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Vascular grafts

1. What is this vascular graft made from?
2. What complications are associated with their use?

This is an 20 mm woven Dacron graft. This type and size of graft is frequently used for abdominal aortic aneurysm surgery. Dacron grafts are manufactured in either a woven or knitted form. Woven grafts have smaller pores and do not leak as much blood. To reduce the blood loss knitted grafts should be pre-clotted prior to insertion. They are less frequently used than woven grafts. Dacron grafts have recently been manufactured coated with protein (collagen/albumin) to reduced the blood loss and antibiotics to prevent graft infection. Impregnated grafts are considerably more expensive than their none coated counterparts

Vascular grafts can be classified as either biological or synthetic. There are two commonly used types of biological grafts. An autograft is one taken from another site in the patient. In peripheral vascular surgery by far the most commonly used such graft is the long saphenous vein. This can be used in situ with the valves surgically destroyed with a intraluminal cutting valvutome. Alternatively the vein can be removed and reversed but this produces a discrepancy between the anastomotic size of the artery and vein. In thoracic surgery the use of internal mammary artery for coronary artery bypass surgery is another example of an autograft.  An allograft is one taken from another animal of the same species. Externally supported umbilical vein is rarely used but is an example of such a graft.

Synthetic grafts are most commonly made from Dacron or polytetrafluroethylene (PTFE). Dacron has already been discussed. PTFE is a velour graft. Its smooth surface is less thrombogenic than Dacron. Its smooth wall is prone to kinking as it passes around joints necessitating it to be externally supported.  Dacron grafts are frequently used in aortic and aorto-iliac surgery. Below the inguinal ligament the results of all synthetic grafts are inferior to those obtained with the use of vein grafts. Suitable vein is not always available and in this situation PTFE should be used. It can be used in conjunction with vein as a composite graft. Neointimal hyperplasia at the distal anastomosis can be reduced by the incorporation of a segment of vein as either a Millar Cuff or Taylor Patch to improve the long-term patency of the grafts.

The commonest complications associated with the use of vascular grafts are:

  • Graft occlusion
  • Graft infection
  • True and false aneurysms at the site of anastomosis
  • Distal embolisation
  • Erosion in to adjacent structures - e.g. Aorto-enteric fistulae

Graft infection is thankfully rare (1-2%) but for the patient concerned is usually disastrous. The most common cause of graft infection is contamination at the time of surgery. Eradication of infection with the graft in situ is difficult and it may require removal. It replacement of the graft is required an extra-anatomic graft is often necessary (e.g. replacement of a aortic with an axillo-bifemoral graft). Anastomotic aneurysms result from partial or total disruption of the anastomosis. They usually result from infection or disruption of the suture line. Most are asymptomatic but some cause symptoms as a result of local pressure . If they are superficial they can usually be easily palpated. A chronic non-pulsatile swelling at the site of an anastomosis is more likely to result from a lymphatic collection (lymphocele) than an aneurysm. Treatment requires a short segment bypass graft to remove the risk of rupture. Most aorto-enteric fistulae present months or years after the initial vascular surgery. The most common site of erosion is at the proximal anastomosis of an aortic graft into the distal duodenum or duodeno-jejunal flexure. Any GI bleed in a patient with an intrabdominal vascular graft should raise suspicion of a aorto-enteric fistula. They often present with a moderate 'herald' bleed prior to an exsanguinating haemorrhage. The site of bleeding is beyond the reach of a conventional endoscope. CT may show an anastomotic aneurysm but early laparotomy, removal of the graft, oversew of the aortic stump and extra-anatomical bypass is usually required.

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