Abstract

Objective To provide family physicians with an evidence-based overview on the various methods of vascular access for hemodialysis (HD) and to provide a framework for the clinical assessment of HD access.

Sources of information A MEDLINE literature search was conducted using the MeSH terms arteriovenous fistula, arteriovenous graft, central venous catheter, and hemodialysis (or haemodialysis), including all relevant English-language articles published between January 1995 and September 2021.

Main message The main types of permanent vascular access for HD are arteriovenous fistulas, arteriovenous grafts, and central venous catheters. A pragmatic, patient-centred approach is required when choosing the type of access for an individual. Common complications of vascular access creation include thrombosis, central venous stenosis, dialysis access steal syndrome, and arteriovenous fistula aneurysms.

Conclusion Family physicians play an important role in the clinical assessment and monitoring of HD vascular access. A thorough clinical assessment can detect a failing arteriovenous fistula and any associated complications, which can allow for prompt investigation and intervention to restore functionality, maintain access longevity, and improve patient quality of life.

The global incidence of kidney failure is rising in tandem with the prevalence of people receiving chronic dialysis.1 Hemodialysis (HD) is the most common form of dialysis, with a worldwide prevalence of 89%, while peritoneal dialysis constitutes the remaining 11%.1 The specific type of vascular access chosen for HD is a patient-centred decision, with arteriovenous fistulas (AVFs) being the preferred method as they are associated with lower rates of complications and have superior long-term durability.2,3 However, AVFs require substantial resource investments to support their use, including preoperative imaging of suitable vessels, surgical creation, cannulation by experienced dialysis staff, and ongoing clinical surveillance. Alternative means of vascular access for HD, including arteriovenous grafts (AVGs) and central venous catheters (CVCs), may be chosen by a patient’s dialysis team based on patient preference, comorbidities, and life expectancy. Since family physicians have consistent and long-term relationships with many of these patients, they are well positioned to help with vascular access surveillance. This article will discuss the various types of vascular access, with the aim of supporting family physicians who provide care to patients with AVFs.

SOURCES OF INFORMATION

A MEDLINE literature search was conducted using the MeSH terms arteriovenous fistula, arteriovenous graft, central venous catheter, and hemodialysis (or haemodialysis), with all relevant English-language articles published between January 1995 and September 2021 included.

MAIN MESSAGETypes of hemodialysis access

There are 3 main types of permanent vascular HD access: autogenous AVFs, AVGs, and tunneled CVCs.

Arteriovenous fistula. An AVF is the most durable form of vascular access for HD and is associated with the lowest rates of complications, including those of thrombosis and infection.2,3 An AVF is created via a surgical anastomosis between an artery and a vein. Diversion of the high-flow arterial blood into the low-pressure vein results in progressive dilatation and wall thickening of the outflow vein, a process referred to as arterialization.4 Arterialization eventually results in maturation, signifying the suitability of an AVF for cannulation and HD.4 Maturation can often be determined using the rule of 6s,5 which comprises the sonographic criteria detailed in Table 1. Table 2 and Figure 1 describe the most common AVF configurations.

Table 1.

Rule of 6s: Sonographic criteria for AVF maturation.

Table 2.

Common autogenous AVF and AVG configurations

Figure 1.

Common arteriovenous fistula and arteriovenous graft configurations

An AVF requires approximately 6 weeks on average to mature,6 with approximately 25% of AVFs never achieving maturation.7 While it is hard to preempt the trajectory of a patient’s kidney function, AVFs should ideally be created 3 to 6 months before their anticipated need.8 This allows enough time for maturation and any surgical revision that may be required, with the goal of mitigating the need for HD via a CVC owing to its associated morbidity. Once an AVF has matured, several steps can be taken to care for it (Table 3).

Table 3.

