Noninvasive Ventilation in Pediatric Patients: Role as a Supportive Technique in the ED
Noninvasive Ventilation in Pediatric Patients: Role as a Supportive Technique in the ED
Authors: Ronald M. Perkin, MD, MA, Professor and Chairman, Department of Pediatrics, Brody School of Medicine at East Carolina University; Attending Physician, Pediatric Intensive Care Unit, University Health Systems of Eastern Carolina Children's Hospital, Medical Director, University Health Systems of Eastern Carolina Children's Hospital, Greenville, NC; and Emily Fontane, MD, FACEP, FAAP , Assistant Clinical Professor of Emergency Medicine and Pediatrics, Brody School of Medicine at East Carolina University, Attending Physician, Adult and Pediatric Emergency Medicine, Pitt County Memorial Hospital, Greenville, NC
Peer Reviewer: Steven M. Winograd, MD, FACEP, Attending Physician, Department of Emergency Medicine, St. Elizabeth Medical Center, Youngstown, Ohio and St. Joseph Medical Center, Warren, OH
Noninvasive ventilation refers to techniques of augmenting alveolar ventilation without an artificial airway.1,2 Traditionally, intubation and mechanical ventilation are used to treat the critically ill infant or child who develops respiratory insufficiency or respiratory failure. Complications may occur with intubation and with artificial airways; therefore, noninvasive ventilatory support is becoming a popular first alternative (especially in chronic disease processes).
— The Editor
Introduction
This article provides a comprehensive discussion of noninvasive ventilation in pediatric patients. There are two types of noninvasive ventilation: positive pressure and negative pressure. Negative pressure ventilation is not commonly used and will be only briefly described. Most noninvasive ventilatory support is now performed via positive airway pressure.
Negative Pressure Ventilators
Negative pressure ventilation is the oldest form of artificial ventilatory assistance.3 A number of types of negative pressure ventilators are available, and all work by applying intermittent negative pressure to the thorax, which leads to a concomitant decrease in transpulmonary pressure.3,4 This stimulates normal tidal breathing more closely than positive pressure ventilation and is particularly useful in respiratory insufficiency due to pump failure.
All negative pressure devices have a significant limitation in that they may precipitate upper airway obstruction, especially during rapid eye movement (REM) sleep.1,5 Upper airway obstruction may occur even in patients without previous evidence of obstruction, as well as in patients with preexisting upper airway anomalies or obstructive apnea.
Another problem with negative pressure ventilation is the lack of airway protection, which may lead to aspiration, especially in patients with bulbar dysfunction. Negative pressure ventilation has limited usefulness in patients who need continuous ventilation or who have significantly increased respiratory system impedance from severe lung disease or chest wall deformity. Finally, personal care is potentially compromised by limited movement, which can result in skin breakdown.
Noninvasive Positive Pressure Ventilation
Recently noninvasive positive pressure ventilation (NPPV) has been more widely recognized.1,6-14 Small, portable, cycling positive pressure ventilators are convenient for placement at bedside or on a wheelchair ventilator tray. NPPV can be applied successfully using critical care ventilators, home care ventilators, or ventilators specifically designed for NPPV.15 Gas is delivered to the patient through the mouth, nose, or mouth and nose via appropriate patient ventilator interfaces (masks).
By definition, this technique is distinguished from those ventilatory techniques that bypass the patient's upper airway with an artificial airway (endotracheal tube [ETT], laryngeal mask airway, or tracheostomy tube).6 Artificial airways are associated with significant risks, including airway injury, barotrauma, hemodynamic instability, nosocomial pneumonia, aspiration during intubation, and increased length of hospital stay.7,12-14
The invasive nature of endotracheal intubation (ETI) may make the physician reluctant to intubate patients early; many caregivers prefer to wait as long as possible, hoping that the patient will respond to medical therapies. Although this approach may seem reasonable given the level of care and risks to which ETI commits the patient, it may not be optimal physiologically. A protracted period of labored breathing may induce muscle fatigue, requiring a longer period of respiratory muscle recovery if ventilatory assistance is eventually required.12 Because NPPV does not involve an invasive procedure, it may be applied and removed frequently and prescribed earlier in the patient's course.
