Interventional Nephrology¶
Chapter 324 | Part 9: Disorders of the Kidney and Urinary Tract
KEY CLINICAL POINTS¶
- Interventional nephrology focuses on dialysis access creation and maintenance, including arteriovenous fistulas (AVFs), grafts, and catheters.
- Peritoneal dialysis (PD) is more common in low-resource settings due to cost, while hemodialysis requires vascular access with AVFs as the gold standard.
- Complications include stenosis, thrombosis, infection, and aneurysm formation, requiring interventions like angioplasty, stenting, and catheter exchange.
- KDOQI guidelines emphasize 'Fistula First' to reduce catheter use and improve long-term access outcomes.
- Physical examination of dialysis access includes assessing pulsatility, flow murmurs, and thrills to detect stenosis or occlusion.
1. DEFINITION & OVERVIEW¶
Interventional nephrology is a procedure-oriented subspecialty focused on dialysis access for hemodialysis and peritoneal dialysis. It involves vascular access creation, maintenance, and salvage using fluoroscopy, ultrasound, and endovascular techniques.
Common Dialysis Access Types¶
| Access Type | Indication | Complication Risk |
|---|---|---|
| Autogenous AVF | Long-term hemodialysis | Stenosis, thrombosis |
| AVG | Poor native vessel quality | Infection, graft failure |
| Tunneled Catheter | Temporary access | Infection, thrombosis |
1.1 History of Vascular Access¶
Early hemodialysis (1924) used glass needles for radial artery access. The Cimino fistula (1968) and arteriovenous grafts (AVGs) revolutionized dialysis access. Modern techniques include drug-coated balloons and tissue-engineered grafts.
1.2 Access Types¶
Autogenous AVFs (radial-cephalic, brachial-cephalic) vs. AVGs (polytetrafluoroethylene grafts). Tunneled catheters (PICCs) are used for temporary access but associated with higher infection risk.
2. EPIDEMIOLOGY¶
Global prevalence of dialysis access complications varies by region. In the U.S., 65% of dialysis patients previously used AVGs, but AVF prevalence increased to ~65% due to 'Fistula First' campaigns. Risk factors include diabetes, hypertension, and systemic vascular disease.
2.1 Demographics¶
Higher incidence in older adults with comorbidities. CKD stages 3-5 require vascular access planning. U.S. patients have higher AVG prevalence compared to Europe.
2.2 Complication Rates¶
10-20% of AVFs fail within 6 months. AVG failure rates are 30-40% within 1 year. Catheter-related infections occur in 10-20% of tunneled catheters.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Access complications arise from hemodynamic changes, vascular remodeling, and infection. Stenosis occurs due to shear stress-induced intimal hyperplasia. Thrombosis results from turbulent flow and endothelial damage. Infections are linked to biofilm formation on catheters.
3.1 Hemodynamic Factors¶
High flow rates (>1500 mL/min) cause venous hypertension, leading to aneurysm formation and skin breakdown. Outflow stenosis increases intra-access pressure, accelerating vessel remodeling.
3.2 Infection Mechanisms¶
Catheter-associated bloodstream infections (CRBSI) result from biofilm formation. Peritoneal dialysis-associated infections are due to glucose-containing solutions and peritonitis.
4. CLINICAL FEATURES¶
Symptoms include arm swelling, pain, and reduced dialysis efficacy. Signs: pulsatile mass, thrill, flow murmur, and skin ulceration. Complications: steal syndrome (ischemia), central vein stenosis, and encapsulating peritoneal sclerosis (EPS).
4.1 Stenosis Presentation¶
Outflow stenosis: high pulsatility, loud murmur. Inflow stenosis: 'empty' access during diastole, reduced softening. Recurrent stenosis in cephalic arch or swing point.
4.2 Infection Signs¶
Local erythema, warmth, purulent drainage. Systemic symptoms: fever, leukocytosis. Catheter-related sepsis may present with hypotension and multiorgan failure.
