Chronic Respiratory Insufficiency

Invasive Positive Pressure Ventilation

The term invasive designates ventilation through a tracheostomy. Some devices are suitable for both noninvasive positive pressure ventilation (NPPV) and invasive ventilation, while other devices are suitable for only one approach. The ideal home ventilator is lightweight, portable, and quiet. All home ventilators differ from hospital-based ventilators in that air movement is affected either by a piston or turbine that is electrically controlled. This contrasts with hospital ventilators which are often gas-driven. A home ventilator should be able to provide continuous flow and have a wide range of settings (particularly for pressure, volume, pressure support, and rate) that allows ventilatory support from infancy to adulthood. Battery power for the ventilator, both internal and external, should be sufficient to permit unrestricted portability in the home and community. The equipment must also be impervious to electromagnetic interference and must be relatively easy to understand and troubleshoot. A variety of ventilators that are approved for home use are available, and familiarity with these devices is necessary to choose the best option for the individual child.

While families and care teams may at first resist placement, a tracheostomy has several advantages. It provides a secure and stable airway, a standardized interface for attaching the ventilator circuit to the patient, and the ability to easily remove airway secretions and deliver inhaled medications. Pediatric tracheostomy tubes typically have a single lumen and may have an inflatable cuff. Tracheostomy tubes with/without cuff inflation should be sized to control the air leak around the tube and promote adequate gas exchange, yet allow enough space around the tube to facilitate vocalization and prevent tracheal irritation and erosion from the tube. The child's caregivers need to learn stoma care, elective and emergent tracheostomy changes, proper securing of the tube, suctioning of secretions, and recognition of emergencies such as tube obstruction or decannulation.

Optimal Ventilator Support

Factors such as underlying neuromuscular disease; medications such as sedatives, analgesics, steroids, and muscle relaxants; and prolonged immobility, as well as utilization of mechanical ventilation, may decondition the respiratory muscles, and more so the diaphragm, resulting in muscle weakness. Consequently, it is important to avoid 24 hr/day patient synchrony with ventilation and titrate the amount of ventilator support to prevent fatigue, yet facilitate spontaneous breathing. While assessing ventilator needs frequent evaluation of gas exchange is needed, but can usually be done noninvasively. Ventilator settings should be stable for a period of time, dictated by severity of pulmonary disease, before discharge home.

Airway Clearance

One of the most important considerations is maintenance of airway patency. Adequate removal of secretions may minimize intercurrent pulmonary infections. In turn, infections may cause a transient increase in secretions requiring an escalation of clearance strategies. If the child has an adequate cough, periodic suctioning may be all that is needed. Some children, however, need additional help mobilizing and clearing secretions. This becomes particularly important in children with neuromuscular disease, for whom regularly scheduled clearance therapies are an imperative. There are 2 main types of devices that are used. Vest therapy (high frequency chest wall oscillation) uses an inflatable vest that encircles the chest. Air inflates and deflates the vest with phasic pulses against the chest wall, loosening secretions. This device still requires a preserved and strong enough cough to expel secretions. The cough assist device provides more active airway clearance, delivering a forceful positive pressure adjunct during inspiration and active negative pressure during expiration. Thus, the cough is more effective due to the rapid pressure changes. The cough assist can be used with an artificial airway or mask. Controls will set the inspiratory and expiratory pressures and periods.

Inhalation Medications

Clearance of secretions may be promoted with delivery of hypertonic (3% saline) nebulizations. These are often timed to cough assist sessions to maximize the clearance benefits of both. Children requiring ventilation also commonly need bronchodilators.

Mucolytics and Anticholinergics

Some patients may need additional interventions due to excess secretions. Anticholinergic drugs, principally glycopyrrolate, are often effective, but must be dosed carefully to avoid thickening secretions excessively, which can lead to inspissated secretions and life-threatening plugging of the airway. Oral secretions are sometimes amenable to localized injection of botulinum toxin, or select surgical ligation of salivary ducts. It is also wise to ensure that the patient is adequately hydrated as dehydration may produce thick tenacious secretions. At times a mucolytic may be used. Hypertonic saline is the most common mucolytic, but a number of other agents have been tried, such as dornase alfa and N-acetylcysteine.

Monitoring

A patient who is ventilated in the home must be electronically and/or physically monitored at all times. Infants and young children, children who are cognitively impaired, and children who are completely tracheostomy dependent for airway patency because of suprastomal obstruction must be under direct observation of the caregivers at all times. Caregivers should also closely monitor children whose pulmonary status is fragile or fluctuant. Continuous monitoring of O ₂ saturation and heart rate is recommended during sleep, and either continuous or intermittent monitoring during the daytime, depending on patient stability. Patients with congenital central hypoventilation syndrome (CCHS) or pulmonary hypertension are particularly vulnerable to episodes of hypoxemia and/or hypercarbia, and those with pulmonary hypertension are particularly susceptible to rapid drops in O ₂ saturation.

Supplemental Oxygen

Supplemental oxygen may be delivered from a tank or concentrator. Whether on room air or oxygen at baseline, even mild intercurrent infections may lead to an increase in oxygen requirement. In these situations, the child should be evaluated in person rather than over the phone to ensure that a more serious illness is not developing.

Nutrition

Ventilated patients may have nutritional needs that are equal to, greater, or lesser than those of comparably aged well children. Growth should be tracked at each well-child and subspecialty visit. Excessive growth is as harmful as inadequate growth, and excess calories may lead to increased carbon dioxide (CO ₂ ) production. Anthropometry or measured energy expenditure may be needed to assure a more precise prescription of nutritional support. Many children with tracheostomies have oral aversion and/or dyscoordination of swallowing, with resultant risk for aspiration. In these children a gastrostomy tube may ensure adequate nutrition in the interim while ongoing speech therapy promotes oral feeding.

