ABG test measures the blood gas tension values of the arterial partial pressure of oxygen, and the arterial partial pressure of carbon dioxide, and the blood's pH

1. Welcome to seminar
presentation
Dr. Ziaul Haque Rupom
IMO, NICU, SWMCH

2. Normal Acid base physiology
Acid base imbalance
Compensation
ABG and Understanding ABG
reports

3. ACID-BASE BALANCE
• Acid - Base balance is primarily concerned with two ions:
– Hydrogen (H+)
– Bicarbonate (HCO3
- )

4. ACID-BASE BALANCE
• Derangements of hydrogen and bicarbonate
concentrations in body fluids are common
in disease processes

5. ACID-BASE BALANCE
H+ ion must be maintained in
narrow ranges in order to be
compatible with living systems

6.  Negative log of the hydrogen ion concentration
Thus, pH = - log [H+ ]
pH

7. A very tight control is needed for normal metabolic
functions.
Hydrogen ions are the toxic end product of metabolism and
they adversely affect all physical and biochemical cellular
process in our body.

8. • pH changes have dramatic effects on normal cell function
– 1) Changes in excitability of nerve and muscle cells
– 2) Influences enzyme activity
– 3) Influences K+ levels

10. 10
The Body and pH
• Homeostasis of pH is tightly controlled
• Blood = 7.35 – 7.45
• < 6.8 or > 8.0 death occurs
• Acidosis (acidemia) below 7.35
• Alkalosis (alkalemia) above 7.45

11. ACIDS
• Physiologically important acids include:
– Carbonic acid (H2CO3)
– Phosphoric acid (H3PO4)
– Pyruvic acid (C3H4O3)
– Lactic acid (C3H6O3)

12. • Sources of Acids
– Glucose Metabolism
– Fat & Protein Metabolism
– Anaerobic Metabolism of Glucose & Fat

13. BASES
• Physiologically important bases include:
– Bicarbonate (HCO3
- )
– Biphosphate (HPO4
-2 )

14. • Sources of Bicarbonate Ions
– Breakdown of carbonic acid
– Intestinal absorption of ingested HCO3-
– Pancreatic production
– Movement of intracellular HCO3- into ECF
– Kidney reabsorption

15. NORMAL ACID–BASE BALANCE
The lungs and kidneys maintain a normal acid–base balance.
Carbon dioxide generated during normal metabolism is a
weak acid. The lungs prevent an increase in the Pco2 in the
blood by excreting the CO2 that the body produces. CO2
production varies according to the body’s metabolic needs,
increasing with physical activity.

16. The rapid pulmonary response to changes in the CO2
concentration occurs via central sensing of the Pco2 and a
subsequent increase or decrease in ventilation to maintain
a normal Pco2 (35-45 mm Hg). An increase in ventilation
decreases the Pco2, and a decrease in ventilation increases
the Pco2.

17. Compensation

18. Renal Mechanisms

21. Acid Base imbalance
Respiratory Acidosis
Respiratory Alkalosis
Metabolic Acidosis
Metabolic Alkalosis

22. Common Causes of acid-base disorder
in newborn
Metabolic Acidosis
 under perfusion
 anemia
 hypoxemia
 sepsis
 renal immaturity
 inborn error of metabolism
 acetazolamide use

23. Metabolic Alkalosis
 Iatrogenic – bicarbonate therapy
 Use of diuretics
 Following blood transfusion – citrate in blood gets
converted to bicarbonate
 Persistent vomiting – CAH
 Prolonged gastric aspiration
 Urea cycle disorder

24. Respiratory Acidosis
 Tube dislodgement
 Tube block
 Increase dead space – long ET tube
 Pulmonary interstitial edema
 Pulmonary air leak
 Collapse consolidation

25. Respiratory alkalosis
 Pulmonary disorder
 Thermal insult
 High altitude areas
 Fever
 Hyperventilation (due to heart disorder or other,
including improper mechanical ventilation)
 Vocal cord paralysis (compensation for loss of vocal
volume results in over-breathing/breathlessness).

