boys with progressive muscular weakness in the 1860s. DMD is inherited as an X-linked recessive trait, which means it is much more likely to occur in males than in females. However, 30% of cases arise from de novo mutations. The incidence is estimated to be 1 in 3600 live male births in the United States. Some women are asymptomatic carriers of the mutation. DMD is caused by mutations in the dystrophin gene at the Xp21.1 locus. Dystrophin is a cytoplasmic protein that plays a vital role in attaching the cytoskeleton of a muscle fiber to its surrounding extracellular matrix. Abnormal dystrophin is associated with other forms of muscular dystrophy, including Becker myotonic dystrophy, which manifests in adulthood.
Infants born with DMD are generally asymptomatic but may have hypotonia. Poor head control in infancy may be an early sign of disease. Pseudohypertrophy of the calf muscles occurs because of fatty infiltration of the muscle. This is typically accompanied by muscle wasting of the thighs. Children with DMD, and those with other forms of muscular dystrophy, exhibit the Gower sign at approximately 3 years of age (use of hands and arms to “walk up” their own body from a squatting position). This is indicative of proximal muscle weakness, particularly of the hips and thighs.
As muscle weakness progresses, patients will have difficulty ambulating and performing activities of daily living (ADLs). Respiratory muscle weakness will result in dyspnea, weak coughing, a nasal voice quality, and an increased risk for aspiration. Contractures of the ankles, knees, hips, and elbows may occur. From 50% to 80% of patients develop cardiomyopathy. Intellectual impairment with an intelligence quotient (IQ) below 70 is present in as many as 30% of patients. Epilepsy and autism-like behavior also have been described.
Myotonic dystrophy is the second most common form of muscular dystrophy. The estimated prevalence is 1 in 8000 worldwide. The incidence ranges from 1 in 100,000 to 1 in 300,000 in developed nations. Types 1 and 2 myotonic dystrophy are each caused by genetic mutations resulting from expansions of repeating nucleotides on specific chromosomes. Type 2 tends to be milder than type 1.
Myotonic dystrophy manifests at any age. Patients may have facial wasting, hypotonia, an arched palate (secondary to weakness of the temporal and pterygoid muscles), and progressive weakness that begins in the distal muscles. Weakness begins as mild in the first few years but progresses slowly throughout childhood and into adulthood. Wasting occurs in the dorsal forearms, anterior lower legs, neck, and tongue muscles. Patients do have difficulty with ambulation and exhibit the Gower sign. Speech is commonly impaired as well.
Myotonia, a very slow relaxation of muscles after contraction, can be elicited by asking patients to make a tight fist and quickly open their hand. It can also be elicited through percussion of the thenar eminence of the hand. Myalgias are not present in myotonic dystrophy. Extraskeletal manifestations include complete heart block, ventricular arrhythmias, thyroid dysfunction, low immunoglobulin levels, cataracts, diabetes mellitus, and intellectual impairment. Type 2 myotonic dystrophy shares many of the same features, but it is typically milder and not associated with a shortened life span.
Emery-Dreifuss muscular dystrophy, also known as scapuloperoneal or scapulohumeral muscular dystrophy, is transmitted in X-linked, autosomal recessive, and autosomal dominant fashions. The overall prevalence of disease is unknown. Symptoms typically begin between the ages of 5 and 15 years and progress relatively slowly in most cases. Patients typically exhibit muscle weakness and wasting in a scapulohumeroperoneal distribution. They develop contractures at the elbows and ankles early in the course of the disease. Muscular pseudohypertrophy does not occur. In fact, patients may exhibit atrophy of the peroneal muscles. Facial weakness may also be present. Intellectual function is normal. Dilated cardiomyopathy is severe and is often associated with significant arrhythmias, including sudden ventricular fibrillation. Implantable cardiac defibrillators may be required to prevent sudden cardiac death.
Limb-girdle muscular dystrophy (LGMD) is a heterogeneous group of disorders characterized by a proximal distribution of weakness. There are many forms of the disease that can be inherited in autosomal recessive or autosomal dominant fashion. Multiple genetic mutations can occur on different chromosomes and lead to the various disease states. The estimated prevalence is about 1 in 20,000 individuals. Patients generally present with progressive weakness and muscle atrophy of the shoulder girdle, pelvic girdle, or both. Onset of symptoms can begin in childhood or adulthood. Adult-onset cases typically manifest with progressive proximal muscle weakness leading to difficulty with mobility. Facial weakness can be mild, but extraocular muscles are spared. Most types have spared distal muscle strength initially; however, distal muscles eventually develop weakness. Calf pseudohypertrophy and ankle contractures develop in some forms of LGMD. Cardiopulmonary involvement and dysphagia are also common.
Facioscapulohumeral dystrophy (FSHD) is an autosomal dominant form of muscular dystrophy. It is the third most common form of muscular dystrophy, with an estimated prevalence of 4 to 12 cases per 100,000 population. Symptoms begin in infancy to middle age, with most becoming symptomatic by the age of 20 years. As the name implies, muscle weakness predominantly affects the muscles of the face, scapula, and upper arms. Facial manifestations include inability to close the eyes tightly, inability to smile or whistle, and characteristic facial expressions. Weakness also involves the abdominal muscles. The distribution of muscle weakness tends to be asymmetric. Dysphagia and respiratory failure are rare. In some instances, patients with respiratory involvement may require noninvasive ventilation (NIV), usually nocturnally. Other manifestations include chronic pain, visual disturbances, retinal vasculopathy, progressive hearing loss, cardiac arrhythmias, and cognitive impairment.
Diagnosis
The diagnosis of muscular dystrophy combines physical examination, laboratory testing, and muscle biopsy findings. Clinical findings of muscular weakness, fatigue, muscle wasting, or dysphagia should prompt evaluation for a myopathic disorder. A thorough family history should be obtained when muscular dystrophy is suspected. In circumstances in which the clinical presentation and inheritance pattern are consistent with a diagnosis, additional testing may not be necessary. Creatine kinase and aldolase are proteins that, if elevated, may suggest muscle damage.
