Oxygen Saturation Assessment for Student Nurses
Understand what oxygen saturation measures, how pulse oximetry is used and why changes in oxygen saturation can be an important sign of patient deterioration.
What does oxygen saturation measure?
Peripheral oxygen saturation, often written as SpO₂, is an estimate of the percentage of haemoglobin in arterial blood that is carrying oxygen. It is commonly measured using a pulse oximeter.
SpO₂
Pulse oximetry provides a non-invasive estimate of peripheral oxygen saturation.
Many acutely ill adults
Many adult patients are managed to an oxygen saturation target range of 94–98%, depending on their clinical condition.
Risk of hypercapnia
Some patients at risk of hypercapnic respiratory failure may have a prescribed target saturation of 88–92%.
How to obtain a reliable reading
Pulse oximeters are easy to use, but the displayed number is only useful if the signal and measurement are reliable.
Assess the patient first
Look at respiratory effort, colour, ability to speak, level of distress and overall clinical appearance.
Select an appropriate site
Use the correct sensor and site according to the equipment, patient needs and local procedure.
Check circulation and movement
Cold peripheries, poor perfusion, movement or tremor can make pulse oximeter readings less reliable.
Allow the reading to stabilise
Do not record the first changing number. Check that the displayed reading appears stable and consistent with the pulse signal.
Check the target range
Compare the reading with the patient's prescribed or clinically appropriate oxygen saturation target.
Record and interpret
Document the value, note whether supplemental oxygen is being given and review the result alongside NEWS2 and the wider assessment.
Do not interpret SpO₂ in isolation
Oxygen saturation can look reassuring while other parts of the respiratory assessment are deteriorating. Equally, an unexpectedly low reading may sometimes reflect a measurement problem rather than the patient's true oxygenation.
| Finding | What to consider | Clinical response |
|---|---|---|
| Falling SpO₂ | Compare with previous observations and prescribed target range. | Assess the patient, review other observations and escalate according to local procedure. |
| Increasing oxygen requirement | A patient may maintain saturation only because more oxygen is being delivered. | Recognise this as a potentially important change and communicate it. |
| Low reading with cold hands | Poor peripheral perfusion may reduce signal quality. | Check the patient, sensor position and signal while avoiding unnecessary delay in escalation. |
| Normal SpO₂ but marked breathlessness | A normal saturation does not exclude significant respiratory illness. | Continue the wider respiratory assessment and communicate clinical concern. |
| Reading inconsistent with the patient | Consider equipment, movement, probe placement and circulation. | Reassess the measurement while continuing to assess the patient clinically. |
The number must fit the patient
If the pulse oximeter says 98% but your patient looks critically unwell, do not allow a reassuring number to override your clinical concern. Look at the whole patient.
Oxygen should be assessed as part of the observation
When interpreting oxygen saturation, establish whether the patient is breathing room air or receiving supplemental oxygen.
- Check whether oxygen is currently being administered.
- Know the prescribed target oxygen saturation where applicable.
- Record oxygen therapy accurately with the patient's observations.
- Recognise that increasing oxygen requirements may indicate deterioration.
- Do not alter prescribed oxygen therapy outside your level of competence or local procedure.
- Escalate if the patient is outside their target range or their clinical condition is worsening.
Student nurse safety point
Oxygen is a medicine. Student nurses should administer and adjust oxygen only within their competence, supervision arrangements and local policy.
Changes that deserve attention
- A falling oxygen saturation compared with previous observations.
- A saturation below the patient's prescribed target range.
- A new or increasing requirement for supplemental oxygen.
- Increasing respiratory rate or work of breathing.
- New breathlessness, inability to speak comfortably or visible distress.
- New confusion, agitation, drowsiness or reduced responsiveness.
- Other NEWS2 parameters becoming abnormal at the same time.
Putting the observations together
Example
Earlier in the shift, a patient was maintaining an oxygen saturation of 97% while breathing room air.
You now record 92%. Their respiratory rate has increased, they look more breathless and they are struggling to complete sentences comfortably.
The significance lies in the pattern of change: falling oxygen saturation, rising respiratory rate and worsening clinical appearance.
As a student nurse, obtain accurate observations, recognise the deterioration and promptly communicate the findings to the appropriate registered practitioner.
Pulse oximetry errors to avoid
- Recording the first displayed number. Allow the reading to stabilise.
- Ignoring signal quality. Movement and poor perfusion can affect readings.
- Assuming 95% is the target for everyone. Check the patient's individual target range.
- Ignoring oxygen therapy. A saturation value means something different when supplemental oxygen is required.
- Looking only at SpO₂. Respiratory rate, work of breathing and clinical appearance remain essential.
- Delaying escalation while repeatedly checking equipment. If the patient appears unwell, seek appropriate help.
Recognise → assess → communicate → escalate
Notice the change
Identify a falling saturation, increasing oxygen need or worsening respiratory symptoms.
Check the whole patient
Confirm the reading, assess respiratory rate and effort, review oxygen therapy and consider the other observations.
Act on concern
Report abnormalities, trends and clinical concern clearly and follow the appropriate escalation process.
Useful professional guidance: Royal College of Physicians — NEWS2 and British Thoracic Society — Emergency Oxygen guidance .
Pulse Assessment for Student Nurses
Learn how to assess pulse rate, rhythm and strength, recognise tachycardia and bradycardia and interpret changes as part of a wider assessment of patient deterioration.
Continue to Pulse Assessment →