Tracheal Intubation

Most adults can accept a tube with an internal diameter of ≥ 8 mm; these tubes are preferable to smaller ones because they

• Have lower airflow resistance (reducing the work of breathing)

• Facilitate suctioning of secretions

• Allow passage of a bronchoscope

• May aid in liberation from mechanical ventilation

For infants and children ≥ 1 year, uncuffed tube size is calculated by (patient’s age + 16)/4; thus, a 4-year-old should have a (4 + 16)/4 = 5 mm endotracheal tube. The tube size suggested by this formula should be reduced by 0.5 (1 tube size) if a cuffed tube is to be used (1). Reference charts (see table Guide to Pediatric Resuscitation—Mechanical Measures) or devices such as the Broselow pediatric emergency tape or Pedi-Wheel can rapidly identify appropriate-sized laryngoscope blades and endotracheal tubes for infants and children.

For adults (and sometimes for children), a rigid stylet should be placed in the tube, taking care to stop the stylet 1 to 2 cm before the distal end of the endotracheal tube, so that the tube tip remains soft. The stylet should then be used to make the tube straight to the beginning of the distal cuff; from that point, the tube is bent upward about 35° to form a hockey stick shape. This straight-to-cuff shape improves tube delivery and avoids blocking the operator’s view of the vocal cords during tube passage. Routinely filling the distal endotracheal tube cuff with air to check the balloon is not required; if this technique is used, care must be taken to remove all the air before tube insertion.

Clinical Calculators

Endotracheal tube size for children (Age 1 to 8 years)

Successful intubation on the first attempt is important. Repeated laryngoscopy (≥ 3 attempts) is associated with much higher rates of significant hypoxemia, aspiration, and cardiac arrest. In addition to correct positioning (see figure Head and Neck Positioning to Open the Airway), several other general principles are critical for success:

• Visualizing the epiglottis

• Visualizing the posterior laryngeal structures (ideally, the vocal cords)

• Not passing the tube unless tracheal insertion is ensured

The conventional laryngoscope is designed to be held in the left hand, and the blade is inserted into the mouth and used as a retractor to displace the mandible and tongue up and away from the laryngoscopist, revealing the posterior pharynx. Avoiding contact with the incisors and not placing undue pressure on laryngeal structures are important.

The importance of identifying the epiglottis cannot be overstated. Identifying the epiglottis allows the operator to recognize critical airway landmarks and correctly position the laryngoscope blade. The epiglottis may rest against the posterior pharyngeal wall, where it blends in with the other pink mucus membranes or gets lost in the pool of secretions that invariably exists in the airway of a patient with cardiac arrest.

Once the epiglottis is found, the operator may use one of 2 techniques to lift it:

• Typical straight blade approach: The operator picks up the epiglottis with the tip of the laryngoscope blade

• Typical curved blade approach: The operator indirectly lifts the epiglottis and moves it out of the line of sight by advancing the blade into the vallecula and pressing against the hyoepiglottic ligament

Success with the curved blade depends on the proper positioning of the blade tip in the vallecula and the direction of the lifting force (see figure Bimanual Laryngoscopy). Lifting the epiglottis by either technique reveals the posterior laryngeal structures (arytenoid cartilages, interarytenoid notch), glottis, and vocal cords. If the tip of the blade is too deep, laryngeal landmarks may be entirely bypassed, and the dark, round hole of the esophagus may be mistaken for the glottis opening.

If identifying structures is difficult, manipulating the larynx with the right hand placed on the anterior neck (while continuing to hold the laryngoscope in the left hand ) may optimize the laryngeal view (see figure Bimanual Laryngoscopy). An assistant can help manipulate the larynx also. Another technique involves lifting the head higher (lifting at the occiput, not atlanto-occipital extension), which distracts the jaw and improves the line of sight. Head elevation is inadvisable in patients with potential cervical spine injury and is difficult in people who have extreme obesity (who must be placed in a ramped or head-elevated position beforehand).

In an optimal view, the vocal cords are clearly seen. If the vocal cords are not seen, at a minimum, the posterior laryngeal landmarks must be viewed and the tip of the tube must be seen passing above the interarytenoid notch and posterior cartilages. Operators must clearly identify laryngeal landmarks to avoid potentially fatal esophageal intubation. If operators are not confident that the tube is going into the trachea, the tube should not be inserted.