NPPV has a role in the management of acute and chronic respiratory failure in many adult and pediatric patients and may have a role in some patients with heart failure.16 Noninvasive approaches can preserve normal swallowing, feeding, and speech. Cough, physiologic air warming, and humidification also are preserved. Also ETI is inherently uncomfortable. Many patients require deep sedation to overcome pain, anxiety, and frustration. This requirement renders an already ill patient even more dependent upon ventilatory support, may prolong the weaning process, and sometimes makes physical examination for intercurrent problems difficult. Also, attempts to limit sedation may precipitate discomfort, agitation, patient-ventilator dyssynchrony, and sympathetic overactivity. Alert patients often find noninvasive ventilation more comfortable and less frustrating.6,12,14
NPPV may be provided by either bi-level positive airway pressure (BLPAP) or continuous positive airway pressure (CPAP). BLPAP provides an inspiratory positive airway pressure for ventilatory assistance and lung recruitment, and an expiratory positive airway pressure to help recruit lung volume and, more importantly, to maintain adequate lung expansion (Table 1).6,14 The singular advantage of the addition of a preset inspiratory pressure over CPAP is the capability to augment the patient's tidal volume.17 This advantage can assist with augmenting ventilation in patients at risk for hypercapnia. However, the added inspiratory assist theoretically should further reduce the work of breathing.14
| Table 1. BLPAP (Bi-level Positive Airway Pressure) |
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CPAP provides only a single level of airway pressure, which is maintained throughout the respiratory cycle.6 It does not actively assist with ventilation. In the acute setting, its main uses are for upper airway obstruction and for hypoxemic respiratory failure.14 It can improve oxygenation by increasing the mean airway pressure, increasing functional residual capacity, and opening underventilated and collapsed alveoli, enhancing gas exchange and oxygenation.18 The work of breathing also is decreased through an increase in lung compliance.14,19 CPAP is usually initiated between 0-15 cm H2O. The level is set low initially and slowly increased to allow adequate oxygenation with as low an FiO2 level as possible. It is important to check the mask for leaks, because they can be an impediment to providing adequate support.
Published studies in pediatric patients predominantly reflect the use of BLPAP; many studies reflect studies in pediatric patients with the BiPap® system (Respironics Corp, Murrysville, PA), a flow triggered, portable device introduced in 1989.20-22 BLPAP systems are primarily flow, triggered machines that can deliver preset adjustable levels of inspiratory and expiratory positive pressure (Table 1). With BLPAP, when the patient initiates a breath, the device delivers a small assist to ventilation along a positive pressure gradient, increasing tidal volume and minute ventilation. Oxygenation and CO2 elimination are improved without increased risk of infection or airway trauma directly related to an artificial airway.
BLPAP ventilators provide continuous high-flow positive airway pressure that cycles between a high positive pressure and a lower positive pressure. In the spontaneous mode, BLPAP responds to the patient's own flow rates and cycles between higher pressure (inhalation) and lower pressure (exhalation).16 It reliably senses a patient's breathing efforts, even if there are air leaks in the patient's circuit. When inspiration is detected, the higher pressure is delivered for a fixed time or until the flow rate falls below a threshold value.16
The spontaneous mode of BLPAP is similar in concept to pressure-support ventilation. The terminology differs, however, in that the expiratory pressure with BLPAP is equivalent to the positive end-expiratory pressure (PEEP) and the inspiratory pressure is equivalent to the sum of PEEP and the pressure-support level. Thus, a BLPAP setting of 12 cm of water for inspiratory pressure and 5 cm of water for expiratory pressure is equivalent to a standard ventilator setting of 7 cm of water for pressure support and 5 cm of water for PEEP.
An automatic cycle feature can be used in patients with periods of central apnea or weak inspiratory effort.8 In this spontaneous/timed mode, BLPAP supports any breathing efforts initiated by the patient, along with a minimum breathing rate set by the clinician.
Physiologic Effects of NPPV
Well-adjusted NPPV may assume much of the work required for ventilation. When the waveform of applied flow or pressure is appropriately matched to patient needs, the patient's breathing workload significantly decreases. Numerous studies have confirmed its efficacy, many through the use of surrogate indicators of patient stress (e.g., respiratory frequency and heart rate).12
The application of positive pressure to the airway may confer benefits beyond those arising from the reduction of ventilatory effort. Relief of respiratory distress and agitation may alter cardiac loading and dramatically reduce cardiac oxygen demands. Moreover, the lessened workload may help to restore balance between systemic oxygen delivery and demand, improving mixed venous PO2 and often causing arterial PO2 to increase as a consequence.
