Flexible scope intubation for anesthesia

INTRODUCTION — 

The flexible bronchoscope is a device that can be used for indirect laryngoscopy for endotracheal intubation, and it is particularly useful when direct laryngoscopy is difficult or impossible or would be dangerous to perform. For endotracheal intubation prior to induction of general anesthesia, flexible bronchoscopy is better tolerated than direct or video-assisted laryngoscopy.

This topic will discuss the equipment and techniques used for flexible bronchoscopic intubation. Retrograde intubation using a percutaneous wire will also be discussed.

While the term "flexible fiberoptic intubation" has been used for this technique in anesthesia, newer bronchoscopes no longer use fiberoptic technology. Therefore, this topic will use the terms "flexible scope intubation" (FSI) for the technique and "flexible intubation scope" (FIS) for the device.

Other airway devices, techniques for endotracheal intubation, and management of the difficult airway for anesthesia are discussed separately.

●(See "Management of the anatomically difficult airway for general anesthesia in adults".)

●(See "Airway management for general anesthesia in adults".)

●(See "Supraglottic airways (SGAs) for airway management for anesthesia in adults".)

●(See "Direct laryngoscopy and endotracheal intubation in adults".)

Flexible bronchoscopy for one-lung ventilation is also discussed separately. (See "Intraoperative one-lung ventilation" and "Techniques to achieve lung isolation during general anesthesia".)

INDICATIONS AND ADVANTAGES — 

FSI can be used for patients and clinical settings with impediments to direct laryngoscopy, including the following:

•Limited mouth opening, as the FIS will pass through a narrow oral opening or through the nose

•Abnormal airway anatomy or a mass obstructing direct visualization of the vocal cords

•Unstable cervical spine, such that movement of the spine should be minimized during airway management

•Airway trauma requiring visualization of the larynx and trachea prior to intubation

•Prone or lateral position requiring rescue intubation

CONTRAINDICATIONS AND DISADVANTAGES — 

There are no absolute contraindications to FSI. Clinical situations in which FSI may be difficult or impossible include the following:

•Blood or copious secretions in the airway

•Need to observe passage of the endotracheal tube (ETT) through the vocal cords (eg, vocal cord trauma), since the ETT is passed blindly over the flexible intubation scope (FIS) (can be mitigated by using a combination technique with video-assisted laryngoscopy)

•Need for rapid control of the airway

•Clinician inexperienced with FSI

•Patient unable to cooperate (for awake FSI)

AWAKE VERSUS ASLEEP INTUBATION — 

FSI may be performed before or after the induction of general anesthesia. Indications for awake intubation include anticipated difficult airway management and the need for a postintubation neurologic exam (eg, unstable cervical spine) (algorithm 1 and figure 1). (See "Management of the anatomically difficult airway for general anesthesia in adults", section on 'Awake intubation'.)

FSI is more difficult to perform under general anesthesia than in the awake patient, as the loss of pharyngeal muscle tone leads to upper airway collapse and limited visualization with a flexible intubation scope [1].

ORAL VERSUS NASAL INTUBATION — 

Most FSIs are performed using the oral route. In the patient under general anesthesia, the use of a supraglottic airway (SGA) as an FSI conduit has become more common as many newer SGAs are designed to facilitate intubation with a standard-sized endotracheal tube (ETT). This technique can be used either as a primary airway plan or as a method of exchanging an SGA for an ETT, such as when an SGA is used for airway rescue in a difficult airway scenario. (See 'Intubation through a supraglottic airway' below and 'Aintree catheter-aided intubation through a supraglottic airway' below.)

The nasal route may be preferred for the patient with a severely limited mouth opening or if a nasotracheal intubation is necessary for the surgical procedure. Nasal intubation may be better tolerated than oral intubation by the awake patient with a strong gag reflex. In addition, a laryngeal view is often easier to obtain using the nasal approach because the flexible intubation scope (FIS) tends to remain in the midline, with the tip directed at the glottis as it enters the oropharynx.

The risks of nasal intubation include epistaxis, trauma to the nasal turbinates, and submucosal tunneling in the nasopharynx. Preparation of the nasopharynx is necessary prior to the procedure to minimize the chance of bleeding. (See 'Nasal preparation' below.)

