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Biomedical subjects

T C McCowan

Publications and source records attributed to T C McCowan.

At least 19 recordsLinked to original sources
PubMed2001

Microbubble potentiated ultrasound as a method of declotting thrombosed dialysis grafts: experimental study in dogs.

Intravenous perfluorocarbon-exposed sonicated dextrose albumin (PESDA) microbubbles in the presence of low frequency ultrasound (LFUS) can lyse very small clots. We develop a similar method to declot full-size arteriovenous dialysis grafts. Dialysis grafts fashioned in three dogs were cannulated and ligated. After thrombosis, three declotting techniques were randomly applied: 1) direct injection of PESDA + LFUS; 2) direct injection of saline + LFUS; and 3) intravenous PESDA + LFUS. Declotting was graded by cine angiography scores of each third of the graft on a scale of 0-4 (maximum total score = 12). Twenty-six procedures showed mean patency scores of 11.1 for direct PESDA and 8.4 for i.v. PESDA, vs 4.9 for direct saline, p = <0.001. All eight direct PESDA injections achieved lysis and good flow, but none of 8 direct saline injections succeeded, p = <0.01. Intravenous PESDA succeeded in 4 of 10 procedures, p = <0.04 vs saline. Direct injection of PESDA with transcutaneous LFUS succeeds in lysing moderate-size clots and recanalizing thrombosed fistulas.

Animals↗
PubMed2000

Relative ultrasonographic echogenicity of standard, dimpled, and polymeric-coated needles.

PURPOSE: To use quantitative ultrasonographic measurements to compare the effect of a polymeric coating designed to increase needle echogenicity to commercially available needles. MATERIALS AND METHODS: Commercially available standard smooth and dimpled echogenic tip 21-gauge needles established reference levels of echogenicity in gelatin-based and turkey breast phantoms. Examples of both types of needles were coated with a thin polymeric film that utilizes entrapped microbubbles of air on its surface to increase echogenicity. Samples of each type in both coated and noncoated versions were placed in phantoms in matched positions and imaged with clinical ultrasound machines. Similar numbers of each category were evaluated at various angles of insonation for a total of 109 images. Similar numbers of each category were imaged at 5-minute intervals for up to 38 minutes for a total of 226 images. Images were recorded, digitized, and evaluated for relative echo strength in arbitrary echogenic brightness units. RESULTS: Coating increased peak echogenicity over the entire needle to a level that closely approximates the peak echogenicity of dimpled needle tips (means: dimpled = 834, coated smooth = 803, coated dimpled = 823; P = .54). Smooth is lower than this group at 468 (P = .0001). Representative area echogenicity increased with coating or dimpling (smooth = 377 vs coated smooth = 778, coated dimpled = 690, dimpled = 775; P = .0001). Coating increased peak values 74% and area values 95% compared to smooth. Decreased angles of insonation moderately reduced echogenicity on coated smooth, coated dimpled, and dimpled, while it decreased to below good visibility threshold on standard smooth needles. The echogenicity of the coated needles fades in saline with time (1%/min). CONCLUSION: Objective measurements show that this coating significantly increases echogenicity of entire needles to match that obtained with a dimpled tip.

Animals↗
PubMed1999

Percutaneous translumbar cardiac catheterization and central venous line insertion: an alternative approach in children with congenital heart disease.

Children with congenital heart disease present major problems with venous access, eliminating conventional routes for cardiac catheterization. Although the transhepatic approach has recently gained popularity, we describe here an alternative approach using percutaneous translumbar approach for cardiac catheterization and/or in-dwelling central line insertion in three children with congenital heart disease. Diagnostic hemodynamic studies, transcatheter delivery of an intravascular stent for left pulmonary artery (LPA) stenosis, and chronic central venous line insertion were performed using this technique. Disadvantages include interventionalist's unfamiliarity with technique, awkward patient positioning, technically more difficult than transhepatic, and potential injury to kidney and bowel. Advantages include avoidance of vascular-rich hepatic parenchyma, thus reducing risk of hemorrhage; providing an alternative where transhepatic entry may be contraindicated; avoidance of bile duct, portal vein, and hepatic artery injury; and providing another alternative for not only transvenous, but also transarterial access that may be required for intravascular aortic stent delivery. The interventional radiologist should be utilized as a valuable resource to the cardiologist to help teach and supervise this technique in selected infants and children with limited vascular access.

