The total pressure that exists across the dialyzer membrane is called which term?

• A. Arterial pressure
• B. Dialysate pressure
• C. Transmembrane pressure
• D. Venous pressure

Answer: (C)

Transmembrane pressure is the driving force for filtration across the dialyzer membrane. It represents the pressure gradient between the blood side and the dialysate side, typically calculated as the average blood-side pressure (often the mean of arterial and venous pressures) minus the dialysate pressure. This across-membrane pressure pushes water and solutes through the membrane, producing ultrafiltration and diffusion. The arterial and venous pressures describe pressures in the blood path, while dialysate pressure describes the pressure on the dialysate side; neither alone equals the across-membrane pressure—the combined gradient that actually moves fluid and solutes is the transmembrane pressure.