PRINCIPLES AND PRACTICE OF

FIBEROPTIC INTUBATION

Presenter : Dr. Bindu

Moderator : Dr. Ranjan R. K.

Physics of Fiberoptic Image Transmission:

Principle:

Law of total internal reflection: Light can be totally reflected

internally by the fiberoptic strand.

a – angle of incidence

b – angle of reflection

Degree of Reflection:

1. Angle of incidence of the light.

2. Refractive indices of the two transmission media.

Critical Angle: Angle at which parallel transmission occurs.

When the incident angle is increased beyond the critical angle total internal reflection of light occurs.

Light striking the boundary of a clad glass fiber will be internally reflected. Ic is the critical angle. Light striking the boundary at an angle greater than the critical angle will undergo total internal reflection.

Fiberoscope consists of fibres arranged in bundles.

Each fibre Core or light transmission port.

Cladding material

Cladding protects the interface surface and increases transmission efficiency

Factors affecting decreased amount of light accepted by the fiber:

1. Light scattered at the interface.

2. Light absorption by the core glass

3. Light entering the bundle at an angle lower than the critical angle.

4. Packing fraction loss.

Packing fraction: Cross sectional area of the cladding material

Cross sectional area of the core material

Individual fibers are grouped into a bundle in a honeycomb pattern

Fiberoscope Components:

Components of a flexible fiberoptic laryngoscope:a. Body : Tip deflection control lever Eyepiece

Focusing ring Working channel sleeveb. Insertion cord : Fiberoptic bundles

Optical systemMechanical system

c. Light transmission cord (Universal cord)

• Fibers are arranged in bundles in a coherent order.

• In a coherent fiber bundle – the arrangement of fibers in one end of the bundle exactly matches the arrangement in the opposite bundle.

• In incoherent bundle – no correlation exists between the fiber arrangement in the two bundles.

• They are used as light conduits light guide bundles.

• Any breakage of illuminating fibres decreases the amount of light that reaches the tip of scope. Breakage of optical fibres results in black spots in the image because those pixels of data are lost.

Optical System:

An objective lens placed at the distal end of the fiberscope forms an image on the distal end of the image bundle.

Since objective lens inverts the image the fiberoptic bundle is internally rotated 180 which compensates for the image inversion.

This image is then magnified by an ocular lens placed in the eye piece.

The eyepiece contains a diopler adjustment to compensate for any visual abnormality of the endoscopist. This results in a well illuminated and magnified image of high resolution.

Mechanical System:

• Image bundles

• Illumination bundles

• Working channel

• Angulation control wires

• Flexible distal joint system

All ensheathed in a tough durable outer covering

Internal components and construction of the insertion tube of the fiberscope.

Working Channels:

They run the length of the endoscope

Uses:1. Suctioning can be applied for clearing of secretions.

2. Medications can be instilled into the airway.

3. Biopsy instruments for diagnostic procedures.

4. Instillation port

Angulation control wires:

1. The distal end of the laryngoscope has a two way angulation system.

2. Angulation wire runs the length of the fiberoscope from the control knob through the metal bands and is fixed at the distal end of the endoscope.

3. Tip deflection is produced by rotating the control knob thus exerting tension on the angulation wire which inturn flexes the metal band.

4. Flexible section of the distal end has a series of metal bands attached together by flexible joints

Light Sources:

Two basic types:

• Low power halogen light source

• High power xenon light source.

Fibre optic laryngoscope with a battery operated light source on the handle

Sterilization and Cleaning of the Flexible Fiberoptic Bronchoscope:

Routine Cleansing of the fiberoscope:

Sterilization:

Ethylene oxide gas

Fiberscopes may be sterilized by this method at a temperature of 130F (54.4C), pressure 20psi and humidity 50% for a period of 4-5 hrs.

Disadvantage: Time consuming

Step 1Step 1 Connect suction port to vacuum suctionConnect suction port to vacuum suction

Step 2Step 2 Aspirate approximately 200ml detergent solution through suction Aspirate approximately 200ml detergent solution through suction channel channel

Step 3Step 3 Clear suction channel with cleaning brushClear suction channel with cleaning brush

Step 4Step 4 Wipe shaft and valves with detergent-soaked spongeWipe shaft and valves with detergent-soaked sponge

Step 5Step 5 Aspirate approximately 200ml sterile water through suction channelAspirate approximately 200ml sterile water through suction channel

Step 6Step 6 Wipe shaft and valves with sterile waterWipe shaft and valves with sterile water

Step 7Step 7 Proceed with disinfection / sterilizationProceed with disinfection / sterilization

Routine Cleaning

Immediate cleaning of the fiberoptic bronchoscope and

valves with detergent solution followed by 20 minutes of

disinfection with 2% alkaline glutaraldehyde (cidex) or succine

dialdehyde solution. It is rinsed and the channel is flushed with

70% alcohol. The scope is then allowed to dry.

Storage of Fiberoptic Instruments:

To prevent the fiberoptic bundles from being bent or

broken, the laryngoscope is stored straight in a cylindrical tube

on the portable chart or stored horizontally within the drawer of

a mobile bronchoscopic cart or stored within the soft molded

foam of its carrying case.

REFERENCES:

1.Anesthesiology Clinics of North America. The Upper Airway and Anesthesia. Fiberoptic Bronchoscopy.

2.Miller’s Anesthesia 6th edition

3.Clinical Anesthesiology- G.Edward Morgan