infected graft segments at a mean (+/- SEM) time interval of 70 +/- 16 months after graft implantation (n = 6) or revision (n = 9). Since 1986, 17 grafts (14 aortofemoral, 2 axillofemoral, and 1 femoropopliteal) infected by bacterial biofilms have been treated. Signs on admission included femoral pseudoaneurysm (n = 7), perigraft abscess (n = 6), or graft-cutaneous sinus tract (n = 4). No patient exhibited septicemia. At operation graft incorporation was absent and Gram's stain of perigraft exudate showed polymorphonuclear leukocytes but no bacteria. Culture of explanted graft material isolated coagulase-negative staphylococci (n = 12), Staphylococcus aureus (n = 1), and no growth (n = 2). All patients were successfully treated by a regimen that included parenteral antibiotics, removal of involved graft material, excision of inflamed perigraft tissue, and in situ replacement with an expanded polytetrafluoroethylene prosthesis. No deaths, graft thromboses, or deep wound infections occurred after operation. Recurrent graft infection did not develop during a follow-up interval that ranged from 5 to 50 months (mean, 21 months). Diagnosis of vascular prosthesis infection caused by bacterial biofilms can be based on signs at admission and operative findings. Complications of this perigraft infection can be eradicated by antibiotic administration, local debridement, and in situ graft replacement.

Aged↗
PubMed1990

Early patency of in situ saphenous vein bypasses as determined by intraoperative velocity waveform analysis.

Intraoperative velocity waveform analysis following in situ saphenous vein bypass grafting can identify abnormal hemodynamic conditions that correlate with the presence of a technical error or likelihood of perioperative thrombosis. Pulsed Doppler spectral analysis was used at operation to measure peak systolic blood flow velocity in the distal graft segment of 83 in situ saphenous vein bypasses to the popliteal (n = 35) or tibial (n = 48) arteries. Blood flow velocities were measured in the smallest diameter graft segment below the knee. Peak systolic blood flow velocity was greater than 40 cm/sec in 77 (93%) of grafts, and no early graft failures occurred. Low blood flow velocity (peak systolic blood flow velocity less than 40 cm/sec) was measured in six bypasses (7%) and was attributed to large (greater than 5 mm) vein diameter, residual hemodynamically significant lesions (intact valve leaflet, proximal arteriovenous fistula), or sclerosed vein segments. With the correction of these abnormalities, the 30 day patency for the entire series was 100%. The measurement of low blood flow velocity in the distal segment of an in situ saphenous vein bypass is an uncommon occurrence and mandates a thorough evaluation of the arterial reconstruction for correctable lesions.

Adult↗
PubMed1990

Impact of postantibiotic effect on bacterial adherence to vascular prostheses.

The brief exposure of bacteria to high antibiotic concentrations can result in prolonged suppression of bacterial growth termed postantibiotic effect (PAE). A pathogenic Staphylococcus epidermidis strain (RP-62) was exposed to 2X and 6X minimum inhibitory concentrations (MIC) of cefazolin, vancomycin, or rifampin for 1 hr and incubated for 2 to 24 hr in inhibitory-free broth. PAE was defined as the difference in time required for a 1.0 log increase in test (T) vs control (C) cultures (PAE = T-C). PAE was observed only for rifampin: 6 hr at 2X MIC and 8 hr at 6X MIC. Bacterial adherence to Dacron grafts was calculated in PAE vs control cultures by a quantitative culture technique for graft specimens incubated 2 to 24 hr. A demonstrable PAE and its impact on adherence were found to be both antimicrobial and concentration dependent. A significant decrease in staphylococcal adherence to velour-knitted Dacron was demonstrated by rifampin at 2X MIC (P less than 0.05) and 6X MIC (P less than 0.01). This phenomena may be useful in reducing bacterial adherence and colonization of bioprosthetics in the perioperative period. Preoperative suppression of staphylococcal skin flora by high dose antimicrobials can alter the capacity of these organisms to adhere to vascular prosthetic grafts and, if incorporated into antibiotic prophylaxis regimens, may reduce graft colonization.

Anti-Bacterial Agents↗
PubMed1990

An outpatient anticoagulation protocol managed by a vascular nurse-clinician.

Lifetime anticoagulation has become a therapeutic option for surgical patients with hypercoagulable states or prosthetic arterial bypass grafts. However, physicians may not achieve optimal anticoagulation or may attempt to limit the length of the therapy period because of the perceived morbidity from hemorrhagic complications of Coumadin therapy. A protocol for anticoagulant therapy monitored and regulated by a vascular nurse-clinician was reviewed. Coumadin was prescribed for 1,891 patient-months to 93 patients to maintain their prothrombin time 1.5 to 2 times control (range: 18 to 24 seconds). The mean (+/- SD) prothrombin time for the study population was 19.8 +/- 1.8 seconds. During follow-up, 472 (14%) of 3,479 prothrombin times measured were below the therapeutic range (n = 232) or prolonged (n = 240), prompting an adjustment in the Coumadin dose in 82 (88%) patients. Four patients developed recurrent vascular graft thrombosis while receiving anticoagulation. There were 6 major and 11 minor hemorrhagic complications. Patients with a chronic risk for arterial or venous thrombosis can have out-patient anticoagulant therapy administered at optimal intensity and regulated safely with a low incidence of hemorrhagic and thrombotic events.

