Questions About PD
Membrane failure can be defined as the inability of the peritoneal membrane to ensure efficient dialysis, including adequate fluid and solute removal, despite a patent PD catheter and an appropriate prescription of PD.
It is most often related to ultrafiltration failure, which is defined – according to ISPD – as a net UF of <400 ml at the end of a 4.25% glucose-based, 4-h peritoneal equilibration test.
UF failure can be divided into 4 different pathophysiological mechanisms, based on associated transport defects:
- Type I UFF – high effective peritoneal surface area (EPSA), reflected by a fast transport status (D/Pcreat >0.81 at 4h), and suggesting angiogenesis
- Type II UFF – low osmotic conductance to glucose (OCG), reflected by a low sodium sieving, and suggesting severe peritoneal fibrosis (and potentially dysfunction of water channels)
- Type III UFF – low EPSA, reflected by a slow transport status, suggesting a small cavity/sequestration of fluid, adherences or severe fibrosis
- Type IV UFF – high fluid loss rate, which theoretically requires evaluate of the disappearance rate of a radiolabelled volume tracer, such as RISA. It can also be suggested by a negative net UF obtained with icodextrin (after a reasonable dwell time, e.g. 8-16 hours)
Although this classification is useful to categorize causes of membrane failure, several transport defects often coexist.
The main causes of membrane failure include:
- Prolonged exposure to dialysis solutions, especially when hypertonic glucose is used
- Acute peritonitis, as well as repeat or severe episodes of peritonitis
- Encapsulating peritoneal sclerosis
- Other factors may contribute to membrane remodelling and dysfunction, including: loss of residual kidney function, fluid overload and salt accumulation, and potentially genetic factors