monitoring & surveillance of vascular access

MONITORING & SURVEILLANCE FOR VASCULAR ACCESS

DR.GAURAV SAGARCONSULTANT NEPHROLOGIST

INDRAPRASTHA APOLLO HOSPITAL

WHAT IS MONITORING & SURVEILLANCE

• Monitoring—the examination and evaluation of the vascular access by means of physical examination to detect physical signs that suggest the presence of dysfunction.

• Surveillance—the periodic evaluation of the vascular access by using tests that may involve special instrumentation and for which an abnormal test result suggests the presence of dysfunction

WHY SURVEILLANCE• Vascular access is the “lifeline” of a patient on

dialysis.• Low Blood flow rates and loss of patency limit

adequate dialysis dose delivery.• 0.1% decrease in Kt/V is significantly associated with

11% more increase in hospitalizations. Am J Kidney Dis 23:661–669, 1994

• Vascular access related complications accounted for 15-25% of all admissions in CKD patients . Am J Kidney Dis 37:1223–1231, 2001

• Thrombosis increases health care spending and effects QOL

CLINICAL MONITORING

• Physical examination • A good fistula has a continuous thrill, is

compressible and is not pulsatile.• A fistula collapses when the arm is elevated,

failure of the fistula to collapse suggests outflow stenosis.

• Absent thrill, discontinuous bruit, edema distal to the fistula and aneurysmal proportion of the vein suggest access dysfunction.

“Worm Hand “

• Presence of collaterals usually indicate outflow stenosis/obstruction

CLINICAL MONITORING

• AUGMENTATION TEST• On compressing the outflow segment of AVF

the thrill is reduced and it becomes pulsatile. If there is no augmentation of the pulse it suggests inflow stenosis which may be the reason for intervention in as high as 1/3rd of cases.

CLINICAL MONITORING• ACCESSORY VEINS• If on occluding the outflow a thrill persists it suggests presence of

accessory veins which may be an important cause of primary non maturation of AVF.

• A juxta-anastomotic venous stenosis is characterized by presence of a water hammer pulse which disappears abruptly as the stenosis is encountered.

• Presence of pseudoaneurysms is commoner than true aneuryms and indicates improper hemostasis.

• Cannulating an access to assess for flow is unacceptable.

CLINICAL MONITORING• Problems during dialysis sessions difficulty in

cannulation, aspiration of clots, inability to reach target blood flow and prolonged bleeding from needle puncture sites.

• Unexplained more than 0.2 decrease in Kt/V on a constant dialysis prescription also suggests access dysfunction.

CLINICAL MONITORING• Disadvantages

i. Not reproducible and requires motivation.

ii. Considered less accurate for fistulas than grafts in stenosis, partly explained by decrease frequency of stenosis in fistula.

iii. One study evaluated 543 fistulograms in 358 grafts and 185 fistulas. The positive predictive value for greater than 50 percent stenosis ( functionally significant) was only 39 percent for fistulas, as compared with 69 percent for grafts. Am J Kidney Dis 2004; 44:859

COMPARISION OF PHYSICAL EXAMINATION& ANGIOGRAPHY

• 142 patients with access dysfunction.• Complete physical examination done by an interventional

Nephrologist.• Included inspection, palpation, auscultation augmentation

and arm elevation• Antegrade and retrograde angiography from feeding artery

to rt atrium.• Stenosis defined as luminal narrowing > 50%.• Both sets of results reviewed by an independent reviewer.• Cohens Κ used as measure of level of agreement.• 121 sets of data analysed.• - Arif et al (2007), Clin J Am Soc Neph 2: 1191 -94

COMPARISION OF PHYSICAL EXAMINATION& ANGIOGRAPHY

Diagnosis Prevalence Sensitivity Specificity PPV NPV

Inflow stenosis

0.64 0.85 0.71 0.84 0.72

Outflow stenosis

0.61 0.92 0.86 0.91 0.87

Coexisting inflow and Outflow stenosis

0.31 0.68 0.84 0.65 0.85

Central vein stenosis

0.23 0.13 0.99 0.80 0.80

Body stenosis

0.10 0.40 0.84 0.23 0.92

- Arif et al (2007), Clin J Am Soc Neph 2: 1191 -94

CLINICAL MONITORING

• No substitute to good physical examination and above all is free of cost.