5. DIFFERENTIAL DIAGNOSIS¶
Distinguish between stenosis, thrombosis, and infection. Differentiate between AVF and AVG complications. Consider central vein stenosis vs. cardiac arrhythmias. Rule out tumor invasion or foreign body reaction in chronic cases.
5.1 Stenosis vs. Thrombosis¶
Stenosis: pulsatile mass, high flow murmur. Thrombosis: occlusive symptoms, absent thrill, possible embolism.
5.2 Infection vs. Inflammation¶
Infection: fever, systemic signs. Inflammation: localized pain without systemic symptoms. EPS presents with peritoneal membrane thickening and ascites.
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnostic tools include Doppler ultrasound, angiography, and venography. Flowmetry measures access flow (target 600-800 mL/min for AVFs). Catheter tip position and sheath length are assessed via imaging.
Access Flow Requirements¶
| Access Type | Target Flow (mL/min) | Complication Risk |
|---|---|---|
| AVF | 600-800 | Stenosis, thrombosis |
| AVG | 1000-1800 | Infection, graft failure |
| Tunneled Catheter | 400-500 | Infection, thrombosis |
6.1 Imaging Techniques¶
Ultrasound: assess patency, flow velocity, and stenosis. Angiography: gold standard for visualizing stenosis and occlusion. Venography: used for peritoneal dialysis catheter evaluation.
6.2 Flowmetry¶
Access flow measured via Doppler or pressure transducers. Target flow: 600-800 mL/min for AVFs, 1000-1800 mL/min for AVGs. Flow ratios (inflow/outflow) guide intervention.
7. MANAGEMENT & TREATMENT¶
Interventions include angioplasty, stent placement, and catheter exchange. Pharmacologic agents: anticoagulants (heparin), antiplatelets (aspirin), and antibiotics for infection. Surgical options: revision of AVFs, graft replacement, or catheter removal.
Interventional Techniques¶
| Complication | Treatment | Success Rate |
|---|---|---|
| Stenosis | Angioplasty/stent | 70-90% |
| Thrombosis | Thrombolysis/angioplasty | 60-80% |
| Infection | Catheter exchange | 80-95% |
7.1 Endovascular Interventions¶
Balloon angioplasty for stenosis, stent grafts for recurrent occlusion. Drug-coated balloons reduce restenosis. Nitinol stents are preferred for central venous stenosis.
7.2 Catheter Management¶
Exchange of infected catheters with disruption of fibrinous sheath. Use of silicone-modified ePTFE grafts for early cannulation. Avoid PICCs in CKD patients >stage 3.
8. PROGNOSIS & COMPLICATIONS¶
Prognosis depends on access type and complication management. Long-term AVFs have better patency (12-24 months) than AVGs (6-12 months). Complications: steal syndrome, central vein stenosis, and EPS in PD patients.
8.1 Patency Rates¶
AVF patency: 12-24 months. AVG patency: 6-12 months. Catheter patency: 1-3 months. Stent placement extends AVG patency to 1 year.
8.2 Long-Term Risks¶
Chronic dialysis access disease: shear stress-induced stenosis. EPS: 5-10% incidence in PD patients. Central vein stenosis: 10-20% in AVF patients.
9. SPECIAL CONSIDERATIONS¶
Pregnancy: avoid catheters due to infection risk. Pediatrics: use smaller catheters and avoid PICCs. Elderly: higher risk of complications due to comorbidities. CKD patients: prioritize AVFs over catheters to reduce infection risk.
9.1 Pregnancy¶
Avoid tunneled catheters. Use AVFs if possible. Monitor for steal syndrome and fetal growth restriction.
9.2 Elderly Patients¶
Higher risk of vascular calcification and stenosis. Use smaller catheters and avoid high-flow AVFs.
10. KEY POINTS & CLINICAL PEARLS¶
- Prioritize AVFs over catheters to reduce infection risk. 2. Use Doppler ultrasound for access evaluation. 3. Stent placement improves AVG patency. 4. Avoid PICCs in CKD patients >stage 3. 5. Early detection of stenosis prevents aneurysm formation.