1. ARTERIAL
BLOOD GAS
ANALYSIS
D R . M AY U R I PAT E L
M . P T. ( C A R D I O - R E S P I R ATO RY )
A S S I S TA N T P R O F E S S O R

2. ABG- PROCEDURE AND
PRECAUTION
• Site (ideally)- Radial Artery
Brachial Artery
Femoral Artery
• Ideally- Pre-heparin ABG syringes
- Syringes should be FLUSHED with 0.5ml of
heparin solution and emptied.
DO NOT LEAVE EXCESSIVE HEPARIN IN THE SYRING
• ABGs are frequently used to monitor the condition of patients in
critical care setting and to help modify respiratory intervention.
A.B.G

3. BLOOD GAS REPORT AND
NORMAL VALUE
PARAMETERS
1. pH
2. PaCO2
3. HCO3
4. PaO2
NORMAL RANGE
1. (7.35 to 7.45)
2. (35 to 45 mmHg)
3. (22-26 mmol/L)
4. (80-100 mmHg)
A.B.G

4. HYDROGEN IONS
• H+ is produced as a by-product of metabolism.
• [H+] is maintained in a narrow range.
• Normal arterial pH is around 7.4.
• A pH under 7.35 or over 7.45 is compatible with life for only short
periods.
• Changes in pH are inversely related to changes in [H+]
A.B.G

5. HYDROGEN ION REGULATION
• The body maintains a narrow pH range by 3 mechanisms:
1. Chemical buffers (extracellular and intracellular) react instantly to
compensate for the addition or subtraction of H+ ions.
1. CO2 elimination is controlled by the lungs (respiratory system).
Decreases (increases) in pH result in decreases (increases) in PaCO2
within minutes.
1. HCO3- elimination is controlled by the kidneys. Decreases
(increases) in pH result in increases (decreases) in HCO3-. It takes
hours to days for the renal system to compensate for changes in pH.
A.B.G

6. CENTRAL EQUATION OF ACID-
BASE PHYSIOLOGY
• The hydrogen ion concentration [H+] in extracellular fluid is
determined by the balance between the partial pressure of carbon
dioxide (PaCO2) and the concentration of bicarbonate [HCO3-] in the
fluid. This relationship is expressed as follows:
[H+] in nEq/L = 24 x (PaCO2 / [HCO3 -] )
where [ H+] is related to pH.
A.B.G

7. HENDERSON-HASSELBALCH
EQUATION:
• pH = pK + log [ HCO3-]/ H2CO3
• The carbonic acid to bicarbonate ion relationship-a complete analysis
of acid-base balance is possible because the amount of hydrogen ion
acth1ty resulting from the dissociation of carbonic acid is controlled
by the interrelationship of all the blood acid, base and buffers. The
Henderson-Hasselblach equation defines pH in terms of this
relationship.
• pH = pK + log (HCO3-)/ s . PaCo2
s= coefficient of Co2 0.08
A.B.G

8. ARTERIAL BLOOD GAS
INTERPRETATION
RANGES
• PaO2 80 - 100 mm Hg
< 80 mm Hg = hypoxemia
< 60 mm Hg may be seen in COPD patients.
(Moderate hypoxemia)
< 40 mm Hg is life threatening.
(Severe hypoxemia)
• SaO2 93 - 100 % is a normal saturation
Hypoxia is decreased oxygen at the tissue level.
A.B.G

9. CONTI…
• pH:
• Negative log of H+ concentration.
• Normal range: 7.35 - 7.45
• Acidosis = pH less than 7.35
• Alkalosis = pH greater than 7.45
• A pH < 7.0 or > 7.8 can cause death
A.B.G

10. CONTI…
• PaCO2: partial pressure of carbon dioxide dissolved in the
arterial plasma.
• Normal: 35 - 45 mm Hg
• A primary respiratory problem is when PaCO2 is:
> 45 mm Hg = respiratory acidosis
< 35 mm Hg = respiratory alkalosis
A.B.G

11. CONTI…
• HCO3 (bicarbonate)
• Normal: 22 -26 mEq/L
• Regulated by the kidneys.
• A primary metabolic or renal disorder is
when the HCO3
< 22 = metabolic acidosis or
> 26 = metabolic alkalosis
A.B.G

12. FACTOR AFFECTING ABG
ANALYSIS
• It is estimated that after 60 years of age, the PaO2 decreases by 1 mm
Hg per year of age from
60 to 90 years.
• Exercise or any increase in activity from rest may result in increased
oxygen consumption for patients with cardiopulmonary dysfunction.
• During pregnancy, hormonal and mechanical factors have a negative
effect on cardiopulmonary function. During the last trimester, women
often observe shortness of breath and difficulty taking a deep breath
secondary to diaphragmatic encroachment.
A.B.G

13. CONTI…
• During sleep, there is a decrease in minute ventilation and a decreased
responsiveness to CO2 and hypoxemia.
• Low barometric pressure associated with high altitude significantly
decreases the amount of oxygen available to the individual.
• Increased temperatures (febrile state) can increase metabolism and
therefore increase oxygen consumption. Decreased temperatures can
decrease the oxygen consumption
A.B.G

14. REFERENCES
• Principle and practice of Cardiopulmonary physical therapy, 3rd
edition, Donna Frownfelter and Elizabeth Dean.
• Essentials of Cardiopulmonary Physical Therapy, 3rd edition,
Ellen hillegass.
• Cobb, J. P. (2003). Cellular injury and adaptation laboratory.
Washington University School of Medicine.
• Hansen, M. (1998). Pathophysiology: Foundations of disease and
clinical intervention. Philadelphia: Saunders.
• Huether, S. E., & McCance, K. L. (2002). Pathophysiology. St.
Louis: Mosby. A.B.G