This document discusses acid-base balance and acid-base imbalances. It begins by explaining that the normal pH range for blood is 7.35-7.45. This balance is maintained primarily by bicarbonate-carbonic acid buffering systems, as well as by lung and kidney function. When the ratio of carbonic acid to bicarbonate falls out of the normal 20:1 range, acid-base imbalances can occur. There are four main types: respiratory acidosis, respiratory alkalosis, metabolic acidosis, and metabolic alkalosis. The document provides details on the causes, physiological effects, and compensatory responses for each type of imbalance.

1. Acid-Base BalanceAcid-Base Balance
Dr. Inayat Ur RahmanDr. Inayat Ur Rahman
Professor of BiochemistryProfessor of Biochemistry
North West School of MedicineNorth West School of Medicine
Peshawar- PakistanPeshawar- Pakistan

2. Normal Acid-Base BalanceNormal Acid-Base Balance
• Normal pH 7.35-7.45.
• Narrow normal range.
• Compatible with life 6.8 - 8.0.
___/______/___/______/___
6.8 7.35 7.45
8.0
Acid Alkaline

3. 3

4. Maintenance of Balance
Balance maintained by:
• Buffering systems
• Lungs
• Kidneys
H2CO3…..HCO3

5. Buffer Systems
• Prevent major changes in pH
• Act as sponges…
• 3 main systems
Bicarbonate-carbonic acid buffer
Phosphate buffer
Protein buffer
H+
H+
H+

6. Buffer Systems
• Bicarbonate buffer - most important
Active in ECF and ICF
• Phosphate buffer
Active in intracelluar (ICF) fluid
• Protein buffer - Largest buffer store
Albumins and globulins (ECF)
Hemoglobin (ICF)

7. 7
Bicarbonate bufferBicarbonate buffer
• Sodium Bicarbonate (NaHCO3) and
carbonic acid (H2CO3)
• Maintain a 20:1 ratio : HCO3
-
: H2CO3
HCl + NaHCO3 ↔ H2CO3 + NaCl
(St. Acid) (Wk. Acid)
NaOH + H2CO3 ↔ NaHCO3 + H2O
(St.Alk) (Wk. Alk)

8. 8
Phosphate bufferPhosphate buffer
• Major intracellular buffer
• H+
+ HPO4
2-
↔ H2PO4-
• (Wk.Acid)
• OH-
+ H2PO4
-
↔ H2O + HPO4
2-
• (Wk.Base)

9. 9
Protein BuffersProtein Buffers
• Includes hemoglobin, work in blood and ISF
• Carboxyl group gives up H+
• Amino Group accepts H+
• Side chains that can buffer H+
are present on
many amino acids.

10. Bicarbonate-Carbonic Acid
• Body’s major buffer
• Carbonic acid - H2CO3 (Acid)
• Bicarbonate - HCO3 (Base)
1 20
pH = 7.4
H2CO3 ……………… HCO3
24 mEq/L1.2 mEq/L

11. Bicarbonate-Carbonic Acid
• Ratio important
• Not absolute values
• Person with COPD (CAL)
1 20
7.4
H2CO3 ……………… HCO3
48 mEq/L2.4 mEq/L

12. Regulation
• Key concept
• Carbonic anhydrase equation
CO2 +H2O H2CO3 H+ + HCO3
Carbon Carbonic Bicarbonate
Dioxide Acid
(ACID) (BASE)

13. • Acid
Substance that contains H+ ions
that can be released (H2CO3)
Carbonic acid releases H+ ions
• Base
Substance that can accept H+ ions
(HCO3)
Bicarbonate accepts H+ ions

14. • As CO2 increases, carbonic acid
increases, H+ ions increase
• pH drops….. becomes more acidic
CO2 +H2O H2CO3 H+ + HCO3
Carbonic Bicarbonate
Acid
CO2 H2CO3 H+ HCO3
(pH Acidic <7.35)

15. • As HCO3 increases, H+ decreases
• pH rises, becomes more alkaline
CO2 +H2O H2CO3 H+ + HCO3
Carbonic Bicarbonate
Acid
CO2 H2CO3 H+ HCO3
(pH Basic >7.45)

16. 16
Rates of correctionRates of correction
• BuffersBuffers function almost instantaneously. (1st
line of defense)
• Respiratory mechanismsRespiratory mechanisms take several
minutes to hours. (2nd
line of defense)
• Renal mechanismsRenal mechanisms may take several hours
to days. (3rd
line of defense)

17. 17

18. 18

19. Respiratory & Renal Regulation
• Lungs control CO2
• Kidneys control HCO3
• pH =
kidneys (bicarbonate)
lungs (carbon dioxide)

20. Respiratory Regulation
Mechanisms of control …
• Hyperventilation -- blow off CO2
• Hypoventilation -- retain CO2
Regulation rapid...
• Seconds to minutes
Measured by PaCO2 - Normal
35-45 mm Hg

