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Direct laryngoscopy and endotracheal intubation in adults

Direct laryngoscopy and endotracheal intubation in adults
Literature review current through: Jan 2024.
This topic last updated: Jul 31, 2023.

INTRODUCTION — Direct laryngoscopy (DL) and endotracheal intubation (ETI) are essential skills for a range of health care practitioners, including anesthesiologists, emergency physicians, and other clinicians expected to serve as first responders in emergency cases requiring advanced airway management. This topic will discuss the indications, contraindications, preparation, equipment, and techniques needed to perform DL and ETI in adults. The use of more sophisticated airway equipment (eg, video laryngoscopes), approaches to airway management in specific clinical circumstances, pediatric laryngoscopy, and rapid sequence intubation are all reviewed separately.

(See "Rapid sequence intubation in adults for emergency medicine and critical care".)

(See "The decision to intubate".)

(See "Overview of advanced airway management in adults for emergency medicine and critical care".)

(See "Approach to the difficult airway in adults for emergency medicine and critical care".)

(See "Airway management for induction of general anesthesia".)

(See "Technique of emergency endotracheal intubation in children".)

INDICATIONS — In emergency medicine, the most common indications for tracheal intubation are acute respiratory failure, inadequate oxygenation or ventilation, and airway protection in a patient with depressed mental status. In the perioperative setting, endotracheal tubes may be placed in many clinical circumstances, including patients receiving general anesthesia, surgery involving or adjacent to the airway, unconscious patients requiring airway protection, or surgery involving unusual positioning [1]. Less frequently, intubation is performed for short-term hyperventilation to manage increased intracranial pressure or to manage copious secretions or bleeding from the airway [2]. (See "The decision to intubate".)

CONTRAINDICATIONS — There are few absolute contraindications to tracheal intubation. Most involve supraglottic or glottic pathology that precludes placement of an endotracheal tube (ETT) through the glottis or which may be exacerbated by insertion of the ETT or laryngoscope. As an example, blunt trauma to the larynx may cause a laryngeal fracture or disruption of the laryngotracheal junction. In such cases, traction from the laryngoscope blade or pressure from a stylet within an ETT could create a false lumen or complete a partial tear of the trachea [3].

Penetrating trauma of the upper airway may also result in conditions exacerbated by laryngoscopy or ETT placement, such as a hematoma or partial transection of the airway [4]. When examination findings suggest such conditions exist, it may be safer to support oxygenation and ventilation using noninvasive means until a definitive airway can be established or to perform an immediate surgical airway, if necessary. (See "Approach to the failed airway in adults for emergency medicine and critical care" and "Emergency cricothyrotomy (cricothyroidotomy) in adults".)

Other conditions associated with difficult intubation include severe laryngeal or supralaryngeal edema as a consequence of bacterial infection, burns, or anaphylaxis [5]. In these cases, visualization of the laryngeal inlet during laryngoscopy may be impossible, and local trauma caused by the laryngoscope blade or attempts at ETT insertion can lead to increased swelling, rendering mask ventilation difficult or impossible. (See "Epiglottitis (supraglottitis): Clinical features and diagnosis", section on 'Subacute (severe sore throat)'.)

Relative contraindications to tracheal intubation involve potential difficulties performing the procedure. Such difficulties may be related to anatomic features, injuries, physiologic status, or the skill set of the clinician. The identification of traits associated with difficult airway management is discussed separately. (See "Approach to the difficult airway in adults for emergency medicine and critical care" and "The difficult pediatric airway for emergency medicine".)

When physical features suggest that direct laryngoscopy and intubation will be difficult or impossible, or the operator is not skilled in bag-mask ventilation and back-up surgical techniques (ie, cricothyrotomy), prudence dictates that noninvasive methods of airway support or an awake intubation be performed (rather than rapid sequence intubation) to avoid creating a life-threatening "cannot intubate-cannot ventilate" situation. (See "Rapid sequence intubation in adults for emergency medicine and critical care".)

Several airway algorithms promulgated for anesthesiologists and emergency medicine physicians recommend that an airway assessment be conducted whenever possible before intubation is attempted [6]. Whenever possible, the airway assessment should include examination of physical and historical features that have been shown to predict difficulty with airway management (table 1 and table 2 and table 3). (See "Approach to the difficult airway in adults for emergency medicine and critical care", section on 'Identifying the anatomically difficult airway' and "Airway management for induction of general anesthesia", section on 'Prediction of the difficult airway' and "Management of the difficult airway for general anesthesia in adults", section on 'Recognition of the difficult airway'.)

ANATOMY — The epiglottis lies at the base of the tongue and provides an essential landmark for direct laryngoscopy (DL). The epiglottis appears as a hood overlying the glottis, which lies caudad. The vallecula (valley) is the cleft between the base of the tongue and the epiglottis. If a curved laryngoscope blade is used for laryngoscopy, the blade is placed into the vallecula. The epiglottis is suspended from the hyoid bone by a midline ligament, the hyoepiglottic ligament (HEL). Pressure of the blade tip against the HEL elevates the epiglottis effectively and efficiently. This is in contrast to placing the blade tip into the vallecula on either side of the HEL, as classically recommended, which results in less efficient elevation of the epiglottis.

Airway anatomy is discussed in detail separately. (See "Technique of emergency endotracheal intubation in children", section on 'Anatomy'.)

The following images show the basic anatomic structures important for DL:

Oral cavity diagram (figure 1)

Laryngeal inlet diagram (figure 2)

Laryngeal inlet photographs (picture 1 and picture 2 and picture 3 and picture 4 and picture 5)

Sagittal airway anatomy (figure 3)

Airway innervation (figure 4)

PREPARATION — Careful preparation for direct laryngoscopy and tracheal intubation is essential. In many cases, knowledgeable support staff help to prepare the implements required. However, this is not always the case, and it is important that the airway manager have a mental or written checklist for the necessary tools and steps (table 4). Essential preparations include the following:

Assess the patient's airway whenever feasible, looking for traits associated with potential difficulty (table 3 and table 2 and table 1). (See "Management of the difficult airway for general anesthesia in adults", section on 'Recognition of the difficult airway' and "Approach to the difficult airway in adults for emergency medicine and critical care", section on 'Identifying the anatomically difficult airway' and "Airway management for induction of general anesthesia", section on 'Prediction of the difficult airway'.)

Preoxygenate the patient to increase the oxygen reserve, increase the time to oxygen desaturation with apnea, and thereby, allow more time to secure the airway. We suggest the use of apneic oxygenation throughout laryngoscopy for emergency intubation and for patients at high risk of difficult intubation or rapid desaturation. Apneic oxygenation can be accomplished most simply with passive oxygen insufflation via nasal cannula at 15 L/minute. Alternatives include the Transnasal Humidified Respiratory Insufflatory Exchange (THRIVE) and Supernova nasal mask ventilation systems, where available. (See "Rapid sequence intubation in adults for emergency medicine and critical care", section on 'Preoxygenation' and "Preoxygenation and apneic oxygenation for airway management for anesthesia".)

Place a functioning suction device (preferably fitted with a tonsil-type tip) and bag-valve mask at the bedside.

Attach necessary monitors, including blood pressure, pulse oximetry, continuous cardiac monitoring, and capnography.

Establish intravenous (IV) access. Whenever possible, two peripheral IV catheters should be placed to ensure IV access in case one becomes non-functioning.

