Applied Nephrology Master Series

Chapter 9 CAPD, APD and Prescription Optimization

CHAPTER MISSION Turn CAPD and APD from modality labels into adjustable physiologic systems: choose the delivery architecture that fits the patient, match dwell time and fill volume to membrane transport and residual kidney function, correct specific clearance or volume problems with the smallest effective prescription change, and verify what was actually delivered rather than what was programmed.

Figure 9.1 - The PD prescription is a control panel.

CAPD and APD use the same fundamental levers. The art of prescribing is choosing which lever to change for the dominant clinical problem while preserving residual kidney function, sodium-volume control, tolerability and life participation.

MASTER PRINCIPLE Do not optimize the machine; optimize the patient. A technically elegant prescription that disrupts sleep, creates recurrent drain pain, increases glucose exposure or is not actually completed is not an optimized prescription.

0. One-page chapter map

Table 9.1 - The eight decisions that govern PD prescription optimization.

Decision	Core question	Bedside output
1. Goal	What problem are we solving now?	Named target: volume, sodium, solute, phosphate, symptoms or burden
2. Delivery	What treatment is actually being delivered?	Verified exchange/cycler record and adherence
3. Membrane	How quickly does this membrane transport solute and dissipate glucose?	PET-informed dwell strategy
4. Kidney	How much residual kidney support remains?	Renal contribution and escalation trigger
5. Architecture	CAPD, APD or combined pattern?	Delivery mode matched to physiology and lifestyle
6. Lever	Which one change is most likely to correct the mechanism?	Dwell/fill/cycle/day dwell/osmotic-agent change
7. Trade-off	What might improve while something else worsens?	Explicit sodium, phosphate, glucose, sleep and pressure consequences
8. Verify	Did the patient improve and was the prescription sustainable?	Clinical + measured + patient-reported reassessment

Learning outcomes

Compare CAPD and APD without assuming that one modality is intrinsically superior.
Use transport phenotype, residual kidney function and the clinical target to choose dwell architecture.
Predict how fill volume, dwell time, number of exchanges, total dialysate volume and osmotic agent alter solute and fluid transport.
Optimize APD by distinguishing programmed treatment from delivered treatment, including lost dwell time and drain interruptions.
Recognize when short APD cycles protect ultrafiltration but compromise sodium or phosphate removal.
Use icodextrin deliberately for the long dwell rather than as a generic marker of an advanced prescription.
Use tidal PD selectively for drain intolerance or recurrent drain-related interruptions after correctable causes are excluded.
Reassess every prescription change for clinical benefit, glucose burden, sleep, pain, adherence and treatment burden.

EVIDENCE POSTURE ISPD 2020 goal-directed recommendations and the 2021 membrane-function recommendations anchor the physiologic approach. The 2024 Cochrane update found low- to very-low-certainty randomized evidence insufficient to establish overall superiority of APD or CAPD. Icodextrin has stronger randomized evidence for improving long-dwell ultrafiltration. Evidence for adapted/tidal APD, sodium/phosphate optimization and remote-monitoring-enabled delivery is supportive but more context dependent. [1–10]

1. CAPD and APD are architectures, not competing definitions of adequacy

Figure 9.2 - CAPD and APD are delivery architectures.

Both modalities can deliver high-quality PD when the prescription fits the membrane, residual kidney function, clinical goals and patient priorities. The randomized comparative evidence does not support a universal modality hierarchy.

CAPD delivers exchanges manually across the waking day, usually creating longer and more continuous dwells. APD uses a cycler to deliver repeated exchanges, commonly overnight, with or without one or more daytime dwells. These time patterns change the balance among ultrafiltration, small-solute clearance, sodium removal, phosphate removal and treatment burden. The 2024 Cochrane update included only two small randomized trials (131 participants) and judged the evidence very uncertain for mortality, hospitalization, peritonitis, residual kidney function, quality of life, volume status and adequacy. [3]

Table 9.2 - CAPD versus APD: what truly differs.

Dimension	CAPD tendency	APD tendency
Exchange timing	Longer manual daytime dwells	Shorter repeated nocturnal dwells
Lifestyle burden	Interrupts daytime activity	Shifts treatment to sleep period
Machine dependence	None during exchanges	Cycler, power, supplies and alarms
Fast transporter UF	Long glucose dwell may lose UF	Shorter glucose dwells can protect UF
Sodium removal	Often greater per day	Can be lower when short dwells dominate
Phosphate removal	Long contact time may help	Can be lower with very short cycles, especially in slower transporters
Drain discomfort	Manual drain pattern	Repeated cycler drains may provoke pain/alarms
Data visibility	Manual logs/weights	Detailed cycle-level data possible on modern platforms

DO NOT AUTOMATE A fast transporter is not automatically an APD patient, and a slow transporter is not automatically a CAPD patient. Transport physiology narrows the prescription options; patient priorities and actual delivery complete the decision.

2. Start optimization by naming the limiting outcome

“Increase dialysis” is not a diagnosis. A prescription can be adequate for urea and inadequate for sodium, adequate for volume and inadequate for phosphate, or biochemically satisfactory but intolerable. Each problem requires a different lever.

Table 9.3 - Clinical problem -> primary prescription question.

