Recognition and Management of Respiratory Dysfunction in Children With Tetraplegia
Susan C. Porth, MSN, CRNP
This article first appeared in the Journal of Spinal Cord Medicine, Volume27, Supplement 1, and is reprinted with permission.
ABSTRACT
Summary: Children less than 15 years of age comprise approximately 3% to 5% of all new spinal injuries each year. Approximately one third of these children sustain injuries to the cervical spine. Respiratory complications of spinal cord injuries at the level of C5 and above may include diaphragm dysfunction, retained airway secretions, recurrent aspiration, nocturnal hypoventilation, and respiratory failure. Although most newly injured children with cervical injuries above the level of C5 will require mechanical ventilation acutely, many eventually will be able to be weaned from technology. Despite their ability to breathe without mechanical support, these children often develop ongoing issues associated with respiratory compromise, which interfere with daily activities and can negatively affect quality of life. Poor endurance, failure to thrive, recurrent pneumonia, and sleep-disordered breathing all may be indications of significant respiratory dysfunction. This article describes assessment tools and management strategies aimed at supporting optimal health and preventing recurrent complications associated with unrecognized or untreated respiratory dysfunction.
Key Words: spinal cord injuries; tetraplegia; paraplegia; diaphragm dysfunction; sleep-disordered breathing; hypoxemia; hypercapnia; child; adolescence
Introduction
Three to five percent of all new spinal cord injuries (SCIs) each year occur in children less than 15 years of age. One third of these children sustain injuries to the cervical spine, putting them at risk for some degree of respiratory impairment (1). Level of injury within the cervical spine, as well as associated injuries to the head or chest, will determine both the severity of symptoms and the potential for recovery of respiratory function. Although children with complete injuries at or above the third cervical vertebrae can be expected to require long-term, continuous, ventilatory support, those with injuries at C5 and below generally are able to be weaned from technology over time (2). Patients with injuries between C3 and C5 (where phrenicnerves emerge from the spinal cord) will have varied symptoms of respiratory dysfunction, and may require intermittent respiratory support.
Despite completeness and level of injury, children who sustain injury above C5 remain at risk for pulmonary complications ranging from dysphagia, recurrent aspiration, chronic atelectasis, and mucous plugging to failure to thrive poor endurance, and nocturnal hypoventilation. Recent advances in technology now make it possible for clinicians to evaluate respiratory function more effectively and design interventions aimed at supporting optimal respiratory performance and preventing recurrent, potentially life-threatening events. In addition, some of the newer, noninvasive biomedical tools now offer “user-friendly” alternatives to the conventional airway clearance and ventilatory devices that required the presence of an artificial airway and vigilance of professional caregivers to maintain.
Respiratory Dysfunction After Cervical SCI
SCI at the level of C5 and above is associated with significant respiratory compromise and dysfunction of phrenic nerves, inspiratory muscles (diaphragm andexternal intercostals), and expiratory muscles (diaphragm, internal intercostals, and abdominals). Disruption of phrenicnerve impulses can result in either partial or complete diaphragmatic paralysis (2). Loss of diaphragmatic function affects ventilation on the inspiratory side by allowing the chest wall to collapse inward rather than expand, causing a reduction in vital capacity (the maximum volume of air that can be inhaled and exhaled). During exhalation, diaphragmatic dysfunction accompanied by the loss of internal intercostal and abdominal muscles dramatically interferes with effective coughing and mucous clearance. In addition, when an individual with tetraplegia is positioned upright, the weight of abdominal organs no longer supported by normal muscle tone can tug on the diaphragm, further reducing vital capacity and worsening dyspnea (3).