Many, but not all, muscular dystrophies are associated with elevations in creatine kinase and aldolase. In Duchenne and Becker muscular dystrophies, genetic testing of the dystrophin gene can be diagnostic and obviate the need for muscle biopsy. Molecular genetic testing is available for other forms of muscular dystrophy as well. A muscle biopsy is indicated when the clinical scenario suggests a myopathic process and the likelihood of obtaining a diagnosis through less invasive means is unlikely. The muscle on which the biopsy is to be performed should be one affected by the disorder. It is important to note that severely affected muscles may only show end-stage morphology that will not be sufficient to provide a diagnosis. Myopathic changes seen on biopsy often show generalized features of muscle damage with superimposed changes consistent with a specific disorder. Table 31.4 also includes histopathologic findings associated with several forms of muscular dystrophy.
Management
There is no cure for any form of muscular dystrophy. Management of muscular dystrophies requires a multidisciplinary approach. A 2016 Cochrane Database meta-analysis evaluated the effect of corticosteroids in Duchenne muscular dystrophy. Corticosteroids were associated with improved muscle strength and function compared with placebo in the short term (6 months to 2 years). Areas of improvement included time to rise from the floor, timed walk, four-stair climbing time, ability to lift weight, leg function grade, quality of life, and forced vital capacity. Deflazacort was shown to stabilize muscle strength versus placebo. Very few studies compared prednisone with deflazacort, and at this time no conclusions can be drawn regarding which steroid is more effective. Corticosteroids are associated with significant side effects, including weight gain, behavioral abnormalities, excessive hair growth, diminished bone density, poor wound healing, and impaired glucose control.
Physical and occupational therapy can improve strength, functional status, and quality of life. Range-of-motion exercises are important to help prevent and treat limb contractures. Patients with severe contractures may require surgical intervention. Gene therapy, using viral or nonviral vectors, is a promising modality for treatment of muscular dystrophies
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that is still under investigation.
Monitoring for pulmonary complications is important because many forms of muscular dystrophy are associated with respiratory muscle weakness, impaired coughing, and ventilatory failure. NIV improves outcomes and quality of life in patients with respiratory failure. Airway clearance therapy is important to prevent atelectasis and subsequent pulmonary infection. Congestive heart failure should be managed according to established guidelines with administration of betablockers, angiotensin converting enzyme (ACE) inhibitors, and appropriate management of salt and fluid intake.
Patients with significant risk for fatal arrhythmias (primarily ventricular arrhythmias) may benefit from antiarrhythmic medications. Automated implantable cardioverter-defibrillators are necessary for primary and secondary prevention of ventricular arrhythmias and to prevent sudden cardiac death. Ventricular assist devices (VADs) should be considered for patients with end-stage cardiomyopathy. However, heart transplantation may be challenging for those with muscular dystrophy because of the risk for respiratory failure and potential need for tracheostomy.
Stroke
Etiology and Epidemiology
Stroke, also known as acute brain attack or cerebrovascular accident, is a condition characterized by decreased perfusion to the brain resulting in cellular damage or cellular death. The two main categories of stroke are hemorrhagic and ischemic. Of acute strokes, 80% result from thrombosis or embolism and the other 20% are the result of hemorrhagic conditions (i.e., subarachnoid hemorrhage or intracerebral hemorrhage). According to the Centers for Disease Control and Prevention (CDC), approximately 800,000 Americans have a stroke each year, and about 140,000 of these individuals will die from this condition. This disorder is currently the fifth leading cause of death in the United States. Furthermore, stroke is a leading cause of long-term disability and results in billions of dollars of health care spending each year. Risk factors for stroke development include hypertension, diabetes mellitus, tobacco use, elevated cholesterol, peripheral arterial disease, and atrial fibrillation.
Clinical Manifestations
The clinical manifestations of a stroke are related to the location of the insult and the degree of ischemia. The onset of symptoms is classically acute. Patients may report a history of transient ischemic attacks (TIAs) with temporary neurologic symptoms in the weeks to months preceding an acute stroke.
Patients who experience a stroke typically experience changes in vital signs with elevation in blood pressure, decreased respiratory rate (because of increased intracranial pressure [ICP] causing decreased respiratory drive), and fever. Weakness of muscles of the face or extremities is common and may be accompanied by sensory, visual, or cognitive impairment. Infarcts involving the middle cerebral artery (MCA) will affect the parietal lobe, resulting in contralateral sensory/motor impairment, contralateral lower face weakness, ataxia, speech impairment, and visual deficits.
Strokes of the anterior circulation will cause sensory and motor impairment of the lower extremities, akinetic mutism, and incontinence. Posterior cerebral artery (PCA) strokes may result in contralateral hemiplegia (paralysis), chorea, hemiballismus, visual field deficits, memory deficits, and visual hallucinations. Strokes impairing the midbrain generally cause cranial nerve deficits (e.g., double vision, taste disturbances, hearing loss, dizziness, and difficulty swallowing). Patients may have strokes involving multiple brain areas, resulting in variable signs and symptoms.
Stroke is associated with several respiratory complications. Acute central nervous system injury can result in acute pulmonary edema with associated tachycardia, tachypnea, and hypoxemia. Pneumonia frequently occurs in patients who have had a stroke. Aspiration of food particles or oral secretions represents the most common cause of pneumonia in these patients. This may occur because of stroke-related oropharyngeal dysphagia and a decreased level of consciousness resulting in impaired cough reflex and ability to protect the airway. The development of pneumonia after a stroke is associated with increased mortality and worse long-term outcomes. The respiratory therapist must recognize the importance of oral secretion management in the prevention of pulmonary complications.
Abnormal breathing patterns (see Chapter 2, The Physical Examination) are common after an acute infarct. Many of these breathing patterns are not prognostic, nor do they result from infarcts in specific locations within the brain or spinal cord. Obstructive and central sleep apnea are both consequences of and risk factors for developing a stroke. CheyneStokes respiration describes a cyclical pattern of breathing in which the respiratory rate and tidal volume gradually increases then decreases in a crescendo-decrescendo pattern with apneic periods between each cycle. This pattern of breathing is seen in patients with congestive heart failure, hypoxia, hypocapnia, and diffuse cerebral injury. Ataxic (Biot) respiration describes chaotic, irregular periods of rapid, deep respirations followed by irregular periods of apnea that last 10 to 30 seconds. Apneustic breathing is characterized by prominent end-inspiratory pauses interrupted by occasional short expirations. This pattern of breathing localizes to the lower half of the pons but also may occur in meningitis, hypoxia, and hypoglycemia. Kussmaul respirations may occur in patients with metabolic acidosis. Agonal respirations occur frequently in patients with bilateral medullary injury or those with terminal brain injury.
