ARDS

1. ARTERIAL BLOOD GAS
ANALYSIS- SIX STEP
APPROACH
Dr. S.RAMYA M.B.B.S., M.D.,
BIOCHEMISTRY DEPARTMENT
GOVT.MEDICAL COLLEGE-KALLAKURICHI

2. NORMAL VALUES
• pH = 7.35 to 7.45
• H+ = 36 to 44 nmol/L
• pCO2 = 35 to 45 mmHg
• [HCO3
-] = 22 to 28 mmol/L
• PaO2 = 95 mmHg

3. SIX STEP APPROACH – ABG ANALYSIS
• STEP 1 : ABG - AUTHENTIC
• STEP 2 : ACIDOSIS OR ALKALOSIS
• STEP 3 : RESPIRATORY OR METABOLIC
• STEP 4 : COMPENSATION
• STEP 5 : ANION GAP
• STEP 6 : DELTA DELTA GAP

4. STEP 1: ABG –AUTHENTIC/VALIDATORY
• Access the internal consistency of the report using Henderson
Hesselbach equation
• pH = - log [ H+]
[H+] = 24(PaCO2)
[HCO3-]

5. pH Approximate [H+]
(mmol/L)
7.00 100
7.05 89
7.10 79
7.15 71
7.20 63
7.25 56
7.30 50
7.35 45
7.40 40
7.45 35
7.50 32
7.55 28
7.60 25
7.65 22

6. • pH = 7.31
• pCO2 = 29 mmHg
• [HCO3
-](P) = 15.5 mmol/L
• PaO2 = 96 mmHg
• Na = 141 mEq/L
• K = 3.3 mEq/L
• Cl= 96 mEq/L
• [H+] = 24(PaCO2)
[HCO3-]
= 24 X 29
15.5
= 45

7. pH Approximate [H+]
(mmol/L)
7.00 100
7.05 89
7.10 79
7.15 71
7.20 63
7.25 56
7.30 50
7.35 45
7.40 40
7.45 35
7.50 32
7.55 28
7.60 25
7.65 22

8. STEP 2- LOOK INTO pH
pH
pH <7.35 pH>7.45
Acidosis Alkalosis
Normal pH does not exclude an acid base disorder

9. STEP 3
IS IT RESPIRATORY OR METABOLIC??
• pH = [ base ]
[ acid ]
ROME
RESPIRATORY OPPOSITE
METABOLIC EQUAL (SAME SIDE)

10. ACIDOSIS
METABOLIC ACIDOSIS
[HCO3-]
pH =
(PaCO2)
RESPIRATORY ACIDOSIS
[HCO3-]
pH =
(PaCO2)

11. ALKALOSIS
METABOLIC ALKALOSIS
[HCO3-]
pH =
(PCO2)
RESPIRATORY ALKALOSIS
[HCO3-]
pH =
(PCO2)

12. IDENTIFY THE ACID BASE DISORDER
IN THIS REPORT
• pH = 7.57
• pCO2 = 46 mmHg
• [HCO3
-](P) = 33 mmol/L
• PaO2 = 96 mmHg
• Na = 141 mEq/L
• K = 3.3 mEq/L
• Cl= 96 mEq/L
METABOLIC ALKALOSIS
• pH - ALKALOSIS
• [HCO3
-]
• pCO2
[HCO3-]
pH =
(PaCO2)

13. STEP 4
• IS THERE APPROPRIATE COMPENSATION ??

14. If primary defect is decrease in bicarbonate , the compensation would
be decrease in PCO2.
COMPENSATION WILL BE IN PARALLEL SIDE

15. FORMULA FOR COMPENSATION
• Metabolic acidosis
• pCO2 = 1.5 X HCO3 + 8
• Metabolic alkalosis
• pCO2 = 0.9 X HCO3 + 16

16. • If its less than expected compensation  uncompensated
• If its exactly the expected  compensated
• If its more than compensation  mixed disorder