In addition to alterations in breathing mechanics and ineffective mucous clearance, children with cervical SCIs are at increased risk for sleep-disordered breathing (4). Nocturnal hypoventilation, hypoxemia, hypercapnia, and disruption of normal sleep patterns can significantly affect cognitive function, appetite, endurance, and quality of life during waking hours. Sleep-disordered breathing can be both central and obstructive in origin. Obstructive sleep apnea, common in patients with tetraplegia, can be a function of poor oropharyngeal tone and tongue laxity associated with bulbar muscle dysfunction, tonsillar and/or adenoidal hypertrophy (present prior to injury), or a combination of these factors (2,5,6). Central apnea is associated more commonly with patients who also have sustained a brain or brainstem injury, or whose injury is associated with a near-drowning event. Children with significant hypoxemia or hypercapnia during sleep have symptoms including daytime fatigue, insomnia, morning headache, loud snoring, anorexia, irritability, depression, and poor school performance (4,7). In the pediatric SCI population, symptoms of sleep-disordered breathing may be subtle and easily blamed on poor adjustment to their disability, lack of motivation, oppositional behavior, or deliberate inattentiveness.
Clinical Assessment Tools
Clinical assessment of respiratory function in children with cervical SCI becomes the work of both professional and nonprofessional caregivers. In many instances, it is parents or educators who recognize emotional or behavioral disturbances, which may be subtle indicators of respiratory or sleep problems. Although the child who is febrile, lethargic, and coughing offers obvious impressions of acute illness, a child who is chronically tired, irritable, and inattentive also may be exhibiting more subtle symptoms of breathing-related difficulties.
Recent advances in technology now provide a variety of ways to objectively measure and monitor pulmonary function outside of the intensive care unit. Pulse oximetry, capnography, pulmonary function testing (PFT), diaphragm fluoroscopy, modified barium swallow, and sleep pneumography all may be useful tools to evaluate the functional pulmonary status of children with tetraplegia.
Pulse Oximetry
Pulse oximetry offers clinicians a noninvasive way to either periodically or continuously measure oxygenation by measuring the arterial saturation of oxygen, heart rate, and pulse amplitude (2,5). Monitoring oxygen saturation (SaO2) during a normal day of wakefulness, sleeping, eating, and social activity can provide valuable information with regard to pulmonary adaptation to potential stressors. SaO2 depends on the oxygen concentration present in hemoglobin (2,5,8). Saturation levels below 95% generally are considered abnormal, and may result from hypoventilation, atelectasis, or mucous plugging. Although SaO2 provides important information with regard to oxygenation, it provides no clues with regard to the other side of gas exchange—namely, the elimination of carbon dioxide (CO2). Without this piece of information, it might be easy to treat low SaO2 levels with supplemental oxygen, and miss ongoing underventilation of the lungs (2).
Capnography
The drive to breathe is regulated not by the amount of oxygen in the blood, but by the concentration of CO2 (7). Cervical-level SCI commonly is associated with inspiratory muscle weakness and hypoventilation, which interferes with normal gas exchange. Anxiety, insomnia, or frequent arousals from sleep all may be symptoms of hypercapnia. Abnormally high levels of CO2 (above 45 mmHg) stimulate hyperventilation and an increased work of breathing, which eventually can lead to fatigue and respiratory failure.
CO2 levels now can be monitored easily and noninvasively by capnography or end-tidal CO2 (ETCO2) (8). ETCO2 monitors sample exhaled gasses from the nasopharynx via cannula, and provide a graphic waveform, which yields information about ventilation, gas exchange, and airflow (5). In patients with SCI, weakness of the chest wall and respiratory muscles cause a weak cough and shallow breathing, which, in turn, causes poor aeration of the lungs. An impaired ability to cough prevents removal of secretions from the airways and leaves patients vulnerable to atelectasis, infection, and airway obstruction (9). Chronic underventilation of the lungs and elevated levels of exhaled CO2 may be associated with the development of respiratory acidosis. As the body compensates for this drop in pH by retaining bicarbonate, increased levels of bicarbonate circulate within the brain, further reducing ventilatory drive (5). Recognition and correction of hypercapnia is an essential component of SCI care to prevent morbidity from progressive respiratory failure.
Pulmonary Function Testing
PFT has long been the gold standard of asthma management in the pediatricsetting and is an excellent tool for assessing the degree of respiratory impairment in the SCI population (9). PFTs can be used to monitor changes in lung function or to determine the effectiveness of therapeutic interventions. Premorbid conditions such as asthma, which cause obstructive changes in lung function, can be assessed and treated to avoid stressing already-impaired respiratory function. In the past, a lack of cooperation or cognitive ability to comply with instructions has made it difficult to obtain PFTs in younger children. New diagnostic tools such as forced oscillation, interrupter respiratory resistance, and exhaled nitric oxide and carbon monoxide measurement now are available to meet the needs of infants and toddlers (10).
