Arterial Blood Gases (ABG's)

1. ABGs Test
(Arterial Blood Gases)

2. Introduction
 Arterial blood gases(ABGs) are important routine investigation to
monitor the acid base imbalance of the patient.
 Blood for ABGs analysis can be obtained by arterial puncture
usually from radial and femoral artery.
 Bicarbonate helps in maintaining blood pH value.
 Kidney and lungs work in our body as compensatory
mechanism.
 The main purpose of the ABGs in which lungs are able to provide
adequate oxygen(O2) and remove carbon dioxide(CO2)
 As well kidney are able to reabsorb or excrete HCO3 (acid base
balance)

3. Recommendation
• Difficulty in breathing.
• infection (sepsis).
• Lung disease such as COPD or asthma.
• A head injury.
• Kidney failure.
• Drug overdose.
• Diarrhea or vomiting.
• Other serious illness.

4. Required material
 Gloves
 2-3ml Syringes with 20,23 and 25 gauze needles
 Heparin tube(1:1000)
 Bandages
 Alcoholic swab
 Antiseptic solution
 Local anesthesia
 Paper bag

5. Preparation of patient
 To record the temperature of the patient.
 Record the inspired oxygen concentration of patient.
 Heparnised the syringe to prevent blood clotting
 To reduce anxiety of the patient.
 Allen’s test

7. Sample Collection (procedure)
 Wash the hands and wear gloves.
 Place pillow under the patient’s wrist.
 Palpate the artery(radial, brachial to be punctured)
 Puncture the artery at the angle of 45-60 degree.
 The arterial blood rushes into the syringe with a great
force.
 We should with draw 2-3ml of the blood for sample.
 These blood draw into the heparin tube.
 Sample suck to ABGs machine.

9. Working principle of ABGs machine
 The blood that have been taken from the patient is introduced to
analyzer.
 The analyser aspirates the blood into the measuring chamber which
has ion selective electrode.
 The pH electrode compares the potential developed at the electrode
tip with the reference potential, the resulting voltage is proportional
to concentration of hydrogen ions.
 The PCO2 electrode is a pH electrode with a silicone rubber CO2
semi permeable membrane covering the tip. CO2 combines with
the water in the space between membrane and the electrode tip to
produce free hydrogen ions in proportional to partial pressure of
CO2. The voltmeter, although actually measuring hydrogen ions is
calibrated in pCO2.

10. Working
 For PO2 , oxygen permeates a polypropylene membrane and reacts
and reacts chemically with a phosphate buffer. The oxygen
combines with water in the buffer producing current in proportional
to number of oxygen molecules. The final result is the production of
OH– ions in the electrolyte and the removal of O2 molecules from
the solution. The current is measured and expressed as partial
pressure of oxygen.
O2 + 2H2O 4OH-
 After measurement the blood is automatically expelled into the
waste container and the sample path is cleaned, ready for next
sample.
 Results may be printed, displayed and sent to the Laboratory
Information system.

13. What measured in ABGs
 Oxygen saturation (O2 Sat) measures how much hemoglobin in your blood is
carrying oxygen. Hemoglobin is a protein in your red blood cells that carries
oxygen from your lungs to the rest of your body.
 Partial pressure of oxygen (PaO2) measures the pressure of oxygen dissolved
in your blood. It helps show how well oxygen moves from your lungs to your
bloodstream.
 Partial pressure of carbon dioxide (PaCO2) measures the amount of carbon
dioxide in your blood and how well carbon dioxide can move out of your body.
 pH measures the balance of acids and bases in your blood, known as your blood
pH level. The pH of blood is usually between 7.35 and 7.45. If it is lower than
that range, your blood is considered too acidic. If it is higher than that range,
your blood is considered too basic (alkaline).
 Bicarbonate( HCO3) is a chemical that helps prevent the pH of blood from
becoming too acidic or too basic.

14. Normal values of ABGs

15. Interpretation of ABGs
Metabolic acidosis Metabolic alkalosis
Respiratory acidosis Respiratory alkalosis
Hypoxia Hypoxemia
pH PaCO2 HCO3 Diseases
Respiratory
acidosis
low high normal Lung diseases,
including
pneumonia or
COPD
Respiratory
alkalosis
high low normal Lung diseases,
including
pneumonia or
COPD
Metabolic
acidosis
low normal low Kidney failure,
shock, diabetic
ketoacidosis
Metabolic
alkalosis
high normal high Chronic
vomiting, low
blood potassium

16. Error in Chemistry Laboratory
Errors are common occurrences in chemistry and there are three specific
types of errors that may occurring during performing tests in chemistry
Lab.

17. Examples

18. Human Error
Blunders are simply a clear mistake that causes an error
during performing tests in chemical laboratory. There
are possibility of error in three phases of laboratory such
as:
Pre Analytical Analytical Post Analytical
• Incorrect time/date
• Incorrect tube
• Incorrect volume
• Incorrect labeled
• Sent to wrong
laboratory
• Incorrect speed/time
of centrifuge
• Freezing
delay/forgotten
• Incorrect reagent
• Expired reagent
• Icterus/hemolytic/lip
edelipidemiae
• Incorrect calculated
• Decimal error
• Typing error
• Result without
patient id
• Deliver report to
wrong patient