Volume, the Heart, and the Kidney

The contract between this chapter and the reader.

1. 1. Assess volume status using clinical signs and objective tools.
2. 2. Explain how sodium and water are removed in PD, and how sieving and icodextrin affect sodium removal.
3. 3. Manage volume overload through the correct hierarchy of levers.
4. 4. Relate chronic volume overload to hypertension, left-ventricular hypertrophy, and cardiovascular mortality.
5. 5. Manage blood pressure starting from euvolemia.
6. 6. Explain why residual kidney function is the strongest modifiable predictor of survival.
7. 7. Apply strategies to preserve residual kidney function.
8. 8. Recognise the interdependence of volume, cardiovascular risk, and residual function.
9. 9. Avoid the harmful shortcuts — hypertonic glucose, over-ultrafiltration, and nephrotoxins.

A sixty-second reading. Each bullet stands alone.

• Volume overload is common in PD and a leading driver of hypertension, left-ventricular hypertrophy, and death.
• Assess volume clinically — blood pressure, oedema, JVP, weight — and, where available, with bioimpedance and lung ultrasound.
• Total fluid and sodium removal is peritoneal ultrafiltration plus residual urine.
• Sodium sieving means early glucose ultrafiltration removes relatively little sodium; icodextrin removes more sodium per litre.
• The first lever for overload is dietary salt and water restriction.
• Increase ultrafiltration with icodextrin and a dwell matched to transport, not by escalating hypertonic glucose.
• Loop diuretics help while residual urine persists.
• Chronic overload causes left-ventricular hypertrophy, which partly reverses with euvolemia.
• Manage blood pressure from euvolemia first, then add antihypertensives; RAAS blockade also protects the kidney.
• Residual kidney function is the strongest modifiable predictor of survival in PD.
• It supplies clearance, fluid and sodium removal, and easier volume and blood-pressure control.
• Preserve it: avoid nephrotoxins, use RAAS blockade, and avoid the hypovolaemia of over-ultrafiltration.
• Volume, cardiovascular risk, and residual function are one interdependent system, and euvolemia is the central goal.
• The harmful shortcuts — hypertonic glucose, over-ultrafiltration, nephrotoxins — fix one problem by worsening another.

The medical core. An expert should agree volume, cardiovascular risk, and residual function are fully covered here.

Why it matters at the bedside

Three things kill or save PD patients together, not separately: how much fluid they carry, how their heart copes, and how much their own kidneys still do. Treat them as one system and the priorities line up; treat them in isolation and a quick fix for one quietly damages another.

The volume–heart–kidney triangle

• Residual kidney function helps remove fluid and sodium, which keeps volume down, which protects the heart. Lose residual function and all three worsen at once: harder volume control, higher blood pressure, more cardiac strain.
• The corollary is that euvolemia is the central goal, residual function is the resource that makes it achievable, and the cardiovascular system is the organ that pays when either fails.

Assessing volume status

• Examination — blood pressure, oedema, jugular venous pressure, weight — catches gross overload but misses the hidden kind. Daily ultrafiltration and residual urine track removal over time.
• Where available, bioimpedance gives an objective fluid measure and lung ultrasound reveals pulmonary congestion, both useful when the examination looks deceptively normal.

How sodium and water are removed

• Fluid and sodium leave by two routes: peritoneal ultrafiltration, which carries sodium convectively, and residual urine. Early in a glucose dwell, aquaporin-mediated free-water transport removes water with little sodium — sodium sieving — so good ultrafiltration volume does not guarantee good sodium removal.
• Icodextrin, working by colloid osmosis across the long dwell, removes more sodium per litre and is useful when sodium balance, not just volume, is the problem.

Managing volume overload — the hierarchy

• Start with dietary salt and water restriction — the cornerstone and the most under-used lever. Then optimise ultrafiltration with icodextrin and a dwell matched to transport, and use loop diuretics while residual urine persists.
• Only then adjust glucose strength, to the minimum needed, and reassess the target weight gradually. Reaching for hypertonic glucose first trades fluid control for metabolic and membrane harm.

Volume and the heart

• Chronic overload raises blood pressure and, with pressure, drives left-ventricular hypertrophy — a powerful predictor of cardiovascular death. Much of that hypertrophy regresses when the patient is brought to true euvolemia, which is why volume control is cardiac treatment.

