- Email: [email protected]
Respiratory care in neuromuscular disorders
Handbook of Clinical Neurology, Vol. 113 (3rd series) Pediatric Neurology Part III O. Dulac, M. Lassonde, and H.B. Sarnat, Editors © 2013 Published by Elsevier B.V.
Chapter 153
Respiratory care in neuromuscular disorders B. ESTOURNET* Reference Center for Neuromuscular Diseases, Raymond Poincar Hospital, Garches, France
INTRODUCTION Neuromuscular disorders (NMD) presenting in childhood are numerous and represent a group in which the involvement of respiratory muscles is common. Deterioration in respiratory function occurs insidiously, contributes to significant morbidity, and is often responsible for mortality. Since symptoms of respiratory involvement are not obvious, especially in the presence of otherwise stable muscular function and maintained ambulation, respiratory failure must be systematically sought for early care.
●
●
CAUSES OF RESPIRATORY INSUFFICIENCY Causes for respiratory insufficiency are numerous: ●
●
●
●
Respiratory muscle paralysis: in myopathies, the diaphragm is more involved than intercostal muscles and vital capacity is better in the sitting position, whereas in spinal muscular atrophy intercostals are weaker and the best position is the lying one. Abdominal muscles are weak in all instances, impeding an effective cough. Decrease in pulmonary growth in congenital diseases: the alveolar number increases rapidly from birth to 4 years of age. Congenital diseases with respiratory muscle involvement always delay this growth and contribute to respiratory insufficiency. Cough deficit increases bronchial congestion and pulmonary infections: paralysis of inspiratory muscles reduces the volume of inspired air, and, paralysis of expiratory muscles impedes pressure increase with glottic closing and expulsion of secretions. Swallowing problems and gastroesophageal reflux are frequent and increase bronchial congestion. especially during the night.
●
Upper airways obstruction: facial growth abnormalities such as maxillary hypoplasia, macroglossia, and/ or tonsil obstruction produce obstructive apnea that is worsened by pharyngeal hypotonia. This augments muscular work and worsens muscular fatigue. Sleep disorders: these are frequent if the vital capacity (VC) is under 40%. They often occur in deep sleep because of muscular hypotonia. In some diseases, sleep disorders occur even when VC remains normal: selenopathies, Steinert disease, or Duchenne muscular dystrophy. Nocturnal hypoventilation produces pulmonary hypertension and acute respiratory failure so it must be sought especially where clinical signs such as headaches, nocturnal sweating, and snoring are present. Orthopedic deformities, especially lordoscoliosis, are frequent in these disorders and worsen respiratory insufficiency.
Respiratory involvement can vary considerably. according to and within each muscular disorder, for the type and severity of symptoms, and both the age and ambulatory status of the patient when symptoms occur (Gozal, 2000; Dohna-Schwake et al., 2004; Shahrizaila et al., 2006; Kennedy and Martin, 2009). Infants and children under 2 years of age may not show typical symptoms of respiratory distress because of profound weakness. Tachypnea and retractions can be seen but respiratory problems cannot be ruled out in their absence. Signs and symptoms described in congenital disorders include weak cry, ineffective cough, choking on feedings or secretions, in addition to weight loss or poor weight gain. These signs and symptoms, along with recurrent respiratory infections, irritability, or a paradoxical breathing pattern, can be the first expression of respiratory involvement (Wallgrin-Pettersson et al., 2004; Shahrizaila
*Correspondence to: B. Estournet, Me´decine Physique et de Re´adaptation Pe´diatriques, Hoˆpital Raymond Poincare´, 92380 Garches, France. E-mail: [email protected]
1486
B. ESTOURNET
et al., 2006). Older children, adolescents, and adults may present with symptoms similar to those of younger children with weight loss, aspiration, and recurrent infections. Typical symptoms of respiratory failure such as breathlessness may not be seen because of motor weakness.
ASSESSMENT OF RESPIRATORY STATUS In neuromuscular weakness, assessment of respiratory status is based mainly on pulmonary function tests. Forced vital capacity (FVC in % predicted) should be performed annually. It is particularly important to perform the measurement in a sitting and supine position since a difference of > 20% between the sitting and supine FVC indicates diaphragmatic weakness and is a predictor of nocturnal hypoventilation (Wallgrin-Pettersson et al., 2004; Mellies et al., 2005). An FVC less than 60% of that predicted is a good predictor of sleep breathing disorder and < 40% it indicates nocturnal hypoventilation. Another test of pulmonary function includes measurement of maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) (Gaultier and Zinman, 1983; Heijdra et al., 1993; Stefanutti and Fitting, 1999; Mellies et al., 2001b, 2005; WallgrinPettersson et al., 2004; Shahrizaila et al., 2006). Normal values of MIP and MEP are 80–120 cm H2O. Values are available for Duchenne muscular dystrophy. A value of less than 60 cm H2O suggests symptomatic respiratory impairment, and 20 cm H2O or less the likely requirement of assisted ventilation (Gozal, 2000). A MIP less than the MEP is an indicator of diaphragmatic weakness. Peak cough flow, polysomnography, and blood gases are also used (Mellies et al., 2001b; Wallgrin-Pettersson et al., 2004; Shahrizaila et al., 2006). A peak cough flow will help estimate a patient’s ability to clear secretions. It can be obtained with a simple peak flow meter although in children or adults with facial weakness a mask may be required to achieve a reliable value. In children, a cough flow of > 160 L/min is required to adequately clear secretions, in adults > 200 L/min. In addition to measuring peak cough flow it is worthwhile to ask the child to cough in order to assess its effectiveness. Polysomnograms can detect or confirm sleep breathing disorders and should include end tidal CO2 monitoring or transcutaneous CO2 monitoring. Arterial or capillary blood gases are also used to assess respiratory failure (Dohna-Schwake et al., 2004; WallgrinPettersson et al., 2004; Shahrizaila et al., 2006).