The positive airway pressure applied during inspiration (IPAP) will increase mean airway pressure, an effect accentuated by also maintaining positive pressure during expiration (EPAP). Increasing mean airway pressure tends to improve oxygen transfer across the lung in patients with acute parenchymal diseases, an effect that has been most clearly documented in the older literature pertaining to the use of mask CPAP in pulmonary edema.23 Improved oxygenation is usually attributed to better recruitment of collapsed lung units, together with beneficial redistribution of lung water and attenuation of the work of breathing. However, excessive increases of mean airway pressure have the potential to decrease venous return, cardiac output, and blood pressure, although this adverse result is much less common during triggered ventilation than during passive inflation.12 Furthermore, in the presence of a focal consolidation of the lung resistant to recruitment, increased alveolar pressure in the uninvolved lung regions may divert blood flow to the consolidated zones. Pulmonary-shunt fraction may then increase as blood flow is directed away from overdistended aerated regions to airless zones of consolidation.
Application of NPPV in Children
NPPV can be an effective alternative to traditional therapies in pediatric patients with both acute and chronic respiratory system dysfunctions.24 An important reason why NPPV should be considered in younger patients with acute respiratory symptoms is, in part, the high morbidity and mortality rates associated with emergent endotracheal intubation and mechanical ventilation. As a result, although few published studies support the use of NPPV as a treatment for pediatric respiratory diseases, application of NPPV in younger patients is keeping pace with its growing use in adults.24
Other factors contributing to the growing popularity of NPPV in the pediatric population are the relative ease and convenience of applying NPPV compared with traditional invasive techniques. The availability of soft nasal masks in a range of pediatric sizes and the introduction of portable pressure-targeted ventilators amenable to home use have encouraged greater use of NPPV.
However, important differences between children and adults in the anatomy and mechanical function of the respiratory system as well as the spectrum of diseases causing respiratory failure bear on the application of NPPV in the pediatric patient.
NPPV is often accomplished in children via a nasal mask interface. If this route of application is to be successful in augmenting alveolar ventilation, the resistance of the upper airway must be overcome. Important anatomic and mechanical features of the developing upper airway should be considered in the application of NPPV to pediatric patients because a relatively high inspiratory pressure setting may be necessary to overcome a high upper airway resistance.
During infancy, resistance of the nasal airway is relatively high and is a significant fraction of the total pulmonary resistance.25 In young children, the nasopharyngeal airway is prone to obstruction for a number of reasons. The adenoids and tonsils develop naturally between 2 and 7 years of age and can enlarge in response to recurrent infections and allergies. Adenotonsillar hypertrophy is the most important cause of obstructive sleep apnea in the pediatric population. In addition, thick copious secretions can obstruct the nasopharyngeal airway in children with respiratory tract infections.
The size and shape of the nasopharyngeal airway are chiefly determined by the development of the midfacial bones.24 Congenital craniofacial anomalies with maxillary hypoplasia, such as those that occur with Down syndrome are often associated with obstructive sleep apnea or, in severe cases, obstructive hypoventilation syndrome. Young infants with choanal atresia or mandibular hypoplasia (Pierre Robin anomaly) also can present with hypoventilation and severe respiratory distress.
Compared with the adult larynx, the immature larynx is positioned relatively anterior and contributes more to upper airway obstructive syndromes. Tonic activation of the laryngeal muscles during the first year of life produces an expiratory "braking mechanism," and thereby preserves lung volume. Infants and young children are more likely than adults to present with laryngeal airway obstruction in association with laryngomalacia, gastroesophageal reflux, and infectious laryngitis. Gastroesophageal reflux can cause laryngeal edema when acid reflux from the stomach reaches the larynx. NPPV may contribute to the tendency to have gastroesophageal reflux in children in situations where it contributes to gastric insufflation. However, the link, if any, between worsened gastroesophageal reflux and use of NPPV has not been established, and gastroesophageal reflux is not a contraindication to NPPV in pediatric patients.