Diagnosis
The initial evaluation of patients suspected of having a stroke should be conducted in an emergent fashion. The sooner a diagnosis can be made, the sooner interventions can be undertaken to improve cerebral ischemia and prevent further neurologic deficits. A thorough neurologic examination can identify clinical findings that may help localize the area of ischemia. CT or MRI studies of the brain are necessary to determine if the stroke is hemorrhagic or ischemic. These imaging modalities also will give information regarding the degree of ischemia and can offer clues to the underlying cause (e.g., identifying cerebrovascular aneurysms or atherosclerosis). Oxygen saturation should be monitored, and supplemental oxygen should be provided to prevent hypoxia. Patients with ischemic stroke require higher blood pressures to prevent worsening of ischemia. In selected patients intracranial pressure (ICP) monitoring may be required.
Management
Patients with ischemic strokes may require tissue plasminogen activator (tPA) to lyse clots and reestablish cerebral perfusion. tPa should be administered within 4.5 hours of the onset of stroke symptoms provided there are no contraindications. Specialized stroke centers may have trained interventionalists who can remove thrombi from within cerebral vessels. Antiplatelet therapy with aspirin and clopidogrel reduces mortality and helps prevent subsequent ischemic strokes. Hyperthermia requires treatment with acetaminophen or external cooling to normalize core body temperatures.
Those with a Glasgow Coma Scale score of 8 or less or worsening mental status with concern for airway protection will require emergent airway control. Patients with increased ICP are at high risk for complications during intubation, including hypotension, an exaggerated sympathetic response to airway manipulation, or further increases in ICP. Preoxygenation is important to prevent hypoxia, which can worsen ICP and cerebral ischemia. Intubation should be performed by an experienced provider to prevent multiple attempts at intubation and delays in securing a stable airway. Pretreatment with an opioid can diminish the rise in ICP caused by rapid sequence intubation (RSI). Topical anesthetics and sedating medications should be used in patients with a decreased level of consciousness because they may still cough and increase their ICP with laryngoscopy. Supplemental oxygen should be used to prevent hypoxemia. When using mechanical ventilation it is important to be mindful that high levels of positive end-expiratory pressure (PEEP) may reduce mean arterial pressure (MAP) and ultimately decrease cerebral perfusion pressure (CPP). CCP is defined as the MAP minus the ICP.
Prevention of respiratory complications is an important component of poststroke care. Bronchial hygiene with incentive spirometry, positive expiratory pressure (PEP) devices, and other airway clearance techniques can prevent atelectasis and pneumonia. Ambulation, when possible, will also improve airway hygiene. Atropine drops given sublingually and botulinum toxin (Botox) injections into salivary glands can reduce oral secretions and decrease the risk for aspiration pneumonia. NIV is used to treat patients with sleep apnea and hypoventilation syndromes. The respiratory therapist should be aware of the abnormal breathing patterns that occur after a cerebral injury, especially Cheyne-Stokes respirations, so the appropriate ventilatory support can be provided.
Head Injury
Respiratory therapists are frequently involved in the care of patients with head injuries. According to the CDC, traumatic brain injury (TBI) contributes to approximately 30% of all injury deaths in the United States. In 2013, about 2.8 million TBIrelated emergency department visits, hospitalizations, and deaths occurred in the United States; falls account for the majority of those injuries. Brain injury can result in multiple respiratory complications. Patients with TBI typically exhibit a depressed level of consciousness, which significantly raises the risk for aspiration. These patients can develop apnea through multiple mechanisms, including functional airway obstruction in the setting of loss of consciousness. Aspiration events and apnea can result in hypoxemia and hypercapnia, which can further compromise cerebral oxygen delivery.
Management
The initial step in the management of patients with TBI is an assessment of the patient's ability to protect the airway. A focused but thorough assessment should be performed to identify additional injuries that might have an effect on airway management, particularly maxillofacial or spinal cord trauma. There is a high incidence of peri-intubation hypoxemia and cardiac arrest (defined as occurring within 60 minutes after initiation of airway management), hypocapnia, and hemodynamic instability in patients with head injuries; therefore intubation should be performed by experienced providers. Maneuvers such as a jaw thrust, use of temporary bag-mask ventilation (BMV), or a supraglottic airway may be lifesaving in emergent situations before placing an endotracheal tube. RSI is the most common technique for airway management in these patients. It is not uncommon for patients to develop peri-intubation hypotension related to induction agents and use of positive pressure ventilation, particularly in a trauma setting in which patients may have acute blood loss.
Attempts should be made to adequately resuscitate patients with packed red cell transfusions or administration of intravenous crystalloid to prevent peri-intubation hemodynamic instability. An awake intubation with a topical anesthetic should be considered for selected patients with an anticipated difficult airway or concern for potentially significant hemodynamic compromise related to RSI. Early tracheostomy should be considered for patients with severe brain injuries who are felt to require prolonged ventilatory support.
Prevention of increases in ICP are important. Head of bed elevation to at least 30 degrees minimizes venous outflow resistance and promotes cerebrospinal fluid displacement into the spinal compartment, reducing ICP in the process. Hypoxemia should be promptly corrected to ensure adequate cerebral oxygenation. Carbon dioxide tension plays an important role in cerebral blood flow. Hypercapnia has been shown to cause vasodilation of cerebral blood vessels, which increases cerebral blood flow and ICP. For patients with increased ICP, careful hyperventilation can be used in emergency situations to decrease cerebral blood flow. However, it is important to note that hypocapnia has the opposite effect, and the resultant vasoconstriction can cause cerebral ischemia. Under most circumstances eucapnia is the goal.
A limited volume of exogenous tissue, cerebrospinal fluid, blood, or edema fluid can be added to the intracranial contents without significantly raising the ICP. Death or severe worsening may follow increases in ICP with a shift in intracranial contents if CPP is elevated or vital brain stem centers are displaced. CPP is the force that drives circulation across and through the brain's capillary system. An ICP pressure port is illustrated in Fig. 31.3. The catheter is inserted into the brain through a burr hole drilled into the skull. Acceptable ICP is 5 to 10 mm Hg. ICP greater than 20 mm Hg suggests that a volume of cerebral fluid is under significant pressure and should be treated. High amounts of PEEP may impair cerebral perfusion by decreasing venous return and cardiac output. Moderate levels of PEEP are typically well tolerated by patients who need them (e.g., patients with acute respiratory distress syndrome provided that the MAP is maintained).
