Choanal Atresia and Stenosis
Choanal atresia and stenosis are congenital defects resulting in abnormal narrowing or blockage of the nasal passages(s), typically by excess bone (90 percent) or membranous tissue (10 percent) which does not recanalize during fetal development. Unilateral stenosis/atresia may be asymptomatic, remaining undiagnosed until later in life, or masquerade as chronic sinusitis. However, bilateral stenosis is a serious problem for the obligate nasal breathing neonate that results in respiratory distress marked by severe chest wall retractions during inspiration at rest and relief of the obstruction when the infant cries [1]. In addition, the infant is also unable to breathe and nurse simultaneously. Insertion of an oral airway or endotracheal intubation may be needed to treat severe obstruction until a surgical consult can be done [2,3]. The diagnosis is suspected after failure to pass a feeding nasogastric tube through either nare. Radiographic confirmation is accomplished by a computerized tomography (CT) scan. The incidence of this defect is 1:7000 births. The ratio of male:female as well as bilateral:unilateral is 1:2. Patients with CHARGE syndrome account for 50 percent of the bilateral cases.
Numerous methods of surgical correction have been described using trans-palatal, trans-septal, trans-antral, sublabial trans-nasal, and trans-nasal approaches [4–6]. Traditional surgical correction involves puncturing the occluding tissue followed by dilating the opening and stenting it to prevent closure. The stent is removed after 5–12 weeks, with longer duration resulting in better results [7]. An alternative method to avoid using a stent is to administer oral steroids for five days followed by a month of intranasal steroids [6]. Newer methods of correction utilize a trans-nasal endoscopic approach to remove the membranous or bony tissue with or without the use of a helium:YAG laser. Anesthetic considerations start with evaluation of associated defects, including the possibility of congenital cardiac disease. General orotracheal anesthesia is performed with required safety considerations if a laser is used. Hemodynamic parameters should be closely monitored as the use of cocaine or other vasoconstrictive agents to decrease bleeding and aid visualization may cause hypertension and/or arrhythmias. Operative complications include cerebrospinal fluid (CSF) leak if excess bone is removed, respiratory distress should the stent become occluded, and re-stenosis.
Laryngeal and Tracheal Issues
Tracheal Stenosis
Tracheal stenosis may be congenital, iatrogenic, or the result of a disease process [1]. It may be classified as being general hypoplasia, funnel-shaped, or segmental [2]. Complete tracheal atresia is a very rare entity that is incompatible with life and is mentioned for completeness. Other congenital problems include complete tracheal rings involving one to all rings and a complete cartilaginous sleeve. The abnormal tracheal structure causes problems with airflow and interferes with clearance of secretions, causing stridor, retractions, and wheezing which may be associated with repeat episodes of pneumonia. Treatment of short segments is by surgical excision and re-anastomosis. Longer segments require more extensive procedures or possibly tracheal autograft. Innovative solutions using 3D printing and biologic materials, e.g., stem cells, to replace the defective trachea are starting to be reported.
Iatrogenic causes of tracheal stenosis are almost exclusively caused by prolonged intubation. Mucosal injury may be caused by high transmural pressure of the inflated cuff of an endotracheal tube, which interferes with perfusion of the mucosa. Mucosal damage is compounded by up-and-down movement of the endotracheal tube, leading to scarring and circumferential contraction. The damaged segment can be small or extensive. Small segments can be treated by dilation, while large segments require excision or posterior cartilage graft to keep the segment from re-stricturing.
Tracheomalacia/Bronchomalacia
Tracheomalacia describes the collapse of the airway when tracheal structures are unable to keep the airway patent in response to transmural airway pressures during respiration. Primary tracheomalacia is caused by an abnormal ratio of the cartilaginous to the membranous section of a tracheal ring. During expiration the posterior membranous section collapses into the lumen of trachea causing a variable degree of obstruction. Primary malacia is often seen in premature and newborn infants and usually resolves by two years of age. Severe cases, however, may require prolonged CPAP, intubation, or tracheostomy for treatment.
