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Interventional Nephrology

Chapter 324 | Part 9: Disorders of the Kidney and Urinary Tract · Part 9 – Renal & Urinary Tract Disorders · Chapter 324

Key Clinical Points

  1. Interventional nephrology focuses on dialysis access for peritoneal and hemodialysis, typically performed under fluoroscopy.
  2. US 'Fistula First' and 'Fistula First, Catheter Last' campaigns reduced arteriovenous graft (AVG) prevalence to <20% and increased autogenous arteriovenous fistula (AVF) to nearly 65%.
  3. High-access flow (>1500 mL/min) can lead to systemic complications including heart failure and pulmonary hypertension.
  4. Physical examination of dialysis access involves assessing pulsatility, murmur, thrill, augmentation, and collapse to detect inflow/outflow stenosis.
  5. Encapsulating peritoneal sclerosis is a late-stage complication of peritoneal dialysis triggered by repeated peritonitis.
  6. Preservation of venous real estate is critical for patients requiring cardiac rhythm management devices (CRMDs).
  7. Banding (using a 2-0 Prolene suture and 3-4 mm spacer) is used to reduce access flows and prevent steal syndrome.
  8. Catheter-related bacteremia is managed by exchange of the catheter and disruption of any fibrinous sheath; sepsis unresponsive to antibiotics requires immediate removal.
  9. Steal syndrome typically presents as ischemia of the hand due to high-access flow.
  10. Omental entrapment of peritoneal catheters may require laparoscopic intervention or omentopexy at placement.

1. DEFINITION & OVERVIEW

• Definition: Interventional nephrology is a procedure-oriented subspecialty focusing on dialysis access for peritoneal and hemodialysis, typically performed under fluoroscopy. • Multidisciplinary Team: Includes clinical nephrologists; access surgeons (vascular, transplant, or general); other interventionists (radiology/cardiology); and dialysis unit staff (coordinators, nurses, technicians). • Core Tenet: Long-term preservation of venous and arterial vascular real estate. • Historical Context: ◦ 1924: First hemodialysis using glass needles (radial artery to cubital vein). ◦ 1943: 'Rotating drum kidney' used for surgical access. ◦ 1961/1968: Introduction of catheter-based approaches with Dacron felt cuffs. ◦ 1972: Modified bovine carotid artery biological graft. ◦ 1976: Expanded polytetrafluoroethylene (ePTFE) grafts. ◦ 2016: Tissue-engineered blood vessels from human fibroblasts and endothelial cells. • Tools & Technology: ◦ Ultra-high-pressure (up to 40 atm) angioplasty balloons for peripheral/central venous therapy. ◦ Nitinol self-expanding stents and stent grafts as rescue tools for unsuccessful angioplasty or vessel rupture. ◦ Drug-coated balloons: Currently under assessment; limited use due to high cost and mixed clinical results.

2. EPIDEMIOLOGY

• US Trends: ◦ Mid-1990s: 65% of prevalent dialysis patients used an arteriovenous graft (AVG). ◦ Current: <20% AVG prevalence; ~65% autogenous arteriovenous fistula (AVF) prevalence due to 'Fistula First' campaigns. • Anatomical Selection: ◦ 75% of AVFs are created in the upper arm where veins have larger diameters and arteries provide higher blood flow rates. • Comorbidities & Constraints: ◦ 8–10% of CKD patients require cardiac rhythm management devices (CRMDs), leading to loss of upper arm cephalic vein and potential central venous stenoses. ◦ Hospitalization Management: Use of internal/external jugular vein tunneled small-diameter catheters instead of PICCs for CKD stage 3 or 3b+ to preserve arm veins.

3. ETIOLOGY & PATHOPHYSIOLOGY

• Peritoneal Dialysis (PD) Catheters: ◦ Placement: Fluoroscopically, peritoneoscopically, laparoscopically, or open surgery. ◦ Positioning: Internal cuff in rectus sheath; external cuff 2–4 cm from skin exit site. ◦ Complications: Fibrinous sheath (disrupted by guidewire); omental entrapment (prevented by omentopexy). ◦ Membrane Issues: Repeated infections and glucose exposure lead to reduced permeability; encapsulating peritoneal sclerosis is a late-stage complication. • Hemodialysis Catheters: ◦ Material: Polyurethane (softens at body temperature); supports 400–500 mL/min flow in 14.5–16 French designs. ◦ Risks: Fibrinous sheath may require exchange or balloon angioplasty; catheter-related bacteremia requires exchange and sheath disruption; sepsis unresponsive to antibiotics requires removal. ◦ Thrombus: Pulmonary embolism risk if thrombus is >2 cm in diameter. • Arteriovenous Fistula (AVF) & Graft (AVG) Pathophysiology: ◦ Flow Requirements: Must provide pump speed + 100–200 mL/min (typically 600–800 mL/min in the US). ◦ Vessel Dimensions: Artery ≥ 2 mm; Vein ≥ 3 mm → flow >500 mL/min when SBP >100 mmHg. ◦ Growth Dynamics: Arteries enlarge until a narrow segment in the venous conduit becomes flow-limiting. ◦ Flow Volumes: ◦ Mature upper arm AVFs: 1400–1800 mL/min (can reach 2000–4000 mL/min after years). ◦ Forearm AVFs: 500–700 mL/min (limited by smaller radial artery diameter). ◦ Chronic Dialysis Access Disease: ◦ AVGs: Venous anastomotic stenoses recur every 3–4 months. ◦ Stent grafts: Extend patency for ~1 year; require re-angioplasty 1–3 times per year due to fibrous deposition. ◦ Cimino (wrist): Prone to low flow due to juxta-anastomotic stenoses. ◦ Snuff box: Side branches/valves may require ligation. ◦ Brachial-cephalic: Cephalic arch stenoses; stent grafts extend patency 9–12 months. ◦ Brachial-basilic: Stenoses at the 'swing point' (where vein is curved during mobilization). ◦ Pressure & Skin Integrity: ◦ High intra-access pressure (>20–35 mmHg) → aneurysm formation and skin breakdown. ◦ High-access flow (>1500 mL/min) → heart failure, pulmonary hypertension, and steal syndrome (hand ischemia). ◦ Management of Flow: Banding (2-0 Prolene suture + 3–4 mm spacer) to create inflow stenosis.

