O2 Transport & Acid Base Chemistry
State the two ways Oxygen is
carried in the blood, explaining
where each occurs.
Dissolved in plasma
Combined with hemoglobin
Define Henry’s Law.
Weight of gas dissolving in liquid is
proportional to the partial pressure
of a gas
Define Graham’s Law.
Rate of diffusion of a gas is directly
proportional to its solubility
coefficient and inversely
proportional to the square root of
its density.
O2 Transport & Acid Base Chemistry
CO2 is ____ times more diffusible
than O2.
20
CO is ______ times more diffusible
that O2.
200
What is Hemoglobin’s affinity for
CO as compared to that of O2?
Hgb’s affinity for CO is 200 times
more than for O2.
O2 Transport & Acid Base Chemistry
How would you find the amount of
dissolved O2 in 1 ml of plasma?
0.003 x PAO2
True or False:
The oxygen in hemoglobin exerts a
partial pressure.
False
How do you calculate the amount of
oxygen combined with
hemoglobin?
1.34 x Hgb x SaO2
O2 Transport & Acid Base Chemistry
True of False:
The oxyhemoglobin dissociation
curve is sigmoidal due to Hgb
affinity for O2 at each of 4 binding
sites
True
True or False:
In the steep portion of the
oxyhemoglobin dissociation curve,
minimal changes in PO2 will cause
minimal changes in saturation and
total O2 content
False – in the steep portion of the curve, minimal
changes in PO2 will cause drastic changes in
saturation and total O2 content
What P50?
P50 is where Hgb is 50% saturated
with O2 and is normally a PaO2 of 27
mmHg
O2 Transport & Acid Base Chemistry
A shift of the oxyhemoglobin
dissociation curve to the right
causes what?
A decreased affinity for O2,
resulting in decreased saturation
but increased O2 to tissues
What factors will cause the
oxyhemoglobin dissociation curve
to shift to the right?
Increased PCO2
Increased H+ (decreased pH)
Increased 2,3, DPG
Increased temperature
A shift of the oxyhemoglobin
dissociation curve to the left
causes what?
Increased affinity for O2, resulting in
increased saturation but decreased
O2 to the tissues
O2 Transport & Acid Base Chemistry
What factors will cause the
oxyhemoglobin dissociation curve
to shift to the left?
Decreased PCO2
Decreased H+ (increased pH)
Decreased temperature
Decreased 2,3, DPG
Describe the Bohr effect.
The effect of H+ or CO2 on Hgb
affinity for O2
At lungs – PCO2 is low –
increased affinity for O2
At tissues PCO2 is high
decreases affinity for O2
Give the formula for total O2
content.
CaO2 = (0.003 x PaO2) + (1.34 x Hgb
x SaO2)
O2 Transport & Acid Base Chemistry
Give three causes of hypoxemia.
1. Decreased alveolar oxygen
tension
2. Alveolar hypoventilation
3. Decreased hemoglobin
saturation
4. V/Q abnormalities –
intrapulmonary shunting
Give two physiologic responses to
hypoxemia.
Increased ventilation
Increased cardiac output
Define hypoxemia.
Deficiency of oxygen in the arterial
blood.
O2 Transport & Acid Base Chemistry
What is the alveolar air equation?
PAO2 = FIO2 (PBar - PH2O vapor) - PaCO2
RQ
What is an intrapulmonary shunt?
Blood going from the right to left
heart without oxygenation.
Name the four types of hypoxemia.
Hypoxic/Ambient
Anemic/Hemic
Stagnant/Circulatory
Histotoxic
O2 Transport & Acid Base Chemistry
Define Hypoxia.
Decreased oxygen to the tissues.
Describe hypoxemic hypoxia.
PaO2 is decreased
(high altitudes)
Describe anemic hypoxia.
Decreased Hgb or the inability of
Hgb to accept O2
(CO poisoning)
O2 Transport & Acid Base Chemistry
Describe stagnant hypoxia
Heart unable to deliver oxygenated
blood to tissues (Low C.O.)
Describe histotoxic hypoxia.
Cells are unable to accept or use
oxygen
(cyanide poisoning)
What is the result of hypoxia?
Anaerobic metabolism
O2 Transport & Acid Base Chemistry
Define the Alveolar-Arterial Oxygen
Difference P(A-a)O2?
Measurement of the pressure
difference between the alveoli and
the arterial blood.
Used to estimate the percent of
intrapulmonary shunt.
What is an increased P(A-a)O2 an
indication of?
Respiratory defects in oxygenation
diffusion abilities
On 100% O2, every 50 mmHg
difference in P(A-a)O2 approximates
what?
A 2% shunt
O2 Transport & Acid Base Chemistry
What is the normal P(A-a)O2 value
on room air?
10 – 15 mmHg
How is Carbon Dioxide produced in
the body?
Produced from normal metabolism
How is CO2 carried in the blood?
1. In plasma and red blood cells
2. dissolved, as bicarbonate, &
attached to plasma proteins
O2 Transport & Acid Base Chemistry
How much percent of CO2 is
dissolved in plasma?
Approximately 8%
80% of CO2 is transported as what?
As Bicarbonate
12% of CO2 is transported where?
