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1. ABG Interpretation.
Ahmad Thanin

2. Introduction
• Interpreting an arterial blood gas
(ABG) is a crucial skill for
physicians, nurses, respiratory
therapists, and other healthcare
personnel.
• ABG interpretation is especially
important in critically ill patients.

3. Arterial blood gasses
provide information
about:
• Oxygenation
• Ventilation
• Acid-Base Balance.

4. 6 STEPS TO INTERPRET ABG RESULT:
Step 1
• analyze the PaO2
and the SaO2
Step 2
• analyze the pH
Step 3
• analyze the CO2
Step 4
• analyze the HCO3
Step 5
• match the CO2 or
the HCO3 with the
pH.
Step 6
• does the CO2 or the
HCO3 go opposite
direction of the pH?

5. normal values for arterial
blood gases
•7.35 – 7.45
pH
•35 – 45 mmHg
PaCO2
•80 – 100 mmHg
PaO2
•23 – 26 MEq/L
HCO3

6. When interpreting ABGs, the most
important values to look at are pH,
PaCO2, and HCO3.
The PaO2 only tells you if you
need to give a patient more
oxygen or if you need to cut
back on supplemental oxygen

7. STEP 1: ANALYZE THE PAO2
AND THE
SAO2
paO2 : Partial pressure of oxygen
molecules dissolved in plasma.
PaO2 is depend upon :
• Age
• FiO2
• Patm

8. PAO2:
If the patient is hypoxemic, the
low oxygen content in his blood
will be reflected in low PaO2 and
SaO2 values.
• Mild hypoxemia ,PaO2 of (60-79) mmHg.
• moderate hypoxemia, (40-59) mm Hg.
• severe hypoxemia, less than 40 mm Hg.

9. SAO2:
Normal range (96% - 100%)

10. P/F RATIO:
• the ratio of arterial oxygen concentration to the fraction of inspired
oxygen.
• It reflects how well the lungs absorb oxygen from expired air.
P/F ratio:
• mild (from 200 to 300),
• moderate (from 100 to 200)
• and severe (≤100 mmHg).
Based on Berlin definition:

11. O2 CONTENT :
Arterial oxygen content CaO2 is the amount of oxygen bound to
hemoglobin plus the amount of oxygen dissolved in arterial blood.
CaO2 = (Hgb x 1.36 x SaO2) + (0.0031 x PaO2)
Normal CaO2 ranges from (16 – 22) ml O2/dl.

12. SCENARIO:
A patient who presented to the ER with headache and dyspnea & h/o
exposure to smoke in a closed room. His first blood gases showed Pao2 80
mmHg, PaCO2 38 mmHg, pH 7.43. and oxygenation was judged normal.
He was sent out from the ER and returned a few hours later with mental
confusion.
This time both SaO2 and COHb were measured; paO2 79 mmHg,PaCO2 31
mmHg, pH7.36,SaO2 53%, carboxyhemoglobin 46%.

13. Answer
CO Poisoning

14. CO Poisoning
CO POISONING:
SaO2 = NORMAL “false value on pulse oximetry”
PaO2 = NORMAL
Symptoms:
Cherry red color instead of cyanosis (even
though there is Hypoxia), its because of the red
pigment of CO, headache and dizziness .

15. CARBOXYHEMOGLOBIN TEST:
Headache and nausea can begin when levels are 10 to 20%.
Levels > 20% commonly cause vague dizziness, generalized
weakness, difficulty concentrating, and impaired judgment.
Levels > 30% commonly cause dyspnea during exertion, chest
pain (in patients with coronary artery disease), and confusion.
Higher levels can cause syncope, seizures, and obtundation.
Hypotension, coma, respiratory failure, and death may
occur, usually when levels are > 60%.

16. STEP
2:
ANALYZE
THE
pH:
• This is usually the primary disorder
• Remember: an acidosis or alkalosis may
be present even if the pH is in the normal
range (7.35 – 7.45)

17. STEP 3: ANALYZE THE CO2

18. STEP 3: ANALYZE THE HCO3:

19. STEP 5+6: MATCH THE CO2 OR THE
HCO3 WITH THE pH.

20. Question:
• What is the relationship between the
direction of change in the pH and the
direction of change in the PaCO2?
Answer:
• In primary respiratory disorders, the pH
and PaCO2 change inapposite
directions; in metabolic disorders the
pH and PaCO2 change in the same
direction.

21. pH
Acidosis
Alkalosis
PaCo2
Respiratory
Metabolic
Anion
Gap
Acute Chronic
Inversely
Proportionally

22. IF IT’S RESPIRATORY: ACUTE OR CHRONIC?

23. COMPENSATED OR NOT:
The body compensates for acid-base imbalance through either the lungs or the kidneys.
If PaCO2 is abnormal and pH is normal, it
indicates compensation.
pH > 7.4 would be a compensated alkalosis.
pH < 7.4 would be a compensated acidosis.
Respiratory compensation Complete within 24hrs
Metabolic compensation Complete within several days
Both the respiratory or renal compensation almost never overcompensates.

24. PARTIALLY
COMPENSATED:
• With partially compensated ABGs, the body has
begun to correct the acid-base problem via either
the lungs or the kidneys.
• The pH has not returned to the normal range.

25. CASE 1A :
A patient’s ABGs pH= 7.30;
PaCO2=31 mmHg; PaO2=76
mmHG; HCO3=17 mEq/L.
First, look at the pH. What
does this pH value indicate?
Acidosis
Alkalosis

26. CASE 1B :
First, look at the pH. What
does this pH value
indicate?
Respiratory Acidosis
Metabolic Acidosis
Respiratory Alkalosis
Metabolic Alkalosis

27. CASE 1C :
A patient’s ABGs pH= 7.30;
PaCO2=31 mmHg; PaO2=76
mmHG; HCO3=17 mEq/L.
Answer
Partially Compensated
Fully Compensated
uncompensated

28. CASE 2 A :
A patient’s blood gases are pH=
7.35; PaCO2= 33;
PaO2= 88; HCO3= 18.
First, look at the pH. What
does this pH value indicate?
Acidosis
Alkalosis

29. CASE 2B :
First, look at the pH. What
does this pH value
indicate?
Respiratory Acidosis
Metabolic Acidosis
Respiratory Alkalosis
Metabolic Alkalosis

30. CASE 1C :
A patient’s blood gases are
pH= 7.35; PaCO2= 33;
PaO2= 88; HCO3= 18
Answer
Partially Compensated
Fully Compensated
uncompensated

31. IF IT’S METABOLIC: ANION GAP

32. CAUSES OF HIGH-ANION-GAP METABOLIC
ACIDOSIS
Elevated anion
gap represents
metabolic
acidosis

33. REFERENCES:
Interpreting Arterial Blood Gases :WILLIAM C. Pruitt CPFT, MBA,
AND MICHAEL JACOBS, RN, CCRN, CEN,MSN.
Interpretation of Arterial Blood Gases (ABGs) David A. Kaufman,
MD Chief, Section of Pulmonary, Critical Care & Sleep Medicine.
Clinical Blood Gases,2nd Edition, Assessment & Intervention:
W.Malley,Imprint:Saunders. ISBN:9780721684222
6 Easy steps to ABG analysis,E-booklet, David W. Woodruff, MSN,
RN-BC, CNS, CMSRN, CEN.