Figure 410

Equation to calculate the intraperitoneal residual volume. Residual volume is the volume of dialysate remaining in the peritoneal cavity after drainage over 20 minutes. The residual volume can be determined by knowing the dilution factor for solutes such as potassium, urea, and creatinine during the next instillation. The calculation of residual volumes is based on the assumption that the mixing of fluid in the peritoneal cavity is instantaneous and complete. This equation is used for the calculation, where Vin is instillation volume; S1 is solute concentration in pretest exchange dialysate; S2 is solute concentration in instilled dialysis solution; and S3 is solute concentration immediately after instillation (0 dwell time). The residual volumes by urea, creatinine, glucose, potassium, and protein are calculated and averaged for accuracy. The measurement of residual volumes is of limited clinical usefulness; however, it is of great value in a research setting in which accurate determination of intraperitoneal volume is required.

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