1. ACID BASE DISORDER DR UZMA MALIK
ASSISTANT PROFESSOR MEDICINE(EAST MEDICAL WARD)
FCPS(Medicine)FCPS (Endocrinology)

2. Example
EXAMPLE
pO2= 76
pH= 7.2
pCO2= 84
HCO3= 28.3

3. SOLUTION Type 2 respiratory failure
EXAMPLE
Po2= 76
pH= 7.2
pCO2= 84
HCO3= 28.3
Type 2 resp. failure
Acidosis
Respiratory acidosis
Metabolic compensation
Calculation forexpected compensation
∆HCO3=0.1 X ( 84-40)
∆HCO3=0.1 X 44
∆HCO3=4.4
Expected HCO3=24+4.4=28.4
Type 2 respiratory failure
Partially compensated acute respiratory acidosis

4. Interpretation of ABGs

5. Interpretation of ABGs
Respiratory failure
Type 1
Type 2
Acid base disorder
Acidosis
Alkalosis

6. NORMAL VALUES pH = 7.35 - 7.45 ( 7.4 ) pCO2 = 33 - 45 ( 40 ) mEq/L
HCO3 = ( 24 ) mEq/L
pO2 = mmHg

7. Interpretation of ABGs
Respiratory failure
Type 1; pO2 low
Type 2; pO2 low, pCO2 high

8. Respiratory Alkalosis
Acid Base disorder
Respiratory Acidosis
Respiratory Alkalosis
Metabolic Acidosis
Metabolic Alkalosis

9. BASIC CONCEPTS
pH~
CO2 ↔ H2CO3 ↔ H+ HCO3

10. Respiratory Acidosis
pH~
PATHOGENESIS
Retention of CO2

11. Respiratory Acidosis Causes Anatomical Site Disorder
CNS depression of resp.centre
trauma, barbiturate
Upper airway obstruction;
Acute epiglotitis
croup
Resp. muscles paralysis
ALS, phrenic nerve injury, GBS, poliomyelitis,
hypokalemia, hypophsphatemia( ATP)
Lungs obstructive diseases; chronic bronchitis, cystic fibrosis
other; pulmonary edema, ARDS, RDS,
severe bronchial asthma

12. Respiratory Acidosis COMPENSATION Metabolic alkalosis
HCO3 < 30 mEq/L in acute respiratory acidosis
HCO3 > 30 mEq/L in chronic respiratory acidosis
CALCULATION OF EXPECTED COMPENSATION
Acute resp. acidosis
∆HCO3=0.1 X ∆pCO2
Chronic resp. acidosis
∆HCO3=0.4 X ∆pCO2

13. Respiratory Acidosis EXAMPLE pH= 7.2 pCO2= 74 HCO3= 27
∆HCO3=0.1 X ( 74-40)
∆HCO3=0.1 X 34
∆HCO3=3.4
Expected HCO3=24+3.4=27.4

14. Respiratory Acidosis EXAMPLE pH= 7.34 pCO2= 60 HCO3= 32
∆HCO3=0.4 X ( 60-40)
∆HCO3=0.4 X 20
∆HCO3=8
Expected HCO3=24+8=32

15. Respiratory Alkalosis
pH~
PATHOGENESIS
Elimination of CO2

16. Respiratory Alkalosis
Causes
Anatomical Site Disorder
CNS over stimulation of resp.centre
anxiety, high altitude, pregnancy, salicylate poisoning,
endotoxic shock, cirrhosis
Resp. muscles rib fracture; hyper ventilate from pain
Lungs restrictive diseases;
sarcoidosis, asbestosis,
others;
pulmonary embolus, mild bronchial asthma

17. Respiratory Alkalosis
COMPENSATION
Metabolic acidosis
HCO3 > 18 mEq/L in acute respiratory alkalosis
HCO3 < 18 but >12 mEq/L in chronic respiratory alkalosis
CALCULATION OF EXPECTED COMPENSATION
Acute resp. alkalosis
∆HCO3=0.2 X ∆pCO2
Chronic resp. alkalosis
∆HCO3=0.5 X ∆pCO2

18. Respiratory Alkalosis
EXAMPLE
pH=
pCO2= 24
HCO3= 21
∆HCO3=0.2 X ( 40-24)
∆HCO3=0.2 X 16
∆HCO3=3.2
Expected HCO3=24-3.2=20.8

19. Respiratory Alkalosis
EXAMPLE
pH=
pCO2= 18
HCO3= 13
∆HCO3=0.5X ( 40-18)
∆HCO3=0.5 X 22
∆HCO3=11
Expected HCO3=24-11=13