Problem	Ask first	Typical lever domain
Volume overload	Intake, urine, net UF or sodium-removal mismatch?	Osmotic agent, dwell pattern, sodium strategy, day dwell
Low small-solute clearance	Collection/delivery valid? RKF changed?	Total effective exchange volume/contact time
Hyperphosphatemia	Diet/binders/RKF vs inadequate long contact time?	Longer dwell or architecture with greater contact time
Poor long-dwell UF	Fast PSTR or intrinsic low UF capacity?	Icodextrin, shorter glucose dwell, membrane pathway
High glucose burden	Is hypertonicity compensating for an uncorrected mechanism?	Icodextrin, sodium strategy, optimized dwell, RKF protection
Sleep disruption	Alarms, drain pain, long therapy or setup burden?	Mechanical correction, cycle redesign, tidal strategy, CAPD
Daytime burden	Manual exchange frequency incompatible with life?	APD or assisted exchange strategy
Recurrent noncompletion	Complexity, dexterity, cognition or device problem?	Simplify/assist rather than merely intensify

3. The core prescription levers

Table 9.4 - Prescription lever -> physiologic effect -> trade-off.

Lever	What it changes	Trade-off to anticipate
Fill volume	Membrane recruitment and solute mass transfer	Higher intraperitoneal pressure, reflux, leaks, discomfort
Dwell time	Diffusion time and osmotic-gradient decay	Longer can improve phosphate/creatinine but reduce glucose UF in fast PSTR
Exchange number	Fresh-gradient frequency and total dialysate turnover	More connections/CAPD burden or shorter APD dwells
Total therapy time	Total contact time	Sleep/time burden
Glucose concentration	Crystalloid osmotic force	Systemic/peritoneal glucose exposure
Icodextrin long dwell	Sustained colloid osmotic UF	One long dwell; product-specific safety considerations
Day dwell / last fill	Adds contact time and daytime removal	Abdominal fullness; long-dwell UF must be appropriate
Tidal fraction	Avoids complete repetitive drains	Residual volume, clearance implications and more complex programming

Figure 9.3 - Dwell time creates competing gains and losses.

Optimization is target-specific: shorter glucose dwells can protect UF in fast transporters, whereas longer contact can improve slower solute and phosphate removal. There is no universally ideal dwell time.

4. Fill volume: recruit membrane without prescribing pressure

Larger intraperitoneal volumes can increase effective peritoneal surface recruitment and solute mass transfer, but the pressure response varies greatly among patients. Historical physiologic studies show that intraperitoneal pressure rises as fill volume increases and is related imperfectly to body size. The clinical prescription should therefore be individualized to tolerance, leak/hernia risk, respiratory mechanics and effective clearance rather than using a single adult fill-volume number as a universal target. [11,12]

Table 9.5 - Fill-volume reasoning.

Finding	Interpretation	Direction
Low volume, comfortable, poor clearance	Potential under-recruitment / insufficient exchange mass	Increase carefully if anatomy and pressure tolerance allow
Reflux, dyspnea, abdominal tension	Pressure intolerance	Reduce fill; assess position and mechanical complications
New leak or hernia	Excess pressure may contribute	Lower intraperitoneal pressure and enter mechanical pathway
Obesity/large BSA	May require larger absolute volume for efficiency	Individualize; do not scale by weight alone
Frail/small patient	Standard large fill may be burdensome	Prioritize tolerance and effective rather than nominal dose

PRESSURE DISCIPLINE A larger patient does not automatically tolerate a larger intraperitoneal pressure, and a smaller patient is not necessarily adequately dialyzed by a small exchange. Treat fill volume as a titratable physiologic variable.

5. Dwell time: match the target to the transport phenotype

Figure 9.4 - Match dwell architecture to membrane transport.

Faster PSTR favors shorter productive glucose dwells for UF; slower PSTR often needs more contact time for solute and phosphate transfer. Icodextrin changes long-dwell osmotic behavior and should be considered separately from glucose.

ISPD membrane recommendations emphasize that faster PSTR is associated with more rapid glucose absorption and lower net UF during long glucose dwells. Shortening glucose-based exchanges and using icodextrin for a long dwell can mitigate this physiology. Conversely, in slower transport, excessively short automated cycles may sacrifice creatinine and phosphate transfer even when urea clearance appears acceptable. [1,2,13–15]

Table 9.6 - Dwell strategy by transport pattern.

Pattern	Useful strategy	Common error
Fast PSTR + poor long glucose UF	Short glucose dwells + icodextrin long dwell	Making every dwell hypertonic and long
Fast PSTR + sodium overload	Protect UF but ensure enough sodium-coupled contact	Equating high water UF with sodium removal
Slow PSTR + low creatinine/phosphate clearance	Longer contact and/or daytime dwell	Adding more very short APD cycles
Intermediate phenotype	Balance dwell objectives using measured response	Overfitting to transporter label
Changing membrane over time	Repeat membrane assessment when clinically indicated	Carrying forward an old PET forever

6. Number of exchanges and total dialysate volume: more is not always better

Increasing the number of exchanges increases exposure to fresh dialysate gradients and can improve small-solute clearance, particularly when residual kidney function falls. But if total treatment time is fixed, adding cycles shortens dwell time. This can improve UF in a fast transporter while reducing phosphate or sodium removal in another phenotype. The prescriber must know whether the intervention increases total contact time, only divides existing time into more cycles, or both.

Table 9.7 - What happens when cycles are added?

