Orotracheal intubation

Orotracheal intubation

1. Indications. Endotracheal intubation is required to provide a patent airway when patients are at risk for aspiration, when airway maintenance by mask is difficult, and for prolonged controlled ventilation. Intubation also may be required for specific surgical procedures (eg, head/neck, intrathoracic, or intra-abdominal procedures).
2. Technique. Intubation is usually performed with a laryngoscope. The Macintosh and Miller blades are most commonly used.
   1. The Macintosh blade is curved and the tip is inserted into the vallecula (the space between the base of the tongue and the pharyngeal surface of the epiglottis) (Figure 13.7A). It provides a good view of the oropharynx and hypopharynx, thus allowing more room for passage of the ETT with decreased trauma to the epiglottis. Blade sizes are designated as no. 1 through 4, with most adults requiring a Macintosh no. 3 blade.
      

      Figure 13.7 Anatomic relations for laryngoscopy and endotracheal intubation.

      A,Curved blade placement.

      B,Straight blade placement.

      C,Glottic exposure with curved blade placement.

   2. The Miller blade is straight and it is passed so that the tip lies beneath the laryngeal surface of the epiglottis (Figure 13.7B). The epiglottis is then lifted to expose the vocal cords. The Miller blade provides excellent exposure of the glottic opening but provides a smaller passageway through the oropharynx and hypopharynx. Sizes are designated as no. 0 through 4, with most adults requiring a Miller no. 2 or 3 blade.
   3. Various modified laryngoscope blades provide better visualization of the cords through epiglottis lifting (eg, McCoy) or indirect visualization of the cords (eg, Siker and Truview EVO).
   4. The sniffing position with the occiput elevated by pads or folded blankets and the neck extended is the classic intubation position. On average, this improves the laryngoscopic view, although intubation and mouth opening may be facilitated in some patients by simple neck extension. Neck flexion may make it more difficult to open the mouth.
   5. The laryngoscope is held in the left hand near the junction between the handle and blade. After propping the mouth open with a scissoring motion of the right thumb and index finger, the laryngoscope is inserted into the right side of the patient’s mouth while sweeping the tongue to the left. The lips should not be pinched by the blade and the teeth should be avoided. The blade is then advanced toward the midline until the epiglottis comes into view. The tongue and pharyngeal soft tissues are then lifted to expose the glottic opening. The laryngoscope should be used to lift (see Figure 13.7B) rather than act as a lever (see Figure 13.7A) to prevent damage to the maxillary incisors or gingiva.
   6. An alternative to the classic sniffing position, the so-called flexion-flexion position, may be trialed if an appropriate glottic view cannot be obtained using conventional positioning. This technique involves first inserting the laryngoscope blade into the mouth as describe above. The head is then lifted, either using the anesthetist’s right hand or the help of an assistant, and supported by the anesthetist’s abdomen such that there is flexion both at the lower cervical level and at the atlantoaxial joint. The laryngoscope blade is then lifted such that the vector of force applied runs parallel to the body of the patient.
   7. An appropriate ETT size depends on the patient’s age, body habitus, and type of surgery. A 7.0-mm ETT is used for most women, and a 7.5-mm ETT is used for most men. The ETT is held in the right hand as one would hold a pencil and advanced through the oral cavity from the right corner of the mouth and then through the vocal cords. The anatomic view for visualization with a Macintosh laryngoscope is shown in Figure 13.7C. If visualization of the glottic opening is incomplete, it may be necessary to use the epiglottis as a landmark, passing the ETT immediately beneath it and into the trachea. External downward pressure on the cricoid and/or thyroid cartilage may aid in visualization. The proximal end of the ETT cuff is placed just below the vocal cords, and the markings on the tube are noted in relation to the patient’s incisors or lips. The cuff is inflated just to the point of obtaining a seal in the presence of 20 to 30 cmH₂O positive airway pressure. Description of the visualization of the glottic opening should be recorded using the Cormack-Lehane scoring system (Figure 13.8).
      

      Figure 13.8 Cormack-Lehane grade for view on direct laryngoscopy.

      Grade 1:Full view of glottis.

      Grade 2:Partial view of glottis.

      Grade 3:Only epiglottis seen.

      Grade 4:Unable to visualize the glottis and epiglottis.

      (Reproduced with permission from Orebaugh S, Snyder JV. Direct laryngoscopy and endotracheal intubation in adults. In: Post TW, ed. UpToDate. UpToDate. Accessed May 12, 2020. Copyright © 2020 UpToDate, Inc. For more information visit www.uptodate.com.)

   8. Proper placement of the ETT must be verified by the detection of carbon dioxide in end-tidal or mixed expiratory gas as well as inspection and auscultation of the stomach and both lung fields during positive-pressure ventilation. If an ETT is inserted too deeply, it usually passes into the right mainstem bronchus. When breath sounds are heard on only one side of the thorax, an endobronchial intubation should be suspected, and the ETT should be withdrawn until breath sounds are heard bilaterally. (In trauma patients, unilateral breath sounds may be indicative of a pneumothorax.) Listening for breath sounds high in each axilla may decrease the chances of being misled by transmitted breath sounds from the opposite lung. A high index of suspicion of an esophageal intubation should be maintained until adequate oxygenation and ventilation are ensured.
   9. The ETT should be fastened securely with tape, preferably to taut the skin overlying bony structures.
3. Complications of orotracheal intubation include injury of the lips or tongue, teeth, pharynx, or tracheal mucosa. Though rare, avulsion of arytenoid cartilages or damage to vocal cords or trachea can occur. High pressures in the cuff of the ETT can lead to ischemia of the tracheal mucosal. Ideally, the cuff pressure, measured with a manometer at the cuff inflation valve, should be between 20 and 30 cm of H₂O.