By necessity, children with obstruction of the nasopharyngeal airway mouth breathe to maintain adequate ventilation. However, this compensatory response may be counterproductive during nasal NPPV, when air leaking through the mouth can significantly limit the efficacy of NPPV.26 Although ventilators designed for NPPV are flow-triggered by the patient's respiratory effort, the onset of inspiration may be difficult to sense in the presence of large leaks. In addition, the duration of the inspiratory phase is dependent upon the decrease in flow coincident with the attainment of the preset maximum inspiratory pressure. When the mouth leak is significant, patient inspiratory efforts may fail to trigger. If a backup rate is used, the timer will trigger inspiratory pressure, but inspiratory flow will be sustained in an attempt to maintain the inspiratory pressure, resulting in a prolonged inflation. The child may attempt to exhale during the inflation, giving rise to patient-ventilator asynchrony, especially common in young children and infants who compensate for respiratory dysfunction by breathing rapidly.
Indications for NPPV in Children
A number of respiratory conditions—acute and chronic—are amenable to a trial of NPPV in pediatric patients (Table 2).
| Table 2. Respiratory Conditions Amenable to a Trial of NPPV in Pedicatric Patients |
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Acute Hypoxemic Respiratory Failure. In children, the reported use of NPPV has primarily been in patients with chronic respiratory failure secondary to neuromuscular disease or chronic lung disease.6-8 However, numerous reports confirm the efficacy of NPPV in preventing intubations in adults with acute respiratory failure.12,13,16 Experience with NPPV in pediatric patients with acute respiratory failure is also accumulating. NPPV acutely improved gas exchange in two critically ill toddlers with diffuse airspace disease in a case report.20 In the intensive care unit of a children's hospital, NPPV with a BiPAP® device improved oxygenation and avoided endotracheal intubation in a sample of children with acute hypoxemic respiratory failure.27 The most common diagnosis in this case series was pneumonia, and a significant number of children with neurodevelopmental disabilities were managed effectively with this method.
Status asthmaticus may be accompanied by severe hypoxemia and respiratory muscle fatigue, that if not quickly reversed, may lead to intubation. NPPV via face mask improved respiratory gas exchange in adult patients with severe hypoxemia from status asthmaticus, but this study was not controlled.28 Recent reports suggest that NPPV may have a role in treating children with acute asthma exacerbation.7,29
Historically, the use of positive airway pressure in patients with airway obstruction has been discouraged because of concerns of worsening lung hyperexpansion. The use of positive end-expiratory pressure (PEEP) in intubated adult patients with asthma was associated with increases in static lung volumes.30 However, the use of continuous positive airway pressure in severely obstructed asthmatic patients was subsequently shown to be therapeutic in a single study.7 More recently, it has been shown that the application of noninvasive positive airway pressure to adult patients with severe chronic obstructive pulmonary disease and asthma results in improvements in patient comfort and in objective measures of respiratory mechanics and gas exchange.31-33 Moreover, NPPV is appealing because of the avoidance of risks associated with intubation and mechanical ventilation in patients with severe obstructive lower airways disease.33,34
Dr. Thill and colleagues have recently reported interesting findings from a prospective, randomized, crossover study in 20 children with acute lower airway obstruction, and they concluded that NPPV can be an effective treatment for children with acute lower airway obstruction.7 In a commentary to this article, Carvalho and Forseca warn that application of NPPV in pediatric acute hypercapneic, hypoxic respiratory failure, or in weaning/post extubation is still controversial.35 Certainly, more investigation is needed; however, in the emergency department or intensive care unit, a trial of NPPV should be considered in children with severe lower airway obstruction refractory to standard medical therapy,36 and who do not have apnea, mental status changes, or other contraindications.7
NPPV also deserves consideration in disorders predominated by alveolar hypoxia, including pneumonia, acute pulmonary edema, and acute respiratory distress syndrome.24,37
Utilization of NPPV in these acute respiratory disorders should not be attempted outside the emergency department, recovery room, or intensive care unit. The appropriate setting should be one that also routinely handles unstable children and has practitioners skilled in the application of NPPV. Children treated with NPPV in acute respiratory conditions must be closely monitored (Table 3). Contraindications to the use of NPPV as a life support therapy in children are similar to those that apply to adults and include cardiovascular instability, respiratory arrest, severe agitation, recent facial or gastrointestinal surgery, craniofacial trauma or burns, high aspiration risk, inability to protect the airway, and fixed anatomic obstruction of the upper airway (Table 4).15, 24
| Table 3. Monitoring Requirements for NPPV in Pediatric Patients as a Life Support Therapy |
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| Table 4. Selection Guidelines for Noninvasive Positive-Pressure Ventilation Use in Pediatric Patients |