Prepare all medications necessary for intubation, including induction agents, neuromuscular blocking agents, adjunctive medications, and emergency medications (eg, anticholinergic and vasoactive medications). (See "Neuromuscular blocking agents (NMBAs) for rapid sequence intubation in adults for emergency medicine and critical care" and "Induction agents for rapid sequence intubation in adults for emergency medicine and critical care" and "Airway management for induction of general anesthesia", section on 'Choice of medications for induction and intubation'.)

Arrange the tools needed to perform laryngoscopy and intubation beside the clinician. These include:

Laryngoscope handle and assorted blades. Ensure bright lighting and the integrity of all parts (may want to use blade with video capacity in case video assistance becomes necessary). (See "Devices for difficult airway management in adults for emergency medicine and critical care", section on 'Video laryngoscopes'.)

Endotracheal tubes (ETTs) and a stylet. Include ETTs one size larger and one size smaller than the ETT to be used initially.

The size of the ETT may vary based on the clinical situation. For short-term intubation during routine general anesthesia, we typically place a 7 to 7.5 mm internal diameter (ID) tube for women, and a 7.5 to 8 mm ID ETT for men. When the patient is likely to remain intubated in the intensive care unit, we place slightly larger ETTs, 7.5 to 8 mm ID for women and 8.0 to 8.5 mm ID for men. Smaller ETTs are associated with less post-intubation sore throat, are easier to place, and may cause less tissue trauma [7-9]. However, in the intensive care unit, a larger ETT facilitates tracheal suctioning and flexible bronchoscopy through the ETT, and may reduce airway resistance during weaning from mechanical ventilation.

In emergency situations, providing oxygen is critical and ETT size is a secondary concern. The largest size ETT that can be placed expeditiously should be used. The ETT sizes described above for routine intubation are reasonable, unless the clinician anticipates difficulty inserting an ETT of that size, in which case a smaller size should be used.

Sterile lubricant for the distal balloon of the ETT; appropriate sized syringe to inflate the ETT balloon.

Adjunct airway management devices (eg, ETT introducer or "bougie"). (See "Endotracheal tube introducers (gum elastic bougie) for emergency intubation".)

Oral and nasal airways. (See "Basic airway management in adults".)

Rescue airway (eg, supraglottic airway [SGA], Combitube, King Airway). (See "Devices for difficult airway management in adults for emergency medicine and critical care".)

End-tidal carbon dioxide monitor (EtCO2; eg, capnography) and esophageal detector to confirm proper ETT placement. (See "Carbon dioxide monitoring (capnography)".)

Esophageal detectors may be used outside of the operating room. They make use of differences in air flow with tracheal versus esophageal intubations to help determine ETT placement; they are described in greater detail below. (See 'Alternative methods' below.)

Equipment to hold the tube in position following intubation (eg, tape, prefabricated ETT holder).

Equipment, such as towels and sheets, that may be needed to position the patient. (See 'Positioning the patient' below.)

Check the cuff of the ETT for leaks by inflating it and removing the syringe (the cuff should remain inflated) and then deflating it. Avoid contaminating the ETT.

Perform all emergency intubations with a malleable stylet in the ETT. The stylet should be straight from the proximal end of the ETT to the proximal end of the ETT cuff, and should be bent no more than 35 degrees. More acute angles at the end of the ETT (eg, "hockey stick" conformation) may cause the tip to become stuck on the anterior trachea, preventing advancement (and possibly traumatizing the airway) [10]. The stylet should not extend beyond the end of the ETT (picture 6).

It is essential to have a clear back-up approach prepared in advance in case of an unsuccessful intubation [11,12]. Bag-mask ventilation (BMV) equipment must be available, and intubators must be proficient in performing BMV. Other rescue devices may consist of a rescue airway (eg, LMA), or in the case of a failed airway, cricothyrotomy. (See "Basic airway management in adults", section on 'Bag-mask ventilation' and "Approach to the failed airway in adults for emergency medicine and critical care" and "Emergency cricothyrotomy (cricothyroidotomy) in adults" and "Management of the difficult airway for general anesthesia in adults", section on 'Planning the airway management approach'.)

Proper patient positioning is crucial to successful laryngoscopy. (See 'Positioning the patient' below.)

Several different mnemonic devices have been promulgated to help practitioners remember the tools and steps for tracheal intubation. The "STOP MAID" mnemonic is described here:

S: Suction

T: Tools for intubation (laryngoscope blades, handle)

O: Oxygen

P: Positioning

M: Monitors, including electrocardiography, pulse oximetry, blood pressure, EtCO2, and esophageal detectors

A: Assistant; Ambu bag with face mask; airway devices (different sized ETTs, 10 mL syringe, stylets); assessment of airway difficulty

I: IV access

D: Drugs for pretreatment, induction, neuromuscular blockade (and any adjuncts)

LARYNGOSCOPE DESIGN

Blades — The purpose of the laryngoscope is to displace the mandible, tongue, epiglottis, hyoid bone, and other soft tissue out of the line of sight of the laryngoscopist in order to expose the glottic opening. The blade of a laryngoscope is typically comprised of a flat element (spatula), a vertical element (flange), and a light source.

These basic parts have been combined in different configurations, of which the straight and curved blades are the most common. The Macintosh (curved) and the Miller (straight) are used most often (picture 7 and picture 8) [13,14].

The curved blade is designed to minimize stimulation of the posterior epiglottis, which is innervated by the superior laryngeal nerve. It is configured to approximate the curvature of the tongue. Its tip fits into the recess at the back of the tongue (vallecula) and elevates the epiglottis indirectly, most effectively by putting pressure on the hyoepiglottic ligament. Many clinicians prefer the curved blade for initial attempts at direct laryngoscopy (DL).

The straight blade is designed to be inserted beneath the epiglottis and then to lift it directly, thereby exposing the glottic aperture. The straight blade may offer advantages in particular circumstances, such as when the glottis is deep or anterior, upper incisors are prominent, or a long, floppy epiglottis obscures the glottis and must be lifted out of the line of sight.

The Miller blade has a sharply curved flange that provides a well-protected view of the glottis but excludes the tube as well as the tongue, and so requires a wider path to accept tube passage lateral to the blade. This can make insertion of the tracheal tube difficult. Some straight blade variants (eg, Phillips, Wisconsin, or Henderson) have a higher flange that allows tube passage via the lumen, although this approach obstructs the view of the glottis (picture 8) [15,16].

Other blades have been described as useful in unusual or anatomically challenging situations, but peer-reviewed literature on the subject is limited (picture 9 and picture 10) [17-20]. Blades of varying angles (along with short laryngoscope handles) may enable the clinician to insert the laryngoscope into the mouth of a patient with a large chest wall or soft tissue at the upper chest that impedes insertion of a standard blade [21].

Modifications of the curved blade include the English version, which curves throughout its length and includes a less prominent flange that extends further toward the tip. In contrast, the standard American blade usually flattens in its midportion before curving again along the distal portion, while its flange tapers more proximally [22]. The German version of the Macintosh blade is similar to the English in shape [23]. The shorter flange of the German and English designs allows easier insertion into a mouth with large front teeth or restricted opening. This design may also reduce the tendency of novices to "lever" the blade against the upper teeth with the intention of improving a limited view of the larynx but which can break teeth. Curved blades with markedly shorter proximal flanges (eg, Callander-Thomas, Biarra-Guiffreda) are designed to reduce the impact of the blade on the front teeth [24].

Another modification is the articulated blade. The McCoy blade and Flexiblade include an articulation controlled by a lever on the handle that allows the laryngoscopist to flex the end of the blade [25]. Blade flexion may increase tension against the glossoepiglottic membrane when the blade tip is in the lateral vallecula, thereby improving the view of the glottis [18,26,27].

