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The Difficult Pediatric Airway
In this chapter we review principles of pediatric difficult airway management, with a focus on those entities that cause anatomic or functional airway obstruction above the level of the glottis. We consider causes and treatments of anticipated and unanticipated difficult intubation and difficult ventilation. Finally, we will touch upon updated equipment and techniques for difficult airway management.
The most important aspect of anesthetic management of the difficult airway is having a clear plan and the multiple steps of the back-up plans. It is not enough to have only one or even two back-up plans, but rather three or four, and an exact plan for the worse possible situation: the development of life-threatening hypoxemia. Every anesthesiologist must know precisely the method to alleviate it and save the child’s life. This could entail a cricothyrotomy or tracheotomy, which are more technically difficult in small children than in adults.
Proper preparation is essential and will depend on the cause of the expected difficulty. A full explanation of the anesthetic risks and benefits should be discussed with the child’s family. An indwelling intravenous catheter is preferred, except when the anesthesiologist feels that provoking or painfully stimulating the child may worsen the upper airway obstruction, as may occur with acute epiglottitis. Another important aspect of pediatric difficult airway management is the presence of adequate help. This could be another experienced anesthesiologist or surgeon or other clinician depending on the clinical circumstances.
The difficult airway is an important cause of cardiac arrest during anesthesia in children. In the first reported pediatric Perioperative Cardiac Arrest (POCA) Registry, respiratory complications accounted for 30 of the 150 reported cardiac arrests, and many of these cases were associated with difficult ventilation or intubation ( Table 18.1 ).
Table 18.1
Respiratory Causes of Cardiac Arrest From the POCA a Registry
(Reproduced with permission from Morray JP, Geiduschek JM, Ramamoorthy C et al. Anesthesia-related cardiac arrest in children: initial findings of the Pediatric Perioperative Cardiac Arrest Registry. Anesthesiology 2000:93:6.)
| Respiratory Cause | Number of Cardiac Arrests |
|---|---|
| Laryngospasm | 9 |
| Airway obstruction | 8 |
| Difficult intubation | 4 |
| Inadequate oxygenation | 3 |
| Inadvertent extubation | 2 |
| Unclear etiology, presumed respiratory | 2 |
| Inadequate ventilation | 1 |
| Bronchospasm | 1 |
| Total | 30 |
Unlike adults, normal-appearing children rarely present with an unexpected difficult intubation. Therefore in this chapter only the anticipated difficult intubation will be reviewed.
Preanesthetic Preparation
The most reliable predictor of a difficult intubation is the patient’s history. If a previous anesthetic record is available, it should be reviewed before administering a subsequent anesthetic. Physical examination should focus on anatomic anomalies that involve the head, face, or neck, especially if the child carries the diagnosis of a congenital airway syndrome ( Table 18.2 ).
Table 18.2
Examples of Congenital Airway Syndromes
| Syndrome | Clinical Characteristics |
|---|---|
| Beckwith-Wiedemann | Macroglossia, organomegaly, omphalocele, hypoglycemia |
| Down (trisomy 21) | Macroglossia |
| Pierre Robin sequence | Micrognathia, cleft palate, glossoptosis |
| Treacher Collins | Hypoplasia of the maxilla and mandible, variable eye and ear deformities |
| Hemifacial microsomia (e.g., Goldenhar) unilateral or bilateral mandibular | Hypoplasia, variable microphthalmia, microtia, macrostomia |
| Apert | Craniosynostosis, syndactyly |
| Freeman-Sheldon (“whistling face”) | Microstomia, facial anomalies, hand anomalies |
| Mucopolysaccharidoses | Redundant facial and pharyngeal soft tissue |
| Klippel-Feil | Cervical vertebral fusion |
| Crouzon | Craniosynostosis |
| Stickler | Mandibular hypoplasia, myopia, retinal detachment, joint stiffness |
| Pfeiffer | Craniosynostosis, polydactyly |
The anesthesiologist should evaluate the size and mobility of the mandible. The exam should also focus on any anatomic features that cause distortion of the airway or symptoms of airway obstruction (e.g., snoring) when supine. The most likely factor that predicts difficulty with intubation in pediatric patients is a small, malformed, or immobile mandible. Scoring systems that predict the likelihood of a difficult intubation do not exist for children.
The stepwise technical approach to securing tracheal intubation should be well-thought-out before the time of surgery ( Fig. 18.1 ). All necessary airway equipment should be present in the operating room (OR), including the equipment necessary for the second, third, and even fourth options should initial attempts fail. In pediatrics, different sized laryngoscope blades and endotracheal tubes should be within easy reach.
In children with a known difficult intubation, it is preferable to secure venous access while the child is still awake. However, if the child is not amenable, or inspection of the limbs does not show promising possibilities, and if one believes the child will not be difficult to ventilate (based on history or physical exam) then general anesthesia may be induced without prior intravenous (IV) access.
