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Is a higher oxygen reading always better?

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The question

Mrs Smith's sats of 91 were a worry, yet for Mr Brown in a COPD flare-up 91 is on target. Why isn't more oxygen always better?

Understand

Mrs Smith's sats of 91% were a worry. Mr Brown, on oxygen for a COPD flare-up, also reads 91%, and that's on target. Why? In hospital, oxygen is a drug: it is prescribed with a target range that has a top as well as a bottom. Australian and New Zealand guidance (TSANZ) aims for 92-96% for most adults who need oxygen, and 88-92% for people at risk of carbon dioxide building up, such as in a COPD flare-up. In some of these people, too much oxygen can let carbon dioxide build up: mainly because extra oxygen sends more blood past parts of the lung that can't clear it, not mainly because they stop breathing. Built-up carbon dioxide makes the blood more acidic and can cause headache, drowsiness and confusion, and a pulse oximeter can't show it. So nurses check each person's target, watch the sats against it and watch for drowsiness. Charts and rules vary: follow your local policy. Mrs Smith, Mr Brown and their numbers are fictional examples; the ranges are guideline ranges for clinicians, not personal targets, and the drawings are simplified.

  1. Oxygen is prescribed with a target SpO₂ range: a top and a bottom.
  2. The top avoids the risks of too much oxygen and shows improvement sooner, so it can be turned down.
  3. In some people with COPD, too much oxygen lets CO₂ build up: mainly because more blood flows past air sacs that can't clear it. Breathing less is only a small part.
  4. CO₂ build-up makes the blood more acidic (headache, drowsiness, confusion). The clip can't show it.

Key takeaways

  • Oxygen in hospital is a drug: it has a prescribed target SpO₂ range with a top and a bottom.
  • Most adults who need oxygen in hospital: 92–96 %. People at risk of CO₂ build-up (e.g. a COPD flare-up): 88–92 %.
  • Too little oxygen is dangerous too: the aim is controlled oxygen, not none.
  • Report readings outside the range, low or high, as local policy says.

In practice

  • Check each person's target range first.
  • Too low or too high: follow local policy.
  • Watch for drowsiness and confusion.

In one line

No. Oxygen is a drug with a target range, a top and a bottom: in hospital 92–96 % for most adults, 88–92 % for people at risk of CO₂ build-up (like a COPD flare-up).

Check yourself

Ms Ward is on oxygen for a COPD flare-up, target 88–92 %. Her sats read 97 % and she is sleepier than an hour ago. Good news?

Show the answer

No. She is above her range, and drowsiness can mean CO₂ build-up. Report it.

Words to know

SpO₂ (sats)
oxygen saturation: how much of the blood's haemoglobin is carrying oxygen
COPD
chronic obstructive pulmonary disease: long-term lung disease
Hypercapnia
too much carbon dioxide in the blood (hyper- (too much) + -capnia (carbon dioxide))

Transcript

Read the narration

Mrs Smith's sats of 91 made Alex report it. In the next bed, Mr Brown has a flare-up of COPD, a long-term lung disease.

He's on oxygen, also at 91, and that's on target. Same number, two answers. Why? Because oxygen is a drug, prescribed with a target range: a top and a bottom.

In hospital, for most adults, it's 92 to 96, so Mrs Smith's 91 was low. For those at risk of carbon dioxide build-up, like Mr Brown, it's 88 to 92.

So why not aim higher, to be safe? Pause and guess. Three, two, one. Too much oxygen can let carbon dioxide build up in some people with COPD.

In the air sacs, blood drops off carbon dioxide to be breathed out. In an air sac with little air, low oxygen narrows its blood vessel, so most blood goes to the good ones.

Extra oxygen opens that vessel again, and more blood leaves still carrying carbon dioxide. That makes blood more acidic, and can cause headache, drowsiness and confusion. The clip can't show it.

So nurses check the target, watch the sats, and watch for drowsiness. Too little is dangerous too, so the care team sets each range. Higher isn't always better: oxygen has a top as well as a bottom.

So Mr Brown's 91? Right on target.

Sources

  1. TSANZ Position Statement on Acute Oxygen Use in Adults: 'Swimming between the flags', Respirology 2022;27(4): oxygen is a drug requiring prescription with SpO2 targets with upper and lower ranges; 92-96% in other acute conditions; 88-92% in COPD exacerbations and chronic respiratory failure; mechanisms of oxygen-induced hypercapnia (read 13 October 2026)
  2. TSANZ Oxygen guidelines for acute oxygen use in adults (2015): an upper level of 96% avoids the potential risks of hyperoxia and allows improvement to be recognised earlier, so oxygen can be down-titrated; blood gas for PaCO2; monitoring and documentation (read 13 October 2026)
  3. ACSQHC Chronic Obstructive Pulmonary Disease Clinical Care Standard (2024), quality statement 8: controlled oxygen keeping saturation between 88% and 92% in a COPD exacerbation; in some people, too much oxygen can lead to high levels of carbon dioxide, which can be dangerous (read 13 October 2026)
  4. Abdo WF, Heunks LMA. Oxygen-induced hypercapnia in COPD: myths and facts. Crit Care 2012;16:323: loss of hypoxic pulmonary vasoconstriction accounts for the largest increase; minute ventilation has a limited effect; Haldane effect contributes (read 13 October 2026)
  5. StatPearls, Hypercapnia: flushed skin, lethargy, inability to focus, headaches, disorientation (read 13 October 2026)
  6. StatPearls, Respiratory Acidosis: CO2 build-up lowers blood pH (read 13 October 2026)
  7. StatPearls, Pulse Oximetry: limitations include inability to detect hyperoxaemia and to measure ventilation (read 13 October 2026)
  8. Austin MA et al. Effect of high flow oxygen on mortality in COPD patients in prehospital setting: randomised controlled trial. BMJ 2010;341:c5462 (Hobart): mortality 4% titrated vs 9% high flow overall; 2% vs 9% in confirmed COPD (read 13 October 2026)

Checked against these sources at the time of publishing. Sources change, so check the date above and your local policy. Spotted an error? Tell us and we'll correct it.

General education, not clinical advice. Check your local policy.