ABG and pedigree analysis

1. ABG Pedigree
Dr. Md. Kawsar Uddin

2. Anatomy of an ABG
 • pH
 • PaO2
 • PaCO2
 • HCO3-
 • Base excess/ deficit
 • Oxygen saturation (SpO2)

3. Acid Base status : Normal values
Mean Normal (1 SD) Normal (2 SD)
pH 7.40 7.38-7.42 7.35-7.45
PaCO2 40 38-42 35-45
PaO2 100 80-100 mmHg
HCO3 24 23-25 22-26
BE 0 -2 to +2 mmol/L
SaO2 95% 92-100%

4. The 7 Steps Approach to Solve Acid-Base
Disorders
Step 1
Primary Problem
Check pH – Academia or Alkalemia
Step 2
Primary cause
Check PaCO2 – is Respiratory the
primary cause?
Step 3
Primary cause
Check HCO3– is Metabolic the
primary cause?
Step 4
Compensation
Is the body compensating?
Step 5 Determine if Compensation is
appropriate or there are other Primary
Disorders
Step 6 Determine Anion Gap & Bicarbonate Gap
Step 7 Determine Oxygenation

5. Terminology
 Acidaemia: pH < 7.35, Alkalemia: pH > 7.45
 Acidosis: Increase in acid or decrease in alkali in body
 Alkalosis: Fall in acid or increase in alkali in body
Compensatory acidosis: When acidosis induces
compensatory changes in the body so that pH
remains within the normal range, it is termed
compensated acidosis. When acidosis produces a
fall in pH below 7.35, it is termed as uncompensated
acidosis. Similarly, alkalosis can be compensated or
uncompensated

6. Step 1: Check pH
. Is the pH Normal, Acidaemia or Alkalemia?
. Try to always start with patient’s baseline values.

7. Remember
 ROME
• For primary respiratory disorder carbon di
oxide change in opposite direction. For
primary metabolic disorder bicarbonate
change in equal direction.

8. Step 2. Check PaCO2
Is Respiratory the Primary cause?
 • Is PaCO2 Normal, ↑ or ↓ ?
 • Normal PaCO2 = 35 – 45 mm Hg
 • Respiratory cause =
↑ CO2 (hypoventilation) and ↓ pH
↓ CO2 (hyperventilation) and ↑ pH
If PaCO2 changes from normal in the
opposite direction of pH, then it is a
respiratory cause, therefore a primary
cause.

9. Step 3. Check HCO3
Is Metabolic the Primary cause?
 • Normal HCO3 = 22-26 mEq/L
 • Is HCO3 Normal, ↑ or ↓ ?
 • Metabolic cause = ↑ HCO3 and ↑ pH or ↓ HCO3 and ↓ pH
 If HCO3 changes from normal in the same direction as pH, then it is a Metabolic
cause, therefore a primary cause

10. Step 4: Is the Body
Compensating?
 If both PaCO2 and HCO3 are abnormal in the same direction then, YES, the body is
compensating.
 Compensation: ↑PaCO2 and ↑ HCO3
Or
↓PaCO2 and ↓HCO3

11. Determine compensation
 Determine if the ABG is Compensated, Partially Compensated or Uncompensated.
 Here’s the trick:
 If pH is NORMAL, PaCO2 and HCO3 are both ABNORMAL = Compensated
 If pH is ABNORMAL, PaCO2 and HCO3 are both ABNORMAL = Partially
Compensated
 If pH is ABNORMAL, PaCO2 or HCO3 is ABNORMAL
= Uncompensated

12. Step 5:
 Determine if compensation is Appropriate: Are there other Primary cause?

13. Compensatory Mechanism
Homeostasis mechanism demands that primary
changes in in PaCO2 lead to secondary changes
in the plasma bicarbonate, so that the pH is kept
constant. The higher the PaCO2 , the greater is
the degree of bicarbonate reabsoption; the lower
the PaCO2 , the lesser the degree of reabsoption
of bicarbonate, and the greater is its excretion.
This enables respiratory acidosis to be
compensated through retention of bicarbonate,
and respiratory alkalosis to be compensated by
increased excretion of bicarbonate

14. Compensation
 The term “acute” and “chronic” for metabolic
disorders are often omitted, because,
Functionally there is usually no time distinction
between acute and chronic metabolic disorders, the respiratory system compensation
is usually immediate.
 All metabolic disorders are
essentially Partially compensated, all metabolic
disorders are simple termed Metabolic acidosis
or Metabolic alkalosis, without any further descriptive terminology.

