1. Arterial Blood Gas
Analysis …..1
Dr Deopujari
Pediatrician
Nagpur

2. The Goal :
To provide simple and bedside approach to ABG
report
In details
Not to:
To teach physiology .
To teach theories on acid-base regulation
To look for alternative approaches to
interpretation

3. A Systematic and pointed
………approach
Use of pH for Hydrogen
Ion Activity ……..
The credit (or Blame) for
introducing the term pH,
the negative log of
hydrogen ion (H+)
concentration, goes to
S. P. L. Sørensen
(1868-1939), who
apparently was tired of
writing seven zeros in a
paper on enzyme
activity and wanted a
simpler
designation…..?.

4. H ION CONC.
OH ION 14 pH
N.MOLS / L.
20 7.70
pH stand for "power of hydrogen"
30 7.52
40 H+ = 80 - last two digits of pH 7.40
50 7.30
60 7.22
H ION
0

5. ----- XXXX Diagnostics ------
The Anatomy
Blood Gas Report
248
Pt ID
05:36
2570 / 00
Jul 22 2000 of a Blood Gas Report
Measured 37.0 C
o Measured Values the most
pH
pCO2
7.463
44.4 mm Hg
important
pO2 113.2 mm Hg
o Temperature Correction:
Corrected 38.6 C
pH 7.439
Is there any value to it?
pCO2 47.6 mm Hg
pO2 123.5 mm Hg
Calculated Data
Calculated Data:
HCO3 act 31.1 mmol / L Which are the useful ones?
HCO3 std 30.5 mmol / L
BE 6.6 mmol / L
O2 CT 14.7 mL / dl
O2 Sat 98.3 %
ct CO2
pO2 (A - a)
32.4
32.2
mmol / L
mm Hg
Entered Data:
pO2 (a / A) 0.79 As important
Entered Data
Temp 38.6 o
C
ct Hb 10.5 g/dl
FiO2 30.0 %

6. ----- XXXX Diagnostics ------
Blood Gas Report
Bicarbonate:
o
Measured 37.0 C
pH 7.463
pCO2 44.4 mm Hg
pO2 113.2 mm Hg
o
Corrected 38.6 C
Calculated Data
HCO3 act 31.1 mmol / L
HCO3 std 30.5 mmol / L
BE 6.6 mmol / L
O2 CT 14.7 mL / dl Henderson - Hasselbach equation:
O2 Sat 98.3 %
t CO2 32.4 mmol / L pH = pK + Log HCO3
pO2 (A - a) 32.2 mm Hg
pO2 (a / A) 0.79 Dissolved CO2
Entered Data
Temp 38.6 o
C
ct Hb 10.5 g/dl
FiO2 30.0 %

7. ----- XXXX Diagnostics ------
Standard Bicarbonate:
Blood Gas Report Plasma HCO3 after equilibration
to a PCO2 of 40 mm Hg
o
Measured 37.0 C
pH 7.463 : reflects non-respiratory acid base change
pCO2 44.4 mm Hg
pO2 113.2 mm Hg
: does not quantify the extent of the buffer
base abnormality
o
Corrected 38.6 C : does not consider actual buffering
capacity of blood
Calculated Data Base Excess:
∆ base to normalise HCO3 (to 24)
HCO3 act 31.1 mmol / L
HCO3 std 30.5 mmol / L
BE 6.6 mmol / L
O2 CT 14.7 mL / dl with PCO2 at 40 mm Hg
O2 Sat 98.3 % (Sigaard-Andersen)
t CO2 32.4 mmol / L : reflects metabolic part of acid base ∆
pO2 (A - a) 32.2 mm Hg
pO2 (a / A) 0.79 : no info. over that derived from pH,
pCO2 and HCO3
Entered Data
Temp 38.6 o
C : Misinterpreted in chronic or mixed
ct Hb 10.5 g/dl
FiO2 30.0 %
disorders