DIAGNOSIS OF PULMONARY INVOLVEMENT A proactive approach is recommended in order to recognize early symptoms before the condition becomes more severe. Specific detailed questioning and annual
respiratory monitoring are most helpful (Mellies et al., 2001a; Wallgrin-Pettersson et al., 2004). Early symptoms may be subtle and include disturbed sleep, increased need to turn at night, feeling unrefreshed when waking in the morning, tiredness, mood disturbances, and poor concentration during daytime. These symptoms may be related to hypoxemia overnight and progress to more severe symptoms, including: morning headaches, nausea, the use of accessory muscles, fear of going to sleep, and nightmares which tend to be associated with daytime and nighttime hypercapnia. Both early and late symptoms associated with abnormal blood gases can also be associated with recurrent chest infections, swallowing difficulties, and weight loss or poor weight gain. Scoliosis, especially lordoscoliosis, and chest wall deformities add to the restrictive lung disease created by weak chest muscles, a weakened diaphragm, and atelectasis. If the patient is able to perform spirometry, FVC measurement and calculation of FVC/TFVC ratio should be performed. For patients unable to perform standard spirometry secondary to age or developmental delay, a cry vital capacity (VC) can be obtained by placing a tight fitting mask over the nose and mouth with a spirometer in line. The cry will give an approximation of a forced vital capacity (FVC). If the patient does not cry, which may be the case in children > 2 years or in a very weak infant, a tidal volume (TV) measurement can be obtained. Diaphragmatic involvement is often asymptomatic and requires a high index of suspicion in patients who are still ambulatory (SEPN1-related myopathies, collagen VI and lamin A/C). In these subtypes, respiratory failure may occur while patients are still ambulatory, requiring a different perspective than in Duchenne muscular dystrophy where the loss of ambulation marks the onset of respiratory involvement. Regular monitoring of pulmonary function may predict potential changes in a patient’s health before it becomes precarious. Spirometry is a routine evaluation that should be done at each clinic visit, and at least annually. Nocturnal oximetry should be added if there are signs or symptoms of respiratory compromise, if the FVC is below 60% of predicted or if there is a more than a 20% difference between sitting and supine FVC, and if sitting FVC is less than 80%. Blood gases should also be performed if there is any suspicion of respiratory compromise. Nocturnal CO2 monitoring or polysomnography with CO2 monitoring should be performed if oximetry is unavailable or abnormal (i.e., baseline under 94% and/or dropping below 90%). Polysomnography may also provide a differential diagnosis in cases of obstructive sleep apnea.
RESPIRATORY CARE IN NEUROMUSCULAR DISORDERS
TREATMENT OF THE PULMONARY INVOLVEMENT Treatment of respiratory insufficiency includes cough assistance and ventilatory support. The literature does not provide support for respiratory muscle training, although appropriate studies may not have been done.
Cough assistance A standard hand or mechanical percussor for percussion and postural drainage, or high frequency chest wall oscillation (otherwise referred to as the vest), have been used under these circumstances but their application in neuromuscular diseases has not been systematically evaluated. The literature supports the use of assisted coughing allowing noninvasive ventilation (Finder, 2010). This can be done by a variety of means, ranging from the simplest manual maneuvers such as the chest or abdominal thrust to chest insufflation in order to improve volume of air in the chest to help achieve a more effective cough flow. Chest insufflation can be done by breath stacking with glossopharyngeal breathing (frog breathing), an AMBU bag, intermittent positive pressure breathing (IPPB) (Dohna-Schwake et al., 2006) and noninvasive positive pressure ventilation (NPPV). Mechanical insufflation-exsufflation (MI-E) (Miske et al., 2004; Vianello et al., 2005) and intrapulmonary percussive ventilation (IPV) (Birnkrant et al., 1996; Reardon et al., 2005; Toussaint et al., 2003) have also proven useful for insufflation as well as the treatment of atelectasis and the clearance of secretions. MI-E adds to this a negative pressure following insufflation in order to enhance expiratory flow and secretion clearance.
Ventilatory support Long-term positive pressure ventilation is required when spontaneous efforts of respiratory muscle are no longer able to sustain adequate alveolar ventilation, causing chronic stable or slowly progressive ventilatory failure. Once transient factors of deterioration (i.e., respiratory infection, congestive heart failure, severe electrolyte disturbance, etc.) have been treated successfully, the indications for NPPV are symptomatic daytime hypercapnia, symptomatic nocturnal hypoventilation ( pCO2 of 50 for 50% of sleep time), failure to thrive, recurrent chest infections (>3 a year) and non-symptomatic nocturnal hypercapnia or hypopneas on an individual basis (Consensus Conference, 1999; Tzeng and Bach, 2000; Vianello et al., 2000; Katz et al., 2004; Hess, 2006). There are conditions in which chronic invasive ventilation is required via tracheostomy. These include recurrent aspiration, severe bulbar involvement, inability to tolerate NPPV, ineffective NPPV, severe retention of
1487
secretions not controlled by noninvasive measures, and ventilatory dependency for more than 20 hours a day.
NONINVASIVE POSITIVE PRESSURE VENTILATION In recent years, the administration of long-term noninvasive positive pressure ventilation (NPPV), usually at home, has become a widespread treatment for neuromuscular (NM) patients with advanced respiratory impairment, mostly due to the availability of comfortable nasal interfaces, efficient bilevel positive airway pressure (BPAP) ventilators with sensitive trigger and appropriate training of the physician. Administration of NPPV to NM patients with chronic hypoventilation may be expected to improve physiological function and quality of life as well as decrease the frequency of episodes requiring acute care facilities. In particular, nocturnal respiratory failure is reversed and daytime arterial blood gas values during spontaneous ventilation tend to normalize promptly after the initiation of NPPV. Thanks to these advantages, in recent years NPPV has assumed a central role in the management of NM patients (Hess, 2006; Tzeng and Bach, 2000; Katz et al., 2004; Ward et al., 2005). There may be a role for chronic NPPV in congenital disorders in the setting of recurrent infection or poor weight gain even in the absence of chronic hypoventilation, or after a patient has been intubated for acute respiratory failure. NPPV has also been used to support lung growth in the absence of chronic hypoventilation and after a rapid decline in pulmonary function tests. Data are accumulating regarding the management of respiratory failure due to Duchenne muscular dystrophies. Evidence on the natural history and management in other childhood NMD is more limited. The institution of NPPV needs to be monitored overnight with pulse oximetry and serial blood gases or polysomnogram, during which the appropriateness of the mask interface, the need for a chin strap and the response to ventilation can be assessed. A possible complication of long-term NPPV with a facial mask interface, when initiated in the young child, is distortion of midface structure and atrophy that require subsequent orofacial surgery. The use of individually fitted masks or alternating between different types of nasal interfaces may help prevent midface atrophy. Facial masks must only be used in patients having the ability to remove it themselves.