Change	Potential gain	Potential loss
More cycles, same total time	More fresh glucose gradients; shorter dwells	Less time per cycle for slower solutes
More cycles + longer treatment time	Higher total dialysate and contact	Greater burden/sleep disruption
More CAPD exchanges	More total daily clearance/UF opportunities	Manual connections and daytime interruption
Add daytime exchange to APD	More sodium/solute/phosphate contact	Daytime fullness and extra handling
Increase last-fill volume	More long-dwell exchange mass	Pressure/tolerance and long-dwell UF must fit

7. CAPD optimization: use long dwell time intentionally

CAPD is not simply “four bags a day.” Its strengths are continuous contact, long dwell time, straightforward observation and relative independence from a machine. Its weaknesses are daytime exchange burden and the risk that a fast transporter spends too long in a glucose dwell after the osmotic gradient has dissipated.

Table 9.8 - CAPD optimization patterns.

Problem	Mechanism	Possible response
Fast transporter, negative/poor long-dwell UF	Rapid glucose absorption	Use icodextrin for the longest dwell; shorten problematic glucose dwell
Low clearance with RKF decline	Total exchange dose no longer sufficient	Increase exchange volume/number if tolerated and indicated
High phosphate	Need more effective diffusive contact + non-dialytic control	Preserve long dwells; address diet/binders/RKF
Daytime work burden	Manual schedule incompatible with life	Re-time exchanges, simplify or consider APD
High glucose exposure	Osmotic overprescription or intake mismatch	Correct sodium/volume mechanism; use glucose-sparing long dwell when appropriate

8. APD optimization: treat the night as a timed transport experiment

APD allows precise manipulation of total treatment time, number of cycles, fill volume, dwell time, drain thresholds and last fill. This flexibility can become counterproductive when the prescription is optimized for a machine metric instead of the patient. A shorter cycle may improve one target while undermining another; a longer night may increase clearance while damaging sleep and adherence.

Table 9.9 - APD control panel.

APD variable	Physiologic purpose	Bedside check
Total night time	Total contact and treatment opportunity	Did the patient actually receive it?
Number of cycles	Fresh-gradient frequency	What dwell time does this create?
Fill volume	Exchange mass and membrane recruitment	Tolerance, pressure, leak risk
Drain settings	Avoid unnecessary interruption	Incomplete drain vs overdrain pain
Last fill	Long daytime contact	Icodextrin/glucose fit and daytime tolerance
Day exchange	Adds clearance/sodium/phosphate contact	Manual burden and schedule
Tidal mode	Reduces repeated complete drains	Use for a defined indication, not routine clearance inflation

9. Adapted APD: vary the cycle because the targets differ

A small randomized crossover trial showed that an “adapted APD” strategy using different fill volumes and dwell durations within the same night improved several clearance measures and sodium removal compared with uniform cycles using the same total treatment duration and dialysate volume. This supports the physiology that one repeated cycle is not necessarily optimal for every transport target, but the evidence base is small and does not justify a universal adapted-APD protocol. [16]

Table 9.10 - Why vary cycles?

Cycle type	Dominant aim	Trade-off
Shorter, smaller early cycles	Fresh gradient and UF	Less per-cycle slower-solute contact
Longer, larger later cycles	Creatinine/phosphate and sodium transfer	More pressure and glucose-gradient decay
Uniform conventional cycles	Simplicity and predictability	May not maximize competing goals
Customized mixed pattern	Mechanism-specific optimization	Programming complexity and evidence limitations

EVIDENCE CALIBRATION Adapted APD is a physiologically attractive strategy supported by a small crossover RCT. Treat it as a tool for selected patients, not an outcome-proven standard for all APD prescriptions.

10. Sodium removal: the water number can mislead

A 2019 systematic review found lower dialytic sodium removal with APD than CAPD on average, despite no significant difference in UF, with substantial heterogeneity and strong modification by transport status. Short APD dwells can favor aquaporin-mediated free-water transport and sodium sieving. Persistent edema or hypertension despite apparently good UF should therefore trigger a sodium-balance review rather than automatic escalation of glucose. [17]

Table 9.11 - How to improve sodium removal when clinically needed.

Mechanism	Prescription direction	Caution
Very short APD dwells	Increase time for small-pore sodium transport	Do not sacrifice needed UF in fast PSTR
No daytime dwell	Add appropriate long contact when needed	Assess daytime tolerance
Poor long glucose dwell UF	Use icodextrin	Follow product-specific safety rules
High dietary sodium	Reduce input first	Do not “dialyze around” uncontrolled intake
Falling RKF	Renal sodium removal lost	Reassess total sodium and water strategy

11. Icodextrin: optimize the long dwell, not the whole day

Icodextrin produces sustained colloid osmotic ultrafiltration during a long dwell and is particularly useful when a glucose gradient dissipates before the dwell ends. In a 2020 meta-analysis of 19 randomized trials (1,693 participants), icodextrin improved ultrafiltration and reduced episodes of fluid overload compared with glucose-based long dwells. It should be prescribed for a defined long-dwell purpose rather than used as a proxy for “stronger dialysis.” [5]

Table 9.12 - Long-dwell selection.

