Apnoeic Oxygenation

Apnoeic Oxygenation

Definition

Apnoeic oxygenation is the continuous delivery of oxygen to the airway during apnoea, allowing ongoing alveolar oxygen uptake without spontaneous breathing or positive-pressure ventilation.

It delays desaturation and prolongs safe apnoea time during airway management.

Important: It maintains oxygenation but does not provide adequate ventilation.

Mechanism

O₂ continues to diffuse from alveoli into blood
(O₂ consumption ≈ 250 mL/min)

↓

Only 10–20 mL/min of CO₂ enters the alveoli
(most CO₂ remains buffered in blood and tissues)

↓

Alveolar gas volume decreases, producing subatmospheric alveolar pressure

↓

Oxygen is drawn from the pharynx towards the alveoli by aventilatory mass flow

↓

Oxygenation continues during apnoea → desaturation is delayed

However, CO₂ continues to accumulate:

• First minute: PaCO₂ rises by approximately 6–8 mmHg
• Thereafter: approximately 3–4 mmHg/min

Prolonged apnoea can therefore cause:

• Hypercapnia and respiratory acidosis
• Sympathetic stimulation
• Arrhythmias
• Raised intracranial pressure
• Physiological deterioration despite preserved SpO₂

Uses

Useful during:

• Direct or video laryngoscopy
• Rapid-sequence induction
• Anticipated difficult or prolonged intubation
• Emergency airway management
• Patients with reduced oxygen reserve:
• Obesity
• Obstructive sleep apnoea
• Pregnancy
• Paediatric patients

Common Techniques

1. THRIVE
2. NODESAT

THRIVE – Transnasal Humidified Rapid-Insufflation Ventilatory Exchange

Delivery of high-flow, warmed and humidified oxygen through a nasal cannula during preoxygenation, induction and apnoea.

Parameter	Details
Device	High-flow nasal cannula
Gas	Warmed and humidified oxygen
Flow	Start at 30–40 L/min and increase up to 70 L/min
FiO₂	Approaches 1.0
Duration	Continued throughout induction, apnoea and laryngoscopy

Technique

Apply HFNO → preoxygenate → induce anaesthesia → maintain airway patency → continue HFNO during apnoea → intubate

After induction, airway patency may require:

• Jaw thrust
• Oropharyngeal airway
• Nasopharyngeal airway

Additional benefits

Apart from apnoeic oxygenation, THRIVE provides:

• Upper-airway dead-space washout
• Continuous pharyngeal oxygen reservoir
• Mild, variable positive airway pressure
• Better comfort and mucosal protection due to humidification

Positive airway pressure is greater with the mouth closed.

Limitations

• Progressive CO₂ accumulation and respiratory acidosis
• Does not overcome complete upper-airway obstruction
• Less effective with severe shunt or significant lung disease
• May cause nasal discomfort or epistaxis
• Requires specialised equipment

NODESAT– Nasal Oxygen During Efforts at Securing A Tube

A simple technique in which oxygen is delivered through a standard nasal cannula and continued during induction, apnoea, laryngoscopy and intubation.

Technique

• Place the nasal cannula before induction
• Preoxygenate using a tight-fitting face mask
• After induction, increase nasal oxygen flow to approximately 5–15 L/min
• Continue oxygen throughout intubation attempts
• Maintain upper-airway patency

Higher flows may be uncomfortable while the patient is awake; therefore, flow is usually increased after induction.

Advantages

• Simple, inexpensive and widely available
• Hands-free and does not interfere with laryngoscopy
• No specialised high-flow equipment required
• Useful in emergency and resource-limited settings

Limitations

• Lower and variable FiO₂ compared with THRIVE
• Oxygen is not warmed or adequately humidified
• Nasal dryness and discomfort at high flows
• Minimal dead-space washout and positive airway pressure
• Does not provide reliable ventilation

THRIVE vs NODESAT

THRIVE	NODESAT
High-flow nasal cannula	Standard nasal cannula
Warmed and humidified oxygen	Non-humidified oxygen
Flow up to 70 L/min	Flow approximately 5–15 L/min
FiO₂ approaches 1.0	FiO₂ is variable
Good dead-space washout	Minimal dead-space washout
Produces mild positive airway pressure	Negligible positive pressure
Better tolerated at high flows	Dryness and discomfort at high flows
Requires specialised equipment	Simple, inexpensive and widely available
More suitable for prolonged or difficult airway procedures	Useful when HFNO equipment is unavailable

Both techniques delay desaturation, but neither is a substitute for ventilation.

References

1. Patel A, Nouraei SAR. Anaesthesia. 2015;70(3):323–329. 
2. Weingart SD, Levitan RM. Ann Emerg Med. 2012;59(3):165–175.e1. 
3. Fayed M, et al. Cureus. 2023. 
4. Jagannathan N, Burjek N. Br J Anaesth. 2017;118(2):127–132. 
5. Gustafsson IM, et al. Br J Anaesth. 2017;118(4):610–617.