Strategies for AVF maintenance and preservation of future access sites

Arteriovenous graft. An AVG is created by subcutaneously tunneling an expanded polytetrafluoroethylene graft, connecting an inflow artery and an outflow vein via a surgical anastomosis. Typically, AVGs are allowed to mature for at least 2 weeks before cannulation, thereby allowing incorporation into surrounding tissue.4 Common AVG configurations are detailed in Table 2 and Figure 1. Arteriovenous grafts are more prone to infection and thrombosis compared with autogenous AVFs, and they are therefore usually considered only when autogenous AVF options have been exhausted.2

Central venous catheter. Central venous catheters are used in patients requiring urgent HD who may be awaiting permanent access creation, access maturation, or kidney transplantation.4 They are also used as permanent HD access in patients who have exhausted their AVF or AVG options, have severe cardiac disease, or have anticipated short life expectancies.4

Central venous catheters have many advantages, including a less demanding technical procedure (typically inserted by radiologists, nephrologists, and intensivists, rather than surgeons), lower resource usage, potential for immediate HD provision, and no need for percutaneous cannulation (unlike AVFs and AVGs), making them a convenient form of vascular access. They could also be preferred as a long-term option in low-resource settings or in patients with multiple comorbidities, limited life expectancy, or needle phobia. However, CVCs are often not the optimal choice owing to their tendency for higher rates of infection, increased risk of developing central venous stenosis, and poor long-term durability secondary to thrombosis.9

Central venous catheters come in 2 varieties: nontunneled catheters and tunneled catheters.

Nontunneled catheters: These are used in critically ill patients and are designed for short-term dialysis.4 These catheters typically need to be removed before discharge from hospital owing to the risk of catheter dislodgement and infection.

Tunneled catheters: These catheters can be used for long-term HD.4 The internal jugular vein is the preferred access vessel,10 with the catheter tunneled subcutaneously over the clavicle and exiting via the skin of the anterior chest wall. The subcutaneous tunnel is sealed by a cuff collar to reduce the risk of catheter infection and dislodgement.11

Assessment of vascular access

An HD vascular access assessment is composed of a history, an assessment of arterial inflow, and an assessment of venous outflow. Box 1 provides an overview of the assessment.

Box 1. Hemodialysis vascular access assessment: Targeted questions to ask prior to examining a patient’s HD access.

History

Have you been recommended to increase your dialysis hours lately? (Suggestive of recirculation and inefficient HD clearance, which may be secondary to venous outflow stenosis. Longer HD sessions may also be required to achieve the requisite ultrafiltration [fluid removal] and target weight)

Is it difficult to achieve hemostasis at the cannulation sites? (Suggestive of venous outflow stenosis)

Do you experience pain in the arm at rest or during exertion? Does this pain worsen during dialysis? (Suggestive of DASS)

Is the thrill palpable? If not, when was the thrill lost? (Suggestive of AVF or AVG thrombosis or nonmaturation)

Assessment of arterial inflow

Look: Inspect for signs of arterial insufficiency such as pallor, atrophy of the limb, or tissue loss (ulceration or gangrene of the hand)

Feel: Palpate for the presence of the upper limb pulses. Assess general limb perfusion by checking temperature and capillary refill time, and by assessing for sensorimotor impairment

Use pulse oximetry, which is an ancillary test where the peripheral oxygen saturation of the tested limb can be compared with that of the contralateral limb, giving an indication of arterial perfusion. This is particularly useful if there are concerns regarding DASS

Assessment of venous outflow

Look: Inspect for signs of venous hypertension, which includes edema of the limb, face, or breast as well as the presence of prominent superficial collateral veins over these same regions. Severe cases may also have skin pigmentation or venous stasis ulceration. Inspect the outflow vein for its calibre and any focal dilatations

Feel: Palpate the outflow vein for its consistency and for a thrill. The palpation characteristics of a mature and functional AVF outflow vein are soft and compressible consistency that indicate patency and arterialization. Presence of a robust, continuous thrill distal to the anastomosis indicates adequate and unobstructed flow. The thrill starts at the site of the anastomosis and progresses for a few centimetres up the outflow vein. The presence of a pulse without a thrill is an abnormal finding and is suggestive of venous outflow obstruction

Listen: Auscultate the outflow vein for a bruit—this supplementary test is used to confirm the findings from palpation. A functional AVF will have a continuous and low-pitched bruit. Like the thrill, the bruit will be loudest at the anastomosis and diminish more proximally toward the shoulder but should maintain a consistent character

AVF—arteriovenous fistula, AVG-arteriovenous graft, DAS5—dialysis access steal syndrome, HD—hemodialysis.

