The distal end also has an inflatable balloon to seal the trachea and prevent the escape of ventilating gases and inhalation of gastric and upper airway secretions. This is connected by a pilot tube which runs within the substance of the tube towards the proximal end where it emerges into an inflatable balloon. The balloon has a one-way valve to allow inflation of the cuff by an air-filled syringe; the inflation of the balloon indicates the state of inflation of the cuff. When cuffs are inflated, this should be to the minimum volume that prevents escape of ventilating gases.
Endotracheal tubes have either high-pressure low-volume cuffs, which are used in anesthesia for short-term intubations, or low-pressure high-volume cuffs, which should be used when intubation is likely to be prolonged. This decreases the likelihood of pressure necrosis of the tracheal mucosa and subsequent tracheal stenosis. Intracuff pressures of 17 to 23 mmHg should prevent gas leak and cause little disturbance to tracheal mucosal blood flow. The pressure can be checked and modified if necessary throughout the patient's period of intubation.
Several other types of tracheal tubes are available and have specific indications in anesthesia ( Fig 1).
Fig. 1 (1) Standard PVC endotracheal tube (unmodified length) with a 15-mm male connector. (2) Armored tube. Note the wire spiral within the substance of the tube. The length should not be modified. (3) Double-lumen bronchocath. The double catheter mount is provided. (4) Nasal or 'north facing' RAE. (5) Laryngeal mask. (6) Standard RAE tube.
1. The original Ring-Adair-Elwin (RAE) tube is a C-shaped preformed PVC oral tube which is used when it is desirable to have ventilating circuit attachments away from the face, as in otolaryngological and maxillofacial procedures.
2. The nasal RAE or 'north-facing' tube is used for nasotracheal intubation; the proximal end is preformed to curve up towards the forehead to allow unimpeded surgical access to the mouth and lower face.
3. Latex rubber tubes which are reinforced with a wire spiral and are longer than normal are used when the patient is operated on in positions other than supine to allow access to the connection and to prevent kinking of the tube.
4. Double-lumen tubes are used when surgery is contemplated in one hemithorax. They allow the deflation of one lung to improve surgical accessor to facilitate differential lung ventilation. The main lumen still remains tracheal with a cuff proximal to it, but an extension intubates either the left or right main bronchus, again with a proximal cuff of its own which allows isolated ventilation of that lung. If possible, the positionshould be checked with a fiber-optic laryngoscope. All plastic tubes soften when left in situ and thus are prone to movement; therefore their location should be checked after each change of patient position or at regular intervals. These tubes are still commonly of the red rubber variety and there are several different types.
a. The Carlens tube is a left-sided endobronchial lumen tube with a hook at the bifurcation to catch on to the carina to aid placement. However, this may make it more difficult to pass through the larynx.
b. The White tube, which is used for right main bronchus intubation, has an aperture in the bronchial cuff to allow ventilation of the right upper lobe and a carinal hook.
c. The Robertshaw tube is available in both right- and left-sided versions with bronchial extensions at different angles allowing for anatomical differences. As there is no carinal hook, it is easier to pass through the larynx, when there is intubating difficulty, than the other types. Newer PVC versions called bronchocaths, which are based on Robertshaw tubes, are also available.
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