This document discusses arterial blood gas (ABG) analysis and interpretation. It covers: - Why ABGs are important for clinical insight and picking up issues like hypercarbia that pulse oximetry cannot. - Key principles like acid-base balance, recognizing simple vs. complex disorders. - When to request ABGs, such as for serious illness, respiratory distress, or suspected metabolic issues. - Factors that can influence ABG results like medications, electrolytes, and compensation time. - Ten "commandments" for proper ABG technique, analysis, and interpretation in the clinical context. - Several case examples are presented and analyzed to demonstrate applying the commandments.

1. ABG in Clinical Practice
Soumya Ranjan Parida
Basic B.Sc. Nursing 4th
year
Sum Nursing College

2. • Why should I learn ?
• What should I know ?
• When to ask for ABG ?
• Hasn’t Pulse oximeter replaced ABG ?
• Factors in interpretation.
• Rules (Commandments)
ABG in Clinical Practice

3. ABG in Clinical Practice
• Why should I learn ?
• What should I know ?
– Principles of Acid-Base Balance
– Recognize simple disorders
– Recognize it is not a simple disorder
• When to ask for ABG ?
• Hasn’t Pulse oximeter replaced ABG ?
• Factors in interpretation.
• Rules (Commandments)

4. • Why should I learn ?
– More insight into the pathophysiology of any
disease
– Hypoxia can be picked up from pulse oximetery
but hypercarbia cannot
– Metabolic acidosis
– Metabolic alkalosis
ABG in Clinical Practice

5. ABG in Clinical Practice
• Why should I learn ?
• What should I know ?
– Principles of Acid-Base Balance
– Recognize simple disorders
– Recognize it is not a simple disorder
• When to ask for ABG ?
• Hasn’t Pulse oximeter replaced ABG ?
• Factors in interpretation.
• Rules (Commandments)

6. ABG in Clinical Practice
• Why should I learn ?
• What should I know ?
– Principles of Acid-Base Balance
– Recognize simple disorders
– Recognize it is not a simple disorder
• When to ask for ABG ?
• Hasn’t Pulse oximeter replaced ABG ?
• Factors in interpretation.
• Rules (Commandments)

7. ACIDOSIS
pH pCO2 HCO3 Compenstn
Respiratory
Metabolic
N HCO3
N CO2

8. ALKALOSIS
pH pCO2 HCO3 Compenstn
Respiratory
Metabolic
N
N
HCO3
CO2

9. COMPENSATION
Time Frame
• Respiratory Compensation
– Starts immediately
– Complete within 4-6 hrs
• Metabolic Compensation
– Starts after 10-12 hrs
– May take 3-7 days

10. NOMENCLATURE
pH Pco2 HCO3 BE
• Respiratory acidosis
Uncompen (acute)
Partly compen(subacute)
Compen (chronic)
• Respiratory alkalosis
Uncompen (acute)
Partly compen (subacute)
Compen (chronic)
N N
N
N
NN

11. ABG in Clinical Practice
• Why should I learn ?
• What should I know ?
– Principles of Acid-Base Balance
– Recognize simple disorders
– Recognize it is not a simple disorder
• When to ask for ABG ?
• Hasn’t Pulse oximeter replaced ABG ?
• Factors in interpretation.
• Rules (Commandments)

12. Exercises: ABG Data
1 2 3 4 5 6 7
pH 7.26 7.52 7.60 7.44 7.38 7.20 7.56
PCO2 56 28 55 24 76 25 44
HCO3 24 22 51 16 42 9 38
BE -4 +1 +26 -6 +14 -17 +14

13. Exercises: ABG Data
1 2 3 4 5 6 7
pH 7.26 7.52 7.60 7.44 7.38 7.20 7.56
PCO2 56 28 55 24 76 25 44
HCO3 24 22 51 16 42 9 38
BE -4 +1 +26 -6 +14 -17 +14

14. Exercises: ABG Data
1 2 3 4 5 6 7
pH 7.26 7.52 7.60 7.44 7.38 7.20 7.56
PCO2 56 28 55 24 76 25 44
HCO3 24 22 51 16 42 9 38
BE -4 +1 +26 -6 +14 -17 +14

15. Exercises: ABG Data
1 2 3 4 5 6 7
pH 7.26 7.52 7.60 7.44 7.38 7.20 7.56
PCO2 56 28 55 24 76 25 44
HCO3 24 22 51 16 42 9 38
BE -4 +1 +26 -6 +14 -17 +14

