Endotracheal intubation is the placement of a tube that extends from the oral cavity into the trachea. It is indicated for
the administration of oxygen and inhalation anesthesia, to ensure a patent airway in unconscious patients, to provide ventilatory
assistance, and to provide a conduit into the trachea to permit diagnostic and therapeutic measures (e.g. endoscopy, tracheal
wash, direct instillation of medications). Intubation provides better airway control than a face mask and minimizes the risk
of aspiration of foreign materials. This is especially important for complex and prolonged procedures, when complications
such as respiratory obstruction and hypoventilation are more likely to occur.
Intubation methods
Blind intubation
By properly positioning the head and neck, the pathway from the oropharynx to the trachea is straightened so that an endotracheal
tube can be placed without direct visualization of the larynx. This is possible with the aid of laryngeal palpation, patient
response (i.e. coughing, gagging), and listening for patient respiration through the endotracheal tube itself. Under special
circumstances, a tube may need to be inserted using a transtracheally-placed catheter as a guide.
Direct visualization
Visualization of the larynx is aided by hyperextension of the head and neck. Usually an assistant must open the mouth an oral
speculum or gauze placed around the upper and lower incisors. A small-bladed (e.g. Miller 0 neonatal) laryngoscope is used
to depress the tongue and elevate the soft palate. Once the vocal folds are visualized, the tube is placed. An atraumatic
stylet (polypropylene catheter) can be placed through the tube so its tip extends beyond the end of the endotracheal tube
in order to guide the tube through the vocal folds.
A canine otoscope can be used instead of a laryngoscope in smaller patients. After adequate visualization is achieved, a 5-fr
polypropylene urinary catheter is guided down the otoscope between the vocal folds and advanced into the trachea. At this
point, the otoscope is removed and the tracheal tube is threaded over the catheter and into the larynx. The catheter guide
is then removed.
Direct visualization of the trachea can also be achieved using an endoscope. The endoscope is positioned so the larynx is
in view, and an endotracheal tube is passed parallel to the scope and into the trachea. Further, with some scopes it is possible
to put the endoscope directly inside the endotracheal tube like a stylet, and to visually guide the scope/tube assembly into
the trachea.
Comments on individual species
Ferrets
Direct placement of an endotracheal tube in ferrets usually requires two people. Over-the-endoscope intubation of ferrets
simplifies intubation because it does not require the jaws to be opened wide or the tongue to be pulled forward. The endoscope/tube
combination is rigid enough force the tongue forward at its base, exposing the glottis. The tube and scope are advanced over
the epiglottis and into the trachea. Either a 2 mm Cole or 2.5 mm straight endotracheal tube is recommended with this technique.