INVASIVE POSITIVE PRESSURE VENTILATION There are conditions in which chronic invasive ventilation with tracheostomy is required. This can occur in case of severe bulbar involvement leading to chronic aspiration and repeated pneumonia or with ineffective clearing of tracheobronchial secretions, despite the use of
1488
B. ESTOURNET
noninvasive manual or mechanical expiratory aids. A tracheostomy may also be required if the patient is unable to tolerate the NPPV or needs ventilatory support for more than 20 hours a day (Consensus Conference, 1999). Based on patient preference, cultural issues or safety concerns (lack of caregiver ability to provide necessary monitoring), a tracheostomy could be performed electively, before the patient has developed major complications of chronic respiratory failure.
PULMONARY CARE IN NEUROMUSCULAR PATIENTS Preventive care There are several therapeutic options to maintain the patient’s health in stable condition (Wang et al., 2007). Methods that improve cough efficiency and improve volume recruitment should be used in any patient with an inadequate cough. MI-E is generally considered as standard for the care of patients with an inadequate cough. It is effective in mobilizing secretions and preventing pulmonary morbidity during upper respiratory tract infections. However, since its success is less likely if initiated during a respiratory crisis, the use of MI-E once a day is recommended in the stable patient in order to maintain skills for use during illness as its successful use is less likely if initiated during a respiratory crisis. Other methods of passive insufflation, such as regular use of IPV or a breath stacking AMBU-bag, can also be recommended in the stable patient to maintain thoracic compliance and reduce the risk of chronic atelectasis (Armstrong, 2009). The use of daily IPV regimen may contribute to pulmonary recruitment and improve vital capacity and its subsequent maintenance in the patient with diminished pulmonary function especially in congenital disorders. Other factors that contribute to pulmonary impairment need to be addressed. Airway obstruction is unusual in NMD but may be consistent with a diagnosis of asthma and treatment with bronchodilators and inhaled steroids is appropriate. Patients with muscle weakness may be prone to gastroesophageal reflux and delayed gastric emptying. Treatment with an H2 antagonist/proton pump inhibitor and a prokinetic agent may be indicated. If there are symptoms of aspiration such as cough, choking, swallowing difficulties, poor feeding, or failure to thrive, speech therapy would be recommended. Thickened food or an alternate method of feeding may need to be utilized. Consistent oral care is also recommended. Pneumococcal and influenza vaccination is suggested for any patient with congenital muscular dystrophy (CMD) as well as respiratory syncitial virus (RSV)
prophylaxis with palivizumab (Synagis) for any child under the age of 2 years. Spinal bracing is required to ensure functional sitting posture and to delay the progression of scoliosis in order to allow adequate thoracic growth for optimal timing of spinal fusion. Spirometry both with and without the brace is recommended to evaluate the impact on respiratory function.
MANAGEMENT OFACUTE ILLNESSES Respiratory tract infections are the most common cause of hospital admissions and death in NMD patients with respiratory muscle involvement. When a child with NMD presents with an acute infection several issues should be considered: 1.
2.
3.
4.
First, the severity of the underlying disease. Parents or primary caregivers are often a reliable source of information regarding the patient’s disease, its severity, and the patient’s normal baseline status. Signs of respiratory distress may be subtle. It is important to notice whether the child has become somnolent, or has a decreased appetite. Retractions, tachycardia, tachypnea can be seen, cough may be weaker and oxygen saturation lower than baseline or under 94%. These signs indicate the need for expedited evaluation of the patient’s respiratory status using various modalities described below, including: peak cough flow, pulse oximetry, chest radiographs and blood work-up. If the patient is already on NPPV at the time of the acute illness, such symptoms may require re-evaluation of the ventilator settings. To evaluate the severity of an acute illness, one can begin by assessing the effectiveness of cough, either using a peak cough flow or asking the patient to cough. Pulse oximetry can quickly demonstrate the presence of hypoxemia. If oxygen saturation is low, additional oxygen may be required but blood gas should then be obtained since oxygen delivered alone may decrease the respiratory drive. If there is evidence of acute CO2 retention or muscular exhaustion, it is appropriate to provide positive pressure ventilation. Chest radiographs contribute to disclose pneumonia and atelectasis, but comparison with a previous film may be needed to accurately evaluate lung fields in patients with severe scoliosis. Respiratory treatments should be intensified by the addition or increased frequency of cough assistance. If patients are on NPPV at home, they are encouraged to be consistent with, or increase its use during acute infections. If chest physiotherapy (CPT) is performed on a patient who uses NPPV he
RESPIRATORY CARE IN NEUROMUSCULAR DISORDERS should be on the ventilator during CPT. If the patient experiences respiratory failure, NPPV should be initiated first, only moving on to invasive ventilation with intubation in case of failure of NPPV, inability to clear secretions with cough assistance and suctioning, or loss of the ability to protect the airway with a high risk of aspiration (Vianello et al., 2000).
