why blood pressure drops during dialysis

First, I would be wondering about whether her dry weight is correct. If her dry weight has been set too low and, thus, more fluid is being removed than her circulation is set to permit, then an exaggerated fall in blood pressure or a ‘crash’ is more likely. Certainly, in the general dialysis population, the removal of too much fluid – or, and I keep coming back to this point, its removal too quickly – is the commonest reason why blood pressure might fall or crash during dialysis.

You need to remember that patients change their base weight, just as you and I do. Just as we put on a kilo or two, and then take it off again, so, too, do dialysis patients. We, as the treating team, need to “roll” with these changes and make adjustments accordingly, otherwise we will be caught out by taking off too much fluid – or taking off too little. No patient sustains the same dry weight, week in, week out. Here, we are constantly looking at BP changes and other signs that might indicate a change in dry weight. This is probably the first thing I would be thinking about.

I am assuming that the BP you have given (140-160), is her pre-dialysis blood pressure. Though a little on the high side, this is not a blood pressure that would be troubling me too much as an entry (pre-dialysis) blood pressure – I would be more troubled by a blood pressure fall from this level to 94/50 during the dialysis treatment.

Many of these have relatively long durations of action, and may interfere with the capacity of the vasculature to respond to fluid removal, accentuating any impact that this fluid removal may have on blood pressure. We certainly would tried to avoid any blood pressure medication in the hours leading up to dialysis.

I have referred before to the heart and the impact of dialysis fluid removal on a heart that is maybe not as strong as it might be. Sick hearts do not well-tolerate big fluid shifts on dialysis. You might want to read back over previous answers to others if you are unclear about this.

And, of course … and I feel like an old and worn-out record as I repeat this again and again … the best way of avoiding blood pressure pertubations during dialysis is to lengthen the treatment. Rapid fluid removal is simply not well tolerated by many – particularly older patients and particulary patients with ‘dicky’ hearts (or is that an Oz-ism?) – and it is the speed of fluid removal that causes the majority of trouble for most dialysis patients. I cannot emphasise this fact enough. I know I go on and on about this, but it is a simple fact yet so many seem to ignore its’ importance. I also know that US dialysis patients tend to be trated with short, hard, aggressive dialysis regimens when compared to their European, Japanes and Australian and New Zealand ‘cousins’ – a factor in the differences we see between US and other national dialysis morbidities.

As for saline administration, I simply abhor ever having to do this to a dialysis patient – yet, how often does it seem that it happens? It is so counter-productive and counter-intuitive to give salt and water to a patient where part of the whole raison d’etre for the dialysis is the removal of them? Think of it! Here we are, trying to remove fluid (and in my view, most try to do this too fast – hence my insistence on lengthening the time of dialysis), and, because fluid is being removed too fast, the BP crashes. What do we do? We give saline! But, isn’t that exactly what we’ve been trying to remove? It is nonsensical! Absolutely nonsensical! I know that if the blood pressure falls, saline administration may be the only choice we have in terms of resuscitation – it is simply that that resuscitation with saline should not have been necessary – is never necessary – with a longer, slower, gentler dialysis.

We use cool dialysate here – our standard is 35.5C. This is certainly has been shown to lessen the incidence of hypotension during dialysis but again, the main game is slower dialysis. All other ‘ploys’ are tricks to avoid ‘ the elephant in the room’, dialysis time!

am surprised that you even raised the issue of bicarbonate versus acetate buffered dialysate. Certainly, we have not used acetate as a buffer here for more than 20 years. In the old days, when acetate was used as the buffer, it certainly was a contributor to circulatory instability during dialysis. Most dialysis systems and services would now use bicarbonate as a matter of course.

Midrodine (and other agents to support the blood pressure) are, in my view, agents of last resort, and not ones that I would think applicable to all but a tiny handful of patients – usually those with very advanced heart trouble.

In order, I would be ensuring she is not on pre-dialysis blood pressure medication, I would be trying to ensure that I had the correct dry weight estimate, I would be using cool, but not cold, dialysate and I would certainly be using bicarbonate buffered fluid. I would be avoiding drug therapy. Above all, however, I would be looking at lengthening the dialysis schedule.

I have written much on the issue of dialysis duration in these pages and I hope you will forgive me if I do not repeat these reasons here yet again. You may wish to turn back to previous questions and their answers – like the question posed by Jane late last year like “what factors determine optimal dialysis” – to reread some of this information.