Lecture 15: (Exam III) Obstructions, Capnography, Blood Gas Physiology, Hemoglobin (Andy's Cards)

Question 1

As expiration starts, why is PCO₂ at 0 mmHg?

Answer 1

The first portion of expired air comes from the anatomical dead space and should have no CO₂ in it.

Question 2

What should the End Tidal CO₂ be at the end of the plateau phase of clinical capnography?

Answer 2

40 mmHg

Question 3

Where in the graph below would we see mixing of V_D and V_A gasses?

Answer 3

In the first upstroke of the waveform there is mixing of V_A and V_D air.

Question 4

Where is the air coming from in the first second of the graph below?

Answer 4

V_D. You can tell that its dead space air due to the lack of CO₂.

Question 5

What should the End Tidal CO₂ be at the beginning of the plateau phase of clinical capnography?

Answer 5

38 mmHg

Question 6

In a perfect situation, P_ETCO2, P_ACO2, and P_aCO2 will all be equal to _______ mmHg.

Answer 6

40 mmHg

Question 7

How will Alveolar Dead Space affect your capnography?

Answer 7

P_ETCO2 will be lower than 40 mmHg

CO₂ will be “diluted”.

Question 8

Normally after gas exchange, our P_ACO₂ is about _______ if we bring in twice as much fresh air, P_ACO₂ should drop down to ________.

Answer 8

40 mmHg

20 mmHg

Arterial PCO2 will mirror the change in alveolar PCO2

Question 9

A decrease in V_T or RR will result in a buildup of _________.

Answer 9

P_ACO₂

Question 10

The best way to maintain a stable PCO₂ on the capnograph is to make small adjustments to ________ rather than to adjustments with ________ on the ventilator.

Answer 10

The best way to maintain a stable pCO2 on the capnograph is to make small adjustments to V_T rather than to adjust with respiratory rate on the ventilator.

Increasing RR will increase alveolar ventilation and dead space ventilation while increasing tidal volume will increase just alveolar ventilation.

Question 11

Where are the blood gas sensors located?

Answer 11

Aortic arch
Carotid bifurcations

Question 12

What happens when our blood gas sensors see we have an elevated PaCO₂?

Answer 12

The blood gas sensors will think there is a problem with ventilation or perfusion resulting in reflexive:

↑CO
↑MAP
↑RR

Question 13

Tight PaCO₂ control will result in tight _____ ______ control.

Answer 13

blood pressure

Question 14

If someone is hypertensive, what can you do with the ventilator to decrease blood pressure?

Answer 14

Blow off CO2 by either adjusting Vt or RR.

Question 15

What is the PCO₂ in our lungs at FRC?

Answer 15

PCO₂ is 40 mmHg at FRC

Question 16

What happens if we expire all of the CO₂ in our lungs?

Answer 16

All of the blood running through the lungs will unload massive amounts of CO₂ into the alveoli. This will result in a very low arterial PCO₂ resulting in decreased cardiac output.

The lungs keep a lid on this and prevent huge amounts of CO2 from being unloaded from the blood in between breaths.

Question 17

If P_ACO₂ became 0, then PaCO₂ would….

Answer 17

Drop considerably

This constitutes loss of buffering capability, all of PaCO₂ will start to be exhaled by the lungs.

Question 18

The higher the _________, the more CO₂ will be in the lungs to act as a buffer resulting in a more stable blood gas.

Answer 18

FRC

A lower FRC will have less CO2, less buffer, and more variation in blood gas.

Question 19

What will PCO2 in the lungs drop to if 350 mL of fresh air is instantly brought into the lungs?

How will the lung PCO2 rise back up to 40 mmHg?

Answer 19

35.8 mmHg (Fresh air will dilute lung CO2 during inspiration)

As blood moves through the lungs and unloads CO2, the lung PCO2 will rise to 40 mmHg.

(53:00)

Question 20

Calculate the concentration of PCO2 in the lungs at FRC.

Calculate the amount of CO2 in the lungs at FRC.

What will be the new concentration of CO2 if 350 mL of fresh air enters the lung?

What will be the new PCO2 in the lungs?

Answer 20

40 mmHg/ 760 mmHg = 0.05263
[CO2] = 5.26%

0.05263 x 3L = 157.89 mL of CO2

157.89 mL / 3350 mL = 0.0471
New [CO2] = 4.71%

760 mmHg x 0.0471 = 35.7 mmHg
New PCO2 = 36 mmHg

Question 21

What happens during the slow rise of PCO2 from 38 mmHg to 40 mmHg?

Answer 21

CO2 is being unloaded from the blood into the alveoli.

Question 22

What is P_aCO2 of the pulmonary artery?

