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Tracheal Intubation

Technique

As previously discussed, because of differences in , there are differences in techniques for intubating the of infants and children compared with adults.[1–4,17–19,99,114,115] Because of the smaller dimensions of the pediatric airway there is increased risk of obstruction with trauma to the airway structures. A technique to be avoided is that in which the blade is advanced into the and then laryngeal visualization is achieved during withdrawal of the blade. This maneuver may result in laryngeal trauma when the tip of the blade scrapes the arytenoids and aryepiglottic folds. There are several approaches to exposing the glottis in infants with a Miller blade. One philosophy consists of advancing the laryngoscope blade under constant vision along the surface of the , placing the tip of the blade directly in the vallecula and then using this location to pivot or rotate the blade to the right to sweep the tongue to the left and adequately lift the tongue to expose the glottic opening. This avoids trauma to the arytenoid cartilages. One can thus lift the base of the tongue, which in turn lifts the , exposing the glottic opening. If this technique is unsuccessful, one may then directly lift the epiglottis with the tip of the blade (see Video Clip 12-1, Coming Soon). Another approach is to insert the Miller blade into the mouth at the right commissure over the lateral bicuspids/incisors (paraglossal approach). The blade is advanced down the right gutter of the mouth aiming the blade tip toward the midline while sweeping the tongue to the left. Once under the epiglottis, the epiglottis is lifted with the tip of the blade, thereby exposing the glottic aperture. By approaching the mouth over the bicuspids/incisors, dental damage is obviated. This is a particularly effective approach for the infant and child with a difficult airway. Whichever approach is used, care must be taken to avoid using the laryngoscope blade as a fulcrum through which pressure is applied to the teeth or alveolar ridge. If there is a substantive risk that pressure will be applied to the teeth, then a plastic tooth guard may be applied to cover the teeth at risk.

Optimal positioning for changes with age. The trachea of older children (6 years of age and older) and adults is most easily exposed when a folded blanket or pillow is placed beneath the occiput of the head (5–10 cm elevation), displacing the cervical spine anteriorly.[116] Extension of the head at the atlanto-occipital joint produces the classic “sniffing” position.[99,][117,][118] These movements align three axes: those of the mouth, oropharynx, and trachea. Once aligned, these three axes permit direct visualization of laryngeal structures. They also result in improved hypopharyngeal patency.[29,][31,][67,][75,][117,][118] Figure 12-14 demonstrates maneuvers for positioning the head during . In infants and younger children, it is usually unnecessary to elevate the head because the occiput is large in proportion to the trunk, resulting in adequate anterior displacement of the cervical spine; head extension at the atlanto-occipital joint alone aligns the airway axes. When the occiput is displaced excessively, exposure of the glottis may actually be hindered. In neonates, it is helpful for an assistant to hold the shoulders flat on the operating room table with the head slightly extended. Some practitioners have adopted the practice of placing a rolled towel under the shoulders of neonates to facilitate . This technique is a major disadvantage when the laryngoscopist stands but may be an advantage when he or she is seated, as otolaryngologists usually are.

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Figure 12-14 Correct positioning for ventilation and tracheal intubation. With a patient flat on the bed or operating table (A), the oral (O), pharyngeal (P), and tracheal (T) axes pass through three divergent planes (B). A folded sheet or towel placed under the occiput of the head (C) aligns the pharyngeal (P) and tracheal (T) axes (D). Extension of the atlanto-occipital joint (E) results in alignment of the oral (O), pharyngeal (P), and tracheal (T) axes (F).

The validity of the three-axis theory (alignment of the mouth, oropharynx, and trachea) to describe the optimal intubating position in adults has been challenged.[119–122] Some authors challenge the notion that elevating the occiput improves conditions for visualization of the laryngeal inlet based on evidence from both MRI and clinical investigation.[119,][121] No comparable studies have been performed in children. An investigation of 456 adults used as their own controls found that neck extension alone was adequate for visualization of the in most adults. However, for obese patients or those with limited neck extension, an optimal intubating position was not determined.[119] Others have argued in favor of the superiority of the sniffing position but with varying support of the three-axis theory.[123–129] Even if the of only a few patients are intubated more easily when placed in the sniffing position compared with only head extension, the routine application of the sniffing position would appear to remain the best clinical practice.

