Endotracheal tube introducers (gum elastic bougie) for emergency intubation

INTRODUCTION — The endotracheal tube (ETT) introducer is an effective and inexpensive adjunct to difficult airway management that is easy to use. We recommend that an ETT introducer be readily available in every emergency department.

This topic will review the types of ETT introducers, indications and contraindications for their use, proper technique for using the devices during emergency tracheal intubation, and evidence of their effectiveness. Other airway devices and aspects of emergency airway management are discussed separately. (See "Devices for difficult airway management in adults for emergency medicine and critical care" and "Overview of advanced airway management in adults for emergency medicine and critical care" and "Rapid sequence intubation in adults for emergency medicine and critical care" and "Emergency airway management in children: Unique pediatric considerations".)

TERMINOLOGY AND EQUIPMENT — Several terms are used to describe the classic ETT introducer. Although the phrase "gum elastic bougie" is common, we find it inaccurate and confusing since the ETT introducer is neither gum nor elastic and is not used as a bougie (ie, dilator). In this topic, we will refer to the device as an ETT introducer.

The ETT introducer consists of a 50- to 70-cm stylet with the distal tip bent at a 30-degree angle. The bend allows the intubator to direct the tip anteriorly under the epiglottis and through the vocal cords, which may not be visible.

ETT introducers come in several sizes:

●Adult ETT introducers are typically 15 French (external diameter approximately 5 mm) and can accommodate an ETT as small as size 6.0.

●Pediatric ETT introducers are 10 French (external diameter approximately 3.3 mm) and can accommodate an ETT as small as size 4.0.

●Neonatal ETT introducers are 5 French (external diameter approximately 1.7 mm) and can accommodate an ETT as small as size 2.5.

Dimensions and use are comparable among the four main types of ETT introducers available:

●Eschmann – Woven Dacron rod with resin coating; can be sterilized and reused. This is commonly referred to as a "gum elastic bougie" (picture 1).

●Standard disposable (several manufacturers) – Solid ETT introducer made with various materials and coatings (picture 2 and picture 3).

●Steerable-tip – Allows intubator to flex the tip of the ETT introducer anteriorly to facilitate entry into the larynx, and then posteriorly to aid passage down the trachea.

●Frova – Hollow, single-use, plastic introducer with fenestrated tip to allow oxygenation; includes 15-mm adapter for standard bag-valve assembly (picture 4).

Although the Eschmann introducer is more expensive, it can be used multiple times, so the average cost per intubation is comparable to that of a single-use introducer. Nevertheless, some clinicians prefer single-use introducers because multiple-use introducers are sometimes inadvertently thrown away. The material of several single-use ETT introducers allows "memory" so J-shaped anterior curvatures can be maintained for use with hyper-angulated video devices. (See "Devices for difficult airway management in adults for emergency medicine and critical care", section on 'Advanced laryngoscopes'.)

INDICATIONS — We concur with the authors of the largest randomized trials of ETT introducers performed to date and suggest the following indications for using an ETT introducer for emergency intubation [1,2]:

●Incomplete view of glottis

●Glottis anterior and difficult to reach with ETT and stylet; can bend ETT introducer to reach glottis

●Glottic edema or other potential obstruction to ETT passage; can pass ETT introducer and use it as guide for ETT insertion (ie, "railroad" ETT)

●Any difficult airway (eg, spinal immobilization, displaced larynx, distorted airway)

In addition, an ETT introducer may be incorporated into routine intubation procedure as a first-pass device.

Traditionally, the ETT introducer has been used for intubations when the epiglottis was visible but the glottis was not (grade III Cormack-Lehane view) [3]. In these circumstances, visual confirmation of correct ETT placement was impossible, so tactile confirmation of ETT introducer placement in the trachea was required before advancing an ETT over the ETT introducer.

ETT introducers are most effective when used with standard geometry (straight and curved) laryngoscope blades during either direct or video laryngoscopy. The ETT introducer is difficult to use with hyperangulated videolaryngoscope blades because the bend required for the introducer to reach the larynx inhibits its advancement into the trachea.

CONTRAINDICATIONS AND PRECAUTIONS — An ETT introducer should be used with caution, if at all, when there is possible laryngeal or tracheal injury. In such cases, the ETT introducer may exacerbate the injury or be advanced outside the airway into adjacent structures.

An ETT introducer is unlikely to be beneficial when no part of the airway can be seen (grade IV Cormack-Lehane view). Blind insertion of an ETT introducer through an extraglottic airway (EGA) to cannulate the trachea (with the intention of converting an EGA to an ETT) risks perforation of glottic structures and is not recommended.

