Fresenius Medical Care multiFiltrate, Инструкция по эксплуатации

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Chapter 7: Functional description
Fresenius Medical Care multiFiltrate IFU-EN-UK 15A-2015 7-25
7.3.2.4 Controlling the systemic acid-base status
Differences between the
various citrate procedures The corrective measures which can be employed to obtain a normal
acid-base status can differ considerably between the different citrate
anticoagulation methods. The following describes the procedure within
the Ci-Ca CVVHD and the Ci-Ca postCVVHDF treatments.
Background on the
resulting acid-base status
when using citrate
anticoagulation The citrate volume necessarily infused systemically is metabolised:
Here, for each complete metabolisation of the citrate ion to carbon
dioxide and water (or to other uncharged substances), three protons are
also metabolised by the process. This results in the production of three
bicarbonate ions. If not compensated, metabolic alkalosis would
develop.
Therefore, an adapted dialysate with 20 mmol/l bicarbonate is used in
Ci-Ca CVVHD and Ci-Ca postCVVHDF. This concentration is lower
than that of other common CRRT solutions. Dialysis to 20 mmol/l
bicarbonate leads to the removal of citrate in the filter and, to a certain
extent, of bicarbonate from the blood. Viewed in isolation, this removal
of buffer bases would lead to metabolic acidosis.
The required balance of buffer bases can be reached by balancing the
addition of buffer bases as an effect of systemic citrate infusion and the
removal of buffer bases as an effect of the dialysis against the adapted
dialysate. In practice, the processes are balanced so that the systemic
acid-base status of the patient is maintained within the required range.
The Ci-Ca postCVVHDF treatment is based on the Ci-Ca CVVHD. In
Ci-Ca postCVVHDF, a calcium-containing bicarbonate-buffered
haemofiltration solution is also infused in postdilution and filtration
across the membrane is increased accordingly. As the additional filtrate
is formed from the citrate-containing blood, a buffer base concentration
which is above the bicarbonate in the substitution fluid (for example,
35 mmol/l) is typically to be expected in the filtrate. (The buffer base
concentration is to be understood here as the total bicarbonate
concentration times a factor of 3 for the metabolism of weighted citrate
concentration, and in the same way as the concentrations of other
metabolisable anions, such as lactate, etc.) With this approach, the
additional convective component results in more buffer bases being
removed than infused – including citrate, among others. This can be
compensated for by increasing the citrate dose above the level required
for anticoagulation in the filter – to approx. 5.0 mmol/l. Since part of the
additionally infused citrate is systemically infused, this helps to equalise
the buffer base balance. One positive extra effect of the increased
citrate dose is that it inhibits a premature increase in the concentration
of ionised calcium following infusion of the calcium-containing
substitution fluid at the postdilution stage.