David D. Schmitt

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.

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.

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.

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.

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.

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.

Giant colonic diverticula—Three distinct entities

A case report and review of the literature support a new theory that giant colonic diverticula are three distinct pathologic entities. The three types can be separated by histologic type.

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 (Fishers 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.

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.

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.