The driving force for ultrafiltration is the transmembrane pressure (TMP), which is determined by the mean hydrostatic pressures in the dialysate (Pd) and blood compartment (Pb), and by the oncotic pressure (Po) in the blood compartment, according to the equation TMP = Pb- (Po + Pd). the ultrafiltration coefficient is used to calculate the quantity of pressure that must be exerted across the dialysis membrane (´transmembrane pressure´) to generate a given volume of ultrafiltrate during a single dialysis session The effective pressure required to achieve a particular intradialytic weight loss is described as the transmembrane pressure (TMP)
It is possible that a small fraction of the negative pressure generated by the blood pump and the transmembrane pressure applied across the dialyzer is transmitted to the capillaries despite the dissipation of the transmembrane pressure in removing the PDF across the dialyzer