PRE- AND POSTSURGICAL MANAGEMENT Another context in which an intensive proactive multidisciplinary approach should be instituted is prior to any surgical procedure requiring anesthesia, sedation, or a prolonged period of supine posture. Respiratory problems and nutritional condition must be evaluated. Common surgical operations in NMD include scoliosis repair and contracture releases. Preoperative assessment should include an evaluation of cough and overnight oximetry in patients at risk. If not already applied, the patient should be trained prior to surgery with a method to assist coughing, particularly MI-E. If by any chance the patient may require assisted ventilation after surgery, NPPV should be introduced preoperatively. If the patient has been on NPPV at home he should be consistent with its use prior to surgery. This will allow earlier and safer extubation to NPPV following surgery. Patients and families need to be taught how to use all equipment prior to surgery and have it available postoperatively. Nutrition should also be addressed before surgery. Nutritional supplementation for patients with borderline respiratory failure should be limited since carbohydrates are metabolized into carbon dioxide which is an additional burden to ventilation.
CONCLUSION The key to care of the respiratory problems in neuromuscular disorders is a proactive, preventive approach. Careful monitoring of symptoms, regular assessment of pulmonary function, appropriate presurgical management, and aggressive treatment of respiratory infections must be considered a standard of care. More research is needed in recognition and evaluation of early respiratory symptoms of infants and the use of insufflation techniques in an attempt to preserve pulmonary function and decrease the risk of respiratory infections.
REFERENCES Armstrong A (2009). Developing a breath-stacking system to achieve lung volume recruitment. Br J Nurs 18: 1166–1169.
1489
Birnkrant DJ, Pope JF, Lewarski J et al. (1996). Persistent pulmonary consolidation treated with intrapulmonary percussive ventilation: a preliminary report. Pediatr Pulmonol 21: 246–249. Consensus Conference (1996). Clinical indications for noninvasive positive pressure ventilation in chronic respiratory failure due to restrictive lung disease COPD and nocturnal hypoventilation. A Consensus Conference report. Chest 116: 1999 521–534. Dohna-Schwake C, Ragette R, Mellies U et al. (2004). Respiratory function in congenital muscular dystrophy and limb-girdle muscular dystrophy. Neurology 62: 513–514. Dohna-Schwake C, Ragette R, Teschler H et al. (2006). IPPBassisted coughing in neuromuscular disorders. Pediatr Pulmonol 41: 551–557. Finder JD (2010). Airway clearance modalities in neuromuscular disease. Paediatr Respir Rev 11: 31–34. Gaultier C, Zinman R (1983). Maximal static pressures in healthy children. Respir Physiol 51: 45–61. Gozal D (2000). Pulmonary manifestations of neuromuscular disease with special reference to Duchenne muscular dystrophy and spinal muscle atrophy. Pediatr Pulmonol 29: 141–150. Heijdra YF, Dekhuijzen PN, van Herwaarden CL et al. (1993). Differences between sniff mouth pressures and static maximal inspiratory mouth pressures. Eur Respir J 6: 541–546. Hess D (2006). Noninvasive ventilation in neuromuscular disease: equipment and application. Respir Care 51: 896–912. Katz S, Selvadurai H, Keilty K et al. (2004). Outcome of noninvasive positive pressure ventilation in paediatric neuromuscular disease. Arch Dis Child 89: 121–124. Kennedy JD, Martin AJ (2009). Chronic respiratory failure and neuromuscular disease. Pediatr Clin North Am 56: 261–273. Mellies U, Ragette R, Schwake C et al. (2001a). Sleepdisordered breathing and respiratory failure in acid maltase deficiency. Neurology 57: 1290–1295. Mellies U, Schultze S, Schwake C et al. (2001b). Respiratory muscle function in 300 healthy children. Eur Resp J 18: P827 (Abstract). Mellies U, Dohna-Schwake C, Voit T (2005). Respiratory function assessment and intervention in neuromuscular disorders. Curr Opin Neurol 18: 543–547. Miske LJ, Hickney EM, Kolb SM et al. (2004). Use of the mechanical in-exsufflator in pediatric patients with neuromuscular disease and impaired cough. Chest 125: 1406–1412. Reardon CC, Christiansen D, Barnett E et al. (2005). Intrapulmonary percussive ventilation vs. incentive spirometry for children with neuromuscular disease. Arch Pediatr Adolesc Med 159: 526–531. Shahrizaila N, Kinnear WJM, Wills AJ (2006). Respiratory involvement in inherited primary muscle conditions. J Neurol Neurosurg Psychiatry 77: 1108–1111. Stefanutti D, Fitting JW (1999). Sniff nasal inspiratory pressure. Reference values in Caucasian children. Am J Respir Crit Care Med 159: 107–111. Toussaint M, De Win H, Steens M et al. (2003). Effect of intrapulmonary percussive ventilation on mucus clearance in
1490
B. ESTOURNET
Duchenne muscular dystrophy patients: a preliminary report. Respir Care 48: 940–947. Tzeng A, Bach J (2000). Prevention of pulmonary morbidity for patients with neuromuscular disease. Chest 118: 1390–1396. Vianello A, Bevilacqua M, Arcaro G et al. (2000). Noninvasive ventilatory approach to treatment of acute respiratory failure in neuromuscular disorders. A comparison with endotracheal intubation. Intensive Care Med 26: 384–390. Vianello A, Corrado A, Arcaro G et al. (2005). Mechanical insufflation-exsufflation improves outcomes for neuromuscular disease patients with respiratory tract infections. Am J Phys Med Rehabil 84: 83–88.
Wallgrin-Pettersson C, Bushby K, Mellies U et al. (2004). 117th ENMC Workshop: Ventilatory Support in Congenital Neuromuscular Disorders-Congenital Myopathies, Congenital Muscular Dystrophies, Congenital Myotonic Dystrophy and SMA (II); 4–6 April 2003, Naarden, The Netherlands. Neuromuscul Disord 14: 56–69. Wang CH, Finkel RS, Bertini ES et al. (2007). Consensus statement for standard of care in spinal muscular atrophy. J Child Neurol 22: 1027–1049. Ward S, Chatwin M, Heather S et al. (2005). Randomised controlled trail of non-invasive ventilation (NIV) for nocturnal hypoventilation in neuromuscular and chest wall disease patients with daytime normocapnia. Thorax 60: 1019–1024.
