Clinica Virgen del Consuelo mrjnefro@vlc.servicom.es

INTRODUCTION

Most Nephrologists will rely on the surgeon decision on the type of dialysis vascular access their ESRD patients are going to get and then complain if the access is not functioning well or is placed in an anatomic position that is difficult to access by the nurse or uncomfortable for the patient. Furthermore the outcome of the vascular access is dependent of the surgeon interest in hemodialysis access procedures.

The purpose of this article is to give an overview of the preoperative planning process and follow up care that should be performed in a patient with a native arteriovenous fistula.

INITIAL EVALUATION

One major cause of an early arteriovenous fistula ( AVF) failure is the selection of a suboptimal vein and artery.

A simple way to improve the patency rates and decrease the numbers of procedures second and third AVF´s or the use of grafts is to do an adequate evaluation on your patients in collaboration with the vascular surgeon (Table I ).

The initial evaluation should be done when the patient is seen in the Nephrologist office early in the course of disease ¹ and not just a few weeks before starting chronic replacement therapy. The time of access placement correlates with access outcomes and with patients mortality². The mortality risk of those patients who had their access placed 30 days before hemodialysis was double when compared with those who had the access placed 6 months before starting hemodialysis. An early AVF construction should be considered in those patients with a Creatinine >4 mg/dl ( or when Creatinine Clearance approaches 25 ml/min ) unless there is a planned living related transplantation ³. The access will have enough time to develop and the use of central lines will be avoided. Patients with a poor vascular system should be referred, if there are no major contraindications, to a PD program.

HISTORY

The patient should have a complete history of the potential factors that may complicate the creation of an AVF (see Table I )⁴ which includes a record of all the venipunctures and procedures involving the upper and lower extremities. The hospital staff (venipuncture teams, nurses etc. ) should have instructions on how to manage these patients to avoid unnecessary use of upper arms veins and patients should be thought to preserve integrity of their veins by refusing needle stiks by lab and nursing personel.

Table I

PHYSICAL EXAMINATION

The physical examination should be done in a warm room after explaining in detail the purpose of the examination to the patient. The arm can be placed in a bowl with warm water to induce venodilatation.

INSPECTION

Inspect both arms from the fingertips up to the shoulders assessing:

-Size and symmetry

-Colour and texture of the skin and nail beds

-Edema

-Any scars from previous surgery

-Presence of collateral circulation in the forearm and shoulder

PALPATION

Arterial Examination

Check the radial pulse in the flexor area of the wrist and compare the volume on each arm. Do the same with the Ulnar Artery (medial in the flexor surface of the wrist) and the brachial Artery (between the biceps and triceps muscle)

According to the physical examination the pulse can be classified:

Absent

Marked diminish

Moderately Diminish

Slight Impaired

Normal

ALLEN TEST

The normal ulnar artery is difficult to palpate, another way to check for patency is to perform the Allen Test.

The patient rests the hand in his lap clenching firmly his fist. The radial Artery is compressed which produces a decrease in perfusion turning the hand pale. The patient will then open his hand and the skin will recover its normal pink appearance if the Ulnar artery is patent. Do the same process is done with the ulnar artery (see Fig.1)

Fig 1 Allen Test

Venous Examination

The tourniquet is placed on the upper portion of the arm. Ask the patient to close and open repeatedly the hand toincrease vein engorgement. The cephalic and basilic vein in the arm, antecubital area and forearm should be assessed. Raise the upper limb and evaluate venous drainage observing a delay suggesting obstruction.

FIG 2 Arterio-venous anatomy upper extremities

PREOPERATIVE ASSESMENT

ULTRASOUND EXAMINATION

Preoperative mapping of the upper limb vascular tree will increase the patency rate of AVF and decrease the rate of early failure. ^{5 6}This procedure can be done, using a portable ultrasound device to assess:

-the diameter and compressibility of the vein

-The diameter of the radial artery ( a powerful predictor of early fistula dysfunction and failure to mature) ⁷

We have been doing vein mapping using the Site RiteR (r) (see Table 2 ). The technique is very similar to the physical examination described previously and takes 15-20 min to exam both arms.