EQUIPMENT — 

An assortment of equipment is required for FSI, including the flexible intubation scope (FIS), bite blocks or specialized oral airways, adaptors for ventilation, endoscopy facemasks, antifogging and lubricating agents, equipment for topicalization, and a video monitor. In addition, supraglottic devices designed to facilitate endotracheal intubation can be used along with flexible scopes and may be included with routinely stocked equipment. Equipment for FSI is often kept on a cart that is transported to the intubating location.

Flexible intubation scope — The FIS is used to locate the vocal cords and acts as a stylet for the endotracheal tube (ETT) once the FIS is placed into the trachea.

The FIS consists of a flexible insertion cord that contains either optical fibers or a small camera and a light source at the tip, used to transmit images to an eyepiece or camera head (figure 2 and figure 3). The cord includes a working channel for suction or administration of oxygen or local anesthetic and a cable that allows the operator to flex the tip of the scope. The cord attaches to a handle with a control lever for flexion/extension of the tip, a working channel port, and either an intrinsic video monitor or a connection to an external monitor.

The FIS is available in various sizes. Bronchoscopes used for intubation need to be narrow enough to fit through an appropriately sized ETT and long enough for the tip to pass beyond the larynx (including the length of the ETT threaded over the shaft):

●Adults – Adult intubating bronchoscopes are typically 60 cm in length, with a diameter of 3.8 to 4.2 mm. Adult scopes fit through a 5.5 mm internal diameter (ID) ETT if adequately lubricated, and they have a working channel 1.2 to 2 mm in diameter.

●Children – Pediatric scopes have diameters of 2.2 (accommodated by a 3 mm ID ETT, with no working channel) to 3.1 mm (accommodated by a 4 mm ID ETT, with a working channel 1.2 mm in diameter).

FISs are often reusable, but disposable single-use flexible videoscopes are increasingly used [2,3]. The cost-effectiveness of single-use FISs compared to reusable versions depends on local factors, such as number of uses as well as capital and maintenance costs [4]; an accounting of the cost of treatment of infections favors the use of single-use devices [5].

Oral airway — Specialized oral airways for FSI are designed to keep the scope in the midline and to act as a bite block for awake oral FSI. Flexible scopes are delicate instruments; a bite block is used to prevent damage to the scope if the patient bites down on it.

There are several types of oral airways for FSI (eg, Ovassapian, Berman, and Williams) (picture 1). The shape is like that of a standard oropharyngeal airway used to maintain an open airway for spontaneous or mask ventilation in deeply sedated or anesthetized patients. Because it rests on the base of the tongue and the posterior pharynx, placement of an oral airway may elicit a gag reflex in conscious patients. Therefore, they are used only in patients with general anesthesia, heavy sedation, or with excellent local anesthetic topicalization of the tongue and pharynx.

Oxygenation equipment — Healthy patients are unlikely to require oxygen administration or ventilation during the brief period required for FSI. However, supplemental oxygen should be administered in patients with decreased physiologic reserve or functional residual capacity (ie, pediatric, pregnant, and patients with obesity), or during difficult FSI, including awake intubation. The use of high-flow nasal oxygen through nasal cannulae or transnasal humidified rapid-insufflation ventilatory exchange (THRIVE) is easy to implement during transoral FSI and should be strongly considered. Oxygen delivery with or without ventilation may also be provided with a standard facemask with a bronchoscopic adapter attached, or with a specialized endoscopy mask constructed with a port for the bronchoscope (picture 2).

Other equipment — We usually have the following additional equipment on hand at the time of flexible bronchoscopy:

●Specialized endotracheal tube – A flexible ETT, the tapered-tip ETT for use with the intubating laryngeal mask airway (LMA Fastrach), or a specialized ETT with a bull-nose tip (Parker Flex-Tip) may facilitate advancement. We usually use a Parker ETT for FSI. (See 'Difficulty advancing the endotracheal tube' below.)

●Supraglottic airway – Many newer supraglottic airways (SGAs) (eg, the Air-Q, Ambu AuraGain, i-gel, and LMA Protector) can accommodate standard-sized ETTs for FSI directly through the device. Other SGAs (eg, the LMA Unique) can be used as a conduit for FSI but will require the use of an exchange technique, such as with the Aintree intubation catheter. (See 'Intubation through a supraglottic airway' below and 'Aintree catheter-aided intubation through a supraglottic airway' below.)

