Oxygenation

Question 1

Hemoglobin (HbA)

Answer 1

2 alpha globins
2 beta globins
-each bound to a Heme
-4 O2 binding sites

T form: taut

• low affinity for O2, give up to tissues
• conditions favoring form: CO2, H+/acidosis, high temp, 2,3-DPG
• cause unloading of O2 into tissues

R form: relaxed
-high affinity for O2

Question 2

Positive cooperativity

Answer 2

once one Hb binds O2, more likely for the others to bind O2

Causes sigmoid shape to oxygen-hemoglobin dissociation curve

Question 3

What shifts the oxygen-hemoglobin dissociation curve to the right

Answer 3

“CADET face Right”

CO2
Acidosis
high 2,3-DPG
increased Exercise
increased Temp

Oxygen unloads
R –> T form shift

Question 4

What shifts the oxygen-hemoglobin dissociation curve to the left

Answer 4

decreased CO2
Alkalosis
Low 2,3-DPG
decreased metabolic need
lower temp

Question 5

Methemoglobin

Answer 5

toxic form
can’t carry O2 as well –> tissue hypoxia

oxidized form of iron - ferriC form, Fe3+
-c third letter

Higher affinity to cyanide

Question 6

Substances known to cause methemoglobiemia

Answer 6

Nitrates, nitrites
antimalarials - cloroquin, primaquine
Dapsone
Sulfonamides
Local anesthetics - lidocaine
metoclopramide

Question 7

Treatment of methemoglobinemia?

Answer 7

Methylene blue
Vit C

If need to give med that causes it long term, give cimetidine (gradually lowers)

Question 8

Cyanide antidote kit

Answer 8

amyl nitrite
sodium nitrite
-form methemoglobin to transport cyanide

Thiosulfate - binds cyanide –> thiocyanate –> renal excretion

Question 9

Carboxyhemoglobin

Answer 9

hemoglobin bound to CO

Hb affinity to CO 200-250X greater than O2

Decreased O2 binding capacity
Shifts O2 dissociation curve to left

Can’t dx w/ pulse oximetry - will look normal as Hb is saturated

Question 10

Total blood O2 content

Answer 10

dissolved O2 + (hemoglobin binding capacity x O2 saturation)

Conceptual, not a calculated equation

Question 11

Anemia effect on blood O2 content

Answer 11

Decreases total O2 content

Causes:
Decrease RBC syntehsis
Increased RBC destruction
loss of RBCs

Pulse Ox will be normal - saturation of hemoglobin present is normal

Question 12

Chronic lung disease effect on blood O2 content

Answer 12

decreased PaO2
Physiologic shunt –> low O2 extraction ratio

Low blood O2 content

Question 13

Exercise/activity effect on blood O2 content

Answer 13

decreases venous PO2
Increases O2 demand
Increases O2 extraction

Question 14

Alveolar gas equation

Answer 14

PAO2 = PIO2 - (PaCO2/R)

PAO2 = 150 - PaCO2/0.8
As PaCO2 goes up, PAO2 goes down and vice versa

Question 15

A-a gradient

Answer 15

PAO2 - PaO2

normal 10-15 mmHg

Things increasing A-a gradient

• shunting or V/Q mismatch
• pulmonary fibrosis - diffusion limitation
• increased FiO2 - flood alveoli w/ O2 but physiologic limit to amount that can diffuse, artificially increased
• advanced age

Question 16

PaO2/FiO2

Answer 16

normal: 300-500 mmHg
less than 300 - gas exchange deficit
less than 200 - severe hypoxia

Question 17

Mechanisms of oxygen deprivation

Answer 17

Inadequate PaO2 (hypoxemia)

• high altitude
• hypoventilation
• high A-a gradient
• –diffusion limitation (pulmonary fibrosis)
• –Right to Left cardiac shunt
• –V/Q mismatch

Inadequate O2 delivery to organs/tissues (hypoxia)

• hypoxemia
• anemia
• CO poisoning
• Low Cardiac Output

Inadequate perfusion (ischemia)

• obstruction of arterial flow (MI or stroke)
• reduced venous drainage

Question 18

Ventilation

Answer 18

O2 from outside body to the alveoli

Question 19

Oxygenation

Answer 19

O2 from alveoli to the blood

Question 20

CO2 transport in blood

Answer 20

1. converted to HCO3- by carbonic anhydrase
2. bound to N terminus of globin as carbaminohemoglobin
3. dissolved in blood (measured w/ ABG)

Question 21

Response to exercise

Answer 21

Increased O2 consumption
Increased CO2 production
Higher ventilation rate

V/Q in apex and base more uniform - dilated pulmonary capillaries in apex

Increased pulmonary blood flow d/t increased cardiac output

decreased pH - lactic acid

No change in PaO2 and PaCO2
Increased venous CO2 content