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Biomedical subjects

M C Proctor

Publications and source records attributed to M C Proctor.

At least 37 records · Page 2Linked to original sources
PubMed1997

An improved process for development and testing of vena caval filters: the percutaneous steel Greenfield filter.

BACKGROUND: The purpose of this study was to develop a reduced profile stainless steel Greenfield filter with an over-the-wire delivery system and to compare its performance with the existing Food and Drug Administration-approved Greenfield filters. In addition, we wanted to standardize a system for evaluating filter prototypes. METHODS: Percutaneous stainless steel filters with various hook configurations were evaluated for efficacy and safety in four in vitro modules designed to reproduce potential liabilities experimentally. Animal studies to assess thrombus capture and resolution, filter stability, migration, and hemodynamics were completed in 4 dogs and 38 sheep. RESULTS: Mathematical modeling suggested that hook angle was the most relevant factor in improving resistance to migration. Prototypes that varied with respect to hook length and angle were evaluated in both the in vitro testing unit and in sheep. The stainless steel filter with two downward directed hooks provided clot capture comparable with the current Greenfield filter, maintenance of flow, and resistance to fatigue and corrosion while providing significant resistance to migration and penetration (p < 0.05). CONCLUSIONS: The percutaneous stainless steel Greenfield filter with the alternating hook design provides a reduced profile device that can be placed over a wire to improve positioning. The use of a standardized testing system reduced both the time and cost of bringing this new device to the market.

Animals↗
PubMed1997

Limb asymmetry in titanium Greenfield filters: clinically significant?

PURPOSE: The purpose of this study was to determine the outcomes for patients with titanium Greenfield vena caval filters (TGFs) and, in particular, to evaluate the effect of filter leg distribution on recurrent pulmonary embolism (PE) and caval occlusion. METHODS: Physical examination, abdominal plain films, and duplex ultrasound examinations of the inferior vena cava and lower extremities were obtained annually and recorded in a Filter Database. RESULTS: Seven hundred eighty-three TGFs have been placed since 1989. Follow-up was available for 373 patients, or 65% of the surviving patients, over 1 to 84 months (mean, 33 months). Asymmetry was identified in 42 placements (5%), and 35 of these patients had at least one follow-up examination. The overall incidence of recurrent PE was 3.2% (12 of 373), whereas the caval patency rate was 97.8% (265 of 271). These outcomes were not significantly different for patients who had asymmetric filters (p = 0.1 and 0.18, respectively). CONCLUSIONS: Filter leg distribution does not appear to be associated with an increased incidence of recurrent PE or caval occlusion. These data support earlier in vitro findings. The long-term results with the TGF are comparable with the results of the original stainless steel Greenfield filter.

Female↗
PubMed1997

Pulmonary embolism: diagnosis, incidence and implications.

The purpose of this study was to determine the prevalence of pulmonary embolism at an academic tertiary care center, to identify the methods of diagnosis, and to characterize the outcomes for this population. A retrospective analysis of multiple data sources including records from the Medical Information System, and the Departments of Pathology, Radiology, Nuclear Medicine and Pharmacy were reviewed for all patients with positive reports of pulmonary embolism. These were verified by the medical records and a listing of all positive cases was developed. A total of 320 patients developed pulmonary embolism during the study period and 121 died before discharge. The prevalence was 3.5 cases per 1000 admissions, with a mortality of 1 per 1000 cases. Significant misclassification of patients and errors in rate estimation would have occurred if multiple sources of information were not used. Definitive diagnosis and appropriate treatment with a Greenfield filter was associated with improved early survival. By relying on ICD-9 coding, 80% of fatalities and 13% of patients with positive angiograms would have been missed.

Adult↗
PubMed1997

Clinical results of Greenfield filter use in patients with cancer.