26. Regulation of Acid – Base Imbalance
Three Systems in the body :
1) Buffers in blood .
2) Respiration through the lungs .
3) Excretion by the kidney .

28. Compensatory mechanism of A-B
imbalance
Metabolic Acidosis :
Compensation :
PH becomes normal but total CO2 decrease due to
hyperventilation

29. Metabolic Alkalosis :
Compensation :
PH becomes normal but total CO2 increase due to
hypoventilation

30. Respiratory Acidosis :
Compensation :
PH becomes normal but total CO2 increase due to
HCO3 generation by the kidney

31. Respiratory Alkalosis :
Compensation :
PH becomes normal but total CO2 due to increase
HCO3 excretion by the kidney

32. Arterial blood gas analysis

33. An ABG test measures the blood gas tension values of
the arterial partial pressure of oxygen, and the arterial
partial pressure of carbon dioxide, and the blood's PH. In
addition, the arterial oxygen saturation can be determined.
Such information is vital when caring for patients with
critical illnesses or respiratory disease. Therefore, the ABG
test is one of the most common tests performed on
patients in intensive-care units.

34. An ABG test can also measure the level of bicarbonate in
the blood. Many blood-gas analyzers will also report
concentrationsof lactate, hemoglobin,several electrolytes,
oxyhemoglobin, carboxyhemoglobin, and methemoglobin.

35. Three ways to measure acid-base
balance in the body :
• Blood PH
• Blood PCO2
• Blood HCO3

36. Assessment of A-B balance
Arterial blood Mixed venous blood
range range
pH 7.40 7.35-7.45 pH 7.33-7.43
pCO 40 mmHg 35 – 45 pCO2 41 – 51
pO2 95 mmHg 80 – 95 pO2 35 – 49
Saturation 95 % 90 – 99 Saturation 70 – 75
BE 2 BE
HCO3
- 24 mEq/l 22 - 26 HCO3
- 24 - 28

37. Indications of ABG in neonates
• Severe respiratory or metabolic disorders
• C/F of hypoxia or hypercarbia
• In ventilated new born
• Shock
• Sepsis
• Decreased CO
• Renal failure
• Ideally any baby on oxygen therapy

38. Sample collection sites
• Radial artery
• Umbilical artery
• Brachial artery
• Femoral artery

39. Things to do before taking sample
Ideally pre heparinised ABG syringes Syringe should be
flushed with 0.5 ml of 1:1000 heparin solution and
emptied. Increase heparin increase dilutional effect
decrease HCO3,PCO2. Syringe usually should have more
then 50% blood, but in some machine one-third may
acceptable

40. Things to do after taking sample
Ensure no air bubbles. Syringe must be sealed immediately
after withdrawing sample.
Air bubble + blood = increase PO2 decrease PCO2
ABG syringe must be transported at the earliest to the
laboratory for early analysis via cold chain.

41. ABG syringe and arterial blood

42. ABG collection technique

46. Steps of ABG analysis
1. What is the PH? Acidemia or Alkalemia?
2. What is the primary disorder present ?
3. Is there appropriate compensation?

47. 1. What is the PH? Acidemic or Alkalemic ?
If PH < 7.35 = Acidosis
If PH > 7.45 = Alkalosis

48. 2. What is the primary disorder present ?

49. 2.What is the primary disorder present ?
Pathology PH PCO2 HCO3
Respiratory
Acidosis
Respiratory
Alkalosis
Metabolic
Acidosis
Metabolic
Alkalosis

50. 3. Is there appropriate compensation?
Uncompensated – PH will abnormal + PCO2/ HCO3
abnormal ( only one )
Partially compensated – All will abnormal
Compensated – PH will normal + PCO2/ HCO3 will
abnormal (both )

54. Key massages
Arterial blood gas analysis plays an important role in
critically ill children with respiratory distress.
Many life threatening metabolic or respiratory conditions
co-exist making pH near normal where the role of serial
ABG estimation is indispensible.
Knowledge of ABG is essential for any physician who
handles a critically ill child.

55. THANK
YOU
ALL