Situation	Glucose long dwell	Icodextrin long dwell
Fast PSTR	Gradient may dissipate with reabsorption	Often physiologically advantageous
Need sustained daytime/night UF	May require higher glucose exposure	Sustained colloid osmotic force
Good glucose long-dwell UF, low burden	May remain appropriate	No automatic need to switch
Diabetes/high glucose burden	Adds systemic glucose absorption	Glucose-sparing advantage
Low osmotic conductance	May not fully solve intrinsic membrane failure	Use within membrane-failure framework

12. Phosphate: the reason urea-only optimization can fail

Phosphate behaves differently from urea. Observational studies show that phosphate clearance is influenced by PD modality, transport status and contact time, and may be lower in APD prescriptions dominated by short cycles. In a 2020 cohort, dialytic phosphate removal was lower in APD than CAPD/CCPD, while earlier studies similarly associated longer dwell regimens with greater phosphate clearance in slower transporters. These data do not make phosphate a stand-alone dialysis dose target, but they explain why hyperphosphatemia can persist despite apparently satisfactory Kt/V. [13–15]

Table 9.13 - Hyperphosphatemia on PD: prescription reasoning.

Question	Why it matters	Action direction
RKF falling?	Renal phosphate removal may have dropped	Reassess total kidney + PD support
Diet/binders adequate?	Dialysis alone is not the whole phosphate strategy	Correct non-dialytic drivers
APD cycles extremely short?	Insufficient diffusive contact for phosphate	Lengthen selected dwells / add contact time
Slow transporter?	May need longer diffusion time	Avoid solving with more short cycles
Kt/V adequate?	Urea clearance does not guarantee phosphate control	Do not stop reasoning at Kt/V

13. Glucose burden: the hidden price of a “successful” prescription

Glucose-based PD is effective because glucose supplies osmotic force, but absorbed glucose contributes metabolic load and long-term peritoneal exposure. The goal is not glucose avoidance at all costs; it is avoiding glucose that is compensating for a correctable problem such as high sodium intake, excessively long glucose dwells in fast PSTR, poor drain mechanics or underuse of icodextrin. Diabetes management must also account for changing glucose exposure when the PD prescription changes. [5,18,19]

Table 9.14 - When glucose exposure is rising.

Ask	If yes	Response
Is congestion driven by sodium intake?	More glucose treats downstream water only	Correct sodium balance
Is the long dwell reabsorbing?	Higher glucose may give only temporary gain	Shorten glucose dwell/use icodextrin
Is RKF declining?	Total support genuinely fell	Increase PD support deliberately
Is catheter drainage impaired?	More osmotic force cannot fix outflow	Mechanical pathway
Is diabetes control worsening?	PD glucose is part of glycemic exposure	Coordinate insulin/diabetes plan

14. Delivered APD: cycler alarms can erase the prescription

Figure 9.5 - Prescribed APD is not always delivered APD.

Modern cycler records can expose slow drains, incomplete cycles and lost dwell time. The clinical dose is what occurred, not what was entered into the program.

In a 2024 inpatient APD study, lost dwell time greater than 30 minutes occurred in 27% of treatments and greater than 60 minutes in 20%; slow outflow and inadequate drain volumes were major contributors. Although inpatient results do not directly define home APD performance, they demonstrate the principle that repeated drain interruptions can materially reduce effective therapy. [8]

Table 9.15 - APD record review after an unexplained problem.

Look for	Meaning	Next action
Repeated slow-flow alarms	Drain resistance/position/constipation/device issue	Localize mechanism
Lost dwell time	Less true transport time than prescribed	Correct cause before increasing dose
Incomplete final drain	Residual volume / drain mechanics	Assess catheter and drain settings
Frequent user overrides	Burden, misunderstanding or recurrent fault	Retrain and diagnose
Large difference prescribed vs delivered UF	Mechanical, data or physiologic mismatch	Verify weights and drain record
Nightly variability	Position, bowel status, adherence or evolving catheter issue	Trend, do not rely on one night

15. Drain pain and tidal PD: comfort can be a prescription endpoint

Drain pain is common enough to threaten sleep and technique persistence. PDOPPS data confirm that drain pain remains a clinically relevant patient-reported problem. Tidal PD leaves a residual intraperitoneal volume between cycles and can reduce pain from repeated complete drains; older physiologic literature suggests no inherent clearance advantage when total dialysate flow is comparable. It should therefore be used for comfort or selected drainage problems after mechanical causes are assessed, not as a routine “stronger” APD mode. [9,20,21]

Table 9.16 - Tidal PD reasoning.

Situation	Tidal strategy?	First safeguard
Pain only at complete drain	Potentially useful	Exclude catheter/constipation/peritonitis causes
Recurrent low-drain alarms from overdrain	May reduce interruption	Confirm true drain mechanics
Poor clearance without pain	Not a default solution	Identify limiting transport/delivery variable
Progressive residual volume accumulation	Potential underdrain	Reassess tidal percentage and final drainage
New severe abdominal pain	Do not mask with programming	Clinical assessment first

16. Remote monitoring: useful delivery intelligence, not a substitute for physiology

Remote monitoring can make treatment completion, alarms, UF and adherence visible between clinic visits. A 2025 cluster-randomized trial reported fewer deaths and cardiovascular/fluid-overload-related events in remote-monitoring-enabled APD, and a 2026 nationwide Taiwan cohort found associations with lower mortality, lower transfer to hemodialysis and fewer hospitalizations. These results are important but do not prove that remote monitoring itself is the active mechanism in every setting; implementation, response pathways and confounding remain relevant. Full digital-care architecture is developed in Chapter 18. [6,7]

DATA RULE Remote data are clinically useful only when they trigger a defined response. A dashboard that records recurrent slow drains without anyone correcting the cause is surveillance without care.

