The MAC Blade, The Vallecula, and the Hyoepiglottic Ligament

Correct placement of the tip of the MacIntosh , or MAC, blade is critical to successful intubation. When learning to intubate, novice intubators often prefer the MAC blade because:

  • curved shape makes it easier to insert under the upper teeth,
  • wide area makes it easier to balance the head on the blade during the lift,
  • easier to control the tongue with the side flange.

However, if you don’t have the tip of the blade positioned properly in the vallecula, you wil not lift the epiglottis and you will have a poorly view of the larynx. Why is this?

How The MacIntosh (MAC) Blade Works

A quick review of the anatomy is warranted. The vallecula is the mucosa covered dip between the back of the tongue and the epiglottis. The hyoepiglottic ligament runs under the vallecular mucosa and connects the hyoid bone to the back of the epiglottis.

Illustration showing the hyoepiglottic ligament running in the vallecula to connect the hyoid bone with the epiglottis

The hyoepiglttic ligament connects the hyoid bone to the back of the epiglottis

Lateral Xray clearly showing the hyoid bone, the epiglottis and the vallecula connecting them

Lateral Xray clearly showing the hyoid bone, the epiglottis and the vallecula connecting them

The curved MAC blade is designed to match the curve of the tongue and to put point pressure on the hyoepiglottic ligament. With pressure in the vallecula on this ligament, the epiglottis is pulled upward. The curved blade can then pull the tongue and soft tissue under the tongue forward, bringing the glottis into view.

The tip of the curved blade presses on the vallecula, allowing you to lift the epiglottis by pulling on the folds at its base. The glottis is revealed with the epiglottis hanging above it.

The tip of the curved blade presses on the vallecula, allowing you to lift the epiglottis by pulling on the folds at its base. The glottis is revealed with the epiglottis hanging above it.

In this video, posted on YouTube by AIMEairway.ca, you can see that if you lift too early, when the blade is not placed far enough into the vallecula to engage the ligament, then pressure from the blade tip does not lift the epiglottis. Advancing a little farther, placing the tip in the vallecula does lift the epiglottis.

If you advance the blade tip too far into the vallecula, it will press on the base of the vallecula and force the epiglottis down, obscuring your view of the glottis. The difference between lifting too early or too late (by placing the blade tip too shallow and too deep respectively) can be just a mm or two.

Size of the MAC Blade matters

MAC blades come in different sizes to match your patient. However, you must choose the correct size to apply th­­­e correct point pressure on the hyoepiglottic ligament. The correct size blade must be long enough to reach into the vallecula. You can estimate the correct size by holding the blade adjacent to the patient’s lower jaw and measuring it against the projected location of the vallecula.

Illustration showing how to estimate the size of a laryngoscope blade for intubating an infant or young child

Laryngoscope blades come in different sizes and you should choose the optimal size if you can.

Blade Too Short

If the blade is so short that it doesn’t reach the vallecula, then lifting the blade will not lift the epiglottis (see video above). Indeed may fold it downward over the glottis.

Blade Too Long

On the other hand, you can use a longer MAC blade. The key to success with a longer blade is to avoid inserting the blade too deep, and covering the larynx. You must restrain yourself and insert only to a depth sufficient to place the blade tip in the vallecula. You will know if you have placed the blade too deep because the larynx will be hidden under the blade.

Photo of view during laryngoscopy, on the left the esophagus is seen "tented" to appear like the larynx, on the right the larynx.

If you insert your blade too deep you will hide the larynx underneath, as on the left. This action also tents the esophagus and can made it mimic the glottic opening if you are not careful.

When using a longer blade in a small patient, you will find that you will have a fair amount of blade outside the mouth. In this case you must be especially careful to avoid lips and teeth.

Altering the Angle Of The MAC Blade To Optimize View

As you can imagine from the above anatomical relationships, a very small change in angle at the handle will markedly alter the angle, location and point pressure of the tip. Any angulation of the blade must be done carefully to avoid damaging the teeth.

Insertion: Always Protect Those Lips and Teeth

Insertion of the blade should always be delicate and deliberate With the mouth open as wide as you can, insert the blade slightly to the right of the tongue. Don’t hit the teeth as you insert. If necessary, you can tilt the top of the handle slightly to insert the blade into the mouth, then rotate the blade back, scooping it around the right side of the tongue as you do so.

Avoid catching the lips between the blade and the teeth. I use my right index finger to sweep the lips out of the way of the blade as I insert it. You may need to angle a curved blade slightly to pass the teeth and then return the blade to a more neutral position once it has entered the mouth.

