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Refresher Courses - Saturday June 9 |
From the Department of Anesthesiology, Children's Memorial Hospital and Northwestern University Medical School, Chicago, Illinois, USA.
Address correspondence to: Dr. Steven C. Hall, Department of Pediatric Anesthesia, Children's Memorial Hospital, 2300 Children's Plaza, no. 19, Chicago, Il 60614-3394 USA. Phone: 773-880-4415; Fax: 773-880-3331; E-mail: schall{at}nwu.edu
THERE is an old saying that goes - "Good judgment comes from experience. Experience comes from bad judgment". Anesthesiologists have long cherished their reputation as experts in airway management. Some of this expertise has come from application of a systematic approach to problems, such as evaluation of an abnormal airway. On the other hand, some of our appreciation of priorities in management and potential complications have come from experiences in which the clinical course was troublesome. It is the purpose of this lecture to discuss a systematic approach to the unique aspects of evaluating and managing the difficult airway in a pediatric patient.
The anesthesiologist should have a detailed understanding of the fundamental differences not only in the airway anatomy and function in children of different ages, but also the signs and symptoms of significant airway compromise, the radiologic features of various lesions, and the common airway abnormalities seen in childhood. In addition, the anesthesiologist must have the variety of equipment and support needed to manage all eventualities in these situations. Lastly, the anesthesiologist must have a clear set of plans and protocols for initial evaluation, preparation, and management that includes the treatment of potential complications, including precipitous complete loss of a patent airway.
Although most anesthesiologists feel confident in their airway skills, many clinicians do not have extensive experience with abnormal pediatric airways. However, when a child with a deteriorating airway needs intervention, the anesthesiologist must be able to respond in an expert fashion quickly. Since this can occur in any hospital, especially any hospital that has an emergency room, all anesthesiologists, no matter what their formal training, must be prepared to effectively recognize and treat the child with a compromised airway. Consequently, the anesthesiologist must ensure that not only are they prepared to manage a child with a difficult airway, but that each facility in which they work has readily available the equipment necessary to promptly intervene.
The difficult airway
Causes of a difficult airway in children can be categorized into four general groups. The first group contains children with congenital abnormalities that present with varying degrees of chronic obstruction. Examples include laryngomalacia, glottic webs, hemangiomas, vascular rings, and hypoplastic mandible. These conditions often present either shortly after birth or in infancy. The second group includes infections of the airway, such as epiglottitis, croup, and diphtheria, that present with progressive airway obstruction, often over a relatively short time frame. The third group consists of children with sudden obstruction of the airway, such as foreign body aspiration or trauma. The fourth group includes patients without known congenital or acquired abnormalities who are unexpectedly difficult to visualize for intubation.
When a child with an at-risk airway is identified, the degree of obstruction and functional impairment must be assessed immediately. The general appearance of the child is an important sign, since agitation, retractions, cyanosis, anxiety, weak or absent cry, and stridor can all be indications of significant obstruction. Further examination includes evaluation of breath sounds, chest excursion, use of accessory muscles, ability to open the mouth, ability to take a deep breath, and mobility of the neck and mandible. If there is time, a history from the parents or care-giver can give valuable information about the timing of the respiratory distress, the presence of cyanosis, choking, or retractions, and other pertinent history. Laboratory evaluation with PA and lateral radiographs of the head and neck can be especially useful, with other examinations like CT scans occasionally offering useful information. Lastly, previous experiences with the airway, such as prior anesthetics, can provide useful information.
The degree and site of obstruction, along with anticipated difficulties in airway management, influence the perioperative approach. An awake intubation with either a fiberoptic or standard laryngoscope may be appropriate in some cases. Preoxygenation and insufflation of oxygen during the procedure can significantly decrease any desaturation. However, it has long been a tradition in pediatric anesthesia that intubation is accomplished after the induction of general anesthesia in most children in order to avoid unnecessary trauma and ensure a quiet field. The advantages of general anesthesia should be balanced against the potential loss of airway protective reflexes and spontaneous ventilation. A variety of methods and their indications and contraindications will be discussed.
