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.

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.

The effect of vein diameter on patency of in situ grafts.

In an attempt to evaluate the effect of vein diameter on early patency and long-term durability of in situ lower limb bypasses, we evaluated 195 femoral-distal, popliteal, and/or tibial bypasses constructed in 189 patients (153 men, 36 women), consisting of tibial bypasses in 116 (60%), and popliteal in 79 (40%). The operative angiograms were reviewed and the vein diameter was measured to the nearest 0.5 mm. Postoperative follow-up consisted of visits every three months where graft patency was assessed by physical examination and measurement of graft flow velocity and ankle-brachial indices. Conduits less than 3 mm had a higher rate of occlusion in the 0-30 day interval, but following that period performed satisfactorily. No conduit less than 2 mm was successfully utilized, because of inability to incise valves without injury in these tiny conduits. Following the perioperative period, conduit diameter does not affect the long-term durability of in situ bypass grafts.

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.

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.

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.

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.

Graft excision and extra-anatomic revascularization: the treatment of choice for the septic aortic prosthesis.

Graft excision and extra-anatomic revascularization is the treatment of choice for the septic aortic prosthesis. From 1979 to 1988, 20 patients underwent resection of aortic grafts and extra-anatomic bypass for the treatment of graft infections (No. 11) and aorto-enteric fistulas (No.9). The mean time interval from primary aortic surgery to the reoperative procedure was 65 months (range 1-192 months). Three patients died (one less than 30 days) after the secondary procedure for a mortality rate of 15%. One patient developed infection of the extra-anatomic bypass graft which resulted in an above-knee amputation. This was the only major limb loss in this series. A second patient developed contralateral buttock necrosis when he had unilateral axillary-femoral bypass without femoral-femoral bypass because of a previous above-knee amputation on the affected side. Major complications occurred in 7 patients (35%). Mean duration of follow-up after the reoperative aortic procedure was 44 months (range 6-120 months). One patient suffered aortic stump blowout 7 months after repair of an aortic duodenal fistula. Aortic graft excision and extra-anatomic revascularization of the lower extremities can be performed with low mortality and risk of limb loss and should remain the treatment of choice for aorto-enteric fistulas and infected aortic prostheses. Bilateral groin revascularization is important even in patients who have had a previous lower extremity amputation to provide pelvic blood flow.

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.

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.

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.

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.

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.

Blunt tibial artery trauma: predicting the irretrievable extremity.

Patients suffering blunt leg trauma resulting in below-knee fracture, tibial artery injury, and soft-tissue damage are at major risk for amputation. In an attempt to identify the factors which may forecast limb loss despite vascular surgical repair, all patients with tibial fractures admitted between 1980-1988 were reviewed. Forty-four of 366 (12%) patients presented with clinical evidence of tibial artery injury. Twenty-seven of these 44 patients had angiographic evidence of at least one patent tibial vessel providing adequate distal flow. The remaining 17 patients required operative repair of injured tibial arteries because of persistent distal ischemia. The amputation rate was 35% (6/17--4 BKA, 2 AKA), three of these having patent vascular repairs at the time of the amputation. Operative indications for amputation were ischemic nonviable muscle in three patients, and severe soft-tissue wound infection in three. Patients who required amputation had a significantly greater incidence (Fisher's exact test) of three or more fascial compartments involved in muscular injury (p = 0.005), two or more injured tibial vessels (p = 0.01), failed vascular reconstruction (p = 0.03), a cadaveric foot at initial exam (p = 0.03), and severe muscle crush injury or muscle tissue loss (p = 0.03). No extremity was salvaged when more than two of these factors was present, and a failed vascular reconstruction led to limb amputation in all cases. These factors will predict an irretrievable extremity following blunt tibial artery trauma, allowing amputation before life-threatening wound sepsis develops.

Use of the internal jugular vein for carotid patch angioplasty.

The internal jugular vein is an excellent source of autogenous tissue for carotid artery reconstruction because of its availability in the operative incision, adequate size, and ability to be harvested without morbidity. For 153 of 453 consecutive carotid reconstructions, the durability of the internal jugular vein (n = 76) and the greater saphenous vein (n = 77) as a patch angioplasty was compared. Mean postoperative follow-up was 17 months (1 to 52 months). The vein-patched carotid-bifurcation was studied by means of duplex ultrasonography to assess patency, detect restenosis, and measure cross-sectional diameter during systole. No carotid bifurcation occluded after operation. No ruptures or aneurysmal dilatations of the vein patches were observed. The maximum diameter (mean +/- SD) of the carotid patch angioplasties constructed with internal jugular vein (9.4 +/- 1.9 mm) was similar to patches made with greater saphenous vein (9.6 +/- 1.7 mm). In 95 patients serial duplex examinations demonstrated maximum diameter changes of the vein-patched internal carotid artery ranging from an increase of 3.5 mm to a decrease of 3.0 mm. Asymptomatic restenosis (greater than 50% diameter reduction) was detected in 2/95 (2.1%) patients. Because of the premium placed on the saphenous vein for peripheral arterial reconstruction and coronary artery bypass grafting, the ipsilateral internal jugular vein should be used more frequently for carotid patch angioplasty.

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.

Coagulase-negative staphylococcal infections in vascular surgery: epidemiology and pathogenesis.

