How can sodium sieving be managed during dialysis with optimal dwell times?

Managing Sodium Sieving in Peritoneal Dialysis Through Dwell Time Optimization

To minimize sodium sieving and optimize fluid removal in peritoneal dialysis, use shorter dwell times (avoiding dwells longer than 4-6 hours with glucose-based solutions) and reserve icodextrin exclusively for any necessary long dwells, as prolonged glucose-based dwells cause progressive sodium reabsorption that directly counteracts ultrafiltration goals. 1, 2

Understanding the Sodium Sieving Problem

Sodium sieving refers to the initial preferential removal of free water over sodium during peritoneal dialysis, creating a transient sodium gradient. However, this phenomenon becomes problematic during extended dwells because:

• The sodium gradient reverses over time, leading to net sodium and water reabsorption back into the patient, particularly after 4-6 hours with glucose-based solutions 1, 2
• High and high-average transporters experience this reversal earlier in the dwell, making them particularly vulnerable to fluid reabsorption during long dwells 2
• APD patients with long daytime dwells (8-16 hours) commonly experience net peritoneal fluid absorption, directly worsening volume overload and hypertension 2

Optimal Dwell Time Strategies by Clinical Scenario

For Volume-Overloaded or Hypertensive Patients

• Implement shorter, more frequent exchanges (4-5 per day) to prevent the equilibration that leads to fluid reabsorption—this is the natural pattern of CAPD 2
• Ultrafiltration should never be negative for any exchange in volume-overloaded patients, making standard APD with long day dwells contraindicated 2
• Shorten dwell times with glucose-based solutions to less than 6 hours, especially for high transporters who equilibrate rapidly 2

For APD Patients Requiring Modification

When APD must be used despite volume concerns, the prescription requires aggressive modification:

• Eliminate or dramatically shorten the day dwell to prevent the 8-16 hour reabsorption period 1, 2
• Use icodextrin exclusively for any long dwell (day or night), as it maintains ultrafiltration throughout extended dwell times without the reabsorption seen with glucose 2, 3
• Drain and replace the day dwell partway through with fresh solution if a long dwell cannot be avoided 2
• Increase the number of overnight cycles rather than prolonging individual dwell times, as more frequent exchanges maximize cumulative ultrafiltration 1

For CAPD Patients

• CAPD naturally provides optimal dwell times (4-6 hours per exchange) that prevent significant fluid reabsorption while maximizing sodium removal 2, 3
• Four to five exchanges per day allow immediate flexibility to adjust dwell times and glucose concentrations based on real-time volume status 2
• Consider icodextrin for the overnight dwell only if additional ultrafiltration is needed, as the shorter daytime dwells with glucose are already optimized 3

The Critical Role of Icodextrin

Icodextrin fundamentally changes the sodium sieving dynamic during long dwells:

• Icodextrin maintains ultrafiltration for 12-16 hours without the sodium and water reabsorption characteristic of glucose solutions 2, 3
• When icodextrin is used optimally for long dwells, sodium removal becomes equivalent between CAPD and APD, eliminating the modality-based difference 3
• Randomized controlled trials demonstrate icodextrin increases peritoneal ultrafiltration and decreases extracellular fluid volume in volume-overloaded patients 2

Dialysate Sodium Concentration Considerations

While dwell time is the primary determinant of sodium sieving effects, dialysate sodium concentration also plays a role:

• Lower dialysate sodium concentrations (132-135 mmol/L) are associated with lower interdialytic weight gain and blood pressure, though they increase risk of intradialytic hypotension and cramps in hemodialysis patients 1
• The ideal dialysate sodium concentration remains uncertain pending results of ongoing trials (SoLID, RESOLVE), and prescribed versus delivered concentrations can differ significantly 1
• Sodium balance should be negative during each dialysis treatment to balance vascular stability during individual treatments with lower interdialytic weight gain across many treatments 1

Critical Pitfalls to Avoid

• Never assume APD provides superior volume control simply because it is automated—no robust data support this assumption, and long day dwells actively worsen volume status 2
• Do not compensate for poor APD ultrafiltration by increasing hypertonic 4.25% glucose frequency, as this damages the peritoneal membrane and causes adverse metabolic effects 2
• Never ignore negative ultrafiltration (net fluid absorption) in any exchange when managing volume overload, as this directly worsens the clinical condition 2
• Avoid "dry day" APD prescriptions in volume-overloaded patients, as eliminating the day dwell severely compromises total ultrafiltration capacity when volume removal is most critical 2

Monitoring and Adjustment Algorithm

Monthly assessment should include:

• Measure drain volume for each exchange type to identify which dwells are producing negative ultrafiltration 2
• Calculate net ultrafiltration (drain volume minus instilled volume) for each dwell period separately 2
• Assess blood pressure and volume status through clinical examination, with particular attention to extracellular fluid volume 1, 2
• Evaluate residual kidney function and adjust the prescription accordingly, as preserved RKF strongly associates with better volume control 2

When negative ultrafiltration is detected:

• Immediately shorten the problematic dwell or switch to icodextrin for that specific exchange 2
• Consider switching from APD to CAPD if multiple dwells show poor ultrafiltration despite optimization attempts 2
• Reassess peritoneal membrane transport status with a peritoneal equilibration test, as high transporters require fundamentally different dwell time strategies 2