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Five Anatomical Features that Affect Ventilation

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Understanding respiratory and airway anatomy can help EMS providers properly ventilate a patient using basic skills. (Illustration JEMS)

I have a huge interest in anatomical studies. Besides finding anatomy just plain interesting, I think a thorough knowledge of the human body helps us do a better job taking care of our patients.

Bag-valve mask ventilation is a real cornerstone of airway management. You have to accomplish it successfully, and you can’t move on to advanced techniques without it.

When encountering difficulty in mask ventilating a patient, it’s usually because of one of the three following problems:

  • A poor mask seal;
  • An obstruction somewhere in the airway; and
  • Increased intra-thoracic pressure.

In one study of more than 1,500 patients, five criteria were recognized as independent factors for difficult mask ventilation: age older than 55 years, body mass index (BMI) of more than 26 kg/m2, presence of a beard, lack of teeth and history of snoring. (1) You should be able to determine the existence of these criteria fairly quickly just by looking at your patient and speaking with their family.

I’ve put together my own list of the top five anatomical features I feel affect our ability to provide quality mask ventilation to our patients. Stop right now and write down the five parts of the airway anatomy you think have the greatest impact; compare your list to mine when you finish the article.

Number 5: The Abdomen
I’d like a nice flat tummy. Hey, who wouldn’t? But the Centers for Disease Control says we’re all getting bigger. They determined the average adult male has a BMI of 26.6 and an adult female a BMI of 26.5. (2) In general, the larger the abdomen, the more difficult it is to ventilate a patient.

As the diaphragm contracts, it moves inferiorly into the abdomen. This movement generates negative pressure in the thoracic cavity and air rushes into the lungs. To exhale, the diaphragm relaxes and returns to its normal position. Air pressure in the thoracic cavity increases and air leaves the lungs. That’s how it’s supposed to work. Add some weight to the abdomen and the diaphragm doesn’t work so well.

Try this: Lay supine on the floor and determine your ease of breathing. Have a trusted friend place a five-pound bag of sugar on your belly. What’s your ease of breathing now? Keep adding bags of sugar until you really have to work just to draw a breath. This is exactly how an obese patient feels when we place them supine.

In a patient with a large abdomen, the additional weight on the abdomen raises intra-abdominal pressure, which pushes the diaphragm superiorly into the chest. This movement reduces space in the thoracic cavity, reduces tidal volume and raises intra thoracic pressure. When the diaphragm contracts, it not only has to move the normal abdominal contents, but it also has to generate enough intra-abdominal pressure to raise the weight of additional tissue sitting on the abdomen. This is why these patients report increased dyspnea when placed supine and why we have a more difficult time ventilating them.

Number 4: The Neck
I have two questions about the neck: How clearly visible are the anterior landmarks? How mobile is the neck?

You should be able to visualize, or at least very easily palpate, the thyroid cartilage and the cricoid cartilage. At times, there can be so much tissue covering these features that it appears the patient doesn’t even have a neck. If you can’t locate these features, it will be difficult to manipulate them to optimize the airway.

The thyroid cartilage is the largest of the laryngeal cartilages. It’s within this structure that the vocal cords and glottic opening lie. External manipulation of the thyroid cartilage can enhance glottic alignment with the upper airway. (3)

The cricoid cartilage is immediately inferior to the thyroid cartilage and anterior to the esophagus. For years, providers applied cricoid pressure in an attempt to improve glottic view during laryngoscopy and to reduce the introduction of air into the stomach during assisted ventilation. Although the 2010 American Heart Association guidelines don’t recommend routine use of cricoid pressure, some major medical institutions and EMS programs continue to find it useful in their programs.

To locate these structures, start with your finger at the sternal notch. Move your finger upward with gentle pressure on the anterior neck. The first hard ring you palpate is the cricoid cartilage. Continue to move your finger slightly upward, and you’ll feel a small depression immediately superior to the cricoid cartilage; this depression is the crico-thyroid membrane. Move your finger further upward, and you’ll feel a large, prominent structure, which is the thyroid cartilage.

Neck mobility directly affects our ability to position the airway. Placing a patient in the sniffing position improves glottic alignment with the pharyngeal area. (4) A good field landmark to obtain the correct position is to elevate the head so the ear canal is even or above the level of the sternum. The more easily you can manipulate the patient’s neck, the easier it is to align the three airway axes and find the right position to maximize air flow.

Number 3: The Teeth
Strictly from an airway management point of view, teeth really just get in the way when you’re trying to obtain a glottic view or attempting to place an adjunct in the patient’s mouth. Try to mask ventilate someone who’s missing teeth, and that’s a completely different story.

A good set of teeth gives form to the face and allows for a good mask seal. No teeth will give you just the opposite. I’ve heard stories of packing the cheeks with gauze to improve the fit—even tried it myself once. But friends, nothing beats a Grade A set of original issue teeth to provide a good mask seal and a stable platform from which to ventilate.

The down side to a full set of teeth is that they take up space in the mouth and reduce mouth opening distance as compared to our edentulous patients. It may be difficult to insert airway adjuncts into the patient’s mouth when the distance between the upper and lower incisors is less than 6 cm (about three fingers).