Secondary tracheal malacia may result from congenital abnormal vasculature, which may compress the trachea at various locations. Other etiologies include compression by an enlarged heart secondary to cardiac defects, bronchopulmonary dysplasia, or a tracheoesophageal fistula. Abnormal development of the major vessels may present as a double aortic arch, pulmonary vascular sling, aberrant right subclavian artery, and right-sided aortic arch [8]. The unifying feature of these conditions is that the trachea is compressed between two vascular structures that cause an increased ratio of the cartilaginous to membranous section of the compressed tracheal rings. Congenital cardiac lesions usually involve the left main stem bronchus, which is normally located between the left pulmonary artery and the left atrium, along with the left pulmonary veins. Cardiac lesions that lead to increased pulmonary pressure and/or left atrial enlargement can encroach on the left main stem bronchus causing malacia. Eighty-six percent of tracheal esophageal fistulas are type C, which consists of proximal esophageal atresia with a distal esophageal fistula to the trachea. The triad of widened cartilages, ballooning of the posterior wall, and collapse of the distal tracheal lumen in one or both bronchi is seen on endoscopy.
The severity of respiratory symptoms associated with tracheomalacia varies. Patients will present with stridor, dysphagia, wheezing, chronic cough, inability to handle secretions, recurrent pneumonias, atelectasis, and cyanotic apneic spells. An inability to wean from mechanical ventilation or the failure of tracheal extubation or tracheostomy decannulation may indicate underlying tracheomalacia. Diagnostic studies include chest radiograph, esophagram, chest CT with dynamic studies, bronchoscopy, and possibly angiography. Treatment may require long-term ventilation and/or surgical correction. Surgical procedures include splinting, stenting, aortopexy, resection, and correction of the underlying problem.
Bronchogenic Cysts
Bronchogenic cysts are the result of abnormal budding of the bronchial tree, which develops independently of normal alveolar formation and growth. They contain ciliated epithelium and pseudostratified columnar epithelium [8]. They may be connected to the bronchial airways, and for that reason spontaneous respiration during anesthesia is preferred. Anticholinergic premedication to decrease secretions and topical local anesthesia are useful adjuncts for sedation. Most often they present in infants as wheezing, cough, or respiratory distress. Airway obstruction may occur if they enlarge. Diagnosis is by radiograph or CT of the chest. Surgical excision is indicated.
Pulmonary Sequestration
Pulmonary sequestration is a collection of abnormal pulmonary tissue that is abnormally connected to the tracheobronchial tree. It may be extralobar or intralobar. The arterial blood supply originates from the systemic circulation from below the diaphragm, but venous drainage may differ. The extralobar type may have its own pleural cavity and systemic venous drainage whereas the intralobar type has no pleural membrane and venous blood drains into the pulmonary circulation. Like other pulmonary problems, it may present with infection, mass effect, and other symptoms. Plain radiographs, CT, MRI, and angiography are used for diagnosis. Treatment is surgical excision.
Congenital Cystic Adenomatoid Malformation
Congenital cystic adenomatoid malformations (CCAMs) are benign cystic lesions that appear during fetal development. They are classified as microcytic, macrocytic, or solid, but differ from bronchopulmonary sequestration by the fact that they do not have a systemic arterial supply. They are found during fetal ultrasonography. The lesions may shrink and disappear or continue to enlarge as the fetus grows. Large lesions may cause fetal distress by causing contralateral lung hypoplasia, cardiovascular collapse, maternal polyhydramnios, and fetal hydrops. For large lesions, fetal surgery, which includes thoracocentesis, thoracoamniotic shunting, or resection utilizing an ex utero intrapartum therapy (EXIT) procedure, may be life-saving. Smaller lesions may wait until after birth to be excised as these lesions may undergo malignant degeneration.
Anesthetic Considerations for Tracheal and Pulmonary Issues
The primary anesthetic consideration is to maintain adequate inspiratory and expiratory air flow through the tracheal branchial tree. Stenotic lesions limit air passage and increase the work of breathing by causing nonlaminar flow. Inhalational induction is prolonged and is best accomplished by using a slow respiratory rate with high concentration of anesthetic gas. Malacia of the tracheobronchial tree leads to collapse of the lumen as transmural pressures change during inspiration and expiration, depending on whether the segment is intrathoracic or extrathoracic. Intrathoracic segments are stented open during inspiration and collapse during expiration. Use of end-expiratory pressure, PEEP or CPAP, keeps the airway patent throughout the respiratory cycle. Thorough intraoperative monitoring and maintenance of deep anesthesia to prevent coughing, laryngospasm, or bronchospasm should be the anesthetic goals for all cases. Mass lesions cause compression of the adjacent lung parenchyma and tracheobronchial structures. Patient positioning may have a dramatic effect on the ability to ventilate the lungs and dictate surgical positioning. Likewise, hypoventilation increases collapse of the distal alveolar segments. Maintaining adequate inflation pressures is necessary to prevent the resultant hypoxia. Finally, for lesions that connect to the tracheobronchial tree, positive pressure ventilation may cause expansion of the lesion. This in turn may increase any mass effect. Spontaneous ventilation should be used in this situation until the connection is severed.
