Oxygen Therapy & Prescribing Safety
Target ranges, delivery devices, and preventing hypercapnic respiratory failure — a clinical masterclass for student nurses.
On the acute ward, oxygen is one of our most frequently administered treatments — yet also one of the most misunderstood. It was once seen as a harmless comfort measure, something you could turn on without a second thought. We know better now. Oxygen is a powerful pharmacological drug — with clear indications, side effects, and real dangers when used without care.
As a student or newly qualified nurse, you need to look beyond the pulse oximeter. You need to know why target ranges differ, which device to pick, and how to keep vulnerable patients safe. This guide takes you through the science, the standards, and what actually matters on shift.
Oxygen is a resuscitation drug first and foremost. In cardiac arrest, anaphylaxis, major trauma, or sudden collapse — give high-flow oxygen immediately via non-rebreathe mask at 15 L/min while you call for help.
Controlled titration for COPD patients matters deeply — but stabilisation comes first. Never let fear of CO₂ retention stop you from saving a life. Adjustments happen after the patient is safe and support is there.
1. Oxygen as a Drug — Governance & Prescription
Like antibiotics or opioids, oxygen needs a prescription in non-emergency situations. The chart should clearly state: target saturation range, delivery device, and flow rate. Every patient should have their target range documented — usually right on their observation chart.
Why Too Much Oxygen Can Be Deadly
Uncontrolled high-flow oxygen isn’t harmless. It damages cells, collapses air sacs, narrows blood vessels to the heart and brain, and — most dangerously — can switch off the drive to breathe in patients with chronic respiratory disease. Knowing your patient’s baseline is just as important as reading the monitor.
2. Target Saturation Ranges — Two Tiers
There are two standard ranges — which one you follow depends entirely on the patient’s respiratory history.
| Target Tier | Range | Who It’s For | Why |
|---|---|---|---|
| Standard | 94–98% | Most patients — pneumonia, asthma, sepsis, PE, post-op, cardiac care | Healthy respiratory drive. Aim for normal oxygenation without excess. |
| Controlled | 88–92% | COPD, cystic fibrosis, obesity hypoventilation, chest wall deformity | Prevents CO₂ retention. Their drive to breathe depends on being slightly low on oxygen. |
The COPD Retainer — Why 88–92% Exists
Years of living with lung damage mean some COPD patients have got used to higher carbon dioxide levels. Their brain has stopped using CO₂ as the trigger to breathe — instead, it relies on low oxygen levels. If you blast them with high-flow oxygen, that trigger disappears. Their breathing slows, CO₂ builds up, and they can slip into confusion, drowsiness, coma — and worse. 88–92% keeps them safe — enough oxygen, but not enough to switch off their drive to breathe.
3. Devices — Which, When, and Why
Getting the right oxygen percentage matters — and that means choosing the right device. They fall into two main groups: variable-performance and fixed-performance.
| Device | Flow Rate | Approx. O₂ % | Best Used For |
|---|---|---|---|
| Nasal Cannulae | 1–6 L/min | 24–40% | Comfortable, can eat/talk. Gentle, steady oxygen for stable patients. |
| Simple Face Mask | 5–10 L/min | 40–60% | Medium levels. Never run below 5 L/min — they’ll rebreath their own CO₂. |
| Non-Rebreathe Mask | 10–15 L/min | 60–85% | Emergency high-concentration. Bag must be filled before putting it on. |
| Venturi Mask | Valve-specific | Exact % (24/28/35/40/60) | ✅ GOLD STANDARD for COPD. Delivers precise oxygen regardless of breathing rate. |
Venturi Masks — Precision That Saves Lives
Venturi masks pull in a fixed amount of room air alongside the oxygen — so the percentage delivered stays exactly what it says on the valve. For a COPD patient aiming for 88–92%, a blue (24%) or white (28%) Venturi is your safest choice. You’ll know exactly what they’re getting — no guesswork, no risk of accidental overdose.
4. Spotting CO₂ Retention Before It Becomes Critical
When oxygen is too high or breathing slows, carbon dioxide builds up. This is Type 2 Respiratory Failure — and spotting it early changes everything.
Signs to Watch For
- Confusion & Drowsiness: Getting muddled, sleepy, harder to wake — often worse in the morning.
- Shallow, Slow Breathing: Less effort, fewer breaths per minute.
- Warm, Flushed Skin & Bounding Pulse: CO₂ dilates blood vessels — they look pink and feel hot.
- Tremor (Asterixis): A flap-like shake in the outstretched hand — a classic warning sign.
What to Do
- Check the setup immediately: Wrong mask? Too high flow? Step down to a Venturi mask at the prescribed target.
- Arterial Blood Gas (ABG): The only way to know for sure — pH dropping and CO₂ rising confirms the problem.
- Call for help: Medical team, outreach, or critical care. Severe cases may need Non-Invasive Ventilation (NIV).
5. Practical Ward Care
- Humidification: Dry oxygen dries airways. High flow or long therapy = add humidifier. It thins secretions and protects delicate tissue.
- Skin Care: Check nose bridge, ears, cheeks. Masks and tubing cause pressure sores. Protect early with silicone dressings.
- Fire Safety: Oxygen feeds fire instantly. No smoking, no naked flames, no petroleum-based creams near equipment.
Treat oxygen with the respect it deserves — as a drug, not just a comfort button. Know your patient, know their target, and know your devices. That’s how you keep them safe.
Written by: Daniel Hancock, Registered Nurse
Focus: Respiratory care, ward safety, prescribing governance
Published: September 2026 | Last reviewed: September 2026
For: UK student nurses — supervised learning only
⚠️ Always confirm target ranges with the medical team and local trust policy. This is clinical reference guidance, not a substitute for individual patient assessment.