Transcript Lasers - Creagh Brown and Co

Lasers
Ben Creagh-Brown
Beware
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Pay attention – there are MCQs at the end!
'LASER'
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Acronym standing for 'Light Amplification by
Stimulated Emission of Radiation‘
Special form of light radiation
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Monochromatic
In Phase
Parallel
High light energy from low power source
Principles
Stimulated emission:
 High energy atom is struck by an incoming
photon, releases 2 photons with same phase
and frequency (coherent)
 Cascade amplification resulting in high
energy light source emitting waves in phase
Laser construction
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An energy source to raise the energy levels
of the electrons (Pumping)
A laser substance capable of stimulated
emission
A system of mirrors to reflect the light
repeatedly backwards and forwards through
the laser substance
Laser materials
Material
Uses
Synthetic ruby
Early use in eye surgery
Argon
Eye surgery and removal Passes through
of birthmarks
vitreous and aqueous
humour.
Absorbed by Hb and
pigmented skin.
Transmitted down
optical fibres
Carbon dioxide
Most commonly used,
removes layers of tissue
Absorbed
Coagulation and cutting
Not
Nd-YAG (NeodymiumYyrium-Aluminium-Garnet)
Properties
by H2O – low
penetration
Cannot be used
endoscopically
absorbed by H2O –
good penetration
Can be used
endoscopically
Safety
Dangers
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High-energy intensity.
Non-divergent which means that increasing the distance from the
laser confers little safety benefit.
Laser light, either transmitted directly, or reflected into the eye,
may be very dangerous.
If the light is in the visible portion of the spectrum, the retina may
be burned (permanent blind spot) or the head of the optic nerve
may be damaged (partial or total blindness).
Infrared laser light can be even more dangerous as it cannot be
seen. Infrared light is particularly damaging to the cornea, lens,
and aqueous and vitreous humours. Exposure of the skin to laser
radiation can give rise to a burning sensation and is therefore
self-protective.
The skin of sedated or anaesthetised patients must therefore be
shielded from the beam.
Precautions
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Appropriate training
Suitably equipped area,
all exposed surfaces
matt finish
All instruments matt
finish
No inflammable
material near patient
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Protective eye goggles
and protection for
patient’s eyes and skin
Well ventilated with
smoke extraction
No inflammable or
explosive anaesthetic
gases
Airway fires
Prevention
1.
Air and oxygen mixtures (less
flammable than nitrous oxide
and oxygen mixtures).
2.
Inspired oxygen
concentration of 25% or less.
3.
Non-reflective matt-black
surgical instruments to
minimise reflection from the
main laser beam.
4.
Non-flammable endotracheal
tubes.
5.
Protecting other tissues with
wet swabs.
Management
1. Switch off the laser and flood
the operation site with saline.
2. Disconnect the anaesthetic
circuit temporarily and, if
feasible, remove the
endotracheal tube – even
‘laser’ tubes can be ignited.
3. Ventilate the patient with air
using a bag-valve-mask circuit.
4. After the fire has been
extinguished, the surgeon
should then inspect the airway
via a rigid bronchoscope.
ET Tubes for laser surgery
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Silicone rubber tubes with metal links incorporated into the tube
wall with either a sponge cuff (Bivona Fome cuff) or a double cuff
(Mallinckrodt ‘Laser flex’) are available.
If the cuff bursts in the former, the sponge will maintain a sealed
airway; in the latter, the second cuff can be used.
Foil wrapped tubes with an outer Teflon coat (Sheridan ‘Laser
Trach’) can be used.
The cuff is filled with methylene blue crystals so that, if the laser
bursts the cuff, this will be detected quickly by the surgeon.
The main problem with laser tubes is that they have a narrow
internal diameter because they have thick outer walls. This can
make spontaneous ventilation difficult, and airway pressures can
be high in the ventilated patient.
Medical uses of lasers
Uses
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Dermatology
ENT
 Laryngeal tumours
 Uvulopalatoplasty
Bronchoscopic removal of airway tumours
GI Endoscopy
Opthalmology
 Photorefractive keratectomy
 Diabetic retinopathy
Cardiology
 Transmyocardial revascularisation
Urology – Laser TURP
Gynaecology - endometriosis
1. With regard to laser safety
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True or False:
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Reflected laser beams are not dangerous.
Safety is covered by specific health and safety
legislation in the UK.
A low oxygen concentration should be used in the
anaesthetic gas mixture.
Spectacle wearers are protected from the laser
beam.
Only a laser protection supervisor can use a laser
in an NHS operating theatre.
2. In laser surgery
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True or False:
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Endotracheal tubes designed for laser surgery are
made of PVC.
Only the visible beam is dangerous.
Volatile anaesthetic agents cannot be used.
Laser treatment of laryngeal carcinoma is often
used prior to radiotherapy.
Laser endotracheal tubes can catch fire.
3. With regard to lasers
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True or False:
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Laser is an acronym for light amplification by the
synchronous emission of radiation
Semiconductor lasers are able to generate a
greater power output than carbon dioxide lasers.
Helium–neon lasers generate light in the red part
of the spectrum.
The ruby laser can generate a continuous light
output.
The argon laser emits green light.
4. With regard to light from a laser
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True or False:
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The beam is an incoherent beam of light.
The beam diverges very little.
The beam consists of a very narrow range of light
frequencies.
The energy of the beam is given by E = hv
The SI unit for the power of the laser beam is the
Joule
5. With regard to the management of
airway fires:
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True or False:
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The FiO2 should be reduced immediately by
adding nitrous oxide to the circuit.
The surgeon should flood the operation site with
saline.
An endoscopic assessment of the airway should
take place after the fire has been extinguished.
Steroids are of no value in preventing airway
oedema.
Respiratory problems are uncommon
Thanks