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FIGURE 31.3 Intraventricular intracranial pressure (ICP) monitoring system with an external ventricular drainage system for controlled drainage of cerebrospinal fluid. A, The system consists of an intraventricular catheter joined by tubing to a drainage system with adjustable height and a drainage bag. The system also typically has a stopcock, an injection sampling port, and a clamp. The zero reference point for the system is typically between the outer canthus of the eye and the external auditory canal (see leveling device placed at that level). B, The drip chamber pressure level (horizontal arrow) is placed at a prescribed height (in cm) above this zero reference point. The drainage stopcock can allow continuous drainage or be turned to allow only intermittent drainage when the patient's ICP exceeds a prescribed threshold. If the system is functioning and the stopcock is turned to drainage, CSF will drain from the patient's ventricle into the collection chamber and ultimately into the drainage bag once the patient's ICP is sufficiently high. If the drip chamber is placed 27.2 cm (rounded to 27 cm) above the child's ventricles, drainage should occur if the patient's ICP equals 27.2 cm H2O or 20 mm Hg (1.36 cm H2O pressure = 1 mm Hg pressure;
27.2 cm H2O pressure = 20 mm Hg pressure). (Redrawn and modified from Owen, A. [2009]. Clinical guideline: external ventricular drainage.
[Revised, September, 2009]. London, UK: Great Ormond Street Hospital for Sick Children, Institute of Children's Health and University College of London. In Hazinski, M. F. [2013]. Nursing care of the critically ill child [3rd ed.]. St. Louis, MO: Elsevier.)
Elevated ICPs are prevented by head of the bed elevation, sedation with benzodiazepine agents or propofol, avoidance of stimulation such as encouraged coughing or suctioning, and/or intravenous mannitol or hypertonic saline. The aim is to keep the PaCO2 at 35 to 40 mm Hg.
Airway clearance therapy is important to prevent atelectasis and respiratory infection. Bronchodilators and chest physiotherapy are acceptable initial measures to improve airway clearance. Devices such as a cough assist, the MetaNeb System,1 or high-frequency chest wall oscillators (vest therapy) may be contraindicated in patients with a concern for increased ICP or unstable head/neck injuries. These devices can be introduced after resolution of increased ICP and clinical stabilization. Early mobilization and physical therapy should be implemented whenever feasible as another means to improve bronchial hygiene. Patients with a tracheostomy should receive standard tracheostomy care.
Overview of the Cardiopulmonary Clinical Manifestations Associated With Neuromuscular Diseases
Neuromuscular diseases (NMDs) are associated with multiple cardiopulmonary manifestations. Respiratory impairment results from weakness of the muscles of respiration, from either loss of normal innervations or direct muscle dysfunction. Atelectasis (see Fig. 10.7) develops from lack of deep breathing, weak coughing, and/or poor chest wall compliance. These factors contribute to the development of alveolar consolidation (see Fig. 10.8) and excessive bronchial secretions (see Fig. 10.11). These patients are also at an increased risk for developing pulmonary infections because of the inability to expectorate secretions effectively. The Airway Clearance Therapy Protocol (for the newborn), Protocol 33.2; Lung Expansion Therapy Protocol (for the newborn), Protocol 33.3; Airway Clearance Protocol (for the pediatric patient), Protocol 34.2; Ventilator Initiation and Management Protocol, Protocol 11.1; and Ventilator Weaning Protocol, Protocol 11.2, are important in preventing these complications.
As respiratory muscle weakness progresses in NMDs, acute ventilatory failure may develop. Patients with severe neuromuscular disorders are at risk for acute ventilatory failure in a variety of settings, including invasive procedures (as a result of receiving sedation or general anesthesia) and critical illness.
Clinical Data Obtained at the Patient's Bedside
The Physical Examination
Respiratory Rate
•Varies with the degree and etiology of respiratory muscle weakness
•Increased in moderate to severe cases (rapid shallow breathing pattern)
Paradoxical Abdominal Respirations
•Caused by decreased chest wall compliance and increased abdominal compliance
•During inspiration the chest wall moves inward instead of outward
•Seen in more severe cases of NMD
Diminished Breath Sounds at the Lung Bases
Egophony
•Can indicate atelectasis or consolidation. Have the patient repeat the “ee” sound while performing auscultation with stethoscope. If the sound changes to an “ay” sound, then egophony is present.
Crackles Babinski Sign
•Reflex great toe extension and fanning of other toes with lateral plantar stimulation
•Sign of upper motor neuron (UMN) disease, such as stroke (not specific to ALS)
•Present in approximately 50% of patients with ALS
Clinical Data Obtained From Laboratory Tests and Special Procedures
Pulmonary Function Test Findings1
(Restrictive Lung Pathology)
FVC2
FEVT
FEV1/FVC ratio
FEF25%–75%
↓
N or ↓
N or ↑ (>0.70)
N or ↓
FEF50%
FEF200–1200
PEFR
MVV
N or ↓
N or ↓
N or ↓
N or ↓
1Progressive worsening of these values is key to anticipating the onset of ventilatory failure.
2Patients with neuromuscular disease may exhibit a decline in FVC when in a supine position.
Lung Volume and Capacity Findings
VT
IRV
ERV
RV
↓
↓
↓
↓
VC
IC
FRC
TLC
RV/TLC ratio
↓
↓
↓
↓
N
MAXIMUM INSPIRATORY PRESSURE (MIP) ↓
Arterial Blood Gases
Moderate to Severe Neuromuscular Diseases
Acute Ventilatory Failure With Hypoxemia3 (Acute Respiratory Acidosis)
pH4
PaCO2
4
PaO2
SaO2 or SpO2
↓
↑
↑
↓
↓
(but normal)
Severe Neuromuscular Diseases
Chronic Ventilatory Failure With Hypoxemia5 (Compensated Respiratory Acidosis)
pH
PaCO2
PaO2
SaO2 or SpO2
N
↑
↑
↓
↓
(significantly)
3See Fig. 5.2 and Table 5.4 and related discussion for the acute pH, PaCO2, and changes associated with acute ventilatory failure.
4When tissue hypoxia is severe enough to produce lactic acid, the pH and values will be lower than expected for a particular PaCO2 level.
5See Table 5.6 and related discussion for the acute pH, PaCO2, and changes associated with chronic ventilatory failure.
