Types of Dialysis

1. Hemodialysis (HD)

Subtypes

• Brenner and Rector's The Kidney, regarding standard IHD: "Patients typically undergo dialysis treatments for 3 to 5 hours on a thrice-weekly, alternate-day, or daily schedule, depending on catabolic demands, electrolyte disturbances, and volume status."

2. Peritoneal Dialysis (PD)

Subtypes

• Comprehensive Clinical Nephrology, 7th ed.: "PD can be prescribed up to 24 hours/day and 7 days/wk to patients in the form of CAPD or CCPD. In CCPD, patients receive treatment with an automated PD (APD) cycler at night plus a final 'fill' that remains in the peritoneal cavity during the day."

• Glucose (1.5-4.25 g/dL) - most common; risk of hyperglycemia and glucose degradation products
• Icodextrin - non-glucose; better ultrafiltration, preserves residual kidney function, avoids hyperglycemia; note: can falsely elevate glucose readings on glucometers using glucose dehydrogenase strips. - Comprehensive Clinical Nephrology, 7th ed.

3. Continuous Renal Replacement Therapy (CRRT)

• Washington Manual of Medical Therapeutics: "CRRT can be used in specialized circumstances, particularly when the patient's hemodynamic status would not tolerate the rapid fluid shifts of IHD... The slower blood flows may necessitate anticoagulation (with either systemic heparin or regional citrate) to prevent the filter from clotting."

• Brenner and Rector's The Kidney (KDIGO guideline recommendation): "CRRT and PIRRT [be used] in hemodynamically unstable patients, and CRRT be used for patients with acute brain injury or other causes of increased intracranial pressure or generalized brain edema."

Key Comparison: HD vs. PD

• Comprehensive Clinical Nephrology, 7th ed.: "Retrospective and prospective nonrandomized comparative studies have failed to indicate a consistent survival advantage for either modality... PD is associated with superior health-related quality of life."

Modality Selection Principles

• Choice is guided largely by patient preference, lifestyle, residual kidney function, and clinical factors. - Comprehensive Clinical Nephrology
• For AKI with hemodynamic instability: prefer CRRT or SLED
• For AKI with increased intracranial pressure: CRRT preferred (avoids cerebral edema worsening)
• For diabetes + ESKD: no evidence that one modality is superior; glucose management differs with PD (use icodextrin when possible). - Comprehensive Clinical Nephrology
• PD is contraindicated (relative) in: recent intra-abdominal surgery, large abdominal hernia, severe respiratory disease, inability to perform exchanges, active abdominal infection

Complete Hemodialysis Procedure

Overview and Principle

• Diffusion - solutes move down a concentration gradient across a semipermeable membrane (removes urea, potassium, creatinine, phosphate)
• Ultrafiltration (UF) - fluid removal driven by a controlled hydrostatic pressure gradient across the membrane
• Convection (in high-flux/hemodiafiltration) - solute drag carried with water movement, improving middle-molecule clearance

Phase 1: Pre-Dialysis Assessment

Patient Evaluation Before Each Session

Phase 2: Vascular Access

1. Arteriovenous (AV) Fistula (Preferred)

• Surgically created connection between an artery and vein (usually radial artery + cephalic vein at the wrist, or brachial artery + cephalic/basilic vein)
• Takes 6-12 weeks to "mature" (dilate and thicken) before use
• Cannulation technique: two 15-gauge large-bore needles inserted - one arterial (blood withdrawal, upstream) and one venous (blood return, downstream); placed 5-8 cm apart using the rope-ladder or buttonhole technique
• Preferred because of lowest infection rate, longest longevity, and best outcomes

2. AV Graft

• A synthetic (polytetrafluoroethylene, PTFE) or biological tube bridging artery to vein
• Can be used within 2-4 weeks of creation
• Cannulated with the same 15-gauge needle technique as a fistula
• Higher complication rate than native fistula (thrombosis, infection, stenosis)

3. Tunneled-Cuffed Central Venous Catheter (Last resort)

• Strict sterile technique and topical 1% Xylocaine; conscious sedation often used
• Access to the right internal jugular vein under real-time ultrasound guidance using a 21-gauge needle
• A guide wire is passed down to the inferior vena cava under fluoroscopy
• A skin pocket (~1 cm) is created at the insertion site
• A subcutaneous tunnel is created laterally and inferiorly, under the clavicle, approximately 5-7 cm from the needle insertion point
• The catheter tip is fed to the junction of the superior vena cava and right atrium
• The cuff is positioned 2 cm from the exit site
• Final X-ray confirms position and checks for kinks

