جامعة االنبار
كلية العلوم التطبيقية – هيت
قسم الفيزياء الحياتية
االجهزة الطبية
Blood Gas Analyzer
Mohammed Qasim Taha
Definition
• Blood gas analysis
• Also called Arterial Blood Gas (ABG) analyzer
• It uses 3 electrodes to test arterial blood
• Used in
1. Respiratory (breathing) therapy departments
2. Clinical and cardiopulmonary (heart and the lungs) labs
3. Critical care units, surgical suites
4. Physician offices, and hospital nurseries to monitor
patients’ acid-base balance and oxygen (O2)- carbon
dioxide (CO2) exchange, providing the clinician with
information to use in patient diagnosis and regulation
of therapy. 2
Purpose
Blood gas/pH analyzers measure:
1. The partial pressure of oxygen (O2) → po2
2. Carbon dioxide (CO2) gases → pco2
3. The (hydrogen ion concentration) p(h+)
4. Sodium, potassium, and calcium concentrations
• Values for PO2, PCO2 and PH reflect the
concentrations of these gases in arterial blood as well
as the concentration of hydrogenions (H+)
• hence, the state of respiration, metabolism and
body’s acid production of a patient can be diagnosed
3
Components of Blood Gas
Blood Gas
Oxygenation Ventilation Acid-Base
PaO2
SaO2
PCO2 pH
Sa: saturation
Pa: partial pressure
4
ABG Analyzer example
5
Calibration
• Calibration: with known concentrations of standard
buffers and calibrated solutions.
1. Gas mixtures with high and low concentrations of
O2 and CO2 are alternately admitted to the sample
chamber,
2. O2 and CO2 electrode responses are used to set
high and low points of the PO2 and PCO2 curves.
3. Calibrations are done by adjusting the electrode
response and are usually referred to:
• One level (either high or low)
• Two levels (both high and low)
• The electrode systems and the sample chamber are
located inside a temperature-controlled block
maintained at 37°C
6
Reference Electrode
•The reference electrode is
used in the measurement
of pH and electrolyte
parameters, located in the
pH/Blood Gas module.
Components
1. Pole: AgCl
2. Electrolyte: KCl
3. Permeable seal
7
pH electrode
•The pH measurement is
performed using two
separate electrodes:
1. Ph-measuring Electrode
2. Reference Electrode
•The pH-sensitive glass
membrane is located at
the tip and seals the inner
buffer solution with a
constant and known pH.
8
pH electrode
• A saturated electrolyte
solution (Potassium
Chloride) in the reference
electrode and a leaky
membrane permit current
flow from the reference
electrode through the
sample in the
measurement chamber to
the measuring electrode.
• The potential difference is
displayed on a voltmeter
calibrated in pH units. 9
pO2 electrode
• Oxygen electrode measures the
oxygen partial pressure in a
blood or gas sample.
1. Cathode: platinum
2. Anode: a silver/silver chloride
3. Electrolyte Solution: sodium
chloride, Cathode and anode
are placed in the electrolyte
4. Applied voltage: 700 mV
5. Permeable membrane:
(Plastic) designed to allow
only O2 to leak
10
pO2 electrode
11
Pco2 Electrode
• The pCO2 electrode is a combined
pH and Ag/AgCl reference
electrode mounted in a plastic
jacket, which is filled with a
bicarbonate electrolyte.
• The PCO2 electrode also contains
a spacer (usually a porous
membrane of nylon) that acts as a
support.
→ As CO2 diffuses through the
membrane and into the support,
The pH of the electrolyte changes
→ The output of this modified pH
electrode is proportional to the
PCO2 present in the sample. 12
Electrode Cartridges
13
Other Electrodes
•The K+ electrode is an ion-selective electrode
• Sensing Element is a PVC membrane containing a
potassium-neutral ion carrier.
• The Na+ electrode is an ion-selective electrode
• Sensing Element is a Na+-sensitive ceramic pin
contained in the tip of the jacket.
•The Ca++ electrode is an ion-selective electrode
• Sensing Element is a PVC membrane containing a
calcium-neutral ion carrier.
14
15
16
17
In-line (extracorporeal) monitors
• Connected to the patient’s existing arterial line
• These devices consist of a sensor, an arterial blood gas (ABG)
module, and a monitor.
Operation:
Blood is drawn into the sensor
→ Fluorescent dyes in the sensor detect the pH, PO2, and PCO2
levels and transmit light of a specific wavelength
The ABG module emits excitation energy
→ dyes transmit light of a specific wavelength (λ1) through a
fiber-optic cable to the instrument.
→ The dyes then emit light of a longer wavelength (λ2) and
transmit it to the instrument through the cable.
→The parameters are then determined by the difference in the
two wavelengths
18
In-line (extracorporeal) monitors
SensicathTM system consists of patented fiber optic technology in a sensor which
T.Elsarnagawy, MASH210, 311,2010 19
attaches directly to the patient’s arterial line
•Continuous intravascular blood gas monitoring
• This technique uses electrochemical and optical
detection methods; however, the measurements
are taken in vivo
20
Modern blood gas analyzers features
•Measure/time:
• pH (15 Seconds)
• Po2 (50 Seconds)
• Pco2 (30 Seconds)
•Have Monitor
•Analog Amplifier and digital control and storage
circuits
•Easy calibration
21
Basic Safety Consideration
When analysis is complete, the blood
specimen is disposed of in one of two ways:-
1. Most analyzers pump the specimen into a waste
container, and the system is flushed with a rinse
or wash solution.
2. Some newer units retain the specimen in the
disposable sealed reaction cartridge which is
then discarded.
22
Important Terminologies
1. Analysis time, sec: The time from sample
insertion to a displayed or printed result.
2. Calibration: The operator can initiate random
calibrations and calibrations during standby
mode.
3. Standby mode: Unit calibrates only when the
unit is in standby mode, otherwise it will
calibrate according to programmed intervals
23
Basic Work Specifications
1. The equipment should possess electrodes
with long life at least 2 years
2. Assessment of the instrument should be
provided by the company.
3. All results should be available within 3 min.
4. The results should be microprocessor
controlled and of latest technology version
24
Basic Work Specifications, cont.
5. The instrument should have facilities like
monitor screen, external keyboard, mouse,
and barcode reader
6. The instrument should have the capability to
interface a computer and a computer should
be supplied for data acquisition and patient
record with recommended software. The
system should have RS232 serial port.
7. Display language should have English
25