Once an optimal view has been achieved, the right hand inserts the tube through the larynx into the trachea (if operators have been applying anterior laryngeal pressure with the right hand, an assistant should continue applying this pressure). If the tube does not pass easily, a 90° counter-clockwise twist of the tube may help it pass more smoothly over the anterior tracheal rings. After the cuff of the endotracheal tube has passed 1 to 2 cm past the vocal cords, the balloon should be inflated and the stylet removed. Before withdrawing the laryngoscope, operators should confirm that the tube is passing between the cords. Appropriate tube depth is usually 21 to 23 cm in adults and 3 times the endotracheal tube size in children (for a 4.0-mm endotracheal tube, 12 cm; for a 5.5-mm endotracheal tube, 16.5 cm). In adults, the tube, if inadvertently advanced, typically migrates into the right mainstem bronchus.

Intubation is unsuccessful in 10 to 30% of critically ill patients, so contingency plans should be established. When intubation fails, oxygenation should be prioritized and alternative interventions should be used while minimizing the number of airway interventions in order to minimize trauma and other procedural complications (1, 2).

Bimanual Laryngoscopy

Pressure is applied on the neck opposite the direction of lift of the laryngoscope. Arrows show the direction for lift of the laryngoscope and for anterior neck pressure.

A number of devices and techniques can be used for intubation after failed laryngoscopy or as a primary means of intubation. Devices include

• Video laryngoscopes

• Laryngeal mask airways (LMAs) with a passage that allows tracheal intubation

• Other supraglottic airways

• Fiberoptic scopes and optical stylets

• Tube introducers

Each device has its own subtleties; practitioners who are skilled in standard laryngoscopic intubation techniques should not assume they can use one of these devices (especially after the patient has been given muscle relaxants) without becoming thoroughly familiar with it.

Video laryngoscopes enable practitioners to look around the curvature of the tongue and usually provide excellent laryngeal views. Video laryngoscopy may increase intubation success rate and shorten the time to successful intubation in adults with difficult airways (1). However, some video laryngoscopes require that the endotracheal tube have an exaggerated bend angle to go around the tongue and thus may be more difficult to manipulate and insert. During the COVID-19 pandemic, many society guidelines recommended using video laryngoscopy (when available) as the primary method for airway management because it increased the distance between the clinician performing the intubation and the patient's face in an attempt to minimize viral transmission (2). In children, video laryngoscopy reduces the risk of failed first intubation attempts compared to direct laryngoscopy. However, more evidence is needed to determine if all video laryngoscope devices provide the same benefit (3).

Some laryngeal mask airways have a passage to allow endotracheal intubation. To pass an endotracheal tube through a laryngeal mask airway, clinicians must understand how to optimally position the mask over the laryngeal inlet; there are sometimes mechanical difficulties passing the endotracheal tube.

Supraglottic airways can allow placement of an airway if an optimal laryngeal view cannot be obtained or an endotracheal tube cannot be passed through the cords (eg, abnormal anatomy, subglottic stenosis).

Flexible fiberoptic scopes and optical stylets are very maneuverable and can be used in patients with abnormal anatomy. However, practice is required to recognize laryngeal landmarks from a fiberoptic perspective. Compared with video laryngoscopes, fiberoptic scopes are more difficult to master and are more susceptible to problems with blood and secretions; also, they do not separate and divide tissue but instead must be moved through open channels.

Tube introducers (commonly called gum elastic bougies) are semirigid stylets that can be used when laryngeal visualization is suboptimal (eg, the epiglottis is visible, but the laryngeal opening is not). In such cases, the introducer is passed along the undersurface of the epiglottis; from this point, it is likely to enter the trachea. Tracheal entry is suggested by the tactile feedback, noted as the tip bounces over the tracheal rings. An endotracheal tube is then advanced over the introducer. During passage over a tube introducer, the tube tip sometimes catches the right aryepiglottic fold. Rotating the tube 90° counterclockwise often frees the endotracheal tube tip and allows it to pass smoothly.

The stylet is removed and the balloon cuff is inflated with air using a 10-mL syringe; a manometer, when available, can be used to verify that balloon pressure is < 30 cm water. The size of the endotracheal tube and cuff size affect the volume of air necessary for the correct pressure.

After balloon inflation, tube placement should be checked by one or more of the following methods:

• Inspection and auscultation

• Carbon dioxide detection

• Esophageal detector devices

• Sometimes chest radiograph

When a tube is correctly placed, manual ventilation should produce symmetric chest rise, good breath sounds over both lungs, and no gurgling over the upper abdomen.