16. Exercises: ABG Data
1 2 3 4 5 6 7
pH 7.26 7.52 7.60 7.44 7.38 7.20 7.56
PCO2 56 28 55 24 76 25 44
HCO3 24 22 51 16 42 9 38
BE -4 +1 +26 -6 +14 -17 +14

17. Exercises: ABG Data
1 2 3 4 5 6 7
pH 7.26 7.52 7.60 7.44 7.38 7.20 7.56
PCO2 56 28 55 24 76 25 44
HCO3 24 22 51 16 42 9 38
BE -4 +1 +26 -6 +14 -17 +14

18. Exercises: ABG Data
1 2 3 4 5 6 7
pH 7.26 7.52 7.60 7.44 7.38 7.20 7.56
PCO2 56 28 55 24 76 25 44
HCO3 24 22 51 16 42 9 38
BE -4 +1 +26 -6 +14 -17 +14

19. COMPENSATION
• Resp. Acute
↑ CO2 by 10 ↑ HCO3 by 1
↓ CO2 by 10 ↓ HCO3 by 2
• Resp. Chronic
↑ CO2 by 10 ↑ HCO3 by 3-4
↓ CO2 by 10 ↑ HCO3 by 3-5
• Metabolic
↓ HCO3 by 1 ↓ CO2 by 1-1.5
↑ HCO3 by 1 ↑ CO2 by 0.2-1
BODY NEVER OVERCOMPENSATES !

20. NOMOGRAM

21. ABG in Clinical Practice
• Why should I learn ?
• What should I know ?
– Principles of Acid-Base Balance
– Recognize simple disorders
– Recognize it is not a simple disorder
• When to ask for ABG ?
• Hasn’t Pulse oximeter replaced ABG ?
• Factors in interpretation.
• Rules (Commandments)

22. • A child with Persistent Pneumonia is shifted from
other hospital. ABG at admission
– pH - 7.47 PCO2 - 108
– HCO3 - 51 BE - + 24
• Interpretation
– ? Is this Metabolic Alkalosis
– ? Is this Bicarbonate administation
– Treatment ?
Case History

23. Case History
• Ankit, a 3 year old admitted 2 weeks back with H/o
loose motions 1 day, 2 vomitings.
• He is a known case of nephrotic syndrome, on 10
mg OD wysolone.
• Now he was passing cholera like stools. Hanging
drop and stool C/s confirmed cholera.
• He had signs of severe dehydration at admission.

24. Case History
• His labs were –
– pH - 7.13 Na - 121
– PCO2 - 31.1 K - 4.0
– PaO2 - 146.9 (under O2) Cl - 106
– HCO3 - 10.2
– BE - -17.3
• Weight – 12 kg
• What is your diagnosis –
Cholera + Severe dehydration + Hyponatremia + ?

25. • Comments on ABG
– pH - Acidosis, moderate - severe
– PaCO2 - Respiratory alkalosis ?
– PaO2 - High (need to reduce FiO2)
– HCO3 - Low
– Base excess - Negative i.e. Metabolic acidosis
• Overall interpretation:
Partially compensated metabolic acidosis ?
Case History

26. • Anion Gap
– (121 + 4.0) - (106 + 10.2) = 9 (normal)
• Treatment
– 0.3 x 12 x 17.3 = 62.2 meq of HCO3
– Give half of this amount stat
– Check ABG repeatedly
Case History

27. ABG in Clinical Practice
• Why should I learn ?
• What should I know ?
– Principles of Acid-Base Balance
– Recognize simple disorders
– Recognize it is not a simple disorder
• When to ask for ABG ?
• Hasn’t Pulse oximeter replaced ABG ?
• Factors in interpretation.
• Rules (Commandments)

28. When to ask for ABG
• Any seriously ill child
• Renal Failure
– Acute
– Chronic
• Respiratory distress - Moderate/ Severe
• Chronic persistent respiratory disorder
• Neurological disorders - GBS
• Cardiac disorders - Acute worsening
• Suspected inborn errors of metabolism

29. ABG in Clinical Practice
• Why should I learn ?
• What should I know ?
– Principles of Acid-Base Balance
– Recognize simple disorders
– Recognize it is not a simple disorder
• When to ask for ABG ?
• Hasn’t Pulse oximeter replaced ABG ?
• Factors in interpretation.
• Rules (Commandments)

30. PULSE Ox versus ABG
• Non invasive
• Continuous
• O2 saturation (SaO2)
• Measures
oxygenation
• Bed side monitor
• Invasive
• Intermittent
• Partial pressure of O2
• Measures O2, pH,
CO2, HCO3
• Gold standard
Hence both may be required