Chapter 153
Respiratory care in neuromuscular disorders B. ESTOURNET* Reference Center for Neuromuscular Diseases, Raymond Poincar Hospital, Garches, France
INTRODUCTION Neuromuscular disorders (NMD) presenting in childhood are numerous and represent a group in which the involvement of respiratory muscles is common. Deterioration in respiratory function occurs insidiously, contributes to significant morbidity, and is often responsible for mortality. Since symptoms of respiratory involvement are not obvious, especially in the presence of otherwise stable muscular function and maintained ambulation, respiratory failure must be systematically sought for early care.
●
●
CAUSES OF RESPIRATORY INSUFFICIENCY Causes for respiratory insufficiency are numerous: ●
●
●
●
Respiratory muscle paralysis: in myopathies, the diaphragm is more involved than intercostal muscles and vital capacity is better in the sitting position, whereas in spinal muscular atrophy intercostals are weaker and the best position is the lying one. Abdominal muscles are weak in all instances, impeding an effective cough. Decrease in pulmonary growth in congenital diseases: the alveolar number increases rapidly from birth to 4 years of age. Congenital diseases with respiratory muscle involvement always delay this growth and contribute to respiratory insufficiency. Cough deficit increases bronchial congestion and pulmonary infections: paralysis of inspiratory muscles reduces the volume of inspired air, and, paralysis of expiratory muscles impedes pressure increase with glottic closing and expulsion of secretions. Swallowing problems and gastroesophageal reflux are frequent and increase bronchial congestion. especially during the night.
●
Upper airways obstruction: facial growth abnormalities such as maxillary hypoplasia, macroglossia, and/ or tonsil obstruction produce obstructive apnea that is worsened by pharyngeal hypotonia. This augments muscular work and worsens muscular fatigue. Sleep disorders: these are frequent if the vital capacity (VC) is under 40%. They often occur in deep sleep because of muscular hypotonia. In some diseases, sleep disorders occur even when VC remains normal: selenopathies, Steinert disease, or Duchenne muscular dystrophy. Nocturnal hypoventilation produces pulmonary hypertension and acute respiratory failure so it must be sought especially where clinical signs such as headaches, nocturnal sweating, and snoring are present. Orthopedic deformities, especially lordoscoliosis, are frequent in these disorders and worsen respiratory insufficiency.
Respiratory involvement can vary considerably. according to and within each muscular disorder, for the type and severity of symptoms, and both the age and ambulatory status of the patient when symptoms occur (Gozal, 2000; Dohna-Schwake et al., 2004; Shahrizaila et al., 2006; Kennedy and Martin, 2009). Infants and children under 2 years of age may not show typical symptoms of respiratory distress because of profound weakness. Tachypnea and retractions can be seen but respiratory problems cannot be ruled out in their absence. Signs and symptoms described in congenital disorders include weak cry, ineffective cough, choking on feedings or secretions, in addition to weight loss or poor weight gain. These signs and symptoms, along with recurrent respiratory infections, irritability, or a paradoxical breathing pattern, can be the first expression of respiratory involvement (Wallgrin-Pettersson et al., 2004; Shahrizaila
*Correspondence to: B. Estournet, Me´decine Physique et de Re´adaptation Pe´diatriques, Hoˆpital Raymond Poincare´, 92380 Garches, France. E-mail: [email protected]
1486
B. ESTOURNET
et al., 2006). Older children, adolescents, and adults may present with symptoms similar to those of younger children with weight loss, aspiration, and recurrent infections. Typical symptoms of respiratory failure such as breathlessness may not be seen because of motor weakness.
ASSESSMENT OF RESPIRATORY STATUS In neuromuscular weakness, assessment of respiratory status is based mainly on pulmonary function tests. Forced vital capacity (FVC in % predicted) should be performed annually. It is particularly important to perform the measurement in a sitting and supine position since a difference of > 20% between the sitting and supine FVC indicates diaphragmatic weakness and is a predictor of nocturnal hypoventilation (Wallgrin-Pettersson et al., 2004; Mellies et al., 2005). An FVC less than 60% of that predicted is a good predictor of sleep breathing disorder and < 40% it indicates nocturnal hypoventilation. Another test of pulmonary function includes measurement of maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) (Gaultier and Zinman, 1983; Heijdra et al., 1993; Stefanutti and Fitting, 1999; Mellies et al., 2001b, 2005; WallgrinPettersson et al., 2004; Shahrizaila et al., 2006). Normal values of MIP and MEP are 80–120 cm H2O. Values are available for Duchenne muscular dystrophy. A value of less than 60 cm H2O suggests symptomatic respiratory impairment, and 20 cm H2O or less the likely requirement of assisted ventilation (Gozal, 2000). A MIP less than the MEP is an indicator of diaphragmatic weakness. Peak cough flow, polysomnography, and blood gases are also used (Mellies et al., 2001b; Wallgrin-Pettersson et al., 2004; Shahrizaila et al., 2006). A peak cough flow will help estimate a patient’s ability to clear secretions. It can be obtained with a simple peak flow meter although in children or adults with facial weakness a mask may be required to achieve a reliable value. In children, a cough flow of > 160 L/min is required to adequately clear secretions, in adults > 200 L/min. In addition to measuring peak cough flow it is worthwhile to ask the child to cough in order to assess its effectiveness. Polysomnograms can detect or confirm sleep breathing disorders and should include end tidal CO2 monitoring or transcutaneous CO2 monitoring. Arterial or capillary blood gases are also used to assess respiratory failure (Dohna-Schwake et al., 2004; WallgrinPettersson et al., 2004; Shahrizaila et al., 2006).
