Oxygenation Basics
Oxygen gets in, carbon dioxide gets out — and the brain is the first to suffer when it fails.
Oxygenation depends on three things working together: ventilation (air moving in and out), diffusion (gas exchange across the alveoli), and perfusion (blood flow to carry oxygen). A problem with any one impairs oxygen delivery to tissues.
Early vs Late Signs of Hypoxia
- Early: restlessness, anxiety, tachycardia, tachypnea, and rising blood pressure. Confusion and restlessness are often the very first signs — the brain is sensitive to low oxygen.
- Late: cyanosis (bluish skin/lips), bradycardia, decreased level of consciousness, and dropping blood pressure.
A newly restless or confused patient may be hypoxic — assess oxygenation before assuming anxiety. Cyanosis is a late sign, so don't wait for blue lips. When a question lists a restless, anxious patient with rising heart and respiratory rates, think early hypoxia.
Every key point in this guide fits on one free printable page. Jump to the free cheatsheet PDF →
Oxygen Delivery Devices
Know the flow rate and the rough oxygen percentage for each — a guaranteed exam topic.
- Nasal cannula1–6 L/min · 24–44%
- Low-flow; patient can eat/talk. Humidify above 4 L/min.
- Simple face mask5–10 L/min · 40–60%
- Need at least 5–6 L/min to flush exhaled CO₂.
- Partial rebreather6–11 L/min · 60–75%
- Reservoir bag must stay inflated.
- Non-rebreather10–15 L/min · 80–100%
- One-way valves; bag must stay inflated. Highest O₂ short of intubation. Emergencies.
- Venturi maskvaries · 24–50% precise
- Delivers an exact FiO₂ — best choice for COPD.
Nasal cannula and simple mask = lower, comfortable oxygen for stable patients. Non-rebreather = the highest concentration you can give without a ventilator — reach for it in an emergency. Venturi = the most precise percentage, which is why it's favored in COPD where exact control matters.
? Which oxygen device delivers the highest concentration without intubation, and what must you check about the reservoir bag?
Oxygen Safety & COPD
Oxygen fuels fire, and in some COPD patients too much can slow breathing.
Fire & Equipment Safety
- Oxygen supports combustion — post "Oxygen in Use" signs and allow no smoking or open flames in the area.
- Avoid petroleum-based products (like Vaseline) near the face; use water-based lubricant for dry lips/nares.
- Check for frayed cords and sparks; keep oxygen away from heat sources.
- Humidify higher flow rates to prevent drying of mucous membranes.
COPD & the Hypoxic Drive
Some long-term COPD patients retain CO₂ and breathe partly in response to low oxygen levels (the hypoxic drive). Very high oxygen can blunt this drive and slow their breathing. The approach is controlled, lower-flow oxygen titrated to a target saturation (often about 88–92% for COPD) — not withholding oxygen from a hypoxic patient. A Venturi mask gives the precise low concentration these patients often need.
Oxygen itself doesn't explode, but it makes everything around it burn faster and hotter. No smoking, no candles, no electric razors near sparks, and no petroleum products. This is a frequent safety question — the "report/intervene" answer is always to remove the ignition source.
Promoting Airway Clearance
Keep the alveoli open and the secretions moving — especially after surgery.
- Turn, cough, and deep breathe every 1–2 hours; splint the incision with a pillow when coughing after abdominal/chest surgery.
- Incentive spirometry: slow, deep breaths to expand the lungs and prevent atelectasis. Use several times per hour while awake.
- Hydration: fluids thin secretions so they're easier to cough up.
- Early ambulation and repositioning mobilize secretions and open the lungs.
- Positioning: high-Fowler's or the orthopneic (tripod) position eases breathing for dyspneic patients.
The key teaching point: inhale slowly and deeply to raise the indicator, hold for 3–5 seconds, then exhale. Patients often try to blow out hard — correct them. The goal is full lung expansion to prevent atelectasis and pneumonia, particularly post-op.
Suctioning
Clears secretions a patient can't cough out — but it also removes oxygen, so technique matters.
