Transcript Acid-Base Balance

Lectures on respiratory physiology
Acid-Base Balance
Some definitions
• An acid is a molecule that releases
hydrogen ions in solution
• A base is a molecule that can accept a
hydrogen ion
• A buffer is a substance that can
reversibly bind hydrogen ions
Titration curve for the bicarbonate buffer system
Law of Mass Action
CA
CO2 + H2O
H2CO3
AT EQUILIBRIUM,
K
=
=
+
H + HCO3
+
[H ] x [HCO3 ]
[H2CO3]
+
[H ] x [HCO3 ]
SOLUBILITY x PCO2
K
=
+
[H ] x [HCO3 ]
0.03 x PCO2
WHICH, AFTER TAKING LOGS, BECOMES:
pH = pK + Log(
[HCO3 ]
0.03 x PCO2
)
- THE HENDERSON - HASSELBALCH EQUATION
Derivation of normal pH
Davenport Diagram
[HCO3-]
)
1.2
PLASMA [HCO3-], meq/l
pH = 6.1 + Log(
50
PCO2 = 40
40
30
24
NORMAL
20
10
7.40
0
6.8
7.0
7.2
7.4
pH
7.6
7.8
8.0
PLASMA [HCO3-], meq/l
50
40
10080
PCO2:
60
30
40
30
20
20
10
10
0
6.8
7.0
7.2
7.4
pH
7.6
7.8
8.0
PLASMA [HCO3-], meq/l
[HCO3-]
pH = pK + Log(
)
0.03 x PCO2
50
40
80
BUFFER
LINE
40
20
30
N
20
10
0
6.8
7.0
7.2
7.4
pH
7.6
7.8
8.0
ACID - BASE DISTURBANCES:
* RESPIRATORY ACIDOSIS
* RESPIRATORY ALKALOSIS
* METABOLIC ACIDOSIS
* METABOLIC ALKALOSIS
RESPIRATORY ACIDOSIS:
PLASMA [HCO3-], meq/l
H+ + HCO3
CO2 + H2O
50
40
BUFFER
LINE
80
40
20
30
N
20
10
0
6.8
7.0
7.2
7.4
pH
7.6
7.8
8.0
RESPIRATORY ACIDOSIS:
PLASMA [HCO3-], meq/l
H+ + HCO3
CO2 + H2O
50
40
BUFFER
LINE
80
40
20
30
N
20
10
0
6.8
7.0
7.2
7.4
pH
7.6
7.8
8.0
RESPIRATORY ACIDOSIS:
PLASMA [HCO3-], meq/l
H+ + HCO3
50
40
BUFFER
LINE
CO2 + H2O
80
40
20
30
N
20
10
0
6.8
7.0
7.2
7.4
pH
7.6
7.8
8.0
RESPIRATORY ALKALOSIS:
PLASMA [HCO3-], meq/l
+
H + HCO3
CO2 + H2O
50
40
80
BUFFER
LINE
40
20
30
N
20
10
0
6.8
7.0
7.2
7.4
pH
7.6
7.8
8.0
RESPIRATORY ALKALOSIS:
PLASMA [HCO3-], meq/l
+
H + HCO3
CO2 + H2O
50
40
80
BUFFER
LINE
40
20
30
N
20
10
0
6.8
7.0
7.2
7.4
pH
7.6
7.8
8.0
METABOLIC ACIDOSIS:
PLASMA [HCO3-], meq/l
H+ + HCO3
CO2 + H2O
50
40
80
BUFFER
LINE
40
20
30
N
20
10
0
6.8
7.0
7.2
7.4
pH
7.6
7.8
8.0
METABOLIC ACIDOSIS:
PLASMA [HCO3-], meq/l
+
H + HCO3
CO2 + H2O
50
40
80
BUFFER
LINE
40
20
30
N
20
10
0
6.8
7.0
7.2
7.4
pH
7.6
7.8
8.0
METABOLIC ALKALOSIS
PLASMA [HCO3-], meq/l
+
H + HCO3
CO2 + H2O
50
40
80
BUFFER
LINE
40
20
30
20
10
0
6.8
7.0
7.2
7.4
pH
7.6
7.8
8.0
METABOLIC ALKALOSIS
PLASMA [HCO3-], meq/l
+
H + HCO3
50
40
CO2 + H2O
80
BUFFER
LINE
40
20
30
20
10
0
6.8
7.0
7.2
7.4
pH
7.6
7.8
8.0
COMPENSATED RESPIRATORY ACIDOSIS
PLASMA [HCO3-], meq/l
COMPENSATED METABOLIC ALKALOSIS
50
40
80
BUFFER
LINE
40
20
30
20
10
0
6.8
7.0
7.2
7.4
pH
7.6
7.8
8.0
Oxygen Delivery to Tissues
VENTILATION
LUNGS
DIFFUSION
CAPILLARIES
HEART AND
CIRCULATION
PERFUSION
CAPILLARIES
DIFFUSION
TISSUE
THE OXYGEN TRANSPORT SYSTEM
Fick equation for diffusion through a tissue sheet
Distribution of PO2 between capillaries
Critical PO2 for mitochondrial respiration
Classification of tissue hypoxia:
*
Hypoxic hypoxia
*
Anemic hypoxia
*
Circulatory hypoxia
*
Histotoxic hypoxia