Guidelines on Oxygen and Oximetry

Oxygen therapy in the acute setting

Oxygen is used in many settings and flow rates should be titrated to achieve a specific target saturation range (SpO2), according to the patient group. 

Oxygen is a drug and should be prescribed according to a target saturation range on HEPMA (hospital electronic prescribing system), or on a drug kardex if your area of practice does not have HEPMA. Refer to the prescribing and administration guide for steps on how to do this on HEPMA. 

Critically ill patients*

  • Use reservoir masks at 15L/minute O2 flow initially in all patient groups pending arterial blood gas (ABG) analysis. 
  • Once stable, if there is a reliable oximetry reading then titrate oxygen to aim saturations at 94-98% (88-92% if ABG confirms hypercapnic respiratory failure). 
  • In carbon monoxide poisoning continue high flow oxygen at 15L/minute regardless.

*Examples of critical illness can include: cardiac arrest or resuscitation, shock, sepsis, major trauma, drowning, anaphylaxis, major pulmonary haemorrhage, status epilepticus, major head injury, carbon monoxide poisoning.

Is there a risk of hypercapnic respiratory failure?

The main risk factor is moderate/severe chronic obstructive pulmonary disease (COPD). Other risk factors include obesity, cystic fibrosis, chest wall deformities, neuromuscular disorders and fixed airflow obstruction. Patients with mild COPD are not necessarily at risk of hypercapnic respiratory failure. 

Acutely unwell patients NOT at risk of hypercapnic respiratory failure

Target saturations: 94-98%

  • If SpO2 <85%, use reservoir mask at 15L/minute O2 flow initially. Remember to titrate down oxygen to achieve target saturation once stable.
  • If SpO2 >85%, titrate oxygen flow via nasal cannula (2-6 L/minute O2) or simple face mask (5-10 L/minute O2) to achieve 94-98% saturation. If unable to achieve or maintain target range, switch to reservoir mask (15 L/minute O2) and seek senior advice.

N.B. Hyperoxia may be harmful in certain conditions (e.g. acute stroke or myocardial infarction). Achieving SpO2 >98% can worsen ischaemic injury. Reduce oxygen flow to remain within 94-98%.


Acutely unwell and at risk of hypercapnic respiratory failure

Target saturations: Pending arterial blood results, target 88-92% or those stated on patient's Oxygen Alert Card. 

  • FiO2 24% or 28% via Venturi mask to target saturations 88-92% (if Venturi mask unavailable, then nasal cannulae 1-2L/minute can be used).
  • Blood gases should be taken once target saturations achieved.
  • If pCO2 <6kPa, target saturations 94-98% and recheck ABG 30-60 minutes later.
  • If pCO2 >6kPa and H+ <45nmol/L (pH >7.35), target saturations 88-92% and recheck ABG 30-60 minutes later. Aim for pO2 on ABG 8-10kPa.
  • If respiratory acidosis present on repeat ABG at 30-60 minutes of controlled O2 with optimal medical therapy, discuss with senior and consider non-invasive ventilation or referral to intensive care (if appropriate to the clinical situation).

N.B. If patients respiratory rate is >30 breaths/minute when using Venturi mask, then flow rate should be increased by 50% to compensate.

Ongoing management

  • If saturation falls by >3% then arterial blood gas should be checked if clinically appropriate. 
  • If saturations are below target range then increase supplemental oxygen to maintain target range. 
  • An ABG should also be checked if increasing breathlessness or features of CO2 retention e.g. drowsiness / deteriorating GCS (Glasgow Coma Scale).

High Flow Nasal Oxygen Therapy (HFNO)

  • HFNO is available in critical care areas and certain acute medical units and respiratory wards. Consider the use of HFNO in patients who are requiring high concentrations of oxygen (e.g. FiO2 >40%) after discussion with senior medical staff.

Guidelines for use of oximetry

  • Continuous pulse oximetry should be used in all patients who are critically unwell.   
  • Pulse oximetry should be used when titrating oxygen dose and should be monitored continuously for 5 minutes after a change in oxygen concentration. 
  • Be aware of the following when using oximetry:
    • Delay of 10-20 seconds between change in patient's saturations and monitor display
    • Oximetry is unreliable in poor perfusion states (e.g. shock)
    • Incorrect reading in methaemoglobinaemia

Venturi masks / valves

Colour Required flow rate* FiO2
Blue 2–4L/minute 24%
White 4–6L/minute 28%
Yellow 8–10L/minute 35%
Red 10–12L/minute 40%
Green 12–15L/minute 60%

*In patients with a respiratory rate of >30 breaths/minute aim for a flow rate 1.5-2 times the maximum suggested. 


Guideline reviewed: May 2022

Page updated: September 2022