How To Know You’re In The Vallecula

With experience, you will develop good instincts on how deep to insert the blade. Always look for the tip of the epiglottis as you insert the blade. Once you see it, continue to advance the blade — usually close to its maximum depth if it’s the correct size. Simultaneously sweep the tongue to the left as you advance. Once you see the full epiglottis you can now start to transfer the weight of the patient’s head onto the blade as you lift. Again, watch for the lips. Leave your blade toward the left side of the mouth with the tongue pushed out of the way. Continue to advance until

As you lift, the pressure from the tip should lift the epiglottis. If it doesn’t, carefully slide the tip a little deeper into the vallecula to engage the ligament and try again.

The list of posts below leads to other articles on intubation technique.

May The Force Be With You

Christine E Whitten MD

Author of Anyone Can Intubate— a Step By Step Guide
and
Pediatric Airway Management— a Step By Step Guide

LINKS TO PRIOR DISCUSSIONS WITH MORE DETAILS OF HOW TO INTUBATE:

 

Button link to see inside or buy the book Anyone Can Intubate, A Step By Step Guide to Intubation and Airway Management, 5th edition on amazon Button to see inside or buy the book Pediatric Airway Management: A Step-by-Step Guide by Christine Whitten

Please click my book covers to preview on amazon.com

Learning Intubation: Head Position Effects Laryngeal View

When first learning intubation,  a beginner often concentrates on memorizing the key laryngeal anatomy. This is important of course. If you can’t recognize the vocal cords, you will not be able to successfully intubate. However, even more important to learning intubation is understanding how the larynx relates to the other structures in the head and neck. In order to intubate you must manipulate those other structures to bring the larynx into view.

A prior post, When Learning Intubation Is Hard, described in detail some of the most common barriers to learning to intubate. Here I will concentrate on helping you see how head position effects your ability to see the larynx.

Larynx Location In The Neck

To feel your own larynx, place your hand on the front of your neck, with thumb and forefinger on either side of the firm, roughly cylindrical shape in the midline.

Illustration showing Relationships thyroid and cricoid cartilage to cricothyroid membrane

Relationships thyroid and cricoid cartilage to cricothyroid membrane

The adult larynx lies opposite the 5th, 6th cervical vertebrae, as opposed to the infant larynx that lies opposite the 2nd, 3rd and 4th. The fact that the infant larynx is higher in the neck leads to greater risk of airway obstruction and a need to slightly alter technique during pediatric intubation. A link to how to intubate the pediatric patient is located at the end of this article. Here we will concentrate on the adult.

The larynx is located in front of the esophagus in the neck. The opening to the larynx, called the glottis, and the opening to the esophagus are immediately adjacent to each other. Misidentification of the esophagus as the glottic can lead to esophageal intubation.

Illustration showing how easy it is to insert a laryngoscope blade too deeply and hide the larynx during intubation of an infant or small child

It’s very easy  to insert the laryngoscope blade too deep, as in the right picture. If too deep you will not see recognizable anatomy because you are looking down the esophagus and hiding the larynx.

 

Photo of view during laryngoscopy, on the left the esophagus is seen "tented" to appear like the larynx, on the right the larynx.

If you insert your blade too deep you will hide the larynx underneath. This action also tents the esophagus and can made it mimic the glottic opening if you are not careful.

How The Larynx Relates To Other Structures

Look at this lateral Xray  of a head in neutral position. The outline of the epiglottis, the hyoid bone, the thyroid cartilage and the cricoid cartilage are easily identified. Notice the relationship of the larynx to the esophagus. The larynx lies in front of the esophagus but the opening to the larynx (the glottis) and the esophagus are right next to each other. Accidental esophageal intubation is a risk with every intubation.

Lateral view Xray showing the distinct outlines of the parts of the larynx and their relationship to the jaw, tongue and cervical spine.

Lateral view Xray showing the distinct outlines of the parts of the larynx and their relationship to the jaw, tongue and cervical spine.

Now imagine yourself intubating this patient. what would you have to do to bring the larynx into view? How deep would you have to insert a Macintosh blade to  place the tip in the vallecula? How deep would you need to insert a Miller blade to lift the epiglottis?

Here is a CT scan of another adult patient. Notice that in this second patient the larynx is located higher in the neck.

Normal CT side view showing relationship of laryngeal structures to external anatomy

Normal CT side view showing relationship of laryngeal structures to external anatomy

Whereas the epiglottis in the first patient is low behind the tongue, this patient’s epiglottis is higher. The depth of insertion and the strategy to lift the epiglottis will change from patient to patient. Straight blades often work better in patients with a larynx higher in he neck and this may be one of those patients.

