ARTERIAL BLOOD GAS lecture and interpretation for every medical students.

1. ARTERIAL BLOOD GAS
ANALYSIS

2. Objective
I. Arterial Oxygenation
A. Hemoglobin
B. Bohr and Haldane Effects
C. Hemoglobin Dissociation Curve
D. Physiology of Arterial Oxygenation
E. Pathophysiologic Mechanisms of Hypoxemia
F. Cardiopulmonary Compensation for Hypoxemia

3. Objective
II. Reference Ranges and Interpretative Guidelines
III. Clinical Approach to Interpretation
IV. Hypoxemia and Oxygen Therapy
V. Obtaining Blood Gas Sample
VI. Blood Gas Analyzers
VII. Quality Assurance in Blood Gas Analysis

6. volume of oxygen carried
attached to Hb
vol% of O2 carried attached to Hb
=(Hb content)(1.34)(HbO2% sat.)
O2 content in vol%
• = (PO2)(0.003) + (Hb content)(1.34)(HbO2% sat)

7. Comparison bet. Bohr
Effect and Haldane Effect
Bohr Effect Haldane Effect
The effect of CO2 on uptake and
release of O2 from Hb molecule is
relatively mild.
The effect of O2 on uptake and release
of CO2 from Hb molecule
CO2 affecting the affinity of Hb for O2 O2 is affecting the affinity for Hb of
CO2
CO2↑ as oxyhemoglobin saturation
decreased
carrying capacity of blood for CO2 is ↓
as oxyhemoglobin saturation increased

8. Factors that can Alter affinity of
Hb in Oxyhemoglobin curve;
Shift to the right (decreases
affinity of Hb for O2)
Shift to the left (increases affinity
of Hb for O2)
↑PCO2 ↓PCO2
↑H+ ↓H+
↑temperature ↓temperature
↑ 2,3-DPG ↓2,3-DPG
↑ CO
Fetal Hb
Methemoglobin

9. pH compensation
• The levels of HCO3 and CO2 always change to keep the
pH within normal range.

10. ABG Interpretation

11. Normal Arterial Blood Gas
Values
pH 7.35 – 7.45
paCO2: 35 – 45 mm Hg
paO2: 80 – 100 mm Hg
HCO3: 22 – 26 mEq/L
BE/BD: - 2 to + 2
SpO2: > 95 %

12. Normal PaO2 levels
• Subtract 1 mm Hg from 80 mmHg for year over 60 to
determine normal PaO2 by age.
Age (year) PaO2 (mm Hg)
<60 80-100
60 80
65 75
70 70
75 65
80 60

13. Levels of hypoxemia
If PaO2 is:
•60 to 79 mm Hg mild hypoxemia
•40 to 59 mm Hg moderate hypoxemia
•<40 mm Hg severe hypoxemia

14. Assessment of Arterial
Oxygenation
Evaluation of Hypoxemia
Room Air (Patient < 60 y/o):
Mild: PaO2 60-79 mmHg
Moderate: PaO2 40-59 mmHg
Severe: PaO2 < 40 mm Hg

15. On Oxygen Therapy:
• Uncorrected hypoxemia:
PaO2 < 80 mm Hg
• Corrected hypoxemia:
PaO2 = 80 – 100 mm Hg
• Overcorrected hypoxemia:
PaO2 > 100 mm Hg
FiO2 (Fractional Inspired
Oxygen Concentration)

16. Inspired Oxygen to PaO2
Relationship
FiO2 Predicted Minimal PaO2
30 % 150
40 % 200
50 % 250
80 % 400
If PaO2 < minimal predicted (FiO2 x 5), the patient
can be assumed to be hypoxemic at room air.

17. Clinically Assess:
• Cardiac status
• Peripheral perfusion
• Blood oxygen transport mechanism
Assess 1 and 2 by the vital signs and PE.
If 1 and 2 are adequate, then only 3 can be
interfering with proper tissue oxygenation.

