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A Quantitative Comparison of Experts and Novices Performing Laryngoscopy Using an Instrumented Laryngoscope Nathan Delson PhD, Randy Hastings MD PhD, Nada Koussa BS, Andrew Lin MD Department of Mechanical and Aerospace Engineering and School of Medicine at University of California San Diego

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A Quantitative Comparison of Experts and Novices Performing Laryngoscopy Using an Instrumented Laryngoscope

Nathan Delson PhD, Randy Hastings MD PhD, Nada Koussa BS, Andrew Lin MD

Department of Mechanical and Aerospace Engineering and School of Medicine at University of California San Diego

Supported by grants from the Society for Technology in Anesthesia, the Anesthesia Patient Safety Foundation, and the Agency for Healthcare Research and Quality (HS11521 to MBW)


The skill of performing laryngoscopy is subtle and can be difficult to learn1,2. To quantify this skill a laryngoscope was instrumented with a 3D force/torque sensor, and a 3D magnetic position sensor. Motion and force trajectories were measured in the operating room during endotracheal intubation procedures of patients under general anesthesia. Additional motion sensors tracked head, jaw, and neck position, to determine laryngoscope motion relative to patient anatomy. Laryngoscopy was performed twice on the same patient; in one group by an expert and a novice, and in another group by two experts. The motion trajectories were segmented into the predefined subtasks of entering the mouth, moving downwards, horizontal motion, beginning to lift, and reaching an endpoint lift position. The differences between the expert and novice group where evaluated to identify aspects of the task that correlate with expertise and thus are significant components of training and skill acquisition. The long term goal of the project is to develop realistic training simulators for laryngoscopy and other procedures.

between patients are relatively large, and that experts are more consistent than novices. Experts were more consistent in coordinating rotation of the patients’ head with lifting of the laryngoscope blade. Both experts and novices began positioning in the epiglottis with similar range of head orientation. However, at the point of exposing the glottis, the average difference between expert and novice was higher than the average difference between two experts on the same patient. For the laryngoscope tip positions along axis from midline to lateral axis, the experts where slightly less consistent than novices during the first two steps of the procedure. However, during the following more critical stages of the procedure the difference between experts and standard deviations become much smaller. Thus, at critical regions of the procedure, the experts exhibited a higher level of consistently. These results identify areas that are important for skill development and where accurate simulation would be required in a realistic simulator.

Study Limitations

This study is limited by a small sample size in light of substantial patient anatomical differences. One would expect that the largest differences between experts and novices to occur in difficult intubation cases. However, most of the patients in the study were easy to intubate with both groups reporting grade 1 views in most cases. In addition, the self-reported grade of laryngeal view is subjective, therefore some components of the task segmentation are estimations. The study would benefit from adding a camera system to capture the view of the laryngoscopist.

Figure 1. : Instrumented laryngoscope

Clinical Study

Patients undergoing general anesthesia were recruited into the study, after IRB approval and informed consent. Prior to undergoing anesthesia, the external anatomy of the patients’ head and neck region were traced with a stylus attached to one of the position sensors, and the location of key anatomical features recorded. Laryngoscopy (Macintosh 3 blade) was performed twice on each patient up to the point of visualizing the vocal cords (only during the second procedure was the endotracheal tube inserted). After the procedure, the laryngoscopist reported the quality of the laryngeal view, ranging from I = cords to IV = not even epiglottis visible. For 13 patients, an expert (e.g. attending physician) and a novice (e.g. resident) performed laryngoscopy on the same patient in random order. For 14 other patients, two experts performed laryngoscopy on the same patient.

Figure 2. : Procedure Subtasks

The motion of the laryngoscope, head and jaw are shown at four time steps during laryngoscopy. The force vector is shown at the tip of the laryngoscope blade, and its magnitude is proportional to the length shown.


At each subtask parameters of the laryngoscope position, force, head angle, and laryngoscope angles were calculated. The statistical results of two representative parameters evaluated are shown

Instrumented Laryngoscope

In order to quantify the skill of laryngoscopy, an instrumented laryngoscope was developed that measures the 3D forces and torques applied to the laryngoscope, and the motion of the laryngoscope through space3,4. The design objective was to make the instrumentation as transparent as possible to the laryngoscopist. Accordingly, the handle diameter, weight, and center of mass were designed to match that of a standard laryngoscope. Force measurements were made with a 6 axis (3D) force/torque sensor, the Mini-45 F/T transducer manufactured by ATI. Position measurements where made with a magnetic a 3D position/orientation sensor-, the miniBird 800 manufactured by Ascension. The miniBird measures the x, y, and z position and orientation relative to a magnetic transmitter. Any standard blade can be attached to the handle. The instrumented laryngoscope is shown in Figure 1 in both its disassembled and assembled states.

  • Data Analysis

  • The force and motion trajectories of each procedure was analyzed and the intubation procedure was segmented into the following subtasks (some of which are shown in Figure 2):

  • Entering oropharynx

  • Sweeping tongue

  • Begin positioning in the epiglottis

  • Final positioning in the epiglottis

  • Exposing the glottis

  • Estimated location of best laryngeal view

  • Release Lift

  • References

  • Benumof, J. (1991). "Management of the difficult adult airway with special emphasis on awake tracheal intubation." Anesthesiology 75: 1087-1110.

  • Wilson, M. E., D. Spiegelhalter, J. A. Robertson and P. Lesser (1988). "Predicting difficult intubation." Br J Anaesth 61(2): 211-6.

  • Delson, N., Koussa N., and Tejani N., “Measuring 3D Force and Motion Trajectories of a Laryngoscope in the Operating Room,” October/December 2003, Journal of Clinical Engineering, 211-217

  • Delson, N., N. Koussa , R. H. Hastings, and M. B. Weinger (2003). "Quantifying…


Statistically significant differences between expert and novice are present in the angle of the head measurements and laryngoscope tip position, especially at critical stages of the procedure. There were larger standard deviations when data from multiple patients are compared, and the standard deviations were generally…