Laryngoscopy Under Normal and Pathologic Conditions

Cervical Spine Injuries

Direct laryngoscopy, the technique commonly used for endotracheal intubation, depends on extension of the head at the atlantooccipital joint to align the oral, pharyngeal and laryngeal axes. In normal patients, the head must be extended approximately 15 degrees to expose the vocal cords. Spine movement with direct laryngoscopy has several implications. Direct laryngoscopy may be difficult if spine movement is limited because of arthritis, disk disease and other spine abnormalities. On the other hand, the spine movement with laryngoscopy may be dangerous in
patients with cervical spine injury because of the possibility of causing new neurologic deficits. In a collection of manuscripts, Dr. Hastings has evaluated the effects of equipment and technique on cervical spine movement with laryngoscopy and reviewed the implications of spine injury for airway management.

Click here for references about airway management and cervical spine injuries

Laryngoscopy Force, Torque and Trajectory

A series of manuscripts have explored the mechanics of laryngoscopy. Dr. Hastings and collaborators were the first investigators to evaluate force and torque simultaneously during tracheal intubation. Their results showed that the torque required to expose the vocal cords in some patients was close to the maximum that could be supported by forearm muscles. They also showed that force changes with time during laryngoscopy even though position and lift remain constant, an effect in biologic tissues known as stress relaxation. Current research in collaboration with Dr. Nathan Delson, of the UCSD Dept of Mechanical and Aerospace Engineering, utilizes new technology to evaluate force, torque and trajectory of laryngoscopy in three dimensions. Dr. Delson and Dr. Hastings recently mentored a UCSD medical student, Shea Aiken, in developing a two dimensional physical model to study laryngoscopy.

Click here for references about force, torque and trajectory

Click here for Laryngoscopy Model Supplement