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What is Apneic Oxygenation?


As I wrote a couple of blogs on pre-oxygenation, I brought up the terminology "apneic oxygenation." I was then barraged with several questions regarding the term.


What is apneic oxygenation?


How do I perform apneic oxygenation?


Does apneic oxygenation really work?


And as we are here now, I plan to answer those questions. But first, let me direct you to the two pre-oxygenation installments that led to these questions. Reading the following hyperlinked blogs may help you understand where these questions came from.


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What is apneic oxygenation?

Apneic oxygenation, or "Ap-Ox" as some call it, is just as simple as the word implies: oxygenation occurring while the patient ceases to breathe (AKA apnea).😱😜


Understanding what it is, is not the difficult part. How it is possible seems to be the portion with which many find difficulties.


During apnea, the difference between the amount of oxygen removed from the alveoli and the amount of carbon dioxide excreted into the alveoli creates a negative pressure gradient between the alveoli and the upper airway. Thus the gas in the oropharynx moves down the trachea and into the alveoli. (1) Essentially, more gases are moving into pulmonary circulation than being removed from pulmonary circulation during apnea. This creates a vacuum, if you will, pulling the gases from above (which is the oropharynx) down and into the alveoli. As long as that "gas" being pulled down is oxygen, our patient can be effectively oxygenated without breathing or receiving any manual ventilation. The process, or phenomenon, is also known as "aventilatory mass flow" or apneic oxygenation as we are using it.


In healthy people under ideal circumstances, PaO2 can be maintained at >100 mmHg for up to 100 minutes without a single breath, although the lack of ventilation will eventually cause marked hypercapnia and significant acidosis. (2) Are we gonna not breathe for our patients for over 100 minutes?! Absolutely not, but the fact is that apneic oxygenation is possible and is used for many procedures in other medical disciplines.


Of course, CO2 will rise in the body during periods of apnea. That's OK. Typically, elevated CO2 levels don't kill our patients... Well, at least it's not as big of an issue as hypoxia. If you are worried about the CO2 (PaCO2, really), there is an approximate raise by 12 mmHg in the first minute of apnea, and a subsequent 3 mmHg raise per minute thereafter (with other sources showing only slight variations in these numbers). Unless the patient is at risk for changes in PaCO2 causing an acidosis to be critical, the increases in PaCO2 shouldn't be problematic in the acute setting.


The process of apneic oxygenation is beneficial for providers during the RSI procedure, especially in patients whose airway management may be prolonged, difficult, or those at risk of rapid desaturation. Apneic oxygenation is used to extend the "safe apnea time" beyond which can be achieved by pre-oxygenation alone (2), discussed in my previous blogs.


*** Image showing the safe apnea time prior to critical desaturation in a healthy adult pre-oxygenated patient. Apneic oxygenation may help increase this safe apnea time. Keep in mind that we can never truly know how long the safe apnea time will be. Severely ill, children, pregnant, and obese patients are at risk for immediate drops in saturation ***



How do I perform apneic oxygenation?


Following the same procedure, I suggested in my previous pre-oxygenation blog, place a standard nasal cannula on the patient under the non-rebreather or bag-valve mask during the pre-oxygenation phase of your RSI. Ensure adequate pre-oxygenation has occurred and push your induction and paralytic agents. Then, while waiting for complete paralysis:


  • Initiate or maintain flow of the nasal cannula at 15 LPM

  • Maintain flow of your non-rebreather mask at a "flush" rate

    • or at whatever the highest flow rate your flow meters will allow

  • If a bag-valve mask was used for pre-oxygenation, maintain your 15 LPM (or more) with a PEEP valve and robust mask seal

    • Deliver manual breaths only as necessary

    • Gentle breaths, if ventilation is indicated

  • While continuing to await complete paralysis, ensure the patient has an open airway to facilitate apneic oxygenation

    • Use a jaw thrust maneuver

    • Airway adjuncts such as an OPA or NPA may be necessary

  • Once complete paralysis is obtained, remove the non-rebreather or bag-valve mask, and continue administration of nasal cannula oxygen

  • Proceed with suction and intubation

  • DO NOT remove the nasal cannula until the tube is placed and there is no longer a need for the apneic oxygenation adjunct


Does Apneic Oxygenation Really Work?