●Antifogging agent – An antifogging agent is applied to the tip of the FIS, or the tip is brought to body temperature in warm saline to minimize condensation. This maintains a clear image on the lens.

●Lubricating agent – A lubricant facilitates passage of the ETT over the FIS. We use water-based lubricants applied shortly before laryngoscopy, keeping in mind that they can become sticky as they dry. Petroleum-based lubricants have traditionally been avoided in the past to minimize damage to the outer coating of the FIS shaft, but this is not a problem with newer scopes. There is a theoretical concern for the development of exogenous lipoid pneumonia with petroleum- or silicone-based lubricants due to the deposition of lipids in the lung, however, the small amounts needed for FSI are likely insufficient to be clinically significant. Lubricant should be kept away from the tip of the FIS because it may obscure the view [1].

●Nasopharyngeal airway – A nasopharyngeal airway may be used as a method of applying lubricating agents or topical anesthetics to prepare the naris for nasal intubation and can help to assess nasal patency. It can also be used to facilitate ventilation during oral intubation in sedated or anesthetized patients.

●Video monitor – Most modern FISs incorporate a video monitor. This provides a clearer view and allows assisting personnel to see the procedure. An external video monitor should be considered when using an older FIS with an eyepiece.

●Airway preparation equipment – Equipment to anesthetize the airway and/or vasoconstrict the nasal mucosa includes atomizing devices, nebulizers, syringes and needles, cotton pledgets, and cotton swabs.

AIRWAY ANATOMY DURING FLEXIBLE SCOPE INTUBATION — 

The airway begins at the nares, the external openings of the nasal passages. The nasal cavity leads to the nasopharynx, followed by the oropharynx, which extends inferiorly to the level of the epiglottis. The hypopharynx begins at the level of the epiglottis and terminates at the level of the cricoid cartilage, where it is continuous with the esophagus (figure 4) [6].

The larynx is a complex structure of cartilage, muscles, and ligaments, which serves as the inlet to the trachea. When viewed from the pharynx, as during flexible bronchoscopy, the larynx begins at the epiglottis (picture 3). The most superior structures within the laryngeal cavity are the false vocal cords. Beneath these are the true vocal cords. The space between the vocal cords is termed the glottis [6].

The trachea begins at the level of the cricoid cartilage and extends to the carina; this length is 10 to 15 cm in the adult (picture 4). At the carina, the trachea bifurcates into the right and left mainstem bronchi (picture 5) [6].

Flexible scope images of the upper airway have posterior structures at the lower part of the image when the operator is standing at the patient's head. When the operator is facing the patient, posterior structures appear at the upper part of the image, rotated 180 degrees.

PATIENT PREPARATION — 

Preparation of the patient for FSI may include administration of antisialagogues; aspiration prophylaxis; topical vasoconstrictors for nasal intubation; and, if awake intubation is planned, local anesthetic topicalization and sedation.

Antisialagogues — Airway-drying agents (antisialagogues) should be administered prior to FSI whether it is performed awake or after induction of general anesthesia. Even tiny amounts of secretions or blood on the optical element can make flexible bronchoscopy difficult or impossible. Secretions can also decrease the efficacy of topical anesthetics. Antisialagogues should be administered at least 15 minutes prior to intubation to achieve optimal effect. We administer glycopyrrolate 0.2 mg intravenously (IV) at least 15 minutes before beginning the procedure.

Aspiration prophylaxis — In the patient at high risk for aspiration (table 1), medication should be administered preoperatively to increase gastric pH and possibly to decrease gastric volume. The choice of these medications is discussed more fully separately. (See "Rapid sequence induction and intubation (RSII) for anesthesia", section on 'Premedication'.)

Our approach to patients at high risk of aspiration who will undergo FSI is as follows:

●For patients at high risk of aspiration because of recent food ingestion, we administer an H₂ receptor antagonist (eg, famotidine 20 mg IV, ideally 40 to 60 minutes prior to induction) and metoclopramide (10 mg IV over one to two minutes).

