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