PreOx & ApOx

Hi team,

Preoxygenation (PreOx) and Apnoeic oxygenation (ApOx) are the terms used to describe procedures to reduce desaturation during intubation.

PreOx was introduced to our CPG as part of RSI procedure and it serves three purposes.

  1. Denitrogenation of the lungs = replacing nitrogen with as much as O2 as possible in the lungs. This is the main reason for the preox. 79% of inspired air is nitrogen and replacing nitrogen to O2 in the lungs is the most effective way of preventing O2 desaturation during RSI. If you let the patient have even one normal breath of air, then you need to start the process all over again!
  2. Achieve as high SaO2 (approximated by SPO2) as possible.
  3. Oxygenate plasma, although this is the least important due to the low solubility of oxygen in blood.

ApOx is a process of passive oxygenation during the apnoeic period once the paralytic drug is given or for those already apnoeic. Nasal Prong (NP) @ 15l added to BVM with PEEP reduces desaturation during the apnoeic period (apnoeic oxygenation) by adding the virtual CPAP effect with PEEP equivalent of approx 6~8cmH2o. This is well demonstrated on the following video.

Two options we have to achieve the purpose of PreOx and ApOx are;

  1. Non-rebreather mask (NRM) + NP
  2. BVM +PEEP + NP (CPAP equivalent)

Non-rebreather mask has poor seal and now has 1 x oneway valve offering only 50~60% FiO2. Due to the leaks, some even advocates its use should be avoided when possible. However it allows us to be hands free while resuscitating critically ill patient with only 2~3 people. (We are not in ED with 4 doctors supported by 6 RNs! )

* CPAP via BVM + PEEP + NP may be the only way to bring SPO2 above critical desaturation level > 93%.

The rule of 15
15l via NP, 15l via BVM, 15 of PEEP is called “The rule of 15”. This approach is detailed in the EMCrit but the author Scott Weingart also recognises that this rule applies in the ED but…

“may not always work for us in the prehospital environment with limited hands and O2 supply…!”

after the point was raised by a retrieval specialist Dr. Minh le Cong who is a Otago graduate for the aeromedical medicine, works in rural Australia, and is the author of PHARM – Prehospital and Retrieval Medicine FOAM site.

Also don’t forget PEEP of 5 is recommended for TBI where the most of our RSI occurs.

* PEEP causes increased ICP, reduced coronary artery perfusion, and reduced venous return resulting in reduced cardiac output.

But…wait there is more!!!

The use of NP for ApOx has its limitations and the Hungarian HEMS method of the use of NPA has recently been suggested and may be more practical for our environment…

……………..Hmmm so much to learn!!!

In summary, I personally believe our CPG for PreOx and ApOx once again is pretty spot on when considering skill set and other resources available to us. However, having deeper understanding has given me the extra strength for making, hopefully, better decision for the specific patient.

My current personal default for the PreOx/ApOx is;

  • Start with NRM @ 10l 15l *1 + NP (placed but not running) during the initial resus and RSI prep. Then switch to BVM + PEEP + NP 2 mins prior (when pushing fentanyl) to RSI.
  • Switch to BVM + PEEP + NP (placed but not running) if above fails *2, or when extra hands are available for 2 persons BVM. Add NP @ 15l if poor seal.
  • DON’T ventilate the bag unless necessary.*3
  • Run NP @ 15l from when paralytic drug is pushed till successful ETI is confirmed.

*1 St John recommends NRM @ 10l but may need to be increased to 15l and may also need to add NP @ 15l if saturation stays < 93%.

* CPG2106~2018 update recommends 15l now!

*2 Intubating hypoxic patients kills. Huge risk with SPO2 < 93%. If you are not getting SPO2>93% then should use BVM + PEEP unless PEEP is contraindicated.

*3 We use this technique to reduce the risk of vomiting caused by positive pressure ventilation. When you have to ventilate, remember to keep it slow and small at 10breaths/min (1 breath every 6 secs) with 1/3 of bag (500ml) for adult.


Please check out the fantastic FOAMs to understand the rationale behind the use of NP, BVM, SPO2<93% etc etc.

I recommend checking out LIFL site first, then you must check out my faviourite EMCrit “Preoxygenation, Reoxygenation and Deoxygenation” blog for an amazing presentation. You can also download Scott and Richard’s article for free.

Other links you should check out include; PHARM Podcast 134 Preoxygenation, and EMCrit Wee – Should a Nasal Cannula be Part of Denitrogenation / Preoxygenation

and also;

Please share your pearls and thoughts!


Let’s keep working towards becoming prehospital resuscitationists!




Weingart, S. D., & Levitan, R. M. (2012). Preoxygenation and Prevention of Desaturation During Emergency Airway Management. Annals of Emergency Medicine, 59(3), 165–175.e1.

Eross, A., Hetzman, L., Petroczy, A., & Gorove, L. (2016). Apneic preoxygenation without nasal prongs: the “Hungarian Air Ambulance method.” Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine, 24, 5.


One Comment Add yours

  1. thegiblett says:

    really interesting stuff Tatsu, thanks for the work you’ve done to find all this info. Jude

    Liked by 1 person

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