Dialysis: Hemodialysis, Peritoneal Dialysis, and Vascular Access

Dialysis is a life-sustaining renal replacement therapy (RRT) that artificially removes waste products, excess fluid, and electrolytes from the blood when kidney function is severely impaired. It serves as a bridge to kidney transplantation or as definitive therapy for end-stage renal disease (ESRD).

[KEY_CONCEPT] Dialysis becomes necessary when glomerular filtration rate (GFR) falls below 10-15 mL/min/1.73m² or when uremic symptoms develop, regardless of GFR.

Epidemiology

• Prevalence: Over 750,000 patients receive dialysis in the United States
• Incidence: Approximately 120,000 new dialysis patients annually
• Demographics: Higher prevalence in patients >65 years, African Americans, and those with diabetes mellitus
• Primary causes: Diabetic nephropathy (37%), hypertensive nephrosclerosis (24%), polycystic kidney disease (4%)

Types of Dialysis

[HIGH_YIELD] The choice between HD and PD depends on patient factors including residual kidney function, cardiovascular status, lifestyle preferences, and contraindications to either modality.

Pathophysiology: Dialysis relies on diffusion (solute movement across concentration gradients), convection (solute drag with fluid removal), and ultrafiltration (fluid removal via hydrostatic pressure) to replicate kidney function.

Absolute Indications for Dialysis (AEIOU Mnemonic)

• Acidemia: Severe metabolic acidosis (pH <7.1) refractory to medical management
• Electrolyte abnormalities: Hyperkalemia >6.5 mEq/L with ECG changes
• Intoxications: Dialyzable toxins (methanol, ethylene glycol, salicylates)
• Overload: Pulmonary edema unresponsive to diuretics
• Uremia: Symptomatic uremia (pericarditis, encephalopathy, bleeding)

[CLINICAL_PEARL] Uremic symptoms may include altered mental status, pericardial friction rub, platelet dysfunction with bleeding, and refractory nausea/vomiting.

Modality Selection Criteria

Hemodialysis Preferred

• Hemodynamic instability requiring rapid fluid/solute removal
• Inability to perform self-care (cognitive impairment, physical limitations)
• Contraindications to PD (extensive abdominal adhesions, inflammatory bowel disease)
• Patient preference for in-center care

Peritoneal Dialysis Preferred

• Residual kidney function >2 mL/min/1.73m²
• Cardiovascular instability (better hemodynamic tolerance)
• Desire for independence and flexible schedule
• Younger age and better nutritional status
• Contraindications to anticoagulation

[KEY_CONCEPT] Incremental dialysis involves starting with reduced frequency (2x/week HD or reduced PD exchanges) in patients with significant residual kidney function to preserve native kidney function longer.

Timing of Dialysis Initiation

KDIGO Guidelines recommend starting dialysis when:

1. GFR 5-10 mL/min/1.73m² with uremic symptoms
2. Inability to control volume status or electrolyte/acid-base balance
3. Protein-energy wasting syndrome

[HIGH_YIELD] The IDEAL study demonstrated that early dialysis initiation (GFR 10-14) does not improve survival compared to late initiation (GFR 5-7), supporting symptom-based rather than GFR-based timing.

Hemodialysis Process

Hemodialysis removes waste products and excess fluid by circulating blood through an extracorporeal circuit containing a semipermeable membrane (dialyzer). Blood flow rates typically range from 300-500 mL/min, while dialysate flows counter-current at 500-800 mL/min.

Key HD Parameters

[CLINICAL_PEARL] Kt/V represents the dialyzer urea clearance (K) × treatment time (t) divided by patient's urea distribution volume (V). Higher Kt/V correlates with improved survival.

Dialysate Composition

• Sodium: 135-145 mEq/L (individualized)
• Potassium: 1-4 mEq/L (based on serum levels)
• Calcium: 2.5-3.5 mEq/L
• Bicarbonate: 32-40 mEq/L
• Glucose: 100-200 mg/dL

Hemodialysis Complications

Acute Complications

• Intradialytic hypotension (most common): Due to rapid fluid removal
• Muscle cramps: Related to volume depletion and electrolyte shifts
• Disequilibrium syndrome: Cerebral edema from rapid urea removal
• Air embolism: Equipment malfunction or line disconnection

Chronic Complications

• Dialysis-related amyloidosis: β2-microglobulin accumulation
• Cardiovascular disease: Left ventricular hypertrophy, accelerated atherosclerosis
• Bone disease: Secondary hyperparathyroidism, adynamic bone disease

[HIGH_YIELD] Dialysis disequilibrium syndrome occurs more commonly in first-time dialysis patients with very high BUN (>100 mg/dL). Prevention involves shorter initial treatments with reduced blood flow rates.

