What is dialysis?

What is Dialysis

Dialysis is a life-sustaining medical treatment that artificially removes accumulated metabolic waste products, excess fluid, and rebalances electrolytes in patients who have total or near-total loss of kidney function. 1

Core Mechanism

Dialysis works through two primary processes 1, 2:

• Diffusion dialysis: Solutes move from blood into a physiological salt solution (dialysate) across a semipermeable membrane, driven by concentration gradients
• Ultrafiltration: Excess body water is removed through pressure gradients across the dialyzer membrane 3, 2

The dialysate composition resembles plasma water, with electrolytes adjusted to compensate for abnormalities of end-stage renal disease 2.

Primary Dialysis Modalities

Hemodialysis (HD)

• Blood is circulated outside the body through a dialyzer containing a semipermeable membrane 1
• Typically performed 3 times weekly for 3-4 hours per session 1
• Requires vascular access via arteriovenous fistula (preferred), arteriovenous graft, or central venous catheter 1
• Can be performed in-center or at home 1

Peritoneal Dialysis (PD)

• Uses the patient's peritoneal membrane as the dialyzing surface 1
• Dialysate is instilled into the peritoneal cavity through a permanent catheter 1
• Can be performed as continuous ambulatory peritoneal dialysis (CAPD) or automated peritoneal dialysis (APD) 1
• Generally less efficient than hemodialysis for solute and fluid removal 1

Continuous Renal Replacement Therapies (CRRT)

• Used primarily in critically ill, hemodynamically unstable patients 1
• Includes continuous hemofiltration, hemodialysis, and hemodiafiltration 1
• Provides better hemodynamic stability and fluid balance control compared to intermittent hemodialysis 1

Clinical Context and Indications

Dialysis is indicated when kidney failure causes 1:

• Persistent hyperkalemia unresponsive to medical management
• Severe metabolic acidosis
• Volume overload unresponsive to diuretic therapy
• Overt uremic symptoms including pericarditis, encephalopathy, nausea, and fatigue 3
• Severe progressive hyperphosphatemia (>6 mg/dL) or symptomatic hypocalcemia 1

Timing of Initiation

The decision to initiate dialysis should be based on clinical symptoms and signs rather than estimated glomerular filtration rate (eGFR) alone. 1, 3

• A randomized trial showed no mortality benefit to starting dialysis at higher eGFR (10-14 mL/min/1.73 m²) versus lower eGFR (5-7 mL/min/1.73 m²) 3
• Initiation requires shared decision-making between patient and physician, considering uremic symptoms, nutritional status, and ability to manage metabolic abnormalities 1

Outcomes and Survival

• More than 540,000 patients in the US receive maintenance dialysis 3
• Five-year survival rate is approximately 40% after dialysis initiation 3
• First-year mortality ranges from 17-20% depending on region and risk factors 4
• Observational data show no significant mortality difference between hemodialysis and peritoneal dialysis 3

Common Pitfalls

Do not initiate dialysis based solely on eGFR thresholds without uremic symptoms present 5, as this leads to earlier treatment without survival benefit and increased resource utilization 1.

Recognize that dialysis is not appropriate for all patients 1—older patients with multiple comorbidities, frailty, or limited life expectancy may benefit more from comprehensive conservative care without dialysis 1.

Alternative to Dialysis

Comprehensive conservative care is a valid treatment option for advanced chronic kidney disease that includes active symptom management, shared decision-making, advance care planning, and psychosocial support—but does not include dialysis 1. This approach may be appropriate for patients unlikely to benefit from dialysis in terms of survival or quality of life 1.