Exhaled air should contain carbon dioxide and gastric air should not; detecting carbon dioxide with quantitative waveform capnography confirms tracheal placement. Colorimetric end-tidal carbon dioxide (ETCO2) devices may be used if waveform capnography is unavailable but are less reliable. Quantitative waveform capnography may not detect ETCO2 initially if cardiac arrest is prolonged prior to intubation. ETCO2, however, may be detected later if resuscitative efforts are successful. Detection of ETCO2 or rising ETCO2 levels reflect effective chest compressions and ventilation.

In prolonged cardiac arrest (ie, with little or no metabolic activity), carbon dioxide may not be detectable even with correct tube placement. In such cases, an esophageal detector device may be used. These devices use an inflatable bulb or a large syringe to apply negative pressure to the endotracheal tube. The flexible esophagus collapses, and little or no air flows into the device; in contrast, the rigid trachea does not collapse, and the resultant airflow confirms tracheal placement.

In the absence of cardiac arrest, tube placement is typically also confirmed with a chest radiograph.

After correct placement is confirmed, the tube should be secured using a commercially available device or adhesive tape. Adapters connect the endotracheal tube to a resuscitator bag, T-piece supplying humidity and oxygen, or a mechanical ventilator.

Endotracheal tubes can be displaced, particularly in chaotic resuscitation situations, so tube position should be rechecked frequently. If breath sounds are absent on the left, right mainstem bronchus intubation is probably more likely than a left-sided tension pneumothorax, but both should be considered.

If patients are spontaneously breathing, nasotracheal intubation can be used in certain emergency situations, eg, when patients have severe oral or cervical disorders (eg, injuries, edema, limitation of motion) that make laryngoscopy difficult. Nasotracheal intubation is absolutely contraindicated in patients with midface fractures or known or suspected basal skull fractures. Nasal intubation was also used when muscle relaxants were unavailable or restricted (eg, out of scope of practice for prehospital personnel and some emergency departments) and in patients with decompensated heart failure and respiratory failure in upright position. However, availability of noninvasive means of ventilation (eg, bilevel positive airway pressure), improved access to and training in pharmacologic adjuncts to intubation, and current airway devices have markedly decreased the use of nasal intubation. Additional considerations are problems with nasal intubation, including sinusitis (universal after 3 days), and the fact that tubes large enough to permit bronchoscopy (eg, ≥ 8 mm) can rarely be inserted nasotracheally.

The nasotracheal tube is then inserted to about 14 cm depth (just above the laryngeal inlet in most adults); at this point, air movement should be audible. As the patient breathes in, opening the vocal cords, the tube is promptly passed into the trachea. A failed initial insertion attempt often prompts the patient to cough. Clinicians should anticipate this event, which allows a second opportunity to pass the tube through a wide open glottis. More flexible endotracheal tubes with a controllable tip improve likelihood of success. Some clinicians soften tubes by placing them in warm water to lessen the risk of bleeding and make insertion easier. A small commercially available whistle can also be attached to the proximal tube connector to accentuate the noise of air movement when the tube is in the correct position above the larynx and in the trachea.

Complications of tracheal intubation include

• Direct trauma

• Esophageal intubation

• Tracheal erosion or stenosis

Laryngoscopy can damage lips, teeth, tongue, and supraglottic and subglottic areas.

Tube placement in the esophagus, if unrecognized, causes failure to ventilate and potentially death or hypoxic injury. Insufflating a tube in the esophagus causes regurgitation, which can result in aspiration, compromise subsequent bag-valve-mask ventilation, and obscure visualization in subsequent intubation attempts.

Any translaryngeal tube injures the vocal cords somewhat; sometimes ulceration, ischemia, and prolonged vocal cord paralysis occur. Subglottic stenosis can occur later (usually 3 to 4 weeks).

Erosion of the trachea is uncommon. It results more commonly from excessively high cuff pressure (> 30 cm water).

Rarely, hemorrhage from major vessels (eg, innominate artery), fistulas (especially tracheoesophageal), and tracheal stenosis occur. Using high-volume, low-pressure cuffs with tubes of appropriate size and measuring cuff pressure frequently (every 8 hours) to maintain it at < 30 cm water decrease the risk of ischemic pressure necrosis, but patients in shock, with low cardiac output, or with sepsis remain especially vulnerable.

1).