●For fasted patients who are at high risk of aspiration of acidic gastric secretions (eg, severe gastroesophageal reflux disease [GERD], pregnancy), we administer an H₂ receptor antagonist, metoclopramide, and usually sodium citrate 30 mL by mouth (PO).

●We position patients at high risk of aspiration head-up for induction and intubation.

Issues to consider when planning FSI for patients at risk for aspiration include:

●Additional time to intubation and airway protection with FSI versus direct laryngoscopy or videolaryngoscopic intubation.

●Cricoid pressure may make FSI more difficult.

●Airway topicalization can impair airway reflexes. (See "Awake tracheal intubation", section on 'Aspiration prophylaxis'.)

Positioning — Usually, FSI takes place in the supine, sitting/beach-chair, or lateral decubitus positions, but it has also been described in the prone position as a rescue technique [7-9].

Awake patients should be placed in the sitting or lateral position, which can improve visualization of the glottis compared with the supine position [10]. When performing FSI with the patient in the sitting or beach-chair position, the clinician should stand at the patient's side [1].

Supine positioning is typically used in patients under general anesthesia, with the clinician at the patient's head (picture 6). With this position the laryngeal view through the flexible intubation scope (FIS) is in the same orientation as during direct laryngoscopy, and the patient and clinician are already in the optimal position to perform mask ventilation or other airway maneuvers, if necessary (picture 6).

Nasal preparation — For nasal intubation, a topical vasoconstrictor should be applied to the nasal mucosa to reduce the chance of bleeding with passage of the FIS and endotracheal tube (ETT). Commercially available nasal decongestants containing either oxymetazoline 0.05% or phenylephrine 0.5% may be used to constrict the vessels of the nasal mucosa. We administer two sprays of phenylephrine or oxymetazoline to each nostril for vasoconstriction.

Preparation for awake intubation — When awake intubation is planned, in addition to the preparations already described, the airway must be anesthetized, and the patient may require sedation. Clinical decision-making regarding the need for awake FSI is discussed separately. (See "Management of the anatomically difficult airway for general anesthesia in adults", section on 'Awake intubation'.)

Awake intubation, including preparation, sedation, and airway anesthesia are discussed separately. (See "Awake tracheal intubation".)

EQUIPMENT PREPARATION — 

All equipment should be prepared and working prior to beginning the intubation. Our general approach is to do the following:

●Place the endotracheal tube (ETT) in warm saline prior to the procedure. A warmed, softened ETT will usually pass through the vocal cords more easily than an unprepared tube, and reduces the risk of nasal trauma during nasal intubation.

●Lubricate the shaft of the flexible intubation scope (FIS). (See 'Other equipment' above.)

●Attach oxygen or suction to the suction port, if desired.

●Apply antifogging agent to the tip of the FIS, or prewarm the tip in saline.

●Prepare the FIS. Check the light and optics and confirm the proper view orientation and the direction of tip movement with control-lever movement. The control lever bends the tip up and down, allowing it to follow the curves of the airway; rotation of the entire instrument allows the tip to move left and right.

●Obtain a standing stool in order to allow the operator to hold the bronchoscope straight above the patient's head during insertion, if necessary, because control of the movement of the FIS shaft and tip are more effective when the shaft is straight (picture 6).

TECHNIQUE — 

FSI is usually performed using the oral route.

Oral intubation — The steps for oral FSI are as follows:

●Load the endotracheal tube (ETT) on the flexible intubation scope (FIS) prior to inserting it. Move the ETT up the full length of the shaft of the FIS to the handle to avoid interfering with movement of the scope. We tape the ETT directly to the scope handle using the pilot balloon to keep it from sliding. Newer, disposable FISs typically have a design feature that allows easy connection of the ETT to the device during bronchoscopy.

●If the ETT 15 mm connector is removed prior to placement on the FIS, do not lose or misplace it; we tape it to the breathing circuit.

●Place a bite block or intubating oral airway if desired. When using an intubating oral airway, it is usually easier to place the ETT into the oral airway to a depth of 5 cm prior to inserting the FIS, rather than loading the ETT directly onto the FIS. (See 'Oral airway' above.)

●Suction the oropharynx prior to inserting the FIS.

●Orient the FIS so that the tip can be moved up and down in the midline.

