30 Laser Flashcards
What do you understand by the term ‘laser’?
Laser is an acronym for ‘light amplification by the stimulated emission of radiation’.
What are the properties of laser
Lasers produce an intense
beam of light that is
- monochromatic (single wavelength),
- coherent (in phase)
- and collimated (parallel).
Laser technology allows
high-energy intensities
to be produced from
relatively low-power sources.
Describe the basic physics underpinning laser technology.
1
> The quantum theory states that
electrons are confined
to certain energy states
but these electrons can move
between these energy states
depending on whether they
absorb or emit energy.
> Einstein demonstrated that if you stimulated an atom with a photon of energy, this stimulated atom would in turn emit a photon of equivalent energy,
which was in phase
with the original stimulating photon.
This new emitted photon could now cause a further similar reaction and as such a chain reaction and hence amplification of the system would ensue.
> In lasers, an external source of energy
(e.g. high voltage or flash of light)
is applied to a laser medium.
> This increases the energy state of the electrons within the laser medium and moves them up from a ‘ground’ energy state to an ‘excited’ energy state.
> When these excited electrons return
to their original ground state they
emit energy in the form of light or radiation.
> This emitted energy can then
stimulate further electrons
within the medium,
thereby amplifying the whole process.
> The wavelength of light produced
depends on the lasing medium that
is used.
What are the fundamental components within a laser
device 7x
> External energy source (to ‘stimulate’ the electrons)
> Laser medium (this can be a solid, liquid or a gas)
> Chamber containing the laser medium
> System of mirrors (to allow ‘amplification’ of radiation)
> A partially reflective mirror (to allow the emitted
radiation to exit the system)
> Windows at each end of the device are inclined to Brewster’s angle
(this is the angle of incidence at which light is perfectly transmitted with no reflection, thereby ensuring that 100% of the light is transmitted through the windows)
> Fibre-optic cable (to direct the laser beam).
List the different types of lasers with their clinical applications.
- > N d-YAG (neodymium-doped-yttrium aluminium garnet) lasers
2.
> Carbon dioxide lasers
3.
> Argon lasers
- Dye lasers
- > N d-YAG (neodymium-doped-yttrium aluminium garnet) lasers
• Crystal used as a lasing medium in solid-state lasers.
• Wavelength of light produced is 1064 nm
(near infrared region).
• Good tissue penetration
(as it is not absorbed by water).
• Used typically for endoscopic surgery (there have been reports of inadvertent pneumothoraces during ENT surgery due to these lasers penetrating and affecting tissues deeper than anticipated).
- > Carbon dioxide lasers
> Carbon dioxide lasers
• Used as a lasing medium in gas-state lasers.
• Highest power laser
currently available
(also used in industry for cutting, welding and engraving).
• Wavelength of light produced is
10.6 μm (infrared region).
• Poor tissue penetration of <200 μm
(as it is absorbed by water
causing it to vaporise
and destroy tissue contents).
• Used typically for superficial surgery
(e.g. dermabrasion and laser ‘facelifts’).
• Unsuitable for endoscopic use.
3.
> Argon lasers
> Argon lasers
• Used as a lasing medium
in gas-state lasers.
• Wavelength of light produced is between
400 and 700 nm
(blue-green region of the visible spectrum).
• Good penetration through transparent tissues
(e.g. aqueous humour,
vitreous humour and
lens of the eye).
• Maximally absorbed by
red-pigmented tissues
(e.g. birthmarks,
haemoglobin).
• Used typically in
eye surgery
(e.g. retinal phototherapy)
and in
dermatological procedures to
cosmetically enhance pigmented lesions.
- Dye lasers
• Organic dye used as a lasing medium
in liquid-state lasers.
• Wavelength of light produced is
broad and varies occurring
to the dye used.
• Used typically in ‘beauty clinics’ to even out skin tone.
How are lasers classified?
> Class 1 –
power does not exceed maximum permissible exposure for the eye.
> Class 2 –
power up to 1 mW
and visible laser beams only.
Eye protected by blink reflex.
> Class 3a – power up to 5 mW and visible spectrum only but now laser beam must be expanded (so that maximum irradiance does not exceed 25 W/m2); eyes protected by blink reflex.
> Class 3b – power up to 0.5 W and any wavelength; direct viewing hazardous; dye protection essential.
> Class 4 – power
0.5 W and any wavelength;
extremely hazardous and
capable of igniting inflammable materials;
eye protection essential
What are the hazards of laser surgery?
Lasers are hazardous to use because
they combine high-energy intensities confined within a small spot size (i.e. very concentrated) and transmitted in a non-divergent beam
(i.e. these devices do not lose power with
increasing distance from the laser source).
For comparison, when looking directly into sunlight the eye is exposed to approximately 150 W/m2 but if inadvertently looking into a laser beam, the eye is exposed to approximately 3 × 106 W/m2!
1. > Environment: • Fire and explosions – flammable spirits, oxygen and nitrous oxide can get collected in the drapes and these can get ignited if the laser beam is directed to it.
- > Staff:
• Eyes –
if the laser beam hits the retina,
a permanent blind spot can develop,
but if it hits the optic nerve permanent blindness can be caused (CO2 lasers do not penetrate the cornea and therefore cannot affect the retina).
• Skin – if the laser beam hits the skin,
a burning sensation is felt and
this will trigger self-protecting manoeuvres.
3
> Laser hazards affecting the anaesthetised patient:
• Eyes – as above.
• Skin –
now self-protecting manoeuvres
do not come to play and
therefore patients are at risk of laser burns.
• Airway fire –
this is a real risk during laser surgery
to the upper airway
(this is an anaesthetic emergency and therefore you must be well versed with both the precautions needed to prevent this and the immediate management required to deal with this).
What precautions are taken to minimise the hazards of laser surgery?
1 > General:
• Designated laser protection supervisor
for each theatre
• Staff all trained and educated in laser use
• Doors locked, windows closed and signs displayed to protect those outside theatre.
2 > Equipment:
• Eye protection goggles
(laser beam wavelength-specific)
for both staff
and patient
• Surgical instruments with a
black or matt finish to
minimise refection of laser beam.
3
> Anaesthetic considerations for upper airway laser surgery:
• Double-cuffed,
laser-resistant endotracheal tube
(these are often flexible stainless steel tubes
with two cuffs to ensure a tracheal seal if
the upper cuff is accidentally damaged by the laser)
• Cuffs filled with saline
(air-filled cuffs may ignite if hit by the laser)
• Throat packed with wet swabs
(to protect adjacent areas from
inadvertent laser burns)
- Oxygen – air mix (as nitrous oxide is more flammable)
- FiO2 < 0.25 if tolerated
What are the basic concepts
in managing an airway fire?
1 > Call for help and inform your immediate theatre team.
2 > Surgeon to switch off laser and flood the operation site with water.
3 > Disconnect the anaesthetic machine.
4 > Remove endotracheal tube if feasible
(remember that even laser-resistant tubes can ignite).
5 >
Ventilate the patient with a bag-valve-mask circuit
(if necessary continue anaesthesia with TIVA).
- > Surgeon to inspect the airway with rigid bronchoscope.
7. > Refer to ITU (airway fires can cause significant lung injury and ARDS – patient may require ventilation, dexamethasone, and humidified oxygen).
