CPR 54-55 - Oxygen Transport, Alveolar Gases, and Diffusion

Question 1

What does the oxygen saturation stat refer to?

Answer 1

The percentage of Hb binding sites that are bound to oxygen.

Question 2

In a health person, how many grams of Hb does 100mL of blood contain?

Answer 2

15g Hb

Question 3

What volume of O2 can 1g of Hb bind?

Answer 3

1.36 mL of O2

Question 4

In 100mL of blood, how much dissolved O2 is present?

Answer 4

0.3mL of O2

Question 5

What is the hemoglobin saturation equation? Describe what each component of the equation respresents.

Answer 5

Question 6

Why is it important that the upper plateau of the Hb binding curve is so long?

Answer 6

This means that there will still be sufficient amounts of O2 loading onto the Hb even if alveolar pO2 falls slightly or the graph shifts to the right slightly.

Question 7

Why is it important that the steep region of the Hb binding curve is located where it is on the graph?

Answer 7

The steep region is where the most drastic changes in % Hb saturation occurs. This region occurs at the ppO2 range of the peripheral tissues that need the oxygen to leave Hb.

Question 8

Does oxygen saturation represent oxygen content?

Answer 8

NO

Oxygen content refers to the amount of oxygen in the blood while oxygen saturation ONLY refers to the saturation of Hb.

Question 9

Will Hb saturation or PaO2 fall in an anemic patient?

Answer 9

Neither

The only thing that falls is total blood oxygen content

Question 10

What factors cause a right shift in the Hb binding curve?

Answer 10

Temperature increase

pH decrease

ppCO2 increase

2,3-BPG increase

Question 11

Answer 11

Question 12

How long does it take blood to flow across an aveolar capillary? How long does it take for gas equilibration to occur?

Answer 12

0. 75s transit time
1. 25s equilibration time

Question 13

What is the Fick’s law equation that is used to determine the rate of gas transport in humans?

Answer 13

V_gas = D_L(P₁ - P₂)

Vgas - rate of gas transfer

D_L - diffusion coefficient

P1 - gas pressure from compartment gas is leaving

P2 - gas pressure from compartment gas is going

Question 14

How is a patient’s lung’s D_L determined?

Answer 14

A small amount of CO is given to a person to inhale and then the amount they exhale is measured. Since CO is absent in the blood initially, Fick’s equation is simplified to:

V_gas = D_L(P₁)

Once the gas exhaled is measured you know how much was inhaled and you can use Fick’s equation to find D_L

Question 15

Will exerciese increase or decrease a healthy person’s lung’s D_L? Why?

Answer 15

Increase, because the blood volume in the lungs increases which increases cross sectional area

Question 16

What is the difference between and anatomical and functional shunt?

Answer 16

Anatomical shunt - an aspect of anatomy is causing the shunt (ie - bronchial circulation)

Functional Shunt - an abnormal non-anatomical condition is causing the shunt (ie - fluid filled aveoli, collapsed lung)

Question 17

What is alveolar atelectasis?

Answer 17

The collapse or closure of an alveoli

Question 18

Describe what the RBC chloride shift is.

Answer 18

In the RBC, CO2 is converted to HCO3- and H+ via the CA reaction. The HCO3-/Cl- exchanger then uses the HCO3- gradient to bring Cl- into the RBC from the plasma.

Question 19

Describe what the Haldane Effect is?

Answer 19

Just like Hb has an O2 saturation curve it has a CO2 saturation curve. This curve is shifted to the right (meaning CO2 dissociates from Hb more easily) when Hb is in a higher ppO2 environment. This is because Hb wants to dissociate from CO2 when in the relaxed state. This is known as the haldane effect.

Question 20

Describe the concept of gas atelectasis and what can be done about it.

Answer 20

Many pathological conditions result in airways not always being patent. If I patient is on pure O2 supplementation when an airway closes off then all of that oxygen could be absorbed causing the alveolus to collapse (atelectasis). This does not occur with room air because nitrogen in the air is not absorbed and acts as a “splint.” A physician should always be cautious about ordering high supplemental oxygen if airway patency problems are suspected.