This document provides information about arterial blood gas (ABG) analysis, including defining ABG, listing its components and normal values, discussing indications for the test, and interpreting abnormal values. It describes how ABG analysis can be used to evaluate respiratory and acid-base conditions and effectiveness of oxygen therapy. The document also outlines acid-base imbalances like respiratory acidosis and alkalosis and metabolic acidosis and alkalosis, and how the body compensates for these imbalances through respiratory and renal systems.

1. Mr. Sarathkumar
Potential C.I.
SDU, Farwaniya
ARTERIAL BLOOD GAS
ANALYSIS

2. OBJECTIVES
By the end of the class S/N will be able to:
1. Define Arterial Blood Gases analysis.
2. List down the indications for ABG analysis.
3. Mention the normal ABG values.
4. Determine the components of ABG.
5. Interpret the abnormal values of ABG.

3. INTRODUCTION
Interpreting an arterial blood gas (ABG) is a crucial skill
for physicians, nurses, respiratory therapists, and other
health care personnel.
ABG interpretation is especially important in critically
ill patients.

4. DEFINITION
Is a test that analyses the arterial blood for oxygen (pO2) &
Carbon Dioxide (pCO2), bicarbonate content (HCO3) &
hydrogen ion concentration (pH).

5. PURPOSE
To evaluate the respiratory conditions that affect the lungs
To determine the effectiveness of oxygen therapy
To provide information about the body’s acid – base balance
To assess the lung & kidney function & the metabolic state of
the body

6. INDICATIONS
Any respiratory distress/failure (acute or chronic).
Any severe illness which could lead to an acidotic
state e.g :-
Cardiac failure, liver failure, renal failure.
Hyperglycemic state (Ketoacidosis).
Sepsis.
Burns.
Poisons/toxins.
Assessment of response to interventions such as
ventilation.

7. An ABG test requires that a small volume of blood be drawn from
the radial artery with a syringe and a thin needle,] but sometimes
the femoral artery in the groin or another site is used. The blood
can also be drawn from an arterial catheter.

8. ALLENS TEST
oThe radial artery is located by palpation and then compressed
with three digits.
oThe ulnar artery is similarly located and then compressed with
three digits for 30 secs.
oWith both arteries compressed, the subject is asked to clench and
unclench the hand 10 times.
oThe hand is then held open.
oThe palm is observed to be blanched.
oThe ulnar artery is released and the time taken for the palm and
especially the thumb and the ulnar eminence to become flush is
noted.
oThe test is then completed with the radial artery tested in a
similar fashion .

11. ABG – PROCEDURE AND PRECAUTIONS
• Ensure no air bubbles.
• Air bubble + blood = Po2 PCo2.
• ABG syringe must be transported at the earliest to the
laboratory for EARLY analysis via COLD CHAIN.
• Patients body temperature affects the values of PCo2 & HCO3.
• ABG sample should always be sent with relevant information
• Sample contains too much heparin (liquid heparin dilutes the
sample, and causes pH changes)

12. • pH
• pCO2
• HCO3
• pO2
• BE
COMPONENTS OF ABG
mmHg value = kPa value x 7.50062

13. pH
Plasma pH is an indicator of hydrogen ion (H+)
concentration.
Normal pH of blood: 7.35 – 7.45
Acidosis-The greater the H+ concentration, lesser than 7.35.
Alkalosis-The lower the H+ concentration, higher than 7.45.

15. The body is very sensitive to its pH.
Outside the range of pH that is compatible with life, proteins are
denatured and digested, enzymes lose their ability to function,
and the body is unable to sustain itself.

16. pCO2
Partial pressure of Carbon dioxide dissolved in the blood.
Normal range is 35-45 mmHg. (4.6 to 6.0 kPa)
Respiratory Component of ABG.
pCO2 > 45 – Acidosis
pCO2 < 35 – Alkalosis

17. HCO3
Calculated amount of bicarbonate in the blood stream.
Normal range is 22-26 mEq/L.
Metabolic component of ABG
HCO3 < 22 – Acidosis
HCO3 > 26 – Alkalosis

18. pO2
The partial pressure of oxygen dissolved in arterial blood
Normal range is 80-100 mmHg (10.5 to 13.5 kPa)
BE(Base excess)
Base excess beyond the reference range indicates metabolic
alkalosis if too high (more than +2 mEq/L) metabolic
acidosis if too low (less than −2 mEq/L)

21. HOMEOSTASIS
The body normally maintains a steady balance between acids
produced during metabolism and bases that neutralize and
promote the excretion of the acids(homeostasis)
Homeostatic mechanisms keep pH within a normal range

