DIGITAL LARYNGOSCOPE

A New Force Measuring Laryngoscope

António Silva

, Pedro Amorim

, Manuel Quintas

, Luis Mourão

and Joaquim Gabriel

Labiomep, IDMEC – Pólo FEUP, Faculdade de Engenharia da Universidade do Porto, Porto, Portugal

Hospital Santo António, Centro Hospitalar do Porto, Porto, Portugal

Department of Biomedical Engineering, Escola Superior de Engenharia e Gestão Industrial,

Instituto Politécnico do Porto, Vila do Conde, Portugal

Keywords: Laryngoscopy, Anaesthesia, Force measurement, Medical devices.

Abstract: A laryngoscope is a medical device commonly used in most hospitals worldwide and used to conduct an

oral or endotracheal intubation which leads to changes in the patient parameters (heart rate, blood pressure,

etc.) due to the force applied on the tongue and other soft-tissues. However, these parameters are being

monitored continuously, and provide guidance for anaesthetists to control the drugs which may lead to an

inadequate dosage. This work aims to develop a laryngoscope capable of measuring the force applied during

a laryngoscopy. To measure the applied force, several solutions, based on different sensors, were analysed

and tested. The traditional laryngoscope xenon lighting lamp was replaced by a high bright LED which

result in a clear illumination and lower batteries consumption. A Bluetooth® communication module was

also include to allow a real-time force acquisition and display.

1 INTRODUCTION

1.1 Context

A laryngoscopy, as analyzed in this work, is a

medical procedure performed by anaesthetists in

order to achieve a good intubation and mechanical

ventilation, when the patients are subjected to

general anesthesia (GA). The anesthesia has three

goals: 1) disable the muscular activity to prevent

inadequate movement of the patient, 2) created an

unconsciousness (achieved by an hypnotic drug)

state and 3) avoid the sense of pain (analgesia).

1.2 Main Goals

This research work intends to achieve the following

objectives:

 Develop a new laryngoscope capable of

measuring and record force in real-time;

 Create wireless communication ability via

standard communication protocols;

 Real-time force warnings based on trigger

values previously defined;

 Keep the common laryngoscopy procedure,

weight and size;

 Analysis software to view the recorded data;

 Replace the usual Xenon light by the LED to

improves visibility.

2 ENDOTRACHEAL

INTUBATION

2.1 Laryngoscope

The laryngoscope is basically composed by two

parts: the handle and the blade (Figure 1). The

handle includes the lightbulb, the automatic switch

(to turn on/off the light), the batteries and the axis to

fit the blade. The blade possesses the correspondent

socket to connect to the handle and a metal protected

optical fiber to guide the light to the tip of the blade

when the laryngoscope is in working position (B).

Laryngoscope failure is extremely rare, but over

the years some have been registered, like

(Desmeules H. 1998). However, when it occurs, it is

in a very critical moment of the anaesthesia process,

since the patient is in apnoea without autonomous

breathing capability.

With the recent improvement in the overall

technologies, new laryngoscopes started to appear

368

Silva A., Amorim P., Quintas M., Mourão L. and Gabriel J..

DIGITAL LARYNGOSCOPE - A New Force Measuring Laryngoscope.

DOI: 10.5220/0003794303680371

In Proceedings of the International Conference on Biomedical Electronics and Devices (BIODEVICES-2012), pages 368-371

ISBN: 978-989-8425-91-1

 2012 SCITEPRESS (Science and Technology Publications, Lda.)

Figure 1: Laryngoscope handle and Macintosh blade size 3

A) closed position, B) opened position.

Whether may be improvements on the materials,

which may lead to disposable laryngoscopes, or

improvements in electronics that includes the video-

laryngoscopes (indirect laryngoscopies).

The disposable solution appears mostly because

of the wars, since it those situations it would be

difficult to have the sterilization equipment at a

hand.