The patient is placed lying flat with his arm hanging on the side of the bed

1. Apply the tourniquet in the mid forearm

1. Measure cephalic vein diameter following it up toward the elbow

1. Apply the tourniquets in the upper portion of the forearm

1. Measure the median basilic vein, median cephalic vein in the elbow

1. Measure the cephalic vein and the basilic vein in the arm

1. Look for the Subclavian vein and the internal jugular vein size

1. Measure the Radial Artery diameter

Fig 3 Antecubital venous anatomy

The following criteria modified from Silva et al are used to assess patients' upper extremities' vein adequacy with a portable ultrasound (see Table 2):

Table 2

Venous Examination

• 2.0 mm with outflow occlusion up tothe elbow

• 3.0 mm with axilla occlusion

• Absence of segmental occlusion/stenosis

• Good compression of the veins

Arterial Examination

• Absence of pressure difference 20 mmHg between both arms

• Arterial Lumen 2.0 mm

PROCEDURE OF CHOICE IN VASCULAR ACCESS SURGERY

We should consider the following general guidelines before access placement

-Select the non dominant arm ( if possible )

-Place the access distally to preserve proximal sites

-Avoid atherosclerotic arteries

-The selected veins should have a long segment to allow for variation in puncture sites.

-Those patients with a small and atherosclerotic radial artery should have the access placed over the elbow.

-Try to use the non dominant arm exhausting all reasonable possibilities before going to the other extremity.

Table 3

* The anatomical snuffbox median primary patency was 36 months vs 64 months at the wrist ⁸. For that reason we do not recommend this procedure in our patients although others authors have published excellent results using this technique ^14,15

**The diabetic is not considered a good candidate for primary native AVF making the PTFE graft the access of choice for most of these patients but this idea is challenged by recent data. Hakaim et al showed that the cumulative primary patency at 18 months was 33% for a radiocephalic fistula and 78% for a brachiocephalic AVF.The diabetic patient ( Type I/II ) with unsuitable arterio -venous vessels in the wrist, the best procedure should be either a primary braquiocepahalic or a transposed brachio-basilic fistulae

***We do not use saphenous vein transposition in the thigh due to the high incidence of cardiovascular morbidity in patients with chronic renal failure However ,this option may be a consideration in those patients with AIDS ¹⁶ or before performing a thigh graft ^12,17 .

FOLLOW UP CARE

POSTOPERATIVE CARE

This is our current immediate postoperative care protocol

1-The patient should be monitor and the new AVF evaluated by a Nephrologist /HD nurse

2-Vital Signs check every 30 min. Call the nephrologist on duty if :

BP Systolic < 100 mmHg Diastolic < 60 mmHg, Pulse <60>110 Temp > 38

3-Examination

Inspection : Presence of a haematoma

Palpation : Thrill

Auscultation :Measure the maximum distance that the murmur is heard in the arm

4-If stable discharge the patient after 4 hours

5-The patient will receive instructions to call us or to return to the hospital:

Bleeding from the AVF

Non a palpable thrill

Note :The established practice of asking the patient to do hand exercise after a radiocephalic Fistula is not supported by access blood flow measurement. Exercise does not increase access blood flow ¹⁸. However it does increase patients' awareness in the importance of caring for his access .

ACCESS MONITORING

INTRODUCTION

The creation of an Arterio-Venous Fistula will cause arterial blood ( high speed laminal flow ) to enter the venous low resistance system creating a laminar flow with a continuous turbulence with a systolic peak at the site of the anastomosis -the area with the highest pressure gradient. These ingredients, the increase in pressure and flow in the venous side combined with the spectacular increase in blood flow in the artery, are needed for successful AVF maturation Note: Blood flow in a normal brachial artery is 85 ml/min and will increase by a factor of 5-10 after the fistula is open. The Arterial flow is dependent in a nonlinear relationship with the cross sectional area of the fistula.

We will wait for at least 4 weeks beforet using the new access. During first two or 3 treatments we use a single needle hemodialysis with no heparin. The hand of the patient is secure with a tape to avoid involuntary movement of the arm and trauma to the vein wall by needle motion. Before accessing the AVF, the nurse does a quick evaluation of the access. We use an ultrasound guided needle stick in those accesses that are difficult to stick, i.e. a brachio-basilic vein or an obese patient.

