Permnent vascular access

Permanent Vascular accessYousaf khanRenal Dialysis LecturerIPMS-KMU

Permanent vascular Access

Fistulae: • Arteriovenous fistula consist of surgical anastomosis of an adjoining

artery and vein.• The diversion of the arterial blood cause the used veins to become

enlarged and prominent and stronger because of the greater flow of the arterialized blood through them.

Anastomosis:• End of the vein to side of the artery• End of the vein to end of the artery• Side of the vein to side of the artery

Permanent vascular Access

Fistulae: • Long term potency, Low complication rates• Low morbidity and improved performance with time in fistulae

rather than graft• Choice of location for AVF• Radiocephalic (wrist)• Brachiobasailic fistula• Brachiocephalic (elbow)• Brachiocephalic transposition ( involves freeing and transposition of

basilic vein at time of AVF formation.• Then forearm prosthetic graft, thigh fistulae and thigh graft and

axillo-axillary graft.

Permanent vascular Access

Synthetic graft:• Should not be first choice for permanent access.• Usually made from PTFE.• The material is porous allowing in grouwth of fibroblasts and

incorporation of the graft into the subcutaneous tissues.• The most common approach uses a forearm loop between the

brachial artery and cephalic vein, extending 10 cm down the forearm.

• Linear radiocephalic forearm graft upper arm loop grafts and upper thigh femoral loops are also placed.

• Short grafts can deteriorate from repeated puncture at a limited number of sites

• Long graft have increased pressure, reduce flow and increase thrombosis risk.

Permanent vascular Access

Disadvantage of permanent vascular accessDisadvantages of AVF:• Slow maturation• Failure of maturation• More difficult to needle• Increase in size with age• Increase aneurysm formation• Cosmetic appearance of

dilated veins

Disadvantage of graft:• More extensive surgery• Substantially increased

infection risk• Increase thrombosis risk• Stenosis at anastomosis• Expected life of only 3-5 year• Difficult to remove• Skin erosion

Formation of permanent access

Formation of fistula:• Radial: anastamosis of radial artery to cephalic vein at the wrist

either end to side or if the vessels overlie each other, side to side.

Brachial:• increase risk of steal and oedema because of increase blood flow

from brachial artery.• Cephalic vein mobilized for anastomosis on the brachial artery or a

deep connecting vein from the median antecubital is used. • Deeper brachial or basilic veins can also be transposed.

Formation of permanent access

• Patient well hydrated prior to surgery.• B.p should not be low nor too high• Preoperative dialysis should leave the patient above their dry

weight.• Patients with renal function should be given intravenous fluids to

avoid dehydration when nil by mouth• Local or regional anaesthesia usually used for distal surgery.• Antihypertensive drug should be avoided postoperatively.• Dialysis should be delayed at least 24 hr postoperatively if possible.

Procedure to enhance fistula maturation c

• fistula hand and arm exercises may promote maturation, or at least increased patient awareness of their access.

• AVF with hematomas or edema should be rested until swelling has resolved.

• Infiltrated or swollen fistula or graft should not be subjected to repeated cannulation.

• Single needle use may be appropriate.

Post operative care• Elevate the arm to minimize edema• Avoid tight dressings• Check the fistula daily for thrill, hematoma and evidence of ischemia• After 4-5 days some exercises could be started.• Arteriovenous fistula could be used after 2 month

Arteriovenous graft• Biologic, semi biologic or prosthetic graft implanted subcutaneously and

attached to an artery and vein.• Used patient who do not have adequate vessels to create an

arteriovenous fistula.• It can used be after 2-3 weeks• Grafts may be placed straight, looped or curved configuration.• Designs that provide the most surface area for cannulation are preferred.

Formation of bridge graft• Appropriate vessels are isolated and then the graft tunnelled

subcutaneously.• Kinking must be avoided• Standard vascular anastomosis are created.• Systemic anticoagulation is rarely needed.• Conflicting evidence for benefit of aspirin or low dose warfarin in

preventing graft thrombosis.• Hydration state preoperatively and postoperatively should be

carefully maintained and hypotension avoided.

Kind of the needle• Sixteen, fifteen and fourteen gouge needle are used for

hemodialysis.• Smaller diameter needles seriously limit the blood flow rate.• Higher flow rate may be possible by using bigger diameter needle

but at considerable increase in negative pressure which increase the possibility of sucking air into the system or damaging the intima of vessels.

• Resistance to the flow occur in long needle therefore the shortest practical needle is desirable.

Selection of the needle depends on:• Amount of subcutaneous tissue to be penetrated• Size of the vein• Angulation of the vein

Placing the needle in the access• Aseptic technique is essential• Local anesthesia may be used in some patient• Localize the fistula or graft, depth: angulation: maximum thrill and

site of insertion, hence the angle of needle insertion is decided ( 45 degree)

• Insert the inlet (arterial) needle proximal to the fistula or close to arterial anastomosis of the graft by 3cm at least to avoid intimal damage and subsequent thrombosis.

• The return needle should inserted pointing toward the heart approximately 5 cm proximal to the arterial needle.

• Opposite direction to avoid recirculation

Needle and insertion of AVF needle

Care required between dialysis• Good hygienic condition is important, instruct the patient to wash

fistula arm with water and soap predialysis.• Advise the patient to remove the dressing few hours after dialysis.• Advise the patient to avoid trauma to the access or to sleep on the

same arm.