Cystic Lesions
Dermoid cysts are structures lined by epithelium which contain various elements derived from epithelium along embryonic fusion plates [9]. They range from 1 to 4 cm in size, are commonly found on the forehead, lateral eye, or neck, and can be fixed or mobile. Most are subcutaneous although there can be extension intracranially or intraorbitally. Treatment is surgical excision so preoperative CT or MR scan to rule out extension is recommended. A tunneled endoscopic approach starting behind the hairline to avoid facial scarring can be utilized.
Thyroglossal duct cysts occur along the tract by which the thyroid descends during embryonic development from the base of the tongue to the normal thyroid position. They are typically noticed as a midline neck mass following an upper respiratory infection, or become primarily infected [10]. These cysts often move when swallowing and can track though the hyoid bone [3]. Preoperative ultrasound is recommended. Treatment is excision to prevent further infection. Recurrence is more likely if the child is under two years of age or has had two or more infections [11].
Branchial cleft cysts are derived from sequestration of first and second branchial cleft elements, resulting in cysts, sinuses, and tags. The incidence is sporadic, although there are reports of autosomal inheritance with equal male to female frequency, and 10 percent are bilateral [9]. These lesions usually present as soft tissue masses along the border of the sternocleidomastoid muscle. First branchial arch cysts are usually high in the neck. The more common second arch cysts are lower in the neck and often communicate with the tonsillar fossa. The less common third arch cysts are low in the neck and can communicate with the pyriform sinus. Branchial cleft cysts usually present after an upper respiratory infection as a tender mass. After treatment of the cysts with antibiotics they are excised in order to prevent reinfection and the possibility of carcinoma [10].
Vascular Malformations
Hemangioma
Hemangiomas are the most common benign tumors in infants [12]. This abnormal collection of blood vessels is characterized by having increased activity of endothelium and mast cells during the growth phase. They can be superficial, “capillary or strawberry” or deep, “cavernous” and can occur in any organ. They may not be present at birth, but appear within a few weeks and rapidly expand for 6–12 months. It is during this growth phase that they are invasive, causing ulceration, expansion, and may involve a vital organ [12]. After the growth phase finishes, they will slowly involute over a period of years. Hemangiomas may be multicentric; so affected patients should be thoroughly evaluated for other lesions. Large segmental hemangiomas about the face may be part of PHACE syndrome (posterior fossa malformation, hemangiomas, arterial abnormalites, cardiac defects, and eye anomalies). Kasabach–Merritt syndrome is the occurrence of hemangioma, thrombocytopenia, and coagulopathy. Treatment with propranolol may slow the rate of growth. Prednisone is very effective in causing rapid involution. Superficial lesions may be treated by laser excision while surgical excision may be needed for others.
Other Vascular Malformations
Unlike hemangiomas, vascular malformations are characterized as having normal growth of the endothelium and mast cells. They grow proportionately with the rest of the body and do not involute [2]. These vascular malformations can be associated with various syndromes such as Klippel–Trenaunay–Weber, Struge–Weber, Maffucci, and Parkes–Weber. All vascular malformations should be thoroughly evaluated using MR/CT scan, Doppler ultrasonography, and contrast radiography to delineate the type and extent of the lesion.
Venous Malformations
Venous malformations are the most common vascular malformations. They present as soft, compressible, blue-colored structures. They are found predominantly about the head and neck. A high percentage of larger lesions have associated deep cerebral malformations that should be investigated. Treatment with sclerotherapy is highly successful, especially when surgical excision would be disfiguring or impossible.
Arteriovenous Malformations
Arteriovenous malformations (AVMs) are the most serious vascular lesions. They can cause high-output heart failure or may spontaneously rupture. Dental extraction in the presence of a mandibular AVM has been known to lead to massive bleeding. Treatment of an AVM is sclerotherapy, quickly followed by surgical excision to prevent new arterial channels from opening.