Acute ventilatory changes superimposed on chronic ventilatory failure6
Because acute ventilatory changes may be seen in patients with chronic neuromuscular disease, the respiratory therapist must be familiar with—and alert for—the following two dangerous arterial blood gas findings:
•Acute alveolar hyperventilation superimposed on chronic ventilatory failure that should further alert the respiratory therapist to document the following important ABG assessment: Possible impending acute ventilatory failure
•Acute ventilatory failure (acute hypoventilation) superimposed on chronic ventilatory failure
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6See Table 5.7, Table 5.8, and Table 5.9 and related discussion for the pH, PaCO2, and HCO3 changes associated with acute ventilatory changes superimposed on chronic ventilatory failure.
General Management of Neuromuscular Disease
Nutrition
Nutrition is a vital, and often underestimated, aspect in the care of patients with NMD. Weight loss and malnutrition are poor prognostic factors in several NMDs, especially muscular dystrophies and ALS. Muscle wasting is associated with an increased energy expenditure and creates an overall catabolic state that promotes disability and further functional decline. Furthermore, dysphagia contributes a great deal to the inability of these patients to adequately consume enough calories to meet their resting energy needs. Protein calorie malnutrition increases the risk for infection and is associated with worsening morbidity and mortality. It is also associated with worsening respiratory function. Respiratory therapists, in conjunction with speech pathologists and dietitians, are important in monitoring for nutritional issues and swallowing complications in NMDs.
Patents should undergo regular assessment of their swallowing and have their weight monitored closely, especially early in their disease. Calorie counting provides an objective measure of caloric intake. Patients experiencing fatigue with meals may benefit from a lung volume recruitment maneuver to reduce the work of breathing associated with swallowing. In addition, nutritional supplements, usually in liquid form, may provide additional calories in a method that is less fatiguing.
Gastrostomy tube placement may be required to supplement nutritional needs and provide enteral access for medication administration. Studies have not consistently proven a survival benefit in many forms of NMD; however, gastrostomy insertion has been shown to reduce anxiety among patients with poor oral intake and their caregivers. The optimal timing of gastrostomy tube placement is uncertain. In ALS some sources recommend that a 5% decrease in premorbid weight should prompt consideration of a percutaneous endoscopic gastrostomy (PEG) tube and initiation of enteral feedings. The American Academy of Neurology recommends PEG placement before the forced vital capacity drops below 50% of predicted to prevent respiratory complications during the procedure. Ultimately the decision to insert a feeding tube should be based on multiple factors (e.g., patient preference, weight trends, objective measurements of caloric intake, age, and underlying disease process).
Although much of the attention regarding nutritional assessments in NMD focuses on weight loss, it is important to note that too much weight gain can be just as harmful. Obesity increases risk for development of cardiovascular disease such as stroke or heart attack. Increased abdominal girth can cause worsening restrictive thoracic disease and impair respiratory function, especially in patients with respiratory muscle weakness. Obesity also further impairs mobility and increases the risk for developing diabetes mellitus and hyperlipidemia, both of which are risk factors for cardiovascular disease. Patients with muscular dystrophy who are on corticosteroids are at an even higher risk for developing obesity and obesity-related complications. This highlights the importance of a balanced diet that is high in protein to promote growth of lean muscle mass.
Ventilatory Management of Patients With Neuromuscular Disease
Mechanical ventilation is an important part of the care for patients with NMD who have respiratory insufficiency. Traditionally, tracheostomy placement and invasive mechanical ventilation was the mainstay of chronic ventilatory management in this population; however, in recent years it has been demonstrated that NIV can be an acceptable strategy for long-term ventilatory support. An understanding of not only the indications for ventilatory support but also the various modalities available is important for the respiratory therapist caring for these patients. Protocol 11.1 outlines a general approach to the initiation of ventilatory support of patients.
Mechanical ventilatory support is indicated for patients with signs and symptoms that are concerning for hypoventilation. It has been shown to prolong survival in ALS and DMD, and it improves quality of life in most forms of NMD. Subjective symptoms that may suggest chronic hypoventilation include dyspnea on exertion, orthopnea, morning headaches, fatigue, daytime somnolence, impaired cognition, and frequent nighttime awakenings. Paradoxical breathing, tachycardia, diaphoresis, and accessory muscle use are signs of respiratory insufficiency and should warrant further evaluation. An arterial blood gas (ABG) determination may show evidence of hypercapnia (PaCO2 greater than 45 mm Hg)
with or without metabolic compensation. Patients may have hypoxemia as well.
Spirometry is a useful tool to both identify patients with respiratory insufficiency and monitor disease progression over time. FVC and MIP are typically decreased. Additionally, patients may have normal spirometry while upright but may exhibit a sharp decline when testing is performed in the supine position. Recurrent episodes of acute respiratory failure requiring intubation is an indication for initiation of chronic NIV even in the absence of ABG or spirometry data. The Centers for Medicare & Medicaid Services (CMS) produced the Respiratory Assist Device (RAD) Qualifying Guidelines for the use of NIV for multiple disorders (Box 31.1).
Box 31.1
Respiratory Assist Device Qualifying Guidelines for Noninvasive Ventilation Use
1.Diagnosis of a neuromuscular disease
2.At least one of the following:
•ABG values (done while awake) with a PaCO2 ≥45 mm Hg
•Sleeping oxygen saturation ≤88% for ≥5 minutes with a minimum of 2 hours recording time
•Forced vital capacity <50% of predicted or a MIP <60 cm H2O (for patients with neuromuscular disease)
Tracheostomy
The choice between a tracheostomy with invasive ventilation and prolonged NIV involves a multitude of clinical factors and patient and caregiver preference. Smaller designs have improved ventilator portability and made chronic mechanical ventilation a much more feasible option. Tracheostomies should be considered when patients have difficulty clearing secretions, impaired mental status (obtunded or uncooperative), uncontrolled seizure disorders, inability to tolerate NIV, NIV failure, or failure to wean from invasive mechanical ventilation. Tracheostomies have the added benefit of immediate airway access to invasive mechanical ventilation in the event of acute respiratory decompensation.