8. Oxygenation
----- XXXX Diagnostics ------
Blood Gas Report
Parameters:
o
Measured 37.0 C
pH 7.463 O2 Content of blood:
pCO2 44.4 mm Hg
pO2 113.2 mm Hg Hb x O2 Sat + Dissolved O2
o
Corrected 38.6 C
Oxygen Saturation:
( remember this is calculated )
Calculated Data
HCO3 act 31.1 mmol / L
HCO3 std 30.5 mmol / L Alveolar / arterial gradient:
BE 6.6 mmol / L
O2 CT 14.7 mL / dl
O2 Sat 98.3 %
t CO2 32.4 mmol / L
pO2 (A - a) 32.2 mm Hg
pO2 (a / A) 0.79
Arterial / alveolar ratio:
Entered Data
Temp 38.6 o
C
ct Hb 10.5 g/dl
FiO2 30.0 %

9. Rt. Shift
Lt.Shift

10. Alveolar-arterial Difference
Inspired O2 = 21 %
piO2 = (760-45) x . 21 = 150 mmHg
palvO2 = piO2 – pCO2 / RQ
O2 = 150 – 40 / 0.8
CO2 = 150 – 50 = 100 mm Hg
partO2 = 90 mmHg
palvO2 – partO2 = 10 mmHg

11. Alveolar- arterial Difference
Oxygenation Failure Ventilation Failure
piO2 = 150 piO2 = 150
pCO2 = 40 pCO2 = 80
palvO2= 150 – 40/.8 palvO2= 150-80/.8
=150-50 =150-100
=100 O2 = 50
CO2
pO2 = 45 pO2 = 45
 = 100 - 45 = 55  = 50 - 45 = 5
PAO2 (partial pres. of O2. in the alveolus.)
760 – 45 = 715 : 21 % of 715 = 150 = 150 - ( PaCO2 / .8 )

12. ----- XXXX Diagnostics ------
Blood Gas Report
Oxygenation:
Limitations of parameters:
Measured 37.0 C
o
O2 Content of blood:
pH 7.463
pCO2 44.4 mm Hg Useful in oxygen transport calculations
pO2 113.2 mm Hg Derived from calculated saturation
o
Corrected 38.6 C Oxygen Saturation:
Ideally measured by co-oximetry
Calculated
HCO3 act 31.1
Data
mmol / L
20 × 5 = 100
Calculated values may be error-prone
Alveolar / arterial gradient:
O2 CT 14.7 mL / dl
Reflects O2 exchange with fixed FiO2
O2 Sat 98.3 % Impractical
t CO2 32.4 mmol / L
pO2 (A - a) 32.2 mm Hg Differentiates hypoventilation as cause
pO2 (a / A) 0.79
Arterial / alveolar ratio:
Entered Data
Temp 38.6 o
C Proposed to be less variable
ct Hb 10.5 g/dl Same limitations as A-a gradient
FiO2 30.0 %

13. ----- XXXX Diagnostics ------
Blood Gas Report The essentials
----- XXXX Diagnostics ------
Measured 37.0 C
o
The Blood Gas Report:
Blood
pH Gas
7.463 Report
pCO2 44.4 mm Hg
pO2 113.2 mm Hg
o
Measured 37.0 C
pH 7.463
Corrected
pCO2 44.4 38.6 C
mm Hg
o
pH 7.40 + 0.05
pH2
pO
pCO2
7.439
113.2
47.6
mm Hg
mm Hg
PCO2 40 + 5 mm Hg
pO2 123.5
Calculated mm Hg
Data PO2 80 - 100 mm Hg
HCO3 act 31.1 mmol / L
Calculated Data
HCO3 act
O2 Sat 31.1
98.3 mmol / L
% HCO3 24 + 4 mmol/L
HCO3 std
pO2 (A - a) 30.5
32.2 mmol / L
mm Hg
BE 6.6 mmol / L
O2 CT 14.7 mL / dl
O2 Sat >95
Entered
O2 Sat 98.3 Data
%
t CO2
FiO2 32.4
30.0 mmol / L
% Always mention and see FIO2
pO2 (A - a) 32.2 mm Hg
pO2 (a / A) 0.79
Entered Data
Temp 38.6 o
C
ct Hb 10.5 g/dl
FiO2 30.0 %

14. Low PaO2 can be the result of
A ) low PAO2 ( Low Alveolar Pressure )
1) low barometric pressure,
2) low fraction of inspired oxygen (FiO2)
3) Hypercarbia – elevated (PaCO2).
B ) Wide A / a gradient ( Normal Alveolar
pressure )
1) Shunt ( cardiac or non cardiac )
2) Diffusion abnormality