15. Respiratory Acidosis
 Definition: Hypercarbia or Hypercapnia
 ↑PaCO2 > 45 mmHg
 Cause: Alveolar hypoventilation or
Ventilatory failure
 Compensation: Renal: ↑ in Base (HCO3)

16.  For every acute increase of 10 mm Hg in PaCO2, pH will decrease 0.08 and HCO3
will increase 1 mEq/L
 For every chronic increase of 10 mm Hg in PaCO2, pH will decrease 0.03 and
HCO3 will increase 4 mEq/L

17. Acute Respiratory Acidosis with a PaCO2 of 60
mm Hg
Expected pH Expected HCO3
7.40 – (0.08 x ∆ PaCO 2)10 24 +( 1 x ∆ PaCO 2 ) 10
7.40 – (0.08 x 60-40) 10 24 +( 1 x 60-40) 10
7.40 – 0.16 = 7.24 24 + 2 = 26

18. Chronic Respiratory (maximally compensated)
Acidosis with a PaCO2 of 60 mm Hg
Expected pH Expected HCO3
7.40 – (0.03 x ∆ PaCO 2)10 24 +( 4 x ∆ PaCO 2 ) 10
7.40 – (0.03 x 60-40) 10 24 +( 4 x 60-40) 10
7.40 –0.06= 7.34* 24 + 8 = 32
*pH doesn't return to normal even with max renal compensation

19. Respiratory Alkalosis
Definition: Hyporcarbia or Hypocapnia: ↓PaCO2 < 35 mmHg
• Cause: Hyperventilation
• Compensaon: Renal: ↓ in Base (HCO3)

20.  For every acute decrease of 10 mm Hg in PaCO2, pH will increase 0.08 and HCO3
will decrease 2 mEq/L
 For every chronic decrease of 10 mm Hg in PaCO2, pH will increase 0.03 and
HCO3 will decrease 5 mEq/L

21. Acute Respiratory Alkalosis with a PaCO2
of 20 mm Hg
Expected pH Expected HCO3
7.40 + (0.08 x ∆ PaCO 2)10 24 - ( 2 x ∆ PaCO 2 ) 10
7.40 + (0.08 x 40-20) 10 24 - ( 2 x 40-20) 10
7.40 + 0.16 = 7.56 24 - 4 = 20

22. Chronic Respiratory (maximally compensated)
Alkalosis with a PaCO2 of 20 mm Hg
Expected pH Expected HCO3
7.40 + (0.03 x ∆ PaCO 2)10 24 -( 5 x ∆ PaCO 2 ) 10
7.40 + (0.03 x 40-20) 10 24 - ( 5 x 40-20) 10
7.40 + 0.06= 7.46 24 - 10 = 14

23. Metabolic Acidosis
 Definion: ↓HCO3 (< 22 mEq/L)
 • Cause: ↑ Acid or ↓ Base
 • Compensation: Hyperventilation

24. For every decrease of 1 mEq/L of HCO3
pH will decrease 0.015 and will PaCO2
decrease 1.5 mm Hg

25. Winter’s formula
 Expected PaCO2 = [ (1.5 x HCO3 ) + 8 ] ± 2
 Note: If PaCO2 levels are higher than expected, there is a secondary respiratory
acidosis
 If PaCO2 levels are lower than expected, there is secondary respiratory alkalosis

26. Determine Compensation
PaCO2 pH HCO3
Respiratory
Acute 10 0.08 1
Chronic 10 0.03 4
Respiratory
Acute 10 0.08 2
Chronic 10 0.03 5
Metabolic HCO3 pH PaCO2
M. Acidosis 1 0.015 1.5
M. Alkalosis 1 0.015 0.7