Tracheostomies can be performed using local anesthetic and NIV support in patients with hypercapnia. Long-term use of a tracheostomy tube can result in tracheal stenosis, necrosis, hemorrhage, stomal infections, and even tracheoesophageal fistula formation. Tracheostomy tube use requires humidification and daily respiratory care management, which can be cumbersome for home caregivers. Swallowing and speech mechanics may be impaired, although devices and ventilatory
techniques can allow for verbal communication while on a ventilator in selected individuals. Tracheostomy use is also associated with an increase in bacterial airway colonization and an increased risk for ventilator-associated pneumonia. The optimal timing for tracheostomy placement varies from patient to patient, and is basically unknown.
Speech in Patients With a Tracheostomy
When counseling patients regarding tracheostomy placement it is important to bear in mind that there are options to restore verbal communication. Under normal circumstances, a subglottic pressure of at least 2 cm H2O and air flow
through the upper airway of about 50 to 300 mL/s is required. As shown in Fig. 31.4, talking tracheostomy tubes are now available (e.g., the Passy Muir type of speaking valve). However, the voice quality is poor. One-way speaking valves placed on the proximal end of the tracheostomy tube allows for much improved speech quality by allowing exhaled air to escape through the vocal cords. It should be noted that their use requires the cuff to be completely deflated, thus increasing a risk for aspiration and impairment in gas exchange while speaking.
FIGURE 31.4 Mechanism of action of the Passy Muir type of speaking valve. The valve is a unidirectional valve that occludes air outflow through the tracheotomy cannula during expiration, thereby forcing air through vocal cords. (From Fernández-Carmona, A.,
Peñas-Maldonado, L., Yuste-Osorio E, et al. [2012]. Exploration and approach to artificial airway dysphagia. Medicina Intensiva 36(6), 423-433.)
Some patients with speaking valves can speak during inspiration and expiration. Patients can also achieve the ability to speak with leak speech. With a deflated tracheostomy cuff, approximately 15% of the delivered tidal volume will leak around the tube and out through the vocal cords. Using PEEP and a prolonged inspiratory time will increase the tracheal pressure and therefore improve the ability to speak, and as much as 60% to 80% of the respiratory cycle can be used for speech. Both volume and pressure modes can be used effectively to provide speech to mechanically ventilated individuals. In volume modes, increasing the tidal volume can help compensate for the air leak. Selecting patients who are appropriate for speech communication while being ventilated specialist requires collaboration between speech-language pathology specialist and respiratory therapists. Those with increased secretions, significant hypoxemia, and significant ventilatory needs may not be appropriate candidates.
Ventilatory Support
NIV can be used as a primary method of ventilatory support in patients with ventilatory failure. Case series have described patients successfully using NIV for ventilatory support 24 hours per day. Reports have also described its use in weaning patients from tracheostomy-assisted ventilation. NIV is most commonly used with a face mask, nasal mask, or nasal pillows.
Ventilatory support is generally initiated nocturnally, with additional use during the day for patients with ongoing respiratory weakness. Several sources recommend volume-cycled ventilation to allow for breath stacking maneuvers; however, patients can be adequately and comfortably ventilated with pressure-cycled ventilation, in particular bi-level positive airway pressure (BPAP). A pressure-controlled style of BPAP is most helpful in NMD by ensuring a complete inspiratory time with each breath.
PEEP can be set to a minimum value (i.e., 2 cm H2O) unless the patient has concomitant obstructive sleep apnea or other
pulmonary pathologic process. When using bilevel ventilation the inspiratory time should be prolonged, generally at least 1 s, to provide an adequate inspiratory volume. It is important to note that spontaneous (S) or spontaneous timed (ST) modes of ventilation can result in premature inspiration-expiration cycling in patients with NMD. This occurs because in these modes patients dictate their own inspiratory time for all spontaneous breaths. In this situation assisted modes of ventilation allow the provider to set a specific inspiratory time for all breaths received by the patient.
Volume-assured pressure support (VAPS) devices are frequently used for NIV in patients with acute and chronic hypoventilation syndromes. This nonconventional ventilatory strategy attempts to combine volumeand pressurecontrolled ventilation by adjusting the pressure support within a prespecified range to target a specific tidal volume. It can be used in S, ST, and PC modes. Clinical trials have found VAPS to be as efficacious, and in some cases more beneficial, for the management of patients with different forms of hypoventilation, including NMD, restrictive thoracic disorders, obesity hypoventilation, and COPD.
The devices automatically adjust the inspiratory pressure within the preset range to achieve a desired tidal volume or minute ventilation, as opposed to conventional bilevel ventilation, which uses one set inspiratory pressure during the entire delivered breath. This ultimately ensures more consistent tidal volumes in the setting of a varying patient respiratory effort and chest wall compliance. It also tends to be more comfortable.
Respiratory therapists should be aware that specific details of modes of NIV will vary across device manufacturers. Therapists will need to become familiar with exact devices that may be available to them. In general, when using S or ST modes, the inspiratory time will not be adjustable or may only become applicable if the patient becomes apneic. In PC mode, an inspiratory time will be fixed and will apply to all breaths, whether spontaneous or delivered by the device. Several VAPS devices are available.
These devices differ primarily in the algorithm used to automatically adjust settings. Specifics of these modes vary depending on the manufacturer. In general, devices are designed to target either exhaled tidal volume or alveolar
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ventilation. These goals are reached by augmenting pressure support and adjusting the backup respiratory rate. Newer devices may also auto-adjust the expiratory positive pressure airway pressure (EPAP) to eliminate obstructive events.
In those with NMD, when using VAPS technology it is important to adjust trigger, cycle, and inspiratory time to ensure patient comfort and ease of ventilation. In NMD, patients will need these settings to be adjusted at the bedside. Automatic ventilator operation algorithms are frequently incapable of meeting the needs of these patients. The trigger should be highly sensitive and the inspiratory time prolonged to optimize patient-ventilatory synchrony.
Mouthpiece ventilation (MPV), also known as sip and puff ventilation or sip ventilation, is a less commonly used ventilatory strategy in NMD. In mouthpiece ventilation, a mouthpiece connected to ventilator can be inserted into the mouth, allowing the patient to take a ventilator-assisted breath intermittently. This is most commonly used for daytime support and can be coupled with nighttime NIV via an alternative interface. MPV reduces the risk for infection compared with that with tracheostomy.
