Respiratory Management of Neuromuscular Disorders




Abstract


Physical medicine inspiratory and expiratory muscle aids can be used for patients with progressive neuromuscular disease to prevent acute, chronic, and acute on chronic respiratory failure, to avoid hospitalizations, intubations, and tracheotomies, and can assist, support, and even take the place of the respiratory muscle function. They can permit ventilator “unweanable” intubated patients to be extubated without resort to tracheotomy, and can be used to remove the tracheostomy tubes (decannulate) patients who are dependent on tracheostomy mechanical ventilation to noninvasive alternatives. This approach greatly preserves quality of life, can prolong life by up to 10 years over tracheostomy mechanical ventilation for some conditions, and can reduce nursing costs $300,000 per year per patient. These methods were largely developed and described by physiatrists and deserve wider application.




Keywords

amyotrophic lateral sclerosis, assisted cough, duchenne muscular dystrophy, glossopharyngeal breathing, life expectancy, mechanical insufflation-exsufflation, noninvasive mechanical ventilation, noninvasive ventilatory support, respiratory therapy, spinal muscular atrophy

 









































Synonyms



  • None

ICD-10 Codes
G71.0 Muscular dystrophy G71.0
G12.9 Spinal muscular atrophy
G12.21 Amyotrophic lateral sclerosis
Z99.01 Dependence on respirator
M62.81 Generalized muscle weakness
G12.0 Infantile spinal muscular atrophy type 1
CPT Codes
E0482 Mechanical insufflation-exsufflation
E0466 Noninvasive mechanical ventilation
E0465 Invasive mechanical ventilation




Definition


The three respiratory muscle groups are: the inspiratory muscles, expiratory (predominantly abdominal and upper chest wall) muscles for coughing, and the bulbar-innervated muscles (BIMs). While the inspiratory and expiratory muscles can be completely supported by physical aids such as continuous noninvasive ventilatory support (CNVS) and mechanical insufflation-exsufflation (MIE) and patients have used these and avoided tracheostomy tubes for over 60 years and counting, there are no effective noninvasive measures to assist BIM function. However, even complete paralysis of BIM function does not preclude noninvasive management of chronic ventilatory muscle failure.


Respiratory, or inspiratory and expiratory muscle aids, are devices and techniques that involve the manual or mechanical application of forces to the body, or intermittent pressure changes to the airway, to assist inspiratory and expiratory muscle function. The devices that act on the body include body ventilators that create pressure changes around the thorax and abdomen. Negative pressure applied to the airway during expiration assists coughing just as positive pressure applied to the airway during inhalation (intermittent positive pressure ventilation or noninvasive ventilatory support [NVS]) assists or supports the inspiratory muscles. Continuous positive airway pressure does not assist ventilation and is not useful for patients with ventilatory impairment on the basis of neuromuscular disorders (NMDs).


Respiratory muscle aids can greatly diminish the need to resort to invasive airway tubes, permit long-term survival, and permit the extubation and tracheostomy tube decannulation of ventilator-dependent (“unweanable”) patients. Physical medicine respiratory muscle aids including NVS and MIE can prolong survival for patients with little or no vital capacity (VC) or any ability to cough. Most aspects of this medical discipline were developed by physiatrists.




Symptoms


While patients with diminished ventilatory reserve who are able to walk complain of exertional dyspnea, wheelchair users’ symptoms may be minimal except during intercurrent respiratory infections when they may complain of anxiety, inability to fall asleep, and possibly dyspnea. Morning headaches, fatigue, sleep disturbances, and hypersomnolence result from nocturnal hypoventilation which is due to decreased ability to recruit accessory respiratory muscles, depressed respiratory drive, and cough during sleep.




Physical Examination


Signs of inspiratory muscle impairment and hypoventilation can include tachypnea, paradoxic breathing, hypophonia, nasal flaring, accessory respiratory muscle use, cyanosis, flushing or pallor, anxiety, and airway secretion congestion. Lethargy, obtundation, and confusion signal CO 2 narcosis. Often there are no signs other than tachypnea despite symptoms of hypoventilation.




Functional Limitations


With diminished respiratory reserve, walking becomes limited by dyspnea; however, wheelchair users’ function is typically not limited by hypoventilation until CO 2 levels rise to the point of obtundation.




Diagnostic Studies


Respiratory muscle dysfunction and hypoventilation are diagnosed by CO 2 monitoring (capnograph or transcutaneous), oximetry, spirometry, and assessment of cough peak flows (CPF). End-tidal CO 2 is typically 2 to 6 mm Hg less than arterial PCO 2 .