Home Hemodialysis

Home HD offers more flexible scheduling and potentially better outcomes but requires:

• Motivated patient with capable care partner
• Adequate home infrastructure
• Extensive training (4-8 weeks)
• More frequent treatments (typically 6x/week) or nocturnal HD

Peritoneal dialysis utilizes the peritoneal membrane as a natural semipermeable barrier, with dialysate instilled into the peritoneal cavity for solute and fluid exchange.

PD Modalities

Continuous Ambulatory PD (CAPD)

• Manual exchanges 3-4 times daily
• 8-10 hour dwell times
• No mechanical equipment required
• Most common PD modality worldwide

Automated PD (APD)

• Cycler-assisted exchanges during sleep
• Multiple short dwells (1-3 hours)
• May include daytime dwell
• Better for working patients

PD Prescription Parameters

PD Adequacy Targets: ├── Weekly Kt/V ≥ 1.7 ├── Creatinine Clearance ≥ 50 L/week/1.73m² └── Residual kidney function preservation

Fluid Removal: ├── Ultrafiltration goal: 1-2L/day ├── Glucose concentration: 1.5%, 2.5%, 4.25% └── Icodextrin for long dwells (7.5%)

[KEY_CONCEPT] Icodextrin is a glucose polymer that provides sustained ultrafiltration during long dwells (8-16 hours) through colloid osmosis, ideal for nighttime exchanges or patients with high peritoneal transport.

Peritoneal Equilibration Test (PET)

Assesses peritoneal membrane transport characteristics:

[CLINICAL_PEARL] High transporters lose glucose rapidly from dialysate, reducing osmotic gradient and ultrafiltration. They benefit from frequent, short exchanges (APD).

PD Complications

Peritonitis

• Incidence: Target <0.5 episodes per patient-year
• Presentation: Cloudy effluent, abdominal pain, fever
• Diagnosis: Effluent WBC >100/μL with >50% neutrophils
• Treatment: Intraperitoneal antibiotics (vancomycin + ceftazidime)

Mechanical Complications

• Catheter malfunction: Poor drainage, migration
• Leak: Pericatheter, pleural, genital
• Hernia: Inguinal, umbilical, incisional

Metabolic Complications

• Glucose absorption: Hyperglycemia, weight gain
• Protein losses: 6-12g/day in dialysate
• Ultrafiltration failure: Loss of osmotic gradient

[HIGH_YIELD] PD patients require higher protein intake (1.2-1.3 g/kg/day) compared to HD patients due to continuous protein losses in dialysate.

Vascular access is the "lifeline" for hemodialysis patients, requiring adequate blood flow (300-500 mL/min) for effective treatment. The hierarchy follows the "fistula first" initiative.

Access Types & Selection

Arteriovenous Fistula (AVF) - Gold Standard

• Procedure: Direct surgical anastomosis of artery to vein
• Maturation: 8-12 weeks before use
• Blood flow: 400-1000 mL/min when mature
• Patency: 5-year primary patency ~50-60%
• Complications: Lowest infection and thrombosis rates

Arteriovenous Graft (AVG)

• Material: Synthetic (PTFE) or biological conduit
• Maturation: 2-4 weeks
• Blood flow: 400-800 mL/min
• Patency: Lower than AVF, higher stenosis rates
• Indications: Poor vein quality, elderly patients

Central Venous Catheter (CVC)

• Types: Non-tunneled (temporary), tunneled (long-term)
• Duration: Non-tunneled <2-3 weeks, tunneled months
• Sites: Right internal jugular preferred, subclavian avoided
• Complications: Highest infection and mortality rates

Access Planning Algorithm

Pre-ESRD Patient (GFR <30 mL/min/1.73m²): ├── Vein mapping (ultrasound/venography) ├── Preserve arm veins (avoid peripheral IVs) ├── Consider fistula creation when GFR <20 └── Patient education on access options

Access Selection: ├── AVF preferred (if adequate vessels) ├── AVG if poor veins or elderly ├── CVC only if immediate dialysis needed └── Consider patient factors (age, comorbidities)

Access Monitoring: ├── Physical examination (thrill, bruit) ├── Access flow measurements ├── Venous pressure monitoring └── Early intervention for dysfunction

[KEY_CONCEPT] The "Fistula First" initiative emphasizes AVF creation as the preferred access due to superior long-term patency and lower complication rates compared to grafts and catheters.