21. Renal Regulation
Mechanism of control
• Excretion or retention of
H+ or HCO3
Regulation….. Slow
• Hours to days to change pH
Normal serum HCO3
• 22-26 mEq/L

22. Acid-Base Imbalances
• Ratio of 20 to 1 out of balance
• Acidosis (acidemia)
• pH falls below 7.35
• Increase in blood carbonic acid
or
• Decrease in bicarbonate

23. Acid-Base Imbalances
• Alkalosis (alkalemia)
• pH greater than 7.45
• Increase in bicarbonate
or
• Decrease in carbonic acid

24. Acid-Base Imbalances
Primary cause or origin:
• Metabolic
Changes brought about by systemic
alterations (cellular level)
• Respiratory
Changes brought about by
respiratory alterations

25. 25

26. Acid-Base Imbalances
Compensation
• Corrective response of kidneys
and/or lungs
Compensated
• Restoration of pH and 20 : 1 ratio
Uncompensated
• Inability to adjust pH or 20 : 1 ratio

27. Four Basic Types of Imbalance
1. Respiratory Acidosis
2. Respiratory Alkalosis
3. Metabolic Acidosis
4. Metabolic Alkalosis

28. Respiratory Acidosis
• Carbonic acid excess
• Exhaling of CO2
inhibited
• Carbonic acid builds up
• pH falls below 7.35
• Cause = Hypoventilation (see chart)
H2CO3

29. Acid-Base Imbalances
• Normal
1 20
7.4
H2CO3 ……………… HCO3
24 mEq/L1.2 mEq/L

30. Respiratory Acidosis
1 13
7.21
H2CO3 ……………… HCO3
24 mEq/L
1.84 mEq/L

31. Respiratory Acidosis
• Compensation: How?
• Opposite regulating mechanism
• Problem = depressed breathing,
build up of CO2 in blood
• Response - Kidney retains HCO3
(Response ….. Slow)

32. 32

33. Respiratory Alkalosis
• Carbonic acid deficit
• Increased exhaling
of CO2
• Carbonic acid decreases
• pH rises above 7.45
• Cause = hyperventilation (see chart)
H2CO3

34. Acid-Base Imbalances
• Normal
1 20
7.4
H2CO3 ……………… HCO3
24 mEq/L1.2 mEq/L

35. Respiratory Alkalosis
1 40
7.70
H2CO3 ……………… HCO3
24 mEq/L
0.6 mEq/L

36. 36

37. Respiratory Alkalosis
• Compensation:
• Problem = excess “blowing off”
of CO2
• Result = decrease in carbonic
acid and increase in HCO3
• Response: Kidney excretes excess
bicarbonate

38. Metabolic Acidosis
• Base-bicarbonate deficit
• Low pH (< 7.35)
• Low plasma bicarbonate (base)
• Cause = relative gain in H+
(lactic acidosis, ketoacidosis)
or actual loss of HCO3
(renal failure, diarrhea)

39. Acid-Base Imbalances
• Normal
1 20
7.4
H2CO3 ……………… HCO3
24 mEq/L1.2 mEq/L

40. Metabolic Acidosis
• Kidney failure (decrease in bicarbonate)
1 10
7.10
H2CO3 ……………… HCO3
12 mEq/L
1.2 mEq/L

41. Metabolic Acidosis
• Lactic acidosis, keto acidosis (increase
acid… no change in bicarbonate)
1 10
7.10
H2CO3 ……………… HCO3
24 mEq/L
2.4 mEq/L

42. 42

43. Metabolic Acidosis
• Compensation:
• Problem = low HCO3 (base) or high
H+ ion (acid)
• Response: Lungs hyperventilate
• Get rid of CO2
(decrease PaCO2 and therefore raise
level of HCO3)

44. Metabolic Alkalosis
• Bicarbonate excess
• High pH (> 7.45)
• Loss of H+ ion or gain of HCO3
• Most common causes vomiting,
gastric suctioning (NG tube)
• Other: Abuse of antacids,
K+ wasting diuretics

45. Acid-Base Imbalances
• Normal
1 20
7.4
H2CO3 ……………… HCO3
24 mEq/L1.2 mEq/L

46. Metabolic Alkalosis
1 30
7.58
H2CO3 ……………… HCO3
36 mEq/L
1.2 mEq/L

47. 47

48. Metabolic Alkalosis
• Compensation:
• Problem = too much base
• Response: Lungs compensate by
hypoventilating
• Retain CO2, increase PaCO2
• Increase acid level in blood

49. Assessing ABGs
• pH 7.35 - 7.45
• PaCO2 35 - 45 mmHg
• HCO3 22 - 26 mEq/L
• Base Excess -2 - +2 mEq/L
• PaO2 80 - 100 mm Hg
• O2 saturation 95 - 100 %

50. Interpreting ABGs
1. Start with pH
–Normal?
–Acidosis?
–Alkalosis?
___/______/___/______/___
6.8 7.35 7.45 8.0
Acidosis Alkalosis

