Understand the Difference Between Clinical Measured UF and Real UF.

The importance of ultrafiltration (UF) and fluid status in peritoneal dialysis has been increasingly aware of over the last two decades. There is growing body of observational evidence showing that low UF is related to unfavorable outcome especially in anuric patients. The other side of the problem of UF is excessive fluid removal could volume deplete patients and result in loss of residual renal function and overexposing the membrane to glucose unnecessarily. UF is a double-edged sword. The correct measure of UF is the bottom line of talking about target.

Measuring UF is supposed to be simple and straight forward. The most common way of measuring UF in clinical practice was to weight the effluent bag and minus the manufacture announced fill volume.

Until about 10 years ago, the society first aware that the measurement error in such way is not acceptable. Overfil (the actual volume of dialysate fill in the bag is more than announced) problem was raised from then.

However, there are several other problems around this issue. Firstly, when the product has just been produced overfill is different between manufactory.

Secondly, the overfill volume does change over transportation and storage. But it is not clear how big the change is.

Thirdly, most of the clinics weight the dialysate effluent rather than measure the volume in CAPD, although the specific gravity of dialysate is clearly not going to be 1g/ml.

Taking the fact measuring weight is much easier than measuring volume in CAPD, the question behind is to understand how big the difference is and consequently whether it is acceptable.

All the patients enrolled in the study would be asked to collect all dialysate effluent of the day of their routine peritoneal dialysis adequacy study and bring to the hospital. The exact weight of the bag for PET test (2.5% glucose concentration and dwell time of 4 hour) before and after the dwell and volume measured of the effluent. The dialysate electrolyte, glucose, protein and creatinine level would also be measured.