Oxygen is the most common medical support families encounter, and the most misunderstood. A plain-language grounding helps you follow doctors’ instructions, manage home oxygen sensibly, and plan any travel safely.
Saturation: the number on the finger clip
The pulse oximeter’s percentage (SpO2) estimates how much of the blood’s oxygen-carrying capacity is in use. Healthy lungs idle in the high 90s. Doctors set a target for each patient — often ‘keep above 92–94%’, sometimes lower targets for chronic lung disease, because some patients’ bodies are adapted differently. Know your patient’s target; chasing 99% is not always the goal and over-oxygenation has its own risks for some conditions.
Litres per minute: the tap, not the tank
Flow rate (1, 2, 5, 10 litres per minute) is how fast oxygen flows to the patient. More breathless usually means more flow, but the prescription belongs to the doctor. What families must know cold is the patient’s usual flow — it is the first question every ambulance operator, airline and hospital will ask.
Masks, cannulas and what fits when
- Nasal cannula: the two-prong tube; comfortable for low flows, lets the patient eat and talk
- Simple mask: mid-range flows; covers nose and mouth
- Non-rebreather mask (with bag): high flows for serious distress — if your patient needs this at home, you should be on the phone with a doctor
- Concentrator vs cylinder: concentrators make oxygen from air endlessly but need power and top out at modest flows; cylinders hold a finite amount at any flow — homes often keep both
The travel question
For any journey, the calculation is the same: flow rate × hours × safety margin = cylinder capacity needed. This is exactly the arithmetic a good ambulance service recites when you ask what’s aboard. For a patient on 2 litres crossing the city, it is trivial; for 6 litres to another state, it is planning — and the reason ‘we’ll manage with the small cylinder’ is a sentence that should end any booking call.
When home oxygen isn’t enough
Rising flow needs to hold the same saturation, breathlessness at rest, blue lips, drowsiness or confusion — these mean the current support is losing, and the next conversation is with a doctor or an emergency service, not the oxygen vendor. Escalate early; oxygen buys time, it does not treat causes.
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