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NPPV in Chronic Respiratory Conditions
Use of NPPV is dramatically increasing as is the range of chronic diseases in which it is utilized. In pediatric patients, studies of noninvasive ventilation include children with acute and chronic upper airway obstruction, obstructive sleep apnea (OSA), cystic fibrosis (CF), muscular dystrophy, and other forms of congenital myopathy, bronchopulmonary dysplasia (BPD), and central hypoventilation.1,8,10,38-42
Respiratory failure in both pediatric patients and adults may be classified according to the presence or absence of alveolar hypoventilation.38 Type I respiratory failure is manifested by hypoxemia with a low arterial PaO2 level and normal to low PaCO2 level. The predominant cause of type I failure is ventilation/perfusion mismatch. Type I failure typically occurs in acute conditions (e.g., status asthmaticus and acute respiratory distress syndrome [ARDS]), in which poorly ventilated air spaces remain perfused despite regional hypoxia-induced vasoconstriction. Type II respiratory failure is caused by alveolar hypoventilation and manifested by an elevated arterial PaCO2 level with or without hypoxemia. This type of respiratory failure is more likely to result from conditions impairing ventilation, such as depressed neural ventilatory drive, neuromuscular weakness, marked obesity, and rib cage abnormalities. In pediatric patients with significant upper airway obstruction, type II respiratory failure may occur during sleep despite sustained activity of the respiratory muscles.43
Respiratory failure in children is typically classified as acute or chronic depending on the time course of presentation and underlying disorder. Children with chronic respiratory failure typically can lead a relatively normal life, provided there is adequate renal compensation for the underlying acid-base disruption associated with hypercarbia. In a common clinical sequence, children with disorders complicated by compensated chronic respiratory failure present with acute or chronic respiratory acidosis brought on by an infection.38 A second common sequence occurs in pediatric patients with respiratory distress and type I respiratory failure. Such patients can develop respiratory muscle fatigue and progress to a mixed or a predominately type II pattern of respiratory failure.27 Another fundamental point to consider in children with disorders of neuromuscular weakness or impaired ventilatory control is that they may not exhibit classic physical signs of respiratory distress in the face of profound abnormalities in respiratory gas exchange. In such patients, an arterial or capillary blood gas analysis is essential to gauge the magnitude of respiratory system compromise.
Young infants with the respiratory distress syndrome are at significant risk for alveolar hypoventilation as a result of a number of derangements in lung mechanical function. In the presence of a significant decrease in dynamic lung compliance, both the respiratory rate and dead space/tidal volume ratio nearly double.38 Because the chest wall is highly compliant, compensatory increases in diaphragmatic contraction manifest in young infants as asynchronous movements of the thorax and abdomen (termed retractions or in-drawing). The compliant chest wall also promotes a relatively low end-expiratory lung volume, so young infants with respiratory disease are particularly prone to hypoxemia. The decrease in respiratory muscle tone during REM sleep enhances the effect of the floppy chest wall in impairing diaphragmatic function.38 REM sleep is a time when infants with respiratory disease are particularly vulnerable to derangements in respiratory gas exchange.
Pediatric patients with chronic lung disease can develop abnormalities in respiratory control through the effects of hypoxemia, hypercarbia, and sleep stage.38 During REM sleep, depressed ventilatory responses to both hypoxemia and hypercarbia in association with lung and chest wall mechanical factors can promote significant episodes of hypoxemia.44
Specific Case Examples
Obstructive Sleep Apnea and Upper Airway Resistance Syndrome. For OSA and upper airway resistance syndrome (similar to OSA in that symptoms of obstructed breathing are present, but the sleep study is normal except for sleep interruption), nasal CPAP and BLPAP systems can be used effectively.39, 40,45-49 This treatment is well accepted by approximately 65% of the patients for whom NPPV is applied.1 NPPV is used for patients who either fail adenotonsillectomy or other attempted surgeries, for those patients between surgeries (e.g., craniofacial syndromes), or for whom surgery is not a warranted intervention. Without correction of OSA, these infants and children may develop severe health problems.50
Obesity Hypoventilation Syndrome. The obesity hypoventilation syndrome is a condition in which morbid obesity causes ventilatory insufficiency.51-53 Increased adipose tissue in the chest wall and elevation of the diaphragm by intra-abdominal fat result in decreased compliance of the chest wall. Inefficient ventilation results in increased work of breathing and increased oxygen requirement. In addition, obesity causes decreases in total lung volume, tidal volume, and functional residual volume. Alveolar hypoventilation occurs, and the patient may become hypoxic and hypercapnic. There is also evidence suggesting abnormal central control of ventilation in the obesity hypoventilation syndrome, with attenuated ventilatory responses to hypercapnia and hypoxemia. Many of these patients also will have OSA.