The forced oscillation technique utilizes pressure oscillations transmitted to the airway during normal tidal breathing. Interrupter respiratory resistance calculates airway resistance from the ratio of pressure verses flow as the airway is occluded briefly during tidal breathing. Exhaled nitric oxide and carbon monoxide have been identified as useful markers of lower airway disease. Levels are obtained by exhalation against resistance within a mask or mouthpiece, with gases collected for later analysis.
The most commonly measured parameters of lung function in children with SCI and neuromuscular disease include forced vital capacity (FVC), maximum inspiratory and expiratory pressures (MIP and MEP), and peak flow or peak expiratory flow rate (PERF). All of these parameters can be measured in the clinical setting with the use of readily available handheld devices. A more complete set of values requires a laboratory and technicians who are trained in performing PFTs on children. It is important to note that computer-generated calculations of lung function are based on accurate measures of height, age, and gender. In the pediatric SCI population, arm span rather than height may reflect a more accurate picture of actual lung function (11).
Forced vital capacity refers to the maximal amount of air that can be exhaled following a maximal inhaled breath. A reduction in FVC is common in children with high-level SCI due to an inability to forcefully inflate the lungs, as well as chest wall dysfunction similar to that seen in other restrictive lung diseases (2). Evaluation of FVC can be useful in predicting the likelihood of maintaining adequate gas exchange for prolonged periods without an unacceptable increase in work of breathing (12). Furthermore, FVC also can be used to detect early respiratory compromise due to acute illness.
MIP is the maximum negative pressure measured during inspiration against an occluded orifice and is useful in evaluating the extent of respiratory muscle weakness (8). MEP measures maximum expiratory force against resistance, and is used to determine the degree of expiratory muscle weakness.
PERF describes the maximum forced expiratory flow that can be generated during rapid exhalation (8). A reduction in PERF may signal progressive airway obstruction due to infection or mucous plugging.
Diaphragm paralysis in the child with SCI can have a devastating impact on spontaneous breathing. Loss of the principle muscle of inspiration may be unilateral, bilateral, complete, or incomplete (13), and may or may not recover over time (14). When diaphragmaticdysfunc tion is unilateral, symptoms can include exertional dyspnea and orthopnea, but otherwise may be well tolerated. When paralysis is bilateral, the abdomen moves inward paradoxically with inspiration, further reducing already compromised lung volumes and placing the patient at high risk for respiratory failure (2,13).
Diaphragm Fluoroscopy
Diaphragm fluoroscopy allows for radiologic observation of diaphragm movement during inspiration. Unilateral paralysis can be detected by asking the patient to sniff, causing the paralyzed side to rise and the unaffected side to descend (7). Electrical stimulation can be applied to the phrenic nerve during fluoroscopy to determine whether diaphragm activity responds to electrical stimulation (15). Because approximately 21% of patients with diaphragm paralysis after SCI eventually recover function (14), clinicians caring for children dependent on mechanical ventilation can use fluoroscopy to evaluate diaphragm function over time, and aid in determining readiness for weaning.
Video Fluoroscopy/Modified Barium Swallow
The ability to chew and swallow following high SCI can be impaired dramatically. Muscle weakness, esophageal dysmotility, and difficulties with posture and balance also can affect swallowing and place children at increased risk for weight loss, aspiration, and recurrent pneumonia (6). Symptoms of dysphagia can include coughing, choking, and gagging during oral feeding (16). Symptoms of distress may be less obvious in patients with SCI, because the cough and gag reflexes are weak or absent. Irritability, cyanosis, and oxygen desaturation during eating should lead to a high suspicion of dysphagia and respiratory compromise. Video fluoroscopy, or modified barium swallow, is a comprehensive evaluation tool for swallowing assessment (5). During a swallowing study, speech therapists trained in dysphagia management are able to observe and document pooling of food in the posterior pharynx, as well as episodes of aspiration. They also may be able to identify food consistencies and feeding positions that are tolerated more easily and reduce the risk of aspiration. Children who demonstrate severe dysphagia and respiratory compromise may require enteral nutrition via nasogastric or gastrostomy tube to provide adequate caloric intake and prevent respiratory distress.