2.2 Other Works

One of the first works on this field was (Grogono,

1983). He used strain gauges to measure the forces

in the patient mouth, Butt he did not explain how the

data was processed to get the force.

Another notorious work was done by (Hastings,

et al, 1996). He use springs and various sensors to

measure the force and torque aplied to the

laryngoscope. But, as previous work he did not tell

which was the precision or sensitivity of the

instrument.

On the other hand, there exist several studies

related to laryngoscopy force and pressure

measurements. But the target of this work was

studying the diference between experienced vs

novice users (Martin. J. L et al, 1994), nothing was

said about the device it self.

In the last years, some new devices arrived to the

market, called video laryngoscopes. These devices

use a small video camera that transmits the image to

a small screen outside of the patient mouth. Some

studies like (Ray, et al, 2009) tried to compare the

video-laryngoscopes with the standard

laryngoscopes, but without a way to measure the

damage or pressure applied to the patient, the

importance or utility of these studies is greatly

diminished.

2.3 Laryngoscopy

The laryngoscopy is a quick procedure which

requires very precise movement and force control

abilities, only achived by well trained professionals.

To perform a correct laryngoscopy the patient

has to lay down on his back and put his neck in a

hyperextension position, this causes the airway to be

in the straightest position. With the Laryngoscope in

the patients mouth, the endotracheal tube is

positioned at the entrance of the mouth and the

laryngoscope handle placed in a 45° (Figure 2 Y

axis) with the patient torso. The endotracheal tube is

then inserted between the vocal cords. This is when

most damage occurs, whether due to an excessive

force (F1) or by pulling the device in a wrong

direction (wrong amount of F2 or/and M1). This

leads to a larger force F that will hurt the patient or

produce an incorrect positioning of the blade.

Figure 2: Forces during laryngoscopy.

By analysing the laryngoscope internal forces, it

is easy to conclude that the force F and F

generate a

compression force in the contact point that occurs

when the laryngoscope is in the open position.

Based on previous studies, the position of the

force F along the blade can be estimated for normal

situations (Silva 2010). Measuring it in real time

may be possible but it requires the design of anew

laryngoscope blade.

To set the trigger value for the maximum force, a

wireless module was designed, in order to record

real data from laryngoscopies (Gabriel 2010). With

these results, a maximum force of 50 N in the tip of

the laryngoscope blade Macintosh type, size 3 was

set.

3 SENSOR POSSIBILITIES

The selection of the sensor that would lead to the

DIGITAL LARYNGOSCOPE - A New Force Measuring Laryngoscope

369

most precise and sensitive situation, three solutions

using the following sensors were evaluated:

1. Piezoresistive sensor

2. Hall effect sensor

3. Strain gauge sensor

In order to test these three sensors, it was build a

testing handle that permit the evaluation of all three

solutions, each one using a different sensor and a

different pin.

3.1 Overall Comparison

Like in the most projects, the sensor should not be

evaluated individually but together with the signal

conditioning circuit and overall characteristics. That

way, table 1 presents a general evaluation of the

idealized solution for each sensor.

Table 1: Overall sensors evaluation.

Sensor

Piezo-resistive Hall effect Strain gauge

Electric noise Medium Low Low

Space saving Medium Medium High

Reliability Low Medium High

Hysteresis High

Low (near

zero)

Low (near

zero)

Equivalent

noise (kgf)

0.2 0.36 0.02 – 0.03

It is notorious that the strain gauges present a far

better solution than any other sensor for this

particular application.

This is natural, since most of the commercial

load cells use also strain gauges. The downfall is

that due to the available size, a commercial load cell

did not fit inside the laryngoscope handle.

Despite the other solutions, it was chosen to

design a custom made load cell to fit in a new and

redesigned laryngoscope handle.

4 FINAL PROTOTYPE

4.1 General Features

The device could be divided in to three different

groups, mechanical parts, electronic circuits and data

acquisition and analyse software.

4.2 Mechanical Parts

The mechanical parts were in a first-hand simulated

using Solidworks®, this enabled the assembly

simulation and mechanical tests using the FEA

method.