27. Step 6
 If metabolic acidosis present, resolve whether it is anion or non-anion gap
acidosis

28. Anion Gap Concept
 Electrochemical Balance: The total anions are the same as
total cations
 Anion Gap is an artifact because some anions are not
measured
 Gap is mainly due to unmeasured proteins, phosphates
and sulfate

29. Anion Gap Concept
Anions Cations
Cl 104 mEq/L Na 140 mEq/L
HCO3 24 mEq/L K 4.5 mEq/L
Proteins 15 mEq/L Mg 1.5 mEq/L
Organic acid 5 mEq/L Ca 5 mEq/L
PO4 2 mEq/L Total: 151 mEq/L
SO4 1 mEq/L
Total: 151 mEq/L

30. AG (anion gap)
 Na+ + UC = (Cl- + HCO3-) + UA
 (Cl- + HCO3-) + UA = Na+ + UC
 UA–UC(AnionGap) =Na+–(Cl-+ HCO3-)
 i.e., AG is calculated by difference between positively charged measured cations
(Na+ ± K+) from negatively charged measured anions (Cl- & HCO3)
 AG = Na- [Cl¯ + HCO3¯]
 Normal AG = Na+- [Cl¯ + HCO3¯]
= 140 –[104 + 24]
= 140-128
= 12 ( ± 4) mEq/L

31.  1. Anion Gap Metabolic Acidosis
(↑Acid) : ↑Acid → ↑ AG
 2. No-Anion Gap Metabolic Acidosis
(↓Base): ↓HCO3-→ ↑Cl
(Also called Hyperchloremic metabolic Acidosis)

32. Anion Gap
 AG = Na+- (Cl- + HCO3-)
 Normal = 12 +/- 4 mEq/L
 Correction for low serum albumin
 Add (4 - serum albumin g/dL) X 2.5 to the anion gap
 If AG is calculated using K+, the normal AG is 16 ± 4 mEq/L

33. Causes of AG Metabolic Acidosis
↑ Acid producon ↑Acid Addion ↓Acid excreon
Organic acids: ↑Lacc acid
(most common cause)
Ketoacidosis (common
cause) ↑PO4 ↑SO4
↑Proteins
(hyperalbuminemia; > 4.4
g/dl)
Toxins: CO poisoning,
cyanide, ethylene glycol
Dehydration
Hypoaldesteronism Renal
failure

34. Causes of Non-Anionic Gap Met Acidosis
↓ Base (loss of HCO3)
↑kidney excreon: Renal
tubular acidosis
(↑HCO3excretion)
Intestinal loss: Diarrhea
(most common cause),
enteric drainage tubes,
ileostomy, small bowl or
pancreatic fistula
Infusion or Ingestion:
Carbonic anhydrase
inhibitors (Acetazolamide),
hyper alimentation, HCL,
NH4Cl, TPN

35. Bicarbonate Gap / Corrected HCO3/ Delta
Gap
 Use: To identify Mixed metabolic disorder
 If anion gap present, determine the presence of any concomitant metabolic
disorders by measuring bicarbonate gap
 BG = Patient’s HCO3 + ∆ AG
 BG Normal = 24 = AG Metabolic acidosis
<20 = AG Metabolic acidosis + Non-AG Metabolic acidosis
>28 = AG Metabolic acidosis + Metabolic alkalosis
∆ AG= delta Gap=measured AG –normal AG = Patients' AG - 12

36. Problem 1 pH=7.3, HCO3=15 mmol/L,
PaCO2= 30 mmHg

37. Problem 1: pH=7.3, HCO3=15 mmol/L,
PaCO2= 30 mmHg
Approach
Step 1: Look at pH. It is 7.3. So acidosis
Step 2: Is the primary disturbance respiratory or metabolic? Here HCO3 is low and
same direction as pH (↓). So it is Metabolic [and acidosis]
Step 3: Look for compensation. See changes in PaCO2
Expected PaCO2= (HCO3+15) +/- 2= (15+15)+/-= 28-32.
So PaCO2 is within expectation
Comment: So it is a simple metabolic acidosis with partial compensation ( if complete
compensation pH would be normal)

