47.4.1 How Exactly Should the Airway of This Patient Be Managed?
Most children will require some form of sedation prior to a procedure, particularly children with multiple prior contacts with health care providers as these children harbor a healthy suspicion of these providers! Midazolam is a reasonable anxiolytic, either as commercially available syrup or the concentrated IV form suspended in flavored syrup (although this concoction is usually unpleasantly bitter). A dose of 0.5 mg·kg−1 (maximum 10 mg) is administered orally at least 15 minutes before attempting any separation from caretakers.10 At this dose, respiratory depression has not been reported. Once IV access is obtained, further small incremental doses of midazolam can be titrated to effect, should a sedation technique be employed.
Most anesthesia practitioners would employ a combined general and regional anesthesia technique using a Laryngeal Mask Airway (LMA) or another of the increasingly available extraglottic devices (EGDs). Inhalation induction is the most common approach in these patients. This takes advantage of the fact that this technique maintains spontaneous ventilation and the ability of reversing the anesthetic at any point should airway maintenance become questionable. This technique is generally considered to be safe, particularly since neuromuscular-blocking agents (NMBA) are not being employed.
While many consider sevoflurane to be the preferred anesthetic agent for induction and maintenance of pediatric anesthesia, it does have several limitations:
Much higher incidence of emergence delirium.11
Marked depression of respiration in high concentration.
Too rapid a change in the level of consciousness.
If an IV is in place, some practitioners advise the administration of glycopyrrolate, 5 to 10 μg·kg−1, as an antisialagogue. Atropine is less desirable as it has less drying action and more tachycardia associated with its use.
IV induction may be easily achieved with a number of agents, but, in the case of potential airway manipulation, propofol is often the drug of choice as it blunts airway responses to manipulation and is easily titratable.
Once anesthetized, an LMA or other EGD should be placed.12 The insertion method for the LMA is described in Chapters 12 and 42. Correct placement is confirmed by hearing breath sounds and can be further validated by successful ventilation with positive pressure as well as a good end-tidal CO2 tracing.
47.4.2 If One Wants to Perform a Caudal Block, How May that Be Done, Especially If an LMA Is in Place?
Once the LMA/EGD is placed and secured, the child is turned into the left lateral decubitus position (for a right-handed practitioner) to perform the caudal block and then returned to the supine position for surgery. Attention to securing the LMA/EGD during any positioning procedure is vital as the seal is easily lost. This is particularly important in the smaller child (<10 kg), where initial placement tends to be more difficult.13
A detailed discussion of caudal block technique is beyond the scope of this chapter. Briefly, an agent with a rapid onset is preferred to avoid potential laryngospasm with surgical incision. An equal mixture of 2% lidocaine and 0.25% levobupivacaine (or 0.2% ropivacaine) 1 mL·kg−1 will achieve this goal and produce a block of long duration as well. The addition of clonidine 1 to 2 μg·kg−1 14 or neostigmine 2 to 4 μg·kg−1 15 has been suggested to prolong the duration of the block. The caudal block can reduce the requirement of the anesthetic vapor and avoid respiratory depression associated with the use of opioid. If airway difficulty is encountered at any stage during the induction, simply turning off the inhalational agent and administering 100% oxygen will result in rapid awakening and recovery of airway reflexes.
47.4.3 How Would One Perform a Flexible Bronchoscopic Intubation in This Child?
If Plan A is unsuccessful or not practically feasible, Plans B and C should be prepared before bringing the patient to the operating room.
Flexible bronchoscopic intubation is ordinarily one of those plans. This can be done awake or asleep in this age group with patience and careful planning. These children can be very challenging, particularly if they have had previous negative interactions with health care personnel. It is difficult to employ logic and reasoning with a 6-year-old child. For this reason, moderate to heavy sedation is usually required. Oral midazolam 0.5 mg·kg−1 (maximum 10 mg) is often effective as an initial sedating agent as one begins the process of preparing for the flexible bronchoscopic intubation.
Initially, both nasal passages are anesthetized with 4% aqueous lidocaine and vasoconstriction achieved with topical oxymetazoline. Nebulization of lidocaine is an effective airway anesthetic. The 4% solution commonly available can be diluted (with water, not saline because saline changes its pH) to 2% to give greater volume. Not more than 5 mg·kg−1 should be placed in the nebulizing chamber and allowed to be slowly inhaled either in the holding area or on the way to the operating room. The finely nebulized particles will anesthetize the glottis and trachea to varying degrees.
