الفهرس 
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Abstract
SUMMARY
The term ”laser” is derived from the process of light amplification by stimulated Emission of radiation. Such a process of stimulated emission follows the transfer of elec-trons of a source material to a higher energy level. Follow-ing the arrangement of the electrons the atoms are said to be in the excited state. As the electrons return to their normal energy level, a photon is released which then bombards other excited atoms and causes more photons to be released. This is called stimulated emission. If the source material can cause stimulated emission, if reflective loses are kept to a minimum, and if the stimulated emissions are increased in number by means of special reflective mirrors at each end of the material, a powerful beam of coherent light can be produced. This beam can be allowed to escape through a partially reflective mirror at one end of the source material, and then focused, aimed calibrated, and controlled as a useful surgical tool.
There are many types of lasers in medical use which include, carbon-dioxide laser, its wavelength is 10.6 microns in the far infrared spectrum; the argon laser, which is a continuous wave laser operating at frequencies between
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0.48-0,515 microns in the invisible blue-green spectrum of light; the neodymium-Yttrium-aluminium-garnet laser which
operates at 1.06 microns in the infrared spectrum and the ruby laser which operates at a wavelength of 0.605 microns
in the region of the invisible spectrum. The use of laser energy in surgery carry several hazards such as, hazards re-lated to the endotracheal tube, hazards related to the pati-ent, or hazards on the operating room personnel.
Those related to the tube include, burns, which can occur as a result of ignition of the endotracheal tubes by the laser beam, tissue trauma, tissue reaction or aspiration
of blood.
To avoid such hazards, the endotracheal tube was wrapped with aluminium foil to prevent its ignition. The use of non combustible tubes such as Norton and Porch tubes can also minimize these hazards.
Laser beam when poorly aimed can damage normal tissue. The hazards to the operating room personnel (0.R) are related to the very high intensity of the typical laser beam. There are significant safety considerations in their
use. The eye being the most susceptible tissue to be injured by laser radiation. All personnel in the operating room must wear safety glasses appropriate to the laser in use.
The application of laser energy in surgery includes mainly the carbon-dioxide, neodymium-YAG and the argon lasers. The other lasers are less frequently used and are mainly used in the field of ophthalmology. The commonest fields in which laser energy is employed include, dermatology, plastic surgery, gastroenterology, general sur-gery, gynaecology, neurosurgery, ophthalmology and laryngeal surgery. The anaesthetic management of a patient undergoing laser surgery of the larynx should include the following :-
1- Preoperative evaluation.
A general medical assessment is always necessary. In addition, in patients with airway lesions, the degree of obstruction and adequacy of ventilation must be carefully assessed.
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2-Premedication.
Atropine of scopalamine can be used prevent the vagal
stimuli and their effects on the cardiac system. Although
glycopyrolate is an excellent drying agent which does not produce as much tachycardia as atropine, yet this later remain the drug of choice.
3-Choice of anaesthetic.
The main consideration in the choice of anaesthesia is the evidence related to falmmability of the agent and the general consideration of the patient. There is a great necessity for the elimination of nitrous oxide and high con-centration of oxygen from the inspired mixture because of the risk of airway fire.
4-Induction of anaesthesia
The main concern is to secure the airway. Once the airway is established either by endotracheal intubation or by bronchoscopic ventilation, the patient can be maintained with intravenous or volatile agents.
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5- Choice of anaesthetic technique. There are three main techniques : A) No tube in the airway.
Following induction and topical anaesthesia of the larynx, maintenance of anaesthesia is accomplished by insuf-flation of nitrous oxide-oxygen mixture with a potent non flammable anaesthetic via nasal catheter.
B3 Wrapping of the external surface of the endotracheal tube with aluminium foil to protect it from ignition if striked by the laser beam.
C.) The use of bronchoscopic manual jet ventilation or high frequency jet ventilation.
6- Muscle relaxation.
For short procedures continuous infusion of succinyl choline can be used. For long procedures, non depolarizing muscle relaxant can be used. However, succinyl choline remains the relaxant of choice due to its evanescent action.
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7-Monitoring.
The patient is monitored as usual fl keeping in mind the risk of inadequate ventilation.
8-Postoperative considerations.
The patient is extubated in the O.R. whenever possibel. Early postoperative laryngeal oedema can occur can be reduced by humidified oxygen and the administration of corticosteroid.