Direct Laryngoscopy

Ocularity and Biomechanics of Laryngoscopy

Traditional laryngoscopy and intubation instruction states that novice intubators hold their head too close to the target, and that experienced intubators maintain a binocular view by keeping a farther distance.  In fact, laryngoscopy is a monocular procedure at the level of the larynx, regardless of experience.  As operators get older, however, their near accommodation point (the point they are capable of focusing at) moves out, so that by age 50, regardless of visual acuity, the near accommodation point is at arm’s length.  This is presbyopia, and leads older people to require lenses to read at a reasonable distance.  Increasing the light improves the ability to focus at a shorter distance; this is yet another reason why laryngoscope light output is a very important variable in intubation performance.

The right and left eyes are separated in the skull by 4 to 5 inches; this disparate view allows the eyes and brain to achieve stereoscopic sight when looking at an object. When the right and left eyes are not capable of fusing an image–because the views are too disparate–then the brain automatically disregards the non-dominant image.  This is what happens during laryngoscopy.  Most operators are right handed, and right-eyed.  Lens wearers and left-hand dominant persons are more likely to be left-eyed laryngoscopists.

Levitan RM, Higgins MS, Ochroch EA. Contrary to popular belief and traditional instruction, the larynx is sighted one eye at a time during direct laryngoscopy. Acad Emerg Med. 1998; 5: 844

Visual restrictions inherent to laryngoscopy create different right and left eye views of the target and prevent binocular (stereoscopic) sighting. Direct laryngoscopy is a monocular procedure at the level of the larynx.
1) Laryngoscopy is visually analogous to looking down a 1” pipe at a target 12-18” away. The “pipe”is created by the laryngoscope blade, mouth, and tongue. Simultaneous sighting of the target by the left and the right eye (or by two persons) is not possible. 2) Right-eyed laryngoscopists keep their head straight toward the target. Left eyed laryngoscopists rotate their head slightly to the right, bringing the left eye closer to the target. 3) More than 80% of persons sight the larynx with their right eye; this is because eyedness follows handedness, and most persons are right handed. Also, the left flange of the laryngoscope blade favors viewing down the right side of the mouth. 4) Left-eyed laryngoscopists tend to be left handed, wear corrective lenses, or have better near visual acuity in their left eye. 5) Near range visual acuity testing (14”) and ocular dominance determination should be a part of initial laryngoscopy training.

Laryngoscope handle should be gripped as low down as possible, so that the blade becomes a mechanical extension of the forearm. Elbow should be kept close to the body.
1) The base of the hand should be positioned very low on the handle, almost in the line of sight down the lumen of the blade. Thumb is pointing upward. This grip provides the best fine control of the blade tip with the least mechanical effort. 2) With the correct grip and elbow position, it is easy to lean forward and apply force along the blade axis to the tip with minimal muscular effort.