17. Prescription response by phenotype

Table 9.17 - Phenotype -> preferred first optimization direction.

Phenotype	First direction	Avoid
Fast PSTR + poor long glucose UF	Shorter glucose dwells + icodextrin long dwell	Long hypertonic glucose dwells by reflex
Slow PSTR + low clearance/phosphate	Increase effective contact time	More very short cycles
Volume overload + good water UF	Assess sodium input/removal	Chasing even higher UF only
Anuria with rising solute burden	Increase total PD support while preserving tolerability	Assuming old incremental prescription remains sufficient
High glucose exposure	Correct mechanism + glucose-sparing long dwell where appropriate	Accepting hypertonicity as permanent baseline
Recurrent APD lost dwell	Fix delivery/mechanics	Increasing programmed dose
Drain pain	Mechanical review + selected tidal strategy	Normalizing nightly pain
Unsustainable treatment burden	Simplify/assist/change architecture	Defining nonadherence as patient failure

Flowchart 9.1 - Choose CAPD or APD by prescription fit.

The correct modality is the one that can deliver the required dwell architecture and clinical goals with acceptable burden, support and reliability.

18. When a target is not met: a universal optimization algorithm

Flowchart 9.2 - A target is not met: optimize by mechanism.

Confirm the target, validate actual treatment delivery, identify the limiting mechanism, change the smallest effective lever and reassess both benefit and trade-offs.

Table 9.18 - Reassessment after any prescription change.

Domain	Pass criterion
Clinical	Symptoms/volume/biochemistry move in intended direction
Delivery	Prescription is actually completed
Membrane	Response matches expected transport physiology
Kidney	RKF/urine contribution remains protected where possible
Burden	Sleep, work, pain and exchange complexity acceptable
Metabolic	No unnecessary escalation of glucose exposure
Safety	No new leak, pressure intolerance, hypovolemia or mechanical problem
Plan	Next trigger for review is documented

19. Recurrent APD alarms: troubleshooting the delivered prescription

Flowchart 9.3 - Recurrent APD alarms or lost dwell time.

Repeated alarm silencing is not prescription optimization. Localize the treatment phase, exclude simple causes, enter the catheter/mechanical pathway when needed, and verify restored delivered therapy.

Table 9.19 - Alarm phenotype -> likely cause -> response.

Pattern	Likely cause	Response
Slow drain after position change	Catheter/tubing geometry	Reposition; inspect; trend recurrence
Slow drain most nights	Constipation, catheter migration, drain settings	Bowel + catheter pathway
Pain at end drain	Overdrain/contact pain	Exclude pathology; consider tidal strategy
Low drain + abdominal swelling	Leak/sequestration	Stop “dose escalation”; investigate leak
Lost dwell from repeated alarms	Delivery inefficiency	Correct source, then reassess adequacy/UF
Alarm only in hospital	Setup/position/environment issue possible	Compare home data and nursing process

20. Patient burden and life participation are prescription outcomes

The ISPD goal-directed framework explicitly places life participation, symptoms and treatment burden alongside biochemical and volume goals. A patient may prefer manual daytime exchanges to protect sleep, or APD to protect work and daytime independence. The choice can change with frailty, employment, caregiver availability, visual/dexterity decline, transplant planning or changing residual kidney function. [1,22]

Table 9.20 - Burden signals that should trigger redesign.

Signal	Interpretation	Redesign option
Repeated skipped CAPD exchanges	Schedule burden or technique barrier	Re-time, simplify, assist or consider APD
Nightly APD sleep disruption	Alarms/pain/therapy duration	Correct mechanism; shorten/reconfigure or consider CAPD
Caregiver exhaustion	Hidden sustainability failure	Assisted PD/resource review
Patient declines day dwell	Life-participation conflict	Rebalance night time/cycles; discuss trade-off
Complex prescription errors	Cognitive/visual/manual overload	Simplify; retrain; assist
Adequate numbers, poor quality of life	Treatment goal mismatch	Shared redesign rather than numeric intensification

21. Clinical pearls and common pitfalls

Table 9.21 - High-frequency prescription errors.

Pitfall	Why it fails	Correction
APD is “better” than CAPD	RCT evidence does not establish superiority	Choose by fit and goals
Fast transporter = APD automatically	Oversimplifies sodium, day dwell and lifestyle needs	Match dwell pattern, not label
More cycles always means more dialysis	Shortens dwell when time fixed	Identify target and contact-time effect
Higher UF means better sodium removal	APD can remove proportionally more water	Assess sodium balance separately
Adequate Kt/V means phosphate is solved	Phosphate needs longer contact and RKF/non-dialytic control	Review phosphate specifically
Escalate programmed dose when APD inadequate	Actual delivery may be interrupted	Review cycler record first
Drain pain is normal	Pain reduces sleep and adherence and may signal pathology	Assess cause; consider tidal only when appropriate
Use hypertonic glucose indefinitely	Raises metabolic/membrane burden	Correct mechanism and use lowest effective osmotic dose
Keep old prescription as RKF falls	Total support declines silently	Reassess urine/RKF and total goals
Optimize numbers at the expense of life	Unsustainable treatment fails in practice	Include patient-reported outcomes

CLINICAL PEARL The best APD prescription is often the simplest one that delivers enough true dwell time. Complexity is not a marker of sophistication.

