Before We Start
Oxygen as a medication — why this framing matters
Nurses often think of oxygen as something automatically given to anyone in distress. But oxygen is a drug — with a therapeutic range, side effects, and contraindications. Too little causes hypoxia. Too much can suppress the respiratory drive in COPD patients, cause oxygen toxicity, and create free radical damage with prolonged high-dose use.
The goal of oxygen therapy is to maintain adequate tissue oxygenation — not to push SpO₂ to 100% in every patient. Know the target for your specific patient before you reach for the oxygen.
💡 Target SpO₂ by Patient Type
Most patients: SpO₂ 94–98%
COPD / chronic hypercapnia: SpO₂ 88–92% (do not over-oxygenate)
MI / stroke / carbon monoxide poisoning: SpO₂ 94–99%
Newborns: SpO₂ 95–100% (varies by gestational age)
FiO₂ = Fraction of Inspired Oxygen — the percentage of oxygen in the air the patient breathes. Room air = 21% FiO₂.
The Devices — Low to High
NC → SM → NRM — increasing FiO₂ as need increases
NC — Nasal Cannula
1–6 L/min → 24–44% FiO₂ · Comfortable · Allows eating and talking
The nasal cannula is two small prongs that sit in the nostrils and deliver oxygen directly. It is the most comfortable and most commonly used device for mild oxygen needs.
Flow rate and FiO₂: Each liter per minute adds approximately 4% FiO₂ above room air (21%):
• 1 L/min = 24% FiO₂
• 2 L/min = 28% FiO₂
• 3 L/min = 32% FiO₂
• 4 L/min = 36% FiO₂
• 5 L/min = 40% FiO₂
• 6 L/min = 44% FiO₂
Advantages: Patient can eat, drink, and talk. Low profile. Comfortable for long-term use.
Limitations: Actual FiO₂ varies with breathing pattern. Flow above 6 L/min does not meaningfully increase FiO₂ and causes nasal dryness — add humidification above 4 L/min.
Use for: Mild hypoxia, stable patients, post-op patients, home oxygen therapy.
💊 Humidify at flows above 4 L/min — dry nasal mucosa at higher flows causes discomfort and nosebleeds. Bubble humidifier attaches to the flowmeter.
SM — Simple Face Mask
5–10 L/min → 35–50% FiO₂ · Minimum 5 L/min always
The simple mask covers the nose and mouth and delivers higher FiO₂ than a nasal cannula. It has small holes on the sides that allow exhaled CO₂ to escape.
Critical rule: Minimum flow rate is 5 L/min. Below 5 L/min, exhaled CO₂ can accumulate inside the mask and be rebreathed — causing CO₂ retention.
Advantages: Higher FiO₂ than nasal cannula. Simple to apply.
Limitations: Must be removed to eat or drink. Patient may feel claustrophobic. FiO₂ is not precise — varies with breathing pattern.
Use for: Moderate hypoxia requiring more oxygen than a nasal cannula provides.
💊 Simple mask minimum = 5 L/min. If ordered at less than 5 — clarify the order. Running a simple mask at 2 L/min causes CO₂ rebreathing.
PRM — Partial Rebreather Mask
6–10 L/min → 40–70% FiO₂ · Reservoir bag stays inflated
The partial rebreather mask has a reservoir bag attached below the mask. The patient inhales from the bag (which contains a mix of oxygen and the first portion of exhaled breath — which is mostly oxygen that didn't participate in gas exchange).
Key assessment: The reservoir bag should remain at least one-third to one-half inflated during inhalation. If it fully collapses — increase flow rate.
Differs from NRM: The partial rebreather allows some exhaled air back into the reservoir. The NRM has a one-way valve that prevents this.
NRM — Non-Rebreather Mask
10–15 L/min → 60–100% FiO₂ · Highest non-invasive oxygen delivery
The non-rebreather mask delivers the highest FiO₂ of any non-invasive device. It has a reservoir bag AND a one-way valve between the bag and the mask that prevents exhaled air from entering the reservoir. Additional one-way valves on the side ports prevent room air from being inhaled.