20. Metabolic Acidosis pH~ PATHOGENESIS
Addition of an acid ( increased anion gap )
Loss of HCO3 or inability to synthesize HCO3( normal anion gap )

21. Metabolic Acidosis COMPENSATION Resp. alkalosis
CALCULATION OF EXPECTED COMPENSATION
∆pCO2 =1.2 X ∆HCO3 +/- 2

22. Metabolic Acidosis EXAMPLE pH= 7.27 pCO2= 27 HCO3= 12
∆pCO2 =1.2 X ∆ HCO3 +/- 2
∆pCO2 =1.2 X ( 24-12) +/- 2
∆pCO2 =1.2 X 12 +/- 2
∆pCO2 = /- 2
Expected pCO2= 40 – 14.4= /- 2= 23.6 to 27.6

23. Metabolic Acidosis INCREASED ANION GAP TYPE Formula
AG= serum Na – (serum Cl + serum HCO3 )= 12 +/- 2
Example
Na = 130 ( )
Cl = 88 ( 95 – 105 )
HCO3 = ( 22 – 28 )
AG= 130 – ( 88+10) = 130 – 98= 32

24. Metabolic Acidosis INCREASED ANION GAP TYPE Causes Lactic acidosis
Ketoacidosis
Renal failure ( retention of organic acids)
Salicylate poisoning
Ethylene glycol poisoning
Methyl alcohalpoisoning

25. Metabolic Acidosis NORMAL ANION GAP TYPE Formula
AG= serum Na – (serum Cl + serum HCO3 )= 12 +/- 2
Example
Na = 136 ( )
Cl = ( 95 – 105 )
HCO3 = 14 ( 22 – 28 )
AG= 136 – ( ) = 136 –124= 12

26. Metabolic Acidosis NORMAL ANION GAP TYPE CAUSES Diarrhoea
Cholestyramine
Drainage of bile or pancreatic secretions
Type 1 distal renal tubular acidosis
Type 11 proximal renal tubular acidosis
Type IV renal tubular acidosis

27. Metabolic Alkalosis
pH~
PATHOGENESIS
Loss of hydrogen ion
Gain of HCO3

28. Metabolic Alkalosis COMPENSATION Resp. acidosis
CALCULATION OF EXPECTED COMPENSATION
∆pCO2 =0.7 X ∆ HCO3 +/- 2

29. Metabolic Alkalosis EXAMPLE pH= 7.58 pCO2= 49 HCO3= 39
∆pCO2 =0.7 X ∆ HCO3 +/- 2
∆pCO2 =0.7 X ( 39-24) +/- 2
∆pCO2 =0.7 X 15 +/- 2
∆pCO2 =10.5 +/- 2
Expected pCO2= = /- 2= 48.5 to 52.5

30. Metabolic Alkalosis CAUSES Vomiting Mineralocorticoid excess
Thiazide and loop diuretics

31. Calculate expected compensation
5 easy steps
Look at pO2
Look at pH
Look at pCO2
Look at HCO3
Calculate expected compensation

32. Type 1; pO2 low Type 2; pO2 low, pCO2 high Respiratory failure
5 easy steps
Respiratory failure
Type 1; pO2 low
Type 2; pO2 low, pCO2 high
Look for pO2

33. 5 easy steps
2. Look for pH
pH acidosis
pH alkalosis

34. 5 easy steps
3. Look for pCO2
pCO2 acidosis
pCO2 alkalosis

35. 5 easy steps
4. Look for HCO3
HCO3 acidosis
HCO3 alkalosis

36. 5 easy steps 5. Calculate for expected compensation
If compensation within expected range
one primary disorder
If compensation outside normal range
more than one primary disorder

37. uncompensated disorder
5 easy steps
5. Compensation
uncompensated disorder
expected compensation in normal range
partially compensated disorder
Expected compensation moves outside the normal range,
But does not bring pH in normal range
full compensation
and brings pH in normal range

38. Primary disorder pH
pCO2
HCO3
Respiratory acidosis
Respiratory alkalosis
Metabolic acidosis
Metabolic alkalosis

39. Example
EXAMPLE
pO2= 76
pH= 7.2
pCO2= 84
HCO3= 28.3

40. SOLUTION Type 2 respiratory failure
EXAMPLE
Po2= 76
pH= 7.2
pCO2= 84
HCO3= 28.3
Type 2 resp. failure
Acidosis
Respiratory acidosis
Metabolic compensation
Calculation forexpected compensation
∆HCO3=0.1 X ( 84-40)
∆HCO3=0.1 X 44
∆HCO3=4.4
Expected HCO3=24+4.4=28.4
Type 2 respiratory failure
Partially compensated acute respiratory acidosis

41. p02
THANK YOU
pH~