An anticipated difficult intubation can be loosely defined as that which the anesthesiologist feels would be difficult to visualize the airway with standard techniques. In other words, the very nature of the anticipated difficult intubation implies that specialized indirect methods are required for tracheal intubation, and direct laryngoscopy should not be attempted first. With each direct laryngoscopy attempt, the severity of airway edema and bleeding will increase and will ultimately decrease the chance of eventual success with more specialized methods.
A Deeper Dive
In a multicenter study involving infants and children from the Pediatric Difficult Intubation (PeDI) Registry, the occurrence of a complication was associated with the number of tracheal intubation attempts; the odds of a complication increased 1.5-fold per attempt ( Fig. 18.2 ). Direct laryngoscopy had a very low first-attempt success rate of 3% (16/461) compared with indirect techniques: fiber-optic bronchoscopy 54% (153/284) and video laryngoscopy 55% (101/183). Twenty percent of children had at least one complication, with 2% (15/1018) experiencing cardiac arrest. Temporary hypoxemia was the most common nonsevere complication and occurred in 9% (94/1018) of patients. Overall, complications were associated with multiple intubation attempts (>2), weight less than 10 kg, short thyromental distance, abnormal airway physical examination, and persistent direct laryngoscopy tracheal intubation attempts. Although hypoxemia may be a reversible complication, children have higher oxygen consumption rates than adults and therefore a much faster rate of arterial oxygen desaturation when apneic. When hypoxemia occurs, multiple intubation attempts are more likely, as the intubation attempt is interrupted to ventilate the patient. These nonsevere complications, such as hypoxemia, easily lead to severe complications such as cardiac arrest. Lessons learned from the PeDI Registry include limiting intubation attempts, using indirect techniques initially, and providing passive oxygenation throughout intubation attempts. Passive oxygenation is effective in children, delays the onset of hypoxemia, and provides more time for tracheal intubation.
Techniques
First-line indirect techniques include video laryngoscopy, intubating supraglottic airway (SGA), or the flexible fiberoptic bronchoscope. This choice is influenced by the patient’s airway anatomy and is dependent on the experience and personal preference of the anesthesiologist. A detailed explanation of the use of these devices is beyond the scope of this book; however, we will briefly describe the advantages and disadvantages of each technique.
Fiberoptic Bronchoscopy
Flexible fiberoptic bronchoscopy is considered the gold standard technique for managing difficult tracheal intubation in adults and children. In recent years, anesthesiologists have become more adept at manipulating the ultrathin bronchoscope, which may be used inside a 2.5- or 3.0-mm internal diameter endotracheal tube (depending on the manufacturer). In addition, the optical aspects of the equipment have improved to allow better screen resolution. The technique must be practiced on mannikins and normal children before managing the difficult airway ( Fig. 18.3 ).
There are several reasons why bronchoscopy can be more difficult in children compared with adults. First, because of the inherently smaller size of children, smaller bronchoscopes are required. Pediatric bronchoscopes range in size from 2.2- to 4.1-mm diameter. The smallest bronchoscopes lack a working channel; thus there is no conduit for suctioning secretions or blood. Administration of an antisialagogue before beginning the procedure should be considered (not evidence based), and the oropharynx should be suctioned before the bronchoscopic attempt. Oxygen insufflation should not be performed via this port in small children because of the possibility of generating dangerously high intrabronchial pressures and development of a tension pneumothorax.
Second, children have a limited time to oxyhemoglobin desaturation. This is caused by the markedly reduced functional residual capacity (FRC) in anesthetized small children and their relatively high oxygen consumption. Therefore small children require alternate means of oxygenation during intubation attempts. See section below on apneic oxygenation.
Third, in smaller children, flexible bronchoscopy performed through an SGA is more difficult than in adults because SGA placement in children is associated with a higher incidence of malpositioning, which leads to an obscured view of the glottic opening. The air-Q intubating laryngeal airway (Salter Labs, Lake Forest, IL, USA) seems to be the optimal choice for an intubation conduit because the lumen of the tube is larger than other types of SGAs, and allows passage of cuffed endotracheal tubes with the pilot balloon.
Finally, the unique anatomic variance of infants and children may influence successful fiberoptic bronchoscopy. If a nasal route is chosen, enlarged adenoidal and tonsillar tissue may obstruct the view and is likely to bleed upon contact. Oxymetazoline can be applied intranasally before insertion of the fiberoptic bronchoscope to minimize bleeding. The relatively more anterior location of the infant glottis may require more extensive anteflexion of the bronchoscope for adequate visualization of the glottic opening.
