Adverse respiratory events are among the most common critical perioperative events in pediatric anesthesia. Proficient management of the pediatric airway requires thorough understanding of its unique anatomical and physiological characteristics (Acta Anaesthesiol Scand 2009;53:1-9; Paediatr Anaesth 2012;22:1008-15; Int J Crit Illn Inj Sci 2014;4:65-70). These differences are most recognizable in infants, toddlers, and young children. The proportionally large head and tongue, restricted submandibular space, high larynx, and a floppy epiglottis present special challenges to airway management. Physiologically, high metabolic demand and low oxygen reserves shorten the time to significant hypoxemia during periods of apnea and laryngospasm. Resistance to airflow through small airways is high, and even the slightest decrease in radius from secretions or inflammation can increase airway pressures manyfold, resulting in acute respiratory compromise.
“Many of the familiar objective physical examination findings commonly used to predict a difficult airway in adults are not easily extrapolated to the young pediatric population. For example, there is no Mallampati classification defined for infants and young children. Similarly, there is no methodology that derives thyromental distance for different age groups.”
Covering the full spectrum of pediatric airway management is outside the purview of this concise review. We will instead focus on fundamentals, clinical subtleties, and new thoughts on positioning children for airway management.
Preoperative assessment of the airway: Identifying the red flags
Pediatric airway evaluation begins with a thorough history and physical examination of the head and neck. When available, previous anesthetic records should be reviewed. Noisy breathing, inspiratory stridor, croup-like cough, and respiratory distress in relation to feeding can provide vital clues. History of recent respiratory tract infection, including COVID-19 pneumonia, should be elicited. Information should be sought from parents about any loose or missing teeth. In this respect, basic knowledge of stages of dentition is useful. The lower incisors are the first two teeth to erupt, at about 6 months of age, followed by the upper incisors. The process of shedding primary teeth begins around age 6 and lasts up to age 12.
Many of the familiar objective physical examination findings commonly used to predict a difficult airway in adults are not easily extrapolated to the young pediatric population. For example, there is no Mallampati classification defined for infants and young children. Similarly, there is no methodology that derives thyromental distance for different age groups. Moreover, depending on age, children may not be reliable participants during an attempted airway exam. As such, physical examination should focus on the global appearance of the face, head, and neck. Does the child appear normal? Are there any obvious anomalies or dysmorphic features? Is there any limitation with neck extension or mouth opening? In this regard, knowledge of syndromes commonly affecting the airway is crucial.
There are physical findings that should certainly raise a red flag for their known potential for difficulty with mask ventilation and tracheal intubation. These are, specifically, micrognathia, macroglossia, and midface hypoplasia. Mandibular hypoplasia, or micrognathia, is invariably the most serious of the abnormalities affecting the pediatric airway. It is a prominent finding in several syndromes, namely Pierre Robin, Treacher Collins, and Goldenhar. Milder degrees of micrognathia are sometime seen in otherwise normal children. Severe micrognathia and the resultant decrease in the hyomental space compromise the airway in profound ways. The larynx is anterior and can be difficult to visualize during direct laryngoscopy. The tongue is displaced posteriorly (glossoptosis) and contributes significantly to upper airway obstruction. Ankylosis of the temporomandibular joint (TMJ) can make jaw thrusting ineffective. Meticulous planning is therefore imperative, and advanced techniques are necessary to manage the airway.
Macroglossia refers to an enlarged tongue that protrudes beyond the alveolar ridge in the resting position. It is most frequently associated with Beckwith-Wiedemann syndrome, Down syndrome, and the mucopolysaccharidoses. In severe cases of macroglossia, upper airway obstruction during anesthesia should be expected and difficulty with tracheal intubation anticipated.
Midface hypoplasia results in underdevelopment of the eye sockets, cheekbones, and upper jaw. The face can appear sunken, and frontal bossing is a prominent finding. Apert, Crouzon, and Pfeiffer syndromes are complex genetic disorders associated with midface hypoplasia and craniosynostosis. The incidence of obstructive sleep apnea is high in this patient population, and mask ventilation can be particularly challenging.
