Why are manual Peritoneal Dialysis (PD) bags preferred over Automated Peritoneal Dialysis (APD) machines for patients with fluid overload?

Manual PD Bags vs. APD Machine for Fluid Overload

Manual PD bags (CAPD) are preferred over APD machines for fluid-overloaded patients primarily because long-duration dwells in APD—particularly the daytime dwell—frequently result in net fluid reabsorption rather than removal, worsening volume overload. 1

The Core Problem: Long Dwells and Fluid Reabsorption

• Net peritoneal fluid absorption commonly occurs with long-duration dwells, such as the diurnal (daytime) dwell in APD, which directly counteracts efforts to remove excess fluid 1
• The American Journal of Kidney Diseases guidelines explicitly state that particular attention should be given to net peritoneal fluid absorption during long dwells because this can be avoided by altering the PD prescription 1
• In volume-overloaded or hypertensive patients, ultrafiltration should never be negative (no fluid absorption) for any exchanges, making standard APD with long day dwells problematic 1, 2

Why Manual CAPD Works Better for Volume Overload

• CAPD allows for more frequent, shorter dwells (typically 4-5 exchanges per day) that prevent the fluid reabsorption seen with prolonged dwells 1
• Manual exchanges provide immediate flexibility to adjust dwell times and glucose concentrations based on real-time volume status without waiting for programmed cycles 1
• Shorter dwell times optimize ultrafiltration by preventing the equilibration that leads to fluid reabsorption, particularly important in high and high-average transporters 1

Specific APD Limitations in Fluid Overload

• APD patients often prefer "dry day" prescriptions (no daytime dwell), which severely compromises ultrafiltration capacity when volume removal is most needed 1
• Even when APD includes a day dwell, the long duration (8-16 hours) allows significant fluid reabsorption, especially in high transporters 1
• The Kidney International guidelines note that APD with long day dwells may require shortening or elimination of the dwell to prevent fluid reabsorption, essentially converting the prescription toward a CAPD-like pattern 1

Evidence-Based Strategies for Volume Overload

When managing fluid-overloaded patients, the preferred approach includes:

• Avoiding long-duration dwells that are associated with ineffective fluid removal or net fluid resorption 1, 2
• Using icodextrin solution for any necessary long dwells (if APD must be used) to maintain ultrafiltration, as RCTs demonstrate it increases peritoneal ultrafiltration and decreases extracellular fluid volume 1, 2
• Implementing shorter, more frequent exchanges to maximize cumulative ultrafiltration—a pattern naturally achieved with manual CAPD 1
• Monitoring drain volumes monthly, with particular attention to overnight dwells in CAPD and daytime dwells in APD, as inadequate drain volumes indicate ultrafiltration failure 1, 3

When APD Can Be Modified for Volume Overload

If APD must be used in volume-overloaded patients, specific modifications are required:

• Shorten or eliminate the day dwell, leaving the patient "dry" for a portion of the day 1
• Drain and replace the day dwell partway through with fresh dialysis solution to prevent reabsorption 1
• Use icodextrin exclusively for the long day dwell to maintain ultrafiltration throughout the extended dwell time 1, 2
• Increase the number of nocturnal cycles with shorter dwell times to maximize ultrafiltration 4

Critical Pitfall to Avoid

• Do not assume APD provides superior volume control simply because it is automated—no robust data suggest APD results in better volume control than CAPD, and modality selection should prioritize ultrafiltration capacity over convenience 1, 5
• Avoid relying on hypertonic 4.25% glucose solutions to compensate for poor APD ultrafiltration, as frequent use damages the peritoneal membrane and causes adverse metabolic effects 1, 2
• Never ignore negative ultrafiltration (fluid absorption) in any exchange when managing volume overload, as this directly worsens the clinical condition 1, 2

The Bottom Line

Manual CAPD bags provide shorter, more controllable dwell times that prevent the fluid reabsorption inherent to APD's long day dwells, making them the mechanistically superior choice for acute volume overload management 1, 2. Once euvolemia is achieved, transition to modified APD (with icodextrin for long dwells or no day dwell) may be considered based on patient preference and transport characteristics 1, 2.