Respiratory failure and VQ matching

Question 1

Normal arterial values

what are the normal limits for PaO2 in arteries, in kPa and mmHg

Answer 1

• 11-15 kPa
• 90-113 mmHg

Question 2

what is the usual partial pressure of oxygen in the veins?

Answer 2

40mm Hg

Question 3

normal arterial values

what are the normal limits for PaCO2 in arteries, in kPa and mmHg

Answer 3

• 4.6-6.4 kPa
• 33-46 mm Hg

Question 4

what is the deficit between PO2 in alveoli (PAO2) and PO2 in arteries (PaO2) known as, and if the deficit is greater than 15 mmHg, what does it indicate?

Answer 4

• known as the PA-aO2 difference
• deficit greater than 15mmHg indicates oxygen is being obstructed in the blood

Question 5

normal arterial values

what can Hypercapnia mean for mechanical breathing mechanisms

Answer 5

it means your mechanical breathing mechanisms aren’t working correctly

Question 6

normal arterial values

what can being outside normal arterial values of PaO2 and PaCO2 mean

Answer 6

can indicate respiratory failure

Question 7

respiratory failure

define respiratory failure and what is it characterised by?

Answer 7

a failure to maintain adequate gas exchange, characterised by abnormalities in arterial blood gas partial pressures

Question 8

respiratory failure

what is type 1 respiratory failure ( include values in you answer

Answer 8

hypoxaemia (< 9kPa) with normal or low CO2

Question 9

respiratory failure

what is type 2 respiratory failure (include values in your answer) and what does this mean for breathing rate?

Answer 9

hypoxaemia with HIGH CO2 (>6 kPa) so breathing rate cannot keep up.

Question 10

respiratory failure: pathophysiological causes

what are 4 main causes of Respiratory failure

Answer 10

• alveolar hypoventilation
• diffusion deficit
• shunts
• ventilation - perfusion (VQ) mismatch

Question 11

define ventilation

Answer 11

ventilation = frequency of each breath X size of each breath

Question 12

hypoventilation

define hypoventilation

Answer 12

decrease in minute ventilation leading to CO2 retention and less O2 absorption

Question 13

hypoventilation

what does hypoventilation increase regarding ventilation

Answer 13

increases proportion of dead space ventilation

Question 14

hypoventilation

what can hypoventilation cause regarding respiratory failure and give one example as to how ?

Answer 14

causes Type II respiratory failure due to respiratory muscle fatigue

Question 15

Diffusion deficit

define diffusion deficit

Answer 15

can’t get oxygen into gas exchange zones

Question 16

what is fick’s Principle/law?

Answer 16

the greater the concentration gradient, the more readily gases diffuse down their concentration gradient

Question 17

diffusion deficit

what is the equation of Fick’s Law

Answer 17

Vgas ∝ A/T x Diffusion coefficient of gas x (P1 - P2)

where:
- A = surface area
- T = tissue thickness
- D = diffusion coefficient of gas
- P1-P2 = partial pressure gradient

Question 18

diffusion deficit

what is the equation for the diffusion coefficient of gas

Answer 18

D ∝ Gas solubility / √gas molecular weight

Question 19

shunts

what are shunts

Answer 19

shunts are when venous blood mixes with arterial blood, so oxygen isnt reaching gas exchange centres

eg: tissues

Question 20

shunts

what are extra-pulmonary shunts

Answer 20

when venous and arterial blood mix but completely bypass the lungs

Question 21

shunts

what are intra-pulmonary shunts

Answer 21

• blood is transported through the lungs without undergoing gas exchange first.

Question 22

shunts

what are the 2 common causes of intrapulmonary shunts

Answer 22

• alveolar fillings (pus, oedema,blood, tumour)
• atelectasis (lung collapse)

Question 23

shunts

True or False: providing Oxygen can correct pure shunt hypoxia in intra-pulmonary shunts

Answer 23

False, pure oxygen CANNOT correct pure shunt hypoxia. The cause of the intra-pulmonary shunts needs to be addressed first

Question 24

What does H.A.S.H and what is this used for

Answer 24

H - hypoxia hypoxemia (when oxygen is not available in the environment)

A - anaemia

S - stagnant ( i.e embolism/ ischemia)

H - histotoxic (I.e poison of he or blood cells such as with carbon monoxide)

Used to remember what causes O2 insufficiency

Question 25

what are 4 factors about haemoglobin

Answer 25

• haemoglobin differences (eg fetal vs normal)
• acidosis
• temperature change
• 23-DPG

Question 26

what is 2 examples of when partial pressure gradient can increase or decrease diffusion

Answer 26

Increase:
- increased metabolism
- 100% O2

decrease:
- altitude

Question 27

what is an example of when gas physical properties effect rate of diffusion

Answer 27

• heavier gas or less soluble gas decreases rate

Question 28

what are 4 examples of when the alveolar-capillary (tissue thickness) membrane can affect rate of diffusion

Answer 28

• pulmonary fibrosis
• oedema
• asbestosis
• fibrosis

Question 29

what are 2 examples of when reduced gas exchange area affects rate of diffusion

Answer 29

• emphysema
• Pneumonia

Question 30

what is the realistic value for Ventilation (air/min) and perfursion (blood/min) in litres and what is the realistic whole lung V/Q ratio because of this?

Answer 30

Ventilation:
- 5L air/min

Perfusion:
- 6L blood/min

whole lung V/Q ratio:
- 0.8:1

where ventilation is 0.8 and perfusion is 1

Question 31

what are the values of ventilation and perfusion at the top, middle and bottom of the lungs and the consequent V/Q ratio at each level because of this.

Answer 31

TOP:
- ventilation: 1.2L/min
- perfusion: 0.4L/min
- V/Q ratio: 3.0

MIDDLE:
- ventilation: 1.8L/min
- perfusion: 2.0L/min
- V/Q ratio: 0.9

BOTTOM:
- ventilation: 2.1L/min
- perfusion: 3.4 L/min
- V/Q ratio: 0.6

Question 32

how many times greater is ventilation AND perfusion at the bottom of the lungs compared to the top?

Answer 32

ventilation at the bottom is 2x greater at the bottom compared to the top

perfusion is 5x greater at the bottom compared to the top

Question 33

how can you measure ventilation at the top middle or base of the lungs?

Answer 33

• use radioactive xenon (1,2 or 3) as a respiratory ventilation marker