Oxygen and the basic airway
Open the airway, prescribe oxygen to a target, choose the right device, and don't trust the pulse oximeter more than the patient.
A 71-year-old man is found snoring loudly after a fall, GCS 9, SpO₂ 88% on 2 L via nasal cannula. There is vomit around his mouth.
In the next bed, a 66-year-old woman with COPD has been on a reservoir mask at 15 L/min since the ambulance. She is now drowsy with SpO₂ 99%.
What do you do with the first man's airway, and what has happened to the woman?
- Look, listen, feelChest movement, see-saw breathing, snoring, gurgling, stridor, silence.
- Open the airwayHead tilt and chin lift. Jaw thrust if neck injury possible.
- SuctionRigid (Yankauer) sucker under direct vision.
- Adjunct if neededOropharyngeal if no gag. Nasopharyngeal if gag present (not with basal skull fracture).
- Oxygen to a targetPrescribe the target and device on the chart.
- Know the CO₂ retainersTarget 88–92% with a Venturi mask until a gas shows otherwise.
- Check the probeGood waveform, warm finger, no nail polish.
- Call anaestheticsGCS 8 or less, airway not maintained with simple measures, or failing on oxygen.
- Snoring, gurgling or stridor not relieved
- See-saw breathing or silence
- GCS 8 or less
- SpO₂ falling on 15 L/min
- COPD or obese patient on high oxygen getting drowsy
- Rising CO₂ with acidosis
- Airway obstruction from vomit, tongue or swelling
- CO₂ narcosis from too much oxygen
- Failing on high-flow oxygen or CPAP
- Carbon monoxide poisoning (normal SpO₂)
- Tension pneumothorax
- Anaphylaxis with airway swelling
| Target, most | SpO₂ 94–98% |
| Target, risk of CO₂ retention | 88–92% |
| Critically ill | 15 L/min reservoir mask, then titrate |
| MI or stroke with normal SpO₂ | No oxygen needed |
| Nasal cannula | 1–4 L/min |
| Simple face mask | 5–10 L/min |
| Oropharyngeal airway size | Incisors to the angle of the jaw |
| Nasopharyngeal size | Usually 6 mm (adult women), 7 mm (adult men) |
| Carbon monoxide | 100% oxygen by reservoir mask regardless of SpO₂ |
Check every dose against a current drug reference and your hospital protocol.
On this page
Oxygen is a drug
It should be prescribed with a target, given through the right device, and reviewed like any other treatment. Too little kills quickly; too much harms some patients with chronic lung disease and gives no benefit to others.
Basic airway management
- Look, listen, feelChest movement, see-saw breathing, cyanosis. Snoring, gurgling, stridor. Air movement.
- Head tilt, chin liftJaw thrust if spinal injury possible.
- SuctionVomit, secretions, blood, with a rigid sucker under direct vision.
- Oropharyngeal (Guedel) airwayOnly if no gag reflex. Size from incisors to the angle of the jaw.
- Nasopharyngeal airwayTolerated with a gag. Avoid with suspected basal skull fracture or major nasal injury.
- Bag-valve-maskIf breathing is inadequate, while anaesthetics arrive.
| Sound | Likely problem |
|---|---|
| Snoring | Tongue falling back: head tilt, chin lift, adjunct |
| Gurgling | Fluid (vomit, secretions, blood): suction |
| Stridor | Upper airway narrowing (swelling, foreign body, anaphylaxis): senior and anaesthetist now |
| Silence with effort | Complete obstruction: emergency |
Target saturations
| Patient | Target SpO₂ |
|---|---|
| Most acutely ill patients | 94–98% |
| At risk of CO₂ retention: COPD, severe obesity, neuromuscular disease, chest wall deformity, bronchiectasis, cystic fibrosis | 88–92% until a gas shows otherwise |
| Critically ill: shock, sepsis, major trauma, cardiac arrest, anaphylaxis | Start 15 L/min reservoir mask, then titrate down |
| Heart attack or stroke with normal saturations | No oxygen needed |
| Pregnancy | 94–98% |
Choosing a device
Nasal cannula 1–4 L/min
Simple face mask 5–10 L/min
Venturi mask 24–28% to start
Reservoir mask 15 L/min
High-flow nasal oxygen, CPAP (type 1) or NIV (type 2), in HDU or ICU
| Device | Flow | Oxygen delivered | Use |
|---|---|---|---|
| Nasal cannula | 1–4 L/min | About 24–40% | Mild hypoxia, can eat and talk |
| Simple face mask | 5–10 L/min | About 35–60% | Moderate hypoxia |
| Venturi mask | Set by valve colour | Fixed 24, 28, 31, 35, 40, 60% | COPD and anyone needing a precise amount |
| Reservoir (non-rebreather) mask | 15 L/min | Up to about 85% | Emergencies, critically ill |
| High-flow nasal oxygen | Up to 60 L/min | Up to 100% | Type 1 failure not coping on a mask |
| CPAP | Continuous pressure | Variable | Type 1 failure, pulmonary oedema |
| NIV (BiPAP) | Two pressure levels | Variable | Type 2 failure (high CO₂), e.g. COPD |
CO₂ retention
- In some COPD and other patients, high oxygen worsens ventilation-perfusion matching and reduces breathing drive, so CO₂ rises.