Adolescent↗
PubMed1990

Anastomotic femoral pseudoaneurysm: an investigation of occult infection as an etiologic factor.

Occult infection was investigated as an etiologic factor in the formation of femoral anastomotic pseudoaneurysms associated with prosthetic vascular grafts. Forty-five femoral pseudoaneurysms with no clinical evidence of infection 10 to 173 months after prosthetic graft placement were consecutively studied. The explanted Dacron or explanted polytetrafluoroethylene graft material was cultured in trypticase soy broth and ultrasonically oscillated to remove adherent bacteria. All patients were treated by excision of the pseudoaneurysm and surrounding perigraft capsule and in situ replacement with an interposition prosthetic graft. Thirty-two bacterial isolates were recovered from 27 (60%) of the specimens, with coagulase negative staphylococci (Staphylococcus epidermidis S. warneri, S. hominis, S. capitis) accounting for 24 of the recovered species. No infection of the replacement graft developed in any patient and no recurrent pseudoaneurysms were observed. Bacterial colonization may occur at implantation or during subsequent procedures when the prosthetic graft is exposed. This chronic infection can be diagnosed by means of sensitive culture techniques that dislodge adherent bacteria from the graft surface. On grounds of the observations reported in this study, there appears to be suggestive evidence that an occult infectious process may be one of the factors that play a role in the development of some femoral anastomotic pseudoaneurysms.

Aged↗
PubMed1990

Sequential analysis of staphylococcal colonization of body surfaces of patients undergoing vascular surgery.

Slime-producing coagulase-negative staphylococci are pathogens in vascular surgery by virtue of their ability to adhere to and persist on prosthetic graft material. Inguinal and abdominal skin sites were cultured in 41 patients upon hospitalization, and slime production and antimicrobial susceptibility were assessed in all recovered staphylococcal isolates. Twenty-one patients eventually underwent lower-extremity revascularization. In the operative population, cultures were also obtained on the day of surgery and fifth postoperative day. All 21 patients received perioperative cefazolin. Of 327 coagulase-negative staphylococci recovered, Staphylococcus epidermidis (47%), S. haemolyticus (21%), and S. hominis (10%) were the predominant isolates. Slime-producing coagulase-negative staphylococci were recovered from 17 of 21 patients at admission but only from 8 of 21 patients on day 5 postoperation (P less than 0.05). S. epidermidis isolates demonstrated increasing multiple resistance from admission to 5 days postoperation to methicillin, gentamicin, clindamycin, erythromycin, and trimethoprim-sulfamethoxazole (P less than 0.05). All coagulase-negative staphylococcal isolates were susceptible to ciprofloxacin and vancomycin. Slime-producing capability was not associated with increased methicillin resistance for the recovered isolates. The data demonstrate that patients enter the hospital colonized with slime-producing strains of coagulase-negative staphylococci and that during hospitalization the staphylococcal skin burden shifts from a predominately susceptible to a resistant microbial population, which may enhance the importance of slime production as a risk factor in lower-extremity revascularization.

Blood Vessel Prosthesis↗
PubMed1990

Therapeutic options for acute thrombosed in situ saphenous vein arterial bypass grafts.

Abnormalities of the conduit, outflow tract, and graft hemodynamics are important elements in the mechanism of vein graft thrombosis, and their role must be defined when planning reoperation. In a consecutive series of 353 in situ saphenous vein bypass graftings performed for occlusive or aneurysmal disease, graft thrombosis occurred in 18 (5%) patients during the perioperative period and unexpectedly in 14 (4%) patients after discharge from the hospital. Assessment of graft hemodynamics (calculation of blood flow velocity) before thrombosis was helpful in predicting success after graft revision. Five grafts with known low flow (systolic flow velocity less than 40 cm/sec) that thrombosed in the perioperative period did not have patency restored by thrombectomy or graft replacement unless the outflow tract was also modified. If poor quality vein or technical error was the mechanism of thrombosis, translocation of the distal anastomosis to a proximal arterial segment (n = 4), and graft replacement with normal autologous vein (n = 5) or prosthetic graft (n = 1) were successful in relieving limb ischemia. After discharge from the hospital, unexpected graft thrombosis was successfully treated by a variety of secondary procedures (thrombolysis/thrombectomy, autologous or prosthetic replacement) if prior surveillance with duplex scanning demonstrated low flow as a result of graft stenosis (n = 7) or normal graft hemodynamics (n = 5). Prosthetic replacement of two failed bypass grafts with low flow caused by diseased outflow did not remain patent. Scrutiny of graft hemodynamics and limb arterial anatomy for alternative outflow sites can identify patients likely to benefit from reoperation after in situ bypass thrombosis.

Adult↗
PubMed1990

Adherence of mucin and non-mucin-producing staphylococci to preclotted and albumin-coated velour knitted vascular grafts.

