LEC 1 Flashcards
- facilitates gas movement
between the lungs and the tissues
SIMPLE DIFFUSION
Used to estimate the efficiency of pulmonary O2
transfer.
A-a GRADIENT
Normal value of A-a gradient
(5 to 10 mmHg)
Frequently used for ventilated patients as a
measure of oxygenation abnormality and is one
of the main criteria for diagnosing ARDS
P/F ratio
MILD ARDS
> 200 mmHg to 300 mmHg
MODERATE ARDS
> 100 mmHg to 200 mmHg
SEVERE ARDS
</= 100 mmHg
is the process whereby gas molecules
move from an area of high partial pressure to an area of
low partial pressure.
diffusion
Barriers to Diffusion:
- alveolar epithelium
- interstitial space
- capillary endothelium
- erythrocyte membrane
portion of the cardiac output that returns to the
left heart without being oxygenated by
exposure to ventilated alveoli.
Anatomic Shunts
what are the Two right-to-left anatomic shunts exist in normal
humans:
- bronchial venous drainage and
- thebesian venous drainage
portion of the tidal volume that enters into
alveoli that are without any perfusion or without
adequate perfusion.
ALVEOLAR DEAD SPACE
Conditions that can lead to alveolar dead space:
○ Pulmonary emboli
○ Partial obstruction of the pulmonary
vasculature
○ Destroyed pulmonary vasculature
(COPD)
○ Reduced cardiac output.
portion of the tidal volume that never reaches
the alveoli for gas exchange
ANATOMIC DEAD SPACE
sum of alveolar and anatomic dead space
PHYSIOLOGIC DEAD SPACE (VD)
Increased dead space or VD/VT ratio causes:
○ Decrease alveolar ventilation
○ Increase PaCO2
Anatomic and alveolar shunts together cause
venous admixture
alveolar shunts can be caused by:
○ COPD
○ Restrictive disorders
○ Any condition resulting in
hypoventilation
portion of venous blood travels from the right
heart to the left heart without being involved in
adequate gas exchange with ventilated portions
of the lung
PHYSIOLOGIC SHUNTS
Each gram of Hb can bind __ of oxygen
1.34mL
SaO2 formula
[HbO2/total Hb] x 100
normal Sao2
95% to 100%
Normal CaO2 concentration is
16-20ml/dl
CaO2 formula
(O.OO3 x PaO2) + (1.34 x Hb x SaO2)
FACTORS AFFECTING OXYGEN
LOADING AND UNLOADING
- pH (Bohr effect)
- body temp
- 2, 3 DPG
- abnormal Hg
fragility leads to hemolysis and thrombi
HbS (sickle cell hemoglobin)
Fe is oxidized
to its Ferric state which cannot combine
with O2
metHb (methemoglobin
partial pressure of O2 at which the Hb is
50% saturated, standardized to a pH
level of 7.40
p50
Approximately _____ mL/dL of CO2 is normally
carried in the blood
45-55
normal P50 is approximately
26.6 mm Hg
transport mechanisms of CO2
1.) Dissolved in Physical Solution - 8%
2.) Chemically Combined With Protein - 12%
3.) Ionized as Bicarbonate - 80%
influence of oxyhemoglobin saturation
on CO2 dissociation
Haldane effect
TYPE OF HYPOXIA CHARACTERIZED BY Decreased carrying capacity of blood for
oxygen
Anemic hypoxia
TYPE OF HYPOXIA CHARACTERIZED BY Decreased CO, resulting in increased
systemic transit time
Stagnant hypoxia
TYPE OF HYPOXIA CHARACTERIZED BY Inability of tissue to use available oxygen
Histotoxic hypoxia
TYPE OF HYPOXIA CHARACTERIZED BY Decreased diffusion of O2 across AC
membrane
Hypoxemic hypoxia
abnormally low PaO2
Hypoxemia
Causes of Hypoxemia:
● V/Q mismatch (most common)
● Hypoventilation
● Diffusion defect
● Shunting
● Low PiO2 (altitude)
Where perfusion exceeds ventilation
Physiologic shunt
DO2 is normal but cells undergo hypoxia
Dysoxia