51. Interpreting ABGs
2. Assess PaCO2
(respiratory value)
_____/________/______
35 45
Respiratory Respiratory
Alkalosis Acidosis
(Note reversal)
(See Chart)

52. Interpreting ABGs
3. Evaluate metabolic indicators
Bicarbonate (HCO3) 22-26
and
Base excess (-2 to +2)

53. Interpreting ABGs
HCO3
_______/_______/________
22 26
BE ______/_______/_________
-2 +2
Metabolic Metabolic
acidosis alkalosis

54. Interpreting ABGs
4. Determine level of compensation
Has the body tried to readjust
the pH?
• Uncompensated
• Partly compensated
• Compensated

55. Interpreting ABGs
Uncompensated
• pH abnormal (high or low)
• One component abnormal (high or
low CO2 or HCO3)
• The other component is normal
(The component not causing the acid-
base imbalance is still normal)

56. Partly compensated
• pH not normal (but moving toward
normal)
• Both CO2 and HCO3 are outside
normal range
• The component that was normal is
changing in order to compensate

57. Interpreting ABGs
Compensated
• pH normal
• Other values abnormal in
opposite directions
• One is acidotic the other alkaline

58. Interpreting ABGs
• Determine amount of hypoxemia
present
• Normal PaO2 (adults - room air)
• < 70 years = 80-100 mm Hg
70-79 = 70-100 mm Hg
• Drops 10 mm Hg for each decade

59. Interpreting ABGs
• Hypoxemia = < 70 mm Hg
(for adult < 70 years old)
• Mild = 60-80 mm Hg
• Moderate = 40-60 mm Hg
• Severe = < 40 mm Hg

60. Interpreting ABGs
• Oxygen saturation (pulse
oximetry)
• 95-100%
• < 91% confusion
• < 70% life threatening

61. • Practice Problems
• A 80 year old female present in medical
OPD of NWGH with severe pneumonia,
fever & lethargy. On lab investigation her
ABG report showed following results.
• pH = 7.25
• PaCO2 = 55 mm Hg
• HCO3 = 34 mEq/L
• PaO2 = 65 mm Hg
• O2 sat = 80%

62. Practice Problems
What is the problem?
Acidosis or alkalosis?
Respiratory or metabolic?
Compensated or not?
Level of hypoxemia?
Diagnoses?
Interventions?

63. Tic-Tac-Toe Method
ACID NORMAL ALKALINE
_pH__________________________
_PaCO2_______________________
HCO3
Problem: _Respiratory acidosis___
Compensated? _Uncompensated_____

64. • Level of hypoxemia?
mild to normal….
• Diagnosis?
• Impaired gas exchange
• R/T lung congestion Dx pneumonia
AMB CO2, acid pH, low PaO2,
crackles, rapid resp rate and HR etc.

65. 65

66. SOME MCQsSOME MCQs
• A young girl age 16 presents with
respiratory alkalosis. The primary event
in respiratory alkalosis is:
a)Decrease in Pco2
b)Decrease in pH
c)Decrease in plasma chloride
d)Increase in plasma bicarbonate
e)Rise in Pco2

67. • Name the acid base disturbance if theName the acid base disturbance if the
pH=7.23, PCOpH=7.23, PCO22=52, PO=52, PO22=50, HCO=50, HCO33=24.=24.
a)Metabolic acidosis
b)Metabolic alkalosis
c)Mixed Abnormality
d)Respiratory acidosis
e)Respiratory alkalosis

68. • Quantitatively, the most significant bufferQuantitatively, the most significant buffer
system in plasma issystem in plasma is
a)Carbonic acid-bicarbonate buffer system
b)Hemoglobin buffer system
c)Lactic acid buffer system
d)Phosphate buffer system
e)Protein buffer system

69. • Respiratory acidosis results from:Respiratory acidosis results from:
a)Chronic renal failure
b)Excessive elimination of bicarbonate
c)Excessive elimination of carbon dioxide
d)Retention of carbon dioxide
e)Retention of bicarbonate

70. • Plasma bicarbonate is decreased in:Plasma bicarbonate is decreased in:
a)Metabolic acidosis
b)Metabolic alkalosis
c)Mixed Abnormality
d)Respiratory alkalosis
e)Respiratory acidosis

71. • The most common cause of MetabolicThe most common cause of Metabolic
acidosis is:acidosis is:
a)Intestinal Obstruction
b)Hysteria
c)Meningitis
d)Pneumonia
e)Uncontrolled diabetes with keto acidosis

72. • Respiratory acidosis occurs in:Respiratory acidosis occurs in:
a)Any disease which impairs respiration like
emphysema
b)High Lactic acid
c)Poisoning by an acid
d)Pyloric stenosis
e)Renal disease

73. • THANK YOU..THANK YOU..
• ANY QUESTION..?ANY QUESTION..?