Pulmonary · Topic 3 of 28

Oxygen Therapy & Delivery Devices

Pulmonary · oxygen delivery

Oxygen Therapy & Delivery Devices

Oxygen is a drug: titrate to a target — SpO₂ no higher than 96% for most, 88–92% when CO₂ retention is a risk.

Key numbers

Keep SpO₂ at 96% or lowerSpO₂ ≤ 96%

CO₂ retainers: target SpO₂ 88–92%SpO₂ 88–92%

Nasal cannula: 1–6 L/min, FiO₂ under 40%1–6 L/min

01 · The numberKeep SpO₂ at 96% or lower

In acutely ill adults, titrate oxygen so SpO₂ stays at 96% or lower (about 90–94% is a reasonable target); liberal oxygen raised in-hospital mortality in a 2018 meta-analysis.

02 · The numberCO₂ retainers: target SpO₂ 88–92%

For patients at risk of hypercapnic failure (COPD, obesity hypoventilation, neuromuscular or chest-wall disease), target SpO₂ 88–92% (PaO₂ about 60 mmHg); titrated oxygen improved survival in prehospital COPD.

03 · The numberNasal cannula: 1–6 L/min, FiO₂ under 40%

Nasal cannula delivers 1–6 L/min (FiO₂ under about 40%); flows above 6 L/min add nothing because the nasopharynx is already full, and FiO₂ varies with mouth breathing.

The rules

Know these

No routine oxygen in MI or strokeDo not start oxygen in acute MI or stroke when SpO₂ is 93% or higher (strong recommendation) and generally not at 90–92%; give it for hypoxemia below 90%.

Never withhold oxygen from hypoxemic COPDOxygen can raise PaCO₂ in COPD, but it is still given to hypoxemic patients: aim for PaO₂ about 60 mmHg, since higher levels add little and raise the hypercapnia risk.

Hypoxemia despite high FiO₂ means shuntIf SpO₂ will not rise above 90% on high-concentration oxygen, suspect shunt (alveolar flooding or intracardiac) and escalate to high-flow, positive pressure or intubation.

Diagnosis & monitoring

Work-up

Non-rebreather mask: FiO₂ 80–90% at mostFiO₂ above 40% needs a reservoir mask; a non-rebreather delivers at most 80–90% because of leak — the highest FiO₂ short of high-flow or positive pressure.

High-flow cannula: up to 60 L/min, humidifiedHigh-flow nasal cannula delivers heated, humidified oxygen up to 60 L/min with FiO₂ up to 100%, washes out dead space, adds 3–5 cmH₂O of PEEP and lowers work of breathing (details in the NIV/HFNC topic).

Recheck a blood gas in CO₂ retainersAfter starting oxygen in a patient at risk of hypercapnia, recheck a blood gas; worsening acidemia or drowsiness means the patient needs ventilatory support (BiPAP), not less oxygen.

Pulse oximetry misleads in CO poisoningSpO₂ tracks SaO₂ within 2–5% from 70–100%, but is falsely reassuring in carbon monoxide poisoning and methemoglobinemia, and less accurate with dark skin pigmentation, hypotension or vasoconstriction — get an ABG with co-oximetry.

Do right now

In this order

First moves

CO₂ retainers: target SpO₂ 88–92%SpO₂ 88–92%

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Venturi mask for precise FiO₂

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Recheck a blood gas in CO₂ retainers

Why each step

CO₂ retainers: target SpO₂ 88–92%For patients at risk of hypercapnic failure (COPD, obesity hypoventilation, neuromuscular or chest-wall disease), target SpO₂ 88–92% (PaO₂ about 60 mmHg); titrated oxygen improved survival in prehospital COPD.

Venturi mask for precise FiO₂A Venturi mask delivers an accurate, fixed FiO₂; in CO₂ retainers give oxygen by Venturi mask or low-flow cannula so it can be closely regulated, and monitor closely.

Red flags & don'ts

Avoid harm

Avoid sustained FiO₂ above 0.6 complicationOxygen toxicity is dose- and time-dependent: sustained FiO₂ above 0.6 causes lung inflammation, infiltrates and eventually fibrosis — use it only when PaO₂ ≥ 60 mmHg cannot otherwise be kept.

Which oxygen device?

Commonly confused

Flow	Cannula 1–6 L/min
FiO₂ delivered	Under 40%; Venturi gives a precise set FiO₂
Best for	Mild hypoxemia; CO₂ retainers (Venturi)
Extra effects	None — FiO₂ varies with mouth breathing

More detail

Reference

Show 4 reference facts

Because the oxyhemoglobin curve is sigmoidal, raising PaO₂ above about 80 mmHg adds very little oxygen delivery; the lowest FiO₂ giving an acceptable PaO₂ should be used.

Oxygen-induced hypercapnia in COPD has traditionally been blamed on blunted hypoxic drive; severe CNS depression is unlikely unless PaCO₂ exceeds about 85 mmHg in chronic retainers.

Many COPD patients sent home on oxygen after an exacerbation no longer need it within 30 days, so reassess home oxygen 60–90 days after discharge.

Hypoxemia from low V/Q, diffusion limitation and hypoventilation all correct with supplemental oxygen; pure right-to-left shunt does not.

Pearl

Prescribe oxygen like any drug — with a target range — and treat SpO₂ above 96% as an overdose.

Sources · Siemieniuk RAC et al. Oxygen therapy for acutely ill medical patients: a clinical practice guideline. BMJ 2018;363:k4169 · Merck Manual Professional — Hypoxia in Hospitalized Patients (oxygen therapy) · Rochwerg B et al. Official ERS/ATS clinical practice guidelines: noninvasive ventilation for acute respiratory failure. Eur Respir J 2017;50:1602426 · Merck Manual Professional — Treatment of Acute COPD Exacerbation · Merck Manual Professional — Noninvasive Positive Pressure Ventilation (NIPPV) and high-flow nasal oxygen · Merck Manual Professional — Acute Hypoxemic Respiratory Failure (AHRF), Including ARDS · Merck Manual Professional — Measurement of Gas Exchange (pulse oximetry, causes of hypoxemia) · Austin MA et al. Effect of high flow oxygen on mortality in COPD patients in prehospital setting: randomised controlled trial. BMJ 2010;341:c5462 · Chu DK et al. Mortality and morbidity in acutely ill adults treated with liberal versus conservative oxygen therapy (IOTA). Lancet 2018;391:1693–1705 · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).