Cardiac Catheterization↗
PubMed1996

Biliary strictures in liver transplant recipients: treatment with metal stents.

PURPOSE: To determine initial and long-term results of metal stent placement in biliary strictures that failed to respond to balloon dilation. MATERIALS AND METHODS: Sixty-one metal stents were placed in 36 liver transplant recipients (age range, 3 months to 71 years) with biliary strictures that failed to respond to balloon dilation. Patients were followed up for up to 5 years. RESULTS: Initial stent placement was successful in all patients. Primary patency was 44% at 3 years and was 0% at 5 years; secondary patency was maintained at 88% at those intervals. Patency associated with the Gianturco Z stent was superior to that with the Palmaz stent. Stents located at anastomotic sites had higher patency rates than those at nonanastomotic sites. Major stent-related complications occurred in eight patients and included two pediatric deaths. CONCLUSION: Metal stents can be useful in the short term but have limited patency, often require repeat intervention, and have substantial complications. Long-term success depends heavily on repeat interventions or stent removal.

Adolescent↗
PubMed1993

Percutaneous inferior vena caval filters: follow-up of seven designs in 320 patients.

Three hundred twenty-four percutaneous inferior vena caval (IVC) filters of different designs were placed in 320 patients from April 1985 through June 1992. No acute mortality or substantial morbidity was attributed to filter placement. Radiologic or pathologic follow-up data were obtained in 227 (71%) patients (230 filters); clinical follow-up data only were obtained in 50 (16%) patients (50 filters). One hundred twenty (43%) patients died; post-filter-placement pulmonary emboli (PE) were related to the cause of death in eight. At IVC filter imaging studies, 26 of 137 (19%) filters demonstrated caval thrombus; 12 of 132 (9%) filters had delayed penetration through the IVC wall of greater than 3 mm; 13 of 230 (6%) filters migrated more than 1 cm; and five of 230 (2%) filters had fracture of a strut or leg. Deep venous thrombosis (DVT) at the insertion puncture site or in the lower extremity was noted in 26 of 117 (22%) cases of filter placement. Among patients without imaging studies, clinical suspicion of complications included PE in four patients, IVC thrombus in 14 patients, and lower-extremity DVT in 10 patients. Long-term clinical and radiologic follow-up of all IVC filters is indicated due to the relatively high prevalence of some complications.

Adolescent↗
PubMed1992

Complications of the nitinol vena caval filter.

Simon nitinol vena caval filters were placed percutaneously in 20 patients. Follow-up (average, 14 months) data were available for 16 patients, and four patients were lost to follow-up. There were no proved or suspected cases of pulmonary embolism after filter insertion. Complications encountered included caval penetration (n = 5, one acute and four at follow-up), caval thrombus (n = 4, two determined radiologically and two clinically), postplacement deep venous thrombosis (n = 2, one radiologic and one clinical), filter migration (n = 1), and delayed fracture of a filter leg (n = 2). Although no deaths or significant morbidity resulted from any complication, the relatively high complication rate, especially of significant caval penetration (documented in 25% of filter insertions), merits continued short- and long-term assessment of patient status after filter placement.

Adult↗
PubMed1992

Vena caval filter use in orthopaedic trauma patients with recognized preoperative venous thromboembolic disease.

This study comprises a series of 35 patients with pelvic or lower extremity fractures requiring surgery who also had a documented significant acute deep venous thrombosis (DVT). The authors treated these with low-dose Coumadin and 36 vena caval filters, which were used prophylactically prior to surgery. The patients received low-dose warfarin after placement of the vena caval filters and were maintained at 1.3-1.5 times the prothrombin control value for 6 weeks to 3 months. In this group of patients, there were no fatal pulmonary emboli and no clinically significant complications from filter placement. There were nine asymptomatic filter complications demonstrated radiographically in eight patients. Additionally, one patient with a tilted vena caval filter required placement of another filter. The combination of vena caval filters and low-dose warfarin appears to be a successful and relatively safe method of managing those patients who have acute DVT and require surgery for their pelvic or lower extremity fractures.