●Insert the FIS (without a bend at the tip) along the midline of the oropharynx. Keep the FIS in the midline while directing it around the base of the tongue to achieve a satisfactory view of the larynx.

●If the tip of the FIS is against the oropharyngeal mucosa (ie, the view is uniformly pink), flex the tip upward and advance the FIS around the base of the tongue until the epiglottis or glottis is seen (picture 3). (See 'Difficulty with the view' below.)

●Use suction or insufflate oxygen as necessary to clear secretions that obscure the view.

●If the patient is not paralyzed, consider spraying local anesthetic (eg, lidocaine 4%, 1 mL) on the vocal cords to decrease reactivity.

●Advance the FIS through the vocal cords (picture 4) to the level of the carina (picture 5).

●Slide the ETT over the FIS. The initial depth for oral intubation should be 22 cm for women and 24 cm for men.

●Visualize the tracheal rings with the FIS in the ETT. Withdraw the FIS from the ETT.

●Connect the ETT to the breathing circuit and confirm placement with capnography and breath sounds in the usual manner. (See "Confirmation of correct endotracheal tube placement in adults".)

Nasal intubation

●Place the ETT in warm saline for several minutes prior to intubation. This is particularly important for nasal intubation, as it softens the ETT, makes it more flexible, and minimizes bleeding caused by trauma to the nasal mucosa.

●Choose the more patent nostril for intubation. This can be determined by manually occluding each nostril separately and asking the patient to inhale through the nose. The patient will usually be able to inhale more easily through one naris. Alternatively, one can use the FIS to visualize the nasal passages or use soft plastic nasopharyngeal airways to gauge patency of the nasal airway.

●Lubricate the ETT with water-based lubricant. Also lubricate the selected naris by passing a nasopharyngeal airway liberally coated with water-based lubricant or 4% lidocaine ointment.

●Suction the oropharynx before inserting the FIS. If secretions obscure the view during the procedure, clear them using suction or oxygen insufflation through the working channel.

●There are two methods for navigating the nasal passage during flexible scope nasal intubation, inserting the ETT in the naris first, followed by inserting the FIS through it, or inserting the FIS, followed by sliding the ETT into the naris over the scope. The authors prefer to insert the ETT first.

Performing nasal endoscopy first ensures that the more favorable route through the nasal passage is taken (beneath the inferior turbinate). This route is associated with less epistaxis and may decrease the incidence of avulsion of a nasal turbinate. The disadvantage of this technique is that one may navigate the FIS through the nasal passage and into the trachea only to find that the nasal passage is insufficient to accommodate the ETT. This problem may be mitigated by making sure it's possible to pass a nasal airway with an outer diameter at least 1 mm larger than the ETT to be placed.

•ETT first:

-Insert the warmed, softened ETT into the naris to a depth of approximately 14 to 15 cm [11], with the bevel facing the lateral wall of the nasal passage. Apply cephalad traction to the proximal end of the ETT against the nostril while advancing it, to encourage the tip to take a more caudad trajectory and increase the odds of passing the ETT below the inferior turbinate, minimizing damage to the turbinates (figure 5).

-Pass the FIS through the ETT. In most cases the larynx will be visible as soon as the tip of the scope exits the ETT.

•FIS first:

-Load the ETT onto the FIS and slide it to the handle, as described for oral intubation above.

-Insert the FIS into the desired naris, navigating the scope along the base of the nasal passage beneath the inferior turbinate.

-Advance the FIS, directing the tip by using the control lever and rotating the entire FIS, advancing or withdrawing the scope until the glottis is visible.

●If the patient is not paralyzed, consider spraying local anesthetic (eg, lidocaine 4%, 1 mL) on the vocal cords to decrease reactivity prior to passing the FIS through the larynx.

●Advance the FIS through the vocal cords to the level of the carina.

●Advance the ETT over the FIS.

●The initial depth of insertion of the ETT for nasal intubation should be 26 cm for women and 28 cm for men [12].

●Visualize tracheal rings with the FIS in the ETT. Withdraw the FIS from the ETT.

●Connect the ETT to the breathing circuit and confirm the position with capnography and breath sounds in the usual manner. (See "Confirmation of correct endotracheal tube placement in adults".)

