Running COLD

I kind of knew what was going on since you described the cold being used for low BP. Your post on the amount of fluid taken off in a short time (3 hours) basically answered the problem. Now right off I want to say I dont know you and all your medical issues etc. There could be a lot of pieces to the puzzle I am missing. Also I cant give you direct medical advice so this is just informational. That said--------This is what I see. ---------
You are taking off up to 3 kg fluid in 3 hours . You weigh 73 kg. At 3 kg per hour you are taking off 1000ml or 1 kg per hour. At your weight of 73 kg that works out to 13.7 ml/kg/hour. That is WAY above what Dr. Agar has written about that is safe. In effect you are crashing the system and your BP is dropping . So they are reacting to it. Even at 2 kg in 3 hours you are running at 9.13 ml/kg /hour which is too fast. I am basing this on the fine work of Dr. Agar in Australia . He wrote about this in Dec. 17, 2013 for the Home Dialyzer Network.
The following is from his writing------

"McIntyre has reported that the risk of myocardial stunning (perfusion failure of the myocardium that results from an excess UFR) becomes clinically threatening if the UFR exceeds 10 ml/kg/hr. This is a removal rate of 3-5 ml/kg/hr in excess of the plasma refill rate. In other words, and this is a difficult concept, if contraction of the intravascular volume exceeds the refill rate by just ~3-5 ml/kg/hr, watch out!

I think in 5's. I remember a plasma refill rate of 5 ml/kg/hr. Then I remember the threat-level for myocardial stunning is 5 ml/kg/hr more than the refill rate. Remember this, and you won't be too far out.

For any dialysis patient, multiply their ideal weight x 5 ml/hr for their plasma refill rate. Each ml/min of UFR above that = the approximate rate of plasma volume contraction, remembering that poor hearts poorly tolerate rapid volume contraction. Exceed a contraction rate >2 x the plasma refill rate, and any heart is threatened."

In other words he feels any speed of UF above 5ml/kg /hour is not good. It becomes dangerous above 10ml/kg/hour. The reason comes down to the fact that UF takes fluid from the blood plasma but much of the excess fluid is in the other compartments and needs to be drawn out . It has a rate limit of 5ml/kg/hour . So going faster pulls fliud out of the blood faster then it can replenish from the cells and interstitial tissue between cells where most of the excess fluid lies. This will drop blood pressure and stun the heart. I beleive that is what may be happening to you.

My question is , why is your dialysis so short?? 3 hours 3 times per week is only 9 hours. That forces you to pull fluid out very fast in such a short time. Dr. Agar again writes ideal time on machine weekly is at least 10% of total time or minimum 16.8 hours. You are way short. Is that your choice or the clinic? That may be your problem . Too short time and too fast UF.
Now again that is all opinion based on very limited facts about you. So take it for what its worth. If however I am correct, you are taking a big risk of damaging your heart and organs. I hope this helps.