Attached to plasma proteins
O2 Transport & Acid Base Chemistry
Describe the Haldane Effect.
Effect of O2 on CO2 transport
At the lungs, PO2 is increased –
CO2 is unloaded off Hgb
At the tissues, PO2 is decreased –
CO2 is loaded on Hgb
Define eucapnea.
Normal CO2 (35-45 mmHg)
Define Hypocapnia.
CO2 below 35 mmHg
O2 Transport & Acid Base Chemistry
Define Hypocarbia.
CO2 below 35 mmHg
Define Hypercapnia.
CO2 above 45 mmHg
Define Hypercarbia.
CO2 above 45 mmHg
O2 Transport & Acid Base Chemistry
State the Henderson-Hasselbalch
Equation.
pH = pk + log (HCO3)
(H2CO3)
In the Henderson-Hasselbalch
Equation, what does pk =?
pk= 6.10
In the Henderson-Hasselbalch
Equation, what is the value of
HCO3?
24 mEq/L
O2 Transport & Acid Base Chemistry
In the Henderson-Hasselbalch
Equation, what is the value of
H2CO3?
1.2 mEq/L
In the Henderson-Hasselbalch
Equation, what is the ratio of HCO3
to H2CO3?
20 to 1
In relation to the HendersonHasselbalch equation, what would a
ratio of HCO3 to H2CO3 of 10/1
indicate?
acidemia
O2 Transport & Acid Base Chemistry
In relation to the HendersonHasselbalch equation, what would a
ratio of HCO3 to H2CO3 of 30/1
indicate?
alkalemia
What is the log of 20?
1.3
What is the purpose of buffer
systems?
To maintain the pH
O2 Transport & Acid Base Chemistry
Name two buffer systems?
1. HCO3/H2CO3 ratio
2. Hgb
3. Blood
phosphates
proteins
sulfates
ammonia groups
60% of the buffer system is made
up of what?
The HCO3/H2CO3 ratio
30% of the buffer system is made
up of what?
The Hgb
O2 Transport & Acid Base Chemistry
What is pH?
1. Negative log of the hydrogen ion
2. Reciprocal of the hydrogen ion
concentration
What is the entire pH scale from
(what to what)?
0-14
What is the normal pH range in
blood?
7.35 – 7.45
O2 Transport & Acid Base Chemistry
Give normal blood gases for
venous blood. (pH, PVCO2, PVO2,
HCO3).
pH 7.36, PVCO2 46, PVO2 40, HCO3 24
What is the normal O2 Saturation for
arterial blood?
95 – 100%
What is the normal O2 Saturation for
venous blood?
75%
O2 Transport & Acid Base Chemistry
What is the normal O2 content for
arterial blood?
18 – 20 vol%
What is the normal O2 content for
venous blood?
15 vol%
In relationship to compensation,
what do the kidneys do?
Excrete H+ which ↑ HCO3 to
compensate for an ↑ CO2
Excrete less H+ & more HCO3 to
compensate for ↓ CO2
O2 Transport & Acid Base Chemistry
In relationship to compensation,
how long does it take the kidneys to
compensate?
May take 3 days
In relationship to compensation,
what do the lungs do?
↓ CO2 to compensate for a ↓HCO3
↑ CO2 to compensate for a ↑HCO3
In relationship to compensation,
how long can the lungs maintain
compensation?
For a short term only
O2 Transport & Acid Base Chemistry
What would you pharmacologically
administer to increase pH?
Sodium bicarbonate (NaHCO3)
What would you pharmacologically
administer to decrease pH?
Ammonium chloride (NH3Cl)
How is hypoxemia assessed
differently for patients of 60 years
old?
Subtract 1 mmHg for every year
over 60.
O2 Transport & Acid Base Chemistry
How is hypoxemia assessed for
patients with abnormal Hgb?
Calculate total O2 content.
(Hgb x 1.34 x SaO2) + (0.003 x PaO2)
In mild hypoxemia what would the
CaO2 be?
CaO2 17 vol%
15-17 vol%
In moderate hypoxemia what would
the CaO2 be?
CaO2 15 vol%
12-14 vol%
O2 Transport & Acid Base Chemistry
In severe hypoxemia what would
the CaO2 be?
CaO2 12 vol%
How is ventilation controlled?
1. Under control of autonomic
nervous system
2. Is controlled by central &
peripheral chemoreceptors
What stimulates the central
chemoreceptors?
1. Increased CO2 in CSF causes
increased H+
2. Causes a stimulation of the
Inspiratory center
O2 Transport & Acid Base Chemistry
What is the purpose of the HeringBreuer Reflex?
Limits inspiration
True or False:
Stretch receptors are located in
smooth muscle of the large airways
only
False – in both large and small
airways
Name the two Peripheral
Chemoreceptors?
Carotid bodies
Aortic bodies
O2 Transport & Acid Base Chemistry
What stimulates the peripheral
chemoreceptors?
Respond to hypoxemia
What does stimulation of the
carotid bodies cause and where are
they located?
Increases ventilation
Located in the bifurcations of the
common carotid arteries
What does stimulation of the aortic
bodies cause and where are they
located?
Stimulate heart rate
Located in the aortic arch