The Grandview blade is approximately 80 percent wider than a standard blade. If the oropharynx is large enough to accommodate it, the Grandview blade can improve visualization through more complete displacement of the tongue.

Other blade types have been designed to aid intubation in patients with less room in the oropharynx, but these are not commonly used [17-20].

Light source — Inadequate light reduces visual acuity and can impair performance during DL [28,29]. Thus, it is important to ensure adequate lighting during the procedure. In a survey of Philadelphia emergency departments, poor lighting among the available laryngoscopes was surprisingly common, with light intensity ranging from 11 to over 5000 lux, and a median of around 700 lux (lux is the SI unit of illumination; recommended lighting for detailed visual work is approximately 1000 to 2000 lux) [30]. Similar findings have been reported elsewhere suggesting the need for regular equipment checks and greater vigilance [31].

Light is emitted from a bulb or fiberoptic bundle near the distal tip of the laryngoscope when the laryngoscope blade is opened, completing an electrical circuit. Varying the distance of the light source from the blade tip has several effects. Shorter distances increase brightness but increase the likelihood of shadowing on the larynx when the epiglottis cannot be fully elevated. A long "floppy" epiglottis can be elevated by pressure against the midline HEL, but such elevation may completely block the light (and video feed if present) when the light source is close to the blade tip.

Newer fiberoptic laryngoscopes tend to provide better illumination than incandescent bulb laryngoscopes. The quality of fiberoptic illumination varies substantially with the size of the fiberoptic bundles [23], battery quality, whether rechargeable or standard, battery age, and whether the battery is fully charged. Over time, repeated sterilization may diminish the quality of light emitted by fiberoptic laryngoscopes [32]. Disadvantages of incandescent bulbs include risk of the bulb dimming over time and becoming loose, flickering, or losing illumination, or possibly falling into the airway.

LARYNGOSCOPY TECHNIQUE

Key points — The following elements should be emphasized when performing direct laryngoscopy (DL):

The critical step in DL is to locate the epiglottis.

The goal of sighting the epiglottis informs every movement of the laryngoscope, including the depth of insertion, angle, lift, and rotation. Limit the initial insertion depth so the laryngoscope does not bypass the epiglottis.

The best ways to improve a limited laryngeal view are to:

Increase elevation of the patient's head and flexion of the lower cervical and upper thoracic spine,

and

Perform bimanual laryngoscopy by manipulating the epiglottis with the laryngoscope and the glottis with the right hand (picture 11).

In cases where cervical immobilization is necessary (eg, trauma involving possible cervical spine injury), head elevation and cervical spine flexion are not permitted. In these cases the cervical collar may be opened if needed, but an assistant must provide in-line head and neck stabilization during the procedure.

DL is best performed with a trained assistant. The assistant lifts the head and flexes the spine, allowing the laryngoscopist to preserve arm strength and perform fine motor movements. Although neck extension (as classically described in the "sniffing" position) may improve glottic exposure compared with a supine position with the patient's head laying flat, neck extension is usually counterproductive and should be avoided. (See 'Optimizing the view' below.)

Bimanual laryngoscopy should be performed routinely. It involves moving the hyoid bone and thyroid cartilage (not the cricoid) with the right hand, helping to bring the glottis into view. (See 'Bimanual laryngoscopy (external laryngeal manipulation)' below.)

Be prepared for unanticipated difficulty.

Prepare meticulously and perform laryngoscopy properly every time, even when no markers for difficult intubation are identified before the procedure. Simplified approaches work in easy cases, but the best patient care requires a carefully planned approach that includes habitual use of bimanual laryngoscopy, ready access to rescue airways, a back-up plan, and the capacity to provide a surgical airway, if necessary. Prepare as if every case is unpredictable.

SpO2 should be monitored continuously during laryngoscopy. Patients are apneic during rapid sequence intubation and despite preoxygenation and apneic oxygenation, SpO2 will fall over time, sometimes precipitously depending on patient comorbidities and clinical circumstances.

Once SpO2 drops below 90 percent, oxygen saturation falls rapidly. Therefore, in many cases – particularly with unstable patients – where the SpO2 has fallen to 90 percent and intubation remains incomplete, it is necessary to stop the procedure in order to raise the patient's oxygen saturation with bag mask ventilations using high flow oxygen.

However, no rules are absolute and clinicians must use their judgment about when it is necessary to halt the procedure to provide oxygen. As an example, this may not be necessary for stable patients in the operating room when an experienced clinician has a clear view of the larynx and the endotracheal tube (ETT) is on the verge of being successfully placed.

Laryngoscopy and intubation occur in a stressful environment and require great concentration, especially in emergency situations. At times, the laryngoscopist may lose track of the duration of the patient's apnea during intubation attempts. Therefore, it is important that an assistant monitor the patient's oxygen saturation (SpO2) continuously.

Overview — The basic steps for performing DL and tracheal intubation include the following:

Obtain assistance.

Prepare equipment, monitors, and medications. (See 'Preparation' above.)

Assess, preoxygenate, provide apneic oxygenation, and position the patient.

Open the patient's mouth, and carefully position the laryngoscope.

Deflect the tongue and soft tissue to the left side of the mouth with the flange

Locate the epiglottis.

Identify and optimize the view of the glottis using bimanual laryngoscopy, head elevation, and lower neck flexion (head elevation and neck flexion are not performed when cervical spine precautions are necessary). (See 'Optimizing the view' below.)

Guide the tracheal tube to the glottis, and insert it through the vocal cords into the trachea under direct vision.

Remove the stylet, and inflate the ETT balloon.

Confirm positioning of the tube within the trachea using CO2 detection and physical examination. Outside the operating room, confirmation generally entails a chest radiograph.

Secure the tracheal tube.

Set parameters for mechanical ventilation.

Provide sedation and analgesia as needed.

Positioning the patient — Proper patient positioning is important for maximizing the chances of successful intubation. However, in the presence of potential cervical spine injury, head and neck manipulation must not be performed, and DL must be modified so as to protect against exacerbating any injury or traumatizing the spinal cord. In this setting, manual in-line stabilization should be used to minimize cervical spine motion, and the directions below about head and neck positioning do not apply [33].

The classic "sniffing" position (atlanto-occipital extension with head elevation of 3 to 7 cm) is adequate for experts to intubate most patients, but further elevation almost always improves glottic exposure [34-38]. Initial positioning with the head elevated as high as necessary but not so high as to interfere with blade insertion, improves the laryngeal view and reduces the need for repositioning during intubation. Such positioning is especially important when intubation is anticipated to be difficult, including patients with hemodynamic instability, inadequate preoxygenation, morbid obesity, and abnormal airway anatomy (eg, recessed jaw, buck teeth, large tongue). An assistant strong enough to lift the patient's upper trunk and head should stand at the bedside to help with positioning, and to provide cricoid pressure when necessary. (See "Approach to the difficult airway in adults for emergency medicine and critical care".)

Hemodynamically stable patients with adequate preoxygenation generally tolerate the slightly prolonged apnea associated with additional head elevation maneuvers when they are well-planned and executed, but it is best to optimize positioning before attempting intubation. Should a second attempt at DL be necessary, bag-mask ventilation can be performed between attempts as needed.

A useful landmark for determining adequate head elevation is the alignment of the patient's ear (external auditory meatus) to the level of the sternal notch when seen from the side (sagittal view) (picture 12 and figure 5) [34]. This positioning can be achieved by using linens or specially designed devices or beds to create a ramp.

