Breathing is under both voluntary and involuntary control during wakefulness. Chemoreceptor activity ensures that minute ventilation is appropriately matched to metabolic needs, whereas voluntary control of ventilation allows the integrated performance of complex behavioral activities. The muscles of even an anatomically narrowed upper airway are usually able to maintain sufficient tone such that breathing can occur without compromise during wakefulness. However, respiratory control and upper airway muscle tone are state specific, and are entirely different during sleep, thus predisposing to upper airway obstruction and instability. As sleep commences in normal individuals, the arterial PcO₂ rises by several mm Hg. The proposed mechanism is “withdrawal of the wakefulness stimulus,” suggesting that the sum total of the sensory input of wakefulness is a nonspecific stimulus to the neurologic centers of respiratory control that is lost with sleep onset (1). Similarly, the wakefulness stimulus has an influence on the resting muscle tone of the upper airway, which when withdrawn at the onset of sleep may favor airway obstruction. Behavioral control of ventilation is absent during non-rapid eye movement (NREM) sleep. Thus, adequate ventilation is critically dependent on chemical control. However, the ventilatory responses to hypoxemia and hypercapnia, both potent stimuli of chemoreceptor activity during wakefulness, are blunted during sleep. Important respiratory reflexes such as coughing and swallowing are inhibited by sleep. The changes in lung volumes that occur with moving from the upright to the supine position reduce the caudal traction on the upper airway, thus increasing airway collapsibility (2). The respiratory pattern becomes irregular during rapid eye movement (REM) sleep
with a variable rate and tidal volume and frequent respiratory pauses. Finally, during REM sleep, the skeletal muscle atonia that is characteristic of this state affects all of the muscles of the upper airway and all of those involved in respiration except the diaphragm. This leads to increased collapsibility of the upper airway and a decrease in functional residual capacity of the lungs, predisposing to upper airway obstruction or obstructive sleep apnea (OSA) and impaired gas exchange. REM accounts for about 20% of normal sleep time in adults and children and 50% of sleep time in newborn infants; thus, the importance of REM sleep is not trivial. In addition, there are important maturational differences that affect sleep and breathing in infancy that will be discussed in the context of ALTEs and apnea of infancy (3).

The most common form of sleep-disordered breathing in childhood is obstructive sleep apnea syndrome (OSAS). OSA is defined as an absence of airflow at the nose and mouth despite continued respiratory efforts. Discrete events that are partial in nature (reduced, but not absent airflow) are termed obstructive hypopneas. Obstructive apneas and hypopneas are often accompanied by hypoxemia, hypercapnia, and sleep disruption. Continuous partial airway obstruction can result in the obstruction or hypoventilation. Children with OSAS present with snoring and difficulty breathing during sleep. Parents may describe gasping, choking, or observed apneas during their child’s sleep. Because OSAS and snoring are often worse in the supine position, parents may reposition their children several times during the night. Nocturnal symptoms may be accompanied by impaired quality of life as well as behavioral or neurocognitive impairment during the day (4,5,6,7).

The patency of the upper airway during sleep is determined by the bony and soft tissue anatomy of the airway and the upper airway muscle tone. The latter is influenced both by state (wakefulness vs. sleep and REM vs. NREM sleep) and by neural and chemical controls. The pharyngeal airway serves more than one purpose. To propel boluses of food, forceful constriction of the pharyngeal muscles is required, whereas speech requires rapid and dynamic changes in structure and rigidity of the pharynx and larynx. Although respiration would be best served by a rigid airway, these other functions require the pharynx to be collapsible. Thus, the neuromuscular function of the upper airway is critical to maintaining airway patency. If neural inputs maintaining airway patency during sleep are inadequate and/or the airway is anatomically narrowed, OSAS may result. Implicit in this feature is the fact that physical exam during wakefulness does not accurately predict the presence of OSAS during sleep nor does correction of the anatomic defect by surgery invariable relieve all of the symptoms. The significant familial pattern to the risk of OSAS is likely related to both heritable anatomic and central nervous system factors (2,3,4).