Specific lesions
Croup
Croup is a generic term that indicates there is inspiratory stridor with a characteristic "barky" cough, often accompanied by retractions, caused by subglottic narrowing. The most common cause of symptomatic croup is infectious laryngotracheobronchitis, usually viral in origin. The most common viruses are parainfluenza, influenza, respiratory syncytial, and adenovirus. There is a seasonal pattern of these infections, peaking in early fall and winter. This infection primarily involves the larynx and trachea, with bronchitis being less common. Because the subglottic larynx at the cricoid level is the narrowest part of the upper airway in children, edema of the mucosa at this level results in significant airway obstruction and the characteristic barky cough.
Croup is most common in children between two months and three years of age, is associated with a low grade fever, and presents gradually over several days, with increasing cough, hoarseness, and stridor. When evaluating patients with the signs of croup, it should be remembered that if the signs appear especially severe, there may be a second condition that is complicating the laryngotracheobronchitis. In particular, if the child has underlying congenital subglottic stenosis, a modest degree of inflammation can produce greater obstruction than expected and in a shorter time frame than expected.
The anesthesiologist sees very few of these patients, since symptomatic therapy with mist, supplemental oxygen, and nebulized racemic epinephrine usually results in symptomatic improvement. Although some controversy remains about the usefulness of steroids, dexamethasone (0.5–1.0 mg•kg–1) is widely used as part of this therapy.
In severe cases, symptomatic therapy is inadequate. In evaluating the child with severe croup, a scoring system developed by Downes is frequently employed. The factors of inspiratory breath sounds, stridor, cough, retractions, and cyanosis are used to monitor the degree of airway obstruction. Soft tissue airway films are often obtained, but are useful primarily for ruling out other processes. There is seldom a need for diagnostic laryngoscopy and intubation, but these are used if there is progressive airway deterioration. In the past, a tracheostomy was inserted if airway intervention was needed, but endotracheal intubation is now the more common approach.
Epiglottitis
Although the term epiglottitis is commonly used, supraglottitis is more appropriate because the inflammation frequently involves not only the epiglottis, but also the aryepiglottic folds, the arytenoids, and the entire supraglottic area. Hemophilus influenza, type B, is the most common cause of the infection, though streptococcus and other bacteria have been implicated. The incidence of epiglottitis has dropped dramatically after the widespread use of the hemophilus influenza vaccine, though it is still seen, especially in populations with limited access to routine medical care. Because supraglottitis has become less frequent, anesthesiologists have less experience with its acute diagnosis and management than in the past.
Unlike croup, supraglottitis usually presents acutely, over hours, with a high fever, inability to swallow (drooling), sore throat, dysphonia, inspiratory stridor, and anxiety. These children often prefer to sit, leaning forward, to prevent the epiglottis from touching the posterior pharynx, producing pain. These children appear toxic, in pain, and anxious. Because of rapid progression of the swelling, there is a real danger of sudden obstruction by the time the family reaches the hospital. Therefore, rapid diagnosis and airway intervention are indicated.
Lateral soft tissue radiography may reveal the classic "thumb sign" of the swollen epiglottis. X-rays may be useful in revealing other causes of airway obstruction, such as foreign bodies. Because of the risk of total obstruction, the child must be accompanied by a physician with airway skills from the time the diagnosis of potential supraglottitis is entertained. Radiographs are often taken in the emergency department or intensive care unit. Although some have suggested that inspection of the oral pharynx with a tongue depressor is an appropriate step in evaluating the possibility of supraglottitis, others feel this is a dangerous technique, with the risk of laryngospasm and total airway obstruction.
The classical teaching for supraglottitis is that airway inspection and insertion of an artificial airway should be done in the operating room under controlled conditions. Each hospital should have a protocol for summoning of the appropriate anesthesia and surgical personnel quickly for a team-based evaluation and treatment of these patients. If the child deteriorates in the emergency department, laryngoscopy and intubation may be necessary there to secure an adequate airway. However, intubation of the child with supraglottitis can be extremely difficult and is best accomplished under controlled circumstances in a setting where there is backup by an otolaryngologist and the facilities for quickly using rigid bronchoscopy, cricothyrotomy, and tracheostomy. After the airway is secure, antibiotic therapy is the key to resolution of the infection.
Foreign body
Children of almost any age can present with foreign bodies in the airway, though it is most common under three years of age. These children may present with a variety of clinical stories. On one extreme, a child may have a long history of pneumonia, cough, or wheezing that is resistant to medical management and a vague history of a choking episode. The other extreme is the child who presents with sudden, complete airway obstruction. The speed of moving to diagnostic and therapeutic manoeuvres depends both on the presentation and the potential for sudden obstruction. Laryngeal foreign bodies are especially dangerous in their potential for sudden obstruction.
