Direct laryngoscopy depends on being able to bring the 3 axes of the airway into alignment to see the larynx. Curved blades are commonly used, especially by beginners because they are more forgiving of less than optimal placement and provide more room to pass the tube. However, it’s important to use them correctly. This article will discuss intubation technique using a curved blade. Straight and curved blades use different techniques for bringing the larynx into view. For a discussion of how to use a straight blade click here.
The illustrations below are from Anyone Can Intubate, 5th Edition.
Positioning The Patient
You can intubate in any position. However, if you have the option, placing the patient’s head at the level of the lower tip of your breastbone, or xiphoid process, gives the best mechanical advantage. From this position you can lift with the strength of your shoulders and upper back, not just your arms. Like correctly lifting a heavy box you want to use good ergonomics to avoid personal injury.
The Act of Intubation Alternates Hands
The act of intubation by direct laryngoscopy alternates hands. One hand positions the patient for the next action by the other hand. With practice, coordinating the alternating hand movements becomes natural. Once optimally positioned, tilt the head into extension with your right hand to bring all the axes into alignment. Anchor it there momentarily using your left hand.
Open The Mouth As Wide As You Can
Anchoring the head frees your right hand. Open the mouth with your right hand by placing your thumb on the lower jaw and your middle finger on the upper jaw.
Position and movement is similar to snapping your fingers. By using a pushing rather than a spreading motion, you can open the mouth wider and more forcefully. Make sure that you place your fingers as far to the right side of the mouth as you can in order to keep your fingers out of the way of the blade. Your right hand now does double duty. It holds the mouth open as wide as possible. Pulling toward you also places the head in extension.
You can now step back from the head and use your left hand to pick up the blade. I personally place my hand lower down on the handle. By positioning the heel of my hand on the junction between blade and handle, I can fine-tune the angle of the blade.
Notice how easily you can change the angle of the blade by tilting your wrist. You must control this motion carefully to avoid tooth damage.
Hold the handle in your left hand, blade down, pointing away from you. Grasp it firmly but don’t clench your fist because this decreases control and causes early fatigue.
Insert the Blade To The Right Of The Tongue
Insertion of the blade during direct laryngoscopy should be delicate and deliberate. With the mouth open, insert the blade, slightly to the right of the tongue. Don’t hit the teeth as you insert. If necessary to avoid the teeth, you can tilt the top of the handle slightly to the side to insert the blade into the mouth, then rotate the blade back, scooping it around the right side of the tongue and sweeping the tongue left as you do so.
Avoid catching the lips between the blade and the teeth. I use my right index finger and/or right thumb to sweep the lips out of the way of the blade. If the lip is pinned between blade and teeth when you lift it will get cut.
Identify The Epiglottis Before Fully Controlling The Tongue
Slowly advance the blade with your left hand. Simultaneously start to sweep the tongue to the left as you advance and begin to lift slightly as you do so. Look for the tip of the epiglottis, your first important landmark. The epiglottis is the same color as the mucosa of the tongue. As you start to lift the tongue, the tip of the epiglottis will move, separate from the tongue, and become more visible.
You can usually identify the epiglottis with minimal upward pressure on the tongue and you shouldn’t aim to fully control the tongue until you actually have identified the tip of the epiglottis. Waiting until you have the epiglottis in sight allows you to tweak the position of the blade with small, precise movements. Once you see the epiglottis, then sweep the tongue left and lift upward and away.
Good Biomechanics during Direct Laryngoscopy
Lift on a line connecting the patient’s head with the intersection of the opposite ceiling and the wall.
Keeping your back straight, your knees slightly bent and your left arm fairly rigid and against your side gives you the strength of your shoulders to lift the head. It prevents you from using the teeth as a fulcrum — dangerous for the teeth. It also allows you to use binocular vision for depth perception.
Bad Biomechanics during Direct Laryngoscopy
The typical beginner mistakenly hunches close to the patient, placing the right eye very near the patient’s mouth. From this position you can’t easily left your arm upward unless you bend it at the elbow and swing it laterally away from the body (Fig. 7-20). This forces the intubator to lift by rotating the wrist. The result is loss of binocular vision, loss of leverage and mechanical advantage, and danger to the patient’s teeth. You lack control. Like lifting a heavy box with a bent back, this poor position can also potentially cause the intubator personal injury.
Tip Of The Curved Blade Presses On Vallecula To Lift Epiglottis
The tip of the curved Macintosh (Mac) blade fits into the vallecula, the dip between the tongue and the epiglottis. Unlike a straight blade, the blade tip does not directly lift the epiglottis. By pressing on the vallecula, the curved blade lifts the epiglottis passively by pulling the tissue folds attached at its base and anchored to the hyoid bone. It acts like a pulley system lifting a trap door. When the intubator lifts the head upward, the blade displaces the tongue forward into the hypoglossal space.