15. Technical Errors
Glass vs. plastic syringe:
Changes in pO2 are not clinically important
No effect on pH or pCO2
Heparin (1000 u / ml):
Need <0.1 ml / ml of blood
pH of heparin is 7.0; pCO2 trends down
Avoided by heparin flushing & drawing 2-4 cc
blood
Delay in measurement:
Rate of changes in pH, pCO2 and pO2 can be
reduced to 1/10 by cooling in ice slush(4o C)
No major drifts up to 1 hour

16. The
5
Steps for
Successful
Blood Gas
Analysis

17. Step 1
Look at the pH
The culprit
Is the patient acidemic pH < 7.35
or alkalemic pH > 7.45
Step 2
CO responsible for this change ( culprit )?
Who is 2 pH
Acidemia: With HCO3 < 20 mmol/L = metabolic
With PCO2 >45 mm hg = respiratory
Alkalemia: With HCO3 >28 mmol/L = metabolic
BICARB pH
With PCO2 <35 mm Hg = respiratory

18. Step 3
If there is a primary respiratory disturbance, is it acute?
(Acute)change in pH = 0.08 for 10 mm change in PCO2
(Chronic)change in pH = 0.03 for 10 mm change in PCO2

19. Step 4
If the disturbance is metabolic is the respiratory
compensation appropriate?
The last two
For metabolic acidosis: digits
Expected PCO2 = (1.5 x [HCO3]) + 8 ) + 2
(Winter’s equation)
( Last two digits of pH )
For metabolic alkalosis:
Expected PCO2 = 6 mm for 10 mEq. rise in Bicarb.
If :
actual PCO2 more than expected : additional
respiratory acidosis
actual PCO2 less than expected : additional respiratory
alkalosis

20. Step 4 cont.
If there is metabolic acidosis, is there a wide anion gap ?
Na - (Cl-+ HCO3-) = Anion Gap usually <12
If >12, Anion Gap Acidosis : Methanol
Uremia
Common pediatric causes
Diabetic Ketoacidosis
1) Lactic acidosis
Paraldehyde
2) Metabolic disorders
Infection (lactic acid)
3) Renal failure
Ethylene Glycol
Salicylate

21. th step
5
Clinical correlation

24. Same direction
HCO3 pH META.
Same direction
PCO2 pH RESP.
Opposite direction

25. 24 CO2
= H ION CONC.
BICARBONATE N.MOLS / L.
24 40 = 960
= H ION CONC.
N.MOLS / L.
BICARBONATE
960
= H ION CONC. = 40
24 N.MOLS / L.
H+ N.MOLS / L. = 80 - last two digits of pH

26. pH HYPER VENTILATION
CO2
BICARB CHANGES
pH in same direction
compensation
HCO3
Primary lesion
Primary lesion
METABOLIC ACIDOSIS

27. pH HYPO VENTILATION
CO2
BICARB CHANGES
pH in same direction
compensation
HCO3
Primary lesion
METABOLIC ALKALOSIS

28. pH
CO 2 CHANGES
pH in opposite direction
BICARB
compensation
CO 2
Primary lesion Respiratory acidosis

29. RESP. ACIDOSIS ALKALOSIS META.
PCO2
+
CO2+H20=H2CO3 = H + HCO3 pH
HIGH
+
H
HIGH
HCO3 HCO3
HCO3
ACUTE RISE : PCO2 10 : pH .08
CHRONIC RISE : PCO2 10 : pH .03

30. pH CO 2 CHANGES
pH in opposite direction
BICARB
compensation
CO 2
Primary lesion
Primary lesion
Respiratory alkalosis

31. RESP. ALK. ACID. META.
+ +
CO2 + H20 = H2CO3 = H HCO3 pH
CO2
+
HCO3
LOW H IONS
…LOW HCO3
ACUTE FALL : PCO2 10 : pH .08
CHRONIC FALL: PCO2 10 : pH .03

32. Pco of 10
2 pH
Acute change .08
Chronic change .03

33. INTERPRETATION OF A.B.G.
FOUR STEP METHOD OF DEOSAT
1) LOOK FOR pH
2) WHO IS THE CULPRIT ?
3) IF RESPIRATORY ACUTE / CHRONIC ?
4) IF METABOLIC / COMP. / ANION GAP
CLINICAL CORRELATION

