Influence of peritoneal residual volume on the results of the peritoneal equilibration test. Prospective study.

BACKGROUND: Categorization of the capacity of ultrafiltration during a peritoneal equilibration test (PET) is a usual step during the monitoring of peritoneal transport characteristics of Peritoneal Dialysis (PD) patients. Quantifying the peritoneal residual volume (Vr) after the dwell preceding the PET (Vrpre) and at the end of the test (Vrpost) could help to improve the accuracy of the estimation of this variable.

METHOD: Following a prospective design, we calculated Vrpre and Vrpost in 116 patients, incident or prevalent on DP, who underwent one or two (n = 27) PET with 3,86/4,25% glucose-based PD solutions and complete drainage at 60 min. We evaluated the consistency of Vr by comparing Vrpre and Vrpost, as also these two parameters in repeated tests. We scrutinized potential associations between demographic and clinical factors, on one side, and the amount of Vr on the other, as also the impact of correcting ultrafiltration during PET for Vr on the categorization of the capacity of ultrafiltration.

RESULTS: As a mean, Vrpost was larger than Vrpre. Consequently, correction of ultrafiltration for Vr resulted in significantly higher values than those obtained according to the standard procedure (494 vs. 449 mL, p < 0,0005). We disclosed marked inconsistencies for different estimations of Vr in the same patients (Vrpre vs Vrpost and repeated PET studies). Moreover, no demographic or clinical variable was able to predict the amount of Vr. We observed a significant deviation (>200 mL) between both methods of estimation of the capacity of utrafiltration in only 12,9% of the patients. However, 21,1% of the patients categorized as cases of ultrafiltration failure according to the standard procedure did not maintain this condition after correction for Vr.

CONCLUSIONS: Correction for Vr of the capacity of ultrafiltration during a PET carries, as a mean, a minor impact on the categorization of this parameter. However, the results of the test can be significantly affected in 12,9% of the cases. We have been unable to detect demographic or clinical predictors of Vr, which suggests a random component for the mechanics of single peritoneal exchanges. We suggest that Vr should be estimated at the time of categorizing the capacity of ultrafiltration, whenever inconsistencies during serial PET studies are detected.