Lasers Ben Creagh-Brown

Beware Pay attention – there are MCQs at the end!

'LASER' Acronym standing for 'Light Amplification by Stimulated Emission of Radiation‘ Special form of light radiation  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 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 MaterialUsesProperties Synthetic ruby Early use in eye surgery Argon Eye surgery and removal of birthmarks Passes through vitreous and aqueous humour. Absorbed by Hb and pigmented skin. Transmitted down optical fibres Carbon dioxide Most commonly used, removes layers of tissue Absorbed by H2O – low penetration Cannot be used endoscopically Nd-YAG (Neodymium- Yyrium-Aluminium-Garnet) Coagulation and cutting Not absorbed by H2O – good penetration Can be used endoscopically

Safety

Dangers 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 Appropriate training Suitably equipped area, all exposed surfaces matt finish All instruments matt finish No inflammable material near patient 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 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 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 True or False:  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. FFTFFFFTFF

2. In laser surgery True or False:  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. FFFTTFFFTT

3. With regard to lasers True or False:  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. FFTFTFFTFT

4. With regard to light from a laser True or False:  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 FTTTFFTTTF

5. With regard to the management of airway fires: True or False:  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 FTTFFFTTFF

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