Intubation through a supraglottic airway — When planning direct FIS-guided intubation through a supraglottic airway (SGA), it is important to ensure that the chosen ETT size will fit through the SGA. SGAs designed for use as a conduit for tracheal intubation usually accept a larger diameter ETT than conventional SGAs. The ETT sizes accommodated by the SGA are often listed on the package and/or directly on the device. The process for intubation through an SGA is as follows:

●Place the SGA and confirm ventilation.

●Remove the 15 mm connector from the ETT and load it onto the FIS. (See 'Oral intubation' above.)

Note: It is important to lubricate the outside of the ETT well so it slides easily through the SGA. If FIS-guided intubation through the SGA is planned before induction of anesthesia, it is helpful to pass the lubricated ETT through the SGA a few times prior to inserting the SGA in the patient's mouth.

●Insert the FIS into the airway shaft of the SGA and visualize the glottis.

●Advance the FIS into the trachea to the level of the carina.

●Slide the ETT over the FIS into proper position with the tip in the mid trachea.

●Remove the FIS, inflate the ETT cuff, reattach the 15 mm connector, and confirm ventilation with capnography and breath sounds in the usual manner. (See "Confirmation of correct endotracheal tube placement in adults".)

After ventilation is confirmed, it is often desirable to remove the SGA while leaving the ETT in place. To remove the SGA:

●Remove the 15 mm connector from the ETT.

●Deflate the ETT cuff to allow the ETT to move deeper as the SGA is removed (to avoid extubation).

●Withdraw the SGA over the ETT while stabilizing the ETT with a Magill forceps, or a small ETT (eg, 6.0 mm internal diameter), or the stabilizing device provided with some intubating SGAs.

●Replace the 15 mm connector on the ETT and confirm ventilation with capnography and breath sounds in the usual manner. (See "Confirmation of correct endotracheal tube placement in adults".)

Aintree catheter-aided intubation through a supraglottic airway — For SGAs that are not designed for direct FIS-guided intubation or are too small to accept the desired ETT, ETT exchange can be facilitated by the use of a FIS and an Aintree intubation catheter. The Aintree intubation catheter is a specially designed, hollow airway exchange catheter that fits over a standard FIS while being short enough to allow the FIS to be maneuvered.

The procedure is as follows:

●Place the SGA and confirm ventilation.

●Lubricate the outside of the Aintree catheter and load it onto the FIS as far as possible. If necessary, tape the catheter to the FIS.

●Insert the FIS into the airway shaft of the SGA and visualize the glottis.

●Advance the FIS into the trachea to the level of the carina.

●Remove the FIS, leaving the Aintree catheter in place in the trachea.

●Remove the SGA, leaving the Aintree catheter in place.

●Load the ETT onto the Aintree catheter and advance the ETT to just outside the patient's mouth.

Note: Exchange of the Aintree catheter for the ETT must be performed very carefully. The Aintree catheter is relatively short and can be displaced out of the trachea if it is withdrawn too far. For ETTs larger than 7.0 mm internal diameter, we either remove the 15 mm connector before the procedure to shorten the overall length of the ETT, or insert a longer airway exchange catheter through the Aintree catheter after removing the FIS.

●Grasp the Aintree catheter near the end of the ETT, and slowly feed it into the ETT just until the proximal end exits the ETT.

●Hold the proximal end of the Aintree catheter while advancing the ETT into the trachea.

●Inflate the ETT cuff and confirm ventilation.

Retrograde intubation — Retrograde intubation is used most commonly in the unstable cervical spine, upper airway malignancy, or mandibular fracture, or when the vocal cords cannot be visualized due to blood, secretions, or anatomic variations. A wire (or catheter) is inserted percutaneously through the cricothyroid membrane and blindly cephalad along the trachea, larynx, pharynx, and out of the mouth or naris; this wire is then used to guide passage of an ETT from the mouth or nose into the trachea.

This technique may be used with or without a FIS. Commercially available retrograde intubation kits have a 0.037 inch guidewire that may not fit through the working channel of some FISs, so compatibility must be checked prior to using this technique with a FIS.

