Intro & Types of Therapy
How dialysis works, and an overview of the kidney replacement therapy (KRT) modalities. Tap any tile to open the details.
Dialysis substitutes for two core functions of the failing kidney: clearing accumulated solutes (uraemic toxins, potassium, urea) and removing excess fluid. It does not replace the kidney's hormonal roles, so anaemia and mineral-bone management continue alongside it.
Solute clearance and fluid removal are separate levers the prescription controls independently — clearance through the dialyser and concentration gradients, fluid removal through ultrafiltration. Much of this app is about tuning those two levers safely.
Solutes move down a concentration gradient; smaller molecules move faster, so it clears small solutes (urea, K⁺) well but larger ones poorly. The dominant mechanism in conventional HD.
Solutes are dragged through pores by bulk fluid flow; removal is largely size-independent, so middle-molecular-weight solutes clear far better than by diffusion alone.
HD relies mainly on diffusion; haemofiltration on convection; haemodiafiltration (HDF) combines both. Middle-molecule (β2-microglobulin) clearance is roughly 80–90 mL/min with convective therapy versus ~50 mL/min with high-flux HD.
Blood is pumped from the vascular access through the dialyser and back. Dialysate — a precisely formulated electrolyte solution — flows on the other side of the membrane, usually counter-current to the blood, maximising the gradients that drive diffusion.
Drawn via access (fistula, graft, or catheter) at a set blood flow rate; anticoagulation prevents clotting in the circuit.
Composition (Na, K, Ca, HCO₃) is set in the prescription; counter-current flow sustains the gradient along the membrane.
Fluid removal (ultrafiltration) is driven by a pressure difference across the membrane, controlled independently of solute clearance. See the Prescription and Vascular Access modules.
Where there are no contraindications, modality choice is guided by shared decision-making with an emphasis on patient preference. When someone is a candidate for several options, education about each helps them choose what fits their life and goals — revisited as circumstances change.
The choice is shaped by availability, the home situation, tolerance of rapid fluid shifts, access type, and clinician experience. The first branch point is usually home versus in-centre; planning ahead allows timely access creation and early transplant evaluation.
Conventional in-centre HD is the most common modality — typically thrice-weekly, around four hours per session. It removes solutes mainly by diffusion across a high-flux membrane, with fluid removed by ultrafiltration. Most of Dialysis Pro is built around prescribing and monitoring this modality.
Its trade-off: fluid and solutes are removed over relatively short sessions, which can mean larger interdialytic gains and more abrupt intradialytic shifts than slower or more frequent schedules.
HDF adds substantial convective clearance to standard diffusive HD, improving removal of middle-molecular-weight solutes. For chronic therapy, most centres use online HDF, where the machine generates the replacement fluid. Postdilution — infusing downstream of the dialyser — is the preferred, most effective mode.
The dose has two targets: the same Kt/V as HD (1.2–1.4) and a minimum effective convection volume (≥23 L/session postdilution), the parameter tied to the survival benefit in high-volume HDF trials such as CONVINCE. It needs reliable high blood flow and is less suitable where bleeding risk or blood viscosity is high.
3–5 nights/week while asleep, ~6–8 h/session (home or in-centre). Longer time → gentler fluid removal, better solute clearance, often better BP control and fewer dietary limits.
Usually 5–7 days/week, ~1.5–2.5 h/session, most often at home. More frequent sessions reduce per-session fluid removal and intradialytic stress.
Both trade convenience for physiology: more frequent or longer dialysis generally allows slower fluid removal and tends to reduce ultrafiltration-related hypotension, with the survival evidence still mixed.
Home modalities offer a more flexible schedule, easier travel, and fewer limits on frequency and time — which can mean better fluid and solute control and less intradialytic hypotension. They require a suitable home environment, training, and the ability to reach the renal team.
The patient (often with a care partner) runs HD at home. Main barrier is lack of suitable vascular access; some programmes accept catheters with low complication rates.
Uses the peritoneal membrane and a catheter, dialysate dwelling in the abdomen — CAPD (manual day exchanges) or APD (overnight cycler). Only absolute contraindication: a non-functional peritoneal membrane.
PD often suits frequent travellers or those reluctant to cannulate; home HD may suit those who swim or bathe regularly. PD can be favoured in symptomatic pulmonary hypertension, where an AV access might worsen flow.
| Modality | Setting | Schedule | Notable point |
|---|---|---|---|
| Conventional HD | In-centre | 3×/wk, ~4 h | The standard; mainly diffusive |
| HDF | In-centre | 3×/wk, ~4 h | Adds convection; ≥23 L target |
| Nocturnal HD | Home/centre | 3–5 nights, 6–8 h | Gentler; BP/diet latitude |
| Short daily HD | Mostly home | 5–7 days, 1.5–2.5 h | Frequent; less per-session stress |
| Peritoneal (PD) | Home | Daily (CAPD/APD) | No vascular access; continuous |
No non-transplant modality is conclusively superior overall. Conventional HD and PD have broadly similar outcomes; home/nocturnal schedules allow slower fluid removal; high-volume postdilution HDF shows a survival signal in some trials. The right choice is individual.
The treatment of choice for most people with kidney failure, reducing mortality and improving quality of life versus maintenance dialysis. Most patients with advanced CKD should be evaluated, in parallel with dialysis preparation.
Active medical management without dialysis — focused on symptoms, quality of life, and individual goals. Worth discussing with most people with advanced CKD, especially older patients or those with significant comorbidity.