#470 Relationship between intraperitoneal volume and intraperitoneal pressure during peritoneal dialysis

Monitoring intraperitoneal pressure (IPP) has been advocated to quantitate intraperitoneal volume (IPV) during peritoneal dialysis (PD). The aim of this study was to investigate the relationship between IPV and IPP during a short PD dwell.

Thirteen patients (age 60.2 ± 13.8 years, 5 females, BMI 28.6 ± 7.8 kg/m²) were studied during a 2-hour dwell (2 L dialysate, 2.5% dextrose) in a sitting position. IPP was measured 4x per minute by a pressure sensor integrated in the Liberty Cycler (Fresenius Medical Care, Waltham, MA, USA). Segmental abdominal bioimpedance (Hydra 4200, Xitron Technologies, San Diego, CA, USA) was done concurrently to measure IPV. Serum and dialysate creatinine and glucose concentrations were measured before and after the dwell. Dialysate density (ρ) was measured by a handheld density meter (Mettler-Toledo, Columbus, OH USA). Ultrafiltration volume (UFV) was recorded by the Liberty Cycler. A simple physical model (IPP = ρ × h × g) was used to explore the relationship between IPP and IPV (Fig. 1). Based on the model, a change in IPP (ΔIPP) depends on the change of apparent dialysate height (Δh) and dialysate density (Δρ); g is the gravity constant. The apparent cross-sectional area (A) of the peritoneal cavity was calculated as IPV/h.

Average UFV was 0.31 ± 0.25 L (range 0.03 to 1.03 L). During the dwell, IPP decreased in 12 patients (UFV 0.03 to 0.49 L; Fig. 2) and increased in one (UFV 1.03 L). The IPP decrease (−3.81 ± 2.78 cmH₂O; −21.2 ± 18%, p < 0.01) was accompanied by a decrease of apparent h (−0.04 ± 0.03 m; −20.9 ± 18.5%, p < 0.01) and ρ (−3.41 ± 0.56 kg/m³; −0.34 ± 0.06%, p < 0.0001). In patients with a decrease in IPP, the apparent dialysate h decreased from 0.19 ± 0.04 to 0.14 ± 0.04 m, and the apparent A increased from 107.8 ± 23 to 154.7 ± 34 cm². In the patient with IPP increase, the apparent h increase from 0.14 to 0.18 m, and the apparent A from 138.4 to 164.6 cm². ΔIPP inversely correlated with Δρ (Fig. 3) and UFV (Fig. 4). Moreover, ΔIPP correlated with D/P creatinine (Fig. 5) and with D/D0 glucose (Fig. 6).

In this proof-of-concept study, a simple physical model was used to explore the relationship between IPP and IPV. Contrary to our expectation, we found that IPP declines in most patients during the dwell. Decrease in IPP is related to increase in the apparent cross-sectional area of the peritoneal cavity. We hypothesize that during the dwell additional spaces of the peritoneal cavity become accessible to IPV. To what extent this opening of peritoneal space is associated with membrane characteristics warrants further studies.

Figure 1:

Open in new tabDownload slide