The VC is measured in sitting and supine positions and their difference should not be greater than 7%. Since hypoventilation begins and is more severe during sleep, the supine VC is the more important. Orthopnea is common when the VC is less than 25% of normal or the VC in supine position is at least 20% less than when sitting. Patients wearing thoracolumbar bracing should have the VC measured both with the brace on and off, since a good fitting brace can increase VC whereas one that restricts abdominal movement can decrease it. Patients are taught glossopharygneal breathing (GPB) and its progress, as well as progress in the use of active (air stacking) and passive (insufflation) methods of lung volume recruitment (LVR), measured spirometrically. Patients air stack by receiving consecutively delivered volumes of air via manual resuscitator or volume-preset ventilator that are held by the glottis to the greatest volume possible. The maximum retained volume is measured spirometrically and termed the “maximum insufflation capacity” (MIC). The maximum passively insufflated volume is termed the “lung insufflation capacity.” Likewise, GPB can often provide volumes of air to or beyond those achieved by air stacking with a manual resuscitator and is also measured spirometrically. A nasal interface or oronasal interface can be used for air stacking when the lips are too weak for air stacking via a mouthpiece. The MIC minus the VC is a direct measure of glottis integrity and, therefore, an objective, quantifiable, reproducible measure of BIM.


CPF are measured using a peak flow meter. CPF below 160 L/m are generally ineffective. The attainment of (unassisted) CPF over 120 L/m is a strong indicator for successful tracheostomy tube decannulation, irrespective of remaining pulmonary function. Patients with VCs less than 1500 mL should have assisted CPF measured from a deep air stacked volume of air with an abdominal thrust delivered simultaneously with glottic opening (manually assisted cough); this assisted CPF is also measured by peak flow meter. The assisted minus unassisted CPF is also solely dependent on glottis function and an indicator of BIM integrity.


For the stable patient without intrinsic pulmonary disease, arterial blood gas sampling is unnecessary and often less accurate, since 25% of patients hyperventilate due to anxiety and pain during the procedure.


For symptomatic patients with normal VC, an unclear pattern of nocturnal oxyhemoglobin desaturation, and no apparent hypercapnia, a polysomnogram is warranted. Polysomnography is unnecessary for symptomatic patients with decreased VC because it is programmed to interpret every apnea and hypopnea as resulting from central or obstructive events rather than from inspiratory muscle weakness.


While all clearly symptomatic patients with diminished lung volumes require a trial of NVS to ease symptoms, if symptoms are questionable, nocturnal continuous capnography and oximetry can be useful and most practically done in the home. A questionably symptomatic patient with decreased VC, multiple nocturnal oxyhemoglobin desaturations below 95%, and elevated CO 2 should be encouraged to try sleep NVS to see if it makes them feel better.




Treatment


The Intervention Objectives


The intervention goals are to promote normal lung and chest-wall growth for children and to maintain lung and chest-wall compliance, to maintain normal alveolar ventilation to prolong survival, and to maximize CPF to avert episodes of pneumonia and respiratory failure, particularly during intercurrent upper respiratory tract infections. Unweanable intubated and cannulated patients can also be extubated and decannulated to CNVS. All goals can be facilitated by evaluating, training, and equipping patients in the outpatient and home setting.


Goal One: Maintain Pulmonary Compliance, Lung Growth, and Chest-Wall Mobility


Pulmonary compliance is diminished, and chest-wall contractures and lung restriction occur when the lungs cannot be expanded to predicted inspiratory capacity because of inspiratory muscle dysfunction. As the VC decreases, the largest breath one can take only expands an increasingly smaller fraction of lung volume. Like limb articulations, regular mobilization is required. This LVR can be achieved passively by providing deep insufflations, actively by air stacking, or for those unable to cooperate for active LVR, by nocturnal NVS. The primary objectives of lung expansion therapy are to increase VC and voice volume, to maximize CPF, to maintain pulmonary compliance, diminish atelectasis, and to master NVS since anyone who can air stack via a mouthpiece can use mouthpiece NVS anytime during the day as well as for successful extubation/decannulation even if not ventilator weaned.


Impaired glottis closure precludes active LVR and indicates need for passive LRV by delivering pressures of 40 to 70 cm H 2 O to the lungs via a pressure-preset ventilator or by using a manual resuscitator with the exhalation valve blocked. In 282 evaluations of VC, MIC, and LIC, the mean values were 1131 ± 744 mL, 1712 ± 926 mL, and 2069 ± 867 mL, respectively.


Before patients’ VCs decrease to 70% or 80% of predicted normal, they are instructed to air stack 10 to 15 times 2 or 3 times daily, usually using a manual resuscitator. Because of the importance of air stacking, NVS is preferentially provided via ventilator volume rather than pressure-preset.