There are a number of conditions that predispose to OSAS; the most common are listed in Table 51.1. Common to all these etiologies is the feature of an anatomically or functionally narrowed upper airway (5,6,8,9). With the onset of the obesity epidemic in children, the landscape of sleep-disordered breathing has changed dramatically, with many children and adolescents now at risk for severe obesity-related OSAS (5,6,10,11,12). Obstructive apneas and hypopneas can result in continuous or episodic hypoxemia and/or hypoventilation during sleep, as well as repetitive arousals. These stimuli alter the function of the autonomic nervous system. Thus, both systemic and pulmonary hypertension are recognized complications of OSAS. Because the protective response to OSA includes arousal from sleep, sleep can be fragmented, and in the most severe cases, results in excessive daytime sleepiness. This sleepiness is the most common presenting feature in adults with OSAS, but is not nearly as common in children because they are less likely to arouse following each obstructive event. An exception to this is the morbidly obese child in whom excessive daytime sleepiness is often severe. Although children with OSAS may not have daytime sleepiness, they may suffer from other neurobehavioral complications, including school failure, hyperactivity, and mood or conduct disorders. It is plausible that the sleep disruption and hypoxemia of OSAS are responsible for the neurologic and behavioral complications, and one large population-based study found a correlation between the severity of OSAS and the extent of these complications (13). A recent randomized trial of early adenotonsillectomy (T&A) versus watchful waiting as therapy for mild to moderate pediatric OSA found that the surgical group had improvements in quality of life and measures of behavior, but not in neuropsychological estimates of attention and executive function (7). Primary snoring (snoring without findings of OSA on formal testing) has been found by others to result in neurobehavioral difficulties (14). Further study is required to explore these relationships. Other complications of OSA include failure to thrive, nocturnal enuresis, and worsening of parasomnias such as sleepwalking (6,9). Recent evidence implicates sleep disruption and hypoxemia as contributors to abnormalities of glucose homeostasis in obese children with SRBD (10,12).

Because neither history nor physical exam is sufficient to firmly establish the diagnosis of OSAS, a polysomnogram (PSG; sleep study) is required to reliably make the diagnosis (5,6). Normative PSG values have been established for children and are quite different from those used in adults with normal children having only one to two obstructive apneas or hypopneas per hour of sleep. Normal adults may have as many as five obstructive events per hour of sleep and be considered normal (5,6,9,15,16).

The first approach to therapy for OSAS is generally adenotonsillectomy. This should be performed following documentation of the syndrome by polysomnography, and usually is completed in the ambulatory surgery center. Some children are at higher risk, and one night of observation postoperatively on the pediatric inpatient unit is indicated (5,6). At least one study has demonstrated that pediatric patients with mild OSAS will do well postoperatively from the respiratory standpoint, irrespective of the use of opiates for analgesia. Polysomnography was performed on the first postoperative night, revealing decreased obstructive events and oxygenation compared with the preoperative PSG, although sleep efficiency was decreased (17). However, there are groups of patients who are at higher risk for postoperative complications who will benefit from a higher level of care. Immediate complications of T&A include postoperative bleeding, upper airway obstruction secondary to airway edema, pulmonary edema, or respiratory failure
(5,6,18,19,20,21). Diagnostic groups at the highest risk for postoperative complications are listed in Table 51.2 (5,6,20,22).

Children at higher risk for postoperative complications should be admitted for overnight observation and may benefit from the intensive cardiorespiratory monitoring afforded by a PICU (18,23). In a retrospective series of 69 patients who were observed postoperatively in the PICU following T&A, 23% had respiratory compromise—defined as oxygen saturation less than 70% and/or hypercapnia. The patients with compromise were younger (3.4 vs. 6.1 years); had higher numbers of obstructive events per hour on pre-op PSGs (49 vs. 19); and were more likely to have failure to thrive, to have abnormalities of cardiac function, or to have craniofacial abnormalities. Multiple regression analysis revealed that age less than 3 years and more than 10 obstructive events per hour of sleep were the most significant risk factors for postoperative respiratory compromise (22). Another retrospective study of 83 children admitted after T&A because of severe OSA revealed that just more than 19% had postoperative airway complications. The authors identified age less than 2 years, apnea hypopnea index (AHI) >24, intraoperative laryngospasm requiring treatment, SpO₂ <90% in the postanesthesia care unit (PACU), and a prolonged PACU stay (>100 minutes) as predictors of postoperative airway complications (22,24). Finally, Kieran and coworkers performed a multicenter, retrospective review of over 4000 patients who underwent T&A in order to identify risk factors for postoperative hypoxemia. This study included patients who had the surgery for OSA or for other indications. Most did not have a preoperative PSG. Almost 300 patients had hypoxemia, and these were compared with a matched comparison group without hypoxemia. They identified Down syndrome, a clinical diagnosis of OSA, neurologic, cardiac or pulmonary disease, young age, and extremes of weight to be risk factors (25). Therefore, a preoperative review of the history and the PSG results accompanied by scrutiny of the immediate postoperative course can aid in the identification of which patients can be safely scheduled for same-day surgery and those who will require postoperative hospital observation or care in the PICU. Omitting the PSG and performing surgery simply on the basis of a history of snoring and the presence of adenotonsillar hypertrophy has the potential to place children at risk for unanticipated complications (5,6,22).

