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INTRODUCTION
Fiberoptic endotracheal intubation is a useful technique in a number of situations. It can be used when the patient's neck cannot be manipulated, as when the cervical spine is not stable. It can also be used when it is not possible to visualize the vocal cords because a straight line view cannot be established from the mouth to the larynx. Fiberoptic intubation can be performed either awake or under general anesthesia and it can be performed either as the initial management of a patient known to have a difficult airway, or as a backup technique after direct laryngoscopy has been unsuccessful.
As with all other procedures, the keys to the success of this technique involve adequate planning and patient preparation. This brief guide reviews the important points in the preparation for, and performance of, a fiberoptic guided intubation.
While the sniffing position is required for most direct laryngoscopies, it is not essential for fiberoptic guided intubation. The chin lift and jaw thrust maneuvers, and protrusion of the tongue, move the soft tissues and improve the view through the fiberscope. These maneuvers also help to prevent airway obstruction in the sedated patient.
Most anesthesiologists prefer to stand at the head of the patient, as they do for direct laryngoscopy. The advantage of this position is that anatomical structures are visualized as most anesthesiologists are accustomed to seeing them. Alternatively, the operator can stand in front of the patient, as do most otolaryngologists.
Fiberoptic bronchoscopy requires a clear visual pathway. Blood and secretions prevent visualation of the laryngeal structures. Administration of an antisialogogue prior to the start of the procedure is therefore essential. In the average adult patient, 0.2 mg of glycopyrrolate given intramuscularly one hour prior to bronchoscopy is satisfactory. If the patient arrives with no premedication, the glycopyrrolate should be given as soon as possible.
Repeated airway manipulation causes edema and bleeding, both of which impair visualation through the bronchoscope. The possibility of a fiberoptic technique should therefore be kept in mind, and employed before blood and secretions have rendered this technique unusable.
The goal of sedation is to produce a cooperative patient, not an apneic patient! Sedation should be administered incrementally, and titrated to drowsiness or slurred speech. Drugs that may be used include fentanyl, midazolam, propofol, and droperidol. Each drug has advantages and disadvantages.
Fentanyl or other narcotics reduce the discomfort and hemodynamic changes associated with topical anesthesia of the airway, nerve blocks, and airway instrumentation. Narcotics also decrease respiratory drive and may cause hypercarbia and apnea. This effect can be reversed with small, incremental doses of naloxone. However, hypoventilation is best avoided by incremental titration of sedatives and narcotics, and waiting for the full effect before giving the next dose.
Proper airway anesthesia is essential to a successful fiberoptic intubation. If the patient is not at risk for aspiration, the entire airway, from mouth (or nose) to carina should be anesthetized. If the patient has a full stomach, however, the risk of aspiration of gastric contents may be greater if the patient has lost his protective reflexes. Although one study suggests that complete airway anesthesia is safe in the patient at risk for aspiration, it would be prudent to weigh the relatively small risk of aspiration against the consequences of coughing or hypertension and tachycardia in response to intubation. In addition, topical anesthesia of the airway increases patient comfort, decreases the response to intubation, and increases the probability of success.
The patient's nasal passages should be treated with a topical vasoconstrictor to shrink the nasal mucosa. This makes the endotracheal tube easier to pass and minimizes the risk of bleeding. The nasal mucosa can be anesthetized and vasoconstricted with either a mixture of lidocaine and phenylephrine (1 cc phenylephrine 1% in 3 cc lidocaine 4% provides anesthesia and vasoconstriction with minimal hemodynamic effects) or a four percent solution of cocaine. Cocaine is an excellent topical anesthetic and vasoconstrictor, but is a controlled substance and is therefore more difficult to handle.
The topical anesthetic / vasoconstrictor solution is applied with pledgets or cotton-tipped applicators. The applicators are gently inserted into each nostril and gently advanced until they reach the posterior wall of the nasopharynx. Alternatively, the solution can be dripped in using a 20 gauge intravenous catheter or sprayed using an atomizer. It is advisable to prepare both nares.
After topical anesthesia and vasoconstriction have been achieved, the next step in preparing the nose is progressive dilation of both nares with nasal airways that have been well-lubricated with lidocaine jelly.