Showing prudence with history and the physical exam can help identify a potentially difficult airway. Diligent planning and preparation are of the greatest importance in mitigating anesthetic risk and decreasing morbidity.
Positioning is everything
The sniffing position is an accepted concept in pediatric airway management (Smith’s Anesthesia for Infants and Children, 10th Edition. 2022; A Practice of Anesthesia for Infants and Children, 6th ed. 2017). In this position, the lower cervical spine is flexed and the head simultaneously extended at the atlanto-occipital joint (Anaesth Intensive Care 2008;36:23-7). When position is optimal, the practitioner’s line of sight aligns with the glottic inlet during direct laryngoscopy with minimal effort and use of lifting force. In adults, reproducible objective anatomical markers are used to confirm proper positioning. The horizontal alignment of the external auditory meatus (EAM) with the sternal notch (SN) is well documented and provides a quick and efficient way to ascertain optimal positioning in both obese and non-obese adult subjects (Obes Surg 2004;14:1171-5; Br J Anaesth 2010;104:268-9). Simultaneously aligning the chin with the sinciput (forehead) in a horizontal plane can be a useful complementary marker. However, no such defined markers exist in the pediatric population, and clinicians position infants and young children according to individual preference and set notions. As an example, it is widely assumed that due to the relatively large head size, gentle head extension reliably achieves sniffing position in infants and toddlers (Smith’s Anesthesia for Infants and Children, 10th Edition. 2022; A Practice of Anesthesia for Infants and Children, 6th ed. 2017). There is no way to verify this assumption, though, nor is it clear how variability in head size and shape, degree of neck extension, and age affect this underlying presumption. Conventionally, clinicians place a shoulder roll to compensate for the large occiput, but again, the practice lacks objectivity. In recent years, there has been growing evidence that infants and children may benefit if positioned using similar objective markers as are utilized in adults (Eur J Anaesthesiol 2016;33:528-34; Eur J Anaesthesiol 2022;39:279-82). Figure 1 A-D demonstrates how the concept can be extrapolated from an adult to an infant. In some children, simple head extension may bring the EAM-SN plane in horizontal alignment, as is evident in Figure 1D. However, in most cases, a combination of a head rest and shoulder roll is required to bring the planes in alignment, as is demonstrated in Figure 1C. A shoulder roll without an accompanying headrest is more likely to hyperextend the neck and may be counterintuitive. It is also important to note that aligning the described horizontal planes perfectly in every case may not be possible. Variations relating to the shape of the head and occiput, degree of neck extension, and differences in the shape of the chin may all play a role.
In school-aged children, a folded blanket placed under the occiput is necessary to optimize neck flexion and atlanto-occipital extension, as is demonstrated in Figure 1B. Children with obesity are positioned using a ramp, as is routine practice in morbidly obese adults.
In summary, positioning infants and children based on reproducible markers can bring more objectivity to the process. Trials with a larger sample size are needed to mainstream this concept.
Maintenance of upper airway patency and the power of jaw thrust
Maintenance of upper airway patency is the cornerstone of effective airway management. In the pediatric population, upper airway obstruction during anesthesia is not infrequent and must be managed expeditiously to prevent serious harm. The hallmark of upper airway obstruction is diminished or absent airflow in the presence of continued respiratory effort. Complete upper airway obstruction is silent, while partial obstruction is accompanied by stertor and inspiratory stridor (J Pediatr 1985;106:863-9; Br J Anaesth 2003;91:31-9). Obstruction can occur at multiple levels from the nasopharynx to the laryngeal inlet. Deepening levels of anesthesia inhibit airway neural and muscle activity, which results in loss of pharyngeal muscle tone and airway collapse. Posterior displacement of the tongue, increased amounts of lymphoid tissue, and velopharyngeal collapse are additional factors that contribute to obstruction. Patients are particularly susceptible during stage II of inhalation induction when airway reflexes are hypersensitive. It is during this time that the child is most vulnerable to laryngospasm. As such, it is imperative to never discount the possibility of partial or complete laryngospasm as a cause of airway obstruction. Early diagnosis and treatment of this condition is essential to prevent serious injury.
