Part of the ICU Emergencies Hub — browse every related guide in one place.
Oxygen therapy is among the most commonly administered treatments in acute care nursing, used to treat or prevent hypoxemia. Understanding which device delivers which FiO2 (fraction of inspired oxygen), how to titrate to an appropriate target, and when specific patient populations require modified oxygen targets is foundational acute care nursing knowledge.
| Device | Flow Rate | FiO2 Range | Best For |
|---|---|---|---|
| Nasal Cannula (NC) | 1–6 L/min | 24–44% FiO2 (roughly: 1 L/min = ~24%, add ~4% per additional L/min) | Mild hypoxemia; patient comfort; allows eating and talking; most commonly used O2 device in hospitals |
| Simple Face Mask | 5–10 L/min | 35–50% FiO2 | Moderate hypoxemia; minimal flow must be at least 5 L/min to prevent CO2 rebreathing; less comfortable than NC |
| Venturi Mask | Varies by Venturi adapter color | Precise FiO2: 24%, 28%, 31%, 35%, 40%, 60% depending on adapter | Patients requiring precise O2 delivery (COPD where controlled O2 is critical); most accurate low-flow FiO2 delivery device |
| Partial Rebreather Mask | 6–15 L/min | 40–70% FiO2 | Moderate-to-severe hypoxemia; patient is exhaling into the reservoir bag but some exhaled air is rebreathed (hence "partial") |
| Non-Rebreather Mask (NRB) | 10–15 L/min | 60–80%+ FiO2; can approach 90–95% FiO2 with tight seal | Severe hypoxemia; acute respiratory distress; trauma; emergency O2 delivery short of intubation; the highest non-invasive conventional O2 delivery |
| High-Flow Nasal Cannula (HFNC) | Up to 60 L/min | Up to 100% FiO2 at full flow and FiO2 setting | Moderate-to-severe hypoxemia; patients who would otherwise require intubation; ARDS, COVID-19 respiratory failure, post-extubation support; requires specific equipment (Airvo, Optiflow) |
| BiPAP (Bilevel Positive Airway Pressure) | Set inspiratory (IPAP) and expiratory (EPAP) pressures | Variable FiO2 (set on device) | COPD exacerbation (primary non-invasive ventilation of choice for hypercapnic respiratory failure); CHF; sleep apnea; reduces intubation rate when used early |
| CPAP (Continuous Positive Airway Pressure) | Single continuous pressure | Variable FiO2 | Obstructive sleep apnea; cardiogenic pulmonary edema; helps recruit collapsed alveoli; less effective for COPD hypercapnia than BiPAP |
The target SpO2 for oxygen therapy is not universally "as high as possible." Research has established that excessive oxygenation (hyperoxia) is harmful in several contexts. Appropriate SpO2 targets vary by clinical situation:
| Patient Population | Target SpO2 | Rationale |
|---|---|---|
| General adult patients | 94–98% | Maintains adequate oxygenation without hyperoxia; standard target for most hospitalized adults |
| COPD patients at risk for hypercapnia | 88–92% | Lower target; see COPD oxygen section below; excessive O2 can worsen hypercapnia in a subset of COPD patients |
| Post-cardiac arrest (ROSC) | 94–98% | Avoid hyperoxia post-arrest; excessive O2 increases reactive oxygen species (ROS) and may worsen post-arrest neurological injury; target normoxia, not maximal oxygenation |
| Acute MI (STEMI/NSTEMI) | 94–98% (only if SpO2 below 94%) | Do NOT routinely give O2 to MI patients with SpO2 at or above 94% — trial evidence shows supplemental O2 in normoxic MI patients may increase infarct size; treat only documented hypoxemia |
| Neonates (NICU) | 90–95% (varies by gestational age) | Hyperoxia in neonates causes retinopathy of prematurity and pulmonary toxicity; highly controlled targets in NICU settings |
In practice: not every COPD patient has this risk, and you should never withhold O2 from a COPD patient who is critically hypoxic. The clinical approach: for a COPD patient in respiratory distress, use a Venturi mask set at 24–28% or titrate NC at 1–2 L/min; target SpO2 88–92%; watch for rising CO2 (obtundation, inability to arouse, worsening acidosis on ABG); escalate to BiPAP if hypercapnia worsens or respiratory effort increases without improvement in oxygenation.
Prolonged high-concentration oxygen (FiO2 above 0.60 for more than 24–48 hours) causes oxidative damage to pulmonary tissue — oxygen toxicity. The pulmonary manifestations include progressive inflammation, diffuse alveolar damage, and findings that can be indistinguishable from ARDS. Signs of oxygen toxicity include worsening respiratory distress despite continued high FiO2, progressive hypoxemia, and bilateral infiltrates on chest X-ray.
Oxygen toxicity is most clinically relevant in mechanically ventilated patients on high FiO2 settings. The goal of respiratory management in ARDS is to reduce FiO2 to 0.60 or below as quickly as possible using PEEP, prone positioning, and other oxygenation strategies — precisely to reduce O2 toxicity risk.
Patients receiving supplemental O2 should be monitored for: SpO2 response (SpO2 improving toward target with the device and flow ordered); respiratory rate and work of breathing (improving vs. worsening despite O2); mental status (improving confusion/agitation = improving oxygenation; worsening = hypoxia or hypercapnia); skin color (cyanosis = central hypoxia); and device fit (a poorly fitting NRB delivers much less than expected FiO2 — check seal consistently).
If a patient fails to respond to escalating O2 therapy (SpO2 not improving despite NRB mask), notify the provider immediately — the patient may need high-flow nasal cannula, BiPAP, or intubation and mechanical ventilation.
Related guides: Acid-base balance | ICU nurse skills | Cardiac arrhythmia nursing | Fluids and electrolytes
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