acid base

1. Acid base balance

2. Normal physiology
• Normal plasma pH 7.35-7.45
• Less than 7.35 – Acidosis
• More than 7.45 - Alkalosis

3. Concept of pH

4. Concept of pH
• Negative logarithm of hydrogen ion concentration
• Dimensionless quantity

5. Concept of pH
Normal pH – 7.4
[H+] = 40 nmol/L

6. Basic concepts…
• Acid
• Base
• pH
• Buffer

7. Strong and weak acids…

8. More concepts…
• pKa
• Henderson Hasselbalch equation

9. To know values…
• pH 7.35 to 7.45
• Hydrogen ion concentration [H+]- 40 nmol/L
• [HCO3-]  22-28 mmol/L
• pCO2  35-45 mm Hg

10. Need for pH regulation…
• Acids constantly produced
• Volatile acids – CO2  20 mol  Lungs
• Non-volatile acids – Lactic acid, sulfuric acid 
70-100 mmol  Kidneys

11. Three lines of defence for pH homeostasis
• Buffers
• Respiratory regulation
• Renal regulation

12. Buffer systems
• Bicarbonate buffer system
• pKa – 6.1
• Highly effective buffer
• High concentration
• Can be easily disposed off or retained by lungs
• Renal absorption can be moderated

13. Buffer systems
• Phosphate buffer system
• pKa – 6.8
• Very less concentration
• Plays a role in renal excretion of acids

14. Buffer systems
• Plasma protein buffer system
• Albumin
• Histidine residue – imidazole ring
• Plays a role in renal excretion of acids

15. Some definitions
• Buffer value – Amount of base required to cause a change of one unit
of pH

16. Respiratory regulation of pH
https://www.youtube.com/watch?v=myag4d5uGa4

17. Renal regulation of pH
• pH of urine in random specimens ranges from 4.5-8.0
• Four mechanisms of renal regulation
Reabsorption of HCO3-
Excretion of H+
Excretion of NH4+
Excretion of H2PO4-
https://www.youtube.com/watch?v=gUe2J400ULo

18. Relation between potassium levels & pH

19. Summary

20. Case 1
As part of a class experiment, a medical student volunteered to give a
sample for arterial blood gas analysis. The demonstrator took some time
to explain the procedure to the class, during which time the student
became anxious and started hyperventilating. As the blood was being
drawn she complained of tingling sensation in her face and all over the
body
Her ABG results were as follows:
pH: 7.61
pCO2 : 20 mmHg
p O2: 90 mmHg (N: >80 mmHg)
Bicarbonate : 20 mmol/L
sO2: 96% (N: 94-98%)

21. Case 2
A 35 yr old man was admitted to the trauma ward following a
road traffic accident. H e had sustained a crush injury of the
chest. His ABG results are as follows
• pH: 7.25
• pCO2: 60 mmHg
• pO2: 60 mmHg (N: >80 mmHg)
• Bicarbonate: 26 mmol/L
• sO2: 88% (N: 94-98%)

22. Case 3
A 42 year old female patient was admitted with a week-long history of
severe vomiting. She was severely dehydrated.
Her ABG results were as follows
• pH: 7.55
• pCO2: 52 mmHg
• pO2: 92 mmHg (N: >80 mmHg)
• Bicarbonate: 45mmol/L
• sO2: 96% (N: 94-98%)
• Chloride - 92 mmol/L (N: 96-106 mmol/L)

23. Case 4
A 24 year old male patient was admitted with complaint of taking illicit
liquor. Many people who have taken from the same shop had died. The
patient was disoriented and the ABG results were as follows
• pH: 7.25
• pCO2: 28 mmHg
• pO2: 92 mmHg (N: >80 mmHg)
• Bicarbonate: 12mmol/L
• sO2: 96% (N: 94-98%)
• Chloride: 96mmol/L (N: 96-106 mmol/L)