- Signs: drowsiness, confusion, flapping tremor, warm hands, bounding pulse, headache.
- Don't switch oxygen off. Change to a Venturi mask (24–28%), target 88–92%, recheck the gas in 30–60 minutes.
- pH below 7.35 with high CO₂ despite treatment: NIV. See COPD.
Pulse oximetry pitfalls
| Situation | Problem |
|---|---|
| Carbon monoxide poisoning | Reads falsely normal |
| Methaemoglobinaemia (dapsone, nitrates) | Reads around 85% whatever the true value |
| Cold hands, shock, poor perfusion | Unreliable or no reading |
| Nail polish, movement, bright light | Errors |
| Darker skin | Can over-read; check a gas if the patient looks worse than the number |
Carbon monoxide poisoning
- Gas heaters and generators in closed rooms in winter, often several family members ill.
- Headache, nausea, vomiting, dizziness, confusion, collapse. Cherry-red colour is rare and late.
- SpO₂ reads normal. Measure carboxyhaemoglobin on a co-oximetry gas.
- 100% oxygen by reservoir mask until COHb is normal and symptoms settle. Pregnant women and severe cases: discuss hyperbaric oxygen where available.
Investigations
| Test | What it tells you |
|---|---|
| Arterial blood gas | PaO₂, PaCO₂, pH; type 1 or 2 failure |
| Venous gas | pH and CO₂ trend for monitoring |
| COHb on co-oximetry | Carbon monoxide |
| Chest X-ray | Cause of hypoxia |
| ECG | Cardiac causes, ischaemia |
Common mistakes
- Giving oxygen without a prescribed target.
- Leaving a COPD patient on 15 L/min for hours.
- Switching oxygen off in a hypoxic COPD patient.
- Using an oropharyngeal airway in a patient with a gag reflex.
- Using a nasopharyngeal airway with a suspected basal skull fracture.
- Trusting a normal SpO₂ in suspected CO poisoning.
- Waiting too long to call anaesthetics for an airway that isn't holding.
Follow-up
- Write the target saturation and device on the drug chart.
- Review oxygen at least daily and wean as the patient improves.
- Recheck the gas 30–60 minutes after any change in a patient with CO₂ retention.
Frequently asked questions
Which oxygen mask is used in COPD?
A Venturi mask (24% or 28%) targeting 88–92%, with a blood gas to check CO₂.
When should an oropharyngeal airway be used?
Only in an unconscious patient without a gag reflex. If the patient gags, use a nasopharyngeal airway instead.
Why is oxygen saturation normal in carbon monoxide poisoning?
Standard pulse oximeters can't tell carboxyhaemoglobin from oxyhaemoglobin. A co-oximetry blood gas measures COHb directly.
When should a nasopharyngeal airway be avoided?
In suspected basal skull fracture (bruising behind the ears or around the eyes, CSF from the nose) and with major nasal injury or bleeding.
Test yourself
Exam-style questions on this guide, from our two question banks. Choose an answer to see why each option is right or wrong.
1. An unconscious patient is snoring with a gag reflex present. Which airway adjunct is suitable?
Answer: Nasopharyngeal airway. A nasopharyngeal airway is tolerated with a gag reflex; avoid with suspected basal skull fracture.
- Endotracheal tube by the house officer: Needs an anaesthetist.
- No adjunct ever: An adjunct helps keep the airway open.
- Oropharyngeal airway: Causes gagging and vomiting with an intact gag.
- Laryngeal mask: Not tolerated with a gag.