The purpose of this report is to examine the outcomes for patients with an underlying diagnosis of malignancy who have had Greenfield vena caval filters placed for protection from pulmonary embolism, and to identify areas requiring further study. This was a retrospective review of data obtained from the Greenfield filter registry and the University of Michigan Tumor Registry for 166 patients treated at the University of Michigan Medical Center between January 1988 and June 1994. The 84 men and 82 women (mean age 57.8 years) had a mean survival time of 10 (range 1-68) months. This differs significantly from patients in the filter registry who do not have malignancy (P<0.0001). Some 51% experienced recurrence of their malignancy at a mean of 20 months; this timing corresponds to development of new or recurrent thrombembolism and filter placement. Distant metastases were present in 72% of patients at the time of filter placement. In conclusion, as anticipated, filter patients with malignancy have a significantly shorter survival time than those with other concurrent diseases. A temporal association between the progression of the malignancy and the occurrence of thromboembolism is observed in this population and requires further study. Future studies regarding the use of vena caval filters in these patients and the role of diagnostic screening for deep venous thrombosis and occult recurrence of malignancy should focus on efficacy, safety, cost and patient quality of life rather than on survival.

Cause of Death↗
PubMed1997

Posttrauma thromboembolism prophylaxis.

PURPOSE: The need to study methods of thromboembolism prophylaxis in high-risk trauma patients is well established. The purpose of this study was to evaluate the feasibility of a proposed study design, including current methods of prophylaxis, performance of a risk assessment profile scale, and the use of serial color-flow duplex studies in detecting deep venous thrombosis (DVT). METHODS: Patients were enrolled into the study, stratified as to their ability to receive anticoagulation and randomized to low-dose unfractionated heparin, low molecular weight heparin, pneumatic compression devices, or foot pumps with or without vena caval filters. Serial ultrasound scans were performed at designated intervals for 4 weeks. Pulmonary angiograms were obtained for clinical signs or symptoms of pulmonary embolism. RESULTS: Fifty-three patients, 32 male and 21 female patients with a mean age of 44 years, completed the study. The incidence of DVT was 43% (23 of 53 patients) and significantly higher in older patients. There were no pulmonary embolisms. Color-flow duplex proved to be a sensitive method for detecting both proximal and distal thrombi. The risk assessment profile for thromboembolism (RAPT) scale identified a group of patients with a high incidence of DVT. However, the occurrence of DVT was not correlated with the magnitude of the RAPT score. CONCLUSION: The ability to identify a population with a high incidence of thromboembolism by using the RAPT score to detect asymptomatic DVT, and the suggested advantage of low molecular weight heparin, all support the need for an appropriately powered randomized clinical trial.

Adult↗
PubMed1997

Endovascular methods for caval interruption.

Current methods for vena caval interruption have developed in parallel with advances in endovascular techniques. Six filters are currently approved by the FDA for marketing: three Greenfield filters, the Venatech, Simon Nitinol, and Bird's Nest filter. These are compared with respect to design and function. In addition, the utility and limitations of temporary filters are addressed. The use of endovascular techniques to correct misplacement of a filter, to free entangled guidewires, or to adjust filter limb distribution is described.

Blood Vessel Prosthesis Implantation↗
PubMed1996

Early placement of prophylactic vena caval filters in injured patients at high risk for pulmonary embolism.

OBJECTIVE: Pulmonary embolism (PE) is a major problem in patients with multiple injuries. We present our experience with early placement of prophylactic vena caval filters (VCFs). DESIGN: Prospective study group with historical control. MATERIALS AND METHODS: From March 1993 to December 1993, VCFs were placed in 40 consecutive patients with three or more risk factors for PE and had demographic, physiologic, venous thromboembolic prophylaxis, and outcome data collected prospectively (VCF group). They were compared to 80 injured patients admitted between November 1991 and February 1993 who survived > 48 hours and who were matched with the VCF group for mechanism of injury and risk factors for PE (NO VCF group). MEASUREMENTS AND MAIN RESULTS: VCF placement affected a significant reduction in the incidence of PE (2.5% vs. 17%) and a clinical reduction in PE-related mortality. Embolic trapping was suggested by a 10% incidence of documented vena caval thrombi and although two patients developed significant venous stasis disease, no other VCF-related morbidity was noted. CONCLUSIONS: In spite of long-term morbidity, early prophylactic VCF placement is safe and should be considered in the prophylaxis of PE in the high-risk injured patients. This intervention may be effective in eliminating PE as a major cause of posttrauma morbidity and mortality.

Adult↗
PubMed1996

Current indications for caval interruption: should they be liberalized in view of improving technology?