METHODS OF SURVEILLANCE

• 3 major types of access surveillance are: 1) Intra access blood flow monitoring 2) Static dialysis venous pressure 3) Duplex Ultrasound

ACCESS FLOW

• QA = P/R

QA = Driving force for access flow P= Pressure Gradient between the artery and the central veins

R= Resistance in Access

INTRA ACCESS BLOOD FLOW MONITORING

• Duplex Doppler Ultrasound (Quantitative colour velocity imaging)

• MRA• Variable Flow Doppler Ultrasound (Specs USA)• Ultrasound Dilution Technique• Critline 3 direct transcutaneous (Hema-metrics)• Glucose Pump infusion technique• Urea Dilution technique• Differential Conductivity( GAMBRO)• In Line Dialysance ( FRESENIUS)

DILUTION METHODS FOR DIRECT FLOW MEASUREMENTS

• Principle:- temporary reversal of blood flow lines, forces obligatory recirculation through the access.

• Percentage of Recirculation depends on the ratio of blood pump speed to access flow rate.

• Access flow rate can be algebraically calculated from percentage recirculation and blood pump rate.

• Sensor placed on the downstream line to detect hematocrit, conductivity, USG pulse or temperature.

• A pertubation induced in the upstream blood line and detected downstream depends on the ratio of blood pump to access flow rate.

HEMATOCRIT DILUTION TECHNIQUE FOR ACCESS FLOW

• Baseline sample drawn for Hct from the arterial needle after priming circuit (Ha)• Arterial and venous needles connected in a reverse direction.• Blood pump set at 300 ml/min and UF at 0.• After 12 seconds of infusing saline into the arterial needle, a 2nd sample (Hv) is

dawn from the venous needle• Saline infusion rate Qs = [1-(Qb -200)/2000] X Qb• By normal dilution balance• Qa.Ha = (Qa + Qs).Hv• = Qa.Hv + Qs.Hv• Qa.(Ha – Hv) = Qs.Hv OR• Qa = Qs.Hv• Ha – Hv• Where Qa = access blood flow

• Validated in 30 subjects with 2 consecutive readings.• Gold standard - Ultrasound dilution technique• -Tirannathanagul (2008), KI; 73: 1082 -- 1086

HEMATOCRIT DILUTION TECHNIQUE FOR ACCESS FLOW

Y = 0.92x + 8.11N = 30R = 0.91

Hematocrit Dilution technique

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-Tirannathanagul (2008), KI; 73: 1082 -- 1086

ULTRASOUND DILUTION TECHNIQUE

• UDT (transonic) is amongst the most commonly used.

• Cold saline is injected in dialysis needle after reversing the lines and a sensor measures rate of change in temperature.

• Access flow is measured from the induced recirculation, the software calculates the AUC as measure of recirculation. { QA= QBP(1/R-1) }

• QBP= Blood pump flow• R= Degree of recirculation induced.

ACCESS FLOW• Duplex Doppler Ultrasound• Requires accurate measurement of cross sectional

diameter of access, operator dependent and subject to error caused by angle of insonation

• Provides anatomic assessment• Costly• Inability to make measurements during HD

ACCESS FLOW

• Duplex ultrasonography measures the peak systolic velocity (PSV) on either side of an area of visual stenosis.

• A PSV ratio greater than two is suspicious for significant stenosis.

ACCESS FLOW PROTOCOL SURVEILLANCE

• Access flow should be measured monthly.• Assessment should be done in the first 1.5 hrs of

dialysis to eliminate errors caused by decrease in cardiac output or ultrafiltration.