34. compensation considered
complete
when the
pH returns
to
normal
range Clinical blood gases by Malley

35. METABLIC ACIDOSIS
COMPENSION LIMITS
CO2 = Up to 10 ?
METABOLIC ALKALOSIS
CO2 = Maximum 6O
RESPIRATORY ACIDOSIS
BICARB = Maximum 40
RESPIRATORY ALKALOSIS
BICARB = Up to 10

37. ----- XXXX Diagnostics ------
----- XXXX Diagnostics ------
Blood Gas
Blood Gas Report
Report
o
Case 1
Measured
Measured 37.0 oC
37.0 C
pH
pH 7.523
7.523
pCO2
pCO2 30.1
30.1 mm Hg
mm Hg 16 year old female with
pO2
pO 105.3
105.3 mm Hg
mm Hg
2
sudden onset of dyspnea.
Calculated
Calculated Data
Data
HCO3 act
HCO act 22
22 mmol / /L
mmol L
3 No Cough or Chest Pain
O2 Sat
O2 Sat 98.3
98.3 %
%
pO2 (A --a)
pO2 (A a) 88 mm Hg ∆
mm Hg ∆ Vitals normal but RR 56,
pO2 (a / /A)
pO2 (a A) 0.93
0.93
anxious.
Entered
Entered Data
Data
FiO2
FiO 21.0
21.0 %
%
2

38. Case 2 6 year old male with progressive respiratory distress
Muscular dystrophy . pH <7.35 :acidemia
----- XXXX Diagnostics ------
----- XXXX Diagnostics ------
Blood Gas
Blood Gas Report
Report
o respiratory acidemia : co2 and pH
Measured
Measured 37.0 oC
37.0 C
pH
pH 7.301
7.301  CO2 =76-40=36
pCO2
pCO2 76.2
76.2 mm Hg
mm Hg Expected  pH ( Acute ) = .08 for 10
pO2
pO 45.5
45.5 mm Hg
mm Hg Expected ( Acute ) pH = 7.40 - 0.29=7.11
2
Calculated Data Chronic resp. acidosis
Calculated Data
HCO3 act
HCO act 35.1
35.1 mmol / /L
mmol L
3
O2 Sat
O2 Sat 78
78 %
%
pO2 (A --a)
pO2 (A a) 9.5
9.5 mm Hg ∆
mm Hg ∆
pO2 (a / /A)
pO (a A) 0.83
0.83
2
Entered
Entered Data
Data
FiO2
FiO 21
21 %
%
2
Hypoxia
Normal A-a gradient
Due to hypoventilation

39. ----- XXXX Diagnostics ------
----- XXXX Diagnostics ------
Blood Gas Report
Case 3
pH <7.35 ; acidemia
Blood Gas Report
o pCO2 >45; respiratory acidemia
8-year-old male asthmatic;
Measured
Measured 37.0 oC
37.0 C
pH
pH 7. 24
7. 24  CO2 = 49 -days9of cough, dyspnea
3 40 =
pCO2 49.1 mm Hg
pCO2 49.1 Expectedand orthopnea not = 0.072
mm Hg  pH ( Acute ) = 9/10 x 0.08
pO2
pO2 66.3
66.3 mm Hg
mm Hg
Expectedresponding 7.40 - 0.072 = 7.328
pH ( Acute ) = to usual
Calculated Data Acute resp. acidosis
Calculated
HCO3 act
Data
18.0 mmol / /L
bronchodilators.
HCO act
3 18.0 mmol L
O2 Sat 92 %
153-66= 87 mm Hg×∆5 = O/E:IN CO2 BICARB MUST RISE ?
WITH∆INCREASE Respiratory distress;
O2 Sat 92 % 30 150
pO2 (A --a)
pO2 (A a) mm Hg
pO2 (a / /A)
pO2 (a A)
suprasternal and
Metabolic acidosis + respiratory acidosis
Entered Data
intercostal retraction;
Entered Data
FiO2
FiO2 30
30 %
% tired looking; on 4 L NC.
Hypoxia
piO2 = 715x.3=214.5 / palvO2 = 214-49/.8=153 Wide A / a gradient

