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Oxygen

Controlled vs uncontrolled — target SpO₂ & device choice

Oxygen is a drug. Prescribe with a target SpO₂ range, not just a flow rate. The single most important decision is whether the patient is a hypercapnic COPD patient — this determines the target and device completely.

What to do

1 · Establish target SpO₂

COPD / known hypercapnia: 88–92%. All others: 94–98%. This drives every other decision — get it right first.

2 · Choose delivery device

COPD: 24% or 28% Venturi mask.

Non-COPD mild: nasal cannulae 2–4L.

Non-COPD moderate: simple face mask 5–10L.

Severe hypoxia: 15L NRB mask.

3 · Prescribe correctly

Write on drug chart: device + flow rate + target SpO₂ range. 'Give O2' is not a prescription — it must include a target range.

4 · ABG if COPD or non-response

COPD with acute deterioration: ABG to check PaCO₂. If rising CO₂ + falling pH: escalate to NIV.

5 · Titrate to target

Adjust up or down to stay within target range. Avoid over-oxygenation — dangerous in COPD and causes absorption atelectasis.

6 · Wean when improving

Gradual step-down. Wait for SpO₂ to stabilise at each step. Review daily and update prescription.

Drugs

Drug	Dose	Route	Notes
24% Venturi	Colour-coded: white	Mask	COPD — starting point. 24% FiO₂.
28% Venturi	Colour-coded: yellow	Mask	COPD — step up if SpO₂ <88% on 24%.
Nasal cannulae	1–4L/min	Nasal	Low-flow, uncontrolled FiO₂. Non-COPD mild desaturation only.
NRB (non-rebreather) mask	15L/min	Mask	High-flow O2 for type 1 RF. Do not use in COPD.

Red flags

COPD patient: SpO₂ >94% — may be over-oxygenating, reduce flow
ABG showing rising PaCO₂ + pH <7.35 — type 2 RF, NIV needed urgently
SpO₂ <88% despite 35% Venturi or 10L mask — escalate, consider HDU/ITU
SpO₂ maintained but patient increasingly drowsy — CO₂ retention, check ABG

Reference: BTS Emergency Oxygen Guidelines 2017 / NICE COPD QS10