What sodium level to set? … aahh! … that opens a can of worms.
It is such a controversial topic and it so depends on the individual … and there-in lies the crux of my answer. What I amswer will be agreed or disagreed by as many as read it and there is no right answer. However, we do tend, whether for our convenience, our laziness, our lack of thought, our desperation, or our lack of understanding, to set both a ‘prescribed’ concentrate sodium and a machine sodium ‘setting’ for and across the dialysis service as a whole - on all machines, for all patients, in all rosters – and, then blushing, and with a sense of shame, look away!
There are two (2) sodium levels … the sodium level of the ‘mix’ that is in the manufactured concentrate (the ‘prescribed’) and the sodium that is dialed up on the machine itself (the ‘set’). In our NHD patients, we use a concentrate with a ‘prescribed’ level of 140 but also ‘set’ the machine at 140. I know this seems quite high – but, given the mean frequency of our NHD (5 nights/week) and the duration (8-9 hrs) and thus the low hourly UFR (mean 225-250), issues of high intra-dialytic weight gains and hypertension on the one hand or of UFR-induced intra-dialytic hypotension do not occur. If we were doing less frequent dialysis … say alternate night or 3 x week – even if still 8-9 hrs … we would likely shoot lower – say 136-138, but 140/140 seems to suit our long, frequent program.
If you are doing less frequent NHD – say 3 x week or alternate night, 136/136 would seem a fair approach.
There was a fad (back in the 1990s) for sodium modeling. This meant trying to work out, for any individual patient, what the set machine sodium level should be relative to the sodium of the concentrate, but this was fraught with problems, was time consuming, often failed to achieve an outcome and has dies a slow death – except from some devotees (to whom I take my hat off ) who still work at this.
We did it (sodium modeling) … we largely failed, or flagged – though by rights we shouldn’t have … and gave it away.
I don’t think Andrew Davenport would mind me copying in here an abstract from a paper he and his co-workers from the PanThames Renal Audit group published in Int J Artif Organs (May 2008 (31:5; 411-417) “ The importance of dialysate sodium concentration in determining interdialytic weight gains in chronic hemodialysis patients: the PanThames Renal Audit.
BACKGROUND AND OBJECTIVES:
There is controversy as to the optimum dialysate sodium to be used for hemodialysis patients, with reports of hypertension and increased interdialytic weight gains with high sodium dialysates and intradialytic hypotension and cramps with low sodium dialysates.
We analyzed the effect of different dialysate sodium concentrations during a one-week period in an audit of 2187 established patients regularly receiving dialysis three times a week. Patients were given general dietary advice to restrict dietary sodium intake, but no systematic assessment of dietary sodium intake was undertaken.
The prescription of a dialysate sodium concentration of 140 mmol/L and >140 mmol/L, was associated with greater interdialytic weight gains, 3.5% and 4.1% respectively, compared to 2.8% and 2.7% for those using dialysate sodium concentrations of 137 and 136 mmol/L, respectively (p0<.05).
The mean pulse pressure was greater patients dialyzing using a sodium of 140 mmol/L, compared to 136 mmol/L, 70 (13) vs 63 (15) mmHg (p<0.011).
In addition, 13.5% of patients using the highest sodium dialysate suffered symptomatic intradialytic hypotension requiring intravenous fluid resuscitation, compared to 2.7% who used the lowest sodium concentrate (p<0.05).
CONCLUSIONS: This analysis would support the use of lower dialysate sodium concentrations to aid in reducing interdialytic weight gains and subsequent intradialytic hypotension.[/I]
This abstract ‘nutshells’ the issues in dialysate sodium.
A higher set sodium … in Andrews’ abstract (above) they used 140+ as ‘high’ … will lead to the loss of less sodium (and water) during dialysis and thus a higher BP (hypertension) and a greater later interdialytic weight gain. As attempts are then made at the next dialysis to correct this greater weight gain, a higher UFR (not stated but inferred) is required, thus leading to a higher risk of intra-dialytic hypotension … and, my own addition (here) to this abstract would be that - there might also be a greater risk of myocardial ‘stunning’ as an association of that inter-dialytic BP drop.
But, as an aside, this was in conventional 3 x week facility-based dialysis … not the 8-9hr x 5-6 nights/week model we broadly embrace in our home NHD program.
A lower set sodium … in Andrews’ abstract they used 136 or 135 … reduced the inter-dialytic weight and, as a result of the lower required UFR during dialysis (inferred) a lower rate of intra-dialytic hypotension. Cramping on dialysis is, however, more likely at the lower set sodium level.
We don’t, in all but problematic patients, dabble in sodium modeling or individual sodium setting. Maybe we should. But, it can get messy. It can lead – especially in facility-based care where the same machine is used for different patients – to muck-ups if the sodium set for one patient isn’t changed for the next.
As for conductivity – we set 13.7-14.3 as our lower/upper limits with a conductivity aim of 14.
Not sure I can be more helpful with this one.