Can lung PCO2 exceed 40 mmHg?

Answer 22

45 mmHg

Yes, at the end of expiration, the lung PCO2 can exceed 40 mmHg if there is a delay in the next breath.

Question 23

What will a catastrophic MI do to your capnograph?

Answer 23

MI will result in low cardiac output and low pulmonary blood flow, resulting in a big drop off in your end-tidal CO2.

If no carbonated blood is circulating, there will be no ETCO2. PE will do the same thing. Watch for big drop-offs in ETCO2.

Question 24

Capnographs are very sensitive to ________.

Answer 24

moisture

Question 25

What is the solubility coefficient of oxygen?

Answer 25

0.003 mL O2/ mmHg PO₂ per dL of blood

Question 26

If the partial pressure of oxygen is 100 mmHg, how many mL of O2 is that per dL?

Answer 26

100 mmHg PO2 x 0.003 mL O2/ (mmHg PO2 x dL) = 0.3 mL O2/dL

Question 27

If the partial pressure of oxygen is 40 mmHg, how many mL of O2 is that per dL?

Answer 27

40 mmHg PO2 x 0.003 mL O2/ (mmHg PO2 x dL) = 0.12 mL O2/dL

Question 28

If a gas is insoluble, it will take _______ pressure to get the gas into a solution.

If a gas is soluble, it will take _______ pressure to get the gas into a solution.

Answer 28

More (O2 is insoluble.)

Less (CO2 is soluble.)

Question 29

What are two ways to think about the pressure of dissolved gasses?

Answer 29

The pressure of dissolved gas can be thought of as the pressure used to get gas into a solution.

The pressure of dissolved gas can also be thought of as the pressure used to escape solution (pressure on the air-water interface).

Question 30

Why does CO₂ from a can of soda escape into the atmosphere?

Answer 30

CO2 bubbles reach the air-water interface and escape into the atmosphere because the atmosphere should have CO2 of about 0. If the soda can is filled with a bunch of CO2, that CO2 naturally wants to move from a place of high pressure of CO2 in solution to a place where there’s a lower pressure of CO2, which would be in the air.

That is why soda becomes flat a couple of hours after you open them.

Question 31

One dL of blood drops off ____ mL of oxygen as it passes through the systemic circulation.

Answer 31

5 mL of O2

Question 32

Does oxygen in the dissolved state meet the metabolic demand of systemic circulation?

What needs to be used to satisfy the metabolic demand of systemic circulation?

Answer 32

No. Oxygen is insoluble in blood; it does not like to be in solution. Only 0.3 mL of O2 per dL is available for delivery in the dissolved state.

Hemoglobin

Question 33

For a 70-kilogram, 30-year-old male who’s entirely healthy, how much Hgb should they have per dL?

Answer 33

15 g of Hgb/dL

Question 34

15 g of Hgb/dL is equal to what hematocrit level?

Answer 34

Hct = 0.4

Question 35

How much O2 can each gram of Hgb carry?

Answer 35

1.34 mL O2/ gram of Hgb

Question 36

How much O2 can be carried with a normal Hgb value?

Answer 36

15 grams of Hgb/dL of blood x 1.34 mL O2/ gram of Hgb = 20.1 mL O2/ dL of blood

Question 37

Each Hgb molecule can hang onto _______ O₂ molecules.

Answer 37

4

Question 38

At a saturation of 100%, how much O2 will be bound to Hgb?

What about at 75% saturation?

Answer 38

20.1 mL O2/dL of blood will be bound to Hgb at 100% saturation.

20.1 x 0.75 = 15 mL O2/dL of blood

Question 39

What is the chemical reaction used to describe the interaction of Hgb with oxygen?

Answer 39

Question 40

What factors will decrease oxyhemoglobin’s affinity for oxygen?

Answer 40

Low pH
Increase CO2
Increase H+
Increase temperature
Increase 2,3 DPG

O2 molecules will be released from Hgb.

Question 41

What conditions will accelerate the reaction to the left?

Answer 41

Low pH
Increase CO2
Increase H+
High temperature
Increase 2,3 DPG

O2 molecules will be released from Hgb

Question 42

What conditions will accelerate the reaction to the right?

Answer 42

High pH
Decrease CO2
Decrease H+
Low Temperature
Decrease 2,3 DPG

Hgb affinity for O2 will increase during these conditions.

Question 43

Look at the anemia curve. At a PO2 of 100 mmHg, how much O2 mL will be carried/ dL of blood?

Answer 43

Anemia = 6 g Hgb / dL of blood
1.34 mL of O2/ g Hgb

6 g Hgb/ dL of blood x 1.34 mL of O2/ g Hgb = 8.04 mL of O2/ dL of blood

Even with anemia, there is still enough oxygen to meet the metabolic demand of 5 mL of O2/dL of blood for systemic circulation.