Although the impressive increase in the number of filters placed since 1988 is not surprising, it is appropriate to continue to review the indications for placement to determine whether abuse of these devices is occurring. Initially, there were very stringent requirements that were appropriate because there were few data to evaluate the efficacy and safety of the device. Now, data have been accumulated indicating the Greenfield filter has a high degree of efficacy (95%) and comparable caval patency (96%)32 for 20 years.1 Knowing that the filter is safe and effective, physicians are electing to place it in patients with greater comorbidity factors or with longer life-expectancy. In addition, advances in the treatment of patients with multiple trauma and malignancy have resulted in improved survival, leaving more patients at risk of DVT and PE. Finally, the number of patients older than age 60 is increasing rapidly, and the number of elective and emergent orthopaedic procedures is growing. All of these factors have led to an increased number of filter placements that should be considered appropriate. Although there are certainly cases in which the filter was placed without sufficient justification, the explosion in use can more accurately be correlated with changes in medical care, the established efficacy and safety of the device, the growing numbers of patients diagnosed with thromboembolism, and the increased awareness of the risk of complications from anticoagulation. When filter placement is preceded by a careful assessment of the patient to determine the risks and benefits of alternative treatments, there is little danger of abuse. However, more clinical investigation will be necessary to determine the optimal, cost-effective approach in situations in which controversy currently exists.

Anticoagulants↗
PubMed1995

Twenty-year clinical experience with the Greenfield filter.

The purpose of this study was to characterize the long-term safety and efficacy of the stainless-steel Greenfield filter. All patients who underwent Greenfield filter placement at three institutions during tenure of the senior author (L.J.G.) were entered prospectively into a filter registry and followed on an annual basis. Follow-up consisted of clinical examination to evaluate the status of venous disease or recurrence of pulmonary embolism, abdominal radiographs to determine the stability of the filter and an evaluation of the patency of the inferior vena cava and lower extremities. This report summarizes the 20-year experience. The rate of recurrent pulmonary embolism was 4% and the caval patency rate was 96%. Some filter movement of no clinical significance was seen in 8% of cases. There was no procedural mortality and morbidity was minimal. Greenfield filter insertion provides long-term protection from pulmonary embolism while preserving caval patency.

Adolescent↗
PubMed1994

Extended evaluation of the titanium Greenfield vena caval filter.

PURPOSE: The purpose of this study was to evaluate the long-term safety and efficacy of the titanium Greenfield filter-modified hook for prevention of pulmonary embolism. METHODS: We conducted a prospective study in 173 patients from four institutions who underwent clinical examination, abdominal radiography, and duplex ultrasound examinations of the vena cava and lower extremities. If indicated by protocol or clinical presentation, computed tomography scans, pulmonary angiograms, or venacavograms were obtained. RESULTS: The most common procedural event was filter limb asymmetry (10%), which had no clinical significance. A variety of other minor procedural events occurred in another 10% of cases. Early follow-up (< 6 months) was completed in 149 patients, and long-term evaluation was completed in 113 (> 12 months). Deaths in 24 patients were from nonembolic causes in all but one. There were four suspected or confirmed recurrent pulmonary emboli, for an incidence of 3.5% (four of 113), with one death (0.9%). Four patients had inferior vena cava occlusion at early follow-up and at long-term evaluation, only one remained occluded (1%). Insertion site venous thrombosis was seen in only two patients (2%). CONCLUSION: The titanium Greenfield filter provides protection comparable to the standard stainless steel Greenfield filter after 1 year with a low incidence of recurrent pulmonary embolism (3.5%) and a high caval patency rate (99%).

Cohort Studies↗
PubMed1994

Staging of fixation and retrievability of Greenfield filters.