• Educate patient to …..• Feel the bruit over the fistula (touch)• Observe for signs of infection redness, pain, swelling, exudates

What to say to the patient to protect his access ?• Make sure your nurse or technologist checks your access before

each treatment.• Keep your access clean at all time• Use your access site only for dialysis• Be careful not to bump or cut your access• Don’t let anyone put a blood pressure cuff on your access arm.• Don’t wear jewelry or tight clothes over your access site.• Don’t sleep with your access arm under your head or body.• Don’t lift heavy objects or put pressure on your access arm .

Complication• Stenosis• Thrombosis• Ischemia in a limb bearing an AV access• Psedoaneurysm• Infection

Stenosis • Less common with AVF than with graft, but can be more severe.• Usually occurs adjacent or just distal to the anastamosis, or in the draining vein

and is caused by intimal and fibrous hyperplasia.• Graft can also develop intragraft stenosis. • Screen by increase in venous pressure, reduce blood flow , or increase

recirculation, recurrent clotting, difficult needle placement, a persistently swollen arm and reduction in the URR or Kt/V.

• Intragraft stenosis do not cause changes in pressure or recirculation.• There is no evidence that repair of hemodynamically insignificant stenosis ( of <

50% vessel diameter) improve outcome or reduce thrombosis rate.

• Repair of stenosis in patent vessels is more effective than in thrombosed vessels :

• Only 50% of graft are patent 4 weeks after angioplasty for stenosis in thrombosed graft, versus 80% patency at 28 weeks fro angioplasty in non-thrombosed vessels.

Stenosis • Surgical repair or angioplasty is less effective for AVF than for graft.• Angioplasty is often difficult in longstanding graft with pronounced

intimal hyperplasia.

• Stents have been used but can subsequently fibrose, make further thrombectomy difficult and restenosis inoperably.

• There are no controlled trials comparing different access intervention.

• Good imaging prior to repair is important. Standard vengraphy with often not visualize the anastamosis of an AVF or any proximal stenosis. Formal angiography ( via femoral artery puncture and catheter insertion up to the axillary artery) provides better imaging of the feeding artery and anastamosis.

Stenosis in AVF and Graft

Thrombosis of fistula and grafts

• Thrombosis is six time more common in graft compared with AVF but more severe in AVF.

• usually secondary to stenosis or low arterial blood flow• Thrombus can by removed by thrombetomy using a balloon-tipped

embolectomy catheter, but the underlying structural cause ( in 80-90%) must be treated.

• Salvage is often unsuccessful ( surgical or angioplasty )• Thrombus can also be removed using thrombolytic agents instilled

locally.• Alternative include mechanical disruption via catheter.• Treatment is rarely successful beyond 48 h of thrombosis.

Thrombosis in AVF and Graft

Other complication of fistulae and graft

Inadequate flow:• Low access blood flow prevents delivery of adequate dialysis and

increase risk of access thrombosis.• Usually requires formal angiogram and management of any arterial

stenosis ( angioplasty or surgical correction).

Ischemia:• Ischemia of the hand and fingers can cause permanent loss of

digits, small regions of infarction or ischemia on exercise.• More common in the elderly and diabetics or in patients with

multiple failed fistulae.• Patient should be told to report changes in sensation, temperature

or weakness.

• Minor degrees of ischamia are common and manifest simply as reduced temperature or paresthesia they do not require any intervention and generally improve with time.

• More severe ischemia may require urgent treatment by closing the fistulae.

Aneurysm formation: • Usually caused by repeated needling of a single site.• Only requires repair if overlying skin becomes thinned, aneurysm

become very large, there is spontaneous bleeding or limitation to needling sites, nerve compression, or for cosmetic reasons.

• Low flow in a aneurysms predisposes to thrombosis.

Pseudoaneurysm • This is due to communication between the graft or fistula and confined

space of surrounding tissue.• It can lead to ischemai of the skin overlying the graft or fistula, poor

hemostasis after needle withdrawal, and prolonged bleeding • It an also prevent full use of the graft or fistula.• Should be repaired when skin is compromised there is a risk of rupture,

nerve compression or lack of sites for needling.

Infection:• Mostly a problem with graft and catheters.• Particularly common in patients with central catheters who develop a

Gram positive bacteremai.• It is difficult to eradicate bacteria once a graft is colonized, and very

prolonged courses of antibiotics or removal of the graft may be required.

Pseudoaneurysm and Aneurysm

Infection

Access recirculation • This occurs when blood that has just been dialyzed returns directly

to the dialyzer inlet.• It is usually caused by retrograde blood flow within a fistula or graft

or when venous blood is drawn up as arterial blood through a dual lumen catheter

• Measured using a two needle urea based technique but non urea based dilution methods increasing common.

• The three method peripheral vein method overestimates recirculation unpredictably, and requires additional venepuncture ( arterial, venous and peripheral venous sample)

• Recirculation > 10% (urea method) or > 5% ( dilution method) requires further investigation

• Recirculation does not occur unless access flow rate is less than the dialyzer blood pump flow rate and is a marker of venous stenosis.

Access recirculation • Two needle measurement of recirculation:• Perform test after 30 min of dialysis with UF switched off.• Take arterial and venous blood samples from the access lines• Reduce blood flow rate to 120ml/min for 10s than switch off pump.• Clamp arterial line above sampling port and take systemic arterial

simple from arterial line

• recirculation= S-A/S-V x 100

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