22. ACID-BASE REGULATION
Acid–base homeostasis is maintained by
multiple mechanisms involved in three lines
of defense
The first line of defense are the various
chemical buffers
The second line of defense is achieved by
the respiratory system
The third line of defense is the renal system

23. ACID BASE IMBALANCES
RESPIRATORY ALKALOSIS
RESPIRATORY ACIDOSIS
METABOLIC ACIDOSIS
METABOLIC ALKALOSIS

24. RESPIRATORYALKALOSIS
• Expelling too much CO2 due to tachypnea.
pH > 45
pCO2 < 35

25. CAUSES
TACHYPNEA
T emperature rise
A spirin toxicity
C ontrolled mechanical ventilation
H yperventilation
HYsteria
P ain
P regnancy
N eurological injuries
E mbolism
E dema
A sthma

27. COMPENSATION
• Kidneys tries to excrete bicarbonate (HCO3) to decrease pH.

28. NURSING INTERVENTION
Teach breathing techniques(slow down breathing, holding
breathing, rebreathing into a paper bag)
Watch for serum Ca and K levels
If on mechanical ventilator, watch for hyperventilation

29. pH < 7.35
pCo2 >45
RESPIRATORYACIDOSIS
• CO2 retention from hypoventilation

30. CAUSES
D.E.P.R.E.S.S.
Drugs
Diseases of neuromuscular system
Edema
Pneumonia
Respiratory centre
Emboli
Spasm of bronchial tube
Sac elasticity of alveolar sac

32. COMPENSATION
Kidneys conserve bicarbonate and secrete increased
concentration of hydrogen ion into the urine

33. NURSING INTERVENTION
Encourage coughing and deep breathing
Hold respiratory depression drugs
Watch for hyperkalemia and ECG changes
Administer O2 as required according to physician orders
Provide respiratory therapy for asthma, COPD, emphysema
Administer bronchodilators and antibiotics as per dr orders
Prepare for mechanical ventilation in the case of respiratory
depression

34. METABOLIC ACIDOSIS
Condition that occurs when the body produces excessive
quantities of acid or when the kidneys are not removing
enough acid from the body.
acid production:
• Diabetic ketoacidosis - HCO3 to go down.
acid excretion:
• Renal failure – wastes are not filtered; bicarbonate can’t regulate the
imbalance.
Loss of too much bicarbonate
-Diarrhea

35. CAUSES
A.C.I.D.O.T.I.C
• Aspirin toxicity
• Carbohydrates not metabolized (due to lack of O2)
• Insufficiency of kidneys
• Diarrhoea,DKA
• Ostomy drainage
• FisTulas
• Intake of high fat diet
• Carbonic Anhydrase Inhibitor
(Diamox)

37. COMPENSATION
• The Respiratory System INCREASE respiratory rate to expel
CO2 (acid) (Kussmaul’s deep rapid breaths in DKA).

38. NURSING RESPONSIBILITIES
• Watch for respiratory distress, electrolyte disturbance
(hyperkalemia and hypokalemia)
• Monitor for seizure
• If patient has renal failure, monitor intake and output, lab values
for creatinine, electrolytes etc.
• If patient is in DKA, monitor the blood glucose level

39. METABOLICALKALOSIS
There is an increase in Bicarbonate due to excessive loss of acid.
pH > 7.45
HCO3 > 26

40. CAUSES
A.L.K.A.L.I
 Aldosterone production excessive(hyperaldosteronism)
 Loop diuretics(urine output and H ion loss)
 Increased AlKali increased
 Anticoagulation use(citrates)
 Loss of fluids(vomiting, NG suctioning)
 Increased soda bicarbonate administration

42. COMPENSATION
• The Respiratory System DECREASE respiratory rate to
RETAIN CO2.

43. NURSING INTERVENTIONS
• Administer antiemetics for
vomiting
• Stop nasogastric and oral
suction, if unavoidable
measure the amount of
aspirate
• Stop diuretics and watch
for K
• Watch for respiratory
distress(CO2 )

45. COMPENSATORY MECHANISM
It is accomplished using delicate
‘buffer mechanisms’
between the respiratory & renal systems.
•Fully compensation
•Partial compensation
•No compensation

48. Disorder Characteristics Selected situations
Respiratory acidosis with
metabolic acidosis
↓in pH
↓ in HCO3
↑ in PaCO2
•Cardiac arrest
•Intoxications
•Multi-organ failure
Respiratory alkalosis with
metabolic alkalosis
↑in pH
↑ in HCO3-
↓ in PaCO2
•Cirrhosis with diuretics
•Pregnancy with vomiting
•Over ventilation of COPD
Respiratory acidosis with
metabolic alkalosis
pH in normal range
↑ in PaCO2,
↑ in HCO3-
•COPD with diuretics, vomiting, NG suction
•Severe hypokalemia
Respiratory alkalosis with
metabolic acidosis
pH in normal range
↓ in PaCO2
↓ in HCO3
•Sepsis
•Salicylate toxicity
•Renal failure with CHF or pneumonia
•Advanced liver disease
Metabolic acidosis with
metabolic alkalosis
pH in normal range
HCO3- normal
•Uremia or ketoacidosis with vomiting, NG
suction, diuretics, etc.
Selected mixed and complex acid-base disturbances