PURPOSE: The purpose of this study was to determine the retrievability of the Greenfield filter, to characterize fixation, and to evaluate the mechanical function of a new retrieval unit. METHODS: Stainless steel, titanium, and two prototype Greenfield filters (n = 82) were placed in 15 sheep at multiple sites and retrieved acutely, and 7, 14, and 21 days after placement. The animals were killed, and appropriate tissues were submitted for histopathologic evaluation. RESULTS: Eighty-two percent of all filters were retrieved. Two animals died during the procedure of cardiac tamponade. Retrieval was easiest immediately after placement, but it was least successful from the right atrium and associated with the highest incidence of damage. By 21 days, the intima around the filter hooks had thickened with myointimal hyperplasia and variable amounts of endothelial regeneration. Guide wire-hook modification was used to improve filter capture. CONCLUSIONS: All models of the Greenfield filter can be retrieved 14 to 21 days after placement, although there is high risk to retrieval from the right atrium and ventricle. The long-term safety of the Greenfield filter in man makes it difficult to justify removal in any but exceptional cases.

Animals↗
PubMed1994

Attitudes toward retirement. A survey of the American Surgical Association.

OBJECTIVE: This study examined attitudes and practices with respect to retirement in a senior group of surgeons. The authors studied the extent of planning for retirement and factors that should determine withdrawal from performing operations. SUMMARY BACKGROUND DATA: Federal law prohibits mandatory retirement or withdrawal of operating privileges based on age. Some surgeons fail to recognize the effects of aging, which may place their patients and themselves at risk. There currently is no established method to deal with these issues until adverse outcomes occur. METHODS: A survey was returned from 75% (659/882) of the members of the American Surgical Association. Work load, level of planning for retirement, and methods to determine when one should cease performing operations were collected. Responses were coded and the data were analyzed. Additional subgroup analyses were conducted, stratified by age and level of operative activity. RESULTS: Less than 50% of respondents reported any retirement plan, and among those who did, 75% planned activities in medicine. The extent of planning varied by age. In the youngest group (40-50 years), only 6.5% had a plan versus 40% of those older than 70 years who were not retired already. With respect to withdrawal of privileges, the majority of those surveyed favored determination by peer review or onset of physical disability rather than age. The level of activity declined significantly between 60 and 70 years; however, 18% of those older than 70 years of age continued to perform operations. CONCLUSIONS: Both personal and institutional problems can arise when surgeons continue to practice despite limitations of aging. More positive attitudes toward retirement are needed as well as methods for evaluation of performance that reflect a surgeon's response to aging.

Adult↗
PubMed1994

Inferior vena caval filters.

Interest in the use inferior vena caval filters has grown consistently during the past 8 years, with 51 articles appearing in the medical literature during the past year. The development and introduction of smaller profile devices capable of percutaneous placement has opened the field to interventional radiologists as well as surgeons. The current periodic literature provides a variety of information regarding indications for use, adverse events, experimental models, case reports, long-term clinical studies, and information regarding new devices still in the experimental phase. In caring for patients, it is important to consider carefully the indications for filter placement, the results of long-term performance studies, and the types of complications that can develop from the underlying disorders as well as the devices. Many of the reports are significant in that they provide new, carefully researched information to assist the clinician; some, however, due to poor design or small sample size, merely confuse the issues.

Equipment Design↗
PubMed1993

Long-term experience with transvenous catheter pulmonary embolectomy.

PURPOSE: Massive pulmonary embolism (PE), defined by systemic hypotension and need for inotropic support, has a high mortality rate. Transvenous catheter pulmonary embolectomy performed with the patient receiving local anesthetic provides an expeditious alternative to lytic therapy or open embolectomy on cardiopulmonary bypass. METHODS: The indication for embolectomy in this series of 46 patients was hypotension despite inotropic support in all but four patients (91%); the latter sustained major embolism and were respirator dependent. In the first 10 patients treated from 1970 to 1974, a metal cup attached to a straight catheter was used. RESULTS: Hemodynamic improvement occurred in nine of 10 initial patients, but recurrent PE and a mortality rate of 50% prompted addition of a vena caval filter and directional control to the catheter. Subsequently 36 patients were treated with this combination from 1975 to 1992. Emboli were extracted in 76% (35 of 46) of the total series with a 30-day survival rate of 70% (32 of 46). Hemodynamic data showed an average reduction in mean pulmonary artery pressure of 8 mm Hg and a significant increase in mean cardiac output from 2.59 L/min to 4.47 L/min (p = 0.003) after embolectomy. Complications included wound hematoma (15%), pulmonary infarct (11%), recurrent deep venous thrombosis (6%), pleural effusion (4%), and myocardial infarction (4%). CONCLUSIONS: Successful embolectomy was most likely for categories of major PE (4 of 4, 100%) and massive PE (27 of 33, 82%) and least likely for chronic PE (5 of 9, 56%) (p < 0.03). Successful embolectomy also predicted long-term survival (p < 0.01), which was 89 months for the series (range 1 to 237 months). Catheter pulmonary embolectomy by surgeon and radiologist is of maximal benefit for major or massive PE but less likely to benefit patients with chronic recurrent PE.

