Chapter 12 Access to the bloodstream
Historical background
Effective hemodialysis became a reality in the 1940s. Each treatment required a surgical cutdown. Hollow tubes (cannulas) of glass or metal were inserted into an artery and a vein. The glass and metal tubes were later replaced with cannulas of polyvinyl chloride or other plastic materials. During the 1950s, attempts were made to leave the cannulas in place for more than one treatment. Different methods of maintaining patency were tried. These attempts, at best, lasted only a few treatments.
In 1960 Scribner, Quinton, and Dillard at the University of Washington devised a cannula that could be left in place much longer. It consisted of Teflon tubes, one placed in an artery and one placed in a vein. These tubes were connected externally, allowing for continuous rapid flow of blood through the device. This technique was improved in 1962 with the use of Silastic (silicone rubber) for the external shunt loop and Teflon for the vessel tips. This allowed for greater flexibility of the tubing and increased comfort for the patient. This innovation not only was effective for a single hemodialysis but also offered a method for repeat treatments.
Another major development came in 1966 when Cimino, Brescia, and co-workers developed the forearm internal arteriovenous fistula. This was created by performing a surgical anastomosis between a forearm artery and vein. The subsequent flow of arterial blood into the vein permitted percutaneous puncture of this vessel that offered adequate flow for hemodialysis.
Use of internal synthetic graft materials began in 1974. Today the most common type of synthetic graft is polytetrafluoroethylene (PTFE). A “button” needle-free form of vascular access was developed in 1980. The button needle-free form worked, but not as well as the other internal synthetic graft material. These new synthetic grafts and devices offered new possibilities for patients who did not have adequate vessels for a Cimino fistula.
Shaldon described temporary access for hemodialysis via cannulation of the femoral vein in 1961. Uldall, in 1979, devised a special catheter for temporary access in the subclavian or internal jugular vein. When the dual lumen catheters were introduced, this further enhanced a means of temporary access, by allowing one catheter to function as both the inlet and the outlet ports.
Vascular access, as used for hemodialysis in the early 1960s, has evolved considerably during the past 30 years or more. However, maintaining patent access with adequate blood flow remains one of the major problems in the chronically hemodialyzed patient (Fig. 12-1).
Internal accesses
The percentage of prevalent hemodialysis patients in the U. S. with an arteriovenous fistula (AV fistula) as their primary vascular access was 32.4% (87,344 patients) at the beginning of 2003. By May 2009 this percentage had increased to 52.6% (179,113 patients) (Fistula First Breakthrough Initiative Strategic Plan, 2009).
The Fistula First Breakthrough Initiative (FFBI) was established in 2005 by CMS to increase AV fistula use in all appropriate hemodialysis patients and to decrease the placement of central venous catheters. A group consisting of CMS and End-Stage Renal Disease (ESRD) Networks has created a coalition that supports and promotes 13 “Change Concepts” that can give all hemodialysis patients the opportunity to receive an AV fistula. These Change Concepts are strategies to provide the patient and staff with the resources, tools, and best demonstrated practices to implement the KDOQI guidelines for vascular access placement.
The order of preference for a vascular access for patients undergoing chronic hemodialysis is: (1) a wrist (radial-cephalic) primary arteriovenous fistula (Fig. 12-2, A), (2) an elbow (brachiocephalic) primary arteriovenous fistula, (3) an arteriovenous graft of synthetic material (Fig. 12-2, B), or (4) a transposed brachiobasilic vein fistula. If an AV fistula cannot be placed, an arteriovenous graft (AV graft) is acceptable. Long-term catheters, such as a cuffed tunneled central venous catheter, should be discouraged as a permanent vascular access. Short-term catheters may be used for acute dialysis but only for a limited duration of time (NKF KDOQI Vascular Access Clinical Practice Guidelines Update, 2006).
Figure 12-2 Options for long-term vascular access for hemodialysis. A, A surgically created venous fistula. The increased pressure from the artery forces blood into the vein. This process causes the vein to dilate enough for fistula needles to be placed for hemodialysis. When the vein dilates in this matter, the fistula is said to be “developed.” B, A surgically placed straight vascular graft in the upper arm. The graft creates a shunt between arterial and venous blood.
