Impact of Body Composition on Intraperitoneal Pressure and Ultrafiltration in Peritoneal Dialysis

Abstract

Introduction: An increase in body mass index (BMI) raises intraperitoneal pressure (IPP), which in turn counteracts ultrafiltration (UF). However, BMI is not directly associated with UF, contrary to what might be expected. We examined these relationships in greater depth by breaking down BMI into fat tissue index (FTI), lean tissue index (LTI), and overhydration (OHI), assessed by bioimpedance spectroscopy (BIS). Methods: Two peritoneal equilibration tests (PETs) using 4.25%/3.86% dextrose (2 L and 1 L fill volumes) were performed in 76 unselected patients. IPP was measured repeatedly and BIS was conducted to calculate LTI, FTI, OHI and phase angle at 50 kHz (PhA). Results: IPP increased with intraperitoneal volume (empty: 7.8 cmH₂O; 1 L: 10.3 cmH₂O; 2 L: 12.2 cmH₂O) and correlated negatively with UF. BMI correlated positively with IPP but not with UF. FTI correlated positively with BMI and IPP and negatively with UF. LTI did not correlate with BMI or IPP but correlated positively with UF. These relationships were mirrored in aquaporinmediated free water transport (FWT). PhA mirrored LTI. Conclusions: The effects of BMI on IPP and of IPP on UF appear to be mediated by FTI, whereas LTI independently enhances UF. Aquaporin-mediated FWT shows similar associations. Routine assessment of IPP and body composition may help identify patients at higher risk for IPP-related UF impairment.