PREPARATION — Lubricant may be applied to the ETT introducer if the ETT is a tight fit. Lubrication allows the ETT to pass over the ETT introducer more easily. If the fit is not tight, lubricant is not recommended, as it can make the ETT introducer difficult to grasp and control.

TECHNIQUE

Standard two-person technique — Placement of the ETT introducer and the subsequent advancement of the ETT over it are performed as described here. A video clip demonstrating the technique is provided (movie 1).

●Identify the epiglottis. External laryngeal manipulation (picture 5) or other positioning techniques may be needed to find the epiglottis (figure 1 and picture 6 and picture 7) depending upon the device being used for laryngoscopy and the clinical scenario.

●Place the ETT introducer. Advance the ETT introducer, with its tip pointing anteriorly and under the epiglottis, into the trachea. When advancing the ETT introducer, be sure to maintain the tip in the midline with its anterior orientation (do not allow it to rotate to either side); if it rotates significantly, the anteriorly located tracheal rings may not be appreciated. Care must be taken to avoid forceful insertion as this can cause injury (ie, bleeding or perforation).

●Confirm placement of the ETT introducer. Two tactile sensations suggest correct placement in the trachea [3,4]. One sign is the feeling of vibrations or "clicks" as the tip of the ETT introducer is advanced over the tracheal rings. However, it is important to remember that the angled tip of the ETT introducer must be oriented anteriorly for it to encounter the rings.

Another sign is resistance to further insertion. As the introducer advances to between 24 and 40 cm from the teeth, the distal tip becomes lodged in smaller airways and cannot advance. This is sometimes referred to as the "stop sign" or "hard stop." In contrast, if the ETT introducer is in the esophagus, the tracheal rings cannot be felt and the introducer advances easily into the stomach, far past the 40 cm mark where the "stop sign" would normally occur if the ETT introducer were in the tracheobronchial tree.

When advancing the ETT introducer, avoid applying too much pressure if resistance is encountered. Excessive force can traumatize the airway [5]. In addition, it may be helpful to withdraw the introducer several centimeters before railroading the ETT over the introducer (next step in the technique) to avoid forceful advancement.

●Place the ETT. Once the ETT introducer is in the trachea, place the distal end of the ETT over the free end of the ETT introducer and advance it using a Seldinger-like technique. This generally requires an assistant to place the ETT on the proximal end of the introducer. Advance the ETT over the introducer and into the trachea while keeping the laryngoscope in place.

●Withdraw the ETT introducer. Once the ETT is advanced the appropriate distance, withdraw the introducer.

●Confirm that the ETT is in the trachea. Confirmation proceeds as usual, and we recommend the use of an end-tidal carbon dioxide (EtCO₂) detector.

One-person techniques — Alternative techniques for intubating with an ETT introducer that do not require a second person to thread the ETT over the ETT introducer have been described. Two of these involve pre-threading the ETT onto the ETT introducer.

●In one such technique, once the ETT introducer is confirmed to be in the trachea, the proximal end of the ETT introducer is released, allowing it to straighten, and the ETT is then advanced over the ETT introducer and into the trachea (movie 2).

●Another technique can be performed as described here (movie 3). Although more complex than pre-threading the ETT, the advantage to this technique is that the ETT introducer is lighter and easier to manipulate.

•Pre-bend the ETT introducer to 90 degrees at its midpoint, in the same plane as the bent tip.

•Hold the ETT introducer at the midpoint bend, which keeps the tip anteriorly directed, and insert the ETT introducer into the trachea.

•When tracheal clicks are felt, transfer the ETT introducer to your left hand, capturing it while holding the laryngoscope in place.

•With your freed right hand, advance the ETT over the ETT introducer into the trachea.

•When the ETT is fully advanced, transfer it to the left hand as well and secure it along with the laryngoscope while removing the ETT introducer.

Tips for placing tracheal tube over introducer — The following suggestions and techniques may facilitate placement of the ETT over the introducer:

●Throughout the procedure, the operator should maintain proper position of the laryngoscope with the left hand. The tendency is to remove the laryngoscope after the introducer is in the trachea, but doing so allows the tongue to fall posteriorly and potentially hinder ETT passage.

●Passage of the ETT is easier if it is close in size to the introducer. The greater the disparity, the more likely the ETT will have an overhanging leading edge that can catch on the arytenoids or aryepiglottic folds during insertion.

This may require using a smaller ETT than would otherwise be used, but this is a small price to pay for success in a difficult situation. ETTs with subglottic suction may be more prone to this problem because they have a larger outer diameter to accommodate the suction channel above the cuff.

●If the ETT impinges on the arytenoids, slight withdrawal of the ETT (to disengage the tip from the arytenoids), followed by careful counterclockwise rotation and relaxation of cricoid pressure (if used), may facilitate passage. A video clip demonstrating the technique is provided (movie 4).