Lymphatic Malformations
Lymphatic malformations are the result of primary lymph sacs that do not coalesce with the rest of the lymphatic system. The resultant cystic structures may be small, microcystic, or large, macrocystic, also termed cystic hygroma. Microcystic lymphangioma are invasive and ill-defined, extending through various tissues and organs. Macrocystic tend to be well circumscribed, although both elements can coexist. Lymphatic malformations present early in life and expand as lymph accumulates within the cysts. Cystic hygromas occur in about 1:12 000 live births, and are located in the posterior triangle of the neck, cephalad to the clavicle [3]. The cyst may extend from the skin internally to the mucosa of the trachea. Lesions can be life-threatening if the trachea becomes compressed [11]. If detected in utero by ultrasonography, the airway may be secured intrapartum while the umbilical vessels are still attached, via an EXIT procedure. Surgical excision is necessary for treatment in most cases. A chest radiograph, ultrasonography, and MR/CT scan are needed to delineate the extent of the lesion. Sclerotherapy may be effective, although for macrocystic lesions a new sclerosing agent, OK432, has been very effective.
Anesthetic Considerations for Vascular Malformations
Airway management and blood loss are the two major considerations. As a large percentage of all vascular malformations occur in the head and neck region, problems arise resulting in distortion of facial structures and causing difficulty with mask ventilation, tracheal intubation, and ventilation/respiratory mechanics. Venous and lymphatic malformations can become disfiguring and grow to large size. They may interfere with the fit of the facemask, making inhalational induction of anesthesia difficult or impossible. Alternatively, when located within the neck or thorax, compression and deviation of the airway is common. Fortunately, typically these malformations are compressible, allowing for instrumentation and the passage of an endotracheal tube. However, they can swell and become non-compressible in response to surgical manipulation, sclerotherapy, or infection. Tracheal extubation should be delayed until airway swelling has subsided, which may require several days after surgery. Hemangiomas and arteriovenous malformations may also present in, or around, the airway. Hemangiomas are friable and thus bleed easily. Endotracheal lesions may ooze if traumatized by an endotracheal tube. Arteriovenous malformations may also bleed if manipulated. The bleeding, however, will be brisk, heavy, and potentially life-threatening. Airway management should be directed to avoid manipulating or touching the malformation.
Blood loss during excision of large hemangiomas can be misleading in the small infant or child. Bleeding occurs at a steady slow rate and is controlled by direct pressure. For the small infant near the physiologic hematocrit nadir, the transfusion threshold may be reached quickly. Mucosal paleness or tachycardia may be signs that a repeat hematocrit is needed for determination if red cell transfusion is warranted. Large venous or mixed lesions may result in large blood volume loss, especially since tourniquets cannot be used in head and neck procedures. Large-bore venous access and possibly an arterial line are needed. Arteriovenous malformations always present the possibility of massive blood loss. Preoperative embolization decreases the risk of bleeding, but an arterial line is mandatory for anything but the smallest lesions.
Craniofacial Problems
Structural abnormalities of the head and neck comprise a diverse set of congenital problems that may be grouped in numerous ways. Syndromes resulting from abnormal ossification of bony structures include Crouzon’s (craniofacial dysotosis), Apert (acrocephalosyndactyly), and Treacher Collins (mandibulofacial dysotosis) syndromes. A defining feature of Crouzon’s and Apert syndromes is the premature closure of cranial sutures and that of the skull base, resulting in midface hypoplasia. The small nares and choanal stenosis cause these patients to be nearly obligate mouth breathers with a high incidence of sleep apnea. Those with Treacher Collins syndrome have midface abnormalities caused by nonfusion and hyoplasic development of the maxilla, mandible, and auditory structures. These patients have a high incidence of glossoptosis with associated Robin sequence.
Other abnormalities are the result of lack of development of bone or soft tissue. These include oculoauriculovertebral syndrome (hemifacial microsomia, Goldenhar’s syndrome), hemifacial atrophy (Romberg syndrome), and congenital facial diplegia (Moebius syndrome). In Goldenhar’s syndrome, the first and second brachial arch structures of the ear and mandible are affected to various degrees. Loss of tissue results in distortion of the face and airway, which worsens with unbalanced growth. Romberg syndrome patients are normal at birth, with progressive atrophy and distortion of the facial features with growth. The congenital palsies of the cranial nerves of Moebius syndrome result in difficulties with feeding, speech, and expression. The mouth opening is usually small.