When available, a history is useful in determining the type of aspirated object. Food particles are particularly common in children, especially peanuts and seeds. Weiner sausages are the most common source of a fatal food aspiration in the United States because their size is large enough to completely occlude the larynx. It is occasionally useful to know if there was a history of cyanosis, collapse, retractions, and wheezing after the noted choking or coughing episode. However, it is the initial physical examination that sets the priority for evaluation and treatment. In the moribund patient, establishing an airway, followed by immediate bronchoscopy, is needed. In the stable patient, chest radiography is useful to determine the site and nature of the object, evidence of air trapping or atelectasis, and evidence of pneumonia or other lung pathology. A lateral film is useful in determining the location of the object(s). If the foreign body is in the esophagus, treatment involves a rapid sequence induction with intubation before therapeutic esophagoscopy. If the foreign body is in the laryngotracheobronchial area, the traditional teaching has been that an inhalation induction and therapeutic rigid bronchoscopy is indicated, thought there is a paucity of published evidence that this is superior to an iv induction.
Operative management
A wide variety of adjuncts and tricks are available for managing the difficult airway. Although blind techniques, such as the lightwand, have some usefulness, the cornerstone of managing the difficult pediatric airway has focussed on direct visualization. The fiberoptic laryngoscope has, in recent years, become immensely useful and popular for all ages of children. However, for this modality to be useful in the difficult patient, the practitioner must make a point of becoming proficient in pediatric patients under controlled conditions.
Other useful equipment includes a variety of oral and nasal airways, specialty blades, stylets, rigid bronchoscope, and equipment for jet ventilation. The laryngeal mask airway (LMA) has become a mainstay of managing the difficult airway in children, much as in adults. The LMA can be used to establish a stable airway through which an endotracheal tube can be inserted blindly or with the assistance of a fiberoptic scope. In addition, the LMA has become very useful in improving the mask airway until a more definitive airway can be inserted. Whenever a difficult intubation is anticipated, the presence of another skilled practitioner can be invaluable in providing intelligent and specific assistance. Although emergency cricothyrotomy or tracheostomy is rarely indicated, its possibility should be anticipated and equipment readily available.
Airway surgery
Procedures involving the airway may be as straightforward as a brief laryngoscopy and bronchoscopy or may involve sharing of the airway with the otolaryngologist for a longer period of time, such as laser microsurgery of the glottic and subglottic regions. It is a great challenge not only to the anesthesiologist, but also to the surgeon. Only by close communication between the surgeon and anesthesiologist can optimal surgical conditions be provided at minimal risk to the patient.
Belladonna premedication has been a useful for infants undergoing airway surgery. Although there is a trend away from premedication of any kind in pediatric anesthesia, atropine or glycopyrrolate before or with induction can be useful for minimizing secretions during these cases. Sedation has the advantage of reducing psychic stress of separation from parents and induction of anesthesia, but is frequently avoided because of potential decreased ventilatory drive, worsening of airway obstruction, increased incidence of dysrhythmias, and delayed emergence. The balance of advantages/disadvantages of both sedation and the even more controversial topic of parents in the operating room is an individual decision based on local preferences, risk tolerance, and personal experience.
A wide variety of equipment and anesthetic techniques can be used. The traditional approach in pediatric anesthesia is an inhalation induction with halothane and oxygen, possibly with nitrous oxide, for patients with a compromised airway. This assumes that the patient does not need immediate establishment of the airway using an awake or rapid sequence technique. Sevoflurane has become increasingly popular for pediatric cases, including for patients with a compromised airway. The clinician's experience and comfort with these agents are important in deciding which to use during an emergency. During the inhalation induction, gentle continuous positive airway pressure (CPAP) is especially useful in patients that have a supraglottic abnormality, such as supraglottitis, laryngomalacia, or webs. Vigorous topical application of lidocaine, especially with an atomizer, provides adequate anesthesia with lower volatile agent concentrations, minimizing the risk of hypoventilation. It has also become popular to supplement the volatile agent, especially if sevoflurane is used, with small doses of opioid or propofol to deepen the anesthetic state at particularly painful parts of the procedure. Muscle relaxants can be used, especially if jet ventilation or apneic oxygenation techniques are employed.