Laryngoscopy can be performed while the child is awake, anesthetized, and spontaneously, or with a combination of and neuromuscular blockade. Most tracheal in children who are awake

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are performed in neonates, an approach not usually feasible or humane in older awake and uncooperative children. Awake intubation in the neonate is generally well tolerated and, if performed smoothly, is not associated with significant hemodynamic changes.[130] However, data suggest that even preterm and full-term infants are better managed with and paralysis so as to minimize adverse hemodynamic responses. [131–134]

Selection of Laryngoscope Blade

A straight blade is generally more suitable for use in infants and young children than a curved blade because it better elevates the base of the tongue to expose the glottic opening. Curved blades are satisfactory in older children. The blade size chosen depends on the age and body mass of the child and the preference of the anesthesiologist. Table 12-1 presents the ranges commonly used.

Table 12-1 -- Laryngoscope Blades Used in Infants and Children Blade Size Age Miller Wis-Hipple Macintosh Preterm 0 - - Neonate 0 - - Neonate-2 years 1 - - 2-6 years − 1.5 1 or 2 6-10 years 2 − 2 Older than 10 years 2 or 3 − 3

Endotracheal Tubes

Since 1967, all materials used in the manufacture of tracheal tubes have been subjected to rabbit muscle implantation testing in accordance with the standards promulgated by the Z79 committee. If the material caused an inflammatory response, it could not be used in the manufacture of tracheal tubes. This resulted in the elimination of organometallic constituents, such as those used in the manufacture of red rubber tracheal tubes.

The selection of a proper size ETT depends on the individual child.[135] The only size requirement for a manufacturer is that they standardize the internal diameter (ID) of an ETT. The external diameter (OD) may vary, depending on the material from which the ETT is constructed and its manufacturer. This diversity in external diameter mandates the need to check for proper ETT size and leak around the tube. An appropriately sized uncuffed ETT may be approximated according to the patient's age and weight (Table 12-2).[136] ETTs of half ID size above and below the selected size should be available because of the variability of patient anatomy. The use of the diameter of the terminal phalanx of either the second or fifth digit is unreliable.[137] Children with Down syndrome will often require a smaller than anticipated ETT.[138] After intubation and stabilization of the child, if there is no air leak around the tube below 20 to 25 cm H2O (short-term intubation perhaps as high as 35 cm H2O) peak inflation pressure (PIP), the ETT should be changed to the next half size smaller. An air leak at this pressure is recommended because it is believed to approximate capillary pressure of the adult tracheal mucosa. If lateral wall pressure exceeds this amount, ischemic damage to the subglottic mucosa may occur.[139] Be aware, however, that if a child is intubated without the aid of muscle relaxants, around the ETT may prevent any gas leak and mimic a tight-fitting ETT.[140] When anesthesia has been deepened, an air leak could become evident. Changes in head position may also increase or decrease the leak.[140] These maneuvers are important for making the occasional diagnosis of unrecognized (see Fig. 36-3A).

Table 12-2 -- Endotracheal Tubes Used in Infants and Children[*] Age Size (mm ID)

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Age Size (mm ID) Preterm 1000 g 2.5 1000-2500 g 3.0 Neonate-6 months 3.0-3.5 6 months-1 year 3.5-4.0 1-2 years 4.0-5.0 Older than 2 years (age in years + 16)/4

ID, internal diameter.

* Uncuffed; one half size smaller for cuffed ETT, see text.

