What are reasons why we always measure blood pressure before hemodialysis ?

Hemodialysis: During hemodialysis some of the blood is pumped outside the body into the dialysis machine. Typically the blood pressure drops during dialysis. If you start with too low a blood pressure, the pressure during dialysis could get dangerously low.

BP and dialysis: Hemodialysis (H) removes both wastes and fluid (F) that failed kidneys cannot. As F is removed on H, BP decreases due to the volume of F lost from the bloodstream. If the H patient has a low BP before the prescribed amount of F is removed, there may be problems with the BP during H. A low BP could also signify some occult blood loss or infection. Taking of the BP before H can identify a problem.