Oxygen Delivery

Question 1

What are ‘variable’, ‘fixed’ performance and ‘100%’ O2 delivery systems?

Answer 1

VARIABLE
FiO2 delivery is influenced by patient:
Eg. NP, Hudson
Both have lower flow rates than normal adult breathing: air entrained.

FIXED
Reliably (more or less) deliver a chosen/ known FiO2 regardless of how patient is breathing
Eg. high flow venturi, oxygen blender
Become variable in very high RRs

100% O2
Eg. NRBM, BVM, Mapleson/Ayres Tpiece
These blow 100% O2 at the patient, which should all get to the patient, provided:
- Flow rate matches or exceeds patient’s breathing
OR
- Reservoir

Question 2

Nasal cannulae:

Answer 2

Variable performance
Above 2L, will create reservoir in nasopharynx
Don’t match patient flow rates
Require nose breathing

Humidify above 4L

FLOW RATE: 1-6L/min
FiO2: up to 45%

1L = 28%, then 4% per extra L

Question 3

Hudson mask:

Answer 3

Variable performance
Don’t match patient flow rates
Open holes in side- entraining

Need 6L + to avoid rebreathing

FLOW RATE: 6 to 15L/min
FiO2: up to 60%

can improve with Tpiece or reservoir bag

Question 4

NRBM:

Answer 4

100% delivery system

Reservoir bag
One way valves- can’t rebreathe (but imperfect seal)
Must have enough flow to prevent asphyxiation:
Plump bag, should remain 1/3 full with inspiration

FLOW RATE: Reservoir (can match patient unless very dyspnoeic)
FiO2: up to 90%

Question 5

HFNP:

Answer 5

Humidified
Warmed
Relies on nose breathing

FLOW RATES: up to 60L/min
FiO2: 100%
Up to PEEP 7 (mouth closed)

———-
Start adult at 60L/100% and downtitrate

Question 6

HFNP (paeds):

Answer 6

Give 2L/kg/min (max 50L/min)
(Over 12kg, can add 0.5L/min for each Kg, up to 50L)

Can uptitrate O2, but not flow.

Consider DOWNtitration once doing well on <40%O2.

Question 7

BVM:

Answer 7

100% delivery system
Non rebreathing
Safety features: entraining valve, 70cmH2O pop off
PEEP

CAUTION when spont venting- asphyxiation if not opening valve. Augment

FLOW RATE: Reservoir (can match patient)
FiO2: 100% (Laerdel)
PEEP: PEEP 20 with valve, more if hold pop-off

Question 8

Venturi system:

Answer 8

Mask with colour-coded jet adaptor attached. Adaptor carefully mixes set flows of O2/entrained air for specific FiO2.

As FiO2 increased, total flow rate decreases. In severe dyspnoea, won’t match patient.

FiO2: 24 - 60%

Question 9

Ayer’s Tpiece/ Mapleson F/ Jackson-Rees:

Answer 9

Up to 20-30kg (ie. under age 5)

Good ‘feel’ of compliance
Low resistance so good for spont breathing (can ‘see’ effort)
PEEP

Is partial-rebreathing (desired in inhalational anaesthetic)
—> make flow 2-3x patient minute vol to minimise

FiO2 100%

Question 10

Complications of oxygen therapy:

Answer 10

Device:
(eg. Distress, communication, pressure areas)

Asphyxia:
- BVM duck bill
- Reservoir or flow exceeded

CO2 narcosis:
- COPD/ hypoxic drive
- Rebreathing

Oxygen toxicity
- Free radicals and peroxidases
- Cerebral metabolism
- Retinopathy
Generally >50% for >24 hours