Acid-Base Balance

Lectures on respiratory physiologyLectures on respiratory physiology

Acid-Base BalanceAcid-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

CO2 + H2O H+ + HCO3-

[H2CO3][H+] x [HCO3

-]

AT EQUILIBRIUM,

K =

[H+] x [HCO3-]

SOLUBILITY x PCO2 =

H2CO3CA

Law of Mass Action

0.03 x PCO2

[H+] x [HCO3-]K =

WHICH, AFTER TAKING LOGS, BECOMES:

pH = pK + Log( ) [HCO3-]

0.03 x PCO2

- THE HENDERSON - HASSELBALCH EQUATION

Derivation of normal pH

Davenport Diagram

6.8 7.0 7.2 7.4 7.6 7.8 8.00

10

20

30

40

50PL

ASM

A [

HC

O3- ],

meq

/l

pH

pH = 6.1 + Log( ) [HCO3-]1.2

PCO2 = 40

7.40

24NORMAL

6.8 7.0 7.2 7.4 7.6 7.8 8.00

10

20

30

40

50PL

ASM

A [

HC

O3- ],

meq

/l

pH

PCO2:40

3020

10

6080100

6.8 7.0 7.2 7.4 7.6 7.8 8.00

10

20

30

40

50

PLA

SMA

[H

CO

3- ], m

eq/l

pH

pH = pK + Log( ) [HCO3-]0.03 x PCO2

4080

20BUFFERLINE

N

ACID - BASE DISTURBANCES:

* RESPIRATORY ALKALOSIS

* RESPIRATORY ACIDOSIS

* METABOLIC ACIDOSIS

* METABOLIC ALKALOSIS

6.8 7.0 7.2 7.4 7.6 7.8 8.00

10

20

30

40

50PL

ASM

A [

HC

O3- ],

meq

/l

pH

RESPIRATORY ACIDOSIS:

4080

20BUFFERLINE

H+ + HCO3- CO2 + H2O

N

6.8 7.0 7.2 7.4 7.6 7.8 8.00

10

20

30

40

50PL

ASM

A [

HC

O3- ],

meq

/l

pH

RESPIRATORY ACIDOSIS:

4080

20BUFFERLINE

H+ + HCO3- CO2 + H2O

N

6.8 7.0 7.2 7.4 7.6 7.8 8.00

10

20

30

40

50PL

ASM

A [

HC

O3- ],

meq

/l

pH

RESPIRATORY ACIDOSIS:

4080

20BUFFERLINE

H+ + HCO3- CO2 + H2O

N

6.8 7.0 7.2 7.4 7.6 7.8 8.00

10

20

30

40

50PL

ASM

A [

HC

O3- ],

meq

/l

pH

RESPIRATORY ALKALOSIS:

4080

20BUFFERLINE

H+ + HCO3- CO2 + H2O

N

6.8 7.0 7.2 7.4 7.6 7.8 8.00

10

20

30

40

50PL

ASM

A [

HC

O3- ],

meq

/l

pH

RESPIRATORY ALKALOSIS:

4080

20BUFFERLINE

H+ + HCO3- CO2 + H2O

N

6.8 7.0 7.2 7.4 7.6 7.8 8.00

10

20

30

40

50PL

ASM

A [

HC

O3- ],

meq

/l

pH

METABOLIC ACIDOSIS:

4080

20BUFFERLINE

H+ + HCO3- CO2 + H2O

N

6.8 7.0 7.2 7.4 7.6 7.8 8.00

10

20

30

40

50PL

ASM

A [

HC

O3- ],

meq

/l

pH

METABOLIC ACIDOSIS:

4080

20BUFFERLINE

H+ + HCO3- CO2 + H2O

N

6.8 7.0 7.2 7.4 7.6 7.8 8.00

10

20

30

40

50PL

ASM

A [

HC

O3- ],

meq

/l

pH

METABOLIC ALKALOSIS

4080

20BUFFERLINE

H+ + HCO3- CO2 + H2O

6.8 7.0 7.2 7.4 7.6 7.8 8.00

10

20

30

40

50PL

ASM

A [

HC

O3- ],

meq

/l

pH

METABOLIC ALKALOSIS

4080

20BUFFERLINE

H+ + HCO3- CO2 + H2O

6.8 7.0 7.2 7.4 7.6 7.8 8.00

10

20

30

40

50PL

ASM

A [

HC

O3- ],

meq

/l

pH

COMPENSATED RESPIRATORY ACIDOSIS

4080

20BUFFERLINE

COMPENSATED METABOLIC ALKALOSIS

Oxygen Delivery to Tissues

CAPILLARIES

CAPILLARIES

DIFFUSION

HEART ANDCIRCULATION

TISSUE

VENTILATION

THE OXYGEN TRANSPORT SYSTEM

LUNGS

PERFUSION

DIFFUSION

Fick equation for diffusion through a tissue sheet

Distribution of PO2 between capillaries

Critical PO2 for mitochondrial respiration

Classification of tissue hypoxia:

* Anemic hypoxia* Hypoxic hypoxia

* Circulatory hypoxia* Histotoxic hypoxia