Once the guidewire is retrieved from either the mouth or naris, retrograde intubation begins by securing the wire with a hemostat outside the cricothyroid insertion site to avoid pulling through and to maintain tension. When this is performed without an FIS, an airway exchange catheter (AEC) is then threaded over the taut wire until it passes the larynx. After removing the wire, an ETT is advanced over the AEC to the appropriate distance (usually to 22 cm for women, 24 cm for men), confirmed in the usual fashion, and secured.

When a FIS is used for assistance, an ETT is placed on the FIS prior to retrieving the end of the wire from the mouth or naris and passing it through the working channel of the FIS from distal to proximal. The FIS is then passed over the guidewire and into the glottis until resistance is met at the cricothyroid membrane. The hemostat that held the guidewire taut may now be released and the guidewire removed. The FIS is advanced until the carina is visualized and the ETT is passed into the trachea.

The primary advantages to using an FIS for this technique are [1]:

●The trachea is accessed under direct vision

●The FIS can be freely advanced to the carina (past the puncture site), minimizing the potential for the ETT to become dislodged when the wire is removed (due to the short distance between the vocal cords and puncture site)

●Oxygen may be continuously administered via the FIS throughout the procedure (including while the guidewire is still in place)

The main disadvantage to the addition of FIS guidance to the retrograde technique is the need for additional equipment and preparation time, which may not be available in emergency cases.

TROUBLESHOOTING — 

FSI is a complex procedure that requires practice and may not be straightforward. A number of strategies can be used to improve success.

Difficulty with the view — When laryngoscopy is difficult, it is critical to always keep the tip of the flexible intubation scope (FIS) in the midline to allow visualization of the larynx. The clinician should always be able to recognize the airway structures; if not, the FIS should be withdrawn until the location can be identified.

Collapse of the upper airway, whether from induction of general anesthesia, administration of neuromuscular blocking agents, or from anatomic pathology, can cause difficult visualization or navigation of the oropharynx. Various maneuvers, some performed by an assistant, can be used to open the upper airway, and improve visualization:

●Placement of an oral airway (see 'Oral airway' above)

●Jaw thrust (picture 7)

●Pulling the tongue forward with a piece of gauze or Magill forceps (gently so as not to injure the tongue on the bottom teeth)

●Cervical extension (when not contraindicated), which lifts the epiglottis anteriorly and exposes the larynx

●External laryngeal displacement (adjusting the position of the larynx by placing pressure on the neck at the thyroid cartilage)

●Insertion of a direct or indirect laryngoscope blade, which may open the airspace and lift the epiglottis off the posterior pharyngeal wall

●Addition of positive airway pressure, when using an endoscopic mask

When performing FSI through a supraglottic airway (SGA), a glottic view obstructed by a down-folded epiglottis can be improved with the "up-down" maneuver, which is accomplished by withdrawing the SGA without deflating the cuff by 5 to 6 cm and reinserting it to release the trapped epiglottis.

In awake patients, instructing the patient to sniff, swallow, vocalize, or breathe deeply can improve visualization of the glottis [10].

If fogging occurs during FSI, the lens may be cleared by gently touching the tip of the FIS to the airway mucosa.

Difficulty advancing the endotracheal tube — Once the FIS has been advanced to the carina, the endotracheal tube (ETT) is advanced over the FIS. This is a blind procedure, and it is not uncommon to encounter difficulty in advancing the ETT over the scope into the trachea. Several techniques may alleviate this problem:

●Difficulty in advancing the ETT may result from it catching ("hanging up") on the right arytenoid. Turning the ETT 90 degrees counterclockwise may facilitate its passage [13].

●A warmed, softened ETT will usually pass through the vocal cords more easily and with less trauma than an unprepared tube.

●A flexible ETT, a tapered-tip ETT for use with the intubating laryngeal mask airway, or a specialized ETT with a bull-nose tip (Parker Flex-Tip) may facilitate advancement (picture 8 and picture 9) [14].

●The gap between the FIS and the larger ETT may allow the ETT to shift off-center and catch as it passes through the larynx. An Aintree catheter loaded over the FIS within the ETT will minimize this gap, but this must be done prior to inserting the FIS.

●A combination technique may be indicated; that is, the use of laryngoscopy, either direct or indirect, may facilitate clearance of the tongue, elevation of the epiglottis, and advancement of the ETT.