Adolescent↗
PubMed1992

Late results of suprarenal Greenfield vena cava filter placement.

Placement of the Greenfield filter above the renal veins was necessary in 71 (9%) of 821 total patients in the filter registries of two institutions. The status of 60 patients (85%) could be verified, with follow-up data ranging from 18 months to 16 years (average, 53 months). Of 24 deaths (34%), none was from recurrent embolism or renal failure; death was most commonly associated with a malignant neoplasm. The recurrent embolism rate was 4%, identical to the infrarenal experience. Duplex evaluation of the filters in 22 patients, representing the majority (61%) of living patients, showed that all the filters were patent. Sixteen patients (41%) had lower-extremity edema that predated filter insertion, and in no patient did the results of noninvasive venous studies worsen. Filter fracture (two patients) or distal migration (two patients) had no clinical sequelae, and there was no evidence of renal dysfunction. For thrombus extending to the level of the renal veins or within them and for pregnant patients or women of childbearing age, suprarenal placement of the Greenfield filter is safe and effective, with no filter obstruction seen in follow-up extending to 16 years.

Adolescent↗
PubMed1992

Thromboembolism: prevention and treatment with vena cava filters.

Mechanical approaches to the prevention of pulmonary thromboembolism have evolved from direct operative procedures to the percutaneous insertion of a variety of filter devices. The longest follow-up experience is with the Greenfield vena caval filter (Medi-Tech, Inc, Watertown, MA), which has a long-term vena caval patency rate of 98% and a recurrent embolism rate of 4%. Alternative filters, such as the Bird's Nest (Cook, Inc, Bloomington, IN), VenaTech (VenaTech, Evanston, IL), and Simon Nitinol (Nitinol Medical Technologies, Woburn, MA), are effective in the prevention of embolism but have a vena caval thrombosis rate of 8% to 20%. The efficacy and safety of prophylactic insertion of the Greenfield filter has been demonstrated in several clinical trials, which appears to justify its use in appropriately selected high-risk patients scheduled for orthopedic procedures.

Equipment Design↗
PubMed1992

Experimental embolic capture by asymmetric Greenfield filters.

An uncommon complication of percutaneous insertion of the titanium Greenfield filter is angulation at discharge with clustering of the limbs to one side of the vena cava. Potential adverse effects of this asymmetry were tested in a perfusion system with cadaver venae cavae. The stainless-steel Greenfield filter (SGF) was compared with the modified-hook titanium model (TGF-MH) and a percutaneous modified-hook model of the SGF (SGF-MH) with flexible plastic emboli in four sizes and varied sequences. There were 458 runs comprised of 2203 embolic events, with an overall successful capture rate of 81% despite tilting, asymmetry, and accelerated flow rates from 1.0 to 2.5 L/min. Significant differences were observed in vena cava with diameters greater than 22 mm where capture rate was 76% as opposed to 86% in venae cavae less than 22 mm (p = 0.01). Larger emboli (8 x 25 mm and 8 x 100 mm) were trapped uniformly, whereas smaller emboli (5 x 10 mm) had 59% capture (p = 0.001). Similarly, the capture rate was less when smaller emboli were released before the larger ones (71% vs 87%; p = 0.001). Capture in small versus large venae cavae was not significantly different for the SGF (75%) or TGF-MH (84% vs 87%) but differed for the SGF-MH (98% vs 67%; p less than 0.001). Logistic regression was used to develop a mathematic model for interaction of the variables and determined two first-order interactions: caval size and limb position and caval size and type of filter.(ABSTRACT TRUNCATED AT 250 WORDS)

Cadaver↗