Variations in the examination findings usually represent a complication and may indicate a functionally threatened AVF. Specific complications and their associated examination findings are outlined in Table 4.

Table 4.

Potential outflow vein complications and associated examination findings

Arteriovenous fistula complications

Failing or thrombosed access. The most common reason for vascular access failure is thrombosis.12 The aim of regular clinical assessment is to detect failing or vulnerable AVFs to facilitate early intervention to prevent thrombosis and restore functionality. If abnormal signs are detected on clinical examination, it can be followed by a duplex ultrasound (DUS), which is used to interrogate any arterial inflow or venous outflow lesions.13 Following preliminary assessment, the patient’s dialysis team (ie, dialysis nursing staff, vascular access coordinators, and nephrologists) are generally the first-line resource to help expedite further assessment, diagnostic testing, and intervention.

There are 3 primary reasons for a failing or thrombosed AVF: the first is inadequate venous outflow, which occurs primarily owing to acquired stenoses of either the outflow vein or the draining central veins. Stenoses often occur because of neointimal hyperplasia in response to the hemodynamic changes from arterialized blood being routed through the venous system.14 The second is inadequate arterial inflow, which occurs because of occlusive disease in the arteries of the upper limb that feed the AVF.15 The third are medical factors, including reduced cardiac function, hypotension,16 or hypercoagulable states.17

Most arterial and venous lesions responsible for failing access are amenable to endovascular intervention in the form of percutaneous transluminal angioplasty.18,19 Some lesions may require a stent or an open surgical revision.20-22

Venous hypertension. Central venous stenosis or occlusion may present clinically as edema of the limb or edema of the ipsilateral neck, face, breast, and chest wall. Severe cases may also be complicated by venous stasis ulceration. Central venous stenosis can occur by neointimal hyperplasia of central veins secondary to altered hemodynamics following AVF creation and by current or previous CVC access. The diagnosis is made based on a computed tomographic venogram or a catheter-based fistulogram. The primary treatment modality is endovascular intervention in the form of percutaneous transluminal angioplasty, which can restore central venous outflow.23,24

Dialysis access steal syndrome (DASS). Most AVFs steal arterial blood from the limb by diverting blood flow from the artery perfusing the limb to the venous outflow of the AVF.25 However, it is the degree of steal that is important. Clinically significant DASS occurs when there is insufficient antegrade arterial blood flow to perfuse the limb.25Table 5 details DASS severity grades.

Table 5.

DASS grades of severity

Patients with suspected DASS can be investigated with DUS, which may demonstrate reversal of flow in the segment of the artery distal to the anastomosis as well as high flow volumes through the outflow vein (>800 mL per min in AVFs26). For patients with clinically mild DASS (grade 1 or 2), management is often conservative, with many patients eventually experiencing improvement in symptoms over time.27,28 Severe DASS (grade 3 or 4) usually warrants acute surgical treatment to improve arterial perfusion, reduce venous outflow, and prevent limb loss.28,29

Arteriovenous fistula aneurysms. Generalized outflow vein enlargement is a normal finding; however, focal dilatations represent an outflow vein aneurysm. There are 2 types of aneurysms: a true aneurysm, which is a dilatation involving all 3 layers of the vein30 and is generally related to degenerative changes in the vessel that may be caused by venous outflow stenosis31; and a false aneurysm, which is caused by a small tear in the outflow vein (usually iatrogenic from cannulation), resulting in a persistent defect that allows blood flow into the subcutaneous tissues outside of the wall of the outflow vein.30

A DUS can be used to identify both true and false aneurysms while also investigating the underlying cause (eg, venous outflow stenosis). Surgical management is indicated for the management of complications such as rapid enlargement, overlying skin necrosis, or spontaneous bleeding, while uncomplicated aneurysms can often just be monitored.4,12 Operative management will depend on the morphology; true aneurysms commonly require excision of the aneurysmal segment followed by reconstruction of the outflow vein (sometimes requiring an interposition graft),32 while false aneurysms are commonly repaired with primary closure of the defect in the vessel wall.33,34