The alignment achieved with this positioning reflects the forward displacement of the head relative to the thorax, which is achieved by flexing the spine, or more specifically the upper thoracic and lower cervical spine. Flexing the upper cervical spine moves the head toward the chest and increases resistance to tongue displacement, thereby increasing intubation difficulty. Tilting the head back by extending the atlanto-occipital joint is helpful, but extension of the cervical spine below the atlanto-occipital joint can compromise the glottic view [37,39]. Arching of the neck away from the table surface indicates undesirable cervical extension, although visible arching is not a reliable way to determine the degree of extension. Flexing the bed at the hips does not change the relationship of the head relative to the thorax and does not by itself improve the view of the glottis.

Despite careful initial positioning, obtaining an adequate view of the larynx may require additional manipulation of the patient's head, neck, and glottis. Therefore, the patient's initial position should allow an assistant to elevate the patient's head and flex the lower neck further with ease. Ideally, an assistant performs any additional lifting of the head and flexion of the neck, allowing the laryngoscopist to maintain a view of the larynx and to concentrate on performing bimanual laryngoscopy to improve glottic exposure. (See 'Optimizing the view' below.)

Opening the mouth and inserting the blade — Opening the patient's mouth and inserting the laryngoscope blade is usually not difficult. The scissor technique is an effective method for opening the mouth with one hand. To perform the technique, hold the tips of the thumb and middle finger of the right hand together, insert them between the upper and lower incisors, and "scissor" them past one another by flexing each digit (picture 13).

The mouth can also be opened by pushing the occiput down, towards the pillow, with the right hand, thereby extending the upper neck and making it possible to change the angle of blade insertion. In patients who are sedated and placed in a supine or slightly head-elevated position, this technique generally opens the mouth sufficiently to allow the blade to be inserted without the handle hitting the chest. Regardless of the method chosen, the blade is inserted in a controlled fashion to avoid injuring teeth or soft tissue.

Difficulty inserting the blade may occur for a number of reasons, including a small mouth, recessed mandible, prominent upper teeth, limited upper cervical spine or atlanto-occipital mobility, or a large chest wall that blocks insertion. Using a smaller blade (eg, Macintosh or Miller size 2), a smaller blade handle, or having an assistant retract the lip laterally may be helpful.

When insertion is prevented because the patient's chest is obstructing the laryngoscope handle, placing towels or blankets under the head and upper back to elevate the head relative to the chest is often helpful. Alternative approaches include rotating the laryngoscope blade for insertion and then rotating it back to the correct plane once it is in place, not snapping the attached blade handle open until after blade insertion, or inserting the laryngoscope blade without the handle and attaching it once the blade is in position. If available, a short laryngoscope handle or one which permits adjustments in the angle between the blade and the handle can be used. Short handles were once popular for the intubation of obese parturients as well as polio patients in the early days of mechanical ventilation (hence the moniker "polio blade") [21].

Optimizing the view

General guidance — The following techniques can be used to improve an inadequate view of the glottis:

Use bimanual laryngoscopy, with external laryngeal manipulation. (See 'Bimanual laryngoscopy (external laryngeal manipulation)' below.)

When performing curved blade laryngoscopy, be certain that the tip of the blade is correctly seated by noting how the epiglottis responds to small brief applications of pressure from the blade tip.

Keep the tongue contained within the left side of the mouth.

Increase head elevation by flexing the lower neck. Have an assistant perform these maneuvers. Avoid the common tendency to extend the neck, which generally does not improve the view.

Should the techniques above fail, use a laryngoscope blade of a different size or shape, or a tracheal tube introducer, or try a different approach (eg, paraglossal straight blade). (See 'Paraglossal technique' below and 'Tracheal tube introducer (bougie)' below.)

Lifting the head and flexing the neck — An inadequate view of the glottis can often be corrected by elevating the patient's head and flexing the lower neck. If the tip of the epiglottis does not appear when the base of the tongue is elevated with the laryngoscope, lifting the head reduces tension on the soft tissues and mobilizes the hyoid, which helps to bring the epiglottis into view. Elevating the head has consistently been shown to improve suboptimal views of the glottis during DL [35-37].

Outside the operating room – Outside of the operating room, some clinicians enlist the help of a knowledgeable assistant to lift the head and flex the neck under the guidance of the laryngoscopist. Use of an assistant allows the laryngoscopist to maintain the view of the larynx, control the tongue, and concentrate on performing bimanual laryngoscopy. In addition, it prevents the laryngoscopist's left arm from tiring, which allows for finer control of the laryngoscope, which is necessary for proper placement of the blade tip during curved blade laryngoscopy. Fatiguing arms can lead to a worsening view of the glottis, as control of the laryngoscope becomes compromised, and may cause the clinician to rush intubation.

The assistant is positioned to the left of the patient's head. Under the direction of the laryngoscopist, the assistant lifts the head and flexes the lower neck (and upper thorax) in a controlled manner until the exposure of the glottis no longer improves. The force required to lift the head and flex the upper thorax can be considerably more than an unassisted operator can manage. However, some clinicians prefer to maneuver the head and neck into the optimal position themselves and then have their assistant maintain that position. The laryngoscopist should maintain the view of the larynx throughout the procedure, regardless of the method chosen.

As the head is elevated and the neck flexed, the force vector of the laryngoscope handle rotates forward (or downward). Obtaining a good view of the glottis may require maximal flexion, which may in turn require that the operator lean far forward. Repositioning may be necessary to accomplish this (eg, lowering the bed or pulling the patient's head to the edge of the bed). Obviously, it is best if this potential need is anticipated and prepared for in advance.

General anesthesia in the operating room – Laryngoscopy for anesthesia is more commonly performed without having an assistant lift the patient's head. It may be accomplished by placing the right hand under the patient's occiput and lifting the head until the most favorable position is achieved. If necessary, the occiput can rest against the clinician's chest or abdomen for stability, while the right hand is used to insert the ETT. Throughout this process, the left hand continues to manipulate the laryngoscope, while the clinician continuously observes the larynx.

Bimanual laryngoscopy (external laryngeal manipulation) — Bimanual laryngoscopy, also called external laryngeal manipulation (ELM), entails manipulating the thyroid cartilage or hyoid bone with the right hand in order to improve the view of the glottis. Observational studies and clinical experience suggest that ELM improves the view of the glottis substantially during most intubations [40,41].

The thumb and forefinger of the right hand can be placed on the thyroid cartilage as soon as that hand is no longer needed to help keep the mouth open and avoid injuring the lips and teeth during insertion of the laryngoscope blade. The intubator then uses the right hand to press and move the thyroid cartilage while observing the larynx (picture 11 and picture 14). Once the optimal glottic view is obtained, the laryngoscopist has an assistant place their fingers in exactly the same spot on the thyroid cartilage, using the same direction and degree of force necessary to maintain the view. Blind attempts by an assistant to manipulate the larynx are not nearly as effective and should be discouraged. When applied early during DL, bimanual laryngoscopy enables the intubator to optimize the laryngeal view more effectively and efficiently than can be done by probing with the laryngoscope alone.

Regardless of blade type, when the hyoid is lifted, the glottis may be pulled anteriorly and out of the laryngoscopist's line of sight. Bimanual laryngoscopy counteracts the lifting forces of the laryngoscope, allowing the laryngeal structures to be brought into view.

Note that bimanual laryngoscopy is different than cricoid cartilage pressure (ie, Sellick's maneuver), which is performed to prevent passive regurgitation from the stomach during laryngoscopy. Performance of Sellick's maneuver is optional and is discussed separately. (See "Rapid sequence intubation in adults for emergency medicine and critical care", section on 'Positioning and protection'.)

