Problems Achieving Preoxygenation

Compliant Patient

If you are unable to achieve high sats in a patient who complies with your PreOx the problem is usually shunt: alveoli that are being perfused are not being ventilated. The solution to this is the addition of PEEP to splint open the alveoli. There are 3 main ways to add PEEP to your PreOx technique in the ED:

1. BVM with addition of a PEEP valve

2. Non invasive ventilation (NIV) machine with associated face mask – set to CPAP mode

3. Face mask attached to ventilator set to CPAP settings


Non compliant patient

If you are unable to achieve high sats because your patient is not compliant with PreOx (eg confusion/delirium/agitiation due to hypercapnoea, hypoxia, head injury, toxicological effects), you have 3 main options:

1. Proceed with standard RSI despite the patient not being adequately preoxygenated & denitrogenated +/- hypoxic

– this could result in a precipitous desaturation during apnoea before or during intubation attempt

2. Perform “modified RSI” where you provide manual ventilations (eg via BVM) after sedation/paralytics but before 1st attempt at intubation.

– this can improve oxygenation at the expense of an increased risk of gastric insufflation and aspiration. This risk is theoretically minimised with gentle, slow ventilations.

3. Perform Delayed Sequence Intubation (DSI)

– DSI is an innovative solution proposed by Dr Scott Weingart of emcrit. DSI is procedural sedation for PreOx.

DSI Procedure:

– Set up for RSI completely (all equipment/drugs/team ready)

– Dissociative dose of IV Ketamine administered (1-2mg/kg): Ketamine is the chosen agent due to its preservation of airway reflexes and respiratory drive.

– Patient enters dissociative state achieving compliance with PreOx.

– PreOx for required time (i.e greater than 3 minutes) with whatever PreOx technique required for this patient (eg with or without PEEP)

– When patient’s PreOx is complete, give paralytic agent and proceed with intubation.


For more information see:

Emcrit podcast on DSI

Weingart article on Preoxygnation, Reoxygenation and DSI

LITFL summary of DSI


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