With the rapid advancement in ENT laser Surgery the anesthetist and laser surgeons are presented with new challenges.Carbon dioxide laser surgery in the airway presents the anesthetist with new problems. The mode of action of carbon dioxide lasers and its effects on anesthetic agents and equipment must be anticipated. Complications, especially of fire hazards in the airway, and methods of avoiding them are most important.
The Mallampati score is a common method used to predict difficult intubation. Difficult intubation was significantly more common in patients with MS score more than 3.
Anesthetic management for laryngeal surgery presents more problems arising from the competing needs of the anesthetist and surgeon for control of the airway which may already be compromised by disease. In view of the narrow margins of safety, the ultimate success of any procedure will depend on close cooperation among the team.Because of the intense heat generated, lasers must not be used with flammable agents. Nitrous oxide, although not flammable, does support combustion at high temperatures and should beavoided with open anesthetic systems. The oxygen concentration should be as low as possible with adequate oxygenation.
With increased use of lasers in the airway, sporadic incidents of tracheal tube ignition, causing burns of the laryngotracheal tissue have been reported. The intense heat generated by a carbon dioxide laser can ignite most non-metallic and non-glass objects unless they are protected from direct or reflected laser beams. The ease with which this occurs depends on the material, environmental gas composition, duration of exposure and the power of the laser. The incidence of damage to an unprotected tube by direct exposure to the beam is high even in experienced hands
The original method of protecting tracheal tubes involved the use of self-adhesive, nonreflective aluminum tape. The tube is carefully wrapped with the tape in a spiral fashion with overlapping edges, commencing just above the cuff or at the distal tip of endotracheal tubes .Tape edges are then smoothed to decrease injury to pharyngeal and laryngeal tissue. This significantly retards ignition of both red rubber and PVC tubes. Although adequate, it is not without danger.
Narrow tubes can become occluded as a result of compression by the foil as it accommodates to the curvature of the pharynx The tape does not always adhere adequately to the tube and may loosen or break off, resulting in acute airway obstruction .The outer wall of the tube is protected, but the cuff and the distal end of the tube can be ignited by direct or indirect contact with the laser beam.
The cuff, when ruptured, allows a massive leak of anesthetic gases, leading to hypoventilation as well as providing a richer environment for ignition of the tube. The cuff can be protected by placing saline-soaked cottonoids around it and these are kept moist throughout the procedure.
Laser-Shield cuffed tracheal tubes made from silicone and having an outer coating of metallic oxide, are more resistant to lasers than red rubber and PVC tubes. However, the cuffs of these tubes do present a hazard when inflated with air, multiple impacts from a laser will penetrate the cuff, which could ignite.
Hence, the cuff is inflated with saline, which acts as a heat sump to dissipate the heat from the beam. The high volume, low pressure floppy cuff may present difficulty during its passage through a narrow larynx.
The development of a flexible metal tube provides a partial solution to the problem. All the flexi metallic tubes in use are non-combustible, easily sterilized, gas tight and non-reactive with human tissue. Wet cottonoids can be placed around the tube to act as a pack, as well as a protective shield for normal tissue distal to the lesion. The walls of these tubes are relatively thick, with a large external diameter which precludes their use in the younger patient. They can be reused many times and provide long-term economy.
Two types of burn injury are produced by laser explosions. The thermal effect from dry heat dissipated by vaporization of cellular and surface water gives rise to a mummified appearance of the tissue. The second type of injury arises from the chemical response of tissues to toxic PVC fumes.
First, stop ventilation, disconnect oxygen and remove endotracheal tube. Place oral airway and ventilate with anesthesia mask. Perform rigid bronchoscopy to remove large foreign bodies, and lavage to trachea. Fibreoptic bronchoscopy to visualize small airways, remove small foreign bodies and lavage to distal airways.Evaluate injury to laryngo-tracheobronchial tree. Remove fragmented mucosa and debris. If necessary, perform a low tracheostomy.
Administer antibiotics and short term steroids. Provide a high humidity environment and positive end expiratory pressure ventilation, where necessary ,keep the patient in reverse isolation. Culture tracheal aspirate daily. Perform endoscopy 3-5 days post burn to evaluate extent of injury. In anterior lesions of the tongue and around the lips, a nasotracheal tube is used, with moist gauze packs in the mouth. Other lesions in the mouth and pharynx require a laser proof tracheal tube. a laryngotracheal tear may result in pneumomediastinum.
Reflection of the beam from a mirror-like surface alters the direction of the beam without
changing its properties. Thus the whole power of the beam is directed to an unintended area.
Because carbon dioxide laser beams are absorbed within the first 200 urn of tissue, they are a hazard to the cornea. Corneal damage is prevented by insisting that all operating room personnel wear safety spectacles appropriate for the laser in use. The patient’s eyes are protected by keeping the eyelids closed and covered with eyepads.When lasers are in use, conspicuous notices to this effect should be placed outside each entrance of the theatre.
Laser energy increases the temperature of intracellular water to boiling point instantly, causing rupture of the cell membrane and release of steam. Cell debris carbonizes and burns with a
flare and smoke is produced. Application of suction close to the oral cavity or point of smoke production reduces alveolar pollution as well as the concentration of anesthetic vapors. Pollution of the operating room environment with anesthetic vapors and smoke can be minimized by using smoke evacuators.