Physical, Occupational, Speech Therapy

The technology needed to support physical well-being should not overshadow the inherent developmental needs common to all children—to play, grow, develop, and interact. Ongoing physical therapy, occupational therapy, and speech therapy can help a child reach full potential, and many achieve complete catch-up development. Early intervention programs and access to play groups are important factors to attaining cognitive and social milestones. When normal development is not attainable, therapies can improve mobilization and muscle strength. Core trunk and abdominal strength is particularly important for pulmonary rehabilitation and essential for successful weaning off ventilation. Other important skills include oromotor skills for feeding and communication. Evaluation of swallow is a key component of therapy for children with chronic respiratory failure. Sign language is frequently used for communication because of delayed speech or hearing loss. Audiology specialists should be involved in the assessment of hearing because there is a higher incidence of hearing loss in patients undergoing long-term ventilation.

Infections

Tracheitis (see Chapter 412.2 ), bronchitis (see Chapter 418.2 ), and pneumonia (see Chapters 426 and 428 ) are common in patients with chronic respiratory failure. Infections may be caused by community-acquired viruses (adenovirus, influenza, respiratory syncytial virus, parainfluenza, rhinovirus) or community- or hospital-acquired bacteria. Common pathogens are Gram-negative, highly antimicrobial-resistant pathogens that may cause further deterioration in pulmonary function. Bacterial infection is most likely in the presence of fever, deteriorating lung function (hypoxia, hypercarbia, tachypnea, and retractions), leukocytosis, and mucopurulent sputum. The presence of leukocytes and organisms on Gram stain of tracheal aspirate, as well as the visualization of new infiltrates on radiographs, may be consistent with bacterial infection.

Infection must be distinguished from tracheal colonization of bacteria, which is asymptomatic and associated with normal amounts of clear tracheal secretions. Colonization may also be distinguished from infection in that colonization usually has few, if any, white blood cells on Gram stain of tracheal secretions. If infection is suspected, it must be treated with antibiotics, based on the culture and sensitivities of organisms recovered from the tracheal aspirate. At times inhaled antibiotic such as tobramycin might avert progression of infection. Antibiotics should be used judiciously to prevent further colonization with drug-resistant organisms. However, some patients who have recurrent infections may benefit from prophylaxis with inhaled antibiotics. Clinical decisions will be based on the child's appearance, any increased need for ventilation or supplemental oxygen, and consultation with the subspecialist. A final caveat is that, if a respiratory viral panel is desired, this must be obtained from nasal secretions similar to a well child; tracheal aspirate does not provide an appropriate specimen.

Ventilator Dependence and Control of Breathing

Patients with CCHS have deficient CO ₂ sensitivity during wakefulness and sleep such that they do not respond with a normal increase in ventilation in either state nor do they arouse in response to hypercarbia and/or hypoxemia during sleep. During wakefulness, a subset of patients may respond sufficiently to avoid significant hypercarbia, but most individuals with CCHS have hypoventilation that is severe enough that hypercarbia is apparent in the resting awake state. Children with CCHS also have altered sensitivity to hypoxia while awake and asleep. A key feature of CCHS is the lack of respiratory distress or sense of asphyxia with physiologic compromise (hypercarbia and/or hypoxemia). This lack of responsiveness to hypercarbia and/or hypoxemia, which can result in respiratory failure, does not consistently improve with advancing age. A subset of older children with CCHS may show an increase in ventilation (specifically increase in respiratory rate rather than increase in tidal volume) when they are exercised at various work rates. This response is possibly secondary to neural reflexes from rhythmic limb movements, although an increase in minute ventilation is often insufficient to avoid physiologic compromise. Report of oral contraceptives improving awake CO ₂ chemosensitivity in 2 adult women suggests need for further exploration.

The greater the number of extra alanines, the more likely the need for continuous ventilatory support, at least among the most common PHOX2B PARM genotypes (20/25, 20/26, 20/27). Thus, patients with the 20/25 genotype seldom require awake ventilatory support, although they do require artificial ventilation during sleep. Patients with the 20/26 genotype have variable awake support needs, but all require artificial ventilation during sleep. Patients with the 20/27 genotype and those with NPARMs are likely to need continuous ventilatory support. Although PHOX2B genotype seems to anticipate severity of hypoventilation, it does not correlate with exogenous ventilatory challenge responses. Infants and young children as a group have improved ventilatory response slopes while awake, but this advantage seems to vanish by school age.

Hirschsprung Disease ( Chapter 358 )

Overall, 20% of children with CCHS also have Hirschsprung disease (HSCR), and any infant or child with CCHS or LO-CCHS who presents with constipation should undergo rectal biopsy to screen for absence of ganglion cells. The frequency of Hirschsprung disease seems to increase with the longer polyalanine repeat tracts (genotypes 20/27-20/33) and in those with NPARMs. Thus far, only 1 infant with the 20/25 genotype has ever been reported to have Hirschsprung disease. Even in cases without frank HSCR disease, individuals with CCHS may display symptoms of gastrointestinal abnormalities such as severe constipation and abnormal esophageal motility, suggesting ganglion cell dysfunction.

Tumors of Neural Crest Origin ( Chapter 525 )

Tumors of neural crest origin are more frequent in patients with NPARMs (50%) than in those with PARMs (1%). These extracranial tumors are more often neuroblastomas in individuals with NPARMs, but ganglioneuromas and ganglioneuroblastomas in a small subset of patients with longer PARMs (20/29, 20/30, and 20/33 genotype only). Thus far, only 1 infant with a PARM (20/33 genotype) has been reported to have a neuroblastoma.