The consideration of the difficult pediatric airway begins first with the understanding of the anatomy and physiology of the normal pediatric airway. The differences in the pediatric and adult airways are greatest between infancy and adulthood. These differences are less striking as the child reaches approximately 8 years of age, when the airway assumes adult (mature) proportions.
The objectives for this lecture are three fold: a) to understand the differences between the infant and adult airway anatomy and physiology b) to review the equipment available for managing the child's airway and c) to discuss some emergency management scenarios unique to pediatrics.
A. Anatomy (see Figure I)
The infant has a large head with a prominent occiput. The midface is small relative to the other parts of the head. The nares are small with small passageways. The nasal conchae are prominent and narrow the passageway further. The adenoids frequently may be enlarged as may the tonsils. The oral passageway contains a large tongue. The hypopharynx is small. The epiglottis is large, floppy and omega shaped. The larynx is short and narrow with prominent false cords (aryepiglottic folds). The larynx is located more rostrally in the infant than the adult; therefore, it appears to be more "anterior" on laryngoscopy. The narrowest portion of the laryngotracheal lumen is located below the vocal cords at the level of the cricoid cartilage, whereas in the adult the chords are the narrowest point. The trachea is short and the tracheal rings may be floppy. The infant's chest wall infrastructure (ribs and sternum) are not completely calcified and are more compliant than that of the adult. The bronchi are small in diameter and "minor" narrowing from respiratory infections or bronchospasm may result in profound airway difficulties. The lung volumes of the child are small in absolute terms. They are also small in relation to the child's metabolic needs.
The anatomical differences put the infant and child at relatively greater risk for airway problems than the adult.
The prominent occiput causes the head to lie flexed in relation to the neck when the infant is supine. This combined with a small neck and the child's internal anatomy can lead to upper airway obstruction. The infant is primarily a nose breather until approximately 3-6 months of age; thus any obstruction (such as nasal secretions) may produce obstructive apnea. Simple upper respiratory infections will lead to inflammation of the nasal mucosa (including the conchae) and result in upper airway obstruction. Adenoidal and tonsillar hypertrophy in the child may result in "snoring" and progress to frank airway obstruction (obstructive apnea). The large, floppy tongue can occlude the oropharynx in a sleeping or sedated child. It may also be a problem in the child with a congenitally small mouth or large tongue (e.g., Down syndrome, Beckwith Wiedemann syndrome). The floppy epiglottis and the hypopharynx may cause breathing difficulties more readily in the child because of viral (URI) or bacterial (epiglottitis) infection or inhalational (e.g., thermal) injuries. Inflammation of the tracheal mucosa from infections (viral laryngotracheobronchitis - croup, or bacterial tracheitis) or inhalational injuries produce subglottic narrowing of the tracheal lumen. This may be a mild "croupy" stridor which can quickly progress to frank subglottic airway obstruction. The tracheobronchial tree of the child is also prone to problems because of relatively narrow lumens which can obstruct and produce significant respiratory distress because of bronchospasm or inflammation. The small lung volumes and functional residual capacity in relation to the infant's metabolic needs means that he has less reserve and apnea (even with adequate preoxygenation with 100% oxygen) can quickly yield significant arterial desaturation and cyanosis.
Finally, the infant and small child are at further risk of respiratory problems because of immature protective reflexes. The infant may become apneic and bradycardic in response to an hypoxic challenge instead of increasing it's respiratory effort and heart rate!
Causes of upper respiratory problems in children are listed in Table II. Table III lists the normal respiratory variables at different age groups. Table IV lists congenital syndromes that are associated with upper airway difficulties.
II. Management of the normal infant airway:
The prominence of the occiput, the small neck and the narrow thorax mean that the infant must be positioned properly to avoid airway obstruction. A pad or folded sheet under the chest lifts the chest and neck to compensate for the large occiput. The neck is kept in the midline in a neutral position. Hyper extending the neck on the chest may occlude the airway. The head is then extended on the neck. A foam pad or folded towels on both sides of the head help stabilize the head. Because of the large tongue, the child may require a jaw thrust or chin lift to open the airway.