Most stenosis will occur in the efferent vein near the arterial puncture. Stenosis may occurs as early as 2 weeks after access placement and they are responsible of early access failure 7 (see below) .

Access monitoring combined with early access intervention will increases significantly cumulative access patency ²⁰ . There are several methods to screen AVF for signs of early dysfunctions. Most of these methods will detect functional changes in the access rather than anatomical abnormalities.

Functional methods are used to evaluate access dysfunctions and are appropriate for periodic access monitoring while angiography (gold Standard ) and ultrasounds are used for anatomical examination of the access. The AVF can either fail to mature for needle cannulation or later become dysfunctional

FAILURE OF AVF TO MATURE

If after 8 weeks the AVF fails to mature, i.e. BFR < 350 ml/min and/or a recirculation higher than 10% a fistulogram should be done . The ultrasound, being very sensitive and specific for detecting graft dysfunctions, is less reliable for the evaluation of AVF anatomy.(see below)

Beathard et al have recently published their results on salvage of early nonfunctional fistulas. Out of 63 patients with inadequate AVF development 74.7 % had their access patent after 1 year using the following techniques after angiography in a stepwise fashion: percutaneous angioplasty, accessory vein ligation, medial vein ligation and mainstream banding ²¹. Therefore most AVF that failed to developed should be evaluated since most early AV access dysfunctions can be rescued and become functional sparing the patient the frustration of having to go through the creation of another access and the placement of a central vein line.

AVF MONITORING (see DOQI Guidelines )

There are different methods to assess periodically the AVF access.

PHYSICAL EXAMINATION

VENOUS PRESSURE

Dynamic

Static

RECIRCULATION STUDIES.

Chemical

Dilutional

INTRA-ACCESS BLOOD FLOW MONITORING

Hemodynamic access

Ultrasound dilution technique

Colorflow Duplex

ACCESS ANATOMY

Colorflow Dupplex

Fistulogram

MRI

PHYSICAL EXAMINATION

Although underused and very dependent on the experience and interest of the examiner, a thorough examination of the AVF ( which takes 3-5 min ) will provide much information about access function . At examination there are different clues that can give an idea of the anatomical abnormalities present in the fistula. (See Table 4)

Table 4

	NORMAL	ARTERIAL STENOSIS	VENOUS STENOSIS
Inspection	vein dilated with no collaterals	decrease or absence of postanastomosis vein dilatation	post-anastomosis segmental vein dilatation
Auscultation	maximum at anastomosis with distal radiation	Weak with no radiation	Bruit in the anastomosis site and a second bruit over the stenotic area
Palpation	maximum thrill at the AVF junction	pulsatile with absence of thrill	Presence of two thrills -AVF and in the stenotic vein segment.
Arm elevation	Complete collapse of the vein's	Complete venous collapse	non collapsible pre stenotic vein segment with normal post-stenosis vein collapse

The goal , nevertheless , is to be able to pick early those accesses that are going to fail so an elective solution can be offer avoiding the risk of a long standing central line,the loss of a very valuable venous area and the need to create another access in a group of patients that cannot afford it.

VENOUS PRESSURE ²²

Useless for monitoring AVF ²³ since, as the intravenous pressure rises, blood flow is diverted through vein collaterals preventing an increase in venous pressure.Once there is a suspicion of venous stenosis the patient should probably have a fistulogram to assess anatomy.

RECIRCULATION

Access recirculation (RC) develops when dialyzed blood returning the patient through the venous side reenters the extracorporeal circuit through the arterial needle. Recirculation decreases significantly the amount of HD delivered and is a marker for access stenosis. Recirculation occurs when the AVF blood flow rate ( average AVF blood flow 1000 ml /min ) ²⁴ is less than the blood pump. There are several systems to measure RC

I will briefly discuss the 2 most common techniques: Urea (or chemical) and ultrasound (or dilutional-based methods.)

CHEMICAL

PERIPHERAL BLOOD

Measure Urea/BUN in a peripheral vein (P) and simultaneously in the Arterial (A) and venous line (V).

The percentage of recirculated blood is calculated as (P-A/P-V)x 100.

