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Additional recommended knowledge
General anaesthesia (unconsciousness) is required for many surgical procedures. However, in addition to effecting the brain by removing awareness, general anaesthesia has a profound impact on other systems of the body, such as the respiratory and cardiovascular systems. It can be difficult or impossible to separate the desired action of anaesthesia on the neurological system, from the less-desirable side effects that are caused to the breathing and circulation.
The impact of anaesthesia on breathing (respiration) is profound. Under normal circumstances the patients’ breathing may reduce or stop entirely. In addition the airway (the nose, mouth and throat) may become blocked, usually due to the tongue relaxing backward and obstructing the air passages (colloquially known as ‘swallowing your tongue’). This situation must be promptly corrected by the anaesthesiologist, or else the patient will become deprived of oxygen and severe harm may result. This correction is usually accomplished by conventional intubation, followed by artificial breathing (mechanical ventilation).
However, if it proves difficult or impossible for the anaesthesiologist to correctly place the endo-tracheal tube, and anaesthesia has already abolished the patients’ normal breathing, then a crisis may develop where the patient is becoming deprived of oxygen, and the anaesthesiologist is unable to remedy the problem. In the worst-case scenario, death or brain damage may occur within a few minutes.
Difficulty in placing the endo-tracheal tube is more likely in patients with an abnormal airway, such as an inability to open the mouth or move the upper spine, patients with tumours or swelling within the throat, the overweight, or those with relatively short jawbone or large neck.
In these patients who are at high risk of difficulty occurring, it is sensible to avoid administering a general anaesthetic and precipitating a crisis. The alternate approach is to insert the endo-tracheal tube before the general anaesthetic, so that normal breathing continues until success in tube placement has been achieved. Then general anaesthesia can be administered with the knowledge that maintenance of the open airway is guaranteed.
Unfortunately, it is impossible for the awake patient to tolerate the insertion of the curved metal plate of the laryngoscope into the throat and the insertion of the endo-tracheal tube into the larynx without severe coughing, gagging and distress to be caused.
Therefore, the technique of fibre-optic intubation is used to overcome these problems. First, the patient is sedated, so that distress and explicit memory is reduced, and tolerance is improved. Then local anaesthesia is applied to the airway and throat, so that the surfaces become numb, gagging is reduced, and tolerance is further increased. Then an endoscope is introduced through the nose or mouth, which contains fibre-optic glass threads to enable the anaesthesiologist to ‘see around corners’. With this, the anaesthesiologist can navigate through the patients nose, throat and voice box and into the trachea by actually seeing and finding a clear path through these structures. If the endo-tracheal tube has been placed around the endoscope prior to commencing the procedure, then once the trachea is visualised, the tube can be made to follow into the correct position. The tube following the endoscope into position is analogous to a train following railway tracks, and is therefore referred to as ‘railroading’.
Once the endo-tracheal tube is in it’s correct position, then general anaesthesia and surgery can proceed as normal.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Fiberoptic_intubation". A list of authors is available in Wikipedia.