1. Oral airways
Oral airways can help maintain a patent airway by reducing or eliminating the pharyngeal obstruction caused by the tongue. (Figure III) The airway must be measured properly before inserting. Too small an airway may push the tongue down and further occlude the passageway. Too large an airway can cause pharyngeal and glottic trauma. If improper technique is used to place the airway, trauma to the maxilla and avulsion of the upper teeth is likely. Do not rotate the airway once it is inside the mouth- use a tongue blade to move the tongue out of the way.
2. Nasal airways
Nasal airways ('trumpets") help bypass the occlusion to airflow created by the tongue. These airways are made in a variety of sizes and for either the left or the right nostril (Figure IV). A proper size must be selected before attempting placement. The tube is then lubricated and inserted gently in the selected nostril. An airway that is too hard or that is placed with force can produce significant nasal damage including damage to the nasal turbinates and retropharyngeal bleeding.
Proper sizes of masks and ventilation bags must be available. The mask must fit appropriately over the nose, cheeks and chin. Figure III shows a variety of masks. Positive pressure ventilation is provided by self-inflating bags or "anesthesia bags" (Mapleson circuits) that require continuous oxygen flows. Using too small a bag will result in inadequate ventilation; using too large a bag may cause rebreathing or overinflation (and possible pneumothorax). These bags require a reservoir attachment to ensure that 100% oxygen is being delivered during the early inspiratory phase when the inspiratory flow rates are the highest.
4. Intubation equipment
Laryngoscope handles and blades come in different sizes and shapes. Generally, the straight blade (Miller or variant) is used for pediatric intubation, especially for infants under 6-12 months of age. For children older than 6-8 years of age, the curved (Macintosh) blade is more useful. Personal preference of the intubationist plays a significant role in which blade is selected for the child 12 months to 6 years of age. The more anterior airway and the floppy epiglottis of the infant and young child make the straight blade the logical choice for this age group.
5. Endotracheal tubes
Many different endotracheal tubes are available of for orotracheal or nasotracheal intubation. The tubes are also available preformed, armored, and especially designed varieties for special procedures. The scope of this lecture does not permit a detailed review of these choices.
In order to provide some stiffness to the tubes and facilitate intubation, stylettes are often used. A coated, metal or plastic stylette permits the intubationist to form the tube with the angles desirable for a certain child's airway. The stylette is placed such that it does not protrude from the Murphy eye in the tube. It is left in place until the tube is introduced through the vocal cords. In order to prevent cord and trachea damage, it is then removed before the tube is inserted further into the trachea.
6. Procedure for oral intubation
For intubation, the blade is inserted while directly observing the course of the blade. Starting with the right side of the mouth, the blade is inserted in a motion that brings it to the midline of the mouth while sweeping the tongue to the left side. The straight blade tip is used to lift the epiglottis, while the curved blade is placed in the vallecula to indirectly lift the epiglottis and open the airway. The force of the left hand is upward (in the direction of the handle) and lifting, NOT backward and flexing at the wrist (which put direct pressure on the maxilla and teeth). The endotracheal tube is inserted through the cords until the desired marks (one or two black marks on the tube) are seen at the cords. The tube is then held stable against the palate until tube position is confirmed by chest auscultation during bag ventilation and by presence of CO2 in the exhaled air. For a preformed tube (oral RAE) the tube is advance until the curve sits firmly on the lower lip. The tube is then secured with the desired adhesive and tape.
