Evaluation of ultrafiltration failure in peritoneal dialysis after excluding causes that are unrelated to dialysis procedure or due to noncompliance*

MRI: magnetic resonance imaging; CT: computed tomography; PET: peritoneal equilibration test; D/P: ratio of dialysate to plasma creatinine.
* Patients are evaluated monthly. At each evaluation, we do the following:

• Assess target weight, based on clinical exam, dietary history, and any change in cardiovascular status.
• Review ultrafiltration volumes with each exchange.
• Measure 24-hour urine volume.
• Review medication use to exclude nephrotoxin use. If there is evidence of fluid overload, we first evaluate for causes that are unrelated to the dialysis procedure.

Common causes and our approach to addressing each problem are defined in the table.
¶ Some centers will not use a catheter flow study but rather go straight to MRI. In our experience, a catheter flow study often reveals causes of obstruction (such as omental wrap) that are not seen on MRI. A catheter flow study requires the administration of iodinated contrast via the catheter. Refer to UpToDate topic on Management of hypervolemia in peritoneal dialysis patients for review.
Δ MRI can distinguish peritoneal fluid from surrounding tissue without gadolinium. CT requires the administration of iodinated contrast via the catheter. Refer to UpToDate topic on management of hypervolemia in peritoneal dialysis patients.
◊ Sodium sieving is a characteristic of a normal PET whereby the initial D/P sodium decreases due to rapid water transport across the peritoneal membrane. The loss of sodium sieving suggests an isolated defect in water transport.
§ Type 1 ultrafiltration failure: Rapid membrane solute transport causes early equilibration and dissolution of osmotic gradient. Type 2 ultrafiltration failure: Decreased aquaporin function results in isolated defect in water transport. Type 3 ultrafiltration failure: Loss of effective peritoneal membrane surface area due to sclerosis or adhesions causes low permeability to both solute and fluid.