Background: Increased intra-abdominal pressure (PIA) leads to venous congestion in splanchnic and adjoining circulations. The aim is to examine whether PIA in peritoneal dialysis (PD) affects the mobilization of extracellular fluid from the lower body in supine body position. Methods: Patients were studied during a regular peritoneal equilibration test (PET) in supine body position using multifrequency bioimpedance analysis to determine extracellular resistance and absolute volume overload (AVO) in wrist-to-ankle (W2A) as well as in ankle-to-ankle (A2A) configurations. Measurements were taken at baseline (T0) after draining the peritoneal cavity, at T1 shortly after filling with 2 L of standard dialysate, and at T2 before taking the 2 h PET samples. PIA was measured from the column height in the PD catheter. Extracellular resistance in the lower extremities (RL) was taken as half of the A2A resistance. Results: Eighteen patients (56 ± 15 years, 76 ± 21 kg, body mass index (BMI) 26.4 ± 7 kg/m2, 13 men) were studied. After having assumed a supine body position for the duration of 17, 77, and 155 min, AVO continuously decreased from 1.6 ± 1.3 (T0) to 1.2 ± 1.5 (T1) and 1.0 ± 1.4 L (T2). RL significantly increased from 238 ± 57 (T0) to 254 ± 62 (T1) and 264 ± 67 Ohm (T2). This increase was negatively correlated to BMI and PIA measured at any time point, but not to net ultrafiltration volume. Conclusions: Orthostatic fluid shifts from the lower limbs may take up to 2 h in supine PD patients, especially with high BMI and PIA because of venous congestion in splanchnic and adjoining circulations.

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