PEDIATRIC CONSIDERATIONS — The techniques described above can be used in children. Pediatric ETT introducers can be used with ETT sizes down to 4.0 to 5.5, and neonatal ETT introducers can be used in ETT sizes 2.5 to 4.0. (See "The difficult pediatric airway for emergency medicine".)

EVIDENCE OF EFFECTIVENESS — Although randomized trials report inconsistent results during routine intubation, evidence suggests that use of an ETT introducer is associated with improved intubation success rates among patients undergoing emergency intubation, especially those with impaired glottic views or features associated with a difficult airway [1,3,6-11].

The strongest evidence supporting the use of ETT introducers for emergency intubation comes from a systematic review and meta-analysis of 18 studies in which use of an introducer was associated with a higher overall rate of successful first-pass intubation (risk ratio 1.11, 95% CI 1.06-1.17) [12]. When analysis was limited to randomized trials (n = 12), the success rate was slightly lower (RR 1.09, 95% CI 1.02-1.17). First-pass success rates were higher using an introducer regardless of the method of intubation (ie, direct versus video laryngoscopy) or where intubation was performed (eg, emergency department, intensive care unit, prehospital). The ETT introducer was most effective in patients (n = 585 in five studies) with a Cormack-Lehane III or IV view (figure 2) (RR 1.60, 95% CI 1.40-1.84). The authors noted that all studies included in the systematic review were at moderate to high risk of bias.

In a single-center trial of over 750 adults undergoing emergency intubation in the emergency department, use of an ETT introducer while performing video laryngoscopy with a Macintosh blade resulted in a higher overall first-pass success rate when compared with video laryngoscopy performed with a standard ETT and stylet (98 versus 87 percent, respectively) [1]. In addition, higher first-pass success rates were noted in patients with at least one characteristic of a difficult airway (96 versus 82 percent, respectively), such as obesity, short neck, small mandible, large tongue, need for cervical spine immobilization, airway obstruction or edema, secretions obstructing the glottic view, or facial trauma.

The authors concluded that the high success rate when using an ETT introducer might be due to improved visibility, as an ETT can block the view of the glottis when it passes in front of the camera at the tip of the video laryngoscope blade. An ETT introducer has a smaller diameter and does not obscure the view of the glottis. The small diameter of the ETT introducer may also be advantageous when anatomic distortion, such as glottic edema or tracheal strictures, creates an obstacle to ETT placement. The smaller ETT introducer, if able to pass the obstruction, can act as a guide for the ETT to follow into the trachea. The center where the study was performed uses an ETT introducer for most intubations, so operators are familiar with their use, and therefore the reported first-pass success rates are among the highest ever published.

A subsequent multicenter randomized trial by the same research group investigated the routine use of an ETT introducer for over 1100 intubations performed in the emergency department and intensive care unit [2]. This study found no significant difference in first-pass success rates between intubations performed with an ETT introducer and those performed with a standard ETT and stylet, including those performed in difficult airways (80 percent with an ETT introducer versus 83 percent with an ETT and stylet). The intubators in this study were from both the emergency department and ICU, had variable levels of training with an ETT introducer, and used both video and direct laryngoscopy.

The results of these well-performed studies suggest that intubation using an ETT introducer can contribute to high first-pass success rates in hospitals with a culture of frequent ETT introducer use and requisite training. However, it may be inappropriate to extrapolate these high success rates to institutions and operators who use ETT introducers less frequently.

Little training is needed before introducers can be used successfully [11,13,14]. This is likely because of the similarity to standard intubating technique and familiarity with the Seldinger technique.

COMPLICATIONS — Complications from ETT introducers are rare and involve mechanical trauma to airway structures [15]. Excessive force while advancing the ETT introducer or the ETT might damage the larynx, trachea, or branches of the airway [5]. The ETT might catch on the arytenoids during placement and impede advancement. Forceful advancement can then dislocate the arytenoid cartilage or cause other trauma to the airway.

OTHER USES — Additional uses of ETT introducers include the following:

●Distinguishing tracheal from esophageal ETT placement – This approach has been advocated in cardiac arrest patients, where end-tidal carbon dioxide (EtCO₂) concentrations may not be high enough to change the color of a colorimetric capnography device. However, there is insufficient evidence to recommend that introducers be relied upon as the sole indicator of proper ETT placement [4,16]. In a study using 20 human cadavers, clinicians without prior experience using an ETT introducer were able, using the techniques described above, to determine esophageal placement in 95 percent of cases (95% CI 88-98) and tracheal placement in 93 percent (95% CI 86-97) [4]. (See 'Technique' above.)