4. CLINICAL FEATURES

• Physical Examination: ◦ Pulsatility: Reflects force of expansion during systole and softening during diastole. ◦ Murmur: Indicates flow dynamics. ◦ Thrill: Palpable vibration of blood flow. ◦ Augmentation: Assessment of pressure wave changes. ◦ Collapse: Evaluation of venous return/pressure. • Skin Integrity Assessment: ◦ Examination of skin thickness and presence of aneurysms (best performed while occluding inflow). ◦ Inspection for signs of central venous stenosis (e.g., chest wall/neck skin veins, venous distention, or ipsilateral arm edema).

5. DIFFERENTIAL DIAGNOSIS

• Stenosis Differentiation: ◦ Identify location-specific stenoses: Cephalic arch (Brachial-cephalic), Swing point (Brachial-basic), or Juxta-anastomotic sites (Cimino/Snuff box). ◦ Distinguish between high-flow issues (>1500 mL/min) and high-pressure issues (>20–35 mmHg).

6. INVESTIGATIONS & DIAGNOSIS

  1. Physical Examination: Evaluate the 5 key components (Pulsatility, Murmur, Thrill, Augmentation, Collapse) to assess flow and identify potential stenoses.
  2. Site-Specific Assessment: Identify specific locations of stenosis based on anatomy: ◦ Cephalic arch (Brachial-cephalic access). ◦ Swing point (Brachial-basic access). ◦ Juxta-anastomotic sites (Cimino/Snuff box).
  3. Pressure & Flow Monitoring: Identify high-access flow (>1500 mL/min) or high intra-access pressure (>20–35 mmHg) to predict skin breakdown and steal syndrome.
  4. Skin Integrity Check: Assess for aneurysm formation, skin thinning, and scab formation; evaluate while occluding inflow to palpate firm thrombus and measure skin thickness.

7. MANAGEMENT & TREATMENT

  1. Catheter Management: ◦ Bacteremia: Exchange catheter + disrupt fibrinous sheath (via guidewire or balloon angioplasty); alternative is removal and delayed reinsertion. ◦ Sepsis (unresponsive to antibiotics): Immediate removal of the catheter.
  2. Access Flow Reduction: ◦ High-flow (>1500 mL/min) or high pressure (>20–35 mmHg) → Banding procedure. ◦ Procedure: Use 2-0 Prolene suture guided around inflow with a 3–4 mm spacer tied snugly to create an inflow stenosis.
  3. Peritoneal Dialysis Management: ◦ Omental entrapment: Laparoscopic intervention or omentopexy at placement. ◦ Fibrinous sheath: Guidewire manipulation or balloon angioplasty.
  4. Interventional Procedures: ◦ Angioplasty: Standard for opening stenoses. ◦ Stent Grafts: Used to extend patency (e.g., cephalic arch, swing point) before fibrous deposition occurs.

8. PROGNOSIS & COMPLICATIONS

• Systemic Complications: ◦ High-access flow (>1500 mL/min) → heart failure, pulmonary hypertension. ◦ Steal Syndrome: Ischemia of the hand due to high-access flow. • Local Access Issues: ◦ Stenosis: Recurrent in AVGs (3–4 months) and Brachial-cephalic (accelerated after angioplasty). ◦ Skin Breakdown: Caused by intra-access pressures >20–35 mmHg → aneurysm, skin thinning, scab formation, full-thickness ulceration. ◦ Thrombus: Risk of pulmonary embolism if thrombus is large (>2 cm) or mobile.

9. SPECIAL CONSIDERATIONS

• Cardiac Rhythm Management Devices (CRMDs): ◦ Impact: Leads to loss of upper arm cephalic vein and potential central venous stenoses. ◦ Strategy: Use tunneled small-diameter catheters instead of PICCs to preserve remaining arm veins. • Transplant Patients: ◦ Consideration: Preservation of venous/arterial real estate for future transplant access. • Hospitalization Access: ◦ Strategy: Avoid PICCs in patients with CKD stage 3 or 3b+ to preserve arm veins for long-term access.

10. KEY PEARLS & CLINICAL TRAPS

• Fistula First: Successfully shifted US practice from AVGs to AVFs, but requires careful management of the 75% of AVFs located in the upper arm. • Banding Logic: Banding is used specifically to reduce flow and prevent 'steal' or skin breakdown; an outflow stenosis will decrease the degree of collapse. • Skin Assessment: Always assess skin thickness while occluding inflow to accurately gauge the risk of rupture/ulceration. • Catheter Rule: If a catheter-related infection is unresponsive to antibiotics, it must be removed immediately.