Critical assessment: The reservoir bag must be inflated before placing on the patient. Keep it at least one-third full at all times — inflate the bag by covering the valve and flowing O₂ before application.
Use for: Severe acute hypoxia, trauma, acute MI, stroke, carbon monoxide poisoning, anaphylaxis — any situation requiring maximum non-invasive oxygen delivery.
Next step if NRM insufficient: High-flow nasal cannula (HFNC), BiPAP, CPAP, or intubation and mechanical ventilation.
💊 NRM = emergency oxygen. SpO₂ not improving on 6L nasal cannula → move to simple mask → if still not improving → NRM. If NRM not enough → call provider for HFNC or intubation discussion.
Venturi Mask
Precise FiO₂ (24–50%) · Best for COPD
The Venturi mask delivers a precise, controlled FiO₂ regardless of the patient's breathing pattern. Color-coded adapters determine the FiO₂ — each adapter specifies the required flow rate for that FiO₂.
Why it's best for COPD: COPD patients with chronic CO₂ retention rely on hypoxic drive to breathe. Too much oxygen suppresses this drive. The Venturi mask allows precise delivery of 24–28% O₂ — just enough to treat hypoxia without suppressing respiratory drive.
NCLEX rule: COPD patient with hypoxia → Venturi mask (controlled FiO₂). Target SpO₂ 88–92%, not 95–100%.
💊 COPD + hypoxia = Venturi mask. Never give uncontrolled high-flow oxygen to a COPD patient with known CO₂ retention — you may eliminate their drive to breathe.
🏥 Clinical Scenario — Escalating Oxygen Therapy
Mr. Adams, 58 years old, admitted with community-acquired pneumonia. No history of COPD. You are managing his oxygen therapy over the course of your shift.
0800
SpO₂ 93% on room air. Apply nasal cannula at 2 L/min. Reassess in 15 minutes. SpO₂ improves to 95%. Target met. Continue NC at 2 L/min.
1100
SpO₂ drops to 89% despite NC at 2 L/min. Increase to 4 L/min. Reassess. SpO₂ 91% — still below target. Increase to 6 L/min. SpO₂ 93%. Notify provider of worsening hypoxia.
1300
SpO₂ 88% on NC 6 L/min. NC at maximum — not adequate. Apply simple mask at 8 L/min per new order. SpO₂ improves to 92%.
1600
SpO₂ 84% despite simple mask. RR 32, labored breathing. Provider notified. Order received for NRM at 15 L/min. Apply NRM — inflate reservoir bag first. SpO₂ improves to 91%. Provider at bedside — ICU transfer initiated. HFNC being arranged.
📌 NCLEX Application
Oxygen delivery is tested constantly on NCLEX. Memorize these facts cold:
• NC: 1–6 L/min, 24–44% FiO₂, each liter adds ~4%
• Simple mask: minimum 5 L/min (CO₂ rebreathing below this), 35–50% FiO₂
• NRM: 10–15 L/min, 60–100% FiO₂, highest non-invasive
• Venturi mask: precise FiO₂, use for COPD
• COPD target: 88–92% SpO₂ (NOT 95–100%)
• Reservoir bag must stay inflated on NRM — if it collapses, increase flow
• Humidify at flows above 4 L/min via NC
Classic NCLEX question: "A patient with COPD has SpO₂ 86%. What oxygen device should the nurse apply?" → Venturi mask at 24–28% FiO₂. Not NRM. Not high-flow NC. Controlled, low FiO₂.
⚠️ The COPD Oxygen Trap
This is one of the most tested and most misunderstood concepts in respiratory nursing.
Normal breathing is driven by rising CO₂ levels. COPD patients with chronic CO₂ retention have adapted — their brains are no longer sensitive to high CO₂ as a drive to breathe. Instead, they breathe because their oxygen levels are LOW (hypoxic drive).
Give a COPD patient too much oxygen → their SpO₂ rises → hypoxic drive is removed → they stop breathing effectively → CO₂ climbs → respiratory failure.
Target 88–92% in COPD. Give just enough oxygen to treat hypoxia — not enough to eliminate the hypoxic drive. Use the Venturi mask for precise FiO₂ control.