Staphylococcal infection of a vascular prosthesis is a relatively uncommon complication of peripheral vascular surgery; however, these infections and their sequelae can be catastrophic. The majority of prosthetic graft infections are caused by mucin-producing strains of Staphylococcus epidermidis, which express varying degrees of adherence to the synthetic substrates. Studies have demonstrated that the components and construction characteristics of the graft, implantation site, administration of antimicrobial agents, and endogenous microbial flora are all identifiable risk factors in vascular graft infections. Mucin production, a known virulence factor, has recently been shown to occur in endogenous coagulase-negative staphylococci (CNS) at the time of hospital admission. While mucin production plays an important role in the persistence of graft infections, there is no evidence that suggests a relationship between mucin and antimicrobial resistance. Identifying characteristics of (CNS) graft infections may include a draining wound sinus, poor graft incorporation, a perigraft exudate or a pseudoaneurysm at the anastomotic site. The occult nature of these infections, in which the patient is often asymptomatic, makes diagnosis and treatment difficult. The graft or graft exudate may be negative when routine culture methods are employed. The recognition of CNS graft infections requires a high index of suspicion and the treatment of these infections requires understanding of the pathogenic process, individualized surgical management, and the judicious use of antimicrobial agents.

Monitoring functional patency of in situ saphenous vein bypasses: the impact of a surveillance protocol and elective revision.

Implementation of a protocol that monitored in situ saphenous vein bypass hemodynamics for low-flow states provided insight into the pathophysiologic characteristics and time course of graft failure. From 1981 to 1988, 250 in situ bypasses to popliteal (n = 83) or tibial (n = 167) arteries were performed in 231 patients. Indications for operation included critical limb ischemia in 232 cases (93%), popliteal aneurysm in 11 cases (4%), and disabling claudication in seven cases (3%). Arterial pressure measurements, continuous-wave Doppler spectral analysis, and duplex ultrasonography were used to assess patency, detect hemodynamic changes indicative of graft stenosis, and localize anatomic hemodynamic changes indicative of graft stenosis. Seventy grafts with correctable anatomic lesions (retained venous valves, graft stenosis, arteriovenous fistula, native vessel atherosclerosis) that decreased graft blood flow or ankle arterial pressure or both were identified. Correction of vein conduit or anastomotic lesions comprised 73 (77%) of the 95 revisions performed. Vein-patch angioplasty of a stenosis was the most common secondary operation performed. Graft revision was highest in the perioperative period (10% at 30 days), decreased to 7% per 6-month interval until 18 months, and was 3% per year thereafter. The primary patency rate of grafts not identified to have a correctable lesion was 86% at 4 years, a level similar to the secondary patency of 81% for grafts requiring one or multiple revisions. The surveillance protocol identified grafts with correctable lesions before thrombosis thereby permitting elective revision of patent grafts. Hemodynamic studies confirmed that a frequent mechanism of late failure of grafts was the development of a low-flow state produced by lesions not amenable to revision.

Bacterial adherence to vascular prostheses. A determinant of graft infectivity.

An in vitro model was developed to quantitatively measure bacterial adherence to the surface of prosthetic vascular graft material. Four strains of bacteria (Staphylococcus aureus, nonmucin-producing S. epidermidis [SP-2], mucin-producing S. epidermidis [RP-12], and Escherichia coli) were used to inoculate expanded polytetrafluoroethylene (ePTFE), woven Dacron, and velour knitted Dacron graft material. After graft specimens were incubated in a 10(7) suspension of bacteria, they were washed to remove nonadherent organisms and ultrasonically oscillated to dislodge adherent organisms. Quantitative culture of the sonication effluent was used to calculate bacterial adherence, expressed as the number of colony-forming units found in each square centimeter of graft material per 10(7) inoculum. All bacterial strains had a greater affinity to velour knitted Dacron graft than to ePTFE (p less than 0.025). E. coli and S. aureus adhered to velour knitted Dacron in greater numbers than to woven Dacron (p less than 0.04). The production of extracellular polysaccharide (mucin) by the RP-12 strain significantly increased adherence to both EPTFE and Dacron grafts compared with the other three bacterial strains tested (p less than 0.04). Although E. coli was less adherent to ePTFE than nonmucin-producing staphylococcal strains (S. aureus and SP-2), no difference in adherence to knitted or woven Dacron graft material was demonstrated. The differential adherence of bacteria to prosthetic vascular grafts pays an important role in the pathogenesis of graft sepsis and determines relative graft infectivity. The in vitro model developed is well suited for further study of the mechanisms by which bacteria adhere to and colonize vascular grafts.

Mucin production by Staphylococcus epidermidis. A virulence factor promoting adherence to vascular grafts.

The production of an exopolysaccharide (mucin) by some Staphylococcus epidermidis strains facilitates bacterial adhesion to prosthetic vascular grafts and may play an important role in adherence-mediated growth. An in vitro model was developed to measure the differential adherence of mucin-producing (RP-12) and nonmucin-producing (SP-2) S epidermidis strains onto expanded polytef and velour knitted Dacron graft material. After incubation in a 10(7)/mL suspension of organisms, graft specimens were repeatedly washed to remove nonadherent organisms and then sonicated to dislodge adherent organisms. Bacterial adherence was calculated from a quantitative culture of the sonication effluent. Both S epidermidis strains adhered in ten to 100 times greater numbers to the knitted Dacron graft material than to expanded polytef. The production of an exopolysaccharide by the RP-12 strain significantly increased adherence to both graft types compared with the SP-2 strain. The increased adherence of the RP-12 strain was inhibited by adding D-mannosamine to the inoculum. The in vitro model developed is well suited for further study of the mechanisms by which bacteria adhere to and colonize vascular grafts.