Questions About PD
We thank you for your question. It looks as though at your PD unit you are using the standardized PET, which requires you to send the first sample of PD fluid after a long overnight dwell. Now, bear in mind, in 1987, when the PET was first described by Twardowski, all patients were on CAPD, therefore the standard overnight dwell time was around 8 hours (1). With the advent of automated peritoneal dialysis (APD), that changed. Most protocols now suggest an 8 – 12 hour dwell before the start of the standardised PET, which necessitates the patient changing from his/her usual APD prescription to an overnight CAPD exchange.
In a follow up study, Twardowski found that results for a PET were satisfactory with any preceding dwell time longer than 3 hours (when looking at small solute clearances, e.g. creatinine and urea) (2). With a longer preceding dwell, however, there will be a higher concentration of protein in the drained PD fluid (protein being a much larger molecule than creatinine, will move only slowly across the peritoneal membrane). According to Twardowski, the absence of an overnight exchange will be more problematic for an accurate standardized PET, than the length of the dwell preceding the PET (2). Thus, rather than focus on the length of time for the overnight dwell, it is probably most important to be sure the patient has had an overnight dwell and drains for at least 20 minutes, before beginning the actual PET.
- Twardowski ZJ, Nolph KD, Khanna R, et al. Peritoneal equilibration test. Perit Dial Bull 1987; 7:138–47.
- Twardowski ZJ, Prowant BF, Moore HL, et al. Short peritoneal equilibration test: impact of preceding dwell time. Adv Perit Dial 2003; 19:53–8.