PRINCIPLES AND PRACTICE OF FIBEROPTIC INTUBATIONPresenter : Dr. BinduModerator : Dr. Ranjan R. K.
Physics of Fiberoptic Image Transmission: a – angle of incidence b – angle of reflectionPrinciple:Law of total internal reflection: Light can be totally reflectedinternally by the fiberoptic strand.
Degree of Reflection:2. Angle of incidence of the light.3. 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 thecritical angle. Light striking the boundary at an angle greater than the critical angle willundergo total internal reflection.
Cladding protects the interface surface and increases transmission efficiencyFiberoscope consists of fibres arranged in bundles.Each fibre Core or light transmission port. Cladding material
Individual fibers are grouped into a bundle in a honeycomb patternFactors affecting decreased amount of light accepted by the fiber:2. Light scattered at the interface.3. Light absorption by the core glass4. Light entering the bundle at an angle lower than the critical angle.5. Packing fraction loss.Packing fraction: Cross sectional area of the cladding material
Fiberoscope Components:Components of a flexible fiberoptic laryngoscope:b. Body : Tip deflection control lever Eyepiece Focusing ring Working channel sleeveb. Insertion cord : Fiberoptic bundles Optical system Mechanical systemc. 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 animage on the distal end of the image bundle.Since objective lens inverts the image the fiberoptic bundle is internallyrotated 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 anyvisual abnormality of the endoscopist. This results in a well illuminatedand magnified image of high resolution.
Mechanical System:• Image bundles• Illumination bundles• Working channel All ensheathed in a tough durable outer covering• Angulation control wires• Flexible distal joint system Internal components and construction of the insertion tube of the fiberscope.
Working Channels:They run the length of the endoscopeUses:4. Suctioning can be applied for clearing of secretions.5. Medications can be instilled into the airway.6. Biopsy instruments for diagnostic procedures.7. Instillation portAngulation control wires:• The distal end of the laryngoscope has a two way angulation system.• 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.• Tip deflection is produced by rotating the control knob thus exerting tension on the angulation wire which inturn flexes the metal band.• 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:Step 1 Connect suction port to vacuum suctionStep 2 Aspirate approximately 200ml detergent solution through suction channelStep 3 Clear suction channel with cleaning brushStep 4 Wipe shaft and valves with detergent-soaked spongeStep 5 Aspirate approximately 200ml sterile water through suction channelStep 6 Wipe shaft and valves with sterile waterStep 7 Proceed with disinfection / sterilizationSterilization:Ethylene oxide gasFiberscopes may be sterilized by this method at a temperature of 130°F(54.4°C), pressure 20psi and humidity 50% for a period of 4-5 hrs.Disadvantage: Time consuming
Routine Cleaning Immediate cleaning of the fiberoptic bronchoscope andvalves with detergent solution followed by 20 minutes ofdisinfection with 2% alkaline glutaraldehyde (cidex) or succinedialdehyde solution. It is rinsed and the channel is flushed with70% alcohol. The scope is then allowed to dry.Storage of Fiberoptic Instruments: To prevent the fiberoptic bundles from being bent orbroken, the laryngoscope is stored straight in a cylindrical tubeon the portable chart or stored horizontally within the drawer ofa mobile bronchoscopic cart or stored within the soft moldedfoam of its carrying case.
REFERENCES:• Anesthesiology Clinics of North America. The Upper Airway and Anesthesia. Fiberoptic Bronchoscopy.• Miller’s Anesthesia 6th edition• Clinical Anesthesiology- G.Edward Morgan