31. ABG in Clinical Practice
• Why should I learn ?
• What should I know ?
– Principles of Acid-Base Balance
– Recognize simple disorders
– Recognize it is not a simple disorder
• When to ask for ABG ?
• Hasn’t Pulse oximeter replaced ABG ?
• Factors in interpretation.
• Rules (Commandments)

32. Interpretation of ABG Reports
• When interpreting an ABG report in serious
patient consider the following:
– Original disease
– Complication – e.g. nosocomial pneumonia.
– Associated medical conditions
– Electrolyte disturbances – (hypohosphatemia shifts
O2 dissociation curve to Left)

33. Interpretation of ABG Reports
• Therapeutic interventions
– type of IV fluids
– ventilator settings
– blood transfusions
– NG aspiration/diarrhea
– drugs
– TPN
– NaHCO3 administration
• Compensatory mechanisms
– time factor
– ability of kidney / lungs.

34. ABG in Clinical Practice
• Why should I learn ?
• What should I know ?
– Principles of Acid-Base Balance
– Recognize simple disorders
– Recognize it is not a simple disorder
• When to ask for ABG ?
• Hasn’t Pulse oximeter replaced ABG ?
• Factors in interpretation.
• Rules ( 10 Commandments)

37. Case: 1
ABG Values in a 1 yr old with mild
respiratory distress, done as a part
of routine workup:
pH 7.38
pCO2 42
pO2 47

38. Commandment I
Thou shalt not…..
I shall confirm that the
sample sent is arterial and
not venous

39. Case: 2
A 7 yr old was admitted with encephalitis.
Two hours later, when clinically she was
deteriorating, a repeat ABG was done to
decide about mechanical ventilation:
at admiss. 2 hr. later
pH 7.4 pH 7.39
pCO2 42 pCO2 10
pO2 82 pO2 148

40. Commandment II
I shall use only minimal
amount of heparin to rinse
the syringe.
(Excess heparin causes ↓ pCO2 &
shift

41. Case: 3
ABG values of a child with
cyanotic heart disease in spell:
pH 7.54
pCO2 21
pO2 88

42. Commandment III
I shall ensure there are no air
bubbles in the blood
samples.

43. Case: 4
ABG values in a child with staph pneumonia
with improving respiratory distress:
At present 12 hrs earlier
pH 7.32 pH 7.38
pCO2 46 pCO2 40
pO2 63 pO2 78
Hb- 6.2 gm%, TLC-32000/ mm3
, Polys- 84%

44. Commandment IV
I shall send the sample in ice
and
analyze it quickly, … and keep
the

45. Case: 5
Bronchiolitis, moderate respiratory distress,
on arrival from another hospital-
pH 7.62
pCO2 60
pO2 76
HCO3
-
48

46. Commandment V
I shall always take the history of
sodium bicarbonate administration
even in respiratory cases.

47. Case: 6
Case of Bronchiolitis, not improving inspite of
aggressive management in a hospital. Now,
transferred to you-
pH 7.51
pCO2 45
pO2 68
HCO3
-
38
Hb- 10.4gm%, TLC- 9600/ mm3
, Na+
- 138, K+
- 1.8

48. Commandment VI
I shall always consider the
effects of furosemide,
steroids, salbutamol, blood
transfusion and

49. Case: 7
5 year old with severe bilateral pneumonia.
Clinically worsening inspite of your treatment
with oxygen etc.:
On admiss Next day
pH 7.34 7.31
pCO2 42 47
pO2 66 88

50. Commandment VII
I shall always take FiO2 into
consideration when
interpreting pO2 values. I
shall also look at the pCO2
values carefully.

51. Case: 8
A 5 month old cerebral palsy child is brought in
with respiratory distress since 1 month age due
to recurrent aspiration pneumonia. ABG values
are:
pH 7.36
pCO2 62
pO2 60
MV- pressure limited / volume limited?

52. Commandment VIII
I shall take the history into
consideration before
instituting therapy for
Chronic respiratory failure

53. Case: 9
A patient of GBS on MV suddenly
deteriorates with ↓ SpO2 & ↑ EtCO2.
ABGs are:
Initial 15 mt later
pH 7.37 7.19
pCO2 35 58
pO 88 47

54. Commandment IX
I shall always remember the
acronym “ DOPE “ in such
situations-
D - Displacement
O - Obstruction
P - Pneumothorax

55. Case: 10
A 3 year old with septicemia, MOSF & ARDS
has the following ABG when clinically stable
on high PIP & PEEP:
pH 7.36
pCO2 44
pO2 58
Both PIP and PEEP were increased.

56. Commandment X
I shall practice gentle
mechanical ventilation
and not try to bring
ABG to perfect normal.

57. Thank You !