The "BURP" maneuver (backward, upward, rightward pressure) is less effective at improving the glottic view than bimanual laryngoscopy [42,43]. This makes sense because the direction of the force needed to obtain the best view of the glottis varies among patients.

Glottic view scores — Two scoring systems are used to describe the view of the glottis obtained by DL. The Cormack-Lehane system provides a general description using four categories: grade I is a full view of the entire glottis; grade II is a view of the posterior portion of the glottic opening; grade III is a view of the epiglottis only; and with grade IV neither the epiglottis nor the glottis can be seen (figure 6) [44]. The percentage of glottic opening (POGO) score provides a more precise estimate of glottic exposure [45]. As an example, POGO scores 10, 50, and 90 convey important differences about the relative ease or difficulty of intubation that are not captured by the Cormack-Lehane system. Extremely limited views (eg, POGO score of 0, Cormack-Lehane score of III or IV) suggest that tube placement will be difficult.

CHOICE OF LARYNGOSCOPE BLADE — Most clinicians prefer to initiate laryngoscopy with a curved blade. The larger spatula and flange of most curved blades provides a greater area for viewing and manipulation of the tracheal tube. In addition, many clinicians prefer the feel of a curved blade, which more closely approximates the shape of the tongue and seats easily in the vallecula.

Nevertheless, the straight blade provides advantages in some circumstances [46]. It frequently allows a more complete view of the laryngeal inlet, since the epiglottis is lifted out of the way. This is true in patients with a long, floppy epiglottis, which can be difficult to control using a curved blade placed in the vallecula. The straight blade may also provide a superior view when the larynx is situated anterior to the line of sight, or in patients with a receding chin or pathology at the base of the tongue [47]. Such pathology blocks access to the vallecula and limits the pressure that can be placed on the hyoepiglottic ligament, which is essential for effective curved blade laryngoscopy.

It is often easier to insert a straight blade, rather than a curved blade, if the patient's mouth is small, mouth-opening is limited, or the front incisors are prominent. Also, when using a straight blade there is less of a tendency to lever back on the laryngoscope handle to elevate the epiglottis, which can damage protuberant teeth.

According to expert opinion and several observational studies, straight laryngoscope blades may be more effective during difficult intubations, particularly if a paraglossal approach is used [48-50]. In the largest of these series, 160 patients undergoing general anesthesia were randomly assigned to intubation using either a paraglossal approach with a Miller blade or a standard approach with a Macintosh blade [50]. The paraglossal approach provided significantly better views of the larynx, providing a grade I Cormack-Lehane view in 95 percent of cases compared with 80 percent in the Macintosh group.

CURVED BLADE LARYNGOSCOPY

Curved blade technique — Below we outline our suggested approach to performing curved blade laryngoscopy.

Step 1: Open the mouth sufficiently to allow blade insertion without traumatizing the teeth (picture 13). (See 'Opening the mouth and inserting the blade' above.)

Step 2: Insert the blade and control the tongue.

The blade may be inserted in the midline, as is easier for novices, or along the right side of the mouth, as experience compensates for less clear navigation landmarks, or when required to push the tongue laterally. With either approach the clinician should first identify and control the tongue [46,51].

Some experts recommend insertion in the midline, preferring to concentrate on identifying the epiglottis first and then maneuvering the flange of the blade to push the tongue to the left side of the mouth [51]. They believe midline insertion, particularly for those learning the technique, makes it easier to find the epiglottis and reduces the risk of anatomic distortion that may occur with lateral insertion and retraction. In either case, the tongue must be kept out of the line of sight while the glottis is located.

Step 3: Carefully advance the blade toward the epiglottis in a controlled manner, gently lifting the blade tip every few millimeters.

Identification of the epiglottis, which lies at the base of the tongue, is the key step to successful direct laryngoscopy. Carefully but steadily advancing and lifting the laryngoscope blade should enable the clinician to find the epiglottis readily. Inserting or advancing the laryngoscope blade in an uncontrolled manner without properly identifying the epiglottis can cause the blade to bypass the epiglottis and even the larynx, potentially resulting in injury or esophageal intubation.

Step 4: Advance the tip of the blade into the vallecula, the recess between the base of the tongue and the epiglottis.

Avoid folding the epiglottis with the blade, which may partially or completely obscure the glottis (picture 15).

Step 5: Identify the best spot for elevating the epiglottis.

Ideally, the tip of the blade is placed against the hyoepiglottic ligament (HEL), the cord-like structure that attaches the epiglottis to the hyoid bone. When the view is optimal, the ligament may be seen as a midline structure dividing the vallecula into two almond-shaped spaces.

Once the laryngoscope blade is seen to raise the epiglottis, the objective is to press the blade tip into the HEL at approximately a right angle to elevate the epiglottis. Usually the HEL cannot be seen directly so positioning is best achieved by "spooning." Spooning consists of advancing the blade a few millimeters at a time, lifting the blade forward in the direction of the handle, and then observing the response of the epiglottis. Lifting during spooning involves small forward pulsing movements of the blade tip. Observing the response to successive small pulsing lifts is invaluable for finding the optimal position.

Brisk elevation of the epiglottis during spooning indicates optimal placement against the HEL in the first few millimeters below the hyoid. Twisting to one side indicates tip placement lateral to the HEL on the corresponding side. Sluggish elevation may be due to inadequate advance (still on the tongue or against the hyoid) or inadequate elevation of the patient's head, resulting in an angle of approach that is too acute. Movement of the tip of the epiglottis away from the operator indicates that the blade tip is placed at too acute an angle on the epiglottis or lies too distal on the epiglottis, which may be due to inadequate caudad displacement of the tongue. In either case, the blade should be pulled back a few millimeters while the head is further elevated, as this improves both tongue displacement and the angle of approach to the HEL.

An alternative approach to identifying the best location for the blade tip is external manipulation of the larynx. This is done by pressing on the thyroid cartilage with the fingers of the right hand and making repeated small, brief movements while gradually adjusting the position of the blade tip. The clinician can thereby determine which blade tip position creates the greatest elevation of the epiglottis. Simultaneous external manipulation of the larynx and spooning reduce the time required for optimal positioning of the blade tip [40]. (See 'Bimanual laryngoscopy (external laryngeal manipulation)' above.)

Step 6: Lift the laryngoscope in the direction of the handle, thereby exposing the glottis; do not lever back on the teeth with the laryngoscope handle (picture 16 and picture 17).

Once the blade tip is properly positioned, lift the laryngoscope. A properly positioned blade tip may allow for an excellent view of the glottis without requiring a great deal of lifting force. However, in some cases significant exertion may be needed. Keep your elbow in (ie, arm adducted) for maximal lifting strength. Many novices begin lifting before the blade is correctly positioned, which may result in a poor view, arm fatigue, or both.

When lifting a laryngoscope with a curved blade, the correct initial force vector points approximately 45 degrees from the plane of the floor. This lifting motion elevates the epiglottis, keeps the tongue out of the line of sight, and maximizes exposure of the glottis. It also prevents levering back on the teeth.

Even when exposure is adequate for endotracheal intubation, we recommend routinely elevating the head to gain optimal exposure for easier intubation, so that when difficult cases are encountered, optimal practice is already the routine. Techniques for optimizing the view of the glottis are described above. (See 'Lifting the head and flexing the neck' above.)

The natural inclination for many novice intubators is to lever backwards on the laryngoscope handle. This motion can not only damage teeth but may interfere with the laryngoscopist's view as well.

Step 7: Optimize the glottic view as needed with external laryngeal manipulation, head elevation, and neck flexion. These techniques are described in detail separately. (See 'Optimizing the view' above.)