Phase 3: The Dialysis Prescription

Dialysate Composition

Phase 4: Anticoagulation

• Small amounts of IV heparin (1,000-2,000 units) prevent thrombosis at the vascular access site - Tintinalli's Emergency Medicine
• Loading dose: ~40 U/kg IV bolus at the start
• Continuous infusion: ~20 U/kg/hour, adjusted to maintain adequate circuit anticoagulation
• Target: activated clotting time (ACT) 200-250 seconds within the circuit

• Regional citrate anticoagulation - citrate infused pre-filter creates regional hypocalcemia in the circuit; calcium replaced post-filter
• Hirudin/lepirudin - direct thrombin inhibitors
• Heparin-free dialysis - frequent saline flushes of circuit; used in active bleeding

Phase 5: Machine Setup and Circuit Priming

1. Dialyzer inspection - check for integrity, correct membrane type, expiry
2. Blood tubing set - arterial and venous lines connected to dialyzer
3. Circuit priming - the extracorporeal circuit is flushed with ~500-1000 mL normal saline to remove air and manufacturing preservatives (e.g., glycerine), and to check for leaks
4. Dialysate preparation - machine mixes concentrated dialysate with purified water to achieve the prescribed ionic composition; online conductivity monitoring ensures correct preparation
5. Water treatment - incoming water undergoes softening, activated carbon filtration, and reverse osmosis to remove ions, organic compounds, and endotoxins; standards for water purity are strict because microbe-generated impurities such as endotoxins can cross the dialyzer membrane and cause inflammation - Brenner and Rector's The Kidney
6. Alarms set - arterial pressure, venous pressure, TMP (transmembrane pressure), air detector, conductivity, temperature, and blood leak detector alarms confirmed

Phase 6: Initiating Dialysis (Patient Connection)

1. Skin cleaned with antiseptic; sterile drape placed
2. Local anesthetic (optional) applied over needle sites
3. Arterial needle (16G or 15G) inserted first, bevel up, at 25-45° angle, in the direction of blood flow upstream
4. Venous needle inserted downstream, 5-8 cm from the arterial needle
5. Needles secured with tape/dressing
6. Blood lines connected; clamps released
7. Blood pump started at a slow initial rate (~100-150 mL/min), then gradually increased to target (300-500 mL/min) over several minutes

1. Sterile technique; mask and gloves mandatory
2. Catheter caps removed; lumens aspirated to check blood return
3. Locked anticoagulant solution (heparin lock) aspirated and discarded
4. Blood lines connected to arterial (red) and venous (blue) ports
5. Blood pump started

• Heparin loading dose administered
• Heparin infusion started
• UF rate set per prescription
• Dialysate circuit opened

Phase 7: During the Dialysis Session (Monitoring)

Common Intradialytic Complications and Management

Phase 8: Terminating Dialysis (Takedown)

1. Blood pump slowed to ~100 mL/min
2. Blood lines rinsed with ~200-300 mL normal saline to return all blood to the patient (saline rinse-back)
3. Blood pump stopped
4. Lines clamped
5. Needles removed from AV fistula/graft; firm pressure held for 5-10 minutes until hemostasis achieved
6. For catheter: each lumen flushed with saline, then locked with heparin solution (1000-5000 U/mL per lumen volume); caps replaced with strict sterile technique
7. Access site inspected and dressed

Post-Dialysis Assessment

• Post-dialysis weight recorded and compared to target dry weight
• Blood pressure and heart rate (supine and sitting) - watch for orthostatic hypotension
• Post-dialysis symptoms: fatigue, lightheadedness, dyspnea
• Blood samples drawn for post-dialysis BUN (to calculate Kt/V)
• Patient monitored for 10-15 minutes before discharge from the unit

Phase 9: Assessing Dialysis Adequacy (Kt/V)

K = urea clearance (mL/min) t = dialysis time (min) V = volume of distribution of urea = total body water (liters)

URR (Urea Reduction Ratio) = [(Pre-BUN - Post-BUN) / Pre-BUN] × 100

• Fluid removal during the session (which reduces V)
• Urea generation during treatment
• Post-dialysis urea rebound (the "double-pool effect" - urea rebounds ~30 min after dialysis ends as intracellular urea equilibrates with the blood)

• Single-pool Kt/V ≥ 1.4 per session (minimum 1.2)
• Standard Kt/V ≥ 2.1/week for thrice-weekly dialysis
• For AKI: Kt/V ≥ 3.9/week (KDIGO recommendation) - Brenner and Rector's The Kidney