The mechanisms involved in bacterial adherence to vascular grafts are important in understanding prosthetic infections. Albumin-coated Dacron (ACD) is a new development in vascular graft fabrication. However, albumin acts as a receptor for certain gram-positive bacterial adhesions. Five pathogenic, coagulase-negative Staphylococcus epidermidis strains were used to measure the differential microbial adherence to ACD versus untreated velour-knitted Dacron (VKD) vascular prostheses. Specimens of VKD, preclotted VKD, and ACD were inoculated with each of the five strains (10(7) colony-forming units/ml) for 2, 4, 8, 12, and 24 hours. After incubation, graft specimens were washed to remove nonadherent organisms and oscillated ultrasonically to remove adherent organisms. The sonication effluent was plated to trypticase soy agar to quantitate the adherent organisms. Adherence was significantly greater (p less than 0.01) to VKD compared with preclotted VKD and ACD at 2, 4, 8, and 24 hours. Four of the five study strains demonstrated significantly greater adherence to VKD than to either ACD or preclotted VKD. Adherence of S. epidermidis increased with exposure time. Albumin bonded to velour-knitted Dacron does not increase coagulase-negative staphylococcal adherence compared with the noncoated vascular prostheses. Binding albumin to vascular prostheses does not increase the risk of staphylococcal colonization.

Bacterial Adhesion↗
PubMed1990

First phase report of cooperative Veterans Administration asymptomatic carotid stenosis study--operative morbidity and mortality.

Ten Veterans Administration medical centers representing all regions of the country participated in a cooperative study to evaluate the etiologic importance of asymptomatic carotid disease in the development of transient ischemic attack and stroke. The study prospectively randomized patients between carotid endarterectomy and nonoperative treatment with both groups receiving 1300 mg aspirin daily. All patients considered for the study had carotid angiography. Inclusion in the study required at least a 50% diameter reduction of the internal carotid artery. Four hundred forty-four patients were randomized between nonoperative (233 patients) and operative groups (211 patients). In the operative group 195 had unilateral carotid endarterectomies, and eight patients had staged bilateral procedures, for a total of 211 carotid operations. Thirty-day mortality was 1.9% (4/211); all resulting from cardiac causes. One patient who died also had a neurologic deficit. The incidence of stroke was 2.4% (5/211), and the combined stroke and mortality rate was 4.3%. Transient ischemic events occurred in two patients (0.9%). Coronary artery disease is the prime determinant of operative mortality and justifies rigorous preoperative cardiac evaluation to identify those patients at risk. This multicenter prospective clinical trial demonstrates that carotid endarterectomy can be safely performed and provides a valid standard with which to compare the nonoperative cohort.

Carotid Arteries↗
PubMed1989

Anastomotic tensile strength following in situ replacement of an infected abdominal aortic graft.

The tensile strength and histologic features of anastomotic bonding were studied prior to and following in situ replacement of aortic vascular prostheses infected by Staphylococcus epidermidis. Sterile (n = 6) and infected (n = 19) Dacron grafts were used to replace the abdominal aorta of 25 dogs. After five weeks, grafts were explanted, and peak tensile force (measured in kilograms) required for anastomotic disruption was measured using a linear gain tensiometer. Anastomotic tensile strength (mean +/- SEM) of infected grafts (5.4 +/- 0.5 kg) was decreased when compared with that of sterile, control grafts (9.0 +/- 0.9 kg). The decreased anastomotic tensile strength of infected grafts was the result of an inflammatory aortitis adjacent to the suture line. Only grafts infected with the study strain of bacteria demonstrated signs of infection. In 19 dogs, the graft infection was treated by graft excision, antibiotic administration, and in situ graft replacement (Dacron or polytetrafluoroethylene prostheses). After five weeks and 12 weeks, anastomotic tensile strength of polytetrafluoroethylene (10.6 +/- 0.6 kg) and Dacron (10.8 +/- 0.5 kg) replacement grafts was similar to that of uninfected control grafts. In situ replacement of vascular prostheses infected by S epidermidis can result in graft healing with normal anastomotic bonding.

Anastomosis, Surgical↗
PubMed1989

Biochemical adaptation of venous patches placed in the carotid circulation.

The influence of venous patching on luminal prostacyclin (PGI2) and thromboxane A2 (TBX) production of endarterectomized arteries was studied in a canine model. Fifteen dogs underwent bilateral common carotid endarterectomies. In each dog, one artery was closed primarily and the contralateral artery was closed by vein-patch angioplasty. At six and 12 weeks after operation, luminal prostanoid production from the venous patch, adjacent endarterectomized artery, and control artery and vein was measured by radioimmunoassay for 6-keto-prostaglandin F1 alpha and thromboxane B2. Venous patches underwent "incomplete" biochemical adaptation with decreased luminal production of PGI2 compared with control and endarterectomized arteries. Thromboxane production from venous patches was increased compared with normal vein but similar to control and endarterectomized arteries. At six weeks, PGI2 production of vein-patched arterial segments was increased compared with arteries closed primarily. These data indicate that vein-patch angioplasty favorably influences surface thrombogenicity of healing, endarterectomized arteries and support its use in reparative carotid surgery.

6-Ketoprostaglandin F1 alpha↗