Increasingly, patients with morbid obesity are presenting with OSAS, and it is often severe in this group with frequent obstructive events, profound hypoxemia, and significant hypoventilation. Similar to adults with OSAS, both systemic and pulmonary hypertension may be present (11). Unlike the majority of children with OSAS, respiratory control can be altered with resetting of the chemoreceptor function, resulting in daytime hypoventilation. In this instance, ventilation may be dependent on hypoxic drive, requiring that supplemental oxygen be used judiciously and necessitating close monitoring both preoperatively and postoperatively. In a retrospective review of 957 children undergoing T&A, 543 were admitted to the hospital after surgery. Fourteen of these were identified as morbidly obese and were admitted to the PICU for observation (26). Three (20%) required assisted ventilation in the postoperative period. Another retrospective review of 26 morbidly obese patients, all of whom were sent to the ICU following T&A as per routine, found that 14 patients (54%) had an uncomplicated postoperative course, but a significant proportion (45%) required respiratory intervention, including one intubation and two with a need for bi-level positive airway pressure (BPAP) support.

Infants and children with craniofacial abnormalities including micrognathia or mid-facial hypoplasia can have severe OSAS. It has been reported that surgery for OSAS in patients with craniofacial malformations is less likely to succeed in infants <12 months of age, and can result in long hospital stays and difficulty with extubation as compared to older infants and children undergoing similar procedures. Although older children with craniofacial abnormalities are more likely to have improvement in OSAS by surgical intervention, they are still at risk for postoperative complications (27). Craniosynostosis with associated midface hypoplasia can result in severe OSAS and a coexisting Chiari malformation can add an element of abnormal central respiratory control, further adding to the risk of complications. Children with Down syndrome have multiple reasons for OSAS, including midface hypoplasia, relative macroglossia, hypotonia, obesity, and occasionally hypothyroidism. Severe OSAS is therefore not uncommon in these children. A series of 16 patients with Down syndrome found that 25% required PICU care postoperatively. In addi tion, the authors commented that persistent symptomatic apnea and hypoxemia were common following T&A (28).

Therapy to support children with respiratory compromise following T&A or other airway surgery can include prolonged intubation or a nasopharyngeal airway. The use of noninvasive ventilation, either continuous positive airway pressure (CPAP) or BPAP is attractive as it avoids intubation and can sometimes be performed on a pediatric unit after the patient is stable. However, some practitioners have questioned the safety of BPAP in the immediate postoperative period with concerns regarding subcutaneous emphysema dissecting at the surgical site, bleeding, and uncomfortable drying of the upper airway. A study of 1321 patients following T&A described that nine patients managed postoperatively with BPAP. Four patients were obese, four had underlying neurologic disease, three had asthma, and three were younger than 3 years of age. All tolerated positive-pressure therapy without complications. Two of the obese patients were eventually discharged home with BPAP therapy. Thus, there appears to be a role for noninvasive ventilation in the management of complicated patients immediately following adenotonsillectomy. Careful attention to the selection of the mask interface to avoid skin breakdown and for adequate humidification is critical (29).

Most children with OSAS will be treated with adenotonsillectomy as first-line therapy, even if there are other anatomic or functional abnormalities that are likely contributing to the upper airway obstruction. However, some will undergo a more extensive procedure, uvulopalatopharyngoplasty, which includes not only removal of the tonsils, but the tonsillar pillars and uvula as well. This procedure is most often reserved for patients with cerebral palsy or Down syndrome where there is a high probability that there will be residual obstruction following T&A alone (1,30,31,32). The use of mandibular distraction osteogenesis is being used with increasing frequency for infants and children with syndromes that include micrognathia. Among them are Robin sequence, Treacher-Collins syndrome, and conditions with hemifacial microsomia (33,34,35). This procedure represents a considerable therapeutic advance, as previously many of these patients would have required a
tracheostomy. Studies evaluating infants with upper airway obstruction treated by internal mandibular distraction osteogenesis have documented success and avoidance of tracheostomy in the majority of infants. The infants are kept intubated for several days postoperatively (34,35). Treatment of OSAS in patients with Beckwith-Wiedemann (and occasionally Down syndrome) may require tongue reduction surgery (30). As a whole, the group of children requiring complex surgical treatment for OSAS tends to have more severe sleep-disordered breathing and other risk factors for postoperative difficulties. Thus, they should be observed for a period of time in the PICU and may require several days of intubation following surgery. Despite surgical therapy, some will have only minimal improvement in OSAS

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