Compared with NIV, using traditional interfaces MPV results in less skin breakdown, facilitates speech, facilitates coughing, facilitates swallowing, has a better appearance, and may have less of a psychological effect on patients. MPV requires active patient participation and may not be appropriate for patients with significant bulbar disease, because of inability to make a seal with the mouthpiece. The ventilator is typically set to assist control (AC) mode and volume control (VC) with a set tidal volume of 10 to 15 mL/kg of ideal body weight. Volume-controlled modes are preferred because it allows for breath stacking, though pressure control (PC) may be preferred when gastric inflation is severe. The respiratory rate and PEEP should be set to zero. Triggering the breath should be made as easy as possible (i.e., flow triggering set at 1 L/min). The apnea alarm should be set to its highest threshold or turned off to prevent unnecessary alarms. The low-pressure alarm should be set to the minimum setting. Box 31.2 provides sample ventilator settings for MPV.
Box 31.2
Sample Mouthpiece Ventilator Settings
AC/VC or AC/PC
Flow pattern: Square waveform (can use ramp if more comfortable for patient) Tidal volume: 10 to 15 mL/kg IBW or 1.5 × FVC
Inspiratory time: 1.2 to 1.5 seconds (can increase up to 2.0 seconds based on patient comfort) Respiratory rate: 0 bpm
PEEP: 0 cm H2O
Low inspiratory pressure: 1 to 2 cm H2O (disable alarm when possible, otherwise minimize to lowest setting) High inspiratory pressure: Up to 70 cm H2O (disable alarm when possible, otherwise maximize to highest setting)
Apnea alarm: Disabled (or set to longest time possible) Trigger: 1 L/min flow
Noninvasive ventilatory support can be started in the sleep laboratory, the inpatient setting (usually an intensive care unit), or at home. Overnight pulse oximetry and ABGs can be used to objectively titrate ventilator settings. The goal of therapy should be to not only normalize objective values but also to improve symptoms and optimize patient comfort.
Case Study Amyotrophic Lateral Sclerosis
Admitting History
A 53-year-old female physician with known ALS presented to the emergency department (ED) with progressive dyspnea and generalized fatigue. Over the course of 6 months, the patient noted worsening dyspnea on exertion, which had limited her ability to work. These symptoms had forced her to significantly decrease her workload. At this time, she only saw patients 2 half days per week in her primary care clinic. Being unable to work full time had been both an emotional and a financial strain on her and her family. She reported frequent coughing with meals. Her friends had commented that her voice appeared softer and her cough sounded weaker but more congested. Three months earlier the patient had been hospitalized for right lower lobe pneumonia. No evaluation of her swallowing was performed at that time, and she recovered fully with antibiotic therapy. At discharge her arterial blood gas (ABG) values were all normal.
The patient confirmed multiple falls at home. The patient added that while walking she occasionally stumbled and “tripped over her own feet.” These falls were not associated with palpitations, lightheadedness, dizziness, or syncopal symptoms. Additionally, she had noted some “muscle twitching” of her tongue. Her medical history was significant for hypertension and hyperlipidemia. Her medications included an antihypertensive and a lipid-lowering agent. She had never smoked and denied the use of alcoholic beverages. She had no family history of respiratory or other neurologic conditions.
Physical Examination
In the ED the patient was calm and alert. She appeared to be in moderately acute respiratory distress. Her vital signs were blood pressure 138/86 mm Hg, pulse 96 beats/min, respiratory rate 28 to 32 breaths/min and shallow, and temperature 37.0°C. On room air, her SpO2 was noted to be 87%. At this time, the respiratory therapist started her on supplemental
oxygen via a 2 L/min nasal cannula. Neurologic examination notes showed decreased motor strength in the arms and legs, increased bilateral patellar tendon reflexes, and fasciculation of the tongue. There was notable muscle wasting of the extremities. The patient's voice was strained with decreased intelligibility of speech. On auscultation, there were fine and coarse crackles throughout her lung bases. Her cough was weak and congested. No sputum was observed. The cardiac examination was unremarkable. Blood was drawn for laboratory testing, and a chest x-ray film was obtained. The chest x- ray film showed atelectasis at the bases without signs of infection or pneumothorax. There was no consolidation or signs of interstitial edema. At this time the patient was admitted to the hospital for treatment and observation.
Two days later, the head nurse sent out a stat call to the physician and respiratory therapist. On observation, the patient was obtunded and nonresponsive to aggressive painful stimuli. Her vital signs were blood pressure 164/96 mm Hg, pulse 121 beats/min, and respiratory rate 16 breaths/min and shallow. The nurse stated that the night shift had reported that the patient was now coughing up moderate amounts of yellow sputum. On a 2 L/min nasal cannula, an ABG sample was drawn
and showed pH 7.04, PaCO2 106 mm Hg, 25, PaO2 58 mm Hg, and SaO2 68%, which was immediately assessed by
the respiratory therapist as acute ventilatory failure with moderately severe hypoxemia.
The patient was emergently intubated because of the acute hypercapnic respiratory failure and inability to protect her airway. The initial ventilator settings were volume-controlled intermittent mandatory ventilation (IMV), respiratory rate 12 breaths/min, tidal volume 500 mL, PEEP 5 cm H2O, an FIO2 0.4, and a decelerating flow at 60 L/min. A chest x-ray film
confirmed that the end of the endotracheal tube was 2.0 cm above the carina and the presence of bilateral atelectasis. The patient appeared to be comfortable without evidence of ventilator-patient dyssynchrony. Some spontaneous breathing was noted—about 4 to 6 breaths/min. A repeat ABG sample 20 minutes after intubation and mechanical ventilation showed pH
7.37, PaCO2 43 mm Hg, 24, PaO2 109 mm Hg, and SaO2 96%. Her vital signs were blood pressure 134/77 mm Hg,
pulse 90 beats/min, respiratory rate 12 breaths/min (mechanical ventilation and 4 to 6 spontaneous). Moderate amounts of yellow and green sputum were being suctioned. On auscultation fine and coarse bilateral crackles could be heard in the lung bases.
Respiratory Assessment and Plan
S N/A (intubated and sedated)
O Vital signs: BP 134/77, HR 90, RR IMV 12 (4 to 6 spontaneous breaths). ABGs: pH 7.37,
crackles could be heard in the lung bases. Moderate amounts of yellow and green sputum. A
•Acute ventilatory failure secondary to ALS
•Acid-base and oxygenation status within normal range on present ventilator settings (ABG)
•Atelectasis (x-ray, bilateral crackles in lung bases)
•Excessive bronchial secretions with evidence of infection (yellow and green sputum suctioned)
P Mechanical Ventilation Protocol: Continue on ventilator settings as now adjusted. Airway Clearance Protocol (e.g., suctioning, PEP devices, increased PEEP). Perform daily a spontaneous breathing trial to assess for readiness for extubation. Monitor SpO2 closely.
