Blood Gas Electrodes
Blood Gas Electrodes
Blood Gas Electrodes
Lactate
Haemoglobin
Working half
There
cells (where the Reference half cells
are 2
actual chemical
types
analysis occurs)
PH
PH is the negative logarithm to the base 10 of the
hydrogen ion concentration
(PH is a measure of the hydrogen ion activity in a liquid)
Base: H+ acceptor
SI Unit used to define the
acidity/ alkalinity of the
blood= [H+] expressed in
nmol.L-1
Hydrogen ion concentration is expressed in terms of PH
units measured using glass electrodes (can also be
calculated using the Henderson-Hasslebalch equation)
Normal Hydrogen ion concentration= 35-45nmol/L
Use of indicators
Based on the linear relationship between PH and log PCO2 over the
physiological range
5. CO2 Electrodes
METHODS USED TO ASSESS
OXYGENATION
Measure the O2 tension (PaO2)
by analysis of a gas bubble Saturation (SaO2) by
equilibrated with a blood sample/ photometric techniques
by using oxygen electrodes
Content of O2 (CaO2) by
vacuum extraction &
chemical absorption or by
galvanic cell analyser
Saturations & tension are necessary to define the dissociation curve
*Versatile
*Compact
DISADVANTAGES
A modified PH electrode
(It is a PH sensitive glass
electrode)
The PH sensitive glass is in
contact with a thin layer of
bicarbonate buffer
CO2 ELECTRODE
CO2 ELECTRODE
COMPONENTS
*A PH sensitive glass electrode with Ag:Agcl reference
electrode forming its outer part
• Sensitivity
Depends on the concentration of the solution
Maximum sensitivity- 0.01mmol/L Bicarbonate solution
MECHANISM OF ACTION
CO2 electrode amplifier should be able to
discriminate small changes (should be very sensitive)
*An oxygen-
permeable Teflon *A sodium chloride
membrane (or electrolyte solution
polypropylene) (or phosphate
separating the buffer stabilised
solution from the with KcL)
sample
MECHANISM OF ACTION
*Oxygen molecules cross
the membrane into the
electrolyte solution at a rate
proportional to their partial
pressure in the sample
Electrolyte Reaction:
NaCl + OH- = NaOH + Cl-
RESPONSE TIME
30-60 seconds
Problems in practice
• Transcutaneous electrodes
TRANSCUTNEOUS ELECTRODE
TRANSCUTNEOUS ELECTRODE
Advantages in
monitoring blood
gases non-invasively
Incorporat
Useful in
ea
infants,
heating
neonates
element
Similar principles to
those used in blood
gas analysers
Electrode is attached to the skin to form an airtight seal
using a contact liquid
*Less accurate