DIAGNOSIS OF PULMONARY INVOLVEMENT A proactive approach is recommended in order to recognize early symptoms before the condition becomes more severe. Specific detailed questioning and annual
respiratory monitoring are most helpful (Mellies et al., 2001a; Wallgrin-Pettersson et al., 2004). Early symptoms may be subtle and include disturbed sleep, increased need to turn at night, feeling unrefreshed when waking in the morning, tiredness, mood disturbances, and poor concentration during daytime. These symptoms may be related to hypoxemia overnight and progress to more severe symptoms, including: morning headaches, nausea, the use of accessory muscles, fear of going to sleep, and nightmares which tend to be associated with daytime and nighttime hypercapnia. Both early and late symptoms associated with abnormal blood gases can also be associated with recurrent chest infections, swallowing difficulties, and weight loss or poor weight gain. Scoliosis, especially lordoscoliosis, and chest wall deformities add to the restrictive lung disease created by weak chest muscles, a weakened diaphragm, and atelectasis. If the patient is able to perform spirometry, FVC measurement and calculation of FVC/TFVC ratio should be performed. For patients unable to perform standard spirometry secondary to age or developmental delay, a cry vital capacity (VC) can be obtained by placing a tight fitting mask over the nose and mouth with a spirometer in line. The cry will give an approximation of a forced vital capacity (FVC). If the patient does not cry, which may be the case in children > 2 years or in a very weak infant, a tidal volume (TV) measurement can be obtained. Diaphragmatic involvement is often asymptomatic and requires a high index of suspicion in patients who are still ambulatory (SEPN1-related myopathies, collagen VI and lamin A/C). In these subtypes, respiratory failure may occur while patients are still ambulatory, requiring a different perspective than in Duchenne muscular dystrophy where the loss of ambulation marks the onset of respiratory involvement. Regular monitoring of pulmonary function may predict potential changes in a patient’s health before it becomes precarious. Spirometry is a routine evaluation that should be done at each clinic visit, and at least annually. Nocturnal oximetry should be added if there are signs or symptoms of respiratory compromise, if the FVC is below 60% of predicted or if there is a more than a 20% difference between sitting and supine FVC, and if sitting FVC is less than 80%. Blood gases should also be performed if there is any suspicion of respiratory compromise. Nocturnal CO2 monitoring or polysomnography with CO2 monitoring should be performed if oximetry is unavailable or abnormal (i.e., baseline under 94% and/or dropping below 90%). Polysomnography may also provide a differential diagnosis in cases of obstructive sleep apnea.
RESPIRATORY CARE IN NEUROMUSCULAR DISORDERS
TREATMENT OF THE PULMONARY INVOLVEMENT Treatment of respiratory insufficiency includes cough assistance and ventilatory support. The literature does not provide support for respiratory muscle training, although appropriate studies may not have been done.
Cough assistance A standard hand or mechanical percussor for percussion and postural drainage, or high frequency chest wall oscillation (otherwise referred to as the vest), have been used under these circumstances but their application in neuromuscular diseases has not been systematically evaluated. The literature supports the use of assisted coughing allowing noninvasive ventilation (Finder, 2010). This can be done by a variety of means, ranging from the simplest manual maneuvers such as the chest or abdominal thrust to chest insufflation in order to improve volume of air in the chest to help achieve a more effective cough flow. Chest insufflation can be done by breath stacking with glossopharyngeal breathing (frog breathing), an AMBU bag, intermittent positive pressure breathing (IPPB) (Dohna-Schwake et al., 2006) and noninvasive positive pressure ventilation (NPPV). Mechanical insufflation-exsufflation (MI-E) (Miske et al., 2004; Vianello et al., 2005) and intrapulmonary percussive ventilation (IPV) (Birnkrant et al., 1996; Reardon et al., 2005; Toussaint et al., 2003) have also proven useful for insufflation as well as the treatment of atelectasis and the clearance of secretions. MI-E adds to this a negative pressure following insufflation in order to enhance expiratory flow and secretion clearance.
Ventilatory support Long-term positive pressure ventilation is required when spontaneous efforts of respiratory muscle are no longer able to sustain adequate alveolar ventilation, causing chronic stable or slowly progressive ventilatory failure. Once transient factors of deterioration (i.e., respiratory infection, congestive heart failure, severe electrolyte disturbance, etc.) have been treated successfully, the indications for NPPV are symptomatic daytime hypercapnia, symptomatic nocturnal hypoventilation ( pCO2 of 50 for 50% of sleep time), failure to thrive, recurrent chest infections (>3 a year) and non-symptomatic nocturnal hypercapnia or hypopneas on an individual basis (Consensus Conference, 1999; Tzeng and Bach, 2000; Vianello et al., 2000; Katz et al., 2004; Hess, 2006). There are conditions in which chronic invasive ventilation is required via tracheostomy. These include recurrent aspiration, severe bulbar involvement, inability to tolerate NPPV, ineffective NPPV, severe retention of
1487
secretions not controlled by noninvasive measures, and ventilatory dependency for more than 20 hours a day.
NONINVASIVE POSITIVE PRESSURE VENTILATION In recent years, the administration of long-term noninvasive positive pressure ventilation (NPPV), usually at home, has become a widespread treatment for neuromuscular (NM) patients with advanced respiratory impairment, mostly due to the availability of comfortable nasal interfaces, efficient bilevel positive airway pressure (BPAP) ventilators with sensitive trigger and appropriate training of the physician. Administration of NPPV to NM patients with chronic hypoventilation may be expected to improve physiological function and quality of life as well as decrease the frequency of episodes requiring acute care facilities. In particular, nocturnal respiratory failure is reversed and daytime arterial blood gas values during spontaneous ventilation tend to normalize promptly after the initiation of NPPV. Thanks to these advantages, in recent years NPPV has assumed a central role in the management of NM patients (Hess, 2006; Tzeng and Bach, 2000; Katz et al., 2004; Ward et al., 2005). There may be a role for chronic NPPV in congenital disorders in the setting of recurrent infection or poor weight gain even in the absence of chronic hypoventilation, or after a patient has been intubated for acute respiratory failure. NPPV has also been used to support lung growth in the absence of chronic hypoventilation and after a rapid decline in pulmonary function tests. Data are accumulating regarding the management of respiratory failure due to Duchenne muscular dystrophies. Evidence on the natural history and management in other childhood NMD is more limited. The institution of NPPV needs to be monitored overnight with pulse oximetry and serial blood gases or polysomnogram, during which the appropriateness of the mask interface, the need for a chin strap and the response to ventilation can be assessed. A possible complication of long-term NPPV with a facial mask interface, when initiated in the young child, is distortion of midface structure and atrophy that require subsequent orofacial surgery. The use of individually fitted masks or alternating between different types of nasal interfaces may help prevent midface atrophy. Facial masks must only be used in patients having the ability to remove it themselves.
