Production of Inferior Vena Cava Umbrella Filter Research Paper

Introduction

Inferior vana cava umbrella filter is also called Greenfield filter was designed in its primitive form in 1968 when a young surgeon named Lazar Greenfield lost a young patient with motorcycle. “This young man came in with broken legs and a broken pelvis, but the fractures were not the cause of death it was a pulmonary embolism, which had started in the man’s legs and then lodged in his lung, plugging up the body’s blood supply and threatening instant death” (Garber, 2006). He tried removing the clots surgically and was able to clear them but the lungs had got severely affected that death could not be prevented. “Greenfield told himself, there ought to be a better way.” (Bernard 1994). And within two years he found a way that was going towards the solution. A suggestion from an oil-industry engineer led the two men to create an implantable filter for trapping blood clots before they can reach the lungs. Since then more than half a million Greenfield filters have been placed in patients” (Garber, 2006).Arterial and venous thrombosis is a life threatening phenomenon and there are different treatment options like pharmacological and non pharmacological available for it. One safest way of treating this problem locally and taking out the blood clots or any other thrombi locally through placement of a filter is a favorable mode of treatment for thrombosis. This removal of clots mechanically is a very safe mode of treatment, but the prognosis mainly depends upon the type, material, size and the design of the filter used. These filters have transformed from non retrievable to retrievable and from the ones that used to require surgical intervention for placement to the ones that can be placed through a peripheral access just like along intravascular canola.

Main body

These filter the way medication come with different brand names with a different set of side effect profile and different efficacy is available form different companies. The design, material used and shape of it carries characterizes to it. It is “A co-axial filtering device for removing particles from arteries and veins comprises of an outer catheter that can be inserted into a blood vessel and an inner catheter with a filter at its distal end” (Bruckheimer 2007). Here its installation is more like an intravenous canola but there the filter is long and it does not function exactly like a canola so it has mechanical problems associated with it. “The filter is a radially expandable receptacle made of an elastic mesh structure of spring wires or plastic monofilaments. The filter expands into engagement with the walls of the blood vessel when it is pushed from the distal end of the outer catheter. A syringe is attached to the proximal end of the inner catheter and particles entrapped within the filter are aspirated through the inner catheter into the syringe. When filtering is no longer necessary, the filter can easily be removed by pulling the elastic material through the outer catheter” (Bruckheimer 2007). The reason for the production of these filters is the high mortality related to pulmonary embolism and the drastic affects we can get with placement of these filters. “Pulmonary embolism is a major killer that barely registers in the public consciousness. Each year about 600,000 Americans experience a PE, roughly the same number that suffers strokes. At least 60,000 pulmonary-embolism deaths occur annually; no one is sure of the exact number, since many people die suddenly from heart failure and their clots go undetected”.

In a lot of cases we know that the patients are at a sudden risk of dying due to embolization of a clot and there these filters have a major role to play. “All kinds of people are at risk, but especially those getting knee and hip-replacement surgery, cancer patients, and trauma victims, like the motorcycle rider” (Garber, 2006). “In the late 1960s a colander-like filter was introduced, but it often filled up with accumulated clots and blocked the vein. This filter was eventually withdrawn from sale. Blood-thinning drugs have proved effective, but many people, especially trauma victims, can’t take them because of the risk of internal bleeding” (Garber, 2006). And sometimes in trauma situation patients come to us with broken bones and seriously injured here it becomes very important that these patients be provided with prophylaxis for thrombosis but there is always a fear of internal bleed so, these patients can easily be taken care of with these filters rather than blood thinner. Greenfield took his dilemma to German kimmell. “Kimmell, a prolific inventor, ran a company that made valves and other machinery for oil and gas wells and pipes, but he also dabbled in medical devices. As Greenfield recalls, upon hearing about pulmonary embolism, Kimmell told him, “That sounds a lot like the problem we have in the oil field with sludge.” (Greenfield 1983). Thw hole design of this filter lies in the thought of this mechanical engineer, it worked exactly the way he thought he said that “In oil pipelines, sludge and debris are trapped by a cone-shaped filter. The geometry of the cone, Kimmell explained, allows oil to continue flowing around its edges while concentrating the sludge in the center, whereas a flat screen, with sludge spread across it, could completely clog the pipeline.

