Introduction to apnoeic oxygenation

What it is (definition) and why it matters

• Apnoeic oxygenation = giving oxygen to the upper airway during apnoea (no breathing) to slow the fall in oxygen saturation (SpO2).
• It does NOT remove carbon dioxide (CO2) effectively, so CO2 rises during apnoea even if SpO2 stays high.
• Main benefit: increases the “safe apnoea time” (time before desaturation) during induction, intubation attempts, and airway rescue.
• Think of it as “oxygen trickling in while you’re not ventilating” — helpful, but not a substitute for good pre-oxygenation and timely ventilation.

Core physiology in simple terms

• Even when apnoeic, the body continues to take up oxygen from the alveoli into the blood.
• This oxygen uptake creates a slight negative pressure in the alveoli, encouraging oxygen to move from the upper airway down into the lungs if a patent airway and oxygen source are present.
• CO2 production continues, but most CO2 does not leave the body during apnoea; it accumulates (hypercapnia).
• Apnoeic oxygenation works best when the airway is open and the lungs were well “filled” with oxygen beforehand (good pre-oxygenation).

When to use it (common first-time scenarios)

• Routine induction and intubation: nasal cannula oxygen left on during laryngoscopy.
• Rapid sequence induction (RSI): especially useful because you are intentionally not ventilating between induction and intubation.
• Anticipated difficult airway: helps maintain oxygenation while you optimize view, change blade, use bougie, or call for help.
• Obesity, pregnancy, paediatrics, severe illness: patients desaturate faster; apnoeic oxygenation can be particularly valuable (but may be less effective if airway collapses).
• Procedural sedation with risk of hypoventilation: can support oxygenation, but you must still monitor ventilation and be ready to assist.

How to do it (practical set-up)

• Always start with good pre-oxygenation: tight mask seal, 100% oxygen, aim for end-tidal O2 (if available) or at least 3 minutes of tidal breathing / 8 vital capacity breaths.
• Apply nasal cannula early (before induction) so it’s ready and not forgotten.
• Typical adult flow rates: 5–15 L/min via standard nasal cannula during laryngoscopy (use local policy; higher flows may be used in selected settings with appropriate equipment).
• Keep nasal oxygen running throughout apnoea (during laryngoscopy/intubation attempts) until you resume ventilation.
• Maintain airway patency: head-up positioning, jaw thrust, oral/nasal airway if appropriate, and avoid excessive sedation without airway support.
• Use continuous monitoring: SpO2, ECG, NIBP; capnography once ventilating (and during sedation if feasible).

High-flow nasal oxygen (HFNO): what’s different?

• HFNO delivers warmed, humidified oxygen at high flow (often 30–70 L/min) via special nasal cannula and machine.
• Potential advantages: more reliable oxygen delivery, some washout of upper airway dead space, and a small amount of positive airway pressure (especially with mouth closed).
• Requires correct kit, set-up time, and familiarity; follow local guidance and escalation pathways.
• Even with HFNO, CO2 still rises during apnoea; do not let a good SpO2 delay ventilation when needed.

Safety and limitations (what it cannot do)

• Does not provide ventilation: CO2 rises and acidosis develops with prolonged apnoea.
• Less effective if airway is obstructed/collapsed (e.g., deep anaesthesia without airway support, laryngospasm, severe OSA, supraglottic obstruction).
• SpO2 can stay high while ventilation is absent: avoid being falsely reassured; watch time, clinical picture, and plan to ventilate.
• Not a substitute for: good pre-oxygenation, skilled laryngoscopy, early use of supraglottic airway, and following the difficult airway algorithm.

Practical tips for new starters

• Position matters: head-up (ramped) in obesity and pregnancy improves pre-oxygenation and airway patency.
• If SpO2 is falling: stop, oxygenate, ventilate (mask or supraglottic airway) rather than persisting with repeated laryngoscopy attempts.
• Communicate clearly: “Nasal oxygen on, flow at X L/min” as part of your induction checklist.
• Be cautious with nasal cannula in facial trauma or base of skull fracture risk; seek senior advice.
• If using diathermy near the airway: be aware of fire risk with high oxygen concentrations; follow theatre fire safety practice and local policy.