CLINICAL PEARL If sodium or phosphate is the problem, ask whether the prescription needs more contact time rather than more cycles.

CLINICAL PEARL A day dwell is a powerful APD lever because it adds time without further fragmenting the night.

CLINICAL PEARL When the prescription is failing, compare what was prescribed, what the machine delivered and what the patient tolerated - three different datasets.

22. Mini-cases: prescription decisions, not trivia

Case 1 - Fast transporter with edema

A patient on CAPD has adequate small-solute clearance but negative UF during the longest glucose dwell and persistent edema. PET shows fast PSTR.

BEST NEXT STEP Shorten the problematic glucose exposure and use icodextrin for the long dwell if appropriate. Reassess sodium intake/removal; do not simply make the long glucose dwell more hypertonic.

Case 2 - Slow transporter on many short APD cycles

An anuric patient has acceptable weekly Kt/V but persistent hyperphosphatemia and low creatinine/phosphate clearance. Night therapy contains many short cycles.

BEST NEXT STEP Do not add more short cycles reflexively. Increase effective contact time - selected longer dwells, longer total therapy and/or an appropriate daytime dwell - while addressing diet and binders.

Case 3 - “Inadequate APD” with alarms

Laboratory adequacy falls after hospitalization. The cycler prescription is unchanged, but nightly records show repeated slow drains and 50-70 minutes of lost dwell time.

BEST NEXT STEP Treat this as delivery failure. Correct constipation, position, tubing or catheter dysfunction and verify restored dwell time before prescribing more dialysate.

Case 4 - Good UF, uncontrolled hypertension

An APD patient removes 1.2 L nightly yet gains weight between visits and has high BP. Short cycles dominate and dietary sodium is high.

BEST NEXT STEP Separate water from sodium. Address sodium intake and assess sodium-removal architecture; consider longer contact/day dwell rather than pursuing still higher water UF.

Case 5 - Drain pain destroying sleep

A stable APD patient wakes repeatedly with sharp pain at the end of complete drains. Catheter position and bowel status are satisfactory and there are no infection features.

BEST NEXT STEP A selected tidal strategy can be reasonable to avoid repeated complete drainage. Reassess residual volume, delivered clearance and symptom response.

Case 6 - Treatment burden despite “perfect numbers”

A working patient on CAPD has excellent biochemical and volume control but regularly misses midday exchanges because they are incompatible with employment.

BEST NEXT STEP This is a prescription failure, not a character flaw. Reconfigure schedule or consider APD/assistance while preserving the physiologic targets.

23. Active recall

MUST MEMORIZE

What did the 2024 Cochrane update conclude about overall APD versus CAPD superiority?
Which prescription variables determine the dwell architecture of APD?
Why can short APD cycles preserve UF yet reduce sodium or phosphate removal?
What is the main long-dwell role of icodextrin?
What is the difference between prescribed APD and delivered APD?

MUST REASON

A fast transporter has poor long-dwell glucose UF but excellent urea clearance. Which lever would you change first and why?
An anuric slow transporter has normal Kt/V but high phosphate. Explain why more short cycles may fail.
How can recurrent slow drains produce biochemical underdialysis without any change in the programmed prescription?
Why can CAPD produce greater sodium removal than APD despite similar net UF?
How do you decide whether to change CAPD to APD when the real problem is treatment burden rather than physiology?

USE AS REFERENCE

Table 9.4 prescription levers and trade-offs.
Table 9.17 phenotype-based first optimization direction.
Flowchart 9.3 recurrent APD alarms/lost dwell time.

24. Flashcards: active recall

1. Q: APD superior to CAPD? A: Not established. The 2024 Cochrane randomized evidence is insufficient/very uncertain.

2. Q: Fast PSTR long glucose dwell? A: Glucose dissipates rapidly; shorten glucose dwell and consider icodextrin for the long dwell.

3. Q: Slow PSTR with poor phosphate clearance? A: Increase useful contact time rather than simply adding short cycles.

4. Q: More APD cycles with same total time does what? A: Shortens each dwell.

5. Q: Why can APD sodium removal be lower? A: Short dwells accentuate free-water transport and sodium sieving.

6. Q: Icodextrin main niche? A: Sustained once-daily long-dwell UF, especially when glucose long-dwell UF is poor.

7. Q: Prescribed dose vs delivered dose? A: Programmed treatment versus what actually occurred after alarms, drains and interruptions.

8. Q: Lost dwell time matters because? A: Transport occurs during dwell; lost time reduces effective therapy.

9. Q: Drain pain at complete drain? A: Exclude pathology/mechanics; tidal PD may help selected patients.

10. Q: Tidal PD gives superior clearance by default? A: No; its main chronic role is comfort/drain management in selected patients.

11. Q: Adequate Kt/V but high phosphate? A: Urea does not represent phosphate; review contact time, RKF, diet and binders.

12. Q: Good UF but edema/high BP? A: Assess sodium intake/removal - water UF alone can mislead.

13. Q: Day dwell in APD can do what? A: Add long contact for sodium, solute and phosphate removal and long-dwell UF.

14. Q: Rising glucose requirement means? A: Reassess intake, RKF, dwell fit, mechanics and membrane before normalizing hypertonicity.

15. Q: When to switch CAPD/APD? A: When another architecture better delivers required physiology with sustainable burden.

16. Q: Remote monitoring role in Chapter 9? A: Verify delivery and detect problems; full digital-care framework belongs to Chapter 18.