Traditional teaching has advocated the use of uncuffed ETTs for children younger than 8 years because an uncuffed ETT with an air leak exerts minimal pressure on the internal surface of the and thus poses potentially less risk for postextubation ().[136,][139,][141] An uncuffed ETT also allows insertion of a tube of larger ID, resulting in less airway resistance.[142] However, recently both clinical data and clinical practice have challenged these assumptions.[143–149] There are now a number of reports that failed to demonstrate differences in the incidence of post-intubation complications between children managed with a cuffed tube and those managed with an uncuffed tube.[143,][148] Other noncomparative, descriptive studies report a low rate for anesthetized children managed with a cuffed tube.[149,][150] Cited advantages of cuffed ETTs include decreased need for repeated laryngoscopy and intubation to place the appropriately fitting tube, reduced subglottic pressure, reduced operating room pollution, decreased risk of aspiration, better ability to accurately measure the sophisticated functions of a pediatric and up-to-date anesthesia , absolute ability to deliver high airway pressures in children with severe restrictive disease, and the ability to control cuff inflation in children who require long-term intubation and thus may have changes in the peak inspiratory pressure required to provide adequate ventilation.[143–150]

A drawback of cuffed tubes is the greater variability in functional external diameter compared with uncuffed tubes because of differences in cuff shape, size, and inflation characteristics.[151] In general, if a cuffed ETT is inserted, an ETT with a smaller ID should be selected to compensate for the ETT cuff. One study found a 99% rate of appropriate cuffed tube size selection for full-term infants through children 8 years of age using the following formula[148]:

To overcome the shortcomings of the many pediatric cuffed tubes available, the Microcuff ETT (Microcuff; PET; I-MPEDC, Microcuff GmbH, Weinheim, Germany, Kimberly-Clark USA) was designed with a high volume/low pressure cuff that is more distally placed along the shaft of the to better accommodate pediatric anatomy (Fig. 12-15).[152] The ultra-thin polyurethane cuff (10 µm) allows tracheal sealing at low pressures and provides a uniform and complete surface contact with minimal formation of cuff folds (Fig. 12-15).[150,152–155] At 20 cm H2O inflation pressure, the cuffs have a cross-sectional cuff area of approximately 150% of the maximal internal tracheal cross-sectional area. Uninflated, the cuff adds only a minimal amount to the external diameter of the tracheal tube. Shortened cuffs and the elimination of a Murphy eye allow a more distal position of the upper cuff border, thereby reducing the risk of pressure being applied to the cricoid ring and adjacent mucosa.[156] The location of the cuff on the shaft of the tube helps to ensure cuff placement below the subglottis, perhaps with the advantage of less risk for endobronchial intubation or of intralaryngeal cuff position. An anatomically based depth mark on the surface of the tube helps to guide correct placement.

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Figure 12-15 The Microcuff endotracheal tube (Microcuff; PET; I-MPEDC, Microcuff GmbH, Weinheim, Germany) is designed with an ultra-thin polyurethane (10 µm) high-volume/low-pressure cuff that has improved position along the shaft of the tube to better accommodate pediatric anatomy (right). In contrast to more traditional pediatric cuffed endotracheal tubes (left), the elimination of a Murphy eye allows a more distal position of the upper cuff border. The location of the cuff on the shaft of the tube helps to ensure cuff placement below the subglottis—perhaps with the advantage of less risk for endobronchial intubation or of intralaryngeal cuff position. An anatomically based depth mark on the surface of the tube helps to guide correct placement.

An investigation of this new specially designed ETT for children used the following guidelines to select cuffed ETT sizes[150]: • For children ≥2 years, ID (mm) = age/4 + 3.5 • For children 1 to 2 years of age, ID 3.5-mm • For neonates ≤3 kg and infants ≤1 year, ID 3.0-mm

These investigators found that using these formulas resulted in the need to reintubate to change tube size in

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1.6% of children (6/500). The incidence of post-intubation croup was 0.4% (2/500 children). A more recent study by the same group proposed using larger tube sizes; however, this study found a slightly greater incidence of reintubation (2.6%, 9/350) and a greater incidence of post-intubation croup (0.9%, 3/350) than in the previous investigation.[149] The safety and efficacy of this new ETT in infants and children has yet to be determined by use in a large cohort of children with adequate power to compare complication rates of standard ETTs with this new design. However, the added cost at present (nearly threefold that of standard ETTs) would seem to limit their use to children anticipated to require prolonged endotracheal intubation. Another concern is that as they warm they become very soft. As a result kinking is a concern that has yet to be adequately investigated. It should be noted that there has been a product recall for sizes 3.0, 3.5, 4.0, and 4.5 because of easy ETT kinking.