Combined Modality Therapy↗
PubMed1991

LGM vena cava filter: objective evaluation of early results.

One hundred one LG-Medical (LGM) vena cava filters were placed in 97 patients at four institutions. Placement was a complete technical success in 90% (91 of 101). In 6% of attempts, LGM filter insertion was complicated by incomplete opening of the filter. Pulmonary embolism after filter placement was not definitely demonstrated in any patient. The probability of inferior vena cava patency was 92% at 6 months after filter insertion. Thrombosis at the insertion site was seen in eight of 35 patients (23%) evaluated with duplex ultrasound or venography. Thrombus was observed in 37% of filters at follow-up examination, with cephalic extension of thrombus above the filter in 20% of all patients examined. Filter migration (greater than 1 cm) was seen in 12%; significant angulation was observed in only one patient (2%). In vitro experimentation demonstrated that incomplete opening of the LGM filter during placement can be avoided, in part, by brisk retraction of the insertion cannula. The low-profile introducer system of the LGM filter allows increased alternatives in selecting the site for filter insertion. The low-profile system also makes outpatient filter placement a possibility. No significant difference in the prevalence of thrombosis at the insertion site following LGM filter insertion was noted compared with previous results reported for percutaneous transfemoral placement of the Greenfield filter. The nonopaque sheath does not permit careful localization prior to filter deposition. Modification of the LGM filter to include a radiopaque sheath is suggested.

Equipment Design↗
PubMed1991

External iliac artery rupture during angioplasty: control by balloon tamponade.

Transluminal angioplasty, particularly of stenoses of the iliofemoral arteries, is an excellent technique with a success rate greater than 90%, an overall complication rate of less than 5%, and a low incidence of major complications. Of these major complications, arterial rupture is one of the most urgent. We have presented a case of external iliac artery rupture during angioplasty that graphically demonstrates the value of balloon tamponade in managing this potentially catastrophic event. The angiographer's sensitivity to the possibility of arterial rupture and prompt management, combined with close collaboration with the vascular surgeon, can lead to a good clinical outcome.

Angioplasty, Balloon, Coronary↗
PubMed1991

Duplex scanning versus venography as a screening examination in total hip arthroplasty patients.

Combined B-mode/Doppler (duplex) scanning and venography were compared in routine perioperative screening for proximal deep vein thrombosis (DVT) in 158 total hip arthroplasty (THA) patients. Preoperative scans were performed in the first 60 patients; the low preoperative prevalence of 2% for proximal DVT was thought not to warrant routine preoperative scanning. Postoperatively, duplex scanning had a sensitivity of 79%, a specificity of 98%, and an accuracy of 97% when venography was considered as the gold standard. The postoperative incidence of proximal DVT was 12% in this group of THA patients treated with mechanical and pharmacologic prophylaxis. Including calf vein thrombosis, 30% had DVT postoperatively. This study demonstrates the efficacy of duplex scanning for diagnosing proximal DVT and describes an effective noninvasive method of screening THA patients for the presence of proximal DVT.

False Negative Reactions↗
PubMed1991

Preoperative venography. A risk factor for postoperative deep venous thrombosis in hip arthroplasty patients?

The incidence of postoperative deep venous thrombosis was compared between patients who had or had not received a preoperative screening venogram. No statistically significant difference in the deep venous thrombosis rate was noted postoperatively. Thirty percent of patients who received a preoperative venogram developed postoperative deep venous thrombosis, and 28% of those who did not have a preoperative venogram developed postoperative deep venous thrombosis. These results suggest that an orthopaedic surgeon may order a preoperative venogram for a patient at potential high risk of thromboembolic complications without predisposing the patient to an increased risk of postoperative deep venous thrombosis.

Causality↗