Number 2: The Mandible
When shopping for a mandible, you want two features: mobility and alignment.

Remember the last time you cared for a patient with a clenched jaw? You can’t open the mouth. You can’t insert an oropharyngeal airway (OPA) device. You can’t insert a suction tip. The ability to open the mouth wide certainly makes it easier to mask ventilate or insert airway adjuncts. The simple capacity to displace the mandible anteriorly and pull the tongue off the back of the throat can make all the difference in moving air. We can induce poor mobility by simply applying a cervical collar or applying posterior pressure on the mandible while trying to get a good mask seal. As with the neck, your ability to move a patient’s mandible can really enhance your ability to ventilate them.

The optimal alignment of the mandible is directly below the maxilla so there’s a smooth transition from the nose to the chin. An uneven surface reduces your ability to obtain a good mask seal. A significantly receding mandible may not allow you to fully displace the tongue off of the throat with a chin life or jaw thrust.

 

Number 1: The Tongue
When I look at a sagittal view of the upper airway, the first feature that always draws my attention is the tongue. Look at the size of it. The tongue takes up about 85–90% of the oral cavity. (5) It’s the largest structure in the mouth, highly vascular and just waiting to obstruct the airway. The tongue presents us with challenges to basic and advance airway techniques.

The superior (intrinsic) muscles don’t attach to any structures outside the tongue, which is great when you need your tongue to change shape to form words. In the less-than-conscious individual, this is the portion of the tongue that relaxes, moves posteriorly and obstructs the airway. You drift off to sleep, your tongue relaxes, and the snoring starts. You get an elbow to the ribs, you roll over, your tongue flops forward and the snoring stops. This is why we place patients in the lateral recovery position. Correct placement of an OPA device holds the superior muscles of the tongue off of the back of the throat to create an open air passage.

The inferior (extrinsic) tongue muscles connect to such external structures as the mandible, hyoid and epiglottis. It’s these connections that are critical to opening a patient’s airway. When using a chin lift technique, the mandible moves anterior along with the attached inferior tongue muscles. Since the inferior muscles are connected to the superior, airway obstructing muscles, the tongue is lifted off of the back of the throat and opens the airway. Since the epiglottis is also attached to the inferior muscle group, it lifts upward as the mandible moves anteriorly. This is an added airway bonus.

There you have it folks, my top five anatomical features that impact our ability to mask ventilate a patient. How did my list compare to yours?

In an upcoming article, we’ll build on this lesson and look at features of the airway anatomy that impact our ability to provide advance airway management.

For now, put this information to work for you: Specifically, look at these airway structures on all your patients and note their variations. Consider the ease with which you could mask ventilate each patient and what you could do to optimize it.

I’ll leave you with a quote from a good paramedic and a great friend.

“The consistent delivery of basic airway skills is usually more helpful than an occasional act of brilliance,” —Robin B. Davis, NREMT-P

Charlie


References

  1. Langeron O, Masso E, Huraux C, et al. Prediction of difficult mask ventilation. Anesthesiology. 2000; 92(5):1229–1236.
  2. Center for Disease Control. National health and nutrition examination survey. Centers for Disease Control and Prevention, National Center for Health Statistics. 2003; Publication no. 03-0260.
  3. Levitan RM, Mickler T & Hollander JE. Bimanual laryngoscopy: A videographic study of external laryngeal manipulation by novice intubators. Ann Emerg Med. 2002; 40(1):30–37.
  4. Levitan RM, Mechem CC, Ochroch EA, et al. Head-elevated laryngoscopy position: Improving laryngeal exposure during laryngoscopy by increasing head elevation. Ann Emerg Med. 2003; 41(3):322–330.
  5. Iida-Kondo C, Yoshino N, Kurabayashi T, et al. Comparison of tongue volume/oral cavity volume ration between obstructive sleep apnea syndrome patients and normal adults using magnetic resonance imaging. J Med Dent Sci. 2006; 53(2):119–126.

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Charlie Eisele, BS, NREMT-P

Charlie Eisele, BS, NREMT-P has been active in EMS since 1975. After 22 years of service, he recently retired from the Maryland State Police, Aviation Command where he served as a State Trooper, flight paramedic, instructor, flight operations supervisor, director of training, and tactical paramedic.

For over 25 years, Charlie has been a collegiate level educator and curriculum developer. He has served numerous programs including the University of Maryland, and its R Adams Cowley Shock Trauma Center, College of Southern Maryland, Grand Canyon National Park, Marine Corps Base Quantico, Virginia Department of Fire Programs, and Maryland State Police.

Charlie is the co-developer of the internationally delivered advanced airway program at the R Adams Cowley Shock Trauma Center. He is the Airway and Cadaver Lab Course manager for the University of Maryland critical care emergency medical transport program. He’s the co-developer of the EMS Today airway and cadaver lab program. Charlie has been recruited nationally to provide airway management curriculum and education for a variety of private, federal, state and local organization.

Charlie is an Eagle Scout and a published author. He serves on the Journal of Emergency Medical Services Editorial Board and is a member of the program board for the EMS Today Conference & Exposition.

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