Blood pressure — euvolemia first

• Most hypertension in PD is volume-dependent, so the first move is to achieve euvolemia through salt, water, and ultrafiltration. Antihypertensives are added on top, with renin-angiotensin blockade preferred because it also helps preserve the kidney.

Residual kidney function — the precious resource

• Residual function is the strongest modifiable predictor of survival in PD. Beyond small-solute clearance, it removes fluid and sodium, clears middle molecules and phosphate, and steadies blood pressure and volume — advantages that peritoneal clearance only partly replaces.

Preserving residual function

• Protect it deliberately: avoid nephrotoxins — non-steroidal anti-inflammatories, aminoglycosides, iodinated contrast; use renin-angiotensin blockade; treat infections promptly; and avoid the hypovolaemia of over-ultrafiltration, which starves the kidney of perfusion. Incremental PD (Chapters 2 and 3) both leverages and may help preserve it.

The harmful shortcuts

• Three tempting fixes each trade one problem for another: hypertonic glucose to control blood pressure adds metabolic and membrane cost; aggressive ultrafiltration to hit a low weight injures residual function; and nephrotoxic drugs for comfort hasten the loss of the very kidney function that makes the patient easier to manage.

Evidence base

• The survival value of residual function and the harm of chronic overload are consistent observational findings; renin-angiotensin blockade has randomised support for preserving residual function; and icodextrin has randomised support for better fluid and sodium removal. Bioimpedance-guided volume control has promising but mixed outcome data.

Five fully-built tables.

Table A — Assessing volume status

Table B — Sodium and water removal

Table C — Volume-overload management hierarchy

Table D — Preserving residual kidney function

Table E — Harmful shortcuts

Visualise & Map

Causal chains, each ending in a named action.

Chain 1 — Overload and the heart

Chronic volume overload → hypertension and left-ventricular hypertrophy → cardiovascular mortality → ACTION: make euvolemia the central goal.

Chain 2 — Residual function as a buffer

Residual kidney function → removes fluid, sodium, and toxins → easier volume and blood-pressure control → ACTION: preserve it deliberately.

Chain 3 — The over-ultrafiltration trap

Aggressive ultrafiltration → hypovolaemia → renal hypoperfusion → faster loss of residual function → ACTION: ultrafiltrate gently and individually.

Chain 4 — The glucose shortcut

Hypertonic glucose to control blood pressure → caloric load and membrane injury → long-term harm → ACTION: control volume with salt/water and icodextrin instead.

Chain 5 — Sodium versus volume

Sodium sieving → early glucose UF removes little sodium → sodium balance lags volume → ACTION: use icodextrin and salt restriction when sodium is the problem.

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.

Every mechanism from Level 3 earns a bedside consequence and an action.

Exhaustive. Every 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

Copy-paste chart notes that map to the real decisions in this chapter.

Template 1 — Volume and blood-pressure review

• Volume assessment: BP ___; oedema ___; weight ___; daily UF ___; residual urine ___.
• Objective tools: bioimpedance ___; lung ultrasound ___.
• Verdict: euvolemic / overloaded / depleted (note any hidden overload).
• Plan: salt/water restriction; UF optimisation (icodextrin / dwell); diuretics; antihypertensives.
• Target weight and how it will be reached (gradually).

Template 2 — Residual kidney function preservation

• Residual urine / residual clearance: ___; trend ___.
• Nephrotoxins reviewed and stopped: NSAIDs / aminoglycosides / contrast ___.
• RAAS blockade: in place? yes/no.
• Over-ultrafiltration / hypovolaemia checked: yes/no.
• Next reassessment of adequacy and volume: ___.

Pre-rounds compression. 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. Hypertonic glucose makes today's blood pressure look good and tomorrow's membrane worse; how do you keep the visible short-term win from crowding out the invisible long-term cost?
2. 2. When the examination and the objective tools disagree about volume, what tips you toward trusting one over the other?
3. 3. Residual function is the strongest survival lever yet only partly in your control; how should that shape how aggressively you ultrafiltrate?
4. 4. Where is the line between a target weight that controls volume and one so low it injures the kidney — and how would you know you had crossed it?
5. 5. Salt restriction is the cheapest and most effective lever and the least used; what makes it so easy to skip, and how would you change that on your unit?

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