Quantifying Expert vs. Novice Skill In Vivo for Development of a Laryngoscopy Simulator

Nathan J. Delson*, Ph.D., Nada Koussa*, Randolph H. Hastings**, M.D, Ph.D., Matthew B. Weinger**, M. D.

University of California, San Diego - *Mechanical and Aerospace Engineering - **School of Medicine Veterans Administration San Diego Healthcare System

Laryngoscopy is used for Airway Intubation

The failure to establish the airway is a major cause of death and brain injury

Laryngoscopy is the most common technique for establishing an airway.

A laryngoscope is used to visualize the glottic opening to the lungs, and then an endotracheal tube is inserted into the trachea.

Experience makes the difference Experts succeed 99.9% Novices succeed 67% to 90%

Project Objectives

Long Term Develop realistic training simulator Provide guidance to trainee Quantitative assessment of trainee

Short Term Quantify expert skill and novice errors Measure relevant physical properties of airway in vivo

Expert Skill Acquisition

Instrument tools to measure: Sensory information used by expert Actions of expert

Collect data under a range of environments Range of patient anatomy

Quantify characteristics of expert actions and novice errorsIdentify physical properties of environment where interaction occurs

Instrumented Laryngoscope

•6 axis force/torque sensor (ATI)

•6 dof magnetic position sensor (Ascension)

Disassembled Assembled

Data Collection in the ORPosition Sensors

SkullAdam’s AppleJaw

ProtocolPatients undergoing AnesthesiaExpert and novice on same patientUse stylus to gather profile and calibration pointsGrade of view reported post procedure

Animation of Expert

Side ViewLaryngoscope in blueForce vector in redClick figure for animation

Data Interpretation is Preliminary

Variation between patients is large Some novices performed well Prior experience Easy patient anatomy

Number of procedures is low Data is presented as indication of method potential rather than definitive characterization of task

Laryngoscope placement seems more important than head position (for this

case!) Laryngoscope final position at maximum force for both expert and novice is very similar relative to the patient’s head anatomy

The expert tilted the head much more forward than novice. However, they both acquired the same grade view

Expert in blue, Novice in red at maximum force

Incorrect laryngoscope placement reduces grade view of novice

Expert in blue, Novice in red at maximum force

Expert vs. Novice in Head c.s.

Novice blade placement is too far into throat

VA_AB 17

Novice Expert

Max Force

75.2 N 43.8 N

Laryn Pitch at Max Y

-75.9o -60.2o

Distance Traveled

126 cm 51 cm

View Attained

Grade II Grade I

Expert vs. Novice in Head c.s.

VA_AB 12

Novice Expert

Max Force

24.2 N 24.9 N

Laryn Pitch at Max Y

-28.9o -26.0o

Distance Traveled

42 cm 75 cm

View Attained

Grade III Grade I

Novice blade placement is not far enough into throat

Expert vs. Expert in Head c.s.

VA_AB 10

Expert Expert

Max Force

34.9 N 35.4 N

Laryn Pitch at Max Y

-80.0o -70.4o

Distance Traveled

52 cm 84 cm

View Attained

Grade I Grade I

Both experts have similar blade placement and trajectory

Expert vs. Expert in Head c.s.

VA_AB 16

Expert Expert

Max Force

38.6 N 38.9 N

Laryn Pitch at Max Y

-85.7o -70.5o

Distance Traveled

85 cm 119 cm

View Attained

Grade I Grade I

Both experts have similar blade placement but vary trajectory at points

Expert vs Novice Comments

When novice blade placement differs from expert, grade view can be lower

Experts have similar blade placement locations on the same patient, although trajectories can vary in certain regions

regions of expertise can be defined

Region of Expertise can be Used to Identify Novice Error

Application of Robot Programming by Human Demonstration Obstacle avoidance example

Deviation from expert region would indicate error, allowing for real time guidance cues during training simulation

start

end

low variation corresponds tohigh precsion area

large variation corresponds tolow precsion requirment

Estimation of Physical Properties In Vivo

Advantages of Skill Acquisition Approach Contact forces are at ranges of interest and at locations of interest

Challenges Unlike probing, motion is not defined for tissue characterization Both sliding and compression occur

Sampling occurs at just a few tissue locations Tissue swelling may occur between procedures

Stiffness Estimation Method

Stiffness is approximated as single dimensional Stiffness is estimated during final loading and unloading when sliding is minimal

Stiffness calculation in head coordinate system estimates compliance of airway tissue

δF - K δX

Kload 41.93/ 50.3 =.833 N/mm

Kunload 32.28 /84.7 = 3.81 N/mm

Unloading occurs rapidly with smaller displacement, resulting in higher stiffness

Stiffness calculation in table coordinate system estimates overall head and neck resistance

δF - K δX

Kload 41.93/ 64.1 =.655 N/mm

Kunload 32.28 /125.6 =2.57N/mm

Stiffness is lower in table c.s. since motion includes head displacement

Stiffness Calculations in Same Patient for both Expert and Novice

Here expert placed blade less deep into the throat and attained same view as novice with lower force

Effective stiffness of expert is lower

Expert loading stiffness = .636 N/mmNovice loading stiffness = 1.29 N/mm

• Expert blade placement may be in “sweet spot” where stiffness is lower• Tissue swelling between procedures may also be a factor

Comments on Tissue Properties

Preliminary stiffness properties have been identified High nonlinearity observed in unloading Realistic simulator should mimic resistance to force (impedance) due to both tissue compliance and head/neck displacementSeparating sliding forces from compressive forces may allow for stiffness estimations at more regions

Future Direction

Comparison of stiffness properties to existing mannequins Add image capture Collect more expert vs expert data

Acknowledgments

Talla Farivar, Lance Feller, Anjali Godbole, William Green, Andrew Linn, and Nabyl Tejani

Society for Technology in AnesthesiaAnesthesia Patient Safety Foundation