Kimmell and Greenfield decided that the conical-filter idea was worth a try in blood vessels. This whole concept if the principal has been used in the umbrella filters and the shape of the filter is identical to the oil filter that had inspired it and that further has resembles with a device patented in 1942 that was meant to protect a car’s gas tank from siphoning” (Garber, 2006). It consists of six legs converging in the center like an umbrella and it has tiny hooks to secure it in place in the blood-vessel wall, corrugations incorporated into the legs proximally that keep clots from slipping through and getting showered to the periphery or centrally. “It has a streamlined taper end distally that allows uninterrupted blood flow even with a clot trapped at the tip. The shape of it can very well explain the principle of its work” (Garber, 2006).

This design was started getting used to check the efficacy of it and it should very healthy results in animal models and the results were so engorging that it started getting used. “The devices were, from current perspective, pretty primitive, But the device worked well [and] the patients did well”(Greenfield, 1973). After this successful experiment other contemporary surgeons also started using this filter with promising results. “Greenfield’s first major paper on the Kimray-Greenfield filter, as it was then called (Kimray was the name of Kimmell’s company), appeared in the journal Surgery in 1973. In he early years brought a number of technical challenges. The filter had to be robust enough to last a lifetime in the hostile environment of the human abdomen. It had to stand up to countless stresses and be mechanically safe, nontoxic, and biologically and chemically inert. An early problem arose when solder in the brazed tip of the filter, where the six legs came together, caused a physiological reaction in some patients that loosened the connection, leading one or more legs to detach. Patients weren’t immediately harmed when this happened, but the defect made the filter less effective at capturing clots” (Garber, 2006).

There needed to be further modification to make it as usful as it felt when the performance of such a filter was seen and assessed in oil filtering. “Kimmell’s machinist solved the design problem by using a machine that exerted high pressure on the cap, compressing the legs together tightly and eliminating the need for brazing” (Garber, 2006). During the process of placement of this filter it was fund that pulling back on the catheter could release the filter prematurely and that can lead to vascular trauma So, Greenfield and Kimmell “designed a cylindrical carrier at the catheter tip to enclose the filter until deployment. They introduced a stiff guide wire that allowed the surgeon to orient the filter precisely, with the help of an X-ray monitor, before withdrawing the catheter and wire exactly the same procedure as for placement of a canola. Now the final product is looks deceptively simple, like a metallic badminton shuttlecock or an open-ended wire whisk” (Garber, 2006). This modification gave it a room to be manipulated to some extent depending on the size of the vessel “Its six legs, when fully deployed, span roughly an inch across the vena cava. “More than 10,000 Greenfield filters go into patients each year” (Garber, 2006). Clot removal used to be a surgical procedure in the past which was obviously hazardous and time consuming and the mortality rate of that was high but now with this invention “Doctors have perfected a fast, safe, and no surgical way to insert the device, as Dr. Kyung Cho very kindly demonstrated for this article.” (Greenfield. 1981) “Once the Greenfield filter is inside it can stay in for life (though other filters designed to do the same job are removable)” (Greenfield, 1973). “The vast majority of patients never have to think about it again. Over time the inner vessel wall spreads over the filter’s hooks, making the filter almost part of the body. Clots collecting in the filter’s conical nose almost always dissolve amid the continuous flow of blood, which has natural clot-dissolving properties” (Garber, 2006).

This aspect of this filter is the most important advantage of it. It increases the efficacy of this intervention drastically and this is one of the best filters for patients who are more prone to embolism like the ones with metastatic cancer or the ones on hormonal therapies. “We don’t limit the activities of any patient who’s had a filter,” says Greenfield. “We have patients with the device who’ve gone back to very active lifestyles. They’ve gone back to playing football; we’ve had fighter pilots taking huge G stresses…. We’ve even said a boxer could go back to boxing, but the boxing commission didn’t think too highly of that.” (Garber, 2006). The safety provided by the shape, size and design of this filter is a very secure feeling for the patient with chronic disease process for which they really need to be on treatment and along with that they also want to continue doing the fun activities of life their as well. “In 1973, at a meeting of the American Heart Association, Greenfield gave a talk about his lung-clot suction cup, with a side presentation on the filter. In the audience was Abele, who was scouting for products for his new medical-device company. Abele introduced himself to Greenfield after the talk, launching 30-year collaboration. First Abele took on the manufacture of the suction cup, and then, in 1980, when he bought Kimmell’s medical-device company, the Kimray-Greenfield filter became part of Boston Scientific’s catalogue. Abele renamed it the Greenfield filter” (Garber, 2006). “The filter helped Abele’s company to grow from two million dollars in sales to six billion today, and Boston Scientific is now the largest life-sciences company in Massachusetts” (Garber, 2006). “In the past years there have been 2 major modification to the design of this filter in 1980 stainless steel to titanium to allow compression of the filter into a sheath for delivery through a catheter and in the mid-1990 it was switched back to stainless steel to make the filter compatible with a guide wire, since some of the titanium filters weren’t going in straight” (Garber, 2006).