Infants cannot air stack or cooperate with passive insufflation therapy. All small children with paradoxic breathing require nocturnal NVS to prevent pectus excavatum and promote lung growth as well as for inspiratory muscle assistance. Children can become cooperative with passive LVR by 14 to 30 months of age.


Goal Two: Maintain Alveolar Ventilation


Respiratory orthopnea, symptoms of hypoventilation, or paradoxic breathing in children indicate need for nocturnal NVS. Since, in general, only patients improperly treated with supplemental O 2 develop CO 2 narcosis, and since respiratory failure is most often caused by ineffective cough flows and airway secretion management, any patient finding that NVS use is more burdensome than beneficial on symptoms we advise to discontinue it until the next reevaluation.


Because negative pressure body ventilators cause obstructive apneas, are less effective than NVS, and become even less effective with age and decreasing pulmonary compliance, they are no longer recommended for ongoing ventilatory assistance. One useful body ventilator, however, is the intermittent abdominal pressure ventilator (IAPV) (BachBelt, ResMed, Dima Italia, Bologna, Italy). The IAPV involves the intermittent inflation of an elastic air sac that is contained in a corset or belt worn beneath the patient’s outer clothing. The sac is cyclically inflated, often to 2500 mL or more, by a positive pressure ventilator. This moves the diaphragm upward to exsufflate the lungs. With bladder deflation, gravity causes the abdominal contents and diaphragm to return to the resting position and inspiration occurs. A trunk angle of 30 degrees or more from the horizontal is required for effectiveness. A patient can add to the IAPV delivered volume by breathing or using glossopharyngeal breathing along with it. The IAPV augments tidal volumes by 300 to as high as 1200 mL and is often preferred to mouthpiece NVS by patients with little autonomous breathing ability during daytime hours.


Noninvasive ventilatory support can be delivered via lipseals, nasal, and oronasal interfaces during sleep or via mouthpiece or nasal interface during daytime hours. Mouthpiece and nasal NVS are open systems that require the user to rely on central nervous system reflexes to prevent excessive insufflation leakage during sleep; thus, supplemental oxygen and sedatives can render it ineffective. NVS can be introduced in the clinic or home setting.


There are numerous commercially available vented and non-vented interfaces to use. For the delivery of mouthpiece or nasal NVS to permit air stacking, an active ventilator circuit—that is, one with an exhalation valve—should be used along with a non-vented interface or a vented interface with the ports sealed. Several nasal interfaces should be tried for sleep and if nasal NVS is used around-the-clock, the nasal interfaces should be alternated every 12 hours to avoid prolonged skin pressure. Excessive insufflation leakage or air out of the mouth can be avoided if necessary by switching from an open to a closed system by using a nasal prongs-lipseal system. Such interfaces deliver air via mouth and nose during sleep and require minimal strap pressure. This optimizes skin comfort and minimizes air (insufflation) leakage.


The most useful method for daytime NVS is via a 15 mm angled mouthpiece. Although some prefer to keep the mouthpiece in the mouth all day, most have it fixed adjacent to the mouth by a flexible metal support arm (gooseneck clamp) that is attached to their wheelchair. The mouthpiece can also be fixed onto motorized wheelchair controls (e.g., sip and puff, chin, and tongue controls) ( Fig. 151.1 ). Large volumes of 800 to 1500 mL are delivered to adolescents and adults so that the patient can take as much of the air as desired for each breath to vary tidal volumes, speech volume, and cough flows as well as to air stack. Neck movement and lip function are needed to use mouthpiece NVS; otherwise, a nasal prongs system or IAPV is used for daytime support. Nasal NVS is also most practical for nocturnal and daytime use by infants since they are obligate nose breathers. Other than perhaps for uncontrollable seizures and inability to cooperate, there are no contraindications to the use of NVS long term.




FIG. 151.1


A 64-year-old woman who depended on continuous noninvasive ventilatory support (CNVS) since 1953 and CNVS via 15 mm angled mouthpiece for 34 years with the mouthpiece fixed adjacent to the chin control of her motorized wheelchair.


Goal Three: Augment Cough Flows


In a study of manually assisted coughing (air stacking and abdominal thrust) for 364 patients, whereas mean VC was 997 mL, mean MIC was 1648 mL, and although CPFs were 135 L/m, mean assisted CPF were 235 L/m. This can be the difference between developing pneumonia or coughing effectively to prevent it. The inability to generate 160 L/m of assisted CPF despite having a VC or MIC greater than 1 L indicates upper-airway obstruction, which can be due to severe BIM dysfunction or other lesion that should be identified by laryngoscopy to correct reversible lesions.