Sleep Studies
Sleep-disordered breathing is commonly associated with cervical SCI (4). Attention, concentration, memory, and learning all can be affected by unrecognized hypoxemia and apnea or hypoventilation during sleep. A sleep disorder also should be suspected when children lose or fail to gain weight, despite adequate appetite and caloric intake (9).
In addition to nighttime observation of SaO2 and CO2 levels, polysomnographicstudies (sleep studies) measuring electroencephalogram, respiratory movement (plethysmography), and airflow via nasal thermistor should complete a thorough evaluation. Sleep studies are performed either at home or in a designated sleep laboratory, and scored by a trained polysomnographer. Patients with severe sleep-disordered breathing accompanied by evidence of related daytime symptoms should be considered for further management.
Respiratory Management Devices
The pulmonary care of children with tetraplegia should focus on maintaining optimal respiratory health and avoiding complications. Respiratory muscle training, abdominal binders to support weakened expiratory muscles, and noninvasive ventilation can assist the child, family, and professional caregivers in overcoming the effects of hypoventilation and poor airway clearance.
Respiratory Muscle Training
Several studies (17,18) in adults with cervical SCI have shown that respiratory muscle training can improve respiratory muscle strength (FVC) and endurance. The studies used both inspiratory and expiratory exercises lasting 15 to 30 minutes, twice a day, 6 days a week. A simple, handheld device called P-Flex proves increasing inspiratory resistance, and also can be used to improve FVC. Long-term improvement, however, depends on a willingness to incorporate respiratory exercise into an already-busy daily routine.
Abdominal Binders
Many patients with tetraplegia have discovered that using an abdominal binder to replace abdominal muscle tone lost after injury can improve symptoms of breathlessness and dizziness while upright. (5,19). Young children who wear a body jacket or brace to slow progression of scoliosis may be more comfortable with an abdominal cutout in the brace leaving room for abdominal organs, but covered with an abdominal binder to prevent a position-dependent fall in lung volumes.
Noninvasive Positive Pressure Ventilation
Noninvasive positive pressure ventilation is a technology designed to treat respiratory insufficiency without the need for endotracheal intubation or tracheostomy. Bilevel positive airway pressure (BiPAP, Respironics, Inc,) delivers positive pressure during inspiration and exhalation in spontaneously breathing patients (19), and can improve oxygenation and CO2 clearance during sleep, providing respiratory muscle rest (20). Positive pressure ventilators that are designed for portability and home-care use now offer the benefits of programmable tidal volume, pressure support, and breath rate in a device the size of a laptop computer (LTV900, 950, 1000 by Pulmonetics) that also can be used with a nasal mask. Use of noninvasive ventilation during sleep can support nighttime breathing, improve gas exchange, and reduce daytime symptoms associated with sleep-disordered breathing.
Diaphragm Pacing
Beyond mechanical ventilation, diaphragm pacing through electrodes surgically implanted on the diaphragm or phrenic nerves offers the opportunity for ventilator-dependent children to wean from their ventilators (21,22). Minimally invasive surgical techniques combined with new pacing options (23) reduce surgical risk and recovery time, and may make freedom from equipment and round-the-clock caregivers a reality for children who were previously unable to wean from technology.
Airway Clearance Techniques/Devices
Airway clearance techniques are interventions used to assist with secretion removal in patients unable to cough effectively. Chest percussion, postural drainage, and abdominal thrust (quad coughing) have been used for years to aid in the removal of retained secretions (2,8). When done properly, chest percussion and postural drainage are an effective aid to mucous removal, but are labor intensive and depend on the patient’s ability to generate an effective cough at the end of therapy, something most children with tetraplegia are unable to do. Quad coughing supports the child’s own efforts to expel secretions by forcefully compressing the abdomen in synchrony with an exhaled breath (5). Timing and coordination are important aspects of this maneuver.