38. Problem 2 ABG of a 60-year-old man
presenting with sudden breathlessness:
pH=7.2, HCO3= 25 mmol/L, PaCO2=60
mmHg.

39. Approach
Step 1: Look at pH. It is 7.2. So Acidosis
Step 2: Is the primary disturbance respiratory or metabolic? Here HCO3 near normal
but PaCO2 high and opposite direction as pH (↓). So it is Respiratory ( & acidosis of
course)
Step 3: Look for compensation. See changes in HCO3. Expected HCO3 = 24 + { (Actual
PaCO240) / 10 }= 24+ {(60-40)/10}= 24+2= 26. So HCO3 is within expectation.
Comment: So it is a simple Respiratory acidosis with partial compensation ( if
complete compensation

40. Problem 3 ABG of a 60-year-old man
having breathlessness on exertion for a
long time: pH=7.2, HCO3=32mmol/L,
PaCO2=60mmHg

41. Approach
Step 1: Look at pH. It is 7.2. So it is Acidosis
Step 2: Is the primary disturbance respiratory or metabolic? Here HCO3near normal
but PaCO2 high and opposite direction to pH(↓). So it is Respiratory ( & acidosis of
course)
Step 3: Look for compensation for chronic condition. See changes in HCO3.
Expected [HCO3] = 24 + 4 { ( PaCO2- 40) / 10}= 24+ 4 { (6040)/10}= 24+4x2=
24+8=32.
So, HCO3 is within expectation.
Comment: So it is a simple Respiratory acidosis with partial compensation ( if
complete compensation pH would be normal

42. Problem 4 pH=7.5, HCO3=29 mm/L,
PaCO2= 42 mmHg

43. Approach
Step 1: Look at pH. It is 7.5. So it is Alkalosis
Step 2: Is the primary disturbance respiratory or metabolic? Here HCO3 is high & same
direction of pH (↑). So it is Metabolic (& alkalosis of course)
Step 3: Look for compensation for chronic condition. See changes in PaCO2
Expected PaCO2= (HCO3+15) +/- 2 = (29 + 15) +/- = 42-46
So, PaCO2 is within expectation
Comment: So it is a simple Metabolic alkalosis with partial compensation ( if complete
compensation pH would be normal)

44. Problem 5 pH 7.39, HCO3- 14, PaCO2 24

45. Approach
Step 1: Look at pH. It is 7.39. So acidosis
Step 2: Is the primary disturbance respiratory or metabolic? Here HCO3 is low & same
direction as pH (↓). So it is Metabolic [and acidosis]
Step 3 & 4: Look for compensation. See changes in PaCO2
Expected PaCO2= (HCO3+15) +/- 2= (14+15)+/-= 27-31
But here PCaO2 is only 24 i.e., lower than expectation
Comment: It indicates that there is associated Respiratory alkalosis. Mixed acid-base
disorder

46. Problem 6 pH 7.30, HCO3 18, PaCO2 38

47. Approach
Step 1: Look at pH. It is 7.3. So acidosis
Step 2: Is the primary disturbance respiratory or metabolic? Here HCO3 is low and
same direction as pH. So it is Metabolic [and acidosis]
Step 3 & 4: Look for compensation. See changes in PaCO2
Expected PaCO2= (HCO3+15) +/- 2= (18+15)+/- 2= 31-35
But here PaCO2 is 38 i.e., higher than expectation
Comment: It indicates that there is associated Respiratory acidosis Mixed acid-base
disorder [Metabolic acidosis & Respiratory acidosis] e.g., sever pneumonia, pulmonary
edema

48. Problem 7 pH 7.55, HCO3- 33, PaCO2 38

49. Step 1: Look at pH. It is 7.55. So it is Alkalosis
Step 2: Is the primary disturbance respiratory or metabolic? Here HCO3 is high and in
the Same direction as pH (↑). So it is Metabolic (& alkalosis of course)
Step 3: Look for compensation. See changes in PaCO2
Expected PaCO2= (HCO3+15) +/- 2 = (33 + 15) +/-2 = 46-50
But here PaCO2 is only 38 i.e., lower than expectation. So it indicates associated
Respiratory Alkalosis
Comment: So it is a mixed ABD ( Metabolic alkalosis & Respiratory alkalosis) e.g., Liver
disease & diuretics

