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ACEP Now: Vol 36 – No 10 – October 2017

(click for larger image)
Dr. Chevalier Jackson‘s drawings of his 1915 bronchoscope
IMAGE: Jackson C. Peroral Endoscopy and Laryngeal Surgery. 1915.

It was a simple idea that actually has a long-standing history in medicine: Oxygen insufflated into the lungs can prevent desaturation, even without ventilation. This phenomenon, proven by M. Jack Frumin, MD, as early as 1959, is a product of the difference in gas solubility between oxygen and carbon dioxide. During apnea, CO2 diffuses passively out from the lungs at only 10 mL/minute, but the engine of hemoglobin absorption across the capillary bed absorbs oxygen at 250 mL/minute, assuming sufficient open alveoli, an oxygen gradient, and adequate hemoglobin are all present.

Even before apneic oxygenation was physiologically studied, Chevalier Jackson, MD, used oxygen insufflation in bronchoscopic surgery in the early 1900s (see Figure 1). Apneic oxygenation via a bronchoscope remains a standard practice during modern lung surgery. In the 1940s, the Boyle Davis gag (a tongue retractor used for tonsillectomy that inspired Robert Macintosh, MD, to invent the Macintosh blade) had an oxygen port (see Figure 2). In the 1980s, the pediatric Oxiport insufflated oxygen via a small port on a straight laryngoscope blade (see Figure 3).

The first use of nasal oxygen to prolong safe apnea during intubation was by Lynn E. Teller, MD, in 1988, using 3 L via a nasopharyngeal catheter. He demonstrated safe apnea for a period of 10 minutes after the use of muscle relaxants.

History of NO DESAT

The Boyle Davis gag, which inspired the Macintosh blade.
PHOTO: courtesy of Melbourne Museum.

I [Dr. Levitan] attended a meeting of the Society for Airway Management in October 2011, and I heard a lecture describing nasal cannula use to prolong safe apnea during intubation in the morbidly obese. A few days after my return to Philadelphia, I had a patient who was profoundly hypoxic and required rapid sequence intubation (RSI). I put on a nasal cannula, used a bag-valve mask for preoxygenation, and, during the RSI, opened up the nasal cannula. During very prolonged attempts at intubation, the nurse described something that completely amazed me: “Pulse ox 94 … no, 96 … now up to 100 percent!” The readings were increasing despite apnea!

The emergency medicine residents at Thomas Jefferson University in Philadelphia were eager to adopt this new technique, as they quickly realized it meant they were not getting pushed out by the attending during repeat intubation attempts. I also noticed a secondary benefit. When the pulse oximeter was not going down, everyone performed better at intubation.

Pediatric Oxiport. A small Miller blade for oxygenating during laryngoscopy of infants.
PHOTO: AliMed

I was eager to share this idea with others in emergency medicine and had just been introduced to Scott Weingart, MD. I came up with an acronym to describe the technique—NO DESAT for “nasal oxygen during efforts securing a tube”—and using the rapidly developing platform of social media, it became one of the first things to go viral. Although Scott was initially reluctant to write an article (believing it was an antiquated way to share knowledge), I convinced him otherwise, and soon thereafter, we published an article in the Annals of Emergency Medicine that became one of the most commonly downloaded articles for the next few years.¹

Now we are five years down the road. Multiple articles and systematic reviews have been published regarding the utility of apneic oxygenation (ApOx) during intubation, and while many emergency physicians changed their practice, much skepticism remains. Here is a review of some of the literature on NO DESAT (ApOx).

• Denton and Howard performed a “shortcut review” and found four trials, concluding that there is emerging evidence that the use of ApOx decreases the incidence of critical desaturation during endotracheal intubation.²
• Silva et al performed a comprehensive search of medical databases and gray literature. The authors included 14 studies for qualitative analysis and eight studies (1,837 patients) for the quantitative analysis (meta-analysis). The authors reported that ApOx was associated with decreased hypoxemia (odds ratio [OR], 0.66), increased first-pass success rate (OR, 1.59,) and increased lowest peri-intubation SpO2 (mean difference 2.2 percent).³
• Pavlov et al included eight studies and 1,953 patients and reported absolute risk of clinically significant hypoxemia of 27.6 percent in the usual care group and 19.1 percent in the ApOx group, plus reduced relative risk of hypoxemia by 30 percent in the ApOx group.⁴
• Binks et al included six trials and 1,822 cases of ApOx during ED and retrieval intubations. The authors reported reductions in desaturation (relative risk [RR], 0.76) and critical desaturation (RR, 0.51), plus improvement in first-pass intubation success rate (RR, 1.09) when ApOx was implemented.⁵

So Does It Work?

Probably. The effect is small; we are very good at intubations in the emergency department, and hypoxemia is uncommon. That is why systematic reviews with more than 1,000 patients are needed to prove efficacy. Smaller studies with better preoxygenation techniques and few hypoxemic events have not demonstrated a difference in the effect.⁶

While there are different ways of providing ApOx, the most common and cheapest is to use a nasal cannula with oxygen up to the maximum flow (providing more than 50 L/min). High-flow nasal cannula or positive-pressure ventilation provide preoxygenation, but they are less available and more expensive.

What all ApOx techniques have in common is that there is a focus on better peri-intubation techniques and better preoxygenation. ApOx in adult patients requiring emergency intubation is a low-cost, universally available technique that can reduce the incidence of hypoxemia and increase first-pass intubation rates. No adverse effects have been reported.

This topic has also been nicely discussed by:

• Salim Rezaie, MD, on Rebel EM.
• Rory Spiegel, MD, on EMNerd.
• John C. Sakles, MD, in the editorial “Maintenance of oxygenation during rapid sequence intubation in the emergency department.”⁷

Dr. Levitan is an adjunct professor of emergency medicine at Dartmouth College’s Geisel School of Medicine in Hanover, New Hampshire.

Dr. Bellolio is an emergency physician at the Mayo Clinic in Rochester, Minnesota.

References

1. Weingart SD, Levitan RM. Preoxygenation and prevention of desaturation during emergency airway management. Ann Emerg Med. 2012;59(3):165-175.e1.
2. Denton G, Howard L. BET 1: Does apnoeic oxygenation reduce the risk of desaturation in patients requiring endotracheal intubation? Emerg Med J. 2016;33(7):517-519.
3. Silva LOJE, Cabrera D, Barrionuevo P, et al. Effectiveness of apneic oxygenation during intubation: a systematic review and meta-analysis. Ann Emerg Med. 2017;70(4):483-494.e11.
4. Pavlov I, Medrano S, Weingart S. Apneic oxygenation reduces the incidence of hypoxemia during emergency intubation: a systematic review and meta-analysis. Am J Emerg Med. 2017;35(8):1184-1189.
5. Binks MJ, Holyoak RS, Melhuish TM, et al. Apneic oxygenation during intubation in the emergency department and during retrieval: A systematic review and meta-analysis [published online ahead of print June 24, 2017]. Am J Emerg Med.
6. Caputo N, Azan B, Domingues R, et al. Emergency department use of apneic oxygenation versus usual care during rapid sequence intubation: a randomized controlled trial (The ENDAO Trial) [published online ahead of print Aug. 9, 2017]. Acad Emerg Med.
7. Sakles JC. Maintenance of oxygenation during rapid sequence intubation in the emergency department [published online ahead of print Aug. 9, 2017]. Acad Emerg Med.