●Adjunct for cricothyrotomy – Evidence supporting "bougie-aided cricothyrotomy" is growing. In this procedure, after the cricothyroid membrane is incised, an ETT introducer is advanced caudally down the trachea to confirm tracheal placement with palpable "clicks" and "stop sign," then the tracheal tube is placed over the ETT introducer and advanced into the trachea. (See "Emergency cricothyrotomy (cricothyroidotomy) in adults".)

●ETT exchanger – If an intubated patient has a malfunctioning ETT (eg, cuff leak), an ETT introducer may be advanced through the ETT to maintain a track into the trachea, over which the malfunctioning ETT may be removed and a new ETT placed. However, this technique can be problematic, as the length of most ETT introducers is 60 to 70 cm, which barely allows the full length of the ETT to leave the mouth. Standard airway exchange catheters are 80 cm long and better suited to this task.

●Adjunct for video laryngoscopes – Some manufacturers (King Vision, Pentax AWS) advocate use of an ETT introducer to assist with difficult intubations [17,18]. In some video laryngoscopes (CoPilot VL), a specific channel for ETT introducers has been created to assist with routine intubations. This approach is different than using hyperangulated rigid stylets with hyperangulated blades, which is the recommended technique for hyperangulated video intubations. (See "Devices for difficult airway management in adults for emergency medicine and critical care", section on 'Video laryngoscopes'.)

●Adjunct with blind digital intubation – Some practitioners prefer to use an ETT introducer, rather than an ETT, when performing digital intubations since the smaller diameter and malleability allow for easier manipulation within the oropharynx when directing the tip towards the glottic opening [19]. In addition, when the ETT introducer enters the trachea, palpable clicks and a positive "stop sign" help to confirm proper placement, as opposed to digital intubations without an ETT introducer in which tactile confirmation of tracheal placement may not be possible. (See 'Technique' above.)

●Adjunct to convert an extraglottic airway (EGA) to an ETT – In patients being ventilated with an EGA, replacing it with an ETT can be complex and potentially dangerous if difficult airway characteristics are present. If the EGA is designed to be used as a conduit for intubation, a flexible endoscope is typically used to intubate "intra-luminally" through the EGA. It may be tempting to place an ETT introducer blindly down an EGA to “find” the trachea, but this approach is not recommended due to the risk of the introducer perforating glottic structures.

Alternatively, some EGAs can be exchanged for an ETT "extra-luminally" using a video laryngoscope with either a standard or hyper-angulated blade [20]. To do so, the video laryngoscope is introduced into the oropharynx with the EGA in place. If the EGA has a cuff, it is deflated and the epiglottis visualized. The blade tip is advanced into the vallecula and the epiglottis elevated, bringing the glottis into view. Under video laryngoscope visualization, the ETT introducer is then placed alongside the EGA and into the glottis, the EGA removed, and an ETT advanced over the ETT introducer into the trachea.

SUMMARY AND RECOMMENDATIONS

●Definitions – The endotracheal tube (ETT) introducer is a simple, effective, and inexpensive adjunct to difficult airway management. We recommend that an ETT introducer be readily available in every emergency department. The ETT introducer consists of a 50- to 70-cm stylet with the distal tip bent at a 30-degree angle (picture 1 and picture 4). The bend allows the intubator to direct the tip anteriorly under the epiglottis and through the vocal cords. This orientation is required for the tip to encounter the anteriorly located tracheal rings and produce palpable "clicks" when advancing into the trachea.

●Indications – The ETT introducer is a useful tool for intubation when the epiglottis is visible but the vocal cords cannot be seen (grade III Cormack-Lehane view (figure 2)). The ETT introducer can be used in conjunction with standard laryngoscopes, video laryngoscopes, and fiberoptic intubation devices.

●Contraindications – An ETT introducer should be used with extreme caution, if at all, when there is possible laryngeal or tracheal injury. An ETT introducer is unlikely to be beneficial when no part of the airway can be seen (grade IV Cormack-Lehane view). Blind insertion of an ETT introducer through an extraglottic airway (EGA) to cannulate the trachea risks perforation of glottic structures and is not recommended.

●Technique and confirmation of placement – Techniques for inserting the ETT introducer and using it for placement of an ETT are described in the text (movie 1), as are other potential uses for the device. Two tactile sensations confirm correct placement in the trachea. One is the feeling of vibrations or "clicks" as the tip of the ETT introducer is advanced over the tracheal rings. Another is resistance to further insertion. (See 'Technique' above and 'Other uses' above.)

●Other uses (including cricothyrotomy) – ETT introducers may be used for other techniques, including the bougie-aided cricothyrotomy procedure. (See "Emergency cricothyrotomy (cricothyroidotomy) in adults".)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Aaron E Bair, MD, MSc, FAAEM, FACEP, now deceased, who contributed to an earlier version of this topic review.