SOCIETY GUIDELINE LINKS — 

Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Airway management in adults".)

SUMMARY AND RECOMMENDATIONS

●Indications for flexible scope intubation (FSI)

•Flexible scope intubation (FSI) is an indirect technique for endotracheal intubation using a flexible bronchoscope. FSI is particularly useful for patients in whom direct laryngoscopy may be difficult or dangerous (eg, limited mouth opening, abnormal airway anatomy, unstable cervical spine). (See 'Indications and advantages' above.)

•FSI may be difficult or impossible if blood or secretions are in the airway. (See 'Contraindications and disadvantages' above.)

•With effective topical airway anesthesia, FSI is better tolerated by the awake or sedated patient than is intubation with direct or video-assisted laryngoscopy. FSI can also be performed after induction of anesthesia. (See 'Awake versus asleep intubation' above and "Awake tracheal intubation".)

●Preparation for FSI

•Equipment must be prepared prior to FSI as described above. (See 'Equipment preparation' above.)

•An antisialagogue (eg, glycopyrrolate, 0.2 mg intravenously [IV]) should be administered at least 15 minutes prior to FSI to aid in drying the airway mucosa. If nasal intubation is planned, a topical nasal mucosal vasoconstrictor should be applied before intubation (eg, oxymetazoline 0.05%, two puffs to each nostril three times at five-minute intervals). (See 'Antisialagogues' above and 'Nasal preparation' above.)

•For awake intubation the airway must be anesthetized and sedation may be required. (See 'Preparation for awake intubation' above and "Awake tracheal intubation", section on 'Airway anesthesia' and "Awake tracheal intubation", section on 'Sedation/analgesia'.)

●FSI technique – FSI can be used for nasal or oral endotracheal intubation.

•Oral intubation steps are as follows (see 'Oral intubation' above):

-Place a bite block or intubating oral airway and the oropharynx is suctioned.

-Insert the endotracheal tube (ETT) into the intubating airway to a depth of 5 cm or is load directly onto and secure it to the handle of the lubricated flexible intubation scope (FIS).

-Orient the FIS so that the tip can be moved up and down in the midline. Insert the FIS without a bend at the tip along the midline of the oropharynx (or into the ETT, if in the oral airway).

-The larynx should be visible in the midline (picture 3); pass the FIS through the vocal cords (picture 4) to the carina (picture 5).

-Advance the ETT over the FIS to 22 cm for women or 24 cm for men.

-Withdraw the FIS and confirm the ETT position in the usual manner. (See "Confirmation of correct endotracheal tube placement in adults".)

•Nasal intubation steps are as follows (see 'Nasal intubation' above):

-Insert a softened (warmed), lubricated ETT into the selected naris to a depth of approximately 15 cm (figure 5).

-After suctioning the oropharynx, pass the lubricated FIS through the ETT.

-The larynx is usually visible distal to the ETT; pass the FIS through the vocal cords to the carina.

-Advance the ETT over the FIS to 26 cm for women or 28 cm for men.

-Withdraw the FIS and confirm the ETT position in the usual manner. (See "Confirmation of correct endotracheal tube placement in adults".)

•The technique for flexible scope intubation through an SGA depends on the design of the SGA; techniques are described above:

-For SGAs that can accommodate a standard-sized endotracheal tube, the ETT is loaded directly onto the FIS. (See 'Intubation through a supraglottic airway' above.)

-For other SGAs, ETT exchange can be facilitated by using an FIS loaded with an Aintree intubation catheter. (See 'Aintree catheter-aided intubation through a supraglottic airway' above.)

●Troubleshooting – Various maneuvers may be used to open the upper airway, improve visualization, locate the larynx, and facilitate passage of the ETT. (See 'Troubleshooting' above and 'Difficulty advancing the endotracheal tube' above.)

●Retrograde intubation – When other methods for intubation are not possible, retrograde intubation can be performed with or without the use of an FIS. A wire is inserted into the trachea through the cricothyroid membrane and passed cephalad, exiting the mouth or nose. The wire is fed through the working channel of the FIS; the FIS, loaded with an ETT over it, is passed over the wire into the trachea. (See 'Retrograde intubation' above.)