A vascular prosthesis is an implant that replaces natural blood vessels. It is mainly used for chronic vasoconstriction, bypass surgery or severe vasodilatation.
What is a vascular prosthesis?
A vascular prosthesis is an implant that replaces natural blood vessels. It is used primarily for chronic vasoconstriction (see illustration), bypass surgery, or severe vasodilatation. A vascular prosthesis replaces natural blood vessels and is used in case of severe damage to an artery. In this case, blood flow cannot be restored with the help of a stent. In the course of an operation, narrowed blood vessels are replaced or dilated blood vessels are replaced. However, a prosthesis is also used in cases of vascular injury, such as after accidents. In the middle of the 19th century, the first attempts were made to replace arteries by implanting tubes made of rubber, silver or glass. However, these attempts failed because the implants became thrombosed. In the second half of the 19th century, Guthrie and Carrell conducted research in this field and carried out experiments with alloplastic, autologous and heterologous replacements. Carrell also received the Nobel Prize for this in 1912. The breakthrough finally came with the Americans Jaretzki, Blakemere, and Voorhees, who implanted tubes made of plastic for the first time.
Function, effect and goals
Vascular prostheses are used for a wide variety of vascular diseases. These include:
- Arteriosclerosis with the formation of occlusions and constrictions.
- Coronary artery disease
- Arterial occlusive disease of the leg and pelvic arteries
- Narrowing of the carotid artery
- Narrowings of the visceral and renal arteries
Normally, vascular prostheses are made of plastic such as polytetrafluoroethylene (PTFE) or polyethylene terephthalate (PET). PET prostheses are used primarily in the aorta, femoral arteries, and internal or external iliac arteries. These prostheses have a folded structure, which ensures great flexibility. PTFE prostheses, on the other hand, are used in bypass surgeries as well as for smaller vessels. The prostheses are covered with a protein layer of collagen, gelatin or albumin, and the inside is lined with fibrin and platelets due to blood flow. To manufacture vascular prostheses, the plastic is melted and processed into yarn. Tubes are subsequently knitted or woven from this. These two prostheses have the advantage that they can be implanted directly without having to be preclotted first. For preclotting, blood is drawn and the prosthesis is saturated with blood inside and out. To ensure that the cavities are also wetted, the surgeon must stretch the prosthesis several times. There are also autologous transplants, i.e. the body’s own arteries or veins are used as vascular substitutes. Bioprostheses are made from heterologous or homologous vessels, whereby cadaveric veins or arteries are often used as homologous vessels. This also includes the Dardik prosthesis from umbilical cord veins. Heterologous vessels are vessels from animals, such as pigs or cattle. Vascular prostheses are used either as an ambient or bridging graft, and the choice of prosthesis depends on the intraluminal pressure, the caliber of the vessel, and the course of the graft. Selection of an appropriate vascular prosthesis is very important, as a prosthesis with incorrect dimensions may obscure or displace vascular branches. A vascular prosthesis is usually inserted with a catheter and then nestles against the vessel wall, where it holds the vessel open or reduces the blood pressure acting on the vessel walls. Usually, a vascular prosthesis is tubular and consists of a wire mesh covered with textile fabric or plastic. For very special applications, there are also branched prostheses called Y-prostheses, which are used, for example, in the case of an abdominal aneurysm. The prostheses can be one-piece or assembled from individual modules.
Risks, side effects, and hazards
About 90 percent of prostheses continue to function five to 10 years after implantation. However, for prostheses that are only about six to eight millimeters in diameter, the chance of success after five years is less than 50 percent.The most common complications that can occur are blockages due to severe tissue formation, problems with the material, or the development of aneurysms or pseudoaneurysms. In contrast to a stent, vascular prostheses are implanted artificially. This increases the incidence of infections, so regular monitoring of the wound during the first two weeks and subsequently at every physical examination is of great importance. It is also advisable to take a daily antiplatelet agent after implantation. The highest rate of infection occurs with a major bypass, but people are also at risk after surgery in the groin area. In contrast, the risk of infection is very low in patients who have had aortic surgery. The infections are mainly caused by staphylococci. These get onto the prosthesis, for example, when the implant comes into contact with the body surface during surgery. However, bacterial colonization is also possible due to tissue damage in the area of the prosthesis, for example if it rubs against the intestine. The bacteria then cover themselves with a mucus capsule so that antibiotics cannot work. However, the rate of infection can be reduced if patients are given antibiotics before or during surgery. If a vascular prosthesis is infected, the infected material must be removed, then the wound is cleaned and a new prosthesis is inserted. In addition, it is possible to implant a special prosthesis. These prostheses are coated with silver and can also be impregnated with antibiotics. This makes it easy to ward off infections.