18. Indications for ABG
• Sudden dyspnea
• Cyanosis
• Abnormal breath sounds
• Sudden or unexplained tachypnea
• Heavy use of accessory muscles
• Change in ventilator setting
• CPR
• Diffuse infiltrates in c xray

19. Criteria for choosing site and
Technique for obtaining ABG samples
must be based on:
• Safety
• Accessibility
• Patient Comfort

20. Site for ABG
• Brachial Artery
• Radial Artery
• Dorsalis pedis
• Femoral Artery

21. ABG Sampling(radial
artery puncture)
1. Explain the procedure to the patient
2. Perform a modified allen’s test
3. Place a folded towel under the patients wrist to keep the
wrist hyperextended
4. Clean the puncture site with isopropyl alcohol (70%)
5. The practitioner must wear gloves for this procedure
6. Aspirate 0.5ml of 1:1000 solution of heparin into the
syringe using gauge needle. Pull the plunger of the
syringe back and forth so that the entire portion of the
syringe is exposed to the heparin

22. ABG Sampling(radial
artery puncture) 7. With the needle/ syringe in one hand, palpate the artery
with the other. The needle should enter the skin at a 45°
angle with bevel pointed up. The needle should be
advanced until blood is pulsating into the syringe
8. After 2 to 4 ml of blood has been obtained a sterile gauze
pad should be applied with pressure over the puncture sithe
for 3 to 5 minutes until bleeding has stopped.
9. Air bubbles should be removed from the syringe, since
they affect the blood gas levels. Air in the blood causes
increased PaO2 levels and decreased PaCo2 levels.
10. A cap or rubber stopper should then be placed over the
needle.to prevent air from entering the syringe.

23. ABG Sampling(radial
artery puncture)
11. The syringe is then placed on ice to slow the
metabolism and keep the ABG levels accurate.
12. The practitioner should record the ff:
a) patients name and room number
b)Fio2 level
c)If patient is on ventilator, record
d)Fio2, Vt, RR, Mode, PEEP,

25. Blood gas
contaminants
Parameters Excessive Heparin Air bubbles
pH ↓ or remain the same ↑
PCO2 ↓ ↓
PO2 May altered May altered
HbO2% sat May altered May altered
HbCO2% sat Will not altered Will not altered
Hb content ↓ Is not altered
HCO3 ↓ ↓
Base Excess ↓ ↓
Oxygen content May be altered Maybe altered

26. Blood gas
contaminants
*If insufficient heparin levels are used;
• Machine clotting is very likely;
• Results are questionable
*Saline and other IV solutions alter blood gas values in a
manner similar to that of heparin except that the pH may
also increase.

27. Significant Problems
• Arteriospasm
• Air or clotted blood emboli
• Anaphylaxis
• Patient or sampler contamination
• Hematoma
• Hemorrhage
• Trauma to the vessel
• Arterial occlusion
• Vasovagal response
• Pain

29. Recommended Equipment for
Percutaneous Arterial Blood
Sampling
• Standard precautions barrier protection (gloves, safety goggles)
• Anticoagulant(liquid sodium, lithium heparin, or dry lyophilized
heparin)
• Sterile glass or low-diffusibility plastic syringe(1 to 5 mL)
• Short-bevel 20 to 22-gauge needle with a clear hub(23 to 25
gauge for children and infants)
• Patient/sample label

30. • Isopropyl alcohol (70%) or providone-iodine (Betadine)
swabs (check patients for iodine sensitivity)
• Sterile gauze squares, tape, bandages
• Puncture-resistant container
• Ice slush (if specimen will not be analyzed within 15
minutes)
• Towels
• Sharps container
• Local anesthetic (0.5% lidocaine)*
• Hypodermic needle(25 to 26 gauge)
• Needle capping device

31. Blood gas analyzers
I. Oxygen Analyzers
• Analyzers that use the thermal conductiity of oxygen
• Analyzers that use Pauling’s principle of paramagnetic
susceptability of oxygen (Beckman D-2)
• Analyzers operating on the polarographic principle
(Clark electrode)
• Analyzers using galvanic cell

32. Blood gas analyzers
II. pH (Sanz) electrode
III. PCO2 (Severinghaus Electrode)
IV. Transcutaneous PO2 (TCPO2) and PCO” (TCPCO2)
monitoring
V. Spectrophotometric Analyzers

33. Blood gas analyzers
Type of units commonly used Spectrophotometric analyzers
are ;
• pulse oximeters
• CO oximeter
• Flame Photometer
• Capnography (end-tidal CO2 monitoring)

34. Blood gas analyzers
• Currently, blood gas analyzers have the following
capabilities
• 1. accurate measurement of pH, PCO2 and PO2
• 2. self calibration
• 3. accurate measurement of base excess or deficit
• 4.accurate measurement of plasma bicarbonate (HCO3)
• 5. correction for temperature
• 6. self troubleshooting abilities
• 7. automated blood gas interpretation

35. references • Egan’s fundamentals of respiratory care 9th edition,
Mosby, 2009
• The essentials of respiratory care third edition,
kackmarek9

36. THE END…