Hypoxemia:Hypoxia

Question 1

Hypoxemia: define

Answer 1

Low partial pressure of oxygen in the arterial blood

Question 2

Hypoxia: define

Answer 2

low PO2 systemically or at tissue level

Question 3

Interpret the measurement, PaO2 < 60mmHg. Hypoxemic or nah?

Answer 3

Hypoxemic

Question 4

Hyperventilation: what are the carbon dioxide levels like?

Answer 4

LOW! PaCO2 <35mmHg

Question 5

Hypoventilation: what are the carbon dioxide levels like?

Answer 5

HIGH! PaCO2 > 45mmHg

Question 6

What’s the difference between SaO2 and SpO2?

Answer 6

While they both measure the saturation of oxyhemoglobin, one does so via arterial blood while the other does so via pulse ox.
Regardless, they should be the same!

Question 7

FiO2…what’s this?

Answer 7

the inspiratory oxygen concentration

Question 8

What are the 5 mechanisms of hypoxemia?

Answer 8

1) Decreased FiO2 or decreased PAO2
2) Hypoventilation
3) Right => Left Shunt
4) Diffusion impairment
5) Ventilation Perfusion V/Q mismatch

Question 9

What are the 3 of the 5 mechanisms of hypoxemia that constitute “venous admixture”?

Answer 9

3) Right => Left Shunt
4) Diffusion impairment
5) Ventilation Perfusion V/Q mismatch

Question 10

What IS venous admixture?

Answer 10

Venous blood mixing up with saturated arterial blood as a result of a R:L shunt, diffusion impairment from some lung disease or even V/Q mismatch which is common in horses.

Question 11

Hypoventilation, a mechanism of hypoxemia, can be due to two things…

Answer 11

drugs

damage to chest wall/respiratory muscles

Question 12

With Hypoventilation, is alveolar ventilation increased or decreased?

Answer 12

decreased

Question 13

Does Hypoventilation increase or decrease the PC02?

Answer 13

Increase it!

Question 14

What does Hypoventilation do to PO2?

Answer 14

Decreases the PO2 unless additional O2 is inspired

Question 15

Is Hypoxaemia caused by hypoventilation reversible?

Answer 15

Yea it’s easy with the addition of O2.

Question 16

What’s the connection between shunts and hypoventilation?

Answer 16

Usually from R:L, blood is shunted away from entering the oxygenated parts of the lungs so it enters the arterial system with insufficient O2.

Question 17

Do shunt patients respond well to additional O2?

Answer 17

Nerp.

Question 18

What are the 4 advantages to using a pulse ox?

Answer 18

• Beat‐to‐beat assessment of oxygenation
• Practical
• Simple
• Non‐invasive

Question 19

What are the 3 disadvantages to using a pulse ox?

Answer 19

• Beat‐to‐beat assessment of oxygenation
• Practical
• Simple
• Non‐invasive

Question 20

T/F

Pulse ox can be used to assess oxygenation with and without supplemented O2

Answer 20

True

Question 21

Arterial Blood Gas Analysis vs Pulse Ox—what do they measure?

Answer 21

Arterial Blood Gas Analysis measures dissolved O2 in the blood
Pulse Ox measures saturation of hemoglobin with oxygen in the blood.

Question 22

PaO2 is related to which measurement?

Answer 22

SpO2 via the oxyhemoglobin dissociation curve

REMEMBER: PaO2 60mmHg = SpO2 90%

Question 23

How will low Hb concentration affect O2 content?

Answer 23

will also decrease

Question 24

Rule of 4

Answer 24

pH 7.4 +/‐ 0.04
pCO2 40 +/‐4 mmHg
HCO3 24 +/‐ 4 mmol/l
BE ‐4 to +4 mmol/l

Question 25

Alveolar Gas Equation

Answer 25

PAO2 = PIO2 – (PACO2/0.8)

Question 26

Can we tell based off PaO2 alone if a patient has pulmonary dysfunction?

Answer 26

Nope. Based on PaO2, it will just tell us how well the patient is oxygenating.

Question 27

Why is Arterial Blood Gas(ABG) analysis critical to assessment of pulmonary function?

Answer 27

Because ventilation influences oxygenation in the wake animal but not so much in the anesthetized animal.
Be sure to factor in PaCO2

Question 28

How do we calculate the relationship between fall in PO2 and the rise in PCO2 that occurs in hypoventilation?

Answer 28

use the alveolar gas equation

Question 29

***We use the A-a gradient/Alveolar gas equation to figure out what?

Answer 29

***Why the animal is hypoxemic/pulmonary dysfunction

Question 30

Normal A‐a should be

Answer 30

<15mmHg

anything greater than this indicates pulmonary dysfunction, some hindrance to ventilation…gas exchange

Question 31

T/F

You can be hypoxemic but maintain pulmonary function.

Answer 31

True

The hypoxemia could be a result of hypoventilation

Question 32

The equation we use to check on pulmonary function?

Answer 32

A-a gradient

Question 33

This equation identifies the presence or absence of a pulmonary gas exchange abnormality

Answer 33

A-a gradient

Question 34

Your ability to ventilate affects…?

Answer 34

oxygenation

Question 35

Does a normal A-a gradient mean the patient is 100% in the clear?

Answer 35

No. A normal A-a gradient only lets you know there isn’t an issue with pulmonary gas exchange. It does not rule out pulmonary pathology.

Question 36

What’s another way we can measure the efficiency of gas exchange?

Answer 36

PaO2 : FiO2 Ratio

Question 37

The use of this PaO2:FiO2 is good for two conditions:

Answer 37

• Useful for patients receiving FiO2>0.21 (21%)

• Useful for patients where FiO2 is known
– Room air
– Anesthesia

Question 38

PaO2:FiO2 normal range

Answer 38

350‐500

Question 39

What’s a limitation to PaO2:FiO2?

Answer 39

– Difficult to quantify FiO2 in non‐ intubated patients

Question 40

P(A – a)O2 in room air—how do you interpret results?

Answer 40

• <15 mm Hg is normal
• 15‐30 mm Hg is mild to moderate impairment of oxygen exchange
• 30 mm Hg severe impairment of O2 exchange

Question 41

PaO2/FiO—how do you interpret results?

Answer 41

• PaO 2/FiO2 ratio > 400: normal
• PaO 2/FiO2 ratio < 300: O2 exchange impairment
• PaO 2/FiO2 ratio < 200: severe lung disease