Renal Replacement Therapy

[Ahenrynephnwo]

I am a dialysis nurse and have a patient that is on 2 hours of Sequential ultrafiltration followed by 1 hour of hemodialysis. He has a tunneled cathether for his therapy. When I start his treatment, he has good blood flow rates and all is good, but then about 30 minutes into the treatment, he starts to have high venous pressures and his machine alarms with low arterial pressure. He is heparinized so he is not clotting the system. I cannot understand why this is continually happening?? Is there more prone to clotting during ultrafiltration than with hemodialysis?? I have tried to research this, but it is so very broad... cannot find much information. Would appreciate any thoughts!!