Video Laryngoscope
In its basic concept, a video or indirect laryngoscope is able to view the larynx using a video camera at the tip of its blade. In the past, pediatric video laryngoscopes were simply smaller adult laryngoscopes. There are now many types of video laryngoscopes manufactured with pediatric-specific designs. One of the simplest ways to classify video laryngoscopes is by whether it is a standard blade or nonstandard blade. Standard (Miller and MacIntosh) blades can be used as direct laryngoscopy, indirect laryngoscopy (completely use the video screen), or as video-assisted direct laryngoscopy. Manipulation of the blade follows the same skills as in direct laryngoscopy. Nonstandard blade video laryngoscopy involves the use of hyperangulated blades such as the traditional GlideScope (Verathon Inc., Parkway Bothell, WA, USA) and the Storz C-MAC D-blade (Karl Storz, Tuttlingen, Germany). Direct laryngoscopy with these blades will not reliably expose the glottic opening; they require different skills. Devices with greater curvature (hyperangulation) of the blade typically provide better visualization of an anterior larynx; however, they also require a more curved trajectory of the endotracheal tube, which increases difficulty. Hyperangulated blades, such as the GlideScope, are advantageous in the management of difficult airways compared with direct laryngoscopy. Having a styletted endotracheal tube that is curved to match the curve of the GlideScope blade will help facilitate manipulation into the field of view and into the glottic opening ( ).
Tracheal intubation of children with micrognathia or macroglossia is challenging with any video laryngoscope because it is often difficult to manipulate both the laryngoscope and the endotracheal tube within the small pharynx. An alternative option is the use of a combined technique (e.g., a fiberoptic bronchoscope along with a video laryngoscope.) Video screens of each device are placed side by side and at least two operators are required. Benefits of this technique include visualization of the laryngeal inlet with video laryngoscopy, and visual control of the passage of the ETT over the fiberoptic bronchoscope into the trachea.
Intubation via a Supraglottic Airway
Supraglottic airways (SGAs) can be life-saving devices, particularly if difficulty with ventilation is encountered. An appropriately placed SGA allows the patient to continue breathing spontaneously throughout the induction and intubation attempts. However, the SGA poses a particular challenge to insertion of cuffed endotracheal tubes, as the pilot balloon may be larger than the proximal opening of the SGA. Newer designs, such as the air-Q (Salter Labs, Park Forest, IL, USA) allow easier placement of an endotracheal tube. The airway tube of the air-Q is shorter than the classic laryngeal mask airway (LMA), and the opening is wider, thus allowing passage of a cuffed endotracheal tube with less resistance. Nevertheless, fiberoptic bronchoscopy should be used to facilitate the advancement of the endotracheal tube into the trachea via the air-Q device. Table 18.3 summarizes the relationship between the size of LMA and the sizes of endotracheal tubes and fiberoptic scopes that fit.
Table 18.3
Pediatric-Sized Laryngeal Mask Airways and Compatible Endotracheal Tubes a
| Inner Diameter of LMA (mm) | Maximum Lubricated Uncuffed ETT Inner Diameter (mm) | Maximum FOB Size b | Maximum Lubricated Cuffed ETT Inner Diameter (mm) |
|---|---|---|---|
| 1.0 | 3.5 | 2.7 | 3.0 |
| 1.5 | 4.0 | 3.0 | 4.0 |
| 2.0 | 5.0 | 3.5 | 4.5 |
| 2.5 | 6.0 c | 4.0 | 5.0 |
| 3.0 | — | 5.0 | 6.0 |
| 4.0 | — | 5.0 | 6.0 |
a Based on experiments performed by author. ETT , endotracheal tube
b As per LMA North America. FOB , Fiberoptic bronchoscope.
c Largest available uncuffed endotracheal tube available at The Children’s Hospital of Philadelphia.
In addition to fiberoptic bronchoscopy and video laryngoscopy, there exist several additional methods to directly or indirectly visualize the glottis and perform tracheal intubation. These include optical stylets such as the Bonfils (rigid) and Shikani (malleable, firm) types and the lighted stylet (also known as the lightwand). Details of the use of these devices are beyond the scope of this book but can be found in textbooks on advanced pediatric airway management.
Apneic Oxygenation
Oxygenation is the most important principle of airway management in any patient. Infants and small children may develop hypoxemia rapidly during apnea because of their relatively higher oxygen consumption along with their decreased FRC while anesthetized. If not immediately corrected, this can quickly lead to cardiac arrest, particularly in the pediatric difficult airway. Therefore it is imperative that apneic time be minimized. Some studies have found benefits in providing supplemental oxygenation to children during prolonged tracheal intubation, such as preservation of normoxemia and decrease in the overall rate of desaturation.
Transnasal humidified rapid-insufflation ventilatory exchange (THRIVE) is a technique that provides high-flow humidified oxygen through a nasal trumpet and allows continuous oxygen delivery during the intubation attempt. THRIVE has proven beneficial in adults, prolonging apneic oxygenation time, and enabling unhurried intubation in adults with difficult airways. A randomized trial found THRIVE to be beneficial in infants and children. Children in the THRIVE arm maintained their transcutaneous hemoglobin saturation at least twice as long as the those in the same age range in the control group. Transcutaneous CO 2 increased to a similar extent in both arms. Nasal oxygen during efforts securing a tube (nasal oxygen during efforts securing a tube [NO DESAT]) uses a simple nasal cannula to provide standard low-flow oxygen while tracheal intubation is performed. In adults and children, apneic oxygenation during intubation delays oxyhemoglobin desaturation. There are a variety of other creative ways to provide supplemental oxygenation during intubation attempts ( Fig. 18.4A–C )
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