Vascular Access Complications

Thrombosis

• AVF/AVG: Most common cause of access failure
• Risk factors: Stenosis, hypotension, hypercoagulable states
• Management: Thrombectomy, angioplasty, surgical revision

Infection

• CVC: Highest risk (2-5 episodes per 1000 catheter-days)
• AVG: Intermediate risk
• AVF: Lowest risk
• Treatment: Systemic antibiotics, access removal if severe

Steal Syndrome

• Mechanism: Retrograde flow from hand to access
• Symptoms: Hand ischemia, pain, coolness
• Management: Access revision, banding, or ligation

[CLINICAL_PEARL] High-output heart failure can develop in patients with high-flow fistulas (>2L/min), particularly those with underlying cardiac disease. Treatment involves access flow reduction.

Access Surveillance

• Monthly assessment: Physical examination, access flow measurements
• Intervention thresholds: Access flow <600 mL/min (AVF) or <650 mL/min (AVG)
• Venous pressure monitoring: Elevated pressures suggest outflow stenosis
• Angiography: Gold standard for stenosis evaluation

[HIGH_YIELD] Central venous stenosis from previous subclavian catheterization can prevent future ipsilateral access creation and should be avoided in potential dialysis patients.

Adequacy Monitoring

Dialysis adequacy ensures sufficient removal of uremic toxins and maintenance of fluid/electrolyte balance. Regular monitoring prevents complications and optimizes patient outcomes.

Hemodialysis Adequacy

• Kt/V measurement: Monthly for stable patients
• Target Kt/V: >1.2 per treatment (>2.1 per week)
• URR target: >65% per treatment
• Frequency: Minimum 3x/week, consider more frequent treatments

Peritoneal Dialysis Adequacy

• Weekly Kt/V: Target ≥1.7 (combined PD + residual kidney function)
• Creatinine clearance: Target ≥50 L/week/1.73m²
• Assessment frequency: Every 4 months initially, then every 6 months

[KEY_CONCEPT] Residual kidney function contributes significantly to overall adequacy and should be preserved through:

• Avoiding nephrotoxic medications
• ACE inhibitors/ARBs (if tolerated)
• Gentle fluid removal rates
• Maintaining euvolemia

Long-term Complications Management

Cardiovascular Disease

• Leading cause of mortality in dialysis patients
• Management: BP control (<140/90), lipid management, diabetes control
• Screening: Annual echocardiography, stress testing as indicated

Bone and Mineral Disorders (CKD-MBD)

Anemia Management

• Target hemoglobin: 10-11.5 g/dL
• ESA therapy: Epoetin alfa, darbepoetin alfa
• Iron supplementation: IV iron preferred in HD patients
• Monitoring: Monthly hemoglobin, iron studies quarterly

[CLINICAL_PEARL] Cinacalcet (calcimimetic) directly suppresses PTH secretion and is particularly useful in patients with severe hyperparathyroidism and hypercalcemia.

Quality Metrics & Outcomes

Dialysis Facility Quality Measures

• Adequacy: Percentage of patients achieving Kt/V targets
• Vascular access: Percentage with functioning AVF/AVG
• Mineral metabolism: Phosphorus and PTH control
• Anemia management: Hemoglobin targets without excessive ESA use

Patient Survival Factors

• Dialysis adequacy: Higher Kt/V associated with improved survival
• Vascular access type: AVF > AVG > CVC for mortality
• Treatment time: Longer sessions (>4 hours) improve outcomes
• Residual kidney function: Preservation correlates with survival

[HIGH_YIELD] The HEMO study demonstrated that high-flux dialyzers improve survival in patients dialyzed >3.7 years, particularly those with diabetes or hypoalbuminemia.

Transition to Transplantation

• Evaluation timing: When GFR <30 mL/min/1.73m² or on dialysis
• Living donor preferred: Shorter wait times, better outcomes
• Preemptive transplant: Optimal strategy avoiding dialysis entirely
• Contraindications: Active malignancy, severe cardiac disease, non-compliance

Recent Evidence: The CREDENCE, DAPA-CKD, and EMPA-KIDNEY trials demonstrate that SGLT2 inhibitors significantly reduce progression to dialysis in patients with CKD, even those without diabetes.