17. RESPIRATORY ACIDOSIS
•Acute
• For every 10 mmHg rise in pCO2, HCO3
- rises by 1
mmol/L
•Chronic
• For every 10 mmHg rise in pCO2, HCO3
- rises by 3.5
mmol/L

18. RESPIRATORY ALKALOSIS
•Acute
• For every 10 mmHg fall in pCO2, HCO3
- falls by 2
mmol/L
•Chronic
• For every 10 mmHg fall in pCO2, HCO3
- falls by 5
mmol/L

19. • pH = 7.2
• pCO2 = 62 mmHg
• [HCO3
-](P) = 30 mmol/L
• PaO2 = 65 mmHg
• pH - ACIDOSIS
• pCO2 = 60 mmHg
• [HCO3
-](P) = 30.2 mmol/L
• RESPIRATORY ACIDOSIS
Acute : For every 10 mmHg rise in pCO2,
HCO3
- rise by 1 mmol/L
Chronic : For every 10 mmHg rise in pCO2,
HCO3
- rises by 3.5 mmol/L
pCO2 = 62 mmHg
= 17mmHg
HCO3
- = 30
= 2
So it is compensated
and it is a case of
acute respiratory
acidosis

20. A RECAP
• ABG AUTHENTIC
• pH
• METABOLIC OR RESPIRATORY
• COMPENSATION

21. STEP 5: ANION GAP
Anion gap is the difference between measured cation and measured
anion.
AG = Na + - (Cl- + HCO3
-)
Normal Anion gap = 8 to 12 mEq/ L
UNMEASURED ANIONS = proteins , phosphate , sulphate, lactate,
Acetoacetate and other organic acids

22. METABOLIC ACIDOSIS
ANION GAP
HIGH ANION GAP NORMAL ANION
GAP
1. DKA
2. LA
3. METHANOL/ETHANOL
4. SALICYLATE
1. GI LOSS
2. Type I RTA
3. Type II RTA
4. Type III RTA
5. Type IV RTA

23. STEP 6: HAGMA- DELTA DELTA RATIO
• DELTA DELTA RATIO = Anion gap – 12
24 – HCO3
-
NORMAL RATIO : 1 to 2
• If it is less than 1  HAGMA + NAGMA
• If its more than 2  HAGMA +Metabolic alkalosis

24. IDENTIFY THE ACID BASE DISORDER
IN THIS REPORT
• pH = 7.28
• pCO2 = 13.2 mmHg
• [HCO3
-](P) = 5.5 mmol/L
• PaO2 = 96 mmHg
• Na = 143 mEq/L
• K = 3.2 mEq/L
• Cl= 118 mEq/L

25. • pH = 7.28 STEP 1 : ABG AUTHENTIC
STEP 2 : ACIDOSIS
• pCO2 = 14 mmHg STEP 3: METABOLIC
• [HCO3
-](P) = 5.5 mmol/L STEP 4 : COMPENSATION
• PaO2 = 96 mmHg pCO2 = 1.5 X HCO3 + 8
• Na = 143 mEq/L = 15
• K = 3.2 mEq/L STEP 5 : AG
• Cl= 118 mEq/L

26. AG = Na + - (Cl- + HCO3
-)
= 19.6
HIGH ANION GAP METABOLIC ACIDOSIS
STEP 6 :
• DELTA DELTA RATIO = Anion gap – 12
24 – HCO3
-
= 19.6 - 12
24- 5.5
= 0.4

27. IDENTIFY THE ACID BASE DISORDER
IN THIS REPORT
• pH = 7.28
• pCO2 = 13.2 mmHg
• [HCO3
-](P) = 5.5 mmol/L
• PaO2 = 96 mmHg
• Na = 143 mEq/L
• K = 3.2 mEq/L
• Cl= 118 mEq/L
CASE OF MIXED DISORDER
HAGMA + NAGMA

28. THANK YOU