This is the less reliable method to calculate recirculation due to a decrease of Urea in the arterial line ( secondary to cardiopulmonary recirculation ) ²⁵ and increase in peripheral blood due to difference in regional blood flow ²⁶

LOW FLOW METHOD (DOQI Guidelines ) ²⁷

Draw samples from the arterial (A) and venous (V) line

Reduce blood flow rate(BFR) to 120 ml/min

Turn blood pump off 10 seconds after reducing BFR

Draw systemic (P) arterial sample from the arterial line

DILUTIONAL

TRANSONIC SYSTEM

The system used intrasonic transit flow measurement with a flow/dilution sensor connected around the arterial and venous line. The Transonic measure's dialyzer blood flow, access flow and recirculation. Patient evaluation using the Transonic System (1 recirculation measurement and 2 access flow) requires about 12 minutes.

DIALYZER BLOOD FLOW (Qb)

The sensor emits an ultrasound beam which will cross the line in both direction. Qb is measured as the difference between the upstream and downstream transit time ultrasound (see Fig. 4)

ACCESS RECIRCULATION

The Ultrasound measurement of blood velocity is dependent on the protein concentration, the greater the concentration of protein in the blood the faster will the ultrasound beams travel through it. The administration of isotonic solution will dilute protein concentration and decrease the ultrasound velocity. By injecting Normal Saline into the venous port the sensor measure this decrease in ultrasound velocity and reflected as a curve -the dilutional curve - If recirculation is present, normal saline will be taken by the arterial line, decreasing ultrasound measured blood velocity-and generating a second dilutional curve. Recirculation is calculated as the ratio of the area under the arterial curve to the area under the venous curve. (See Fig 5 )

Fig 5 and Fig 6

ACCESS FLOW

The lines are reversed and normal saline is injected in the venous side (see Fig. 6 ) Access Flow is calculated from the ratio of the venous area to the arterial area times the dialyzed blood flow. Access flow measurement should be done during the first 90 min of treatment and avoided if there is a 10% or more change in MAP ²⁸ . Neyra et al ²⁹ has shown that a time dependent decline in vascular access blood flow is highly predictive of access thrombosis. Using the transonic system they measure the access blood flow rate in 95 patients ( 23 with native AVF and 72 with Grafts ). A decline in baseline blood flow rates of more than 15% was associated with a relative risk (RR) of thrombosis of 4.4.The RR increased to 34 when the decline of BFR was above 50%. The study was limited by the small number of thrombosis ( 4) and patients with AVF . Nevertheless, emphasis the importance of doing sequential evaluation of the access rather than looking to an absolute number to assess for early vascular dysfunction.

Fig.7

HEMODYNAMIC RECIRCULATION MONITOR (HDM)

The HDM is a non invasive electronic device that uses magnetic principles to measure difference in conductivity between the arterial and venous side. Lindsay et ^30,31 al has shown that the HDM is very accurate measuring access recirculation with excellent repeatability.

ACCESS ANATOMY

ULTRASOUND

Most of the data available on Doppler ultrasound for evaluation of access dysfunction has been done in grafts. Gadallah et al ³² evaluated 38 unselected patients with doppler US followed by digital substraction angiography .They found a good correlation in diagnosing access stenosis between Doppler US and fistulography. There were 13 patients with a native AVF and only 3 had a significant stenosis.The result on the ultrasound evaluation is very dependant on the experience and interest of the operator. Possible sources of error:

-Measurement of the vessel cross section

-Poor Doppler wave forms related to an inadequate angle (keep the angle less than 60 )

-Different measures of flow volume calculation

FISTULOGRAPHY

Venous Fistulography is the gold standard for evaluating AVF anatomy .It is simple, very accurate and with a low complication rate and is the procedure of choice for preoperative evaluation of a malfunctioning access although should not be used for routine AVF screening. The venous angiography will outline:

-the size and type of Fistula

-Size, shape and position of the veins used for cannulation

-Presence of aneurysm and/or thrombi,

-Locations of venous stenosis

MRI³³

The AVF anatomy can be visualized in those patients who are allergic to iodine contrast with MR -imaging. The MRI is a non invasive procedure that offers 2 methods for evaluating AVF:

-PHASE CONTRAST MRI: measure flow rates and gives an idea of the AVF access anatomy but it will overestimate stenosis due to motion artefacts induced by the post stenosis turbulent blood flow.

