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
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19
of 24
Last printed:
5 August 2009
( David Harrison )
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Document in Microsoft Internet Exp
lorer
APPENDIX B
CO
-
oximetry
This module, if present, measures Haemoglobin and other related compounds in whole blood at the same time as
blood gas analysis.
Principle of a
nalysis
The CO
-
oximeter measures haemoglobin and related compounds by passing polychromatic light through a lysed
sample of blood. The reflected light is measured at several wavelengths so differentiating between the
compounds according to their absorbanc
e spectra.
Interferences
CO
-
oximetry is affected by the presence of turbidity, bilirubin, cyanmethaemoglobin and dyes in the sample.
Haemoglobin
Haemoglobin is a tetrameric protein consisting of two pairs of polypeptide chains, each chain having
a haem
group containing one atom of Iron. Each molecule of Haemoglobin can bind up to four molecules of oxygen,
one at each haem group. Haemoglobin has a key role in the transport of oxygen from the lungs to the tissues.
Haemoglobins ability to bind & rel
ease oxygen depends on several factors:
-
pH, PCO
2
, PO
2
,
diphosphoglycerate concentration & temperature.
The presence of dyshaemoglobins such as carboxyhaemoglobin, methaemoglobin, sulfhaemoglobin may also
affect normal oxygen transport mechanism. Abnormal
concentrations of haemoglobin variants such as foetal
haemoglobin may also affect this.
The measure of total haemoglobin includes all these fractions of haemoglobin plus the oxygenated and reduced
forms.
Reference Range
12.0
18.0 g/dL
Oxyhaemoglobin
(O
2
Hb)
This is the fraction of haemoglobin that is reversibly bound to oxygen
Reference Range
94.0
97.0% (Arterial)
Deoxyhaemoglobin
(HHb)
Refers to the haemoglobin capable of binding oxygen (sometimes referred to as reduced haemoglobin)
Refer
ence Range
0.0
5.0% (Arterial)
Methaemoglobin
(MetHb)
Methaemoglobin is haemoglobin whose iron has been oxidized to
Fe
3+
and is unable to bind oxygen.
Reference range
0.0
1.5% (Arterial & Venous)
Carboxyhaemoglobin
(COHb)
Carboxyhaemoglobi
n is haemoglobin covalently bound to carbon monoxide.
Reference range
0.1
-
0.4% (venous or arterial, non smokers)
Air pollution and smoking may result in significantly higher levels than this.