These changes required years of research for design work and it as multiple trials on animals before it was actually launched. It has been mentioned in one of Greenfield article says that “KG is one of the best of all the filters and this is now a standard for comparing the rest with” (Greenfield, 1997)

Pulmonary embolism which is a fatal phenomenon occurs because of the mechanical obstruction at capillary levels mostly due to clot formation or already mobilized clot. This kind of obstruction is better treated with mechanical intervention which is achieved through implantation of this umbrella filter into the vessel. Clots are formed in specific set of people either post trauma or after a period of prolonged immobilization, patients with some drug reaction, chronically ill patients and pregnant female so the design has to be such that it should be suitable for all the scenarios. The material of it is such that it can withstand with any intravascular trauma easily in most of the cases. Over the time the design has been changing with an over the results after modification. There have been a number of filters that are FDA approved and the shape of most of them is umbrella type but the best out of all still considered the Greenfield’ filter. “In one research study that was conducted in which three inferior vena cava (IVC) filters of different designs were studied to identify the potential links between published clinical results for thrombosis and recurrent pulmonary embolism (PE) rates and in vitro homodynamic patterns in the region of the filters” (Harlal, 2003). Results showed that for both the totally unclouded and partially occluded Mobin-Uddin and TrapEase filters, points of decreased blood supply or stagnation, recirculation and turbulence developed downstream of the filter and all these factors are prothrombotic in nature but with the Greenfield filter did not produce any prothrombotic flow patterns for either the totally non occluded or partially occluded states. “Results of published clinical studies supported the homodynamic findings, with the TrapEase and Mobin-Uddin filters having high rates of IVC occlusion and recurrent PE compared with those of the Greenfield filter” (Harlal, 2003).

So it is concluded that due to the best fitting design and other characteristics the Greenfield Umbrella filter is good in terms of low risk of prothrombotic activity and the recurrence rate with this one is low that are the 2 main focused points of success. (Harlal, 2003). “The effectiveness of an inferior vena cava (IVC) filter in preventing pulmonary embolism while preserving caval flow is significantly affected by its homodynamic characteristics. In a research study flow fields surrounding two types of IVC filters were compared to assess how the design of a filter may influence performance”( Couch. 2000) “Results showed that reductions in near-wall axial velocity and wall shear stress caused by the VenaTech filter were more extensive and severe than those caused by the Greenfield filter. These changes were the consequence of differences in the geometry and dimensions of the struts of the two filters. The measurements showed the flow fields to be laminar, with no evidence of turbulence in both cases” ( Couch. 2000). “On the basis of these results it can be concluded that two factors that have been linked to thrombogenesis, near-wall velocity and wall-shear stress were significantly affected by the larger frontal profile area of the VenaTech filter” ( Couch. 2000). “Although a larger area may increase clot-trapping efficiency, as shown by previous studies, the reduced near-wall velocities and wall shear stresses may increase the potential for thrombogenesis and, thus, caval occlusion. In contrast to other in vitro flow visualization studies, no turbulence was observed with either filter. ” ( Couch. 2000).

Conclusion

Inferior vana caval filters of different brands have been studied for their consistency, durability, and design and on the basis of all these it has been concluded that the Greenfield one which is also called KG filter or umbrella shaped filter are said to be the best out of all. Since the time of its invention it had been going through modifications depending on the out come. The design, material, and durability are all very important parameter that one should take into consideration for producing such a production that is dealing with lives specially. While designing and making this product a lot of consideration has been put in understanding the normal anatomy of human being’s vessels and even normal and abnormal anatomical variations have also been taken in consideration. Along with anatomical physiological variation have also been taken care of in the designing of this product so that the before putting the filter in the coagulation profile of the patients be know due to the prothrombotic affect of these filters. The design and the material of the new umbrella shaped inferior vana caval filter is such that they can be left inside the body for life long despite the hostile nature of human body and they do not need to be retrieved.

References

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