Anesthetic Considerations
Airway management is the major anesthetic concern of these patients as they typically are difficult to bag-mask ventilate, difficult to intubate, or both. Patients with midface hypoplasia have high resistance to nasal breathing and are essentially mouth breathers. Standard airway maneuvers, which close the mouth to get a better mask fit, increase the degree of obstruction. Care should be taken to keep the mouth open to allow for air passage. Early insertion of an oral airway is helpful. Topical anesthesia applied to the oral cavity prior to induction anesthesia will minimize the risk of laryngospasm from the early insertion of the oral airway.
Other patients who have mandibular hypoplasia or associated Robin sequence are at high risk of airway obstruction and difficult tracheal intubation. Alternative methods other than direct laryngoscopy to secure the airway include insertion of a laryngeal mask airway (LMA), fiberoptic instrumentation, and surgical instrumentation. Also see ‘Robin sequence’ below.
Cleft Lip and Palate
Cleft lip and palate are the most common congenital anomalies, occurring in 1 in 500 live births [13]. They may occur singly, together, as part of a syndrome, or the result of Robin sequence. The exact causative genetic factors are unknown but there is a strong familial inheritance. The problems associated with cleft lip/palate include difficulties with breathing, feeding, speaking, hearing, and general psychological well-being. The repair of the cleft lip may be staged or done as a primary repair. A dentomaxillary appliance may be inserted prior to repair to align the discontinuous alveolar ridges of the palate. Correction of the cleft palate should be performed before the child starts speaking. Some surgeons will use the Rose positon, resting the patient’s head in their lap, for the palate repair. Similarly, some will use a balsam of Peru-soaked pack sewn on the palate repair to promote wound healing. This dressing effectively obstructs the oral airway and thus patients must breathe nasally postoperatively.
Robin sequence
Robin sequence is defined by the three findings of micrognathia, glossoptosis, and airway obstruction. It was Pierre Robin who first identified the airway obstruction as being the result of glossoptosis as the posteriorly displaced tongue contacts the pharyngeal wall. Cleft palate occurs in 90 percent of Robin sequence patients as the displaced tongue mechanically interferes with closure of the palatal plates. Both the airway obstruction and the cleft palate are the result of micrognathia. Robin sequence may occur by itself or be associated with any syndrome that includes micrognathia.
These patients may have failure to thrive as the result of chronic hypoxia, increased work of breathing, and poor feeding. Treatment is directed at relieving the airway obstruction. Nonsurgical modalities include using the prone position with or without a nasopharygeal airway. Surgical therapies include tongue–lip adhesion, mandibular distraction, and tracheostomy. Additional alimentation may be provided via a feeding tube or a gastrostomy tube. If the Robin sequence is not associated with a syndrome, the mandible eventually will grow to near normal size, alleviating the airway obstruction. However, if associated with a syndrome, the mandible may remain hypoplastic.
Anesthetic Considerations
Patients with cleft lip or palate usually do not have airway management problems unless they are associated with other facial abnormalities. Airway obstruction may occur during inhalational induction if the tongue falls posteriorly into the cleft palate. Obstruction is relieved by insertion of an oral airway. Tracheal intubation is likewise without problem unless a bilateral cleft exists. The midline prolabial segment is angulated forward and upward, interfering with insertion of the laryngoscope and alignment of the axis of larynx visualization. Oral RAE endotracheal tubes are preferred as they don’t distort the facial symmetry around the upper lip. When properly inserted, the distance from the bend in the tube to the tip is a fixed distance. Flexion of the neck may move the tip into a mainstem bronchus. Secondarily, RAE tubes are not easily suctioned and are easily clogged.
The safe induction of anesthesia and tracheal intubation for Robin sequence patients is always a problem. General anesthesia relaxes the oropharyngeal musculature, augmenting the airway obstruction. Techniques that bypass the obstruction allow safe inhalational anesthesia. These include awake insertion of an LMA or insufflation of anesthesia gas after insertion of a nasal pharyngeal airway/endotracheal tube within the nasopharynx. The second step is to safely secure the airway with an endotracheal tube. Options include intubating through the LMA, use of a glidescope once the patient is anesthetized, or using a fiberoptic bronchoscope for nasal/oral intubation with the patient breathing spontaneously.