50. Problem 8 pH 7.45, HCO3 42, PaCO2 67
Step 1: Look at pH. It is 7.45. So it is Alkalosis
Step 2: Is the primary disturbance respiratory or metabolic? Here HCO3 is high & in
the same direction as pH (↑). So it is Metabolic (& alkalosis of course)
Step 3: Look for compensation. See changes in pCO2.
Expected PaCO2= (HCO3+15) +/- 2 = (42 + 15) +/-2 = 5559.
But here PaCO2 is 67 i.e., higher than expectation. So it indicates associated
Respiratory Acidosis
Comment: So it is a mixed ABD ( Metabolic alkalosis & Respiratory acidosis) e.g., COPD
on diuretics

51. Problem 9 pH 7.4, HCO3 25, PaCO2 40,
Na+ 140, K+ 3, Cl- 95, AG 23

57.  pH=normal,HCO3- normal, PaCO2 normal •
 So every thing is normal!!
 Nowlook at anion gap: it is high; 23
 High AG indicates metabolic acidosis
 Normal pH indicates another disorder (alkalosis) compensated the pH
 Now what is the compensatory factor: Respiratory or Metabolic?
 PaCO2 is normal but HCO3- is up normal indicating metabolic alkalosis has
compensated the pH towards normal
 So it is mixed ABD i.e., Met acidosis & Met alkalosis e.g., uremia & vomiting

58. CAUTION !!!
TEMPERATURE CORRECTION: (Body temp - 37°C)
PO2 ↑/↓ by 5mmHg for each degree Celsius temp. ↑/↓
PCO2 ↑/↓ by 2mmHg for each degree Celsius temp. ↑/↓
SAMPLE SHOULD BE SEND WITH ICE:
Without ice , analyze within 15 min.
With ice, analyze within 1 hr.
The main effect of cellular metabolism is to ↓ PO2
Remarkable↓PO2 if the blood contains ≥100,000 WBC/mm3 even when the sample is on ice
SAMPLE SYRINGE should not CONTAIN TOO MUCH ANTICOAGULANT:
Heparin has slightly acidic pH

59. CAUTION !!!
NOT AN ARTERIAL SAMPLE:
Venous PO2– 35-40mmHg
SVO2—70-75%
Venous pH and PCO2 are often close to arterial values.
So venous blood gases can be interchangeably used instead of ABG .Oxygenation value can be obtained by
Pulse-oxymetry
PATIENT NOT IN A STEADY STATE:
Patient should be in a steady state in terms of oxygenation and ventilation. As a general rule, wait at least 30
min. before drawing a blood sample if there has been a change in FIO2/Ventilation.
SAMPLE CONTAINS AN AIR BUBBLE OR THE SAMPLE HAS BEENLEFT OPENTOAIR:
Will ↑ PO2 and ↓ PCO2 as ambient air contains almost no CO2. Resulting pH will rise.

60. Pedigree analysis
 Pedigree charts show a record of the family of an individual
 They can be used to study the transmission of a hereditary condition
 To trace a genetic trait or disease over several generations.

61. Symbols used in pedigree

62. Basic patterns of inheritance
 autosomal, recessive
 autosomal, dominant
 X-linked, recessive
 X-linked, dominant (very rare)

63. Autosomal recessive
• Trait is rare in pedigree
• Trait often skips generations (hidden in heterozygous carriers)
• Trait affects males and females equally

64. Autosomal dominant
• Trait is common in the pedigree
• Trait is found in every generation
• Affected individuals transmit the trait to ~1/2 of their children (regardless
of sex)

65. X-linked recessive
• Trait is rare in pedigree
• Trait skips generations
• Affected fathers DO NOT pass to their sons,
• Males are more often affected than females

66. X-linked dominant
• Trait is common in pedigree
• Affected fathers pass to ALL of their daughters
• Males and females are equally likely to be affected

67. Mitochondrial Inheritance
 All of a human’s mitochondria are passed down from the mother
 Sperm mitochondria are not absorbed into the fertilized egg
 All offspring of an affected female have the disorder, but not an affected male