If the surgery involves microlaryngeal laser excision of a lesion, the three most common techniques are insufflation, jet ventilation, and intubation with a protected tube. Several types of endotracheal tube have been advocated for use in the presence of a laser. Red rubber tubes are less flammable than the standard PVC tubes, and coverage with a copper-based foil adds further protection. Silicone tubes are available; they have the advantage of not burning, but have the disadvantage of melting and dripping. Metal articulated tubes are available in smaller sizes and are useful in this situation. When using techniques where the laser beam goes through the anesthetic gases, it has been suggested that nitrous oxide be eliminated because it can support combustion. However, nitrous oxide and oxygen both only support combustion and will not ignite unless another object, such as a tube, is ignited first.
Hypoventilation with subsequent dysrhythmias is probably the most common complication of airway surgery. Hypoxemia is usually the result of hypoventilation based on the airway lesion, pulmonary disease, or insertion of a bronchoscope too distal to provide adequate ventilation. Hypercapnia and subsequent dysrhythmias are caused by the same conditions; hypercapnia is often more a problem than hypoxemia because of the use of enriched oxygen mixtures. The potential for sudden airway obstruction demands that the team of anesthesiologist and endoscopist communicate easily and have a clear understanding of who will restore the airway if lost and whether this will be done by mask, endotracheal tube, or rigid bronchoscope.
Postintubation croup is not unusual after extensive airway manipulation. Traditional therapy consists of mist, racemic epinephrine, and steroids. Because "rebound" can occur about an hour after the racemic treatment, the patient should be reevaluated by someone familiar with the child's baseline airway before discharge from the postanesthetic recovery area. If steroids are used, only a single dose is needed, especially if dexamethasone is used, because of the long action of the drug. If there is question about progression or degree of edema, consultation with the endoscopist and possible overnight observation in-house may be warranted.
Proper preoperative evaluation, along with a rational and calm approach to the perioperative management, will minimize the problems of handling the difficult pediatric airway. Flexibility and preparation for sudden, total obstruction serve to minimize the danger to the patient and psychological trauma to the practitioner.
Further reading
American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Practice guidelines for management of the difficult airway. Anesthesiology 1993; 78: 597–602.[Medline]
Auden SM. Additional techniques for managing the difficult pediatric airway. Anesth Analg 2000; 90: 878–80.[Full Text]
Benjamin B. Anesthesia for pediatric airway endoscopy. Otolaryngol Clin North Am 2000; 33: 29–47.[Medline]
Borland LM. Airway management for CO2 laser surgery on the airway: venturi jet ventilation and alternatives. Int Anesthesiol Clin 197; 35: 99–106.
Davis L, Cook-Sather SD, Schreiner MS. Lighted stylet tracheal intubation: a review. Anesth Analg 2000; 90: 745–56.[Full Text]
Heard CMB, Caldicott LD, Fletcher JE, Selsby DS. Fiberoptic-guided endotracheal intubation via the laryngeal mask airway in pediatric patients: a report of a series of cases. Anesth Analg 1996; 82: 1287–9.[Medline]
Litman RS, Ponnuri J, Trogan I. Anesthesia for tracheal or bronchial foreign body removal in children: an analysis of ninety-four cases. Anesth Analg 2000; 91: 1389–91.[Abstract/Full Text]
Roth AG, Wheeler M, Stevenson G, Hall SC. Comparison of a rigid laryngoscope with ultrathin fiberoptic laryngoscope for tracheal intubation in infants. Can J Anaesth 1994; 41: 1069–73.[Abstract]
Shulman GB, Connelly NR, Gibson C. The adult Bullard laryngoscope in paediatric patients. Can J Anaesth 1997; 44: 969–72.[Abstract]
Spalding MB, Ala-Kokko TI. The use of inhaled sevoflurane for endotracheal intubation in epiglottitis. Anesthesiology 1998; 89: 1025–6.[Medline]
Stern Y, McCall JE, Willging JP, Mueller KL, Cotton RT. Spontaneous respiration anesthesia for respiratory papillomatosis. Ann Otol Rhinol Laryngol 2000; 109: 72–6.[Medline]
Walner DL, Ouanounou S, Donnelly LF, Cotton RT. Utility of radiographs in the evaluation of pediatric upper airway obstruction. Ann Otol Rhinol Laryngol 1999; 108: 378–83.[Medline]
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