Once in the operating room, IV access is mandatory before proceeding further, and, once secured, 5 μg·kg−1 glycopyrrolate IV should immediately be given. Monitoring should be instituted (pulse oximetry, noninvasive blood pressure, and ECG at a minimum); suction, oxygen, emergency drugs, and airway equipment should be checked as discussed earlier. An experienced assistant will be required to help. If there is a failed airway and ventilation is not possible at any point during the intubating attempt, a surgeon should be immediately available to perform a rigid bronchoscopy or a surgical technique.
It is prudent to avoid the use of bolus doses of sedatives. For sedation, incremental doses of IV midazolam and propofol administered via an infusion pump should be done slowly. Importantly, one must allow time for the onset of drug effect to occur after titrating dosages. Haste is strongly discouraged as it increases the risk of losing the airway of a spontaneously breathing patient. If the patient becomes unconscious and apneic with the propofol infusion, it can be turned off and return of spontaneous ventilation should occur rapidly. It is a matter of personal preference to employ drug infusions instead of volatile agents for sedation or anesthesia for this procedure. Generally, infusions are easier to control than volatile agents, which can pollute the operating room environment. Additionally, it may be difficult to achieve a constant anesthetic concentration during the intubation procedure.
Flexible bronchoscopic intubation through the mouth without a guide to maintain the pediatric flexible bronchoscope (FB) in the midline is difficult to achieve without practice. Some practitioners use an LMA/EGD to keep the FB in the midline position. However, most find the nasal route much easier, since the tip of the bronchoscope usually emerges in the pharynx in the midline just above the glottis. The nasal passages may be dilated by passing increasingly larger diameter nasal trumpets, well lubricated with lidocaine jelly, every few minutes. The aim is to pass a trumpet slightly bigger than the proposed nasotracheal tube. As there is no contraindication to use cuffed tubes in pediatric patients, a smaller cuffed tube should be used to secure the airway of this patient.16 Gentleness cannot be over emphasized; bleeding from the nasal passages can turn an elective controlled procedure very rapidly into an emergency disaster. Blood in the airway may render the FB nasal intubation technique difficult or impossible.
Some manufacturers (eg, Karl Storz Endoscopy, CA) stiffen neonatal and pediatric bronchoscopes that are intended for intubation. Although bronchoscopes as small as 2.3 mm in diameter are available, the procedure is usually performed with device that has a 3.0- to 3.5-mm tip diameter. The major disadvantage of pediatric and neonatal bronchoscopes is the small ineffective working channel for suctioning. Generally, the insufflation of high-flow oxygen through the working channel is discouraged due to the risk of gastric insufflation, perforation, and death.17,18 However, some practitioners adopt a low-flow oxygen insufflation technique through the working channel at about ½ L·min−1 to blow secretions out of the way while being extremely careful to regulate the flow of oxygen and never advance the bronchoscope unless under vision.
Before using the bronchoscope, it is important to confirm the correct functioning of the light source and the controls and to ensure that it is in focus. In the event one plans to inject local anesthetic through the working channel, 2 to 3 mL air flush is needed to flush the drug out of the distal lumen.
Once the nasal passages are dilated and anesthetized and the patient is adequately sedated, the appropriately sized and softened (hot water works well), and externally lubricated endotracheal tube (ETT) is passed into the chosen nares (the larger of the two) and advanced until the tip passes beyond the nasopharynx into the upper oropharynx. This point is generally appreciated as an abrupt loss of resistance associated with advancing the ETT. Any adenoidal tissue dissected by the tube tip and lodging in the distal ETT must be evacuated usually by gently pulling the ETT into the oral cavity with Magill forceps and blowing it out. The bronchoscope is inserted through the lumen of the ETT (previously lubricated with a silicon-based solution) to emerge just above the larynx in the oropharynx and then maneuvered into the trachea and advanced to the carina. Then, the ETT can be advanced over the bronchoscope into the trachea and positioned in midtrachea with the bronchoscope.
The process of repeated nasal trumpet insertion can be quite stimulating, and therefore, once the final nasal trumpet has been passed and the patient is comfortable with it in place, the need for deeper sedation ought to be minimal.
