Oxygen Prescribing

Question 1

What is prescribed to patients who are critically ill

Answer 1

15L/min via non re-breather (bag-mask valve for respiratory arrest)

Question 2

How do you determine oxygen targets + supplementation if not critically ill

Answer 2

Are they at risk of type 2 resp failure?

Yes: target = 88-92%
- start 1-2L/min via nasal cannulae/28% FiO2 (white venturi)
- Perform ABG
If CO2 >6 → target change to 88-92% + seek senior help
If CO2 normal → target change to 94-98%

No: target = 94-98%
- 85-93% → 1-2L/min via nasal cannulae/28% FiO2 (white venturi)
- <85% → 15L/min via non re-breather

Question 3

Oxygen management if there is respiratory acidosis

Answer 3

Continue with 88-92% target
Seek senior help and consider NIV

Question 4

Oxygen management if there is hypercapnia

Answer 4

Continue with 88-92% target
Repeat ABG in 60 mins

Respiratory acidosis → Seek senior help and consider NIV

Question 5

Oxygen management for normocapnia/hypocapnia

Answer 5

Change target to 94-98%

Repeat ABG in 60 mins
CO2 >6.0kPa → get senior help
- No known hypercapnia risk → Continue 94-98%
- Known hypercapnia risk → aim 88-92%

Question 6

What constitutes high risk of hypercapnic respiratory failure

Answer 6

Moderate-severe COPD
Neuromuscular disease
Severe spinal/chest wall deformity
Morbid obesity

Question 7

What should be considered if not responding to 15L/min non-rebreather

Answer 7

Repeat A-E
Inform senior clinician
Consider:
High-flow nasal oxygen (HFNO): compared to a non-rebreather mask, can deliver oxygen at a greater FiO2 (up to 100%) and flow rate (up to 60L/min). Usually only available in high-dependency/intensive care environments.
Continuous positive airway pressure (CPAP): used in type 1 respiratory failure (PaO2 <8.0kPa), for example cardiogenic pulmonary oedema
Non-invasive ventilation (NIV): used in type 2 respiratory failure (PaO2 <8.0kPa AND PaCO2 >6.0kPa), for example a COPD exacerbation

Question 8

What is the flow rate of nasal cannulae and when is it used

Answer 8

Low-flow = 24-30%
2-4L/min
Used in mild hypoxaemia

Question 9

What is the flow rate of venturi masks and when is it used

Answer 9

Delivers set FiO2:
Blue = 24% (set at 2L/min)
White = 28% (set at 4L/min)
Orange = 31% (set at 6L/min)
Yellow = 35% (set at 8L/min)
Red = 40% (set at 10L/min)
Green = 60% (set at 15L/min)

Used in COPD

Question 10

What is the flow rate of the simple face mask (Hudson)

Answer 10

5-10L/min (30-40%)

Question 11

What is the flow rate of the non-rebreather mask and when is it used

Answer 11

Delivers 15L/min (70-90% FiO2)
Used if the patient is critically unwell or has high oxygen requirements
Ensure to fill the reservoir bag with oxygen by obstructing the valve

Question 12

What is the P/F ratio

Answer 12

Used to check for adequate response to oxygen
P/F ratio = PaO2 on ABG (“P”) divided by FiO2 (“F”) (expressed as a decimal)

Normal = 55kPa (400mmHg)

Question 13

When can you consider weaning off oxygen

Answer 13

Consider weaning when sats are at the higher end of their target sats for 4-6 hours
Wean by small increments (e.g. from a yellow Venturi/35% FiO2 to a white Venturi/28% FiO2).
Once the patient is stable on 1-2L/min via nasal cannulae, you can cease oxygen completely.