The optimal head and neck position is determined empirically by the best view of the glottis that can be obtained. Early manipulation of the thyroid cartilage with the laryngoscopist's right hand should be used routinely to improve the view.

Step 8: Place the tracheal tube.

Perform all emergency intubations with a stylet in the tracheal tube. The angle of the endotracheal tube (ETT) stylet should not exceed 35 degrees, and the stylet (and ETT) should be straight from the proximal end to the cuff. More acute angles at the end of the ETT (eg, "hockey stick" conformation) may cause the tip to become stuck on the anterior trachea, preventing advancement (and possibly traumatizing the airway) [10]. In this shape, the ETT can pass lateral to the blade as it enters the mouth and dorsal to (ie, below) the blade as it is advanced, allowing the clinician to maintain the view of the glottis as the tube is advanced.

It is helpful to have an assistant retract the right side of the lip laterally to increase the space available to insert the ETT. Experienced operators can use the little and ring fingers of the right hand to retract the lip, while the other fingers grasp and pass the ETT, although this approach is more challenging.

Avoid putting the ETT into your line of vision while advancing it into the oropharynx. The ETT should enter the mouth lateral to the blade and travel along the palate below the line of sight. It then should be manipulated so the tip appears from below at the glottic opening. This allows the clinician to watch the ETT advance into the glottis. In addition, this approach makes the leading edge of the ETT appear vertical and enables the clinician to watch the bevel enter the slit-shaped opening between the vocal cords.

Once the tip of the ETT has passed the vocal cords, the laryngoscopist should pause and ask an assistant to remove the stylet. Inserting the ETT further with the stylet in place may cause injury or obstruct tube passage. While the stylet is removed, the laryngoscopist should maintain a firm grasp of the ETT to prevent dislodgement and should keep the glottis and tube in view.

ETT insertion depth — The ETT should be advanced under direct vision until the proximal edge of the cuff is at least 3 to 4 cm beyond the vocal cords, ideally placed at the mid-trachea. The goal is to place the tip of the ETT 2 to 4 cm from the carina (to avoid endobronchial intubation) and the proximal edge of the cuff at least 3 cm below the vocal cords (to avoid vocal cord damage and inadvertent extubation).

The contributors to this topic advance the tube under direct vision until the black intubation guide mark on the ETT passes through the cords and expect the tube to sit at 21 cm at central incisors or alveolar ridge in women, and at 23 cm in men, adjusted for patients who are especially tall or short.

Some studies suggest that more accurate ETT depth estimates are obtained by using measurements of individual patient anatomy, including a height-based formula [52,53], or measurements between external anatomic features of the head and neck (eg, corner of the lip, manubrium, cricoid cartilage, sternal notch) [54-56]. Regardless of the method used for initial ETT placement, proper placement must be confirmed to exclude esophageal intubation or mainstem bronchus intubation, using one of the methods discussed below. (See 'Confirming proper tracheal tube placement' below.)

STRAIGHT BLADE LARYNGOSCOPY

Straight blade techniques — A straight blade may be inserted to the right of the tongue (paraglossal technique) or in the midline [57,58]. The paraglossal approach involves inserting the straight blade into the natural gutter between the tongue and the lower molars. The Miller blade, with its short flange and narrow spatula, is particularly useful in this relatively cramped space. By inserting the blade in the paraglossal gutter, the tongue is generally well displaced with minimal effort and a better view is obtained. In addition, the distance to the epiglottis is shorter compared with a midline approach.

The "retromolar" or "molar" approach uses a more lateral insertion [59]. This approach is not well studied but has been described as an alternative rescue technique.

Midline technique — When using a midline approach, the technique is much like that for a curved blade, with the exception of lifting the epiglottis. (See 'Curved blade technique' above.)

When a straight blade is inserted in the midline, it can be difficult to control the tongue, which often envelops the blade and obscures the view, particularly in the unconscious, relaxed adult.

Paraglossal technique — The paraglossal technique using a straight laryngoscope blade is performed as follows (picture 18):

Step 1: Insert the tip of the straight blade into the right paraglossal gutter. This may require inserting the blade tip initially at the midline or even the left side of the oral cavity to capture and control the tongue and keep it corralled at the left of the mouth, thereby allowing a proper view and adequate space for insertion of the blade into the right paraglossal gutter.

Step 2: Advance the tip of the blade along the gutter beside the tongue to just past the anterior pillar, then swing the tip toward the center.

Step 3: In a controlled and deliberate manner, continue to advance the blade tip while looking for the epiglottis.

Step 4: Use lateral and anterior pressure to keep the tongue displaced to the left.

Assuming cervical spine precautions are unnecessary, moving the head slightly to the left, with slight left rotation, may improve exposure of the glottis.

Proper tongue control is crucial. The tongue should be well displaced to the left, creating adequate space to view the glottis and insert the tracheal tube.

Avoid pushing the blade past the larynx into the hypopharynx. Blind thrusting of the blade against the mucosa in the periglottic region may injure the larynx, pharynx, or esophagus. Furthermore, lifting the laryngoscope while it is positioned in the hypopharynx may reveal the orifice of the proximal esophagus and mislead the inexperienced laryngoscopist, leading to an esophageal intubation [46].

Step 5: Once the epiglottis is identified, advance the tip of the blade posterior to the epiglottis and into the laryngeal inlet. Use the blade tip to lift the epiglottis, exposing the glottis (picture 19 and figure 7).

Avoid levering back with the laryngoscope (picture 17).

Step 6: Optimize the glottic view as needed with external laryngeal manipulation, head elevation, and lower neck flexion. (See 'Optimizing the view' above.)

Step 7: Insert the tracheal tube.

Insert the endotracheal tube (ETT) from the right side of the mouth. Avoid using the barrel of the blade to guide insertion of the ETT. Rather, pass it below (cephalad to) the blade, close to the roof of the mouth. Often it will not be visible until it arrives at the posterior commissure. Insert it directly into the trachea while watching the tube pass between the vocal cords. This allows one to retain control of the direction of tube insertion and permits visualization of the tip as it passes into the laryngeal opening.

The lips often impede the view and placement of the ETT when using a paraglossal approach. Avoid this obstacle by having an assistant retract the lip laterally. Alternatively, use the ring and little fingers of the right hand to do so, although this is generally more cumbersome.

The ETT should not be inserted through the barrel of a straight laryngoscope blade, as doing so obscures the view of the glottis. If there is not enough space to insert the ETT beside the blade, a tracheal tube introducer (ie, bougie) may be placed through the cords, and the ETT then inserted over the introducer.

TIPS FOR ADVANCING A STUCK TRACHEAL TUBE — Sometimes entry into the glottis is problematic due to its position (so-called "anterior" larynx) or crowding of structures in the oral cavity and pharynx, which may obstruct the course of the styletted tube during insertion. One maneuver that may help in such situations is to rotate the endotracheal tube (ETT) clockwise 90 degrees as the ETT tip approaches the glottis, which causes the ETT to approach more laterally and allows for a better view of the glottis, and then rotating the ETT back counterclockwise to the original position (vertical orientation) to place the tip through the glottis.

