An interactive physiology lab for the dialysis care team: what high and low transporters are at the membrane level, why solute clearance and ultrafiltration so often pull in opposite directions, and how the PET result guides the PD prescription.
Developed by Craig G. Hurwitz, MD
Set how fast this patient's peritoneal membrane moves small solutes, then watch what happens on both sides of the membrane at the same time: solute crosses for clearance, and glucose crosses the other way and dismantles the engine that pulls water.
How quickly urea and creatinine equilibrate across the membrane.
Net water removed before the glucose gradient fades.
Illustrative. Particle speeds and meter levels are conceptual teaching aids, not measured patient values.
These two goals pull in opposite directions across the transport spectrum. As you speed the membrane up, one gauge climbs and the other falls. There is no setting where both are maxed out at once.
Illustrative. Gauge positions are conceptual teaching aids, not measured patient values.
Follow one glucose dwell across four hours in a fast membrane. The glucose that pulls water in is also the glucose the membrane absorbs fastest, so the engine for ultrafiltration runs down before the dwell is over.
The bag is loaded with glucose. Maximum pull on water.
Water is flowing into the bag.
The membrane works so well that it ruins its own ultrafiltration. A fast membrane absorbs the glucose before it can finish its job, so by the end of a long dwell the gradient is gone, water removal stops, and the bag can even start reabsorbing fluid back into the patient.
Illustrative. Gradient and ultrafiltration levels are conceptual teaching aids, not measured patient values.
A slow membrane is the opposite problem. Ultrafiltration is never the issue, but solute equilibrates so gradually that the dwell has to be long to capture it. Drag through the dwell and watch how late good clearance arrives.
Still climbing. A standard 4 hour dwell only captures part of this membrane's clearance.
Long dwells are how a slow membrane earns its adequacy.
In a slow membrane, creatinine is still crossing well past hour 4. Automated PD runs many short overnight dwells, so each one is cut off long before equilibration. The clearance simply never gets captured. A low transporter usually does better with fewer, longer dwells, often CAPD or CCPD with a long daytime dwell.
Illustrative equilibration curve for teaching the shape of slow transport, not a specific patient's PET.
Enter a 4 hour peritoneal equilibration test result. The dial places the membrane on the transport spectrum and translates the number into what you should expect, where it is strong, where it is weak, and what it means for the prescription.
A patient walks in. Pick the strategies that fit their membrane and their situation, then check your reasoning. Often more than one choice is right, and sometimes a tempting one is a trap.
Select all that apply:
Illustrative teaching scenarios. Real prescriptions depend on the full clinical picture, adequacy targets, and the patient\u2019s goals.
Two identical high transporters, one long dwell each. Patient A uses hypertonic glucose; Patient B uses icodextrin. Scrub through 16 hours and watch the cumulative fluid removed by each. This is the single clearest reason icodextrin matters most in fast membranes.
Glucose is a small molecule, so a fast membrane absorbs it quickly: the gradient collapses, ultrafiltration peaks early, and a long dwell can drift into reabsorption. Icodextrin is a large glucose polymer that is not absorbed quickly, so it pulls fluid by colloid osmosis steadily for 12 to 16 hours. The faster the membrane, the more glucose fails on a long dwell, and the more icodextrin stands out.
Illustrative. Curves show the characteristic shapes, not a specific patient\u2019s measured ultrafiltration.
Set the membrane, then dial in a prescription. The four gauges respond in real time so the logic becomes visible: which knobs buy clearance, which buy ultrafiltration, what they cost in glucose load, and whether the whole plan actually fits the membrane.
Driven by exchanges, fill, dwell length vs membrane speed, and residual function.
Glucose loses ground on long dwells in fast membranes; icodextrin sustains it.
Lower is better. More glucose dwells and higher fills raise the load; icodextrin lowers it.
How well this whole plan fits the membrane in front of you.
Illustrative model for teaching prescription logic. Gauge values are conceptual and do not replace measured adequacy or ultrafiltration.
Total clearance is the sum of what the peritoneum does and what the native kidneys still do. That second part hides the weakness of a slow membrane, until it disappears. Press the button and watch residual function fade.
With residual kidney function present, every patient clears above target. The low transporter is leaning on the kidneys to cover for a slow membrane, so it looks fine right now.
Illustrative. Clearance contributions are conceptual teaching values toward a normalized target, not measured Kt/V or creatinine clearance.
Transport status is not a fixed label stamped at the start of PD. The membrane changes. Add the insults a peritoneum accumulates over years and watch it drift upward, toward faster transport and harder fluid management.
Transport status is dynamic, not fixed. Repeat the PET over time, especially after peritonitis or when ultrafiltration starts to fail. Some drivers are partly modifiable: minimizing glucose exposure, preventing peritonitis, and using icodextrin can slow the drift.
Illustrative. The upward drift and consequence levels are conceptual teaching aids, not a validated predictive model.
Select a transport category and compare the risks that historically track with it. Notice the pattern: the danger of fast transport is not poor clearance, it is the difficulty of keeping the patient out of fluid overload.
High transport status is not dangerous because clearance is poor. Clearance is actually excellent in fast membranes.
It is dangerous because fluid management becomes difficult: ultrafiltration fails, volume overload follows, and that is what drives the worse outcomes. Manage the fluid, with short dwells, icodextrin, and close volume control, and much of the excess risk is addressable.
Illustrative comparison of relative risk direction, not measured outcome rates.
Tap a card to flip it. The membrane sets the strategy, but the patient sets the plan.
The membrane sets the strategy. Volume status, residual function, nutrition, and the patient\u2019s life set the plan.
This module is a staff and clinician teaching tool for Northern Nephrology & Hypertension. It explains transport physiology and prescription logic; it does not replace clinical judgment, measured adequacy and ultrafiltration, current ISPD guidance, or local protocol. Interactive values labeled illustrative are conceptual teaching aids, not patient data.
To be completed from the reference review (e.g. ISPD peritoneal dialysis prescription / adequacy guidance; Twardowski peritoneal equilibration test; key transport-and-outcomes studies). Replace this line with the finalized, verified citation list before publishing.
