Active
Siemens Critical Care Analysers SOP
Version:
2.00
Author
:
D Harrison
Doc Manager
:
D Harrison
Authorised by
:
Kath Ash
ton
Signature
: .
Ver Date
:
03/08/09
Do not photocopy this document
Page
20
of 24
Last printed:
5 August 2009
( David Harrison )
DMS Ref
:
Document in Microsoft Internet Exp
lorer
APPENDIX C
ELECTROLYTE ASSAYS
Sodium
Principle of analysi
s
The sodium sensor is a half
-
cell that forms a complete electrochemical cell when combined with the external
reference sensor. The Na sensor contains a Silver/Silver Chloride wire surrounded by an electrolyte solution
with a fixed concentration of Na & Cl
ions
A glass membrane that is highly selective for sodium ions over other clinically encountered cations,
separates the sample from the electrolyte solution.
When sample comes into contact with the glass membrane the exchange of Na
+
ions generates a pote
ntial,
which is measured by a voltmeter. This reflects the Na
+
concentration when compared to the constant
potential generated by the reference electrode.
As the sample is not pre
-
diluted as with the routine laboratory analysers, this assay (direct ISE) i
s not subject
to pseudo dilution effect and therefore is the method of choice when paraproteinaemia or
hypertriglyceridaemia is suspected.
Reference range
135
145 mmol/l (Plasma)
Whole blood slightly lower (Reference range
not established)
Reporting range
: 100
200 mmol/l (400 series analysers)
70
200 mmol/l (800 & 1200 series analysers)
Interfering substances
The following substances were found to interfere with the Sodium assay:
-
Substance
Concentration tested
Level of int
erference
Dobutamine
5mg/dl
+6.0 mmol/l
Benzalkonium Heparin
> 50 mM
Heparine Leo
800
850 U/ml
-
12.6 mM
It is recommended that the sample be treated as mixed venous when Benzalkonium Heparin is used. Some
pulmonary artery catheters may also conta
in the Benzalkonium ion, which interferes with analysis.
Potassium
Principle of analysis
The potassium sensor is a half
-
cell that forms a complete electrochemical cell when combined with the
external reference sensor. The K sensor contains a Silver/Silv
er Chloride wire surrounded by an electrolyte
solution with a fixed concentration of potassium ions
Ionophore valinomycin immobilised in a plasticised PVC matrix forms the membrane that separates the
sample from the electrolyte solution. Valinomycin is a
neutral ion carrier that is highly selective for
potassium ions over other clinically encountered cations.
When sample comes into contact with the valinomycin membrane the exchange of K
+
ions generates a
potential, which is measured by a voltmeter. This reflects the K
+
concentration when compared to the
constant potential generated by the reference electrode
Reference range
3.5
5.0 mmol/l (Plasma)
Whole blood slightly lower (Reference range
not established)
Reporting range
: 0.50
15.0 mmol/l (
400 series analysers)
0.50
9.99 mmol/l (800 & 1200 series analysers)
