Dialysis Adequacy

The contract between this chapter and the reader.

1. 1. Define dialysis adequacy as more than a single clearance number.
2. 2. Calculate and interpret total weekly Kt/V urea as peritoneal plus residual.
3. 3. Measure residual kidney function and explain why it weighs so heavily.
4. 4. Assess volume status and ultrafiltration as core adequacy domains.
5. 5. Interpret a peritoneal equilibration test to grade membrane transport.
6. 6. Diagnose ultrafiltration failure using the ultrafiltration-capacity test.
7. 7. Apply guideline clearance targets without over-relying on them.
8. 8. Construct an adequacy-assessment schedule and act on its results.

A sixty-second reading. Each bullet stands alone.

• Adequacy is euvolemia, solute clearance, nutrition, and symptom control together — not a single number.
• The guideline floor is a total weekly Kt/V urea of at least 1.7, combining peritoneal and residual clearance.
• Randomised evidence shows that pushing peritoneal small-solute clearance above target does not improve survival — meet the floor, do not chase the number.
• Residual kidney function predicts survival and supplies clearance and ultrafiltration; it weighs more than peritoneal clearance.
• Measure residual function from a timed urine collection as the average of urea and creatinine clearance.
• Euvolemia is a core adequacy domain — judge it from blood pressure, oedema, weight, daily ultrafiltration, and urine.
• The peritoneal equilibration test grades transport from the 4-hour dialysate-to-plasma creatinine ratio.
• The ultrafiltration-capacity test detects ultrafiltration failure when net ultrafiltration is below 400 mL after a 4-hour hypertonic dwell.
• Anuric patients lose the residual buffer, so peritoneal clearance and ultrafiltration must carry the whole load.
• Nutrition matters: appetite, weight trend, and protein markers are part of the adequacy picture.
• Assess the membrane about six weeks after starting, then periodically; reassess clearance, residual function, and volume at each review.
• A normal Kt/V in an overloaded or symptomatic patient is not adequate dialysis.
• When a patient feels unwell, exclude anaemia, acidosis, and other causes before blaming the dialysis dose.

The medical core. An expert should agree adequacy assessment is fully covered here.

Why it matters at the bedside

Adequacy is the question every PD review must answer: is this therapy keeping the patient well? It is tempting to reduce that to one clearance number, but the number is a floor, not the goal. Read all of adequacy — fluid, clearance, nutrition, and how the patient feels — and the prescription decisions become obvious.

What adequacy actually means

• Adequate dialysis is clinical: a euvolemic, well-nourished patient free of uraemic symptoms whose clearance meets a minimum. Each domain can fail independently, so each is assessed in its own right.
• Numerical targets exist to stop under-dosing, not to be maximised. A patient can sit above every target and still be inadequately dialysed if overloaded or wasting.

Solute clearance and Kt/V

• Small-solute clearance is summarised as the weekly Kt/V for urea, reported as the sum of peritoneal clearance (from a 24-hour dialysate collection) and residual renal clearance.
• The guideline floor is a total weekly Kt/V urea of at least 1.7. Below it, increase the prescription; at or above it, look to the clinical domains rather than to a higher number.
• Randomised trials settled a long debate: raising peritoneal small-solute clearance above target did not improve survival. The lesson is to meet the floor and protect residual function, not to escalate dose for its own sake.

Residual kidney function

• Residual function is measured from a timed urine collection, taking the average of the urea and creatinine clearances. It contributes directly to total clearance and to fluid removal.
• It also predicts survival more strongly than peritoneal clearance does, which is why its decline — not a fixed prescription — drives reassessment and dose increases over time.

Volume and ultrafiltration

• Fluid control is at least as important as solute clearance. Assess it clinically — blood pressure, oedema, weight — alongside daily ultrafiltration and residual urine.
• Persistent overload is a form of inadequacy even when clearance numbers are met, and points back to ultrafiltration (Chapter 1) and the prescription (Chapter 2).

Membrane function assessment

• The peritoneal equilibration test grades transport from the 4-hour dialysate-to-plasma creatinine ratio and is repeated periodically to track the membrane.
• The ultrafiltration-capacity test measures net ultrafiltration after a standardized 4-hour hypertonic dwell; below 400 mL defines ultrafiltration failure, and the sodium-sieving dip then localises the mechanism.

Nutrition and the whole picture

• Appetite, weight trend, and protein markers signal nutritional adequacy; protein-energy wasting predicts poor outcomes and is part of the assessment, not an afterthought.

What else explains feeling unwell

• Before labelling a symptomatic patient underdialysed, exclude anaemia, metabolic acidosis, depression, and intercurrent illness — each can mimic inadequate dialysis and each has its own fix.

How and when to measure

• Collect a 24-hour dialysate and a timed urine sample for clearance, and run a PET for the membrane. Assess membrane function about six weeks after starting, then periodically or whenever the clinical picture changes.

Evidence base

• The clearance floor and the futility of exceeding it rest on randomised trials of small-solute targets. The weight given to residual function rests on consistent cohort data linking it to survival. Volume control and nutrition complete an evidence base that is clinical as much as numerical.

Five fully-built tables.

Table A — Domains of adequacy

Table B — Clearance measures

Table C — Transport categories (PET)

Table D — Membrane function tests

Table E — Assessment schedule

Visualise & Map

Numbered rules. These numbers are the cross-reference handle for the cases and flowcharts.

Clinical Reasoning

Four cases. Each stops you at a decision before it answers it.

Exhaustive. Every threshold and rule in the chapter is here.

Safety & Evidence

Panel A — Red flags

Panel B — NEVER DO

Anti-patterns clinicians fall into. Each becomes a Level 22 distractor.

The grade reflects strength of evidence, not importance.

Patient Decisions

Outcomes as natural frequencies. Figures are representative; the direction of effect is given where precise numbers are uncertain.

Apply & Test

Included by author decision: an adequacy review is a real chart note.

Template 1 — Adequacy review note

• Volume: BP ___; oedema ___; weight ___; daily UF ___; residual urine ___ — euvolemic? yes/no.
• Clearance: peritoneal Kt/V ___; residual Kt/V ___; total ___ (floor 1.7 met? yes/no).
• Nutrition: appetite ___; weight trend ___; wasting? yes/no.
• Symptoms / wellbeing: ___.
• Membrane (if tested): D/P creatinine ___ (category ___); UF-capacity ___ mL.
• Assessment: adequate / inadequate (domain ___).
• Action and next review: ___.

Template 2 — Membrane function (PET) interpretation note

• Indication: baseline / scheduled / clinical change.
• 4-hour D/P creatinine ___ → transport category ___.
• UF-capacity test: net UF ___ mL (UF failure if < 400).
• Sodium-sieving dip present? yes/no — implication ___.
• Prescription implication (Chapter 2): ___.

Pre-rounds compression. Numbers and rules only.

Active recall. At least one card per objective.

Micro-teaching for rounds. Two scenarios, five steps each.

Metacognition anchored to this chapter's tensions. No answers provided.

1. 1. Why is a single, defensible number so much more comfortable to act on than a four-domain clinical judgement — and how does that comfort mislead you?
2. 2. Residual function drives outcomes but lies largely outside your control; how should that shape what you do measure and change?
3. 3. When a patient feels unwell with a normal Kt/V, what stops you from reflexively adding dialysis dose?
4. 4. How would you explain to a trainee that meeting the target and stopping is the right answer, not a lack of ambition?
5. 5. What would tell you that your assessment schedule is too sparse for a patient whose kidney is fading?

Eight items, each anchored in this chapter. At least one per objective.