-CONTRAST ENHANCED MRI: Will define the venous anatomy with precision but would not give any information about access flow and the measurement is done in the axial plane.

PERCUTANEOUS TRANSLUMINAL ANGIOPLASTY (PTA ) ³⁴

Most of the data on PTA comes from the radiology literature and applies to the treatment of the failing graft. The advantages of PTA are numerous (see Table 5) .The results on PTA access patency available on the radiology literature are difficulty to compare with the results obtained from surgical literature. For instances primary patency in the radiology literature is expressed after pta access dilatation while in the surgical literature the data is expressed as either primary patency ( creation of the access until the surgical intervention ) or cumulative patency (as the access patency regardless of the number of procedures done on that access).Therefore is complicated to compare the different series since there are being expressed in a different way . Table 5 summarized the results published in the literature .

Table 5

PERCUTANEOUS ANGIOPLASTY -SUMMARY
Advantage	Outpatient procedure Vein preservation Avoids Temporary Access High Technical Success Repeated PTA
Disadvantage	Not permanent Risk of Arterial Steel Syndrome in upper arm access
Author	PRIMARY PATENCY			CUMULATIVE PATENCY
	6 months	1 year	2 years	6 months	1 year	2 years
Castellan et al35	79%	61%	61%	90%	83%	83%
Bohndorf et al36	80%				65% *
Romero et al 37	51%	37%	85%		82%
Turmel-Rodrigues et al 38	Forearm	51%	37%		85%	82%
	UpperArm	35%	24%		82%	69%

The cumulative patency of PTA on AVF is excellent and comparable to the results obtain with surgical revision but with the added benefit of vein preservation and minimal invasive technique. This result emphasizes the important role that the interventional radiologist or nephrologist have in management of AVF complications and in increasing the life span of the AVF.
Except for elastic lesions, which are centrally located , there is little or no use of stenting a proximal stenosis. The stent itself is going to induce father hyperplasia with post-stent stenosis and early dysfunctions of the access.

COMPLICATIONS

CARDIAC FAILURE ( High Output) ^{29 39}

High output cardiac failure is a rare complication occurring more frequently in patients with a braquiocephalic or transposed basilic vein access. The treatment is either banding or ligation of the access. Banding can be complicated with venous hypertension and the development of an upper arm edema.

NEUROPATHY

This complication ,Ischemic monomelic neuropathy, is seen in patients with peripheral vascular disease -most frequently in diabetics.The patient developed a severe excruciating pain of the involved extremity with wrist drop suggestive of radial injury at the levels of the elbow secondary to peripheral ischemic neuropathy ^40-42 .Treatment consist in fistula ligation .

VENOUS HYPERTENSION ^43-45

The hand distal to the access is swollen with thickening and hyperpigmentation of the skin .In extreme cases there is distal extremities ulceration or the development of a kaposi -like sarcoma⁴⁶.The use of central Vein lines may lead to central vein stenosis or thrombosis with the development of massive upper extremity edema after access placement .

STEEL SYNDROME ^47,4849,50

Some degree of retrograde flow occurs in almost every AVF being higher in side-to side anastomosis and in braquiocephalic fistula .For example in a normal radiocephalic fistula 20 % of blood will come from the distal artery .(Anderson ) The steel syndrome occurs due to a retrograde flow from the distal artery of the anastomosis to the low resistance venous system causing the blood flow tol go from the ulnar to the radial artery through the palmar arch with hypoperfusion of the palm and forefingers .The incidence is higher in the artherosclerotic and diabetic patients . The clinical presentation is a painful, cold and clammy hand that gets worst on hemodialysisIt can lead to acral gangrene and finger amputation . To prevent this problem in high risk patient distal radial artery ligation can be performed . End-to-end anastomosis is complicated by technical problems like vessel rotation during the anastomosis or higher percentage of stenosis which will increse the risk of poor blood flow rate and early thrombosis .

ACKNOWLEDGEMENT

I am indebted to Vo Nguyen MD ( Memorial Clinic Olympia, WA ) for his critical review and comments of this manuscript .

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