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The Ins & Outs of Apneic Oxygenation

Posted on 17 June 2013

Apneic oxygenation is an important process when performing a rapid sequence intubation.

Apneic oxygenation is an important process when performing a rapid sequence intubation.

A medical student in his fourth year of training recently asked me about apneic oxygenation. I told him that, based on the pulmonary physiology, it didn’t make much sense to me. It was then very ironic that just two days later, I witnessed an apneic oxygenation technique employed on a patient in one of our trauma bays. The emergency medicine physician placed a nasal cannula in the patient’s nose and assisted the patient’s breathing with a bag-valve mask (BVM) even though the BVM was also connected to an oxygen supply. Then, induction agents were given, and the patient was intubated with the nasal cannula still in place.

Watching this process first-hand piqued my interest. Why was I not aware of this new “extra-oxygen” process and what evidence supports apneic oxygenation? I decided to share my findings with you.

The Scientific Process
To understand how apneic oxygenation works, we must first focus on the physiology of respiration. Gases flow down their concentration gradients. The air we breathe has a higher concentration of oxygen than the tissues that metabolize it. This means the oxygen in the air inside our lungs is readily absorbed by the alveoli, flows through our blood stream, diffuses into the body’s tissues and is converted into carbon dioxide.

Because the oxygen is converted into another molecule, it will keep moving forward in this process as long as the lungs contain oxygen, blood is circulating and tissues are consuming it. Apneic oxygenation allows this cycle to continue when the patient isn’t breathing by putting oxygen into the lungs.

In one study, “Apneic Oxygenation in Man,” volunteers were intubated and pharmacologically paralyzed to prevent breathing.(1) With the endotracheal tube filled with pure oxygen and connected to a circular circuit, one volunteer subject maintained a 100% oxygen saturation level for almost an hour without taking a breath. The other volunteers similarly maintained their oxygen saturation levels for extended periods of time.

While oxygenation was occurring, the patients developed an acidosis and their carbon dioxide tension increased three mmHg per minute on average. The lowest pH recorded was 6.72.

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In another study, patients were pre-oxygenated before induction and, after the patients became apneic, a catheter was inserted nasally.(2) Patients were divided into two groups: the first had its pharynx insufflated through the catheter, while the second group did not. After the patients desaturated or 10 minutes had elapsed, they were pre-oxygenated manually. Then, the process was repeated while the second group received insufflation and the first did not.

The study showed that without oxygen insufflation, the participants began to desaturate at around seven minutes.(2) However, all the anesthesia providers maintained their patient’s oxygen saturation for 10 minutes with oxygen insufflation.

Note: Although there’s a mechanism to entrain oxygen into the lungs outside of breathing, there’s no mechanism to expel carbon dioxide. The carbon dioxide in the blood stream rapidly eqiulibriates with teh carbon dioxide in the lung. For more discussion on the differences between oxygen and ventilation, see the November JEMS article, “Oxygenation & Ventilation Are Not the Same Thing.”

The goal is to increase the amount of time it takes for the patient to become critically hypoxic (less than 70% oxygen saturation) in case there are problems with intubation.

The goal is to increase the amount of time it takes for the patient to become critically hypoxic (less than 70% oxygen saturation) in case there are problems with intubation.

Why, When & How to Use It
Understanding the benefit of apneic oxygenation, you can see why it’s an important process to use when performing a rapid sequence intubation. Your goal is to increase the amount of time it takes for the patient to become critically hypoxic (less than 70% oxygen saturation) in case there are problems with intubation.(3) In a 2010 study, apneic oxygenation was shown to increase the time until an obese patient started to become hypoxic by about 2.5 minutes.(4)

To perform apneic oxygenation when performing a rapid sequence intubation, the patient should either be placed head up or in reverse Trendelenburg at a 20–30° angle.(3) Insert a nasal cannula and set it for at least five liters of oxygen per minute. If possible, the patient should then be pre-oxygenated by allowing three minutes of tidal volume breathing, or eight vital capacity breaths(.)3 This involves providing 100% oxygen to the patient either while they breathe or while the medical provider assists the patient’s breathing.

Ideally positive end-expiratory pressure (PEEP) or continuous positive airway pressure (CPAP) should be added for optimal pre-oxygenation.(5) There doesn’t seem to be a clinical benefit to pre-oxygenating longer than four minutes.6 Lastly, make sure to keep the nasal cannula properly placed when the clinician removes the mask and performs a laryngoscopy.

How to be Prepared to Perform Apneic Oxygenation
There are just a few downsides to apneic oxygenation, but they don’t outweigh the benefits. First, there needs to be a second oxygen source for the nasal cannula. This is rarely an issue in a room or bay equipped to handle critically ill patients. However, this may be difficult in the prehospital setting. Second, the nasal cannula itself can complicate getting a good seal on the patient’s face.

If you cannot get an adequate seal, you can position the nasal cannula above the mask and quickly place it in the nares once the mask is removed to perform intubation.

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Conclusion
The key to apneic oxygenation is that it can significantly increase the amount of time before an apneic patient becomes critically hypoxic. With the correct equipment available, this process is an easy and effective way to provide additional oxygen to patients when they aren’t breathing. Providers experienced in advanced airway placement should strongly consider discussing adding an apneic oxygenation technique to their protocols for scenarios when intubating conditions are less than ideal.

Joshua Sappenfield, MD, is a fellow at the R Adams Cowley Shock Trauma Center, Department of Anesthesiology, University of Maryland Medical Center. He can be reached at jsappenfield@anes.umm.edu.

 

References

1. Frumin MJ, Epstein RM, Cohen G. Apneic oxygenation in man. Anesthesiology. 1959;20:789–798.

2. Teller LE, Alexander CM, Frumin MJ, et al. Pharyngeal insufflation of oxygen prevents arterial desaturation during apnea. Anesthesiology. 1988;69(6):980–982.

3. Weingart SD, Levitan RM. Preoxygenation and prevention of desaturation during emergency airway management. Ann Emerg Med. 2012;59(3):165–175.

4. Ramachandran SK, Cosnowski A, Shanks A, Turner CR. Apneic oxygenation during prolonged laryngoscopy in obese patients: a randomized, controlled trial of nasal oxygen administration. J Clin Anesth. 2010;22(3):164–168.

5. Weingart SD. Preoxygenation, reoxygenation, and delayed sequence intubation in the emergency department. J Emerg Med. 201; 40(6):661–667.

6. Mort TC, Waberski BH, Clive J. Extending the preoxygenation period from 4 to 8 mins in critically ill patients undergoing emergency intubation. Crit Care Med. 2009;37(1):68–71.

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