Knowledge of specific age-related causes of upper airway obstruction during anesthesia is useful. In neonates and infants, laryngomalacia is a common cause of inspiratory stridor. The abnormally soft epiglottis and arytenoid cartilages dynamically collapse into the glottis during inspiration, resulting in partial airway obstruction. In the vast majority of patients, laryngomalacia improves without intervention by one year of age. In toddlers and older children, adenotonsillar hypertrophy is a major contributing cause of airway obstruction.
Several strategies are clinically employed to overcome upper airway obstruction during anesthesia. No single maneuver or methodology has been shown to be 100% effective in all circumstances. Combining different techniques has been shown to be the most effective strategy. Broadly, the underlying principles governing each of these maneuvers and methods aim to 1) decrease collapsibility, 2) increase pharyngeal cross-sectional diameter and patency, 3) decrease turbulence, and 4) improve airflow.
Mastering the art of mask ventilation is a fundamental skill. A properly sized anesthesia mask should fully cover the nares and the mouth, extending from the glabella to the chin. It is easy to inadvertently occlude the nares if one is not observant. A good seal is important and required to deliver positive pressure breaths and maintain continuous positive airway pressure (CPAP). In the classic one-hand C-E technique, the little finger is positioned at the angle of the mandible, ring and middle fingers on the ramus, and the index finger and thumb forming the “C” shape over the mask (Figure 2). The importance of staying on the bony parts of the mandible cannot be overemphasized because pressure to the soft tissues on the neck and under the chin can obstruct the airway. In the two-handed technique, the index and/or middle finger is positioned behind the angle of the mandible, pushing the jaw forward. The thumbs are used to hold and seal the mask over the face (Figure 2B). The two-handed technique is preferred for its ability to deliver a better seal, adequate mouth opening, jaw thrust, and chin lift (Anesthesiology 2010;113:873-9).
Positioning is crucial and should always be optimized. The sniffing position provides adequate “chin lift” and improves pharyngeal patency by increasing the longitudinal tension on muscles and decreasing velopharyngeal turbulence and collapse (Acta Anaesthesiol Scand 2011;55:530-4).
“Direct laryngoscopy remains the gold standard for endotracheal intubation in the young pediatric population. Strategies and techniques for intubation differ in infants and small children due to the distinctive aspects of their anatomy.”
Under anesthesia, the tongue often falls to the back of the pharynx, reducing retrolingual space. An appropriately sized oropharyngeal airway (Like the Guedel or Berman) is commonly used to maintain airway patency. Caution is advised in lightly anesthetized patients, as this can trigger laryngospasm and breath holding.
CPAP is routinely employed to counter upper airway obstruction during induction and emergence. CPAP improves inspiratory-expiratory airflow and airway patency by its pneumatic stenting effect on the collapsing airways. In addition, CPAP also augments oxygenation by its positive effect on alveolar recruitment.
Of all the airway maneuvers, jaw thrust remains the most effective in reversing upper airway obstruction (Anesth Analg 2002;94:494-9; Resuscitation 2012;83:411-6; Anesth Analg 2004;99:1638-41; Anaesthesia 1998;53:203-4). Jaw thrust is defined as the advancement of the mandible forward (anteriorly) until the lower teeth protrude in front of the upper teeth. Jaw thrust is most effectively provided using a two-handed technique. It is difficult to maintain forward displacement with one hand due to the tendency of the mandibular head to retract back into the TMJ socket. Forward displacement of the mandible has several advantages: 1) the base of the tongue and epiglottis are lifted off the posterior pharyngeal wall, widening the pharynx and improving patency, and 2) the stretch on the suprahyoid muscles and ligaments reverses dynamic collapse of the epiglottis and arytenoids due to laryngomalacia.
