Indications of Laser:

CO2 laser is most commonly used in ENT:

1. Larynx: Done with microlaryngoscopy for juvenile laryngeal papillomatosis, laryngeal web, vocal nodules, capillary hemangioma, T1 carcinoma of mobile vocal cords, arytenoidectomy and subglottic stenosis.
2. Oral cavity: Debulking of large inoperable tumors, tonsillectomy in cases of blood dyscrasias, superficial lesions and palatal surgeries like uvulopalatopharyngoplasty.
3. Nose: Inverted papilloma, hemangioma, nasal polyps, turbinectomy and nasal tumors. This is combined with sinoscopy.
4. Tracheobronchial tree: Respiratory papillomatosis, tracheal stenosis, granulation tissue, bronchial adenoma.
5. Ear: Myringotomy, Stapedotomy, Acoustic neuroma.

LASER-tissue interaction:

The reaction of laser energy with tissue can be photo-ablative, photochemical, photomechanical or photothermal.

1. Photo-ablative reactions occur when molecular bonds are divided. The ruby laser, for example, can split the molecular bonds of tattoo. Macrophages remove the tattoo ink after the molecular bonds are broken.
2. Photochemical reactions occur when laser light interacts with photosensitizers to produce chemical and physical reactions. This forms the basis for photodynamic therapy.
3. Photomechanical effect occurs when the laser energy is pulsed to disrupt tissue or stones by the mechanism of shock waves. Example, Holmium YAG laser used to shatter ureteric and renal calculi. 
4. Photothermal reaction occurs when laser light converts into heat. The tissue effect can be cutting, coagulation or vaporization depending on the laser wavelength and the laser delivery device.

Complications of LASER:

1. Ocular Injuries: Infrared light produced by laser can cause corneal and retinal injury. Hence, protective glasses must be worn by surgeon, staff and anesthetists.
2. Cutaneous injuries: Direct and reflected laser energy can cause skin burns to the patient and others in the operation theatre.
3. Damage to surrounding structures like trachea, oral cavity and vocal cords.
4. Anesthetic complications: Damage to endotracheal tube can lead to fire from direct or reflected laser beam. Hence, the endotracheal tube is coated with an aluminium foil and proper selection of the anesthesia gases are made.

Precautions need to be taken while using lasers:

1. A laser beam may hit or damage objects outside the target area and cause a fire, tissue damage or eye / visual damage. 
2. The patient should be shielded by wet gauze or fireproof material from accidental strikes. 
3. The endotracheal tube and airway should be protected from accidental strikes that could produce a fire. 
4. All personnel in the operating room should wear correct eye protection. 
5. A warning sign plus locked doors should prevent unprotected and unprepared individuals from walking into the operating room. 
6. The key to switch on the laser should be held by a senior member of the operating team to ensure only properly qualified individuals use the laser. 
7. The operating room and windows should be laser protected. 
8. Endoscopic equipment should be blackened to reduce accidental reflective strikes of the laser.