INVASIVE POSITIVE PRESSURE VENTILATION There are conditions in which chronic invasive ventilation with tracheostomy is required. This can occur in case of severe bulbar involvement leading to chronic aspiration and repeated pneumonia or with ineffective clearing of tracheobronchial secretions, despite the use of
1488
B. ESTOURNET
noninvasive manual or mechanical expiratory aids. A tracheostomy may also be required if the patient is unable to tolerate the NPPV or needs ventilatory support for more than 20 hours a day (Consensus Conference, 1999). Based on patient preference, cultural issues or safety concerns (lack of caregiver ability to provide necessary monitoring), a tracheostomy could be performed electively, before the patient has developed major complications of chronic respiratory failure.
PULMONARY CARE IN NEUROMUSCULAR PATIENTS Preventive care There are several therapeutic options to maintain the patient’s health in stable condition (Wang et al., 2007). Methods that improve cough efficiency and improve volume recruitment should be used in any patient with an inadequate cough. MI-E is generally considered as standard for the care of patients with an inadequate cough. It is effective in mobilizing secretions and preventing pulmonary morbidity during upper respiratory tract infections. However, since its success is less likely if initiated during a respiratory crisis, the use of MI-E once a day is recommended in the stable patient in order to maintain skills for use during illness as its successful use is less likely if initiated during a respiratory crisis. Other methods of passive insufflation, such as regular use of IPV or a breath stacking AMBU-bag, can also be recommended in the stable patient to maintain thoracic compliance and reduce the risk of chronic atelectasis (Armstrong, 2009). The use of daily IPV regimen may contribute to pulmonary recruitment and improve vital capacity and its subsequent maintenance in the patient with diminished pulmonary function especially in congenital disorders. Other factors that contribute to pulmonary impairment need to be addressed. Airway obstruction is unusual in NMD but may be consistent with a diagnosis of asthma and treatment with bronchodilators and inhaled steroids is appropriate. Patients with muscle weakness may be prone to gastroesophageal reflux and delayed gastric emptying. Treatment with an H2 antagonist/proton pump inhibitor and a prokinetic agent may be indicated. If there are symptoms of aspiration such as cough, choking, swallowing difficulties, poor feeding, or failure to thrive, speech therapy would be recommended. Thickened food or an alternate method of feeding may need to be utilized. Consistent oral care is also recommended. Pneumococcal and influenza vaccination is suggested for any patient with congenital muscular dystrophy (CMD) as well as respiratory syncitial virus (RSV)
prophylaxis with palivizumab (Synagis) for any child under the age of 2 years. Spinal bracing is required to ensure functional sitting posture and to delay the progression of scoliosis in order to allow adequate thoracic growth for optimal timing of spinal fusion. Spirometry both with and without the brace is recommended to evaluate the impact on respiratory function.
MANAGEMENT OFACUTE ILLNESSES Respiratory tract infections are the most common cause of hospital admissions and death in NMD patients with respiratory muscle involvement. When a child with NMD presents with an acute infection several issues should be considered: 1.
2.
3.
4.
First, the severity of the underlying disease. Parents or primary caregivers are often a reliable source of information regarding the patient’s disease, its severity, and the patient’s normal baseline status. Signs of respiratory distress may be subtle. It is important to notice whether the child has become somnolent, or has a decreased appetite. Retractions, tachycardia, tachypnea can be seen, cough may be weaker and oxygen saturation lower than baseline or under 94%. These signs indicate the need for expedited evaluation of the patient’s respiratory status using various modalities described below, including: peak cough flow, pulse oximetry, chest radiographs and blood work-up. If the patient is already on NPPV at the time of the acute illness, such symptoms may require re-evaluation of the ventilator settings. To evaluate the severity of an acute illness, one can begin by assessing the effectiveness of cough, either using a peak cough flow or asking the patient to cough. Pulse oximetry can quickly demonstrate the presence of hypoxemia. If oxygen saturation is low, additional oxygen may be required but blood gas should then be obtained since oxygen delivered alone may decrease the respiratory drive. If there is evidence of acute CO2 retention or muscular exhaustion, it is appropriate to provide positive pressure ventilation. Chest radiographs contribute to disclose pneumonia and atelectasis, but comparison with a previous film may be needed to accurately evaluate lung fields in patients with severe scoliosis. Respiratory treatments should be intensified by the addition or increased frequency of cough assistance. If patients are on NPPV at home, they are encouraged to be consistent with, or increase its use during acute infections. If chest physiotherapy (CPT) is performed on a patient who uses NPPV he
RESPIRATORY CARE IN NEUROMUSCULAR DISORDERS should be on the ventilator during CPT. If the patient experiences respiratory failure, NPPV should be initiated first, only moving on to invasive ventilation with intubation in case of failure of NPPV, inability to clear secretions with cough assistance and suctioning, or loss of the ability to protect the airway with a high risk of aspiration (Vianello et al., 2000).