17. Q: Optimization endpoint? A: Target achieved + treatment actually delivered + burden acceptable + no disproportionate trade-off.

18. Q: Best first response to unexplained low APD adequacy? A: Validate collection and inspect delivered cycler treatment before increasing dose.

25. Rapid troubleshooting table

Table 9.22 - Prescription problem -> likely mechanism -> next step.

Problem	Likely mechanism(s)	Next step
Poor long-dwell UF	Fast PSTR or intrinsic low UF capacity	PET context; shorter glucose dwell/icodextrin or membrane pathway
Low Kt/V after stable period	Collection error, noncompletion, RKF loss	Verify delivery/collection + urine; then increase effective dose if needed
High phosphate on short-cycle APD	Insufficient contact time + non-dialytic factors	Longer selected dwell/day exchange + diet/binders
Good UF + high BP/edema	Sodium mismatch	Review sodium input/removal and dwell architecture
Recurrent slow-drain alarms	Constipation/catheter/position/setup	Mechanical pathway before dose escalation
Nightly drain pain	Overdrain/contact pain or pathology	Assess; tidal strategy only after exclusion
High glucose burden	Intake/RKF/dwell/membrane mismatch	Correct driver; glucose-sparing strategy
Patient missing CAPD exchanges	Lifestyle/technique burden	Simplify, assist or consider APD
APD prescription “adequate” but symptoms persist	Wrong target or delivery mismatch	Reopen goal-directed assessment

26. Final revision sheet

TEN TAKE-HOME RULES 1) CAPD and APD are delivery architectures, not adequacy rankings. 2) Randomized evidence does not establish universal APD superiority. 3) Name the clinical target before changing the prescription. 4) Dwell time is the central trade-off between UF and slower-solute/sodium/phosphate transfer. 5) Fast PSTR often benefits from shorter glucose dwells plus an icodextrin long dwell. 6) Slow PSTR may be harmed by too many short APD cycles. 7) Water UF is not sodium removal. 8) Inspect delivered APD before escalating programmed dose. 9) Drain pain and sleep burden are legitimate prescription outcomes. 10) Optimization succeeds only when the target improves sustainably with acceptable glucose and treatment burden.

Table 9.23 - Final revision grid.

Core concept	Remember
Architecture	CAPD = manual long daytime pattern; APD = programmable nocturnal cycles +/- day dwell
Evidence	2024 Cochrane: insufficient/very uncertain RCT evidence for superiority
Fast PSTR	Shorter glucose dwell; icodextrin for long dwell when indicated
Slow PSTR	Protect contact time; avoid excessive cycle fragmentation
Sodium	Short APD can remove proportionally more water than sodium
Phosphate	Needs contact time; Kt/V is not a proxy
Icodextrin	Long-dwell sustained UF tool
APD delivery	Alarms/slow drains can erase dwell and true dose
Tidal	Selective comfort/drain strategy, not routine clearance enhancer
End point	Clinical + measured target + delivered treatment + sustainable burden

Figure 9.6 - Prescription optimization is a feedback loop.

Name the problem -> localize the limiting mechanism -> change the smallest effective lever -> verify both benefit and trade-offs -> iterate or redesign the modality if the goals remain unsustainable.

FINAL MENTAL MODEL Goal -> actual delivered therapy -> membrane transport -> residual kidneys -> CAPD/APD architecture -> dwell/fill/exchange/osmotic lever -> trade-offs -> reassessment -> redesign or transition when the prescription no longer serves the patient.

Rapid oral viva

Why is APD not simply “more dialysis” than CAPD?
Walk through the prescription consequences of fast versus slow PSTR.
Explain why adding APD cycles can worsen phosphate clearance even while improving urea clearance.
How would you investigate low adequacy in a patient with frequent cycler alarms?
Explain when tidal PD is appropriate and what it does not accomplish automatically.
Give a goal-directed reason to switch from CAPD to APD and a separate reason to switch from APD to CAPD.

SCOPE BOUNDARY This chapter teaches CAPD/APD architecture and prescription optimization. Peritonitis prevention/treatment follows in Chapter 10; exit-site/tunnel infection in Chapter 11; mechanical complications in Chapter 12; long-term membrane failure in Chapter 14; remote monitoring and connected cyclers are developed fully in Chapter 18.

27. Selected authoritative references

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2. Morelle J, Stachowska-Pietka J, Oberg C, et al. ISPD recommendations for the evaluation of peritoneal membrane dysfunction in adults: classification, measurement, interpretation and rationale for intervention. Perit Dial Int. 2021;41(4):352–372. https://doi.org/10.1177/0896860820982218. PMID: 33563110.

3. Driehuis E, Eshuis M, Abrahams AC, Francois K, Vernooij RWM. Automated peritoneal dialysis versus continuous ambulatory peritoneal dialysis for people with kidney failure. Cochrane Database Syst Rev. 2024;9:CD006515. https://doi.org/10.1002/14651858.CD006515.pub2. PMID: 39258519.

4. Boudville N, de Moraes TP. 2005 Guidelines on targets for solute and fluid removal in adults being treated with chronic peritoneal dialysis: 2019 update of the literature and revision of recommendations. Perit Dial Int. 2020;40(3):254–260. https://doi.org/10.1177/0896860819898307.

