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Table 1 Prerequisites for performing a difficult intubation

Anesthetic protocols appropriate for sedation for fiber-optic tracheal intubation must always avoid respiratory depression. We use very light conscious sedation by titration of midazolam and alfentanil upon request to maintain the patient both conscious and co-operative. This has provided good results. In awake patients, fiber-optic intubation maintains a wide margin of safety while producing minimal patient discomfort. However, adequate local anesthesia of the nasopharyngeal and laryngeal mucosa is required. This is initiated with a spray of 10 per cent lidocaine (lignocaine), followed by a 10 per cent viscous solution of cocaine for the nasal mucosa by topical application to the anterior ethmoidal nerve and the sensory nerves of the posterior nasal cavity as they emerge from the sphenopalatine ganglion. The cocaine solution is soaked into cotton-tipped applicators that are held in position for 5 to 10 min. The internal branch of the superior laryngeal nerve is blocked by the external approach or by direct application of 1 per cent lidocaine sprayed through the vocal cords by the fiber-optic device. Intimate familiarity with the fiber-optic bronchoscope and the anatomy of the upper airway is essential. The main cause of failure of intubation is lack of expertise in maneuvering the fiberscope.

A more challenging situation occurs when the difficult airway is confronted unexpectedly. When a difficult airway is not recognized and anesthesia is induced, the airway will usually first be controlled by mask ventilation prior to conventional laryngoscopy. If conventional laryngoscopy fails, help should be summoned and the airway controlled by mask ventilation. If endotracheal intubation by conventional laryngoscopy is still unsuccessful after further attempts (perhaps using a different blade or head position) and special alternative techniques fail, the patient should either be awakened, and a laryngeal mask inserted (if an emergency), or a semielective surgical airway (cricothyroidotomy) should be performed. If, at any point, mask ventilation and/or laryngeal mask ventilation prove impossible and the patient still cannot be intubated, transtracheal jet ventilation (Manujet) through a percutaneous intravenous catheter or a transtracheal catheter (acc Ravussin, VBM Medizintechnik GmbH, Germany) should be initiated. Once life-sustaining gas exchange is achieved by transtracheal jet ventilation, the patient should either be awakened, and a semielective tracheostomy or cricothyroidotomy performed, or intubated with a special endotracheal tube intubation technique. Retrograde intubation, a technique consisting of intubation of the trachea over a wire or cannula that has been placed percutaneously through the cricothyroid membrane and threaded up through the vocal cords, remains a viable alternative in this situation.

Complications of intubation include trauma to the tissues of the oronasopharynx and larynx; this can be avoided by proper care and expertise. Prolonged contact of the tube or its cuff with the airway mucosa can produce, sequentially, edema, ulceration, fibrous scarring, and stenotic lesions of the larynx, or trachea.

Endotracheal intubation is frequently used as the initial method of securing a patient's airway in anesthesia and critical care. Respiratory catastrophes are the most common cause of anesthesia-related brain injury and death. Therefore all staff undertaking patient intubations must be adequately trained in both the recognition of difficult intubation and the application of accepted algorithms for management of the compromised airway.

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