ANNA's Peritoneal Dialysis Special Interest Group (PD SIG) is excited to present this column, which focuses on peritoneal dialysis topics. We welcome your comments and suggestions.

 
The Peritoneal Dialysis Special Interest Group members have received many questions concerning the peritoneal equilibration test (PET) and methods for quantifying peritoneal dialysis (PD) adequacy. As a group, we have consolidated these inquiries into two questions. We hope this is helpful information for your daily practice. We look forward to other questions and ideas for future columns.

Question #1: When Should the PET
Be Performed?
The PET was first developed by Dr. Zbylut Twardowski, from the University of Missouri, to measure the solute equilibration of various solutes between dialysate and plasma (D/P) of the peritoneal membrane, the rate of absorption of glucose from the peritoneal cavity and the net ultrafiltration rate at 4 hours (Twardowski, 1987). The results of the PET (see Table1) will guide the clinician in developing individualized prescriptions and is useful in predicting the response to a specific modality (CAPD, CCPD, High Volume PD).

Current practice is to perform the PET 4 to 6 weeks after the initiation of peritoneal dialysis. This allows for healing of the catheter exit site, reduction of surgical inflammation to the peritoneal  membrane, and achievement of an acceptable fluid balance  (Burkart et al., 1996).

The next question frequently asked is when should the PET be repeated? One year? Two years? Several studies have documented individual patient’s membranes do not change over time. However, in select patients, it may change. For example, peritoneal dialysis solute transport increases during peritonitis and recovers  approximately 1 month after resolution of peritonitis. Long term exposure to glucose also may result in membrane changes. Therefore, it is recommended to monitor clearance and ultrafiltration (NKF, 2000).

Anecdotally, repeating a PET is often good practice when the patient has had repeated episodes of peritonitis, surgical injury to the peritoneum, or an unexplained clinical change.
We suggest that you confer with your individual nephrologists and medical directors to develop a policy for your PD unit. Some nephrologists have suggested performing a PET every 2 years.

 
Question #2: How should specimens for PD
adequacy studies be collected?
 
The two methods available are “batch” and “aliquot.”

Batch Method: CAPD

• Collect all drain bags for 24 hours.
• Weigh/measure effluent to determine 24-hour total volume.
• Combine all drained effluent in one large container.
• Mix well.
• Take sample for BUN, creatinine (check with your lab for the desired amount for the sample).

Aliquot Method: CAPD

Example:   #1   2700 ml
                 #2   2600 ml
                 #3   2750 ml
                 #4   2850 ml

• Note the total 24 hour volume: 10,900 ml.
• Take a  .1% sample from each bag (the volume of the bag is recorded in mls,and the decimal point is moved 3 places to the left… example: a .1% of 2700 mLs is 2.7)

    Example  #1    2.7 ml
          #2    2.6 ml
          #3    2.75 ml
          #4    2.85 ml

• Combine the samples together, mix well
• Send sample for BUN, creatinine.

• Instruct patient to collect APD drain volume in drain bag (instruct patient to bring entire drain bag to dialysis unit or PD nurse may make a home visit to obtain sample, or instruct patient to take a sample of the drain bag).
• Instruct patient to save drain bag and note treatment data from APD machine (nighttime prescription
• volume, initial drain and UF).
• Calculate 24 hour drain volume.
• Agitate drain fluid in bag to mix  well.
• Take an appropriate sample for lab and send for BUN and creatinine.

• IInstruct patient to collect APD drain volume in drain bag.
• Instruct the patient to save the drain bag from the manual exchange.
• Instruct patient to bring 200 cc from the APD drain bag and the entire manual drain bag to the dialysis unit, or PD nurse may do home visit to obtain sample.
• Instruct patient to note treatment data from APD machine (nighttime prescription volume, initial drain, and UF).
• Calculate 24 hour drain volume from APD and manual exchange.
• Agitate drain effluent in bag to mix well.
• Take a .1% sample of APD drain volume (e.g., total APD drain volume: 11,400 (.1%=11.4 mL).
• For the manual exchange (e.g., 2,600 mL  (.1%=2.6 mL)).

References
Burkart, J, Schreiber, M.,Korbet, S., Churchill, E., Hamburger, R.,Moran,J., Soderblom, R., & Nolph, K. (1996). Solute clearance approach to adequacy of peritoneal dialysis. Peritoneal Dialysis International, 16, 457-470.

National Kidney Foundation. (2000), KDOQI clinical practice guidelines for peritoneal dialysis adequacy. American Journal of Kidney Disease, 37, Suppl 1, s65-136.

Rodby, R., & Firanek, C. (2003). Aliqout versus batch sampling methods in measurement of peritoneal dialysis adequacy in patients receiving CAPD. Peritoneal Dialysis International, 23, 87-89.

Twardowski, Z. (1987). Peritoneal equilibration test. Peritoneal Dialysis Bulletin, 7, 138.