Phase 10: Machine Disinfection After Session

• Dialyzer (if for reuse program) rinsed, tested for volume/clearance, and chemically disinfected
• Blood tubing discarded as biohazardous waste
• Machine exterior wiped with appropriate disinfectant
• Dialysate pathways disinfected (heat or chemical)
• Reuse of dialyzers is prohibited by law in some countries (e.g., Egypt) and not practiced in others (Saudi Arabia, Libya, Iran) - Brenner and Rector's The Kidney

Summary: Complete HD Session Timeline

BEFORE SESSION
├── Patient assessment (weight, BP, labs, access inspection)
├── Prescription review & adjustment
└── Machine setup, priming, dialysate preparation

INITIATING DIALYSIS
├── Vascular access cannulation (AV needles) or catheter connection
├── Heparin loading dose
└── Blood pump started slow → ramp to target Qb

DURING SESSION (3-4 hours)
├── Continuous machine monitoring (pressures, alarms)
├── Vital signs every 30 min
├── UFR adjusted per fluid removal target
└── Intradialytic complications managed as they arise

TERMINATING DIALYSIS
├── Saline rinse-back of extracorporeal blood
├── Needles/catheter disconnected with sterile technique
├── Hemostasis (needles) or heparin lock (catheter)
└── Post-dialysis weight, BP, symptom check

POST-SESSION
├── Post-dialysis BUN for Kt/V calculation
├── Machine disinfection
└── Patient education and next appointment

Wet Weight in Dialysis

Definition

The Key Weight Concepts in Dialysis

"Dry weight reflects the lowest tolerated post-dialysis weight at which the patient experiences minimal signs and symptoms of either hypovolemia or hypervolemia. According to this definition, the management of dry weight is based on an iterative process of gentle and gradual intensification of ultrafiltration guided by the patient's symptoms." - Comprehensive Clinical Nephrology, 7th ed. (Sinha and Agarwal, 2009)

How Wet Weight is Used

Calculating How Much Fluid to Remove

UF target = Wet weight - Dry weight

• Pulmonary edema
• Hypertension
• Excessive rapid fluid removal (with hypotension, cramping, cardiac stress)

What Drives Fluid Accumulation Between Sessions (Wet Weight Rise)

• Drinking fluids
• Water content of food
• Sodium intake (stimulates thirst and water retention)
• IV fluids or medications received
• Residual urine output (if any)

Clinical Significance of Wet Weight

1. Guides the Ultrafiltration Prescription

UFR = (Wet weight - Dry weight) ÷ Session time

2. Assesses Volume Status Trend

• Poor dietary fluid/sodium restriction
• Incorrect (too high) dry weight target
• Volume overload - a leading cause of hypertension in dialysis patients

3. Reflects Success of Previous Session

Dry Weight Assessment: Not as Simple as It Looks

• Muscle mass or fat mass can change (illness, nutrition changes)
• A patient who appears clinically euvolemic may actually be covertly volume-overloaded

"Among hypertensive dialysis patients, the management of dry weight should not be based on the presence or absence of clinically overt hypervolemia. In such patients, volume excess is more often covert. The discriminatory power of physical examination in ruling in or out volume overload is low." - Comprehensive Clinical Nephrology, 7th ed.

Importantly: High IDWG does not always equal volume overload, and low IDWG does not rule it out. Studies showed that dialysis patients with low IDWG were often volume overloaded. - Comprehensive Clinical Nephrology, 7th ed.

Clinical Signs of Volume Excess (suggesting dry weight needs to be lowered):

• Shortness of breath / signs of congestive heart failure
• Uncontrolled hypertension confirmed on home BP monitoring
• Use of multiple antihypertensive medications
• Low IDWG (patient drinking little but still hypertensive - suggests chronic volume excess, not acute gain)
• Persistent BP elevation during dialysis (intradialytic hypertension)

Objective Tools to Assess Dry Weight

Clinical Example

Summary

• Wet weight = pre-dialysis weight = patient's weight arriving with accumulated excess fluid
• Dry weight = target weight = the euvolemic post-dialysis weight goal
• The difference between the two = fluid to be removed by ultrafiltration
• Accurate dry weight assessment is one of the most important and challenging aspects of dialysis management
• Subclinical volume overload (low wet weight gain but chronically elevated dry weight) is a major, underappreciated cause of dialysis hypertension