The mouth can be anesthetized with lidocaine spray or viscous lidocaine. A commercial, flavored preparation of a ten percent solution of lidocaine is available. This preparation is sold in pressurized bottles that deliver a metered spray. Alternatively, a four percent solution of lidocaine can be sprayed in the mouth with an atomizer. If an atomizer is used, it is sometimes possible to remove the bulb and replace it with oxygen tubing that is connected to an oxygen source. This provides a continuous spray. After the tongue and oropharynx have been sprayed, the patient should be given viscous lidocaine to "swish and swallow." Alternatively, the entire airway can be anesthetized by placing five cc of a four percent lidocaine solution into a nebulizer and instructing the patient to breathe deeply.
(Video
Courtesy of S Deluty, MD)
The transtracheal block provides rapid anesthesia of the entire trachea between the carina and the vocal cords. It is relatively simple to perform, and requires no equipment other than a ten cc syringe and 23 gauge needle. Complications of the transtracheal block include bleeding, tracheal injury, and subcutaneous emphysema.
The transtracheal block should be performed approximately one minute prior to the start of the bronchoscopy. Three cc of lidocaine 2% are drawn into a ten cc syringe with a 23 gauge needle. The cricothyroid membrane is identified, and the syringe is directed posteriorly, perpendicular to the floor. The needle is in the trachea when a sudden loss of resistance is felt. The position of the needle is confirmed by aspirating air through the syringe. The lidocaine is then injected rapidly, and the needle withdrawn. The patient will cough, drawing the local anesthetic down to the carina, and then spraying it over the entire trachea, up to the vocal cords.
(Video
Courtesy of Francis Kors, MD and Robert Karpinos, MD)
The superior laryngeal nerve, a branch of the vagus nerve, provides sensory innervation to the epiglottis, arytenoids, and vocal cords. It can be blocked as it passes into the larynx through the thyrohyoid membrane. The skin of the neck is retracted caudad over the thyroid cartilage. A syringe containing 2.5 cc lidocaine 1% and fitted with a 23 gauge needle is used. The needle is inserted until it rests on the lateral portion of the hyoid bone. It is then withdrawn slightly and walked off the hyoid bone in an inferior direction. The needle is then advanced and passed through the thyrohyoid membrane, which should be felt as a slight resistance. The syringe is then aspirated, and the lidocaine is injected. The procedure should be repeated on the opposite side.
If the patient is to be nasally intubated, a small endotracheal tube (7 mm for a normal adult) should be used. Prior to insertion, the tube should be softened by soaking in warm saline, and well-lubricated with lidocaine jelly. The endotracheal tube is gently inserted into either nare after satisfactory anesthesia and vasoconstriction have been accomplished. The tube should be inserted until the cuff just disappears.
If an oral intubation is planned, an endotracheal tube should be threaded through an oral intubating airway (e.g. Ovassapian, Williams, or Berman airway). The airway is then lubricated with lidocaine jelly and gently placed in the patient's mouth.
The head of the fiberscope is held in the right hand, with the right thumb on the control lever. The left hand holds the insertion cord. Prior to inserting the bronchoscope, the proper function of the control lever should be verified by moving it and observing the tip of the bronchoscope. The fiberscope should then be gently inserted into the endotracheal tube. It is crucial to keep the bronchoscope taut between the left and right hands so that the orientation of the tip is the same as that of the control lever.
The fiberoptic bronchoscope is advanced until the tip passes out of the endotracheal tube. It is then advanced until the vocal cords are seen. The patient is then asked to take a deep breath and the bronchoscope is passed through the cords. If this precipitates coughing, additional lidocaine can be sprayed through the working channel of the bronchoscope.
After passing through the vocal cords the fiberscope is advanced until the tracheal rings come into view. The carina should be easily identifiable in the distance.
When the tip of the fiberscope is at the carina, the next step is to pass the endotracheal tube. At this point, the fiberscope is no longer a visualization device; it is now a guide for the endotracheal tube. The attention of the operator should now be directed towards the endotracheal tube. As the patient takes a deep breath, the tube is passed into the trachea.
(Video
Courtesy of D. John Doyle, MD)
If the fiberscope passes through the vocal cords, but the endotracheal tube does not pass, the tube may be getting caught on the arytenoid cartilages. Rotating the endotracheal tube ninety degrees counterclockwise directs the tip into the trachea.