As a rule, if a cuffed ETT is chosen, inflation of the cuff should be adjusted to provide a seal at the lowest possible pressure that is required to ensure adequate ventilation and, as for uncuffed tubes, this should be 20 to 25 cm H2O peak inspiratory pressure to minimize the risk of post-intubation croup.[150,][157,][158] This air leak must be reevaluated during the anesthetic procedure if is used, because the gas may diffuse into the cuff, producing excessive tracheal mucosal pressure.[157–159] In particular, the Microcuff ultra-thin polyurethane tube cuff has been shown to have a greater permeability for nitrous oxide than conventional polyvinyl chloride cuffs and thus a more rapid increase in cuff pressure. Routinely checking cuff pressure or filling the cuff with nitrous oxide is recommended.[160] A pressure relief valve that can be connected to the pilot balloon of a cuffed ETT to limit cuff pressures to 20 cm H2O when N2O is used has been described.[161]

Endotracheal Tube Insertion Distance

The length of the trachea ( to carina) in neonates and children up to 1 year of age varies from 5 to 9 cm.[37] In most infants 3 months to 1 year of age, if the 10-cm mark of the ETT is placed at the alveolar ridge, the tip of the tube rests above the carina. In preterm and full-term infants, the distance is less. In children 2 years old, 12 cm is usually appropriate. An easy way to remember these lengths is 10 for a newborn, 11 for a 1-year old and 12 for a 2-year old. After 2 years of age, the correct length of insertion (in centimeters) for oral intubation may be approximated by formulas based on age or weight (Table 12-3).[162–165]

Table 12-3 -- Distance for Insertion of an Oral Endotracheal Tube by Patient Age Age Approximate Distance of Insertion (cm) Even with Alveolar Ridge Preterm <1000 g 6 Preterm <2000 g 7–9 Term newborn 10 1 year 11 2 years 12 6 years 15 10 years 17 16 years 18 20 years 20

Some practitioners suggest anatomic markers to choose appropriate tube insertion distance in neonates. [166,][167] An advantage of anatomic measurements is that the infant's weight may not be available immediately after birth or in sick neonates who present to the with urgent respiratory or cardiac

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compromise. One study that used chest radiographs to evaluate final tracheal tube position found that foot length was as accurate as weight-based formulas to determine insertion distance for a nasotracheal tube (44% vs. 56% rate of optimal placement and 83% vs. 72% satisfactory placement).[167] Another paper suggested that nasal-tragus length (the base of the nasal septum to the tip of the tragus) or sternal length (the suprasternal notch to the tip of the xiphoid process) predicted ETT insertion distance. Either distance plus 1 cm accurately estimated orotracheal tube insertion distance; either distance plus 2 cm accurately estimated nasotracheal tube insertion distance.[166] Both measurements compared favorably with weight-based formulas when tube position was determined by chest radiography.

After the ETT is inserted and the first strip of adhesive tape is applied to secure it, one must observe for symmetry of chest expansion and auscultate for equality of breath sounds in the axillae and apices (not on the anterior chest wall). A CO2 monitor confirms intratracheal positioning but does not confirm that the tip of the tracheal tube is not in an endobronchial position. Visible humidity on the walls of the tracheal tube during expiration also confirms tracheal placement, but the humidity may not be visible in younger infants. It is also important to auscultate over the stomach and to observe for desaturation or cyanosis. Once satisfactory position is achieved, a second strip of tape ensures secure fixation (Fig. 12-16). We have observed a number of children whose ETT moved into a mainstem after initial correct position during repositioning for the surgical procedure; this manifested as a slight but persistent decrease in saturation (e.g., changing from 100% to a range of 93% to 95%). Several studies have demonstrated that simply flexion or extension of the neck moved the tracheal tube sufficiently to cause an endobronchial intubation or dislodgement of the tube from the trachea. [168,][169] When a small but persistent change in is noted, rather than increase the inspired oxygen concentration (Fio2), one must first investigate the cause and reassess the position of the ETT.[170]

Figure 12-16 Securing the endotracheal tube. After insertion of the oral endotracheal tube and examination for proper position, the area between the nose and upper lip and both cheeks is coated with tincture of benzoin. A, After the benzoin is dry, tape that has been split up the middle is applied to the cheek and the endotracheal tube is placed at the division of the split tape. B, One half is wrapped circumferentially around the tube, and the other half is applied to the space above the upper lip. C, A second piece of tape is applied in similar fashion from the opposite direction. A nasal endotracheal tube may also be secured with this technique.

