Hemodialysis (HD) is a renal replacement therapy (RRT) that removes waste products, excess fluids, and toxins from the blood in patients with kidney failure (usually end-stage renal disease - ESRD). It mimics the filtration function of healthy kidneys.
Key Objectives:
- Correct fluid and electrolyte imbalances.
- Remove nitrogenous waste products (e.g., urea, creatinine).
- Manage acid-base disorders.
- Control blood pressure in volume-overloaded states.
Clinical Pearl: Hemodialysis is not a cure but a lifesaving supportive therapy for patients with ESRD or acute kidney injury (AKI) when conservative treatment fails.
Indications for Hemodialysis
Hemodialysis is indicated in both acute and chronic kidney failure. The following acronym "AEIOU" is useful for remembering emergency dialysis indications:
"AEIOU" Indications for Emergent Dialysis:
| Acronym | Meaning | Examples |
|---|---|---|
| A | Acidosis (severe, refractory) | pH < 7.1 despite treatment |
| E | Electrolyte imbalance (esp. hyperkalemia) | K⁺ > 6.5 mmol/L with ECG changes |
| I | Intoxications | Lithium, methanol, ethylene glycol |
| O | Overload (volume overload unresponsive to diuretics) | Pulmonary edema |
| U | Uremia | Encephalopathy, pericarditis, bleeding |
Chronic Indications:
- Glomerular filtration rate (GFR) < 10 mL/min/1.73 m²
- Symptoms of uremia
- Severe fluid overload
- Intractable hypertension
The Hemodialysis Machine
The hemodialysis machine functions as an artificial kidney. It pumps the patient’s blood through a dialyzer where diffusion, ultrafiltration, and osmosis occur to purify the blood.
Major Components:
| Component | Function |
|---|---|
| Dialyzer | The "artificial kidney" with semi-permeable membrane |
| Blood pump | Moves blood from the patient to the dialyzer |
| Dialysate pump | Delivers dialysate to the dialyzer |
| Heparin pump | Administers anticoagulant to prevent clotting |
| Monitors | Track blood flow, pressure, temperature, air bubbles, and safety |
| Air detector/clamp | Detects air embolism risk and stops flow |
Parts of the Dialysis Machine & Circuit
1. Dialyzer (Artificial Kidney)
- Contains thousands of hollow fibers with semi-permeable membranes.
- Blood flows inside fibers; dialysate flows outside → waste and excess solutes move across the membrane.
2. Dialysate
- A solution containing electrolytes and bicarbonate.
- Does not contain urea or creatinine, promoting diffusion from blood into dialysate.
- Adjusted to meet patient-specific needs (e.g., potassium concentration).
3. Tubing System
- Arterial line: Carries blood from the patient to the dialyzer.
- Venous line: Returns clean blood to the patient.
4. Blood Pump
- Ensures continuous flow (usually 300–500 mL/min) through the dialyzer.
5. Ultrafiltration System
- Controls fluid removal via transmembrane pressure (TMP).
Vascular Access for Hemodialysis
Effective dialysis requires high blood flow (≥300 mL/min). Access is typically through:
Arteriovenous (AV) Fistula
- Preferred access: connects a vein to an artery (e.g., radial-cephalic).
- Matures over 6–12 weeks.
- Long-term use with low complication rate.
Clinical Tip: Always assess the "thrill and bruit"—absence may suggest thrombosis.
Arteriovenous (AV) Graft
- Synthetic tube connects artery and vein.
- Used if veins are unsuitable.
- Higher risk of infection and thrombosis than AV fistula.
Central Venous Catheter (CVC)
- Temporary access (e.g., internal jugular, femoral vein).
- Used in emergency or acute dialysis.
- High risk of infection, stenosis, and thrombosis.
Hemodialysis Procedure Overview
- Pre-Dialysis
- Assess vitals, fluid status, access site.
- Check labs (especially K⁺, BUN, creatinine, Hb).
- Weigh the patient.
- During Dialysis
- Monitor vitals, machine alarms, blood flow rate.
- Watch for complications: hypotension, cramping, nausea, clotting.
- Post-Dialysis
- Reassess weight and vitals.
- Check access site.
- Monitor for signs of bleeding or complications.
Complications of Hemodialysis
| Complication | Description / Features |
|---|---|
| Hypotension | Most common; due to fluid removal |
| Cramps | Electrolyte or fluid shifts |
| Dialysis Disequilibrium Syndrome | Cerebral edema due to rapid urea removal |
| Infection (Access-related) | Especially in CVCs |
| Anemia | Due to reduced EPO and blood loss |
| Amyloidosis | β2-microglobulin accumulation in long-term dialysis |
Nursing and Clinical Considerations
- Daily Assessments: Monitor weight, fluid status, and access patency.
- Education: Teach patients to avoid compression or venipuncture on fistula arm.
- Asepsis: Critical when handling catheters.
- Nutrition: Limit sodium, potassium, phosphorus; adequate protein intake.
- Medication Timing: Some meds (e.g., antihypertensives) may be held before dialysis.
