Alveolar Air Equation: Calculates partial pressure of O2 in Alveoli

PAO2 = (( - 47)) - (PaCO2/)

Shortcut: PAO2 = (7 x FiO2) - (PaCO2 +10)

A-a Gradient: Measures difference between aveolar and arterial O2

A-aDO2 = PAO2 - PaO2

25-65 on 100% O2 is
66 - 300 is mismatch
>300 =

Arterial O2 Content (CaO2) Best measurement of O2 delivered to tissues

CaO2 = ( x x SaO2) + (PaO2 x )
O2 in red blood cells plus O2 in plasma

Normal value is - vol% (mL/dL)

Mixed Venous O2 Content (CvO2) Total O2 in venous blood

CvO2 = (Hb x x ) + x .003)

Normal - vol%
CvO2 will when cardiac output decreases
SvO2 will decrease also.

Arterial - Venous O2 Content Difference Ca-vO2 - Provides estimate of Tissue O2 consumption
Ca-vO2 = CaO2 - CvO2

Normal is - vol %

Used in Fick equation to calculate Output

Cardiac Output Qt
Modified
Used to calculate Cardiac output when O2 consumption and O2 content differences are known
Qt = ( / (Ca-vO2())
Normal value is 4-8 L/min
VO2 = Qt x Ca-vO2 x 10

Shunt Equation
Qs / Qt

Portion of cardiac output that is shunted and does not participate in gas exchange

Qs/Qt = ((A-aDO2) x .003) / (A-aDO2) x .003) + Ca-vO2

Normal is - %
Can be estimated: Assuming 5% shunt increase for each 100 torr of A-aDO2

SaO2 Arterial O2 Saturation
% of Hb that is bound by O2 calculated by ABG analyzer
Measured by hemoximeter or co-ox

Large differences in calculated and measured could be because of increased carboxyhemoglobin levels

PaO2 is estimated by subtracting from

HB / Hct
HB is normally - g/dl
HCT is usually times HB in percent

Deadspace to Vt Ratio
VD/Vt
% of gas that doesn't participate in gas exchange
Normal is -%

((PaCO2 - PeCo2) / ) x 100

Increased VD/VT indicates deadspace disease like a

Normal Values

PCO2
Arterial
Range -
venous

PO2
Arterial
Range -
Venous

pH
Arterial
Range -
Venous
SO2
Arterial %
Range - %
Venous - %

HCO3-
Arterial
Range -
Venous
Normal BE +-
Hb
Arteral/Venous
Range -

CaO2
Arterial vol%
Range - vol%

CvO2
Venous vol%
Range - vol %