1. What is vascular access?

We talk about vascular access in patients who need frequent cannulation of the blood vessels for either haemodialysis or administartion of drugs that either have to be given for prolonged periods or when the drugs are powerful and will cause thrombosis if given through a peripheral vein that has low flow. In the conditions mentioned above, the peripheral veins cannot be used, and another mechanism is needed, in order to avoid the complications and the pain asociated with multiple cannulations.

We can use either artificial devices or we can join a peripheral artery to a vein [arteriovenous fistula or via a synthetic graft, a plastic tube]. In the former, a central vein is cannulated and the catheter is either brought out through the skin [usually in acute renal failure or in other acute conditions], or connected to a small chamber that is buried underneath the skin; the chamber is easily punctured with a needle [for frequent drug administration]. In the latter, blood from the artery is diverted into the veins which becomes engorge and readily visible; the vein can then be easily punctured with needles whenever needed.

2. Why do patients with end stage renal failure need vascular access?

The main functions of the kidne are:

a.        Blood filtration of waste products

b.        Elimination of excess fluid

c.        Formation of hormones to control anaemia

When the kidney does not function well [the cause is diabetes in 42%, hypertension in 25% and chronic infection in 10% of the cases], water accumulates into the body, hypertension ensues and the blood vessels harden; the waste products of metabolism cannot be filtrated and serious complications may arise. As there are treatments available for this type of renal insufficiency [peritoneal dialysis or haemodialysis with an artificial kidney machine], early intervention, before the kidneys stop to function completely, is necessary.

3. What is haemodialysis?

In haemodialysis, blood is pumped from the body [via plastic tubes called blood lines] through the dialyzer [figure on left], which in fact, is a bundle of tiny synthetic fibers. The membrane of these fibers is so thin that water is allowed to pass, and varying the pressure across the membrane allows the dialysis machine to remove the excessive fluid buit up between treatment and the dialysis solution to carry away the waste products. The haemodialysis machine pumps the blood, adds anticoagulants [to thin the blood] and regulates the purification process by the dialysis solution. The purest blood is then returned to the patient.

This type of dialysis requires that either an arteriovenous fistula or synthetic graft access be created. The reason is that the machine needs a flow of 140-150ml per minute, something that cannot be achieved by cannulating peripheral veins. With the fistula the veins become dilated, have a thick wall [arterialised]and can be easily cannulated for placement of the dialyis machine blood lines.

Alternatively, a double lumen catheter inserted into one of the big veins in the neck can be used. This method is usually performed in patients with acute renal failure or in patients that either do not have an arteriovenous fistula or there are problems with it [i.e. thrombosis, imaturity, etc].

4. What is a double lumen venous catheter?

A double lumen catheter is made from inert plastic tubes [in order to avoid reactions when blood runs through it] joined together and is inserted into a large vein in the neck [jugular or subclavian]. It may be either temporary or longterm. Temporary catheters are usully inserted percutaneously by the anaesthetist or one of your doctors, under local anaesthesia. Those used longterm, are generally cuffed, tunneled under the skin [as in figure 1], and are surgically placed [local or general anaesthesia can be used].

These cathetes, although useful, may develop serious infections or may thrombose [block by clot] and fail. They can also stimulate cloting in the vein they are inserted and cause thrombosis of the vein itself. Patients in whom this happens in the subclavian vein, it makes it difficult for them to sustain an arteriovenous fistula on the same arm. Therefore, these catheters should be avoided whenever possible, in lieu of placing a more permanent access.

5. What is an arteriovenous fistula?

An arteriovenous fistula [AVF] is an artificial communication [surgical connection] between an artery and  a vein. Early placement of such a fistula eliminates starting dialysis as an in-hospital patient in the majority of the cases.

There are many types of arteriovenous fistulae used for dialysis, but generally, they can be made by either directly connecting surgically an artery to a vein or by placing an artificial graft [tube] between them.

As a general rule, direct arteriovenous fistulae are prefered to grafts whenever possible, because the complication rate is substantially less and the life span of them is considerably longer [>4 years] compared to that of the grafts [1-1.5 years]. The only advantage that the graft has is that it can be used almost immediately [1-2 weeks].

