Vascular Access in Patients on Hemodialysis

Arvind Kohli
Hemodialysis is the most common method used to treat advanced and permanent kidney failure, hemodialysis is still a complicated and inconvenient therapy that requires a coordinated effort from whole health care team, including nephrologist, Vascular Surgeon dialysis nurse, dialysis technician, dietitian, and social worker
Vascular Access
Vascular access, . is the site on patients body where blood is removed and returned during dialysis. .
A vascular access should be prepared sometime before the start of dialysis. The early preparation of the vascular access will allow easier and more efficient removal and replacement of blood with fewer complications. The ideal access should provide adequate blood flow for an indefinite time, so that dialysis delivery is maximized upon each cannulation. Complications such as thrombosis, infection and hemorrhage should be absent. It is difficult to have such an ideal access .
The three basic kinds of vascular access for hemodialysis are an
Arteriovenous (AV) fistula
Native AV Fistula . is an opening or connection between an. artery and vein, .AV fistula is useful because it causes the vein to grow larger and stronger for easy access to the blood system. The AV fistula is considered the best long-term vascular access for hemodialysis because it provides adequate blood flow, lasts for a long time, and has a lower complication rate than other types of access. If an AV fistula cannot be created, an AV graft or venous catheter may be needed.
Arteriovenous graft
In small veins that won’t develop properly into a fistula, patient can get a vascular access that connects an artery to a vein using a synthetic tube, or graft, implanted under the skin in arm. The graft becomes an artificial vein that can be used repeatedly for needle placement and blood access during hemodialysis. A graft doesn’t need to develop as a fistula does, so it can be used sooner after placement, often within 2 or 3 weeks.
Compared with properly formed fistulas, grafts tend to have more problems with clotting and infection and need replacement sooner. However, a well-cared-for graft can last several years.
Venous catheter
For very urgent vascular aceess. we need to use a venous catheter as a temporary access.
A catheter is a tube inserted into a central vein in neck, chest, or leg near the groin. It has two chambers to allow a two-way flow of blood. Catheters are not ideal for permanent access. They can clog, become infected, and cause narrowing of the veins in which they are placed.
For some people, fistula or graft surgery is unsuccessful, and they need to use a long-term catheter access. Catheters that will be needed for more than about 3 weeks are designed to be tunneled under the skin to increase comfort and reduce complications.and are called as Permacaths
Problems In Vascular Access
Both AV fistulas andAVgrafts are most frequently lost because of thrombotic events, which are mainly related to mechanical damage to the vascular wall and to abnormal flow patterns, with shear?stress?related damage to the endothelium The most frequent direct cause of late access thrombosis is severe venous stenosis Many of the conditions that predispose a patient to vascular disease, such as diabetes mellitus, increasing age, enhanced thrombogenicity, inflammation, dyslipidaemia and hyperhomocysteinaemia, also predispose them to the loss of the vascular access system .
Central Venous Stenosis Manifest as high venous pressures Inefficient dialysis Prolonged bleeding AV graft failure and Caput Medusae
Early detection of failing vascular access requires Regular assessments of venous and arterial pressures, along withVisual inspection of the fistula and surrounding structures. To measure blood flow, specific apparatus (Transonic system) is necessary, which is based on the ultrasound dilution technique and the inversion of the inlet and outlet dialyser blood lines The blood flow rates of access systems prone to thrombosis overlap considerably with the flow rates in the non?thrombosing systems Next to the Transonic system, blood flows can also be measured by Doppler ultrasonography.
Clinical criteria for venogram Venogram is a test to delieneate the AX fistula and proximal blood vessels If there is decreased access blood flow using the saline dilution technique or Increased venous pressures.or Impaired access maturation and Arm or face edema Venogram should be done to rule out a proximal vein stenosis
What are Dialysis and Fistula/Graft Declotting and Interventions?
When fistulas and grafts become clogged or narrowed, which can prevent a patient from undergoing dialysis, interventionalists use image-guided interventions to fix the problem:
Catheter-directed thrombolysis, which dissolves blood clots that build up in fistulas and grafts by injecting a medicine.
Catheter-directed mechanical thrombectomy, where the clot is physically removed or mashed up.
* Angioplasty and vascular stenting, which use mechanical devices, such as balloons, to open fistulas and grafts and help them remain open. After the balloon is removed, a small wire mesh tube called a stent may be implanted to keep the fistula or graft open if angioplasty alone fails..
Therauptic Usage
Patients on hemodialysis having narrowing of dialysis fistula or grafts. When there is decreased flow in a graft or fistula, angioplasty or angioplasty with vascular stenting may be performed.
Thrombosis of dialysis fistulas or grafts. When blood does not flow smoothly, it can begin to coagulate, turning from a free-flowing liquid to a semi-solid gel, called a blood clot or thrombus. When blood clots in a fistula or graft prevent dialysis from being performed, catheter-directed thrombectomy (clot removal), or thrombolysis with clot-dissolving drugs may be performed.
(The author is Vascular Surgeon SSH Jammu)