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Complications of Endotracheal Intubation

Post-intubation Croup

Perioperative post-intubation croup (also referred to as post-extubation croup) occurs in 0.1% to 1% of children. [149,][150,][171,][172] Factors associated with increased risk of croup include a tracheal tube with an external diameter that was too large for the child's airway (no leak at >25 cm H2O pressure or resistance at the time of insertion), changes in position during the procedure, a position other than supine, repeated attempts at intubation, traumatic intubation, age between 1 and 4 years, duration of greater than 1 hour, coughing on the ETT, and previous history of croup.[171,][172] Concurrent upper respiratory infection has been variously reported to be both a risk factor and to be unrelated.[88,][172] Treatment of post-intubation croup consists of humidified mist, nebulized epinephrine, and dexamethasone. The rationale for these treatments is based primarily on experience with the treatment of infectious croup in children.[173–182] Caution should be exercised when translating treatments from one type of croup to another because the two types of croup are not identical processes and efficacy of the interventions for the treatment of post-intubation croup have not been proved in controlled trials. Studies that examined the effect of dexamethasone given before extubation in children who have had prolonged intubation are contradictory; some support the use of dexamethasone to reduce and others do not.[183–185] Methylprednisolone given intramuscularly for the same indication has been reported to reduce post-intubation stridor.[186]

Laryngotracheal (Subglottic) Stenosis

Ninety percent of acquired subglottic stenoses are the result of endotracheal intubation, particularly prolonged intubation (see Video Clip 12-1, Coming Soon).[187–190] Preterm infants and neonates may have a reduced incidence after prolonged intubation because of the relative immaturity of the cricoid cartilage. At this age, the cartilage structure is hypercellular and the matrix has a large fluid content, making the structures more resilient and less susceptible to ischemic .[191]

The pathogenesis of acquired subglottic stenosis results from ischemic injury secondary to lateral wall pressure from the ETT. results in edema, necrosis, and ulcerations of the mucosa. Secondary infection results in exposure of the cartilage. Within 48 hours, granulation begins to form within these ulcerations. Ultimately, scar tissue forms, resulting in narrowing of the airway (Fig. 12-17).[192–194] Specimens obtained from partial cricotracheal resection in children were found to have severe and sclerotic scarring with squamous metaplasia of the epithelium, loss of glands and elastic mantle fibers (tunica elastica), and dilation of the remaining glands with formation of cysts. Also, the cricoid cartilage was affected on the internal and external side, with irreversible loss of perichondrium on the inside and resorption by macrophages of cartilage on both sides.[194]

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Figure 12-17 The pathogenesis of intubation . A, Schemata of a cross section through the glottis. Pressure necrosis causes ulcerations at the vocal processes of the arytenoids with exposed cartilage. Flaps of granulation tissue are present anterior to these ulcerations. B, Cross section of the glottis at this same level; straight arrows indicate flaps of granulation tissue and curved arrows the absence of mucosa and ulcerations with exposed cartilage on the vocal processes of the arytenoids. C, Intubation injury to a 2-month-old infant; straight arrows indicate granulation tissue and curved arrows indicate area of ulcerations (white area). The most severe area of injury is generally at the level of the cricoid cartilage, resulting in subglottic stenosis. (Reproduced with permission from Holinger LD, Lusk RP, Green CG: Pediatric and Bronchoesophagology. Philadelphia, Lippincott-Raven, 1997.)

Factors that predispose to subglottic stenosis are intubation with too large an ETT, laryngeal trauma (traumatic intubation, chemical or thermal inhalation, external trauma, surgical trauma, gastric reflux), prolonged intubation (particularly >25 days), repeated intubation, and infection, chronic illness, and chronic inflammatory disease.[190,][195,][196]

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