Four Days After Admission
The patient remained on the mechanical ventilator. She had been receiving aggressive airway clearance therapy and had minimal secretions. She had clear lung sounds bilaterally and no peripheral edema. Her x-ray film showed resolution of basilar atelectasis. On this morning a spontaneous breathing trial was performed. Ventilator settings were pressure support of 5 cm H2O, FIO2 of 21%, and PEEP of 5 cm H2O. After 2 hours on these settings, her average exhaled tidal volume
was approximately 400 mL with a respiratory rate of 21, giving a rapid shallow breathing index (RSBI) of 52. On physical examination she was following commands.
At this time, the patient was successfully extubated and liberated from the mechanical ventilator without difficulty. She initially received supplemental oxygen at 2.0 L/min via nasal cannula with a goal saturation of 88% to 92%.
Unfortunately, after about 2 hours it was noted that her respiratory rate increased to 35 breaths/min. She complained that it was difficult to catch her breath even at rest. On auscultation, her lungs were clear and without wheezes or crackles. Even though the patient was oriented to person, time, and place, she appeared very anxious. Her vital signs were blood pressure 144/88 mm Hg, respiratory rate 35 breaths/min and shallow, and heart rate 102 beats/min. On a 2 L/min
nasal cannula, an ABG sample showed a pH of 7.16, PaCO2 of 83 mm Hg, 28, PaO2 62 mm Hg, and SpO2 80%.
The respiratory therapist paged the attending physician stat and informed her of the patient's recurrent acute ventilatory failure with moderate hypoxemia and the need for ventilatory support. The patient was reintubated, and a chest x-ray was ordered. At this time, the following SOAP was documented.
Respiratory Assessment and Plan
S Patient states it is difficult to catch her breath
O Appears drowsy but follow commands appropriately. Vital signs BP 144/88, RR 35 & shallow,
HR 102 beats/min. ABGs on 2 L/min nasal cannula pH 7.16, PaCO2 83, 28, PaO2 62, and SpO2 80%. CXR: No report at this time.
A
•Acute ventilatory failure with moderate hypoxemia secondary to neuromuscular weakness
P Mechanical Ventilation Protocol: Initiate noninvasive ventilation. Start with pressure control (PC) ventilation, IPAP 20, EPAP 5, inspiratory time 1.2 s, respiratory rate 15. Monitor the exhaled tidal volume achieved with these settings, and adjust the inspiratory pressure, driving pressure (IPAP – EPAP), and inspiratory time to achieve the goal minute ventilation with resolution of tachypnea. Continue Airway Clearance Therapy Protocol (e.g., suctioning, PEP devices, increased PEEP).
Over the next 3 days the patient was again liberated from the ventilator. Her strength returned, and she was discharged from the hospital with additional patient and family education for ventilatory support for her symptomatic hypoventilation —nocturnal noninvasive ventilation (NIV).
Discussion
ALS is a progressive neuromuscular disorder associated with upper and lower motor neuron findings. The patient in this clinical case had signs and symptoms compatible with ALS, although she had not had a formal evaluation before her presentation. Before her first mechanical ventilation, her ABGs were consistent with acute ventilatory failure with moderately severe hypoxemia.
Although it very possible that patients with severe neuromuscular disorders can develop chronic ventilatory failure (also called compensated respiratory acidosis) during the advanced severe stages, this was not the case in this patient at this time. Nevertheless—and precisely like the patient with chronic obstructive pulmonary disease (COPD)—it is important for the respiratory therapist to be on the alert for acute ventilatory changes superimposed on chronic ventilatory failure when
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confronted with patients with severe NMD (see Acute Ventilatory Changes Superimposed on Chronic Ventilatory Failure,
Chapter 5, page 78). Similar to the patient with severe COPD, patients with chronic respiratory muscle weakness caused by NMD are also at high risk for developing acute hypercapnia (i.e., on top of chronic ventilatory failure) when exposed to excessive supplemental oxygen. Be careful not to overoxygenate these patients.
Our patient met several criteria for the initiation of ventilatory support, including respiratory distress, altered mental status, and acute ventilatory failure with moderately severe hypoxemia. Clearly on day 2 mechanical ventilation was
justified with a pH of 7.04, PaCO2 106 mm Hg, 25, PaO2 58 mm Hg, and SaO2 68%. Note how quickly her blood
gases returned to normal once she was placed on ventilatory support. On day 5, the objective data strongly supported that she be discontinued from the ventilation—for example, average exhaled tidal volume of 400 mL, respiratory rate of 21, a RSBI of 52, following commands, and clear lung sounds bilaterally. Unfortunately, in this case, additional ventilatory support was needed after the patient was liberated from the mechanical ventilator on day 5, because of the postextubation acute ventilatory failure.
After another 3 days of mechanical support and routine airway clearance therapies, the patient was successfully liberated from the ventilator. On discharge, the attending physician documented the following in the patient's progress notes:
After recovery from her acute illness episode, the patient will likely require additional ventilatory support at home for her symptomatic hypoventilation. The following is recommended: Nocturnal noninvasive ventilation (NIV) because symptoms of hypoventilation (such as dyspnea, shallow breathing, somnolence, and fatigue) and acute changes in arterial blood gas measurements can improve with nocturnal NIV. I will discuss this recommendation with the patient and family. This will be followed by arrangements to have the NIV equipment placed in the patient's home. Patient and family education for the nocturnal NIV will be prescribed—both before discharge and in the patient's home.
Nocturnal NIV improves overall survival and quality of life. ALS is a progressive disease, and as respiratory muscle weakness evolves, the patient may need more than just nocturnal respiratory support. In some clinical practices, patients are instructed to use their noninvasive ventilation after meals or other physically exhausting activities. In end-stage ALS, patients may require ventilatory support 24 hours a day, which can be accomplished both invasively (with a tracheostomy) and noninvasively (generally with nasal pillows or sip ventilation).
Our patient had evidence of bulbar dysfunction (i.e., strained voice and slurred speech) on clinical examination. Furthermore, atelectasis of the bases was present, which was the result of inability to take full, deep breaths. Adding airway clearance techniques as part of the patient and family education program would be helpful and allow