A variety of new tools now are available to assist caregivers in maintaining airway patency. From small, portable devices that create vibration and mild expiratory resistance (Flutter, Scandipharm, Birmingham, Ala; Acapella, DHD Healthcare, Wampsville, NY), to more sophisticated devices such as the In-Exsufflator, Vest Airway Clearance System, and Intrapulmonary Percussive Ventilation (IPV), these new products may be useful adjuncts to traditional therapy in maintaining pulmonary health.
Positive Expiratory Pressure Devices
Oscillating positive expiratory pressure devices are small, handheld items attached to a mouthpiece or mask. The Flutter and the Acapella are designed to vibrate as the patient exhales, loosening secretions from airway walls. Gentle resistance keeps the airways open, allowing secretions to move and be expelled by coughing (24). Resistance to airflow is adjustable, to accommodate patients with varying degrees of muscle strength. These devices are useful tools for children who breathe spontaneously and are able to generate an effective cough with or without help from a caregiver.
In-Exsufflator
The In-Exsufflator cough machine operates with a blower and valve that applies a predetermined positive pressure breath via facemask, followed by a rapid shift to negative pressure, thus creating high expiratory flow similar to a normal cough (5). Pressures can be adjusted for patient comfort and tolerance, but should provide deep insufflation for maximum benefit. Inspiratory and expiratory times also can be set for patient comfort. Coughing sessions generally take approximately 15 minutes, and involve rapid cycling between positive and negative pressure for 5 or 6 breaths. Rest periods between cycles prevent hyperventilation. When secretions are mobilized, they can be spit out or gently suctioned from the mouth. Children with tracheostomies can use the system attached to their tracheostomy tubes, and can be suctioned as usual when secretions appear in the tubing.
The Vest Airway Clearance System
The Vest Airway Clearance System consists of an air-pulse generator and hoses, which attach to an inflatable vest. Rapid inflation and deflation of the vest causes chest wall oscillation. These rapid oscillations increase airflow within the lungs, and move secretions into the large airways where they are cleared more easily by coughing. Use of the vest has been associated with improved secretion removal and a reduction in recurrent pneumonias in a variety of pediatric conditions, including cystic fibrosis and cerebral palsy (25).
Intrapulmonary Percussive Ventilation
IPV involves the use of a pneumaticdevic e called a “percussionator,” which delivers high-flow minibursts of air into the lungs through a facemask or mouthpiece (26). A high-output aerosol generator delivers humidification (and airway medications, if desired), to loosen secretions and relax spasms in the small airways. During therapy, continuous intra-airway pressure is provided, which dilates the airways and enhances secretion mobilization. Percussive intervals are programmed to allow for exhalation at the end of each cycle, and the mouthpiece or mask is removed when the patient needs to cough or spit.
Conclusion
Pediatric SCI has a devastating, lifelong impact on function and independence, and pulmonary complications contribute significantly to poor quality of life, recurrent hospitalization, and high mortality. Even children lucky enough to wean from respiratory support are likely to struggle with breathing-related issues such as sleep- disordered breathing, poor endurance, and frequent respiratory infections. It is critically important for clinicians involved in the care of these children to be aware of subtle symptoms of respiratory dysfunction, and develop assessment and management strategies aimed at preserving optimal lung function and overall health. Families should be encouraged to maintain close relationships with primary healthcare providers who can make sure that immunizations are kept up to date and help to guide them through acute illnesses. Family, friends, educators, and caregivers must work together to understand the potential complications of underventilation and poor airway clearance, and intervene early to avoid undesirable outcomes. Families should be fully educated about normal respiratory function, symptoms of respiratory compromise, and the use of airway clearance devices that can be used at home to promote respiratory health and avoid the need for recurrent hospitalization.
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Susan C. Porth, MSN, CRNP, is affiliated with the Spinal Cord Injury Program at Shriners Hospitals for Children, Philadelphia, Pennsylvania.
Please address correspondence to Susan C. Porth, MSN, CRNP, Shriners Hospital for Children—Philadelphia Unit, 3551 N. Broad St., Philadelphia, PA 19140 (e-mail: sporth@shrinenet.org).