The custom made load cell was also analysed

using a FEA that enabled the optimization of the

sensitivity vs mechanical strength to support the

forces applied to it (using a safety factor of 2.2). The

result was verified experimentally to prevent any

future failure.

4.3 Software

The goal of the software was to receive the data

from the digital laryngoscope interpret it and convert

the raw data so it could be displayed as force and

angles.

The final version could be installed in a

computer whether use Microsoft windows, Mac

OSX or Linux operating systems. This provides a

big flexibility whether it may be install in an

operation room or to analyse data in any other place.

The software is divided into four different tabs:

Setup, Reader, DL Analyser and Quick Help.

5 RESULTS

One of the most notorious differences is the

visibility increase provided by the illumination LED,

Figure 3.

Figure 3: Light visibility comparison.

The appearance of the Digital Laryngoscope,

Figure 4, is similar to the common one, being a little

longer (12 mm) and thicker, the diameter was

increased by 1.7 mm.

The device was tested in two different situations,

with an intubation simulator and real life situations.

In the simulator, trained doctors reached a

maximum force of 4.5 kgf (without warnings) and

non-experienced user were able to complete the

intubation with a maximum force around 2.7 kgf

(with the Digital Laryngoscope warnings).

The real life tests (Figure 5) served to validate

the device and the software. The global opinion was

that the Digital Laryngoscope was very similar to

Standard Laryngoscope Digital Laryngoscope

BIODEVICES 2012 - International Conference on Biomedical Electronics and Devices

370

Figure 4: Standard Laryngoscope (left) and Digital

Laryngoscope (right).

the other not requiring any special training or

readjust of the global anaesthesia procedures.

Figure 5: Force example.

6 CONCLUSIONS

The Digital Laryngoscope was accepted by the

medical doctors with great enthusiasm. The overall

opinion was that the visibility improvement was

very good, greatly facilitating the intubation

procedure. The force warnings were very easy to

interpret and did not distract the doctor from the

main goal (look at the vocal cords).

Another positive aspect is that the this device is

completely compatible with the standards

laryngoscope blades, meaning it is not necessary to

buy a complete set of laryngoscope blades.

One other application for this device is in the

training and teaching of the intubation procedure.

The laryngoscope can be used at medical schools, to

train future doctors and to help them to avoid

possible damage in real patients. So, in relaxed and

control environment, it is possible to train the

intubation and have some numerical parameters that

can give a helpful feedback to their training.

ACKNOWLEDGEMENTS

This research was sponsored by FCT-Fundação para

a Ciência e a Tecnologia, under the project

PTDC/EEA-ACR/75454/2006.

REFERENCES

R. T. C. F. B. A. J. G. A. W. Grogono, "A measuring

laryngoscope handle: a device for measuring the

forces applied during laryngoscopy" Med. & Biol.

Eng. & Comput., 1983.

R. H. Hastings, et al., "Force, torque, and stress relaxation

with direct laryngoscopy," Anesthesia & Analgesia,

vol. 82, pp. 456-461, March 1, 1996 1996.

Martin. J. L. B. MD, et al., "Does experience influence

the forces exerted on maxillary incisors during laryn-

goscopy? A manikin study using the Macintosh

laryngoscope " pp. 1,2,3, 16, october, 1994 1994.

D. C. Ray, et al., "A comparison of McGrath and

Macintosh laryngoscopes in novice users: a manikin

study," Anaesthesia, vol. 64, pp. 1207-1210, 2009.

Desmeules H., T. P.-R. (1998). Laryngoscope blade

breakage during intubation.

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G. Postolache, Pedro Amorim (2010). Measuring

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Silva, A. T., J.; Gabriel J.; Teixeira, C.; Amorim, P.;

Quintas, M.; Natal, R. (2010). Measuring the Pressure

in a Laryngoscope Blade. TMSi 2010 - 6th

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