Myringotomy and Tympanostomy Tubes
Otitis media, commonly called an “ear infection,” is a very common diagnosis and is the most common indication for pediatric outpatient antimicrobial therapy in the United States [14]. Recurrent otitis media may result in fibrosis and scarring of the middle ear, formation of a cholesteatoma, and conductive hearing loss. The treatment of recurrent otitis media is drainage via a myringotomy, a small incision in the tympanic membrane, followed by the insertion of a small tube to facilitate drainage. The tubes are naturally extruded in 6–12 months, although retained tubes may be surgically removed. The procedure is generally less than ten minutes in duration. General anesthesia is commonly administered using an inhalation agent by mask for induction and maintenance. Intravenous (IV) access is generally not required. The postoperative pain is mild and can be addressed with acetaminophen, ketorolac, or intranasal fentanyl. As always, a careful preoperative history and physical is important to discover comorbid conditions, the most common being cleft palate.
Middle Ear Surgery
Cholesteatoma
A cholesteatoma is squamous epithelium and its accumulated debris within the middle ear and pneumatized temporal bone. It may be characterized as congenital or acquired, with or without an infection. Acquired cholesteatoma is the most common etiology as the result of middle ear disease and is seen in older children. Congenital cholesteatoma is usually diagnosed by a pediatrician and is differentiated from the acquired form by being diagnosed in infancy or early childhood, in patients with no history of prior ruptured eardrums. Treatment is surgical excision either by a tympanoplasty or can be more extensive with a mastoidectomy. A general anesthetic with a secure airway and IV access are required for the surgery.
The patient is positioned supine with the head rotated laterally for exposure of the affected side. Care should be used for patients with limited neck range of motion or those at risk for cervical instability (e.g., patients with trisomy 21). For these patients, consideration for lateral decubitus positioning may be warranted. The facial nerve is usually monitored, necessitating avoidance of long-acting neuromuscular blocking agents. Sevoflorane and/or isoflurane are generally used, but nitrous oxide should be avoided. Tympanometry has shown increased fluctuations in middle ear pressure when nitrous is added to other inhaled anesthetics [15]. Diffusion of nitrous oxide into the middle ear will increase the pressure, causing outward movement of the tympanic membrane. Once the nitrous oxide is turned off, the rapid absorption of gas will create negative pressure, resulting in backward displacement of the tympanic membrane and disrupting the surgical repair. The movement may also be significant enough to cause disarticulation of the ossicles, leading to conductive hearing loss than can persist for several weeks postoperatively. The incidence of postoperative nausea and vomiting (PONV) after tympanoplasty is greater than 50 percent in some studies, although rarely occurs in infants, and the use of nitrous oxide may be contributory. Both dexamethasone and ondansetron have been shown to be efficacious as prophylactic agents for the treatment of PONV [16] in older children. If possible, a deep extubation is desirable to facilitate a smooth wake-up without excessive coughing or head movement.
Cochlear Implants
Cochlear implants are a popular and effective treatment for children with severe to profound sensorineural hearing loss. Unlike hearing aids which simply amplify sounds, the cochlear implants transform acoustic energy into electrical energy and stimulate the remaining inner ear neurons, partially restoring the child’s hearing. The surgical procedure involves attaching an internal processor to the mastoid process and connecting the electrodes to the cochlear neurons. There has been a trend toward earlier placement, with the procedure being performed on children as young as six months of age. The procedure is best completed in tertiary care centers where experienced pediatric surgeons, anesthesiologists, and perioperative care teams can take care of these young children [17].
The procedure requires a general anesthetic with a secure airway for children, though sedation with regional techniques has been used in adults. Use of muscle relaxation for optimal surgical conditions should be discussed with the surgeon as intraoperative facial nerve monitoring may be used. After insertion into the cochlear nerve, the implant is calibrated by two electrically evoked potentials, the evoked stapedius reflex threshold (ESRT) and the evoked compound action potential (ECAP). The ESRT is the loudest stimulus than can be tolerated without pain, while the ECAP is the smallest stimulus that can be perceived as sound. Volatile anesthetics suppress the ESRT in a dose-dependent fashion, resulting in inaccurate calibration, and a stimulus which may be painful when awake. Propofol does not cause this decrement and can be safely used, making it prudent to switch to a total intravenous anesthesia (TIVA) for the calibration portion of the procedure [18]. If volatile anesthetics are used early in the procedure it is important to communicate with the surgeon about the concentration and timing of the inhaled agent in relation to the actual implantation. Alternatively, the device can be calibrated when awake postoperatively, though this is very difficult in an infant. As with tympanoplasty, the PONV rate can be quite high and prophylactic antiemetic agents should be utilized in children older than one year.
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