PRE- AND POSTSURGICAL MANAGEMENT Another context in which an intensive proactive multidisciplinary approach should be instituted is prior to any surgical procedure requiring anesthesia, sedation, or a prolonged period of supine posture. Respiratory problems and nutritional condition must be evaluated. Common surgical operations in NMD include scoliosis repair and contracture releases. Preoperative assessment should include an evaluation of cough and overnight oximetry in patients at risk. If not already applied, the patient should be trained prior to surgery with a method to assist coughing, particularly MI-E. If by any chance the patient may require assisted ventilation after surgery, NPPV should be introduced preoperatively. If the patient has been on NPPV at home he should be consistent with its use prior to surgery. This will allow earlier and safer extubation to NPPV following surgery. Patients and families need to be taught how to use all equipment prior to surgery and have it available postoperatively. Nutrition should also be addressed before surgery. Nutritional supplementation for patients with borderline respiratory failure should be limited since carbohydrates are metabolized into carbon dioxide which is an additional burden to ventilation.
CONCLUSION The key to care of the respiratory problems in neuromuscular disorders is a proactive, preventive approach. Careful monitoring of symptoms, regular assessment of pulmonary function, appropriate presurgical management, and aggressive treatment of respiratory infections must be considered a standard of care. More research is needed in recognition and evaluation of early respiratory symptoms of infants and the use of insufflation techniques in an attempt to preserve pulmonary function and decrease the risk of respiratory infections.
REFERENCES Armstrong A (2009). Developing a breath-stacking system to achieve lung volume recruitment. Br J Nurs 18: 1166–1169.
1489
Birnkrant DJ, Pope JF, Lewarski J et al. (1996). Persistent pulmonary consolidation treated with intrapulmonary percussive ventilation: a preliminary report. Pediatr Pulmonol 21: 246–249. Consensus Conference (1996). Clinical indications for noninvasive positive pressure ventilation in chronic respiratory failure due to restrictive lung disease COPD and nocturnal hypoventilation. A Consensus Conference report. Chest 116: 1999 521–534. Dohna-Schwake C, Ragette R, Mellies U et al. (2004). Respiratory function in congenital muscular dystrophy and limb-girdle muscular dystrophy. Neurology 62: 513–514. Dohna-Schwake C, Ragette R, Teschler H et al. (2006). IPPBassisted coughing in neuromuscular disorders. Pediatr Pulmonol 41: 551–557. Finder JD (2010). Airway clearance modalities in neuromuscular disease. Paediatr Respir Rev 11: 31–34. Gaultier C, Zinman R (1983). Maximal static pressures in healthy children. Respir Physiol 51: 45–61. Gozal D (2000). Pulmonary manifestations of neuromuscular disease with special reference to Duchenne muscular dystrophy and spinal muscle atrophy. Pediatr Pulmonol 29: 141–150. Heijdra YF, Dekhuijzen PN, van Herwaarden CL et al. (1993). Differences between sniff mouth pressures and static maximal inspiratory mouth pressures. Eur Respir J 6: 541–546. Hess D (2006). Noninvasive ventilation in neuromuscular disease: equipment and application. Respir Care 51: 896–912. Katz S, Selvadurai H, Keilty K et al. (2004). Outcome of noninvasive positive pressure ventilation in paediatric neuromuscular disease. Arch Dis Child 89: 121–124. Kennedy JD, Martin AJ (2009). Chronic respiratory failure and neuromuscular disease. Pediatr Clin North Am 56: 261–273. Mellies U, Ragette R, Schwake C et al. (2001a). Sleepdisordered breathing and respiratory failure in acid maltase deficiency. Neurology 57: 1290–1295. Mellies U, Schultze S, Schwake C et al. (2001b). Respiratory muscle function in 300 healthy children. Eur Resp J 18: P827 (Abstract). Mellies U, Dohna-Schwake C, Voit T (2005). Respiratory function assessment and intervention in neuromuscular disorders. Curr Opin Neurol 18: 543–547. Miske LJ, Hickney EM, Kolb SM et al. (2004). Use of the mechanical in-exsufflator in pediatric patients with neuromuscular disease and impaired cough. Chest 125: 1406–1412. Reardon CC, Christiansen D, Barnett E et al. (2005). Intrapulmonary percussive ventilation vs. incentive spirometry for children with neuromuscular disease. Arch Pediatr Adolesc Med 159: 526–531. Shahrizaila N, Kinnear WJM, Wills AJ (2006). Respiratory involvement in inherited primary muscle conditions. J Neurol Neurosurg Psychiatry 77: 1108–1111. Stefanutti D, Fitting JW (1999). Sniff nasal inspiratory pressure. Reference values in Caucasian children. Am J Respir Crit Care Med 159: 107–111. Toussaint M, De Win H, Steens M et al. (2003). Effect of intrapulmonary percussive ventilation on mucus clearance in
1490
B. ESTOURNET
Duchenne muscular dystrophy patients: a preliminary report. Respir Care 48: 940–947. Tzeng A, Bach J (2000). Prevention of pulmonary morbidity for patients with neuromuscular disease. Chest 118: 1390–1396. Vianello A, Bevilacqua M, Arcaro G et al. (2000). Noninvasive ventilatory approach to treatment of acute respiratory failure in neuromuscular disorders. A comparison with endotracheal intubation. Intensive Care Med 26: 384–390. Vianello A, Corrado A, Arcaro G et al. (2005). Mechanical insufflation-exsufflation improves outcomes for neuromuscular disease patients with respiratory tract infections. Am J Phys Med Rehabil 84: 83–88.
Wallgrin-Pettersson C, Bushby K, Mellies U et al. (2004). 117th ENMC Workshop: Ventilatory Support in Congenital Neuromuscular Disorders-Congenital Myopathies, Congenital Muscular Dystrophies, Congenital Myotonic Dystrophy and SMA (II); 4–6 April 2003, Naarden, The Netherlands. Neuromuscul Disord 14: 56–69. Wang CH, Finkel RS, Bertini ES et al. (2007). Consensus statement for standard of care in spinal muscular atrophy. J Child Neurol 22: 1027–1049. Ward S, Chatwin M, Heather S et al. (2005). Randomised controlled trail of non-invasive ventilation (NIV) for nocturnal hypoventilation in neuromuscular and chest wall disease patients with daytime normocapnia. Thorax 60: 1019–1024.