Ultrafiltration during dialysis is influenced primarily by which factor?

Ultrafiltration during dialysis is primarily influenced by transmembrane pressure. This pressure difference drives the movement of excess fluid from the patient's blood across the dialyzer membrane into the dialysate. Essentially, the transmembrane pressure creates a force that pushes water out of the blood, helping to remove the extra fluid that patients on dialysis cannot eliminate naturally due to their kidney function being compromised.

The transmembrane pressure is adjusted by varying the pressure applied on the blood side of the dialyzer and by the pressure in the dialysate compartment. A higher transmembrane pressure promotes greater ultrafiltration, leading to effective fluid removal, which is vital for maintaining patient's electrolyte balance and blood pressure.

Other factors mentioned, such as concentration gradient, dialysate temperature, and solute drag, play roles in the overall dialysis process and solute removal but do not primarily govern the mechanism of ultrafiltration. Concentration gradient affects solute diffusion rather than fluid removal, dialysate temperature can influence the efficiency of the dialysis but not directly ultrafiltration, and solute drag is more related to the movement of solutes along with the fluid rather than fluid movement itself. Thus, transmembrane pressure stands out as the critical factor for ultr