- Use sterile technique for tracheal/ET suctioning.
- Hyperoxygenate the patient before suctioning.
- Insert the catheter without suction; apply suction only while withdrawing, rotating the catheter.
- Limit each pass to 10–15 seconds (suctioning removes oxygen).
- Allow the patient to recover and re-oxygenate between passes.
- Watch for hypoxia and bradycardia (vagal stimulation) — stop if they occur.
Applying suction while inserting the catheter strips oxygen and damages the mucosa. Insert first, then suction intermittently while withdrawing and rotating, for no more than 10–15 seconds. If the heart rate drops or the saturation falls, stop and re-oxygenate.
Pulse Oximetry & ABGs
SpO₂ for quick monitoring; ABGs for the full acid-base and oxygenation picture.
Pulse Oximetry (SpO₂)
- Normal is 95–100%; generally keep it above 90% (often 88–92% target in COPD).
- Falsely low/inaccurate readings: cold extremities, poor perfusion, dark nail polish, motion, hypotension.
- Carbon monoxide poisoning can make the reading falsely high.
Normal ABG Values
- pH
- 7.35–7.45
- PaCO₂respiratory
- 35–45 mmHg
- HCO₃⁻metabolic
- 22–26 mEq/L
- PaO₂oxygenation
- 80–100 mmHg
- SaO₂
- 95–100%
For full ABG interpretation using the ROME method, see the Acid-Base Balance guide.
If the pulse ox suddenly reads low, look at the patient first: are they pink, alert, and breathing comfortably? A cold finger, nail polish, or movement can drop the reading falsely. Reposition the probe and reassess before escalating — but never ignore a low number in a symptomatic patient.
Artificial Airways
From simple oral airways to tracheostomies — know the basics and the safety points.
- Oropharyngeal airway (OPA): for unconscious patients only — it triggers gagging/vomiting in anyone with a gag reflex.
- Nasopharyngeal airway (NPA): tolerated by conscious patients.
- Endotracheal (ET) tube: inserted for mechanical ventilation; short term.
- Tracheostomy: surgical airway for long-term needs.
Tracheostomy Care Basics
- Use sterile technique for trach care and suctioning.
- Keep the obturator and a spare trach tube at the bedside in case of accidental decannulation.
- Secure ties snugly (one finger should fit underneath); provide humidification.
- Suction only when needed, following the suctioning rules above.
If a fresh tracheostomy tube comes out, you need the obturator to reinsert it — so it (and a spare tube) must stay taped at the bedside at all times. For a brand-new trach, an accidental decannulation is an emergency: call for help and be ready to maintain the airway.
Breath Sounds
Match the sound to the cause — high-yield for prioritization questions.
- Crackles (rales)
- Fine popping/crackling. Fluid in alveoli — heart failure, pneumonia, pulmonary edema.
- Wheezes
- High-pitched, musical. Narrowed airways — asthma, COPD, bronchospasm.
- Rhonchi
- Low-pitched, snore-like. Secretions in larger airways — often clears with coughing.
- Stridor
- Harsh, high-pitched (heard without a stethoscope). Upper-airway obstruction — emergency.
- Diminished / absent
- Faint or no sound. Atelectasis, pneumothorax, pleural effusion.
Unlike wheezes or crackles, stridor signals a narrowing of the upper airway (laryngeal edema, foreign body, post-extubation swelling). It's audible without a stethoscope and can progress to complete obstruction. Stridor always gets immediate attention.
Frequently Asked Questions
Common student questions on this topic.
What are the flow rates and oxygen concentrations for a nasal cannula?
Which oxygen delivery device gives the highest concentration of oxygen?
Why must you be careful giving high-flow oxygen to a COPD patient?
What are the key safety rules when suctioning a patient?
What is incentive spirometry used for?
What do crackles, wheezes, and rhonchi indicate?
Quick-Reference Cheatsheet
Every key point from this guide on a single printable page.
Oxygenation & Airway Cheatsheet
One-page PDF — free download.