7. Procedure for nasal intubation
In addition the equipment for oral intubation, a set of proper sized Magill forceps must be available. In addition, topical vasoconstricting agents such as phenylephrine spray and lubricant jelly is necessary. Several sizes of nasal airways are used to dilate the nasal passage prior to intubation. Prior to intubation, the vasoconstrictor is applied to both nostrils. Then the nasal airways are inserted starting with the smallest selected, which is then replaced by the next successive size until the largest selected is placed. The largest size of airway that can be easily placed suggests the largest size endotracheal tube that can be inserted. A well lubricated endotracheal tube is then inserted and advanced gently until it enters the oropharynx. It is then advanced to the glottis under direct laryngoscopy. The Magill forceps are used to lift the tube into proper position to be advanced straight into the glottis and NOT to push the endotracheal tube. Securing a nasal tube is more difficult and several methods will be demonstrated. Inserting a nasal tube into someone with a basilar skull fracture, severely deviated nasal septum, enlarged adenoids and/or a bleeding diathesis is not advised.
If the child cannot be adequately ventilated because the airway cannot be maintained patent for BVM ventilation or if endotracheal tube placement is unsuccessful, emergency cricothyrotomy may be necessary. The equipment needed for this procedure in a child should be readily available in most patient care settings: intravenous cannula (18, 16 or 14 gauge), intravenous infusion extension tubing, stopcock, oxygen supply line and an oxygen supply, such as a cylinder. Figure X shows the approach to the cricothyrotomy. In infants and young children this procedure may be quite difficult because of the short neck, floppy/redundant soft tissues and small diameter of the trachea. Use of commercial products for cricothyrotomy and emergency tracheostomy have not met universal success not acceptance.
9. Securing the airway from below
a. Retrograde intubation
Borland et al described a method of retrograde intubation that may be useful in children. A red rubber catheter with a #2 silk suture is tied to the tip is passed through the naris and retrieved from the mouth. A needle cricothyrotomy is performed using a 20 gauge needle. Once the needle is in the trachea, a 0.021 inch diameter extra long flexible tip guide wire is passed through the needle superiorly and retrieved from the mouth. The suture is then tied to the wire tip and retrieved through the naris. A well lubricated endotracheal tube is threaded over the wire (using the Murphy eye) through the naris and oropharynx. Tension is maintained on both ends of the wire during this procedure. The tube is then advanced through the glottis. The wire is removed and the tube is advanced further into the trachea.
b. Fiberoptic intubation in infants and children
Fiberoptic intubation scopes can help guide the placement of and endotracheal tube in a child. Because of the small diameter of the nares, fiberoptic intubation is more commonly performed vis the oral rout in infants and small children. The smallest intubating bronchoscope is approximately 3.6 mm in outer diameter and will fit snugly through a 4.5 mm ID endotracheal tube. A 2.2 mm OD fiberoptic scope is available; however, the instrument is so thin and pliable that it is inadequate as a guide to the stiffer endotracheal tube. In the adult and older child, the fiberscope may be used as the guide over which the tube is advanced into the glottis. In infants and small children, it often is necessary to use the fiberscope along side the endotracheal tube to direct its placement.
10. Medications for intubation
a. hemodynamically stable patients
Patients who are hemodynamically stable may tolerate a variety of agents. A sedative/anesthetic such as ketamine, etomidate or thiopental is generally used. Neuromuscular blockade can be achieved with nondepolarizing drugs such as pancuronium or vecuronium. Because infants and children have a relatively higher vagal tone, a vagolytic agent such as glycopyrrolate or atropine should also be used.
b. Hemodyanmically compromised patients
Children who are at risk for hemodynamic compromise because of severe dehydration, bleeding (e.g., trauma patients) or underlying cardiac disease require a modified drug regimen. The dose of ketamine or etomidate may need to be reduced. If these drugs are contraindicated, a combination of fentanyl (2-4 mcg/kg) and midazolam (0.05-0.1 mg/kg) may be used. Thiopental should not be used. Neuromuscular blockade can be achieved with the same dose as above. Anticholinergic medications can be given as ususal.
c. head injured patients
Children with head injuries who need intubation may benefit from the use of etomidate, the combination of fenatanyl and midazolam, or an adjusted induction dose of thiopental (to blunt intracranial hypertension). Ketamine is contraindicated in children with elevated intracranial pressure. Neuromuscular blockade can be achieved with the same dose as above. Anticholinergic medications can be given as usual.
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