Lasers

Describe the principles of surgical lasers, their safe use and the potential hazards

A laser is a device for light amplification by stimulated emission of radiation. Laser light is:

• Non-divegent
  All photons move in parallel.
• Coherent
  All photons are in phase.
• Monochromatic
  All photons have the same wavelength.

Lasers are used clinically for:

• Precise incisions
  Destruction of cells by localised vapourisation of water.
• Destruction of chemicals
  Tattoos, oncological drugs.
• Tissue destruction without heating
  Opthalmology.

Principles

Method:

• An energy source is passed through a lasing medium, housed in a resonator made of mirrors
• As the lasing medium is excited, electrons enter a higher energy level
  When more than 50% of electrons are at a higher energy level, population inversion has occurred.
• As electrons fall back to their resting state, they release a photon
  • A spontaneous emission occurs when an electron enters its resting state spontaneously
  • A stimulated emission occurs when an electron enters its resting state after being struck by a photon released from a spontaneous emission
    • Stimulated emissions result in amplification of light release
• The mirrors in the resonating chamber ensure most light is reflected back into the chamber, causing more stimulated emissions
• The exit from the chamber can be be adjusted so only certain polarities of light are emitted
• A lens may be used to focus the laser beam

• Lasers may be:
  • Pulse wave
    Uses short bursts of laser light to minimise collateral damage.
  • Continuous wave
    May lead to excessive heating.

Pros

• Precise surgery and haemostasis

Cons

• Require multiple safety precautions
  • Laser safety officer
  • Eye protection
  • Warning signs on doors
  • Cover theatre windows
  • Non-combustible drapes
  • Matte finish on equipment to minimise chance of reflection
• Additional risks in airway surgery
  • Use lowest FiO₂ possible
  • Avoid N₂O
  • Consider use of heliox
  • Use specialised laser tubes
    Normal PVC ETTs are combustible.

References

1. Aston D, Rivers A, Dharmadasa A. Equipment in Anaesthesia and Intensive Care: A complete guide for the FRCA. Scion Publishing Ltd. 2014.