Access Flashcards
What is the minimum vein diameter for forearm access?
2-2.5 mm
What creatinine clearance should ESRD be referred to vasc surgeons for access?
Cr clearance < 25 ml/min (2005 SVS guidelines)
How long before IHD should you create access?
6 months for autogenous
3-6 weeks for graft
Name 7 patient factors that can affect patency of access
1 - age
2 - smoking
3 - diabetes
4 - anemia
5 - parathyroid hormone
6 - certain medications
7 - atherosclerotic disease
In elderly patients (>50) - what would be your first choice for AV access?
Upper arm autogenous or prosthetic. Distal radial have poorer patency and given short life expectancy you want to have reliable access sooner.
In diabetics - why is it advantageous to have as distal access as possible?
Higher risk of steal in diabetic patients
Given calcification and atherosclerosis - should you offer proximal or graft as first line for diabetics?
No - increased risk of steal with proximal. No difference in abilty to create autogenous fistulas despite increased calcification
What medications can improve access patency?
Antiplatelet, ACE inhibitors for autogenous, Calcium channel blockers for grafts, ARBs but no consensus
What are the minimum arterial requirements for AV access?
2 mm, patent palmar arch, no pressure gradient between bilateral upper extremities
What access flow rate should prompt further investigation?
< 600 mL/min or < 1000 mL/min with 25% reduction over 4 months
What are 7 access complications recognized by the 2006 KDOQI guidelines?
1 - infection
2- neuropathy
3 - seroma
4 - pseudoaneurysm/aneurysm
5-access related hand ischemia
6 - venous hypertension
7 - bleeding
How does anemia contribute to increased bleeding in ESRD patients?
Low hematocrit causes an increase in NO activity which causes vasodilation and platelet inhibition
How does uremia affect platelets (3 ways)?
1) Reduced expresion of GPIb which impairs platelet adhesion to subendothelium
2) Conformational change of GP2a3b which inhibits fibrinogen binding and platelet aggregation
3) Decrease in dense granules reduces storage of platelet ADP and serotonin and creases endothelial production of prostacyclin which inhibits plately activation
Name 3 reasons ESRD are prone to bleeding
1) Uremia platelet dysfunction
2) Medications - 20% have afib and on anticoag, betalactams can cause platelet dysfunction at high levels
3) thrombocytopenia
How do antibiotics increase risk of ESRD patients bleeding?
Betalactams (penicillins/cephalosporins) have long half lives and only partially cleared by dialysis. At high concentrations they can cause platelet dysfunction. At very high concentrations it can alter antithrombin III and act like heparin.
Name 4 ways of managing bleeding post access surgery
1 - DDAVP
2 - Platelet transfusion (only lasts 4 -5 h because platelets become dysfunctional in a uremic environment)
3 - Cryoprecipitate - rich in fibrinogen, vWF, factor 8. Works within minutes, effect max at 4-12 h and lasts up to 24 h
4 - Protamine if on heparin during surgery or after dialysis
How does DDAVP help with access related bleeding (3 ways)?
DDAVP is a human made form of ADH.
1) It induces rapid release of autologous vWF and 2) factor 8 and 3) transiently decreases activity of protein C.
Name 4 ways of optimizing patients bleeding risk for elective access surgery
1) Check hemoglobin - <100 in 20% of ESRD patients. May require EPO to induce erythrpoesis and correct anemia but takes several weeks to show effect.
2) Schedule surgery 24 after dialysis
3) DC antiplatelets 1 week prior
4) Consider conjugated estrogens (increase vWF synthesis, reduce protein S and NO and correct bleeding time)
How does EPO help with bleeding in ESRD patients (2 ways)?
1) induces erythropoieses thus correcting anemia
2) increases platelet expression of GP2b3a and enhances platelet aggregation
How does estrogen help with bleeding in ESRD patients?
1) Increase vWF synthesis
2) Reduces protein S
3) Reduces NO
Requires IV treatment for 5 consecutive days or transdermal 2 weeks prior
What are the 3 recommended SVS reporting standards for classifying access infections?
1) early < 30 d vs late
2) culture positive or neg
3) site (anastomotic, mid AV access, outflow veins)
What organism is most often responsible for access related infections?
Staph aureus
What is the probability of developing an access related infection in 1 year for autogenous AV fistulas versus prosthetic grafts?
5% vs 20%
What is a risk of the buttonhole technique?
Increased risk of infection compared with rope ladder or area techniques
How should you treat access related infections?
Broad spec antibiotics - vanco and gent chosen because of ease of dosing and spectrum. In centres with low MRSA, can use ancef.
What are the specific anatomic requirements for an autogenous femoral vein transposition (eg GSV) for access?
