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1

2

What is the actual value of hypoxemia?

PaO2

3

What is V/Q?

ventilation/perfusion ratio

4

What are the 5 five major causes of hypoxemia

1 Hypoventilation

2 Reduced PIO2 - altitude, anesthetic machine malfunction

3 Diffusion impairment – exercising race horse

4  V/Q mismatch

5  Shunt

5

  1. What is the normal V/Q?
  2. How is that number arrived at?

  1. Normal V/Q = 0.8 
  2. 4 Liters Ventilation (Air) / 5 Liters Perfusion (Blood)  4/5 = 0.8

6

What does V/Q ratio determine?

Determines the adequacy of gas exchange

7

What can cause an ventilation-perfusion mismatch

  1. Differences in airway geometry and lung expansion produce uneven regional ventilation.
  2. Differences in vascular geometry and hydrostatic pressures produce uneven regional blood flow.
  3. Pathologies that lead to regional changes in ventilation (e.g. bronchoconstriction) or changes in perfusion (e.g. pulmonary embolism) will cause a V/Q mismatch.
     

8

Are V/Q ratios the same across normal healthy lung

vary across regions within normal healthy lung.
 

9

What is the scale range for V/Q ratio

0 to infinity

10

  1. What would the idea situation for V/Q be?
  2. Does this always happen in the normal body?

  1. Millions of alveoli would receive air and blood in amounts that are equal and optimal for gas exchange
  2. Never occurs – always some V/Q mismatch
    • Branching patterns of bronchi and vessels
    • Gravity – to some extent
       

11

What is the significance of a low V/Q ratio?

12

What are the causes of a low V/Q ratio?

  1. obstructed airway
  2. alveoli filled with exudate
  3. local blood flow obstructions

13

  1. What is the normal PO2?
  2. when there is a low V/Q ratio what will happen to PO2
  3. high V/Q ratio what will happen to PO2

  1. 100 mm Hg
  2. decreased
  3. increased

14

  1. What is diagram saying
  2. is it a high or low V/Q ratio?

  1. Both alveoli are being perfused equally but low V/Q (bronchiole is narrowed) will decrease amount of ventilation entering alveolus
    • The resulting mixture will still be hypoxemic
  2. There is a low V/Q ratio

15

If one alveolus has a normal V/Q while another has a low V/Q will the mixture of blood be a 50:50 of oxygen?

no!

16

  1. What are the pink spots?
  2. red?
  3. what will happen to V/Q?

  1. Pink is normal lung parenchyma

  2. Red, abnormal, alveoli filled with exudate

  3. Will lead to a low V/Q ratio

17

Can a high V/Q compensate for a low V/Q where oxygen is concerned?

High V/Q does not compensate for low V/Q where oxygen is concerned
 

18

If you mix two equal quantities of blood how do you calculate PO2

  • Take average of the 2
  • 20+17 = 37/2 = 18.5
  • Then draw line over and find the PAO2

19

  1. Generally what is happening when V/Q = 0,
  2. Is there perfusion?
  3. What will the body do to try and rectify?
  4. what is this called?

  1. No ventilation to alveoli (atelectasis)
  2. Perfusion still exists
  3. Hopefully, hypoxic pulmonary vasoconstriction has reduced the perfusion
  4. shunting

20

  1. When V/Q is high what has happened tp perfusion?
  2. does ventilation still exist?
  3. does it cause hypoxemia?

  1. No perfusion, maybe pulmonary embolism
  2. Ventilation still exists,
  3. Does not cause hypoxemia

21

  1. what is a right to left shunt

  1. Right Ventricle outflow bypasses ventilated lung and returns to the left atrium

22

  1. Give examples of anatomic shunts
  2. physiologic shunts

  1. Anatomic- Right to left shunt =Foramen ovale, between atria, 
    • left to right shunt= PDA (patent ductus arteriosus) between pulmonary artery and aorta
  2. Physiologic shunts – complete airway obstruction,
    • alveoli filled with exudate
    • atelectasis (collapsed alveoli)
       

23

  1. What is happening at 1
  2. ?
  3. ?

  1. atelectasis
  2. Thicker septum of alveoli
  3. exudate

24

What will you see if you place an animal with a shunt on oxygen (increase FIO2)

  • Shunts are unresponsive to increasing FIO2

25

Explain why an animal with hypoxemia due to shunts will not improve with the administration of oxygen

  • in a shunt V=0
  • so even if you increase Q, the result will still be 0
  • Cannot get oxygen into a collapsed or diseased alveolus, so will not improve

26

Describe the significance of a V/Q ratio = ∞

  • Inspired air that does not participate in gas exchange
  • Anatomic dead space
  • Alveolar (physiologic) dead space
    • high V/Q
  • Regions with V/Q > 1.0 do not contribute to hypoxemia.
     

27

regarding the 5 causes of hypoxemia, hypoventilation

  1. What will you see with PACO2 (increase, normal, decrease)
  2. (A-a) O2 difference (increase, normal)
  3. Will the patient be responsive to increased FIO2 (giving oxygen)

 

28

regarding the 5 causes of hypoxemia, Low PIO2

  1. What will you see with PACO2 (dincrease, normal, decrease)
  2. (A-a) O2 difference (increase, normal)
  3. Will the patient be responsive to increase FIO2 (giving oxygen)

29

regarding the 5 causes of hypoxemia, shunt

  1. What will you see with PACO2 (increase, normal, decrease)
  2. (A-a) O2 difference (increase, normal)
  3. Will the patient be responsive to increased FIO2 (giving oxygen)

30

regarding the 5 causes of hypoxemia, V/Q mismatch

  1. What will you see with PACO2 (increase, normal, decrease)
  2. (A-a) O2 difference (increase, normal)
  3. Will the patient be responsive to increased FIO2 (giving oxygen)