• If access flow is < 600ml/min in a graft or < 500ml/min in a fistula patient should be referred for a fistulogram

• If access flow 1000ml/min decreases by more than 25% over 4 months patient should be referred for a fistulogram

STATIC INTRA ACCESS PRESSURE SURVEILLANCE

• Establish a baseline and follow with trend analysis.• Calibration of pressure transducers within +/-

5mmHg.• Measure MAP in contra lateral arm.• Stop blood pump & clamp venous line proximal to

venous drip chamber, on the arterial line the occlusive roller pump serves as a clamp.

• Wait for 30s until venous pressure is stable and then record venous and arterial IAP

STATIC INTRA ACCESS PRESSURE SURVEILLANCE

• Determine height correction h between the access and the drip chamber.

• Offset in mm Hg= 3.6+0.35x• Static IAP ratios by formula• Arterial ratio= (arterial IAP+ Ht.Correction)/ MAP• Venous ratio= (venous IAP + Ht.Correction)/ MAP

STATIC INTRA ACCESS PRESSURE SURVEILLANCE

• The above method is tedious, time consuming and not very “user friendly”.

• There are sophisticated electronic transducers or a device consisting of a hydrophobic Luer Lok which can be connected to an aneroid manometer

WHEN TO REFER

• In grafts static venous pressure ratios more than 0.5 and arterial ratio more than 0.75

• In fistulas static venous pressure ratios more than 0.34 and arterial ratio more than 0.43

• In central stenosis with good collateral circulation especially in AVF’s the pressures may be “normal” and these are the situations where clinical exam. Is of utmost importance

KDOQI GUIDELINES• 4.1 Physical examination (monitoring): Physical examination to detect dysfunction in fistulae and grafts at

least monthly by a qualified individual. (B)

• 4.2 Surveillance of grafts:• 4.2.1 Preferred: 4.2.1.1 Intra-access flow. (A) 4.2.1.2 Directly measured or derived static venous dialysis pressure.

(A) 4.2.1.3 Duplex ultrasound. (A)• 4.2.2 Acceptable: 4.2.2.1 Physical examination(B)• 4.2.3 Unacceptable: 4.2.3.1 Unstandardized dynamic venous pressures (DVPs) should not

be used. (A)

KDOQI GUIDELINES• 4.3 Surveillance in fistulae: 4.3.1 Preferred:• 4.3.1.1 Direct flow measurements. (A) 4.3.1.2 Physical examination(B) 4.3.1.3 Duplex ultrasound. (A)• 4.3.2 Acceptable: 4.3.2.1 Recirculation using a non–urea-based

dilutional method.(B) 4.3.2.2 Static pressures (B), direct or derived. (B)

PITFALLS OF SURVEILLANCE• Observational studies showed improvement in graft

thrombosis with surveillance.• In a Meta-analysis of six randomized trials comparing

graft surveillance to clinical monitoring on graft outcome, 5 out of 6 showed no improvement in graft thrombosis. Kidney Int. 2005;67(4):1554-8, J Am Soc Nephrol. 2003;14(10):2645-53.

• Current published evidence suggests surveillance with pre-emptive angioplasty did not improve graft thrombosis or longevity.

• Conflicting results may be due to high incidence of restenosis, and probably due to advantages of intervention in newer grafts only.

PITFALLS OF SURVEILLANCE

• In contrast to grafts in fistulas the role of QA surveillance appears to be more established.

• Larger randomized trials would be required to confirm whether surveillance techniques would improve longevity of vascular access.

TO END

• Whether surveillance can prolong access survival is unproven.

• However it fosters the ability to salvage vascular access sites through planning, rather than urgent procedures or replacement which is an important consideration for both physicians as well as patients.

THANK YOU FOR YOUR KIND ATTENTION