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Tracheal Intubation

Technique

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

Optimal positioning for laryngoscopy 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-occipitaljoint 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 demonstratesmaneuvers for positioning the head during airway management. In infants and younger children, it is usuallyunnecessary to elevate the head because the occiput is large in proportion to the trunk, resulting in adequateanterior displacement of the cervical spine; head extension at the atlanto-occipital joint alone aligns the airwayaxes. 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 slightlyextended. Some practitioners have adopted the practice of placing a rolled towel under the shoulders ofneonates to facilitate tracheal intubation. This technique is a major disadvantage when the laryngoscopiststands 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 ofthe head (C) aligns the pharyngeal (P) and tracheal (T) axes (D). Extension of the atlanto-occipital joint (E) results in alignment of theoral (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 optimalintubating position in adults has been challenged.[119–122] Some authors challenge the notion that elevating theocciput improves conditions for visualization of the laryngeal inlet based on evidence from both MRI and clinicalinvestigation.[119,][121] No comparable studies have been performed in children. An investigation of 456 adultsused as their own controls found that neck extension alone was adequate for visualization of the larynx in mostadults. However, for obese patients or those with limited neck extension, an optimal intubating position was notdetermined.[119] Others have argued in favor of the superiority of the sniffing position but with varying support ofthe three-axis theory.[123–129] Even if the tracheas of only a few patients are intubated more easily when placedin the sniffing position compared with only head extension, the routine application of the sniffing position wouldappear to remain the best clinical practice.

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


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are performed in neonates, an approach not usually feasible or humane in older awake and uncooperativechildren. Awake intubation in the neonate is generally well tolerated and, if performed smoothly, is notassociated with significant hemodynamic changes.[130] However, data suggest that even preterm and full-terminfants are better managed with sedation 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 itbetter elevates the base of the tongue to expose the glottic opening. Curved blades are satisfactory in olderchildren. The blade size chosen depends on the age and body mass of the child and the preference of theanesthesiologist. Table 12-1 presents the ranges commonly used.

Table 12-1 -- Laryngoscope Blades Used in Infants and Children Blade SizeAge Miller Wis-Hipple MacintoshPreterm 0 - -Neonate 0 - -Neonate-2 years 1 - -2-6 years − 1.5 1 or 26-10 years 2 − 2Older 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 muscleimplantation testing in accordance with the standards promulgated by the Z79 committee. If the material causedan inflammatory response, it could not be used in the manufacture of tracheal tubes. This resulted in theelimination 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 amanufacturer is that they standardize the internal diameter (ID) of an ETT. The external diameter (OD) mayvary, depending on the material from which the ETT is constructed and its manufacturer. This diversity inexternal diameter mandates the need to check for proper ETT size and leak around the tube. An appropriatelysized uncuffed ETT may be approximated according to the patient's age and weight (Table 12-2).[136] ETTs ofhalf 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 withDown syndrome will often require a smaller than anticipated ETT.[138] After intubation and stabilization of thechild, if there is no air leak around the tube below 20 to 25 cm H2O (short-term intubation perhaps as high as 35cm H2O) peak inflation pressure (PIP), the ETT should be changed to the next half size smaller. An air leak atthis pressure is recommended because it is believed to approximate capillary pressure of the adult trachealmucosa. 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, laryngospasm around theETT may prevent any gas leak and mimic a tight-fitting ETT.[140] When anesthesia has been deepened, an airleak could become evident. Changes in head position may also increase or decrease the leak.[140] Thesemaneuvers are important for making the occasional diagnosis of unrecognized subglottic stenosis (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 3.0Neonate-6 months 3.0-3.56 months-1 year 3.5-4.01-2 years 4.0-5.0Older 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 anuncuffed ETT with an air leak exerts minimal pressure on the internal surface of the cricoid cartilage and thusposes potentially less risk for postextubation edema (croup).[136,][139,][141] An uncuffed ETT also allows insertionof a tube of larger ID, resulting in less airway resistance.[142] However, recently both clinical data and clinicalpractice have challenged these assumptions.[143–149] There are now a number of reports that failed todemonstrate differences in the incidence of post-intubation complications between children managed with acuffed tube and those managed with an uncuffed tube.[143,][148] Other noncomparative, descriptive studies reporta low complication rate for anesthetized children managed with a cuffed tube.[149,][150] Cited advantages ofcuffed ETTs include decreased need for repeated laryngoscopy and intubation to place the appropriately fittingtube, reduced subglottic pressure, reduced operating room pollution, decreased risk of aspiration, better abilityto accurately measure the sophisticated functions of a pediatric intensive care unit and up-to-date anesthesiaventilators, absolute ability to deliver high airway pressures in children with severe restrictive lung disease, andthe ability to control cuff inflation in children who require long-term intubation and thus may have changes in thepeak inspiratory pressure required to provide adequate ventilation.[143–150]

A drawback of cuffed tubes is the greater variability in functional external diameter compared with uncuffedtubes because of differences in cuff shape, size, and inflation characteristics.[151] In general, if a cuffed ETT isinserted, 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 thefollowing 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/lowpressure cuff that is more distally placed along the shaft of the tracheal tube to better accommodate pediatricanatomy (Fig. 12-15).[152] The ultra-thin polyurethane cuff (10 µm) allows tracheal sealing at low pressures andprovides a uniform and complete surface contact with minimal formation of cuff folds (Fig. 12-15).[150,152–155] At20 cm H2O inflation pressure, the cuffs have a cross-sectional cuff area of approximately 150% of the maximalinternal tracheal cross-sectional area. Uninflated, the cuff adds only a minimal amount to the external diameterof the tracheal tube. Shortened cuffs and the elimination of a Murphy eye allow a more distal position of theupper cuff border, thereby reducing the risk of pressure being applied to the cricoid ring and adjacentmucosa.[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. Ananatomically 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 withan ultra-thin polyurethane (10 µm) high-volume/low-pressure cuff that has improved position along the shaft of the tube to betteraccommodate pediatric anatomy (right). In contrast to more traditional pediatric cuffed endotracheal tubes (left), the elimination of aMurphy 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 cuffplacement 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 cuffedETT 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 studyby the same group proposed using larger tube sizes; however, this study found a slightly greater incidence ofreintubation (2.6%, 9/350) and a greater incidence of post-intubation croup (0.9%, 3/350) than in the previousinvestigation.[149] The safety and efficacy of this new ETT in infants and children has yet to be determined byuse in a large cohort of children with adequate power to compare complication rates of standard ETTs with thisnew design. However, the added cost at present (nearly threefold that of standard ETTs) would seem to limittheir use to children anticipated to require prolonged endotracheal intubation. Another concern is that as theywarm they become very soft. As a result kinking is a concern that has yet to be adequately investigated. Itshould be noted that there has been a product recall for sizes 3.0, 3.5, 4.0, and 4.5 because of easy ETTkinking.

As a rule, if a cuffed ETT is chosen, inflation of the cuff should be adjusted to provide a seal at the lowestpossible pressure that is required to ensure adequate ventilation and, as for uncuffed tubes, this should be 20 to25 cm H2O peak inspiratory pressure to minimize the risk of post-intubation croup.[150,][157,][158] This air leakmust be reevaluated during the anesthetic procedure if nitrous oxide is used, because the gas may diffuse intothe cuff, producing excessive tracheal mucosal pressure.[157–159] In particular, the Microcuff ultra-thinpolyurethane tube cuff has been shown to have a greater permeability for nitrous oxide than conventionalpolyvinyl chloride cuffs and thus a more rapid increase in cuff pressure. Routinely checking cuff pressure orfilling the cuff with nitrous oxide is recommended.[160] A pressure relief valve that can be connected to the pilotballoon 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 (vocal cords to carina) in neonates and children up to 1 year of age varies from 5 to 9cm.[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 2years old, 12 cm is usually appropriate. An easy way to remember these lengths is 10 for a newborn, 11 for a1-year old and 12 for a 2-year old. After 2 years of age, the correct length of insertion (in centimeters) for oralintubation 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 AgeAge Approximate Distance of Insertion (cm) Even with Alveolar RidgePreterm <1000 g 6Preterm <2000 g 7–9Term newborn 101 year 112 years 126 years 1510 years 1716 years 1820 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 immediatelyafter birth or in sick neonates who present to the emergency department with urgent respiratory or cardiac


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compromise. One study that used chest radiographs to evaluate final tracheal tube position found that footlength 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 thatnasal-tragus length (the base of the nasal septum to the tip of the tragus) or sternal length (the suprasternalnotch to the tip of the xiphoid process) predicted ETT insertion distance. Either distance plus 1 cm accuratelyestimated orotracheal tube insertion distance; either distance plus 2 cm accurately estimated nasotracheal tubeinsertion distance.[166] Both measurements compared favorably with weight-based formulas when tube positionwas determined by chest radiography.

After the ETT is inserted and the first strip of adhesive tape is applied to secure it, one must observe forsymmetry of chest expansion and auscultate for equality of breath sounds in the axillae and apices (not on theanterior chest wall). A CO2 monitor confirms intratracheal positioning but does not confirm that the tip of thetracheal tube is not in an endobronchial position. Visible humidity on the walls of the tracheal tube duringexpiration also confirms tracheal placement, but the humidity may not be visible in younger infants. It is alsoimportant to auscultate over the stomach and to observe for desaturation or cyanosis. Once satisfactory positionis achieved, a second strip of tape ensures secure fixation (Fig. 12-16). We have observed a number of childrenwhose ETT moved into a mainstem bronchus after initial correct position during repositioning for the surgicalprocedure; this manifested as a slight but persistent decrease in oxygen saturation (e.g., changing from 100% toa range of 93% to 95%). Several studies have demonstrated that simply flexion or extension of the neck movedthe 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 oxygen saturation is noted, rather than increase the inspiredoxygen 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, thearea between the nose and upper lip and both cheeks is coated with tincture of benzoin. A, After the benzoin is dry, tape that has beensplit 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 wrappedcircumferentially around the tube, and the other half is applied to the space above the upper lip. C, A second piece of tape is applied insimilar 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 externaldiameter that was too large for the child's airway (no leak at >25 cm H2O pressure or resistance at the time ofinsertion), changes in position during the procedure, a position other than supine, repeated attempts atintubation, traumatic intubation, age between 1 and 4 years, duration of surgery greater than 1 hour, coughingon the ETT, and previous history of croup.[171,][172] Concurrent upper respiratory infection has been variouslyreported to be both a risk factor and to be unrelated.[88,][172] Treatment of post-intubation croup consists ofhumidified mist, nebulized epinephrine, and dexamethasone. The rationale for these treatments is basedprimarily on experience with the treatment of infectious croup in children.[173–182] Caution should be exercisedwhen translating treatments from one type of croup to another because the two types of croup are not identicalprocesses and efficacy of the interventions for the treatment of post-intubation croup have not been proved incontrolled trials. Studies that examined the effect of dexamethasone given before extubation in children whohave had prolonged intubation are contradictory; some support the use of dexamethasone to reduce stridor andothers do not.[183–185] Methylprednisolone given intramuscularly for the same indication has been reported toreduce post-intubation stridor.[186]

Laryngotracheal (Subglottic) Stenosis

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

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


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Figure 12-17 The pathogenesis of intubation injuries. A, Schemata of a cross section through the glottis. Pressure necrosis causesulcerations at the vocal processes of the arytenoids with exposed cartilage. Flaps of granulation tissue are present anterior to theseulcerations. B, Cross section of the glottis at this same level; straight arrows indicate flaps of granulation tissue and curved arrows theabsence of mucosa and ulcerations with exposed cartilage on the vocal processes of the arytenoids. C, Intubation injury to a2-month-old infant; straight arrows indicate granulation tissue and curved arrows indicate area of ulcerations (white area). The mostsevere 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 Laryngology andBronchoesophagology. Philadelphia, Lippincott-Raven, 1997.)

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

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