The combination of chin lift, jaw thrust, and CPAP has proven to be even more effective in reducing stridor and improving airway patency (Anesth Analg 2002;94:494-9).
Laryngeal mask airway (LMA) or a similar supraglottic device can be used to manage upper airway obstruction if other methods prove ineffective during induction. Awake LMA placement prior to inhalation induction is an ingenious approach in neonates and small infants with dysmorphic features when difficulty with mask ventilation is anticipated.
Lastly, preservation of spontaneous ventilation during inhalation induction is a good strategy. Residual muscle tone keeps the airway from collapsing and complements other techniques described in this section.
Direct laryngoscopy remains the gold standard for endotracheal intubation in the young pediatric population. Strategies and techniques for intubation differ in infants and small children due to the distinctive aspects of their anatomy. The tongue takes up more space in the oral cavity, making it difficult to displace during laryngoscopy. The jaw is underdeveloped, and the submental space is restricted. The larynx is located more cephalad in the neck, and the epiglottis angles away from the tracheal axis covering the laryngeal inlet. Due to all these reasons, a straight blade (e.g., Miller and Wis-Hipple) is preferred in infants and toddlers to achieve an optimal view. The straight blade is designed to directly lift the epiglottis; however, this is not always necessary. In most situations, engaging the tip of the straight blade deep in the vallecula can indirectly lift the epiglottis and bring the vocal cords into view. Irrespective of the technique, identifying the epiglottis during direct laryngoscopy is good practice and can prevent many instances of inadvertent esophageal intubation. Sweeping the tongue to the left using the paraglossal approach has advantages in infants and toddlers. The straight blade is inserted through the right corner of the mouth and advanced in the space between the tongue and the lateral pharyngeal wall until the epiglottis and glottis come into view (Figure 4). A slight amount of external laryngeal pressure may be necessary to further optimize glottic view. Jaw thrust provided by an assistant can also aid visualization during laryngoscopy. The ETT should be shaped to match the straight blade with a gentle curve at the tip. The traditional hockey stick shape increases the radius of curvature and can make it harder to precisely guide the tip of the tube into the glottis. In school-aged children, a curved blade like the Macintosh is preferred. The ETT should be shaped to match the curvature of the Macintosh blade. As in adults, sweeping the tongue from right to left is proper technique.
The use of cuffed ETTs in neonates, infants, and young children is becoming standard practice. The new microcuff ETTs have an ultra-thin, high-volume, low-pressure cuff that creates a superior tracheal seal at lower pressures. Traditional concerns about risk of ischemic injury and post-extubation stridor are not supported by new evidence (Br J Anaesth 2009;103:867-73; J Anesth 2016;30:3-11). The microcuff ETT has a more distal cuff that seals the trachea below the subglottis. The use of microcuff ETTs has several advantages, including better protection against aspiration, decreased need to exchange inappropriately sized ETTs, and ability to ventilate with more precision, higher pressure, and accurate tidal volumes.
Indirect video laryngoscopy techniques are slowly mainstreaming into pediatric anesthesia practice. Several straight and curved blade designs are commercially available for use in infants and children. Each design has its own ergonomics, field of view, blade shape, and sizes. Successful adoption into clinical practice depends on familiarity and experience with a particular design. Higher degrees of blade curvature do not necessarily translate into easier intubation. With the advent of better optics and new designs, video laryngoscopy promises to become part of our standard clinical practice in the foreseeable future.
Airway management in neonates, infants, and young children presents its own unique challenges. Knowledge of relevant aspects of anatomy and physiology is fundamental to providing safe care. The value of meticulous preparation and adherence to a set routine cannot be overstated and remains essential to safe and effective airway management. Learning to anticipate potential problems and having a clear treatment plan can decrease ambiguity, mitigate risk, and improve outcomes for our little patients.