1) Patent femoral vein > 3-6 mm (both written?)
2) Patent, noncalcified superficial femoral artery
Who is autologous femoral vein transposition accesses ideally suited for (3 groups)?
1 - Pediatric/young healthy patients
2 - Hypercoagulable patients with no other access options
3 - Patients at high risk for infection (poor hygiene, immunosuppressed, previous access infections)
What are 4 contraindications to autogenous femoral vein transposition for dialysis access?
1 - obese thigh
2 - “medically fragile”/elderly
3 - Temporary catheter sites not readily available
4 - Pts at high risk of access-related ischemia of the lower extremity
What 2 anatomic requirements are there for prosthetic midthigh loop femoral-femoral access
1 - patent femoral vein or common femoral vein
2 - patent SFA or CFA
Who are ideally suited for prosthetic midthigh loop femoral femoral AV access?
elderly with significant comorbidities
What are contraindications to prosthetic midthigh loop femoral-femoral access (2 types)?
1 - high risk of infection (immunosuppressed, prev infection, hygiene)
2 - morbid obese
What are the anatomic requirements for prosthetic chest wall access for dialysis (2)?
1 - Patent axillosubclavian artery and vein
2 - Patent central vein
Who is prosthetic chest wall access for dialysis ideally suited for?
1 - Morbid obese
2-Pts at high risk of access related limb ischemia
What are the anatomic requirements for tunneled dialysis catheter?
Patent central vein
Who are tunneled catheters ideally suited for (2)?
1 - “Medically fragile” patients with life expectancy < 6 months
2 - Pts who failed all other access options
What are the anatomic requirements for Hemoaccess Reliable Outflow vascular devices?
1 - Guidewire access to a patent central vein
2 - Brachial artery > 3mm
What type of patients are ideally suited for a HeRO (2)?
1) Central venous stenosis/occlusion that precludes upper extremity autogenous or prosthetic access options
2) Patients otherwise relegated to tunneled line
What are contraindications to HeRO graft?
Active infection
sBP < 100
EF < 20%
What type of access is this?
Brachioaxillary with transposed autogenous femoral vein
What are the 2 year patency rates of brachiobasilic transposition access?
~ 50% (1 year varies 40-92% depending on source)
What time interval should you have between 1st and 2nd stages of a brachiobasilic transposition?
4-6 weeks
When would you consider a single stage brachiobasilic transposition procedure?
If the basilic vein > 4mm
When performing a 2nd stage brachiobasilic transposition, what nerves are at risk?
medial antebrachial cutaneous and median
After the second stage of a brachiobasilic vein transposition, when can it be accessed?
When wounds have healed, usually in 3 weeks
What is a necklace access?
axillary artery to contralat jugular vein
What is an advantage and disadvantage of chestwall access compared with lower extremity?
Pro: Lower infection rates, better for obese patients
Con: if graft becomes infected and needs removal, proximal control of axillary artery is challenging.
Where does access related neointimal hyperplasia occur in prosthetic and autogenous AV access?
1 - Prosthetic: outflow anastomosis
2 - Autogenous anywhere along the outflow vein
Also: central venous on the ipsilateral side.
What is the most common measure of access function? What is an acceptable value?
Kt/V
K = rate of clearance of urea (calculated from the pre and post dialysis measurements)
t = duration of dialysis
V = urea distribution volume
KtV is generally monitored to ensure > 1.2
What is dialysis “recirculation”
Retreatment of blood already filtered by dialysis machine. Can result when afferent needle pulls blood that has just been returned to the patient via efferent needle.
Name 4 causes of recirculation problems with IHD
- Venous outflow stenosis - classic problem of prosthetic grafts
- Arterial inflow stenosis - both needles are distal to the stenosis - can result in complete collapse of the outflow vein. A problem seen with autogenous AV access
- Inadquate separation of cannulation needle
- Puncturing of psuedoaneurysms which are sufficiently large that they have stagnant flow within them.
Name 3 ways of clinically determining access failure.
- Thrill not detectable or pulse present near the venous outflow
- Collateral veins in shoulder and anterior chest wall or upper extremtiy edema
- High venous pressures resulting in long access bleeding times
Name 2 ways of determining failing access during dialysis
- Venous pressure > 50% of MAP
- Flow measurement. (Bolus isotonic saline dilutes blood and U/S velocity, sensors registers an indicator curve as saline passes through the blood lines to calculate the flow rate)
What is the most preferred site for tunneled HD line placement and why?
