Dr. Gaurav Sagar expained monitoring and sureveillance of vascular access.

1. MONITORING & SURVEILLANCE
FOR VASCULAR ACCESS
DR.GAURAV SAGAR
CONSULTANT NEPHROLOGIST
INDRAPRASTHA APOLLO HOSPITAL

2. 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

3. 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

4. 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.

5. “Worm Hand “
• Presence of collaterals usually indicate
outflow stenosis/obstruction

8. 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.

9. 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.

10. 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.

11. 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

12. 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

13. 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

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

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

16. 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

17. 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)

18. 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.

19. 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

20. HEMATOCRIT DILUTION TECHNIQUE FOR ACCESS FLOW
Y = 0.92x + 8.11
N = 30
R = 0.91
Hematocrit Dilution technique
USGdilutiontechnique
-Tirannathanagul (2008), KI; 73: 1082 -- 1086

21. 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.

22. 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

23. 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.

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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)

30. 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)

31. 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.

32. 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.

33. 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.

34. THANK YOU FOR YOUR KIND
ATTENTION