Children and adolescents with morbid obesity are at risk for severe sleep disordered breathing (SDB). Once the exact nature of the child's sleep disordered breathing is clarified, the proper noninvasive support can be determined.
The application of BLPAP is the accepted mode of treatment in individuals with REM sleep-related diaphragmatic insufficiency because CPAP is less well tolerated.54
Nocturnal Hypoventilation in Neuromuscular Diseases. Episodes of apnea, acute respiratory failure, nocturnal hypoventilation and, chronic respiratory failure occur more commonly than is clinically suspected in children with a diverse group of respiratory and neuromuscular diseases.42
Respiratory muscle weakness is the inevitable consequence of many childhood neuromuscular disorders (NMD). It causes severe ventilatory restriction, results in progressive respiratory failure, and is the major cause of early death. Respiratory failure relates directly to the loss of respiratory muscle force and vital capacity, and it shows characteristic evolution from normal ventilation during daytime and sleep-induced hypopneas at mild degrees of ventilatory restriction, to REM and non-REM sleep hypoventilation in severe ventilatory restriction.42 Continuous hypoventilation—common at inspiratory vital capacity (IVC) less than 40% predicted— precedes daytime hypercapnia. Daytime respiratory failure is highly prevalent at IVC less than 20% predicted and represents an accepted indication for supportive noninvasive (positive-pressure) ventilation.55 NPPV, applied intermittently and preferably during sleep, relieves respiratory muscles from the work of breathing and augments alveolar ventilation.55,56
In adolescents with Duchenne muscular dystrophy (DMD) and adults with various slowly progressive NMD or restrictive thoracic disease, NPPV applied during sleep, consistently improves diurnal and nocturnal gas exchange, symptoms, quality of life, and survival.42,55,57 NIV, therefore, is considered as a highly effective treatment of chronic respiratory failure due to NMD and a consensus conference has recently published guidelines on the initiation of NIV including NMD.58
The usual first indications of nocturnal hypoventilation are restless sleep, early morning headaches, and daytime drowsiness. If the condition is not diagnosed at this stage, the patient is likely to seek medical attention during an acute respiratory infection because of ventilatory failure and cor pulmonale. Provision of ventilatory support at night provides a marked improvement in daytime symptoms and better tolerance of respiratory infections. Similarly, nocturnal ventilatory support can improve alveolar ventilation, ameliorate daytime hypoxia and hypercapnia, and improve mean nocturnal oxygen saturation in patients with acute or chronic ventilatory failure of various etiologies including cystic fibrosis, severe kyphoscoliosis, and progressive neuromuscular diseases.
The key in all these disorders is the recognition of hypoventilation in these patients, especially with neuromuscular disease. NPPV is well tolerated and highly effective in reversing sleep-disordered breathing and chronic respiratory failure in children with NMD.42
Congenital Central Hypoventilation Syndrome (CCHS). Alveolar hypoventilation in the absence of lung or neuromuscular disease is uncommon. CCHS is characterized by normal ventilation while the patient is awake but hypoventilation with normal respiratory rates and shallow breathing during sleep.59-61 These children experience progressive hypercapnia and hypoxemia during sleep. The diagnosis of CCHS depends upon the documentation of hypoventilation during sleep that does not occur because of airway obstruction, ventilatory muscle dysfunction, or lung disease.
Infants with CCHS do not respond to respiratory stimulants and, therefore, typically undergo diaphragm pacing, invasive positive-pressure ventilation, or both. Although there are isolated case reports of successful NPPV in older children with congenital central alveolar hypoventilation syndrome, the use of NPPV for the treatment of infants with CCHS in place of standard invasive positive pressure ventilation has not been well studied.60 However, in studies done outside the United States, noninvasive ventilation has been proven to be safe and effective even in very young children and should be given consideration.60
Central Hypoventilation – Other Etiologies. A role for nasal mask CPAP or NPPV in the treatment of children with central hypoventilation from other causes is also yet to be established. Conditions with a reduced central respiratory drive in which NPPV could be a useful therapy include myelomeningocele with the Arnold-Chiari malformation and idiopathic central apnea. In adults with central sleep apnea, CPAP therapy does reduce the frequency of central respiratory pauses.1
The Arnold-Chiari malformation is present in 95% of patients with myelomeningocele.62 The Arnold-Chiari II deformity is characterized by an abnormal position of the cerebellum and the brainstem. Many of these infants have clinically significant SDB. They may have apnea (central and obstructive) and hypoventilation related to abnormalities in control of ventilation.62-69
Bronchopulmonary Dysplasia (BPD). There may be a role for NPPV in the care of children with BPD.1 A technical issue that may limit the use of NPPV in children with BPD is the limited peak inspiratory pressure capability of portable units. These peak pressures may not be adequate to overcome the high mechanical impedance to ventilation inherent in conditions in which airway resistance is great.