Mechanically assisted coughing is the use of MIE along with an exsufflation-timed abdominal thrust when this has been demonstrated to further increase exsufflation flows (MIE-EF). MIE insufflation and exsufflation pressures of 50 to 60 cm H 2 O via a mouthpiece or oronasal interface are used unless these pressures cause stridor, in which case flows as low as 40 cm H 2 O may maximize MIE-EF. MIE is also effective via translaryngeal and tracheostomy tubes at pressures of 60 to 70 cm H 2 O. When delivered via invasive airway tubes their cuff, if present, should be inflated. Most MIE devices on the market can be manually or automatically cycled. Manual cycling facilitates caregiver-patient coordination of inspiration and expiration with insufflation and exsufflation, but it requires hands to deliver an abdominal thrust, to hold the interface on the patient, and to operate machine cycling. The pressure preset ventilator can also be used to permit the user to trigger every MIE.


One treatment consists of about five MIE cycles followed by a short period of normal breathing or ventilator use to avoid hyperventilation. Insufflation and exsufflation times are adjusted to provide maximum observable chest expansion, then full lung emptying. In general, 2 to 3 seconds are required. Treatment continues until no further secretions are expulsed and secretion-related oxyhemoglobin desaturations are reversed. Use can be required as often as every 20 minutes around the clock during upper respiratory tract infections.


The use of MIE via the upper airway can be effective for children as young as 11 months of age who can occasionally facilitate its efficacy by not crying or closing the glottis. Between 2.5 and 5 years of age, most children fully cooperate with it. Before that the insufflations and exsufflations are timed to the child’s own breathing cycle or triggered by the child to maintain normal O 2 sat to avert pneumonia and respiratory failure. Triggering can greatly facilitate effective use by infants. While conventional airway suctioning misses the left main stem bronchus about 90% of the time, MIE effectively expulses debris from both left and right airways without the discomfort or airway trauma. Patients prefer it to suctioning. Deep suctioning, whether via tube or upper airway, becomes unnecessary for most patients.


VC, pulmonary flow rates, and oxyhemoglobin saturation (O 2 sat) when abnormal can improve immediately with clearing of airway secretions by MIE. An increase in VC of 15% to 42% was noted immediately following treatment in 67 patients with “obstructive dyspnea,” and a 55% increase in VC was noted following MIE for patients with NMDs. We have observed 15% to 400% (200 to 800 mL) improvements in VC and normalization of O 2 sat for patients during chest infections.


MIE takes the place of the inspiratory and expiratory muscles. However, ventilator users with intact bulbar muscles can usually air stack to volumes of 3 L or more, and, unless very scoliotic or obese, can achieve effective assisted CPF of over 300 L/m and may not need MIE. Thus, the patients who need it the most have moderately to severely impaired BIM function that limits assisted CPF to less than 300 L/m. This is typical of spinal muscular atrophy, Duchenne muscular dystrophy (DMD), and other myopathies. Remarkably, MIE is effective even for patients with no inspiratory, expiratory, or BIM function at all. Our 20+ year-old patients with SMA type 1 who have 0 mL of VC and absolutely no BIM function for over 15 years can achieve over 350 L/m of MIE-EF and, therefore, very effective expulsion of airway debris using MIE. A type of pressure-preset ventilator permits measurements of MIE-EF. Flows generally over 150 L/m are effective. Whereas MIE is effective for these patients with SMA type 1 and all other severe NMDs who have no BIM at all, it eventually becomes ineffective for patients with ALS, whose BIM dysfunction is from upper motor neuron disease or central nervous system disease that causes stridor due to reflex hypertonicity of the larynx and upper airways. For these patients, MIE-EF may not exceed 100 L/m at the point at which they require tracheotomy for continued survival. Patients with respiratory muscle weakness complicated by scoliosis with inability to capture the asymmetric diaphragm by abdominal thrusting can also greatly benefit from MIE.


Glossopharyngeal Breathing


Both inspiratory and, indirectly, expiratory muscle function can be assisted by GPB. This is the glottis pistoning boluses of air into the lungs. One GPB breath usually consists of 6 to 9 gulps of 40 to 200 mL each ( Fig. 151.2 ). During the training period, its efficiency can be monitored by spirometrically measuring the milliliters of air per piston action, actions per breath, and breaths per minute. A training manual and numerous videos are available, the most analytical of which was produced in 1999. Approximately 60% of ventilator users with no autonomous ability to breathe but with good bulbar muscle function can use GPB for ventilator-free breathing up to all day. This includes patients with no VC at all.


Jul 6, 2019 | Posted by in PHYSICAL MEDICINE & REHABILITATION | Comments Off on Respiratory Management of Neuromuscular Disorders
Premium Wordpress Themes by UFO Themes