5. LASER

LASER’ is an acronym: Light Amplification by Stimulated Emission of Radiation.

produces an intense beam of light, which is monochromatic The beam is coherent, with photons in phase, and is collimated, with the photons in almost parallel alignment so there is negligible divergence.

It is produced by directing an energy source such as an intense flash of light or a high voltage discharge into a lasing medium. Atoms within the medium absorb the photons of absorbed energy, which drive their electrons to a higher energy level. As the excited atom falls back to its stable state, it emits a photon of energy. The energy of the laser radiation is given by the equation E = h  v, where E is the energy, h is Planck’s constant, and v is photon frequency,

The wavelength of the light is dependent on the lasing medium that is used used. It is the wavelength that determines the depth of tissue penetration lasing medium may be a gas, such as carbon dioxide, argon or helium; a solid such as neodymium: yttriumaluminium garnet (Nd:YAG); or a liquid

CO2 lasers: these produce infrared light (10,600 nm) whose energy is absorbed by water, which is vaporized. These lasers penetrate tissue no further than 200 μm and so are used for cutting superficial tissues. The beam simultaneously coagulates blood vessels.

Argon: blue–green argon laser light (480 nm) penetrates between 0.5 and 2 mm and is absorbed maximally by red tissues. It is used, for example, to treat diabetic retinopathy and skin lesions such as port wine birthmarks.

Nd:YAG: these lasers produce energy in the near infrared spectrum (1,064 nm) and penetrate tissues deeply between 2 and 6 mm. at higher power it vaporizes tissue and can be used for the surgical removal and debulking of large tumours

Excimer lasers: these are ‘cold’ ultraviolet lasers which do not heat tissues but which break chemical bonds in protein molecules. Their main use is in refractive corneal surgery.

eyesight of theatre personnel.

eyesight of theatre personnel. The non-divergent beam of laser light, even when reflected, may be focused by the lens of the eye onto the fovea and cause irreversible blindness. Distance offers no protection. Other parts of the retina may also absorb the energy, as may the lens and the aqueous and vitreous humours. Staff should be issued with goggles which protect specifically against the wavelength that is being generated, and, ideally, surgical instruments should have a matt finish to minimize the likelihood of reflection.

There is a specific hazard associated with laser surgery to the upper airway. A normal PVC tracheal tube will ignite within a few seconds should it be exposed directly to a laser beam. specially designed tracheal tubes available for use with laser surgery on the upper airway Although these have flexible metal bodies (either stainless steel or aluminium), they still have cuffs and pilot balloons which should be filled with saline as a precaution Air/oxygen gas mixtures are safer than nitrous oxide/oxygen mixtures, and ideally the FiO2 should be kept at no greater than 25%. Surgical swabs or packs can also ignite, and so these must be kept moistened with saline.