How Does Neck Position Affect The Larynx During Intubation

Let’s look at a lateral Xray of our first patient, but now with his head tilted all the way back in full extension. Patients with respiratory distress, will often tilt their heads back. You can see that this position more fully opens the airway and decreases resistance to breathing.

lateral Xray of the neck in full extension showing how the relationship of the larynx changes with respect to the rest of the neck structures. Extension without placing the patient in the sniffing position will hide the larynx behind the tongue, or a so-called anterior larynx.

Lateral Xray of the neck in full extension showing how the relationship of the larynx changes with respect to the rest of the neck structures. Extension without placing the patient in the sniffing position will hide the larynx behind the tongue, or a so-called anterior larynx.

During intubation, we need to tilt the head back to bring the axis of the oral and pharyngeal axes into alignment. But if the patient is not in a good sniffing position,  with the head moved slightly forward  in addition to being tilted, the larynx may remain hidden behind the tongue during laryngoscopy.

Let me rotate this image to show you what I mean.

Lateral neck Xray showing how extreme head extension, without the sniffing position, can make visualization of the larynx difficult.

Lateral neck Xray showing how extreme head extension, without the sniffing position, can make visualization of the larynx difficult.

You can now see how anterior that larynx would look during laryngoscopy. Pushing down on the cricoid cartilage might help rescue a difficult intubation in a situation like this, but optimal head and neck positioning from the beginning would work better.

When getting ready to intubate, always glance at the side of your patient and assess whether the head and neck are in an optimal position before you start. If it’s not optimal, try to fix it. That several seconds can save you, and your patient, potential trauma.

Head Position Also Affects Laryngeal Opening

As long as we are looking at X-rays, let’s look at our first patient with his head flexed fully forward. When the head is flexed forward, the structures in the posterior pharynx and the tongue tend to obstruct the airway. You can test this by flexing your head forward as far onto your chest as you can. It becomes much harder to take a breath.

lateral Xray showing that With the head flexed fully forward onto the chest, the airway is almost fully obstructed. Visualization of the larynx wold be impossible.

With the head flexed fully forward onto the chest, the airway is almost fully obstructed. Visualization of the larynx would be impossible.

While no one would position a patient’s head this way for intubation, it’s common for novices to place too many pillows under the head trying to obtain a good sniffing position. If the head is too high, the patient, and the intubator, will not be able to tilt the head back.  In other words, our novice intubator, trying to maximize sniffing position, sabotages himself. Again, prior to intubation take a look to the side of your patient. Try to tilt the head back (or have the patient tilt their head back).

When learning to intubate, learn the anatomical relationships, not just laryngeal anatomy.  A good intubator understands that knowledge of how those structures move in relationship to each other gives you the power to manipulate that anatomy to give you the best possible view during intubation.

Please share with your fellow students. I’ve included a list with links below to previous posts on learning intubation to help you perfect your skills. Feel free to ask questions. Let me know if there are any topics that you would find helpful.

May The Force Be with You

Christine Whitten MD, author
Anyone Can Intubate, A Step By Step Guide
and
Pediatric Airway Management, A Step By Step guide

LINKS TO PRIOR DISCUSSIONS WITH MORE DETAILS OF HOW TO INTUBATE:

 

Button to see inside or buy the book Pediatric Airway Management: A Step-by-Step Guide by Christine Whitten  Button link to see inside or buy the book Anyone Can Intubate, A Step By Step Guide to Intubation and Airway Management, 5th edition on amazon

Please click on the covers to preview my books at amazon.com

Intubation: Step By Step

Learning intubation technique can be challenging. Fall is the time of year when new students commonly begin to learn how to intubate. My first intubation was one of the first times I literally held someone’s life in my hands. I was nervous. The anesthesiologist teaching me tried to not look too anxious as I awkwardly grabbed my laryngoscope blade, fumbled while opening the patient’s mouth, and cautiously maneuvered the endotracheal tube into the trachea. It felt like time stopped until the tube was in place, after which the three of us (me, my teacher and my patient) all took a deep breath. Since then, over the last almost 37 years, I’ve intubated thousands of people in the U.S. and, as an international volunteer, eight countries.

So I thought it would be helpful at this time of year to discuss a step-by-step approach to intubation with the commonly used curved blade. Intubation, like a dance, is composed of steps that flow naturally from one to the next. The trick to a smooth intubation is to allow each step to blend seamlessly into the next. The text and illustrations below are excerpted from my book Anyone Can Intubate, as well as from my upcoming book on pediatric intubation, which I’m busy writing. Continue reading