49. To diagnose an acid-base imbalance, you need to ask yourself
three questions:
1. Does the pH indicate acidosis or alkalosis?
2. Is the cause of the pH imbalance respiratory or metabolic?
3. Is there compensation for the acid-base imbalance?

50. ABG problems can be solved work using
the tic-tac-toe method

51. ABG problems can be solved work using the
tic-tac-toe method
• The column that the pH is tells you acidosis, or alkalosis.
• The relative positions of the pH, PaCO2, & HCO3- reveal the
origin of any acid base imbalance:
If the pH and PaCO2 fall in the same column – other than
normal – the problem is respiratory.
If the pH and HCO3- fall in the same column, the problem is
metabolic.

53. Reference
PH = 7.23
PCO2 = 60 mm of Hg
HCO3 = 34 meq/L
Example - 1
Answer = Respiratory Acidosis, Partially Compensated

54. Reference
PH = 7.21
PCO2 = 50
HCO3 = 28
Example - 2
Answer = Respiratory Acidosis, Partially Compensated

55. Reference
PH = 7.53
PCO2 = 23
HCO3 = 18
Example - 3
Answer = Respiratory Alkalosis, Partially Compensated.

56. Reference
PH = 7.20
PCO2 = 38
HCO3 = 17
Example - 4
Answer = Metabolic Acidosis, Uncompensated

57. Reference
PH = 7.30
PCO2 = 30
HCO3 = 17
Example - 5
Answer = Metabolic Acidosis, Partially Compensated

58. Reference
PH = 7.48
PCO2 = 42
HCO3 = 35
Example - 6
Answer = Metabolic Alkalosis, Uncompensated

59. Reference
PH = 7.50
PCO2 = 47
HCO3 = 27
Example - 7
Answer = Metabolic Alkalosis, Partially Compensated

60. PH PCO2
(mmHg)
HCO3
(meq/L)
7.21 60 24
7.48 28 20
7.50 29 24
7.28 40 18
7.48 42 30
Diagnosis compensation
Respiratory
acidosis
No compensation
Respiratory
alkalosis
Partial
compensation
Respiratory
alkalosis
No compensation
Metabolic acidosis No compensation
Metabolic
alkalosis
No compensation

61. In case of a complete compensation
• If pH is within the normal range but the other parameters are
not, you’re looking at a case of complete compensation.
• You will need to do one extra step to diagnose the origin of the
imbalance.
• You will be noting two pH values on the grid….

62.  Record the one in the normal range as “pH(1)”
 Recalculate pH using the exact midpoint of the normal range, or
7.40, for your reference point.
Thus, a pH of less than 7.40 would indicate acidosis, & a pH
greater than 7.40 would be alkalosis
 Note this adjusted pH in the appropriate box as “pH(a)”

63. Reference
PH = 7.36
PCO2 = 50
HCO3 = 34
Example - 7
Answer = Respiratory Acidosis, with complete
Compensation
7.40
acidosis alkalosis
pH
(1)

64. kPa to mmHg Conversion
Using the values for each in SI pressure units, any pressure in
kilopascals can be converted to millimeter of mercury units using
the conversion factor below:
• 1 mmHg = 133.322 Pascal's (Pa)
• 1 kPa = 1000 Pascal's (Pa)
• mmHg value x 133.322 Pa = kPa value x 1000 Pa
mmHg value = kPa value x 7.50062

65. CONCLUSION
• Measuring ABG can be useful adjunct to the assessment of
patients with either acute or chronic diseases. When combined
with patient’s clinical features, blood gas analysis can facilitate
diagnosis and management. Nurses play an important role as
they use considerable time in drawing, documenting, reporting
and interpreting blood gases.

67. • https://www.sciencedirect.com/topics/medicine-and-
dentistry/renal-compensation
• https://study.com/academy/lesson/how-the-kidneys-
regulate-acid-base-balance.
• htmlhttps://www.anaesthesiamcq.com/AcidBaseBook/ab4
_5.php
• https://www.thoracic.org/professionals/clinical-
resources/critical-care/clinical-education/abgs.php
• https://courses.lumenlearning.com/boundless-
ap/chapter/acid-base-balance/
• https://en.wikipedia.org/wiki/Acid%E2%80%93base_home
ostasis