Question 44

What can bind to Hgb at a greater affinity than oxygen?

Answer 44

Carbon Mononixide

Question 45

How does carbon monoxide affect oxygen binding to hemoglobin?

Answer 45

Carbon monoxide binds to those oxygen binding sites displacing some oxygen that could otherwise be transported.

Carbon monoxide reduces the ability of oxygen to unload from hemoglobin molecules that have one or more CO molecules stuck to the Hgb.

Question 46

50% carbon monoxide Hb curve represents a normal amount of Hgb, but half of the oxygen bindings sites are filled with carbon monoxide. What will be the O2 bound to Hgb?

Answer 46

Since half the sites are bound to carbon monoxide, the oxygen bound to hemoglobin will be cut in half to 10 mL O2/dL of blood.

Question 47

How will “thinning” the blood out (decrease Hgb) be beneficial?

Answer 47

Thinning the blood will result in less hemoglobin and fewer red blood cells. The blood will be less viscous and easier to pump.

This will not be great for oxygen delivery.

Question 48

What will the carrying capacity be for normal blood if PO2 is at 40 mmHg?

Answer 48

15 mL O2/ dL of blood (75% saturation)

Question 49

Why is the carrying capacity for the 50% Carbon Monoxide Hb curve the same at a PO2 of 100 mmHg and 40 mmHg?

Answer 49

Hemoglobin’s affinity for the oxygen that it’s carrying is going to be high if half of its binding sites are occupied by carbon monoxide.

Question 50

With carbon monoxide poisoning, we tend to have an oxygen ______ problem.

Answer 50

unloading

Question 51

In arterial blood, the hemoglobin oxyhemoglobin saturation at PO2 of 100 is about 97.4%. Why is it not at 100%?

Answer 51

Methemoglobin which makes up 2% of the circulating Hgb, does not like to carry oxygen.

The pulmonary venous blood is super oxygenated; it should have a PO2 of 104 mmHg. There is an admixture of some deoxygenated blood that comes from the bronchiolar circulation that mixes with pulmonary arterial blood, which drops the PO2 to about 100 mmHg and reduces the hemoglobin saturation.

Question 52

For the HbA (Adult) curve, what is the range of PaO2 most healthy individuals operate at?

Answer 52

PaO2 of 70 mmHg to 100 mmHg
(Hbsat 94% when PaO2 70mmHg)

Question 53

When we’re in a _____ PO2, we’re much more likely to have oxygen fall off the hemoglobin and be used somewhere for metabolism.

Answer 53

Low PO2

Question 54

What components make up the total oxygen that is in blood?

Answer 54

Dissolved oxygen in the blood
Bound oxygen to hemoglobin

Question 55

Calculate total oxygen in arterial blood.

Answer 55

20.1 + 0.3 = 20.4

CaO2 = 20.4 mL O2/dL of blood
Dr. Schmidt used 100% saturation instead of 97.4% saturation

Question 56

Calculate total oxygen in venous blood.

Answer 56

15.08 + 0.12 = 15.2

CvO2 = 15.2 mL O2/ dL of blood

Question 57

What will be the difference in total oxygen between arterial blood and venous blood?

Answer 57

About 5 mL of O2/ dL of blood

This is the amount of O2 dropped off in the systemic circulation.

Question 58

Where will the dissociation curve shift if there is an increase in PCO2?

Answer 58

The curve will shift right, making it easier to unload oxygen. The unloaded oxygen will increase the PO2 value of the tissue.

Question 59

Where will the dissociation curve shift if there is a low pH?

Answer 59

The curve will shift right, making it easier for O2 to leave the Hgb and increase the PO2 value of the tissue.

Question 60

What is 2-3-BPG?
Where will the curve shift if there is an increase in 2-3 BPG?

Answer 60

A byproduct of metabolism.
Increasing metabolism and increasing 2-3 BPG will shift the curve right.
Increase O2 unloading in the tissues.

Question 61

Where will the curve shift if there is an increase in temperature?

Answer 61

Shift right. O2 will be unloaded and hopefully satisfy metabolic requirements.

Question 62

What term describes the amount of oxygen Hgb in the blood can carry?

Answer 62

Carrying Capacity

Doesn’t factor in the quantity of O2 dissolved. Only considers how much O2 is carried by Hgb.

Question 63

If P_ACO₂ became 0, then PaCO₂ would….

Answer 63

Drop considerably

The constitutes loss of buffering capability, all of PaCO₂ will start to be exhaled by the lungs.