Learning to intubate is easier for some people than for others. Sometimes, no matter how knowledgeable you are about the theory of the technique, the novice can still struggle to bring it all together to pass the endotracheal tube. The anatomy can be confusing. Understanding how to place the laryngoscope blade and manipulate that anatomy can be challenging. And all the while you must be ever vigilant to protect those precious front teeth, avoid hypertension and tachycardia, and breathe for the patient at regular intervals.
I believe there are 4 chief barriers that inhibit learning how to intubate:
- Failure to visualize how the outside anatomy links with the inside anatomy makes it hard to predict how deeply to insert the blade.
- A mistaken belief that placing the laryngoscope blade itself is all that is needed to align the axes of the airway and reveal the larynx.
- Failure to grasp the dynamic nature of the larynx, and the need to actively manipulate it during intubation.
- A lack of understanding that intubation is not a sequence of isolated steps, but is instead a complex dance of interacting steps, each setting the stage for the next.
This discussion is going to assume some knowledge of the basic technique of intubation. If you’d like to review those basics you can find links for multiple prior in depth discussions at the end of this article. (Illustrations and animation from Anyone Can Intubate, 5th edition, C Whitten MD.)
Failure to Visualize The Anatomy
In order to intubate, the tip of the laryngoscope blade must be precisely placed at the optimum depth to manipulate the epiglottis and reveal the larynx. Too deep and you will cover the larynx and be looking into the esophagus. Too shallow and you won’t have a good view of the glottic opening, and you won’t be able to manipulate the laryngeal structures to bring the axes of the airway into alignment.
To know how deep to insert the blade, you need to have some idea of how deep the larynx is on your patient. The larynx is higher or lower in some people than in others, but in all it lies just below the chin in the upper part of the neck.
Look at this CT scan. You can see that the hyoid bone is roughly level with the bottom of the mandibular bone. The top of the thyroid cartilage is just below it. However, this means that the top of the epiglottis itself rises higher into the posterior pharynx than this, behind the tongue. The vocal cords are lower, about mid distance between the top and bottom of the thyroid cartilage.
Visualizing these relationships as you are inserting the blade helps you estimate the approximate depth correctly. You can then make minor adjustments as needed.
Place the Laryngoscope Blade Is Only One Step
Knowledge of the axes of the airway and how to optimize position is crucial to success. The laryngoscope blade performs the final adjustment of those axes, but can’t bring the larynx into view by itself.
To orally intubate you need to bring the path from the incisor teeth to the larynx into a straight line. This path has three axes:
- axis of the cavity of the mouth (oral axis)
- axis of the cavity of the pharynx (pharyngeal axis)
- axis of the larynx and trachea (laryngeal axis)
The angle of the axis of the mouth to the larynx is 90°. That of the pharynx to the trachea is obtuse. Aligning them is merely a matter of applied mechanics. You make this alignment by positioning the patient’s head and neck and then using the laryngoscope blade to make the final adjustment. (Other techniques can be used if you shouldn’t move the patient’s head, such as in cervical trauma and some facial fractures.)
To get the average, non-obese patient’s head into this position, raise the head about 10 cm (4 inches) off the bed by placing a folded sheet or other object under their head. Leave the shoulders on the bed.This positioning aligns the pharyngeal and laryngeal axes. The cervical spine is now straight and the patient is in the so-called “sniffing position.” The sniffing position typically places the ear canal level with the anterior shoulder.
You will have difficulty, and potentially fail to see the larynx, if you don’t align the axes. Picture how someone out of breath holds her head: forward and tilted slightly back. We automatically straighten the airway to minimize resistance when we want to move a lot of air easily. Another analogy is picturing the sword swallower. In order to pass the sword without injury down the esophagus, which is parallel to the trachea, everything has to be in as straight a line from the mouth downward as possible.
The Larynx is a Dynamic Structure
The larynx is not a static structure sitting on top of the trachea. The larynx is a dynamic valve, with multiple joints. The vocal cords, and their attachments, are highly mobile. Click on the image below to go to an animation showing some of those movements.
When you intubate, you have to actively manipulate those joints.
With a curved blade, you place the blade tip in the vallecula under thee epiglottis at the base of the tongue. With the blade tip in the proper spot, lifting the weight of the jaw and the head creates point pressure on that spot. That precisely placed pressure pulls the aryepiglottic folds taught. Like a pulley system on a trap door, this tension swings the epiglottis up and opens the path to the glottis.
However the novice intubator is afraid they will hurt the patient, and is often tentative. Common mistakes with the MAC blade
- Placing the blade tip on the back of the tongue, instead of in the vallecula.
- Pressure from the tip of the blade has to be in the right spot in the vallecula to work the pulley, otherwise the epiglottis stays folded down. Pressing on the tongue itself can push the epiglottis down.
- Failure to physically lift the jaw and the head.
- Without weight on the blade, the pulley system does not work. In addition, without weight on the blade the blade slides freely inside the mouth and does not control the tongue or the head position .
- Insertion of the blade so deeply that the entire larynx is covered, leaving the epiglottis in view.
While using a straight blade, you slide the blade over the epiglottis, then slowly lift it as you insert the blade tip toward the anterior commissure of the vocal cords. The straight blade lifts the epiglottis and flattens the tongue. Common problems with the straight blade include:
- Failure to look for and identify the tip of the epiglottis during insertion, leading to inserting the blade too deep and into the esophagus.
- Failure to lift the epiglottis with the tip of the blade.
- Failure to physically lift the jaw and/or the head with the blade. Without weight on the blade, the blade slides freely, losing control of the tongue. Lift is also required to align the airway axes and lift the epiglottis.
As you insert your blade, have your blade hug the tongue as it goes into the posterior pharynx. Look for the epiglottis tip to assist in getting that optimal positioning. You must be gentle, but you must physically lift the jaw and head or intubation will be hard.
Intubation Is NOT A Sequence Of Isolated Steps
The act of intubation alternates hands. One hand positions the patient for the next action to be taken by the other hand. With practice, coordinating alternating hand movements becomes natural. However, in the beginning, novices often perform each step in turn, without realizing that one step actually leads to, and makes more successful, the next step.
Tilting the head back with your left hand starts to align the axes and prepares for your right hand to open the mouth. Opening the mouth with your right hand prepares for insertion of the blade with your left. Done correctly, holding the mouth open with your right hand keeps the head tilted back. Placing the laryngoscope blade tip precisely and applying lift (and therefore weight) holds the head and neck in position with the airway axes aligned and freeing your right hand to pick up and insert the endotracheal tube.
It’s like a complicated series of dance movements. Performed as a coordinated series of steps, the dance is smooth, and your partner glides effortless under your control. Performed as individual steps, the dance is awkward, and your partner can stumble.
In conclusion, pre-visualization, precision placement of the tip of the laryngoscope blade, and control are the key factors for successful intubation. If you’re being gentle, you can trust yourself not to injure your patient as you physically lift and maneuver the structures.
May The Force Be With You
Christine Whitten MD, author Anyone Can Intubate 5th Edition
Links to prior discussions with more details of how to intubate: