General anesthesiologists that occasionally anesthetize children should be intimately familiar with the anatomy of the pediatric upper airway. In this chapter, the pertinent features of the pediatric airway and the correct ways to manage the pediatric airway are detailed. Several common and serious complications related to airway management are reviewed. These include laryngospasm, pulmonary aspiration, and negative-pressure (postobstructive) pulmonary edema.
Anatomy of the Pediatric Upper Airway
Unique anatomic airway differences that influence airway management in children include ( Fig. 17.1 ) the following:
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A relatively large occiput in infants, which naturally flexes the neck when in the supine position, causing the infant to assume a natural “sniffing” position.
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A more anterior and cephalad larynx than in the adult, which causes it to be more easily visualized using a straight, rather than a curved laryngoscope (the exact vertebral level is irrelevant).
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A relatively narrow and short epiglottis that is angled into the lumen of the airway, and is often difficult to displace anteriorly during laryngoscopy.
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Smaller size than one might be used to. Small nasal passages are more likely to become obstructed with blood or secretions, and tracheal edema is more likely to increase airway resistance. “Seasoned” anesthesiologists with dwindling eyesight may have trouble with the tiny view of the neonate’s larynx through the relatively small view space of a Miller 0 blade.
Dental Development
There are 20 primary (“baby”) teeth that are identified by a lettering system that begins with the right upper molar and ends at the right lower molar. Primary teeth erupt starting at about 1 year of age (give or take a few months on either end) and are shed between 6 and 12 years of age. Loose or chipped teeth should be sought for and documented on the anesthetic record. Primary teeth that are very loose should be removed after induction of general anesthesia and before airway instrumentation. To do this, grasp the tooth firmly with gauze and rock it back and forth while pulling or twisting until you oust it from its home. Minor bleeding in the tooth socket abates with firm pressure and, most importantly, all personnel in attendance are expected to contribute to the tooth fairy fund. In adolescents, broken or loose orthodontic hardware should be documented and rubber bands should be removed.
Assessment of the Pediatric Airway
Unlike adults, there are no validated physical characteristics of children (i.e., Mallampati score) that have been definitively associated with the inability to perform mask ventilation or tracheal intubation. Mask ventilation may be difficult for a variety of reasons, including the small size of the neonate, the large tongue of the child with trisomy 21, or the presence of large tonsil and adenoid tissue in toddlers. On the other hand, it is rare that tracheal intubation cannot be accomplished in the prepubertal child unless the child has altered facial or airway anatomy.
Pediatric Airway Management Techniques
Mask Ventilation
In children with normal facial anatomy aged 4 years and older, effective mask ventilation is usually easy to perform. The proper mask ventilation technique for all children is to hold the mask over the mouth and nose with the thumb and forefinger while the middle finger is placed on the bony portion of the mandible. The middle finger lifts the chin to extend the head without externally compressing the anterior neck. The upper part of the mask should rest on the bridge of the nose ( Fig. 17.2 ). Inexperienced practitioners often make the mistake of holding the mask too low, which obstructs the nasal passages. To avoid gastric distention, peak inspiratory pressures should not exceed 15 cmH 2 O, or less in infants (See ).
Airway Obstruction During Mask Ventilation
Difficult mask ventilation during induction of general anesthesia is almost always because of some form of intrinsic airway obstruction. In neonates and small infants, the obstruction is usually caused by soft tissue collapse around the area of the epiglottis. In older children, large tonsils or adenoid tissue is usually responsible. When upper airway obstruction occurs, the practitioner should have in mind a sequential series of corrective maneuvers to relieve the obstruction before more advanced airway instrumentation techniques. The first is chin lift, which stretches and tightens the soft tissue structures along the length of the upper airway and results in an increase in the anteroposterior dimensions of the upper airway ( Fig. 17.3 ). If chin lift is not effective, the next maneuver is jaw thrust (See ), which primarily alleviates obstruction caused by the epiglottis protruding posteriorly into the airway. The third maneuver, which is usually done simultaneously with the first two, is application of continuous positive airway pressure (CPAP), which distends all the soft tissues of the pharynx and larynx. Occasionally, when upper airway collapse is severe, as may occur in neonates, it is also necessary to increase peak inflating pressures beyond the recommended 15 cmH 2 O to distend collapsed airway mucosal surfaces. However, doing so risks gastric insufflation, which may further compromise effective air entry into the lungs. If all of the above maneuvers (which, in aggregate, should not take more than about 30–45 seconds to perform) do not result in an unobstructed upper airway, the next steps include oral or nasal airway insertion, supraglottic airway (SGA) insertion, or tracheal intubation.
Oral Airway Insertion
Insertion of an oral airway establishes airflow by bypassing soft tissue obstruction, or more commonly in preschool-aged children, enlarged tonsils or adenoids. The most commonly used oral airway in pediatric patients is the Guedel type, which contains a central lumen that allows the passage of air and, if needed, a suction catheter. It can be inserted with the aid of a tongue depressor or by initially orienting the distal tip cephalad and then turning it 180 degrees at the posterior aspect of the palate.
Oral airways are sized based on their length (50–80 mm sizes are suitable for most children) or based on an arbitrary scale designated by the manufacturer. The appropriate size is determined by placing the airway adjacent to the child’s face to approximate its position in the oral cavity ( Fig. 17.4 ). When appropriately positioned, the distal end of the oral airway should curve along the posterior portion of the tongue, without the proximal end protruding out of the mouth or the distal end extending near the epiglottis. If the chosen size is too small, it can push the tongue against the posterior pharyngeal wall, and if it is too large, it may obstruct the laryngeal inlet.
Nasal Airway Insertion
A nasal airway is a soft flexible tube that can be used to relieve upper airway obstruction and to provide a conduit for delivering oxygen and anesthetic gases. Nasal airways are usually available in sizes 12- to 36-French (French = outer diameter divided by 3 in mm). A “custom” nasal airway can be fashioned by cutting off the appropriate length of an endotracheal tube but this would be less flexible than commercially made nasal airways and cause more trauma to the nasal mucosa.
Before insertion of a nasal airway, the nose should be inspected to assure the absence of significant septal deviation, or other visible causes of narrowing (e.g., polyp) that would interfere with placement of the device. However, nasal patency is not reliably predicted by external visualization. To avoid trauma and bleeding of the delicate nasal mucosa, the nasal airway should be well lubricated and inserted in a posterior caudal direction along the floor of the nasal cavity. A topical vasoconstrictor, such as 0.05% oxymetazoline, can be sprayed into the nasal canal before airway insertion. The proper diameter is determined by approximating the circular diameter of the nasal opening. The proper length of the nasal airway is estimated by measuring the distance from the nares to the tragus of the ear. When appropriately placed, its distal tip should lie at the level of the angle of the mandible between the posterior aspect of the tongue and above the tip of the epiglottis. Some red rubber nasal airways are supplied with a movable ring at the proximal end, with which to adjust the proper length at the tip of the nasal opening.
The most common complication from nasal airway insertion is trauma to the nasal or pharyngeal mucosa that results in bleeding. Adenoidal tissue may be disrupted and bleed into the oropharynx. Occasionally, a friable vessel is encountered in the nasal mucosa and bleeding is brisk. A lesser-known, though not rare, complication is the insertion of the nasal airway device into a false passage behind the posterior wall mucosa of the nasal and oral pharynx. This is not usually accompanied by bleeding, so it may be caused by a patent Thornwaldt bursa. Nasal airways should not be inserted in children with a coagulopathy, neutropenia, or suspicion of a traumatic basilar skull fracture.
Supraglottic Airways (SGA)
In the 1990s, the original laryngeal mask airway (LMA) revolutionized airway management and patient safety. It had its shortcomings and improved versions gradually became available. In this section, we discuss the basics about supraglottic airway (SGA) use in children ( Table 17.1 ), using the original LMA as an example because the most has been written about it; but if you want a more detailed discussion, check out the chapters we wrote for the latest editions of Smith or Cote’s encyclopedic books on pediatric anesthesia. There, we discuss newer types of SGAs such as the Cobra (Cobra = Engineered Medical Systems, Indianapolis, IN), laryngeal tube, and iGel (iGel = Intersurgical, East Syracuse, NY). Over the years, each of us has developed our favorite SGA for use in children, but there really are no striking clinical differences between them. At The Children’s Hospital of Philadelphia (CHOP), we mainly use the Ambu (Ambu = Ambu Inc, Columbia, MD) disposable airways because their preformed shape seems to fit well into the pediatric upper airway without too much displacement or malpositioning.
| LMA Size | Appropriate Weight (kg) | Cuff Volume (mL) |
|---|---|---|
| 1 | <5 | 2–5 |
| 1.5 | 5–10 | 3–8 |
| 2 | 10–20 | 5–10 |
| 2.5 | 20–30 | 10–15 |
| 3 | 30–50 | 15–20 |
| 4 | 50–70 | 25–30 |
When the classic LMA was first introduced, it was primarily used as a substitute for the face mask. But over the years, it has also become a substitute for the endotracheal tube in certain procedures such as eye surgery and tonsillectomy (with the flexible LMA). In children with normal airway anatomy, positive-pressure ventilation is easily accomplished through an LMA, but the peak inspiratory pressure should not exceed 15 cmH 2 O to prevent gastric insufflation. Because of its inability to reliably seal off the trachea, the LMA is not indicated for use in children at increased risk for pulmonary aspiration of gastric contents.
The original models of the LMA were not ideally suited for use in small children. Because of the relatively cephalad location of the pediatric larynx, the LMA (especially sizes 1, 1.5, and 2) was hard to “seat”, or position, and commonly became dislodged during surgery. This required either repositioning or replacing with an endotracheal tube. Fiberoptic bronchoscopy and magnetic resonance imaging (MRI) studies demonstrated a high incidence of the epiglottis situated within the aperture of the LMA, despite adequate ventilation. The application of jaw thrust during LMA insertion may prevent downfolding of the epiglottis.
A variety of methods of LMA placement in children have been described. The “Brain” method (named after Archie Brain, the creator of the LMA) consists of pushing the flattened LMA cuff against the hard palate while simultaneously guiding the LMA to slide down into position. Alternatively, it can be inserted with the cuff partially or fully deflated, or inserted with the aperture facing posterior and then turned 180 degrees after passing behind the tongue. There are no advantages to any one method. We usually put some water-based lubricant on the posterior surface of the LMA to decrease the resistance to insertion, and use the Brain method while pulling the jaw anteriorly by grasping behind the lower incisors. In some children, insertion is difficult and causes pharyngeal bleeding. Some children may have a sore throat after LMA placement, but it is not as common as after endotracheal intubation.
During emergence from general anesthesia, the LMA can be removed at any time after suctioning the oropharynx (the child does not need to be deeply anesthetized to prevent laryngospasm, as with “deep” extubation of an endotracheal tube). Removal with the cuff inflated will also facilitate removal of blood or secretions that collect above the cuff. Some providers routinely place an oral airway at the same time as LMA removal.
Endotracheal Intubation
Laryngoscopy
In most children older than about 2 years of age, laryngoscopy is relatively straightforward and technically easy. An unexpected difficult view of the glottis is unusual in children with normal airway anatomy. In neonates and small infants, laryngoscopy can be challenging because of the smaller and more cephalad location of the larynx, and the narrower view through the oropharynx. At CHOP, videolaryngoscopy for infants less than 2 months of age has become mandatory (see A Deeper Dive box, below). The optimal position for laryngoscopy is different than for adults. The relatively large occiput of the small infant naturally flexes the head, while the shoulders lie flat on the table ( Fig. 17.5 ). The anesthesiologist’s line of sight should be nearly directly over the child’s airway, and the laryngoscope blade is inserted almost perpendicular to the operating room (OR) table to obtain the easiest view of the glottis ( Fig. 17.6 ). This is in contrast to adults, in whom the best glottic view is usually obtained with the laryngoscope blade almost parallel to the OR table.
A variety of pediatric-sized laryngoscope blades are available. A straight blade is most often used to obtain the best glottic view. In infants and small children, the straight blade is usually inserted into the vallecula to tilt the epiglottis anteriorly to view the glottic opening. The infant’s small size and anteriorly placed larynx afford the anesthesiologist the opportunity to use the fifth finger of the left hand to push the larynx in a posterior direction to improve the glottic view ( Fig. 17.7 ).
Endotracheal Tubes
Many formulas have been developed to predict the most appropriate size endotracheal tube in children, based on age, weight, or height. All of these formulas have reasonable reliability. The most popular formula for predicting the correct uncuffed oral endotracheal tube size is Cole’s formula:
16+Age4
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