(From Ignatavicius DD, Workman ML: Medical-surgical nursing: critical thinking for collaborative care, ed 6, St. Louis, 2010, Saunders.)
The time of vascular access placement should be well before the need for dialysis treatment. The 2006 NKF KDOQI Clinical Practice Guidelines for chronic kidney disease (CKD) recommend initiation of a vascular access when the glomerular filtration rate (GFR) is less than 30 mL/min/1.73 m2. The goal is for the patient to have permanent and functioning access at the time when hemodialysis therapy is initiated. Early referral and placement provide the time needed for the fistula to properly mature and develop. Duplex ultrasound is the preferred method for preoperative vascular mapping and should be performed on all patients prior to placement of the vascular access (NKF Clinical Practice Guidelines and Recommendations, 2006).
Arteriovenous fistulas
What is an arteriovenous fistula?
An AV fistula is an internal access surgically created by a vascular surgeon using the patient’s own blood vessels. In an internal AV fistula, a small (5 mm) opening is created surgically in an adjoining artery and vein, and the two vessels are joined at this opening, creating an AV fistula. The two blood vessels used are anastomosed in a side-to-side, end-to-side, or end-to-end connection (Fig. 12-3). The diversion of arterial blood into the vein causes the vein to become enlarged, distended, and prominent, allowing placement of large-gauge needles for the dialysis treatment. The blood flow rate (Qb) and diameter of the access will increase in response to the high pressure of the arterial blood entering the venous system. KDOQI has issued the rule of 6s as an objective measure used to assess access maturation. At six weeks after creation the fistula should have a diameter of at least 6 mm with discernable margins with a tourniquet in place and the depth should be no more than 0.6 mm below the skin surface. The FFBI defines a fully matured AV fistula as one that can sustain three consecutive two-needle cannulations with no infiltrations at the prescribed needle gauge and blood flow rate (NKF, 2006)(FFBI Coalition, Clinical Practice Workgroup, 2010).
Figure 12-3 A, Vessels for the creation of elbow AV fistula. B, Brachiocubital AV fistula. C, Brachiocephalic AV fistula.
(From Floege J, Johnson RJ, Feehally J: Comprehensive clinical nephrology, ed 4, St. Louis, 2011, Mosby.)
Eventually the access will be able to deliver a blood flow of 300 to 500 mL/min. Maturation occurs when there is dilation and thickening of the venous segment of the fistula. This is due to the increase in blood flow and pressure of arterial blood. The vein used to create the AV access will sometimes develop additional branches, which will also enlarge and mature enough to be cannulated for dialysis. This is called collateral circulation, and it increases the available surface area for cannulation. However, if the collateral circulation prevents the development of the main vein, ligation would be necessary.
The AV fistula can be placed in either the upper or the lower arm. The radial artery and cephalic vein (lower arm) (Fig. 12-4) and brachial artery and cephalic vein (upper arm) are commonly used. Proper evaluation of the patient’s vasculature and physical assessment plays a role in determining the access of choice for that patient. A major cause of early AV fistula failure is the selection of suboptimal vessels. Venography allows for identification of appropriate veins and helps to rule out sites that are not suitable for use. Doppler flow studies may also be used if venography is not available.
Figure 12-4 Mid-forearm radiocephalic fistula is used if the distal radial artery is not suitable.
(From Wilson SE: Vascular access: principles and practice, ed 4, St. Louis, 2002, Mosby.)
Every attempt is made to use the patient’s nondominant arm to help the patient maintain the present standard of living and to facilitate self-cannulation if the patient performs his or her own dialysis care. The patient must have sufficient arterial blood flow to maintain the access and to provide an adequate dialysis treatment. The AV fistula may take up to four months, or longer, to mature enough to allow for cannulation.
What is basilic vein transposition?
Basilic vein transposition is a technique used to create a vascular access in patients with inadequate vessels in the wrist. This transposed vessel technique involves dissecting the basilic vein and transposing it anteriorly and subcutaneously while anastomosing it to the brachial artery (Fig. 12-5). This transposed vessel provides a large surface area for cannulation and requires only one anastomosis. The incision for this access is rather large, with the start of the incision being at the midantecubital fossa and extending to the medial aspect of the arm to the axilla. The main advantage of this type of access placement is the avoidance of using a synthetic graft. As with other autologous grafts, you will see a longer patency rate and fewer risks of infection.