5. Goossen K, Becker M, Marshall MR, et al. Icodextrin Versus Glucose Solutions for the Once-Daily Long Dwell in Peritoneal Dialysis: An Enriched Systematic Review and Meta-analysis of Randomized Controlled Trials. Am J Kidney Dis. 2020;75(6):830–846. https://doi.org/10.1053/j.ajkd.2019.10.004. PMID: 32033860.

6. Paniagua R, Ramos A, Avila M, et al. Remote monitoring of automated peritoneal dialysis reduces mortality, adverse events and hospitalizations: a cluster-randomized controlled trial. Nephrol Dial Transplant. 2025;40(3):588–597. https://doi.org/10.1093/ndt/gfae188. PMID: 39165115.

7. Chung MC, Yu TM, Cheng BC, et al. Remote Patient Monitoring-Enabled Automated Peritoneal Dialysis and Clinical Outcomes: A Nationwide Real-World Cohort Study from Taiwan. Clin J Am Soc Nephrol. 2026 Jul 14; ahead of print. https://doi.org/10.2215/CJN.0000001112. PMID: 42447366.

8. Browne MC, Elavia N, Flowers A, et al. Lost dwell time and cycler alarms in inpatient automated peritoneal dialysis at a tertiary care hospital. Ren Fail. 2024;46(2):2408432. https://doi.org/10.1080/0886022X.2024.2408432. PMID: 39352771.

9. Aga Z, McCullough K, Pisoni RL, et al. Peritoneal Dialysis-Related Drain Pain and Patient and Treatment Characteristics: Findings From the Peritoneal Dialysis Outcomes and Practice Patterns Study (PDOPPS). Am J Kidney Dis. 2023;82(6):779–782. https://doi.org/10.1053/j.ajkd.2023.04.005. PMID: 37393052.

10. Reimann F, Tomlins M. Prescribing and peritoneal dialysis. Aust Prescr. 2023;46(1):5–8. https://doi.org/10.18773/austprescr.2023.001. PMID: 38053668.

11. Ventura MJ, Amato D, Correa-Rotter R, Paniagua R; Mexican Nephrology Collaborative Study Group. Relationship between fill volume, intraperitoneal pressure, body size, and subjective discomfort perception in CAPD patients. Perit Dial Int. 2000;20(2):188–193. https://doi.org/10.1177/089686080002000205. PMID: 10809242.

12. Dejardin A, Robert A, Goffin E. Intraperitoneal pressure in PD patients: relationship to intraperitoneal volume, body size and PD-related complications. Nephrol Dial Transplant. 2007;22(5):1437–1444. https://doi.org/10.1093/ndt/gfl745. PMID: 17308323.

13. Debowska M, Gomez R, Pinto J, Waniewski J, Lindholm B. Phosphate clearance in peritoneal dialysis. Sci Rep. 2020;10(1):17504. https://doi.org/10.1038/s41598-020-74412-2. PMID: 33060672.

14. Badve SV, Zimmerman DL, Knoll GA, Burns KD, McCormick BB. Peritoneal phosphate clearance is influenced by peritoneal dialysis modality, independent of peritoneal transport characteristics. Clin J Am Soc Nephrol. 2008;3(6):1711–1717. https://doi.org/10.2215/CJN.00190108. PMID: 18815242.

15. Courivaud C, Davenport A. Phosphate Removal by Peritoneal Dialysis: The Effect of Transporter Status and Peritoneal Dialysis Prescription. Perit Dial Int. 2016;36(1):85–93. https://doi.org/10.3747/pdi.2014.00173. PMID: 26224788.

16. Fischbach M, Issad B, Dubois V, Taamma R. The beneficial influence on the effectiveness of automated peritoneal dialysis of varying the dwell time and fill volume: a randomized controlled trial. Perit Dial Int. 2011;31(4):450–458. https://doi.org/10.3747/pdi.2010.00146. PMID: 21454393.

17. Borrelli S, La Milia V, De Nicola L, et al. Sodium removal by peritoneal dialysis: a systematic review and meta-analysis. J Nephrol. 2019;32(2):231–239. https://doi.org/10.1007/s40620-018-0507-1. PMID: 29978446.

18. de Moraes TP, Pellizzari C, Lins PRG, Calice-Silva V. Current approaches to prescription and optimization of peritoneal dialysis: a practical review. J Bras Nefrol. 2026;48(2):e20250288. https://doi.org/10.1590/2175-8239-JBN-2025-0288en. PMID: 42284506.

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21. Vychytil A, Horl WH. The role of tidal peritoneal dialysis in modern practice: a European perspective. Kidney Int Suppl. 2006;(103):S96–S103. https://doi.org/10.1038/sj.ki.5001923. PMID: 17080119.

22. Corbett RW, Goodlet G, MacLaren B, et al. International Society for Peritoneal Dialysis Practice Recommendations: The view of the person who is doing or who has done peritoneal dialysis. Perit Dial Int. 2020;40(3):349–352. https://doi.org/10.1177/0896860820918822. PMID: 32301374.

SOURCE NOTE Guidelines and contemporary evidence were checked 2 September 2026. CAPD-versus-APD outcome comparisons are presented with the low/very-low certainty identified by the 2024 Cochrane update. Adapted APD, tidal PD and remote-monitoring findings are not generalized beyond the populations and mechanisms studied. Exact cycler settings, drain algorithms, fill limits and product-specific icodextrin/glucose safety remain device-, patient- and program-specific.