In difficult intubations, when the tip of the ETT may not be visible during attempts to insert it into the glottis (eg, percentage of glottic opening [POGO] <10 percent, and guidance provided by posterior cartilages), it is not unusual for the bevel of the ETT to catch on the aryepiglottic folds. This is more common if a "bougie" or other ETT exchange device is being used, or when intubating over a fiberoptic scope, as the space between the ETT and the device within it can permit lateral movement of the tip of the tube relative to the device, allowing the tip to catch on soft tissues as it enters the glottis. In this situation, when resistance is perceived it is often helpful to retract the ETT a short distance (1 to 2 cm) to disengage it from the soft tissues, rotate it 90 degrees clockwise or counterclockwise, and then attempt re-insertion [60]. Specialized ETTs with flexible, bull-nose tips (ie, Parker Flex-Tip) have been found to reduce the incidence of such difficulty during entry into the glottis (picture 20) [61].

During insertion, sometimes the ETT comes into contact with the anterior tracheal wall after the tip passes between the vocal cords, where it may meet resistance and fail to advance [62]. When such resistance develops, in most cases withdrawing the stylet allows the tip to drop away from the anterior wall and the ETT to be advanced. Clinicians should avoid using excessive force to advance the ETT or to "screw" it into position as injury may result.

Another means of coping with this problem is to gently rotate the ETT 90 degrees clockwise after the tip passes between the vocal cords, which positions the bevel facing upwards (anteriorly), and helps to deflect the ETT from the anterior wall. In an extreme situation, the ETT may have to be rotated further to cope with a sharp posterior angulation of the trachea relative to the axis of the larynx [62].

NASAL INTUBATION USING DIRECT LARYNGOSCOPY — Nasotracheal intubation is rarely performed outside the operating room but may be required for a variety of surgical procedures. Nasal intubation can be performed using a flexible intubating scope, or with direct laryngoscopy (DL). Preparation of the naris to avoid epistaxis and the technique for flexible scope intubation through the nose are discussed separately. (See "Flexible scope intubation for anesthesia", section on 'Nasal intubation' and "Flexible scope intubation for anesthesia", section on 'Nasal preparation'.)

Magill forceps should be available for nasal intubation with DL. This instrument is used to grasp the endotracheal tube (ETT) in the posterior pharynx, to advance or direct the ETT into the laryngeal inlet. Magill forceps have a bend in the handles such that they are out of the line of sight, on the right side of the mouth, when being used (picture 21).

Steps for nasotracheal intubation using DL are as follows:

Insert the ETT Insert the ETT through the prepared nostril into the posterior pharynx. (See "Flexible scope intubation for anesthesia", section on 'Nasal intubation'.)

Perform laryngoscopy Visualize the glottis and the tip of the ETT in the posterior pharynx. (See 'Laryngoscopy Technique' above.)

Advance the ETT Using the right hand, advance the ETT. It will tend to go posterior to the glottis; the tip may be elevated by rotating the tube or extending the head. If necessary, grasp the tube with Magill forceps proximal to the cuff, to aim the tube at the glottic opening. The forceps can be used to pull the tube forward, but it is often easier to have an assistant advance the tube into the nose while using the Magill forceps to direct the tip.

Confirm ETT placement Confirm correct ETT placement as for oral intubation. (See 'Confirming proper tracheal tube placement' below.)

TRACHEAL TUBE INTRODUCER (BOUGIE) — The tracheal tube introducer, also known as an intubating introducer or gum elastic bougie (or simply "bougie"), is an effective and important adjunct to direct laryngoscopy and difficult airway management. When the view of the glottis is limited, the introducer can be placed in the trachea using tactile and limited visual cues and then a tracheal tube can be inserted over it. Discussions of the types of tracheal tube introducers, their use, and the evidence for them are found separately. (See "Endotracheal tube introducers (gum elastic bougie) for emergency intubation".)

CONFIRMING PROPER TRACHEAL TUBE PLACEMENT — Proper endotracheal tube (ETT) placement in the trachea must be confirmed immediately.

Excluding esophageal intubation — Esophageal intubation can lead to devastating complications, and must be recognized immediately. Several methods may be used to confirm tracheal, rather than esophageal, tube placement.

End-tidal carbon dioxide — End-tidal carbon dioxide (EtCO2) determination (either colorimetric or quantitative capnography) is the most accurate means of confirming ETT placement in the trachea in the non-cardiac arrest patient and should be used with every intubation (picture 22) [63-65]. Quantitative capnography is routinely used in the operating room. Clinicians should be aware that the esophagus may yield small but detectable amounts of CO2 during the first few positive pressure ventilations [66]. Thus, at least five exhalations with a consistent CO2 level must be evident before one can confidently assume that the ETT is in the trachea. Physical examination and plain chest radiography may provide useful information but cannot be used as proof of proper placement. Capnography is discussed separately. (See "Carbon dioxide monitoring (capnography)".)

In patients without detectable pulses, gas exchange in the lungs is markedly reduced and CO2 may not be detectable despite proper positioning of the ETT [67]. Patients in cardiac arrest may not generate CO2, making the absence of CO2 detection unhelpful. However, when CO2 is detected in the cardiac arrest patient and persists for six breaths, the ETT is in the airway.

Clinical findings — Published reports and clinical experience make clear that clinicians cannot rely on clinical findings, such as visualization of the ETT through the cords, misting of the tube with ventilation, or auscultation of breath sounds over the lung fields, as the sole means for confirming ETT placement [64,65,68-70]. Nevertheless, such findings may help support the likelihood of proper placement or suggest misplacement. Listen for equal breath sounds in both axillae and absence of breath sounds over the epigastrium. Other findings consistent with tracheal placement, but which also may be misleading, include rise of the chest wall with positive pressure ventilation and mist in the ETT with each exhalation.

Alternative methods — Alternative methods for determining proper ETT placement have been used successfully in pulseless patients.

Esophageal detector device (EDD) – EDDs use suction applied with syringes [68,71,72] or bulb suction devices [73-75] to distinguish between the trachea (which is rigid and allows a free flow of air into the device) and the esophagus (which is collapsible, permitting little airflow when suction is applied). EDDs can be useful (eg, in cardiac arrest) but are not infallible [76]. The likelihood of tracheal placement is high if over 30 mL of gas can be withdrawn from the ETT into the bulb without resistance.

Endotracheal introducer – There is some evidence that an ETT introducer (Eschmann introducer, or bougie) may be useful as an ETT confirmation device [77]. After passing the introducer through the ETT, the clinician can feel the introducer tip move over the tracheal rings. In addition, as the introducer is gently advanced, the clinician will feel the introducer stop moving as its tip comes to rest within a bronchus. No such halt to the tips advancement is encountered if the ETT has been misplaced into the esophagus, as the introducer will pass easily without significant resistance. Use of the introducer for emergency airway management is reviewed separately. (See "Endotracheal tube introducers (gum elastic bougie) for emergency intubation".)

Chest radiograph A single view (usually anteroposterior, or AP) chest radiograph is helpful for determining the depth of the ETT in the trachea and should be obtained in the emergency setting for this purpose, but it cannot reliably exclude esophageal intubation [78].

Ultrasound – Ultrasound is the subject of ongoing study in both adult and pediatric populations as a method for assessing ETT placement [79-83]. A 2020 meta-analysis of 30 prospective studies involving 2534 adult patients reported a pooled, estimated sensitivity of 98 percent (95% CI 97-98) and specificity of 96 percent (95% CI 90-982) for identifying endotracheal tube location after intubation [84]. Subgroup analyses revealed no significant difference by technique, ultrasonographic sign, clinical specialty, or transducer type.

Despite this encouraging data, some limitations of ultrasound should be noted. Availability may be limited in some settings, particularly in some places where emergency intubations are performed, such as in the field or at smaller hospitals. The most accurate way to evaluate ETT placement with ultrasonography is with dynamic scanning of the tracheal region during the intubation, which requires that a skilled second clinician be present to perform and interpret the ultrasound scan. This may not be possible in many cases. Finally, ultrasound interpretation is user-dependent, and the high sensitivity and specificity reported in studies may not apply in the hands of individuals with less training or experience [85].

