Oxygen Therapy

Question 1

How easy is it for the first oxygen molecules to bind to Hb?

Answer 1

• very hard

- needs to be saturated

Question 2

How easy is it for the second oxygen molecule to bind to Hb?

Answer 2

• co-operative binding via confirmational change
• easy for 2nd one to bind
• same for 3rd and 4th

Question 3

What does the oxygen-Hb dissociation curve show you?

Answer 3

• O2 sat % against change in PO2

- sigmoid shape due to co-operative binding

Question 4

What factor shifts the ox-Hb curve right?

Answer 4

• CO2 increase (Bohr Shift)
• pH decrease
• Temp
• exercise
• 2-3 DPG

Question 5

What happens to oxygen release when you move the curve to the right?

Answer 5

• easier

Question 6

Supply of oxygen forms in hospital

Answer 6

• wall

- cylinder

Question 7

BTS Guideliness

Answer 7

• above 94% sats target
• 88-92% target if at risk of T2 resp failure
• COPD use venture mask

Question 8

BTS Critical Illness Ox advnce

Answer 8

High levels of oxygen supplementation

15L of high flow

Question 9

BTS Stable Patients Ox advice

Answer 9

• nasal cannulae low dose

Question 10

Harmful effects of oxygen

Answer 10

• free radicalisation = toxicity
• flammable = explosion risk
• can cause vasoconstriction of pulmonary circulation
• loss of hypoxic drive

Question 11

Oxygen delivery devices

Answer 11

• venturi = fixed conc.
• simple face mask
• non rebreathe reservoir bag
• nasal cannulae

Question 12

Nasal cannulae

Answer 12

• 2-5L/min
• conc between 25-50%
• resp failure
• for stable patients
• over face mask as more comfortable
• low cost
• no-rebreathing
• easily tolerated

Question 13

Simple face Mask

Answer 13

• medium conc
• variable performance
• type 1 resp failure
• 5-10L/min
• variable conc 35-60%
• flow at least 5L/min to avoid CO2 build up

Question 14

Humidification purpose and how

Answer 14

• done normally by nasal cavities
• stops airways becoming dry so less thick secretions
• if giving medium to high flow oxygen for more than 24 hours should be humidified

Question 15

High Conc Reservoir Mask

Answer 15

• non-rebreathe
• trauma/critical illness
• post-cardiac or resp arrest
• ST treatment
• 70-80% conc

Question 16

High Flow Nasal Cannulae

Answer 16

• critical illness
• flows up to 60L/mind
• humified and warm
• LT use if higher conc required
• can provide PEEP 7.4cm H20 at 60L/min

Question 17

Define PEEP

Answer 17

Positive End Expiratory Pressure

• normally 5cm of water
• keeps alveoli open when expire
• prevents alveoli collapsing

Question 18

Venturi or Fixed Peformance Masks

Answer 18

• colour coded
• deliver constant ox conc
• fixed performance device
• increasing flow does not increase ox conc.
• fixed sized air slots allowing fixed size concentration of air
• conc depends on size of air slot

Question 19

Blue venturi mask

Answer 19

24%

2L min

Question 20

White venturi mask

Answer 20

28%

4L min

Question 21

Yellow venturi mask

Answer 21

35%

8L min

Question 22

Red venturi mask

Answer 22

40%

8L min

Question 23

Green venturi mask

Answer 23

60%

5L min

Question 24

What is the worry with COPD patients?

Answer 24

• some are CO2 retainers (5-15%)
• hypercapnic state is what induces oxygen drive
• if give oxygen = wont have drive to breathe = hypercapnia

Question 25

Is hypercapnia or hypoxia worse?

Answer 25

Hypoxia

When in doubt for COPD patient = give oxygen

Question 26

Normal PCo2

Answer 26

4.8-6.1

Question 27

Normal PaO2

Answer 27

10.6-13.3

Question 28

Normal HCO3-

Answer 28

22-26

Question 29

97% sats equivalent to what PaO2 and PaCo2

Answer 29

13-13.3

5-5.3 CO2

Question 30

P50 sats equivalent to PaO2

Answer 30

3.5