As you lift, the epiglottis will separate from the tongue and you will see it hanging over the larynx. Placement of the tip of the blade is critical. As you gently wiggle the MAC blade tip upand down (being careful of the teeth) and change pressure in the vallecula you will see the epiglottis raise and lower like a trap door . When you lift the jaw upward you will have an unobstructed view of the glottic opening .
Don’t place the blade in the center of the tongue. The tongue will mound blocking your view. Sweep the tongue to the left or you will see nothing.
Pass The ETT Smoothly and Gently
The head is now suspended from the blade held in your left hand, freeing your right hand to place the tube. Use a 6.5-8 for a woman and a 7.5-9.0 for a man. The larger the tube, the less resistance to breathing there will be. Hold the preselected tube in your right hand like a pencil, curve forward.
Pass the tube to the right of the blade and through the cords in one smooth motion. If the patient is breathing, time the forward thrust for inspiration when the cords are fully open. During expiration, the tube may bounce off the closing cords into the esophagus. You can understand why the blade should optimally be as far to the left side of the mouth as possible: otherwise there is no room to pass the tube.
Try to watch the tube pass through the cords into the trachea. Although there may be a blind spot impairing your view at the moment of intubation, you can often see the arytenoid cartilages behind the tube after proper placement. Don’t relax and pull the blade out without trying to be sure of success with your own eyes.
Always try to see the tube pass between the cords. Stop advancing the tube when you see the cuff completely pass the cords: usually 21-22 cm at the front teeth in an adult. Carefully hold the tube where it exits the right side of the mouth and remove the blade with your left hand.
If you’ve used a stylet, it’s best to pull it back at least 1-2 cm before fully advancing the tube fully down the trachea. Pulling the stylet back slightly makes the tip of the endotracheal tube softer and less likely to injure the trachea while still leaving it rigid enough to guide.
Once the intubation is done, completely remove the stylet. Grip the tube firmly where it exits the mouth because the force needed to remove the stylet will sometimes threaten to pull the tube out with it.
Inflate The Cuff And Verify Placement
To inflate the cuff, slowly inject air through the pilot tube until the pilot balloon just starts to get full. Don’t overfill. You don’t want the pilot balloon to feel tense when you squeeze it or the cuff may apply excessive pressure to the tracheal mucosa, impairing its blood supply.
After inflating the cuff and before doing anything else, make sure that the tube is in the trachea. Listen for the presence and equality of breath sounds over both lung fields and for the absence of gurgling sounds over the stomach. Never assume that the tube is in the trachea until you have checked it yourself. Verification with a carbon dioxide detector is recommended.
To check minimal seal, suction the airway free of secretions. Apply constant airway pressure of about 20 mmHg. Remove some air from the pilot balloon until you just start to hear a leak, and then refill the cuff until the tracheal leak just disappears again.
If You Have Difficulty, Stop And Ventilate
If you can’t intubate easily, stop and ventilate the patient briefly before your next attempt in order to maintain oxygenation. As long as you can ventilate the patient you have time. Time to alter your technique, change the position of the head, or use a different type of laryngoscope blade. Keep your suction handy and use it. Don’t be afraid to ask for help.
Here is a photo sequence of intubation with a curve blade in an adult.
When to Use a Straight Blade vs. a Curved Blade
Direct laryngoscopy depends on being able to bring the 3 axes of the airway into alignment to see the larynx. Straight and curved blades use different techniques for bringing the larynx into view.
A curved blade depends on displacing the soft tissue at the base of the tongue forward into the hypopharyngeal space in order to lift the epiglottis and bring the larynx into view. In contrast, the straight blade depends on directly lifting the epiglottis and flattening the tongue.
You can take advantage of the different mechanisms of action to address particular anatomical challenges.
Many beginners find the curved Mac blade easier when first learning. Its large flange and broad base make it easier to control the tongue and balance the head. It’s more forgiving of placement errors. While straight blades often give a better view they ar eless forgiving. The narrow and flangeless blade requires more meticulous placement to control the tongue.
However, curved blades depend on displacing the tongue and soft tissue forward to lift the epiglottis. If you can’t displace the tongue forward, you can’t lift the epiglottis and won’t be able to see the larynx.
Straight blades are very helpful in situations where there is little room to displace the tongue and attached tissues forward. Examples include:
- young children (larynx higher in the neck)
- short chins
- short necks
- larynxes higher in the neck
- large tongues
- obesity, especially with double chins
- larynxes fixed from scar, trauma, or mass effect
However, to be able to see the larynx with a straight blade you have to be able to extend the head backward. If your patient can’t tilt his head back, a straight blade will be more difficult. Here a curved blade might be better.
You should practice direct laryngoscopy with both types of blades on easy patients so that when you really need to use one type of blade over the other you will be able to confidently intubate. For video showing intubation with both curved and straight blades click here.