Hemorrhagic risk does always exhist in hemodialysis patient. Usually I do not use unfrationated heparin, but low molecular weight heparin. At any rate when dialysis session starts blood pressure decreases
I think there is not an high cut off for hemodialysis patient. So you can use drugs if dyastolic is over 120 or systolic over 240 ONLY after dialysis starting IF values increase.
If you give drugs before dialysis and you use aggressive ultrafiltration blood pressure can abruptly fall down
some nephrologists advise to decrease BP to below 180 sys with Iv oral Nitroglycerine and then start hemodialysis . but as you said there isnt any cutoff for upper limit .