2. Learning Objectives
Clinical Implications of Acid Base Balance

3. Terms
Acid
Any substance that can yield a hydrogen ion (H+) or hydronium ion when dissolved in water
Release of proton or H+
Base
Substance that can yield hydroxyl ions (OH-)
Accept protons or H+ pH
Negative log of the hydrogen ion concentration
Represents the hydrogen concentration

4. Terms Normal pH is 7.35-7.45 Acidosis Alkalosis pH less than 7.35
pH greater than 7.45

5. For optimal functioning of cells…
Acids and bases in the body must be in balance

6. The Body and pH
Homeostasis of pH is tightly controlled as pH has an effects on:
Protein function
Enzyme function
Hormones
Electrolyte Balance (Na+, K+, Cl-)

7. 2 Important Questions Why does body pH change?
How does body resist change in pH?

8. Changes in pH
We all consume every day food and drinks which contain acids, metabolism produces also acids...

9. PH IS CONSTANTLY ALTERED BY METABOLISM

10. You get acidotic every day !
While living, eating and drinking...there is..
Production of 1 mmol of fixed acid/kg body weight per day (60 kg=60 mmol/day)

11. Body pH Balance Maintained by chemical and physiologic buffer systems
Resist change in pH
Buffer pairs – weak acid and a base
Exchange a strong acid or base for a weak one
Take up H+ or release H+ as conditions change

12. Buffer Systems

13. Organs involved in the regulation of Acid-Base Balance
CO2 production from complete oxidation of substrates
20% of the body’s daily production
metabolism of organic acid anions
such as lactate, ketones and amino acids
metabolism of ammonium
conversion of NH4+ to urea in the liver results in an equivalent production of H+
Production of plasma proteins
esp. albumin contributing to the anion gap
Bone inorganic matrix consists of hydroxyapatite crystals (Ca10(PO4)6(OH)2]
bone can take up H+ in exchange for Ca2+, Na+ and K+ (ionic exchange) or release of HCO3-, CO3- or HPO42-

14. Organs involved in the regulation of Acid-Base Balance
Equilibrium with plasma
High buffer capacity
Haemoglobin – main buffer for CO2
Excretion of CO2 by alveolar ventilation: minimally 12,000 mmol/day
Reabsorption of filtered bicarbonate: 4,000 to 5,000 mmol/day
Excretion of the fixed acids (acid anion and associated H+): about 100 mmol/day

15. pH is determined by CO2 tension and HCO3
Kidney works by 2 mechanisms:
Bicarbonate reabsorption
Acid Secretion

16. Rates of correction Buffers function: almost instantaneously
Respiratory mechanisms: take several minutes to hours
Renal mechanisms: may take several hours to days

17. Interpretation of ABGs

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

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

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

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

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

23. Respiratory Acidosis
pH~
PATHOGENESIS
Retention of CO2

24. 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

25. 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

26. 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

27. 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

28. Case study 1 Arterial blood gas analysis reveals:
A 21-year-old woman is thrown from her horse at a local event. On the way to hospital she has become increasingly drowsy and the paramedics have inserted an oropharyngeal airway and given high flow oxygen via a face- mask. An arterial blood gas sample has been taken.
Arterial blood gas analysis reveals:
Inspired oxygen % (FiO2 0.4)
PaO kPa >10 kPa (75 mmHg) on air
pH – 7.45
PaCO kPa – 6.0 kPa
Bicarbonate mmol/ l – 26 mmol l-1
Base excess mmol/l /- 2 mmol l-1

29. Case study
A 65-year-old man with severe COPD has been found collapsed in the respiratory unit. On initial assessment by the ward nurse he is apnoeic but has an easily palpable carotid pulse. The nurse is attempting to ventilate his lungs with a bag-mask and supplemental oxygen (with reservoir) and has called the cardiac arrest team.
On arrival:
Oropharyngeal airway, ventilated with bag-mask, oxygen at 15 l min-1, Carotid pulse palpable, 90/ min, SpO2 99%,Comatosed (GCS 3)
Arterial blood gas analysis reveals:
Inspired oxygen % (FiO2 0.85) estimated
PaO kPa (147 mmHg) >10 kPa (75 mmHg) on air
pH – 7.45
PaCO kPa (135 mmHg) – 6.0 kPa (35 – 45 mmHg)
HCO mmol/ l – 26 mmol/ l
BE mmol/ l /- 2 mmol/ l

30. Respiratory Alkalosis
pH~
PATHOGENESIS
Elimination of CO2

31. 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

32. 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

33. 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

34. 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

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

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

37. 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

38. 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

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

40. 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

41. 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

42. Case study
An 18-year-old insulin dependent diabetic is admitted to the emergency department. He has been vomiting for 48 h and because he was unable to eat, he has taken no insulin. On arrival: Breathing spontaneously, RR 35 min-1, oxygen 4 l min-1 via Hudson mask, SpO2 98% P 130 min-1, BP 90/65 mmHg GCS 12 (E3, M5, V4) Arterial blood gas analysis reveals: Inspired oxygen 30% (FiO2 0.3) estimated PaO kPa (129 mmHg) >10 kPa (75 mmHg) on air pH – 7.45 PaCO kPa (19 mmHg) 4.7 – 6.0 kPa (35 – 45 mmHg) HCO3 4.7 mmol/ l 22 – 26 mmol/ l BE mmol/ l +/- 2 mmol/ l The blood glucose is 30 mmol l-1 and there are ketones +++ in the urine.

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

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

45. 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

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

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

48. 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

49. 5 easy steps
2. Look for pH
pH acidosis
pH alkalosis

50. 5 easy steps
3. Look for pCO2
pCO2 acidosis
pCO2 alkalosis

51. 5 easy steps
4. Look for HCO3
HCO3 acidosis
HCO3 alkalosis

52. 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

53. 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

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

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

56. 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

57. p02
THANK YOU
pH~