What is a proximal radial artery arteriovenous fistula?
The proximal radial artery arteriovenous fistula (PRA-AVF), also known as a “reverse flow” fistula, is a newer advanced surgical procedure for native AV fistula placement. In this type of access, the proximal radial artery is used for the arterial inflow. The arterial anastomosis is made higher in the arm and the vein develops both above and below the anastomosis. With this configuration, blood will tend to flow in two directions at the same time, allowing cannulation in both the forearm and the upper arm. When cannulating, if both needles are to be placed in the forearm, the venous needle should be placed downstream (retrograde) with the needle top pointing toward the hand, which is the direction of blood flow. If the upper arm is used for the venous return, the flow goes toward the heart, so the needle would be placed upstream (antegrade) with the needle top pointing toward the shoulder (Jennings, Ball, & Duval, 2006) See Fig. 12-6.
What is an arteriovenous graft?
When a patient is not a candidate for a native AV fistula, a vascular graft is substituted. An AV graft can be of biologic or synthetic material; however, synthetic grafts are used most frequently. The graft material is implanted subcutaneously into either the forearm or the upper arm. In some circumstances when the arm cannot be used, the chest or leg area may be used. The graft bridges an artery on one end and a vein on the other end. Blood flow direction is from the artery to the vein. With the AV graft, the needles for cannulation are placed directly into the graft material.
The synthetic graft is used most often in patients who do not have adequate vessels to create an internal AV fistula. The graft may be placed in several configurations: straight, looped, or curved. NKF KDOQI guidelines recommend the use of PTFE over biologic or other synthetic materials. The AV graft may be used as early as two to six weeks after placement, with the surgeon’s approval. The tissue surrounding the graft will grow into and around the graft, helping to stabilize this vessel.
Why do you need to know the direction of blood flow in the arteriovenous graft?
It’s necessary to know the direction of blood flow in the access to properly place the needles for the hemodialysis treatment. The venous needle should always be placed in the direction of the blood flow (artery to vein). Placing the venous needle against the flow of blood will cause increased resistance to the blood returning to the patient. This will be signified by a high venous pressure reading on the machine.
How do you determine the flow of blood in a looped arteriovenous graft?
In a looped or horseshoe AV graft, after gently depressing the graft at midpoint you can listen for a bruit or feel for a thrill on each side of the graft. Because you have occluded the flow of blood at midpoint, you will still be able to feel a thrill or hear a bruit on the side where the blood is entering the access (arterial side). The side of the graft with little or no thrill or bruit would be the venous side. Another technique used to determine the flow of blood is to palpate the graft at midpoint after the needles are placed. The arterial needle will continue to have a flashback of blood when the graft is compressed at midpoint.
What types of arteriovenous grafts are available?
Synthetic grafts are the most common AV grafts currently in use. Many synthetic materials (Dacron, PTFE) are available in various diameters and lengths. A newer form of PTFE allows for needle insertion immediately after placement, although the manufacturer recommends waiting five to seven days. Fig. 12-7 shows two types of placement for synthetic grafts.
What are the advantages of an arteriovenous graft?
AV grafts can be used sooner than AV fistulas, usually after two weeks. Maturation time for the vessel to enlarge is not required. The larger vessel size allows for easier cannulation. Table 12-1 lists the advantages and disadvantages of internal accesses.
Table 12-1 Advantages and Disadvantages of Internal Accesses
| Arteriovenous fistula | Arteriovenous graft | |
|---|---|---|
| Advantages | Excellent patency rateCan last for decadesHighest blood flow ratesLowest rate of complications (infection, steal syndrome, stenosis)Improved performance over time as access developsDevelopment of collateral circulation, which creates additional branches for cannulation | Large surface area for cannulationAbility to span large areas of the bodyEasy to cannulateLittle time required for maturationVariety of shapes and configurationsEase of surgical implantation |
| Disadvantages | Failure of vein to enlargeMore difficult to cannulate than graftCosmetically unattractiveMust find healthy veins that are in proximity and not too tortuousRequires time to mature before use | Higher rates of infectionMay reject graft materialHigher rates of thrombosisStenosis at venous anastomosis from intimal hyperplasiaNo development of collateral circulation |
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