Right IJ - best patency likely due to less kinking
Name 5 causes for prolonged access site bleeding
- Uremia related platelet dysfunction
- Anemia related increased NO causing vasodilation/platelet inhibition
- Beta lactams at high doses cause platelet dysfunction and at very high doses affect ATIII
- 20% of patients have afib and on anticoag
- Venous outflow stenosis
How does uremia cause prolonged bleeding? (3 mechanisms)
- Reduces expression of glycoprotein 1b which impairs platelet adhesion to subendothelium
- Conformational change in GP 2b3a which inhibits fibrinogen binding and platelet aggregation
- Decreased content of dense granules thus reduces storage of ADP and serotonin which in turn inhibits platelet activation
How does DDAVP treat bleeding in uremic patients (3 ways)?
- Induces rapid release of autologous vWF
- Induces rapid release of autologous Factor 8
- Transiently decreases activity of protein C.
What is a grade 3 access infection?
Loss of limb
What is a grade 2 access infection?
Loss of AV access because of ligation, removal and bypass
What is a grade 1 access infection?
Resolved with antibiotic treatment
What is a grade 0 access infection?
No infection
What is the most common access-related infection bacteria?
Staph aureus
What is the risk of access infection at 1 year: autologous vs. graft?
4.5% vs 19.7%
Why is the “button hole” access technique worse than the “rope ladder”?
Higher infection rate. This is due to inappropriate use of sharp needles after tract developed, inadequate use of disinfecting agents and incomplete scab removal.
Which antibiotics are used for access related infections?
Typically vanco and gentamicin because its broad spec and easy to dose.
If there is a low prevalence of S. Aureus - ancef may be used.
How do you treat a AV access graft infection?
Broad spec antibiotics + local resection if possible. Salvage is most frequently feasible when infection involves the midportion of the graft. A new graft can be tunneled through clean tissue planes.
(Anastomotic infection requires complete graft excision to prevent disruption/hemorrhage)
Name 4 treatment options for AV pseudoaneurysms
- Interposition graft/bypass around lesion
- Autogenous can be converted to graft “graftula” where arterial anast is kept and venous anast new
- Fistula reduction with resection of portion of vein wall (10 mm rubber catheter used as a sizing dowel)
- Endovascular self expanding covered stent graft.
What is the rate of steal with autogenous brachial access?
4-8%
What is the rate of steal with autogenous wrist access?
1-2%
What is a Grade 3 steal?
Severe - ischemic pain at rest, tissue loss
What is a Grade 2 steal?
Moderate - intermittent ischmeia only during dialysis, claudication
What is a Grade 1 steal?
Mild - cool extremity, few symptoms, flow augmentation with access occlusion
What is a Grade 0 steal?
No symptoms
When do you have to intervene for steal?
Grade 2 sometimes needed (claudication/ischemia during dialysis), Grade 3 (rest pain and tissue loss) mandatory to intervene.
Name 2 other conditions on differential for steal
- Carpal tunnel syndrome
- Ischemic monomelic neuropathy
How do you treat grade 1 mild steal (transient mild symptoms)
- Serial examinations
- Reduce antihypertensive medications
- Re-warm
Name 6 treament options for severe steal.
- Banding/flow limiting procedures
- Proximalization of arterial inflow
- Revision using distal inflow (RUDI)
- Distal revascularization with interval ligation (DRIL)
- Angioplasty
- Ligation (last resort)
What is the MILLER procedure? Why is it used?
Minimally invasive limited ligation endoluminal assisted revision
A 4 or 5 mm balloon placed percutaneously as a sizing dowel, cut down on anastomosis, secure a suture around the access with a balloon inflated.
Difficult to determine how much to stenose access to maintain patency but relieve ischemic steal symptoms and anesthesia can make intra-op flow measurements inaccurate.
What are 3 risks of DRIL procedure
- High mortality - 6.8%
- Invasiveness/wound complication rates of 9-19%
- Hand perfusion is dependent on the bypass
What is the best treatment option when steal is associated with low or normal flows (happens in 1/3 of steal patients)?
Likely inadequate collaterals due to atherosclerotic disease - best treated via revascularization - DRIL, proximalization, or angioplasty
Which treatment options are well suited for high flow steal (autogenous > 800 mL, prosthetic > 1200 mL/min)
Banding and RUDI
Which treatment options for steal require an autogenous conduit?
RUDI and DRIL. Proximalization typically uses prosthetic.
What is the central vein stenosis rate for IJ catheters? What about subclavian vein? Any theories as to why?
IJ 10%
Subclavian 40-50%
Maybe due to endothelial repetitive trauma with cardiac and respiratory cycles
What does KDOQI guidelines recommend for treating central vein stenoses/occlusions?
Asymptomatic - no treatment
Symptomatic - PTA
Ligation last resort.
What is the 6 month and 1 year patency of central vein stenoses after angioplasty?
Poor - 20-50%, 12-40%
What is the most common cause of neuropathy in dialysis patients?
Uremia