The answer to this comes down to who you ask and what research article they read about the topic. Because... as you know, we can all find an article that aids in that confirmation bias we all want or are searching for. But ALSO, reading and understanding the limitations to each of the articles out there is of critical importance as well. Using Ap-Ox in a well pre-oxygenated elective intubation in an operating suite will fare differently than a critically ill patient with poor pre-oxygenation technique who is exsanguinating with shunt physiology in the emergency room... DUH!


So, what I'm gonna offer you all who are taking the time to read this is my quick and to-the-point "extrapolation" of the many articles available on this topic.

  • Yes, it works.

    • Relies on a patent connection and oxygen supply between the mouth and glottic opening

      • Oxygen needs a path to the lungs to be effective

    • It seems to be a desired adjunct if a prolonged intubation procedure is predicted/anticipated.

      • Pre-oxygenation should be more heavily relied on when attempting to increase the "safe apnea" time 😃

  • Studies have demonstrated its ability to reduce the incidence of critical desaturation in a variety of clinical settings. (1)

  • Shunt physiology is believed to reduce the effectiveness of apneic oxygenation

    • PEEP is required in these instances

    • Passive O2 from Ap-Ox is likely not effective in the presence of shunt.

  • There is also no harm in attempting to utilize apneic oxygenation in an attempt to increase your safe apnea time and prevent possible hypoxemia from occurring.

    • It's safe and easy -- Just DO IT!


For you needy nerds 🤓 who want just a tad more:


Three prominent systematic review and meta-analysis studies:


There seems to be a general consensus of a reduction of peri-intubation hypoxia. There is also mention of an increase in first pass endotracheal tube success as well and a recommendation for inclusion of apneic oxygenation in everyday clinical practice.



Our Australian HEMS Friends Working their Magic



Conclusion: Introduction of apneic oxygenation was associated with decreased incidence of desaturation in patients undergoing rapid sequence intubation.



Western Journal of Emergency Medicine



Conclusion: Nasal cannula Oxygenation during intubation procedures appears to prevent or delay desaturation in all patients except those with primary respiratory failure. Incorporating the use of nasal cannula during intubation has the potential of being integrated into a new standard of care for intubation, whether in ED's or operating rooms.



A "Quick Hit," aiming at the EDNAO Trial (Emergency Department use of Apneic Oxygenation Versus Usual Care During Rapid Sequence Intubation: A Randomized Control Trial)

  • Flush rate nasal cannula for apneic oxygenation VS. no apneic oxygenation (usual care) in the EMERGENCY DEPARTMENT (in an urban level I trauma center).

    • 206 patients enrolled

      • 104 receiving Ap-Ox | 102 usual care (no Ap-Ox)

  • Patients requiring intubation were included

    • Cardiac arrest intubations excluded

  • Amazing pre-ox strategy for both cohorts.

    • Three minutes of pre-ox with flush rate NRB, CPAP, or BVM

    • If patients weren't pre-oxygenated, they were excluded.

  • Over 70% of the patients were intubated within the first minute.

    • 80% by 80 seconds

    • 90% by 100 seconds

    • 100% by 195 seconds

Author Conclusion: The study demonstrated that in patients that are properly pre-oxygenated during rapid sequence intubation in the ED, the application of apneic oxygenation did not lead to any differences in lowest mean oxygen saturation, desaturation rates between the two groups, or intubation success without hypoxemia.


Jared's Opinion: Them bastards were so fast at intubating and so great at pre-oxygenation the patients in both groups... No 💩 there wasn't a significant difference between saturation levels. This doesn't disprove the usefulness of Ap-Ox... It adds proof to the effectiveness of pre-oxygenation.



Boom! 💥

Jared Patterson, CCP-C, One Rad Medic



Killin' It Since 1989


Twitter: @OneRadMedic

Instagram: OneRadMedic




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CITES:

  1. Patel, A., & Gilhooly, M. (2021). Preoxygenation and apneic oxygenation for airway management for anesthesia. Retrieved 24 July 2021, from https://www.uptodate.com/contents/preoxygenation-and-apneic-oxygenation-for-airway-management-for-anesthesia#H3409703469

  2. Nickson, C. (2020). Apnoeic oxygenation. Retrieved 1 August 2021, from https://litfl.com/apnoeic-oxygenation/


URLs to Research Articles:








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