This document provides an overview of arterial blood gas analysis. It discusses: - How arterial blood gas analysis measures pH and partial pressures of oxygen and carbon dioxide in arterial blood to assess acid-base balance and lung function. - The basics of pulmonary gas exchange where oxygen is supplied to cells and carbon dioxide is removed from blood by the lungs. - Key concepts like partial pressure and hemoglobin oxygen saturation that are important for understanding gas exchange. - The normal values for pH, partial pressures of oxygen and carbon dioxide, and how these are interpreted to diagnose acid-base imbalances and their respiratory or metabolic causes.

1. ARTERIAL
BLOOD GAS
ANALYSIS
By:- Dr. Rekha Marbate

2. CONTENT
• Introduction
• Basics of pulmonary gas exchange
• Partial pressure
• Physiology of gas exchange

3. INTRODUCTION
• Arterial blood gas [ ABG] analysis refers to the measurement of
pH and partial pressure of Oxygen [PaO2] and carbon dioxide
[PaCO2] in arterial blood.
• From these values we can assess the acid-base balance in blood
and how well lungs are performing their job of gas exchange.

4. BASICS OF PULMONARY
GAS EXCHANGE
• Our cells use oxygen (02) to generate energy and produce
carbon dioxide (CO2) as waste.
• Blood supplies cell with the O2 they need and clears the
unwanted CO2.
• This process depends on the ability of our lungs to enrich blood
with O2 and rid it of CO2

6. CARBON DIOXIDE
ELIMINATION

7. PARTIAL PRESSURE
 Partial pressure describes the contribution of one individual gas
within a gas mixture(such as air) to the total pressure.
 When a gas dissolve in liquid (e.g. blood), the amount dissolved
depends on the partial pressure.

10. HAEMOGLOBIN OXYGEDN
SATURATION
• Oxygenation is more complicated than CO2 elimination.
• first thing to realize that the PO2 does not actually tell us how
much O2 is in blood.
• It only measures free, unbound oxygen molecules- a tiny
proportion of the total
• 02 molecules in blood are bound to a protein called heamoglobin
Hb

11. NORMAL VALUES

12. ACID-BASE BALANCE
• The pH is a measurement of the acidity or alkalinity of the blood.
• It is inversely proportional to the number of hydrogen ions (H+) in
the blood. The more H+ present, the lower the pH will be.
• Changes in body system functions that occur in an acidic state
include a decrease in the force of cardiac contractions, a
decrease in the vascular response to catecholamines, and a
diminished response to the effects and actions of certain
medications.

13. THE RESPIRATORY
BUFFER RESPONSE
• CO2 is carried in the blood to the lungs, where excess CO2
combines with water (H2O) to form carbonic acid (H2CO3).
• The blood pH will change according to the level of carbonic acid
present.
• This triggers the lungs to either increase or decrease the rate and
depth of ventilation until the appropriate amount of CO2 has
been re-established.

14. THE RENAL BUFFER
RESPONSE
• In an effort to maintain the pH of the blood within its normal
range, the kidneys excrete or retain bicarbonate (HCO3-).
• As the blood pH decreases, the kidneys will compensate by
retaining HCO3- and as the pH rises, the kidneys excrete HCO3-
through the urine.

15. STEPS OF
INTERPRETATION
Step 1: Assess the pH to determine if the blood is within normal range,
alkalotic or acidotic. If it is above 7.45, the blood is alkalotic. If it is below
7.35, the blood is acidotic.
Step 2: assess the PaCO2 level.
Remember that with a respiratory problem, as the pH decreases below 7.35,
the PaCO2 should rise. If the pH rises above 7.45, the PaCO2 should fall.
Compare the pH and the PaCO2 values. If pH and PaCO2 are indeed moving in
opposite directions, then the problem is primarily respiratory in nature.

16. Step 3: assess the HCO3 value.
Recall that with a metabolic problem, normally as the pH increases,
the HCO3 should also increase. Likewise, as the pH decreases, so
should the HCO3. Compare the two values. If they are moving in the
same direction, then the problem is primarily metabolic in nature.

17. ACID BASE DISORDER

18. EXAMPLE

19. COMPENSATION
• When a patient develops an acid-base imbalance, the body
attempts to compensate.
• Remember that the lungs and the kidneys are the primary buffer
response systems in the body.
• The body tries to overcome either a respiratory or metabolic
dysfunction in an attempt to return the pH into the normal range.
• A patient can be uncompensated, partially compensated, or fully
compensated.

21. EXAMPLES

23. Thank you