Lung ultrasound can also be used to confirm correct placement of an endotracheal tube in the trachea once ventilation is established [86]. (See "Overview of perioperative uses of ultrasound", section on 'Diagnosis of specific abnormalities'.)

Flexible intubation scope (FIS) – If immediately available, an FIS can be passed through the ETT to confirm placement in the trachea. Tracheal rings and the carina should be visualized beyond the tip of the ETT if it is correctly placed.

Excluding mainstem bronchus intubation — Although less acutely dangerous than esophageal intubation, endobronchial intubation (ETT inserted into a mainstem bronchus) can produce major complications over time, such as hypoxia, hypercapnia, and pneumothorax [87]. Endobronchial placement occurs more often in women and during emergency intubations [88].

EtCO2 detection does not distinguish between endotracheal, endobronchial (too deep), and supraglottic (too shallow) ETT placement. Other methods for excluding endobronchial intubation include the following:

Unequal breath sounds Breath sounds that are significantly louder on one side suggest endobronchial intubation. Listen for breath sounds in both axillae. This helps to avoid being misled by transmitted breath sounds, which can occur when listening in the center of the chest.

Chest radiograph A single view (usually anteroposterior, or AP) chest radiograph is helpful for determining the depth of the ETT in the trachea, including possible endobronchial intubation [78]. The tip of a properly placed ETT should lie approximately 2 cm above the carina [89].

Flexible scope intubation (FSI) In the operating room, an FIS is occasionally used to confirm endotracheal, rather than endobronchial, intubation. The FIS is passed through the ETT; visualization of the carina beyond the tip of the ETT confirms correct placement.

Depth of ETT insertion The appropriate depth for ETT placement has historically been guided by the measurements on the side of the ETT. We prefer to use the teeth or gums to determine the depth of insertion (rather than the lips) because they are fixed landmarks. The ETT should generally be inserted to a depth of 20 to 21 cm in women, and 22 to 23 cm in men [90,91].

Ultrasound Ultrasound can be used to confirm ventilation by observing the "lung sliding sign," which represents the movement of the pleural membranes as the lung expands and contracts [80,81]. This may allow for rapid diagnosis of bronchial intubation if lung sliding is seen in only one lung [81].

The results of a small randomized trial suggest that bedside ultrasound can provide an accurate assessment of ETT depth, and is superior to auscultation to rule out endobronchial intubation [92]. In this study, bedside ultrasonography was used to identify pleural "lung sliding" (a sign of proper ventilation) and the position of the inflated ETT cuff. Further study is needed to confirm these findings in a broad array of patients.

POST-INTUBATION MANAGEMENT — Once tracheal placement is confirmed, the endotracheal tube (ETT) should be secured with tape or a commercially available tube holder. Tube holders are often easier to manage, particularly if the position of the ETT must be changed and may be more comfortable for patients. However, a systematic review of studies evaluating different means of securing ETTs found that no method was superior to the others in preventing ETT displacement [93].

In the emergency setting, mechanical ventilation, medication (eg, sedatives, analgesics), and arrangements for transfer to an intensive care setting are the next steps in post-intubation management. Appropriate parameters for positive pressure ventilation are determined based upon the disease process, and sedation and analgesia are provided using validated treatment algorithms. These issues are reviewed separately. (See "Mechanical ventilation of adults in the emergency department" and "Sedative-analgesia in ventilated adults: Management strategies, agent selection, monitoring, and withdrawal".)

COMPLICATIONS — Complications may occur during laryngoscopy, particularly with difficult intubations. Sore throat is the most common complication of intubation. Other complications include hypoxia, hemodynamic changes, aspiration, bronchospasm, and airway trauma. Complications of airway management are discussed in detail separately. (See "Complications of airway management in adults".)

VIDEO AND OPTICAL LARYNGOSCOPY — Indirect means of viewing the larynx using devices such as video and optical laryngoscopes are gaining popularity. These devices are portable and provide high quality images, and multiple trials have demonstrated their usefulness in airway management. Nevertheless these devices are expensive and not universally available, and the direct laryngoscopy techniques described in this topic are likely to be used for years to come. Video and optical laryngoscopes are discussed separately. (See "Devices for difficult airway management in adults for emergency medicine and critical care", section on 'Advanced laryngoscopes'.)

AIRWAY MANAGEMENT FOR PATIENTS WITH COVID-19 — In patients with novel coronavirus (COVID-19 or nCoV) disease, there may be a high risk of aerosol spread of the virus during laryngoscopy and other airway management procedures. Techniques for minimizing infectious risks to care providers and spread of the virus during intubation are discussed separately.(See "COVID-19: Respiratory care of the nonintubated hypoxemic adult (supplemental oxygen, noninvasive ventilation, and intubation)", section on 'The decision to intubate' and "Overview of infection control during anesthetic care", section on 'Infectious agents transmitted by aerosol (eg, COVID-19)'.)

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: COVID-19 – Index of guideline topics" and "Society guideline links: Airway management in adults".)

SUMMARY AND RECOMMENDATIONS

The most common indications for emergency tracheal intubation are acute respiratory failure, inadequate oxygenation or ventilation, and the need for airway protection. These are discussed separately. (See "The decision to intubate" and 'Indications' above.)

There are few absolute contraindications to tracheal intubation. Most involve supraglottic or glottic pathology that precludes placement of a tracheal tube via the mouth or nose. (See 'Contraindications' above.)

Careful preparation is essential for direct laryngoscopy (DL) and tracheal intubation and includes: calling for assistance, performing an airway assessment, preoxygenating and positioning the patient, placing monitors, establishing intravenous (IV) access, and preparing medications and tools (table 4). Rescue airways and a back-up plan must be in place before the clinician embarks upon the procedure. (See 'Preparation' above.)

DL is performed with a straight or a curved laryngoscope blade. The different types of blades are described in the text. (See 'Laryngoscope design' above.)

The basic steps of DL and detailed descriptions of curved blade laryngoscopy and straight blade laryngoscopy are described in the text. (See 'Laryngoscopy Technique' above and 'Curved blade laryngoscopy' above and 'Paraglossal technique' above.)

The following concepts are important regardless of the laryngoscopy technique employed:

The critical step in laryngoscopy is to locate the epiglottis.

Bimanual laryngoscopy should be a habitual part of DL.

The clinician must be prepared for unanticipated difficulty.

When difficulty is experienced in obtaining an adequate view of the glottis, we suggest elevating the head and flexing the neck (inferior cervical spine) in patients who do not require cervical spine precautions. (See 'Optimizing the view' above.)

Use of a tracheal tube introducer (or "bougie") or a straight blade paraglossal approach are often effective techniques when a difficult airway is encountered. (See "Endotracheal tube introducers (gum elastic bougie) for emergency intubation" and 'Paraglossal technique' above.)

Once intubation is performed, confirmation of proper endotracheal tube placement (ETT) is crucial; unrecognized esophageal intubation leads to devastating complications. An end-tidal carbon dioxide (EtCO2) determination (either colorimetric or quantitative) should be performed to determine proper placement. In cardiac arrest patients not producing CO2, alternative means of confirmation, such as syringe or bulb devices, may be needed if CO2 is not detected. A single-view chest radiograph is useful to determine depth of placement (eg, tracheal versus right mainstem) but is not useful for distinguishing endotracheal from esophageal intubation. (See 'Confirming proper tracheal tube placement' above.)

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Topic 260 Version 51.0

References

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