Cystic Fibrosis and Other Chronic Lung Diseases. Cystic fibrosis is a genetic disease with a pervasive reduction in chloride transport across epithelial apical membranes due to impaired function of a transmembrane regulatory protein. Children with advanced cystic fibrosis typically have severe obstructive pulmonary dysfunction and bronchiectasis associated with endobronchial colonization with various bacteria, including Pseudomas aeruginosa. Although survival rates in recent years have significantly improved, most patients die in young adulthood from respiratory failure. There is a general consensus among clinicians that mechanical ventilation is rarely justified for cystic fibrosis patients with advanced pulmonary involvement because weaning is typically prolonged and survival post-extubation is only for a few weeks.38,66
Early reports of intermittent NPPV treatment in patients with cystic fibrosis are encouraging.10, 66-68 In young adult patients with advanced disease, nocturnal NPPV eliminated the increase in PaCO2 levels associated with supplemental oxygen therapy.67 In a case series of patients with severe gas exchange abnormalities, intermittent NPPV was well tolerated, improved the quality of life, and was viewed as a successful bridge therapy to lung transplantation.66 Further studies are needed to examine the role of intermittent NPPV in cystic fibrosis patients regarding specific outcomes. Similar to adults with COPD, the role of NPPV may well be to reduce hospitalization and improve functional, but not physiologic, outcomes.
Patients Who are Not Candidates for Intubation. Another potential use for noninvasive ventilation in the emergency department is to support the patient with respiratory failure of treatable cause who is not a candidate for intubation, either because of a prior directive or as a result of poor prognosis related to an underlying disease.12,69-71 In this setting, a patient with acute respiratory compromise may be supported with noninvasive ventilation while efforts are undertaken to reverse the acute process or gather further information regarding patient preferences regarding life closure.
Recommendations for Initiation of NPPV
Recommended settings for the initiation of NPPV in pediatric-age patients should reflect the category of respiratory dysfunction and whether the child has a depressed ventilatory drive. We typically initiate NPPV in pediatric patients at inspiratory pressures of 8-10 cm H2O and expiratory pressure of 4-6 cm H2O (Table 5). Children with central hypoventilation syndromes and depressed ventilatory drive must have a unit with a backup rate that will cycle in the absence of spontaneous respiratory effort. Relatively high IPAP levels may be necessary to improve gas exchange in children with obesity hypoventilation syndrome and other conditions that reduce respiratory system compliance or increase inspiratory airway resistance. In children with severe status asthmaticus and hypoxemia, NPPV at inspiratory pressures less than 20 cm H2O may improve oxygenation, but does not consistently reverse hypercarbia.24
| Table 5. Steps in Initating NPPV |
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NPPV via a bi-level ventilator may not reduce a child's PaCO2 level when exhaled CO2 does not clear the in-line exhalation valve or when the dead space of the nasal mask is large.24 The problem with CO2 rebreathing may be eliminated by raising the positive end-expiratory pressure level above 4 cm H2O or substituting an isolated one-way exhalation valve in the ventilator circuit. Higher EPAP settings are also often necessary if the patient has atelectasis, hypoventilation associated with ventilation/perfusion mismatch, or a component of obstructive sleep apnea.
With bi-level ventilation, the FiO2 level can be raised by connecting oxygen tubing to a port on the mask or a T-connection in the ventilator circuit. The problem with this method is that FiO2 delivery is not precise. Alternatively, oxygen can be blended into the circuit by diverting the connection tubing between the pressure-targeted unit and nasal mask through a conventional heater/ humidifier/oxygen source. This method has the advantages of conditioning the inspired gas and allowing some estimate of the FiO2 level via an oxygen sensor electrode in the circuit. Patients with profound hypoxemia may be better served by oxygenation using a critical care ventilator with an oxygen blender.