With a spontaneously breathing patient, regular movement of the airway may help to guide the bronchoscope to the right direction. If the patient is cooperative, one can ask the patient to stick out their tongue, or ask an assistant to gently pull the tongue forward with a gauze swab. This serves to open the hypopharynx, which often will help expose the cords. Alternatively, a gentle jaw thrust in a drowsy patient will also help to elevate the tongue and epiglottis.19-24
At this point, 0.5 to 1.0 mL of 1% or 2% lidocaine can be instilled through the working channel onto the cords to allow easy passage of the FB between the cords, followed by the nasotracheal tube. In some situations, particularly if violent coughing occurs, a small bolus of propofol can be administered rapidly by an assistant to facilitate the advancement of the ETT. The FB is then removed and general anesthesia is induced.
The nasal route is not always available, either due to anatomical difficulties or surgical considerations. In this case, the oral route may be used. While the nebulized lidocaine often adequately anesthetizes the nasal passages of children, oral topical anesthesia is often inadequate using this technique. Persuading a 6-year-old child to gargle lidocaine may work in selected patients. Attention to the cumulative dose of local anesthetic is important. Applying lidocaine jelly to the tongue slowly and progressively with a tongue depressor may also be effective. In an awake child, eliminating the gag reflex may be achieved by one quick squirt of local anesthetic on the uvula, which can be achieved with patience.
Passing an appropriately sized LMA/EGD has been shown to facilitate oral flexible bronchoscopic intubation.25-31 Prior to starting the procedure, lubricate the inside of the LMA/EGD shaft with a silicon spray. Find an ETT that fits the lumen of the LMA. Because there are a number of manufacturers, it is difficult in a chapter such as this to publish size guidelines since outer diameters of ETTs vary from manufacturer to manufacturer.
A standard ETT may be of insufficient length. In this event, the following work-around is advised. Obtain a second, identical tube. Take the tube connector of one of the tubes and cut the shaft off the connector as close as possible to the hub. This short (about 1-2 cm) connector can be used to join the two ETTs together back to back, giving you one long ETT (Figure 47-1).32 Since it is very slightly thickened at the joint, make sure that this new tube will fit through the LMA/FB combination. Alternatively, a long Microlaryngeal Tube (MLT, Rusch Inc., Duluth, GA) can be used.
The equipment needed to perform a flexible bronchoscope-guided intubation through an LMA. A tube connector is created by cutting the shaft off the connector from a similar size ETT. This short connector can then be used to join the two endotracheal tubes together back to back, thus providing a sufficiently long endotracheal tube to pass through the LMA. (Reproduced with permission, from Muraika L, Heyman JS, Shevchenko Y. Fiberoptic tracheal intubation through a laryngeal mask airway in a child with Treacher Collins syndrome. Anesth Analg. 2003;97:1298-1299.)
It is also a reasonable technique to advance the ETT blindly into the trachea through the LMA and then use the FB to confirm placement. Once the ETT is in place, the LMA may be withdrawn over the elongated tube without extubating the patient. This works for both regular tubes and RAE (Ring, Adair, and Elwyn) preformed tubes, and can even be done with a cuffed tube, provided that the LMA is loaded from the distal end with the balloon and pilot tube of the cuff protruding from the distal end of the LMA.
Cobra manufactures a disposable perilaryngeal airway that comes in pediatric sizes. It is placed in a similar fashion to, and functions similarly to the LMA-Classic™. Its major advantage as a guide for oral flexible bronchoscopic intubation is that the bore of the shaft is larger than that of the LMA, allowing the easier passage of the FB and accompanying ETT. Similarly, the air-Q™ airway (Mercury Medical, Clearwater, FL) is a disposable EGD designed to facilitate blind intubation. The reuseable variant is called the Cook-ILA. It functions similarly to the Intubating LMA (LMA-Fastrach™, LMA North America, San Diego CA) in adults, but is available in sizes appropriate for infants and small children (see Chapter 42).33
47.4.4 What About the Use of a Video Laryngoscope?
Video laryngoscopes have the advantage of being able to see around corners and possessing a wide field of view. While initially developed for adult patients, many manufacturers have made models available for pediatric practice. Manufacturers include Verathon (GlideScope®, Bothwell, WA) and Storz (Tuttlingen, Germany). A novel disposable video device possessing an ETT delivery channel and supplied in sizes appropriate for infants and small children is the Airtraq™.34
47.4.5 What If a Flexible Bronchoscopic Intubation or the Use of a Video Laryngoscope Is Unsuccessful?
In the event that the flexible bronchoscopic intubation cannot be achieved in a child with a difficult airway, or the use of the video laryngoscope is unsuccessful, a tracheotomy in a spontaneously breathing anesthetized patient may be the best course of action, and is quite commonly done.35