The fistula takes about 2-3 months to mature and the veins to become engorged and dilated, in order to be easily cannulated. Previous cannulization or thrombosis of the veins may lead to phlebitis and permanent damage to the vessel wall, making it impossible to sustain a fistula.

Therefore all patients with ESRD should receive education regarding vein preservation and the fistula should be placed early, when the glomelural filtration rate [creatinine clearance] is less than 25ml/min or the creatinine is more than 3 times normal.

Regarding the site of vascular access, a specific rule is used:

·    the non-dominant arm should by used first

·    the more distal sites [wrist] should be used first,

·    followed by the more proximal sites [elbow]

·    if there is no way of  using your arm veins, an artificial graft is placed, firstly in the forearm and, if it fails,

·    in your upper arm.

·    In extreme conditions the veins in your leg can be also used but a graft is put there in the majority of cases. Usage of the leg vessels, however, is extremely rare.

However, despite all these options, the radial and elbow AVFs represent more than 90% of all surgical access  procedures carried out electively for patients in ESRD.

1. How is the operation carried out?

The operation is usually done under local anaesthesia but can, under certain circumstances, be done under general anaesthetic. It is usually performed as a day case. Day case surgery means that after surgery, when you recover from anaesthesia [3-4 hours if general, 1-2 hours after local anaesthesia]] your escort will take you home, with all instructions given to you before [by the surgeon] and after surgery [by the nursing staff].

2. The operation

The procedure site will be washed and shaved. Sterile drapes will be placed over you to guard against infection and local anaesthetic is injected on the incision line [along the elbow crease for a brachial or at the left side of your distal forearm for a radial] with a syringe. You will feel the initial scratch and then you may feel a burning sensation, but soon the area becomes numb.

The skin incision is then performed, vertical for a radial, transverse for a brachial AVF. The artery and the vein are mobilized, circulation is stopped [for about 15minutes] and they are joined together with a fine non-absorbable stitch.When completed, blood is allowed to flow again, this time through the fistula. The wound is closed by dissolvable or nylon stitch and a simple drape over it. You will be able to feel a thrill above the fistula, caused by the turbulence of flow through it.

3. What about after surgery?

·    The wound can be exposed within 24-48 hours and, depending on the site, you will carry on your normal activities.

·    You can return to work when you feel sufficiently well, generally after a day or so. Heavy work should be avoided and thereafter activity should be judged in relation to any discomfort present.

·    For the first week you should keep your arm elevated whenever possible. Some swelling that may develop usually resolves within 5-10 days.

·    If there are any stitches to be removed, they are removed in 7 days.

·   Most patients need no pain-killers or antibiotics following this type of surgery.

·    As with any surgical procedure, bleeding and infections are probably the more common complications, but the risk is minimal [0.2-0.6%]

·    You should avoid any injury to the arm following surgery and blood pressure measurements should be taken from the other arm.

·    Your physician will keep an eye on things by regular appointments in his outpatients clinic

4. What are the major risks of AVFs?

.  Early thrombosis is a risk in patients with small veins or veins that had been cannulated previously [15-20%].

.  Aneurysm formation [in brachial AVFs] is rare. The same is true for arm ischaemia, as the fistula “steals” blood from the distal arm. Both are late complications and the true incidence is difficult to assess, but it is believed to be less than 10%.

.  Infections related to surgery are also rare. The risk of infection increases the longer the fistula is used for dialysis.

.   Late thrombosis is another risk and it may be related to infections, but the commonest cause is damage to the wall of the arterialised vein by the needles that are inserted into it.

5. How long do AV fistulas last?

.  Wrist fistulae. In patients with undamaged forearm veins [excluding the 15% early thrombosis], the first wrist AVF is still used in about 90% of patients after 3-4 years [75% for all] and in 50% after 7 years.

.  Brachial AVFs. If they mature, they remain open in 90% of cases after 3 years.

.  Arm vascular grafts. Only 70% last for a year, dropping to 50% at 3 years and 0% at 5-7 years.

.  Leg vascular grafts. The results are similar or slightly worse to the arm grafts, however, the risk of serious complications is significantly higher.