The most important goals of NPPV with pressure-targeted ventilators in young patients are to alleviate respiratory distress, decrease the work of breathing, and maintain an acceptable comfort level. In children with acute respiratory distress, this is done primarily by raising the inspiratory pressure support level incrementally until the respiratory rate falls, retractions diminish, and there is less visible recruitment of the accessory muscles of breathing. In most applications, the patient's PaCO2 level decreases coincident with a reduction in respiratory distress, but the change in PaCO2 level may be delayed, especially in very obese children or in cases of severe status asthmaticus.24 Typically, with most types of chronic hypercarbic respiratory failure in children, the PaCO2 level gradually decreases, even at relatively low inspiratory pressures (i.e., 10-12 cm H2O).
For patients with persisting hypoxemia despite high flow supplemental O2, the expiratory pressure can be increased in 2-cm H2O increments until the SaO2 level is consistently above 90%. If an expiratory pressure exceeding 8 cm H2O is required to maintain oxygenation, switching to a ventilator with an oxygen blender that delivers accurate, high FiO2 is recommended before increasing the expiratory pressure further.
Obstacles to Successful Uses of NPPV
Absolute contraindications to NPPV are uncommon in children.8 In general, for NPPV to be successful, a patient should possess the following characteristics: 1) capable of spontaneous ventilation, 2) cooperative and fully conscious, 3) ability to protect his/her airway (adequate cough and minimal sputum retention) , and 4) hemodynamically stable.
Excessive secretions may be a problem in children with depressed sensorium or impaired bulbar function and are a relative contraindication to NPPV in settings in which they cannot be monitored and evacuated consistently.8 Adequate expiratory muscle function is critical for clearing airway secretions and bronchial mucus plugs, particularly during respiratory tract infections. Patients utilizing NPPV must be able to generate adequate peak cough expiratory flows either unassisted or by assisted means. Techniques of manually assisted coughing involve the use of an applied abdominal thrust. When manual assistance is inadequate or contraindicated, the most effective alternative for generating optimal cough flow and clearing airway secretions is the use of mechanical insufflation-exsufflation.
It may be impossible to achieve a secure mask fit in children with normal or unusual facial anatomy.8 A major key to the success of NPPV is interface comfort. A ventilation interface acts as a common boundary between the ventilator circuit and the user (patient). Interfaces for NPPV include nasal masks, nasal pillows, mouthpieces, full face masks, and helmets (Table 6).72
| Table 6. Interfaces |
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Selection of a well-fitting interface is important because inappropriate selections may cause excessive air leakage, patient discomfort, and facial sores. Proper fit of the mask and optimization of the headgear are primary tasks. If the patient cannot tolerate a nasal mask, then nasal pillows might be tried.
Sinusitis or deviation of the nasal passages can contribute to increased resistance and may cause the practitioner to choose a full face mask rather than a nasal application.
Complications of NPPV
Minor complications are commonly reported with NPPV and include local skin irritation, drying of the nasal and pharyngeal mucosa, nasal congestion, and eye irritation (Table 6).8, 73 These interface-related problems are the most commonly encountered complications during NPPV. Skin irritation may be reduced by the use of special adhesives or by replacing the mask with nasal pillows.8 Mucosal drying can be reduced by adding a humidifier to the inspiratory circuit.8 Major complications of NPPV have not been reported frequently. Isolated case reports include pneumocephalus, bacterial meningitis, conjunctivitis, massive epistaxis, and atrial arrhythmia as serious complications of nasal mask CPAP therapy.8 Potential complications include pneumothorax, pneumopericardium, and aspiration from gastric distention.73-75
Conclusions
It is apparent that NPPV provides effective ventilatory support in several settings germane to the ED. When successful, NPPV avoids the need for intubation and its attendant complications. Early intervention and appropriate patient selection are keys to its benefits.
NPPV is a valuable, safe, and effective mode of therapy for children with respiratory dysfunction. To use NPPV optimally in pediatric patients, a coordinated and multidisciplinary approach must be established that outlines patient selection and goals of therapy. Once NPPV is considered a treatment option, considerable time is required to properly educate parents and patients and to monitor the patient's response to therapy.
References
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There are two types of noninvasive ventilation: positive pressure and negative pressure. Negative pressure ventilation is not commonly used and will be only briefly described.Subscribe Now for Access
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