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Dry Atmospheric Gas at Standard Barometric Pressure

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- Po2159.0 torr
- Pco2 0.3 torr
- PN2600.6 torr

- PIo2149.0 torr
- PIco2 0.3 torr
- PIN2564.0 torr
- PIH2O 47.0 torr

Alveolar Gas at Standard Barometric Pressure

- PAo2104.0 torr
- PAco2 40.0 torr
- PAN2569.0 torr
- PAH2O 47.0 torr

ALVEOLAR AIR EQUATION

PACO2

PAO2 = PIO2 - + F

R

PACO2

PAO2 = FIO2

2

R

( PB - PH O) -

Mixed Expired Air at Standard Barometric Pressure

- PEo2120.0 torr
- PEco2 27.0 torr
- PEN2566.0 torr
- PEH2O 47.0 torr

At 37°C 1 ml of plasma contains

0.00003 ml O2 / torr PO2

1 gram of hemoglobin can combine with 1.34ml of oxygen when fully saturated

O2 bound to Hb

% Hb saturation = x 100%

O2 capacity of Hb

Pco2 , pH

temp, BPG

100

80

Pco2 , pH

temp, BPG

60

Hemoglobin saturation, %

50%

40

20

20

40

60

80

100

120

140

160

P50

Partial pressure of oxygen, torr

- Occurs when more than 5 grams of hemoglobin/100 ml of arterial blood are in the “deoxy” state
- Absence of cyanosis does not rule out hypoxemia (anemia)
- Presence of cyanosis does not always indicate hypoxemia (polycythemia)

Solubility of CO2 in Plasma

At 37°C 1 ml of plasma contains 0.03 mmol of CO2 / torr Pco2

Or

0.0006 ml of CO2 / torr Pco2

H

COO-

H

H

R - N + CO2 R - N + H+

Terminal amine group

Carbamino compound

Carbamino Compound

Transport of CO2 by the Blood

CO2

(Gas phase)

Carbonic

Anhydrase

_

CO2 + H2O

H2CO3

H+ + HCO3

(Dissolved in the aqueous phase)

TISSUE

PLASMA

ERYTHROCYTE

CO2

CO2

dissolved

CO2

H2O +

CO2

H2O

CO2

Carbonic anhydrase

dissolved

H2CO3

Cl-

Cl-

CAPILLARY WALL

HCO3-

HCO3- + H+

H+ + HbO2

O2

O2

O2 + HHb

HHb+CO2

O2

Carbamino compounds

ALVEOLUS

PLASMA

ERYTHROCYTE

CO2

CO2

dissolved

CO2

H2O +

CO2

H2O

CO2

Carbonic anhydrase

dissolved

H2CO3

Cl-

Cl-

CAPILLARY WALL

HCO3-

HCO3- + H+

H+ + HbO2

O2

O2

O2 + HHb

HHb+CO2

O2

Carbamino compounds

Pvo2

Cvo2

A Classification of the Causes of Hypoxia

Increased

FIo2

helpful?

PAo2

Pao2

Cao2

Classification

Hypoxic hypoxia

Low alveolar Po2

Diffusion impairment

Right to left shunts

V/Q mismatch

Anemic hypoxia

CO poisoning

Hypoperfusion hypoxia

Histotoxic hypoxia

Low

Norm

Norm

Norm

Norm

Norm

Norm

Norm

Low

Low

Low

Low

Norm

Norm

Norm

Norm

Low

Low

Low

Low

Low

Low

Norm

Norm

Low

Low

Low

Low

Low

Low

Low

High

Low

Low

Low

Low

Low

Low

Low

High

Yes

Yes

No

Yes

No

Possibly

No

No