2. A family is brought in with headaches after sleeping with a gas heater. SpO₂ is 99%. What oxygen do they need?
Answer: 15 L/min via reservoir mask. Carbon monoxide poisoning: high-flow oxygen regardless of SpO₂; check carboxyhaemoglobin.
- 28% Venturi: Too little.
- None, as SpO₂ is normal: Oximeters read carboxyhaemoglobin as oxyhaemoglobin.
- 2 L via nasal cannula: Too little.
- Oxygen only if SpO₂ falls: It won't fall.
3. Which device gives a fixed, controlled oxygen concentration for a CO₂ retainer?
Answer: Venturi mask. Venturi masks deliver fixed concentrations (24–60%) by colour.
- Reservoir mask: Too high.
- Simple face mask: Variable concentration.
- Nasal cannula at 6 L: Uncontrolled.
- Bag-valve-mask: For ventilation.
4. A 45-year-old non-smoking man has a painless cystic neck lump at level II; biopsy of a small tonsillar lesion shows squamous carcinoma that is p16-positive. Compared with HPV-negative tumours, what is the prognosis?
Answer: Better. HPV (mainly type 16)-associated oropharyngeal squamous cell carcinoma (tonsil, base of tongue): younger non-smokers, often presents with a cystic level II node (may be mistaken for branchial cyst in adults), p16 immunohistochemistry surrogate marker; better response to treatment and survival than HPV-negative (tobacco/alcohol-related) cancers; separate TNM staging. Treatment: chemoradiotherapy or transoral surgery ± adjuvant therapy.
- Worse: HPV-positive tumours do better, not worse.
- Identical: HPV-positive tumours respond better to treatment, so prognosis is not identical.
- Untreatable: These tumours are treatable.
5. A family is found drowsy with headache and vomiting in a closed room heated by a gas heater during winter in Quetta. Pulse oximetry reads 99%. What is the treatment?
Answer: 100% oxygen. Carbon monoxide binds haemoglobin with ~240× the affinity of O₂ and shifts the dissociation curve left, causing tissue hypoxia. Pulse oximetry is falsely normal (COHb read as oxyHb) — measure COHb by co-oximetry. Features: headache, nausea, confusion, cherry-red skin (late), seizures, coma, delayed neuropsychiatric syndrome. Treat with 100% oxygen (half-life of COHb falls from ~5 h to ~1 h); hyperbaric oxygen for severe cases and pregnancy where available. Gas heaters in closed rooms cause deaths in Pakistani winters.
- Room air — SpO₂ is normal: Oximetry is falsely normal in CO poisoning.
- IV naloxone 400 µg: This is not opioid toxicity.
- Sodium nitrite infusion: Sodium nitrite is for cyanide.
6. While ligating the superior thyroid artery during a hemithyroidectomy, the surgeon damages a nerve that runs with it. The patient, a professional singer, later cannot reach high notes. Which muscle is paralysed?
Answer: Cricothyroid. The external branch of the superior laryngeal nerve runs with the superior thyroid artery and supplies cricothyroid, the only intrinsic laryngeal muscle not supplied by the recurrent laryngeal nerve. Cricothyroid tilts the thyroid cartilage forwards and tenses the vocal cords, raising pitch.
- Posterior cricoarytenoid: The only abductor of the cords; supplied by the recurrent laryngeal nerve.
- Lateral cricoarytenoid: Adductor; supplied by the recurrent laryngeal nerve.
- Thyroarytenoid: Relaxes the cords; recurrent laryngeal nerve.
- Transverse arytenoid: Adductor; recurrent laryngeal nerve.
7. Both recurrent laryngeal nerves are cut during thyroid surgery. Which laryngeal muscle still works?
Answer: Cricothyroid. The recurrent laryngeal nerve supplies all intrinsic laryngeal muscles except cricothyroid, which is supplied by the external laryngeal nerve (from the superior laryngeal). Losing both recurrent nerves paralyses both posterior cricoarytenoids, the only abductors, so the cords lie near the midline, causing stridor and airway obstruction.
- Posterior cricoarytenoid: Only abductor; paralysed.
- Lateral cricoarytenoid: Adductor; paralysed.
- Transverse arytenoid: Adductor; paralysed.
- Thyroarytenoid: Relaxes cords; paralysed.
References and dose sources
International guidance is linked where it reflects good practice. Where your hospital’s protocol differs, follow your hospital.