40. Case 4 8 year old diabetic with respi. distress fatigue and loss of appetite.
----- XXXX Diagnostics ------
----- XXXX Diagnostics ------
pH <7.35 ; acidemia
Blood Gas
Blood Gas Report
Report
Measured
o
37.0 oC Last two digits of pH
Measured 37.0 C
pH
pH 7.23
7.23 Correspond with co2
pCO2
pCO2 23
23 mm Hg
mm Hg
pO2
pO2 110.5
110.5 mm Hg
mm Hg
Calculated
Calculated Data
Data
HCO3 act
HCO act 14
14 mmol / /L
mmol L
3
HCO3 <22; metabolic acidemia
O2 Sat
O2 Sat %
%
pO2 (A --a)
pO2 (A a) mm Hg ∆
mm Hg ∆
pO2 (a / /A)
pO2 (a A)
If Na = 130,
Entered
Entered Data
Data Cl = 90
FiO2
FiO2 21.0
21.0 %
% Anion Gap = 130 - (90 + 14)
= 130 – 104 = 26

41. Case 5 : 10 year old child with encephalitis
----- XXXX Diagnostics ------
----- XXXX Diagnostics ------
Blood Gas
Blood Gas Report
Report
Measured
o
37.0 oC pH almost within normal range
Measured 37.0 C
pH 7.46 Mild alkalosis
pH 7.46
pCO2
pCO2 28.1
28.1 mm Hg
mm Hg
pO2
pO2 55.3
55.3 mm Hg
mm Hg Co2 is low , respiratory
Co2 low by around 10
Calculated
Calculated Data
Data ( Acute ) by .08
HCO3 act
HCO act 19.2
19.2 mmol / /L
mmol L
3 (Chronic ) by .03
O2 Sat
O2 Sat %
%
pO2 (A --a)
pO2 (A a) mm Hg ∆
mm Hg ∆ Bicarb looks low ?
pO2 (a / /A)
pO2 (a A) Is it expected ?
Entered
Entered Data
Data
FiO2
FiO2 24.0
24.0 %
%
More cases

42. ABG OF THE DAY
The arterial blood gas report : Room air
pH 7.39
PCO2 l5mniHg
HCO3 8mmol/L
PaO2 90 mmHg
PCO2 24
H ION CONCENTRATION =
BICARBONATE
= 45 nmol/lit

43. pH 7.39
PCO2 l5mniHg
HCO3 8mmol/L
PaO2 90 mmHg
1) These findings are most consistent with….
a) Metabolic acidosis with compensatory Hypocapnia.
b) Primary metabolic acidosis with
respiratory alkalosis.
c) Acute respiratory alkalosis fully compensated.
d) Chronic respiratory alkalosis fully compensated.
For metabolic acidosis: FULL COMPENSATION
Expected PCO2 = (1.5 x [HCO3]) + 8 ) + 2
(Winter’s equation)
PCO 2 ……SHOULD BE 20

44. pH 7.39
PCO2 l5mniHg
HCO3 8mmol/L
PaO2 90 mmHg
2) What is the oxygenation status
a) Normal oxygenation status
b) Hypoxemia
c) None of the above
palvO2 = piO2 – pCO2 / RQ
= 150 – 15 / 0.8
= 150 – 18 = 132 mm Hg
132 – 90 = 42 WIDE A / a gradient

45. pCO2 pH
70 7.10
60 7.20
50 7.30
40 7.40
30 7.50
20 7.60

46.  When pH is normal and:
Bicarbonate is high ( Metabolic alkalosis + respiratory
acidosis )
Bicarbonate is low ( Metabolic acidosis + resp. alkalosis)
 Bicarbonate is normal and:
anion gap is high ( Metabolic Acidosis + Metabolic alkalosis)
 When bicarbonate is normal and:
pH is in acidic range ( Chronic resp. acidosis + resp alk.)
pH is in alkalemic range ( Metab.alk. + resp alk.)
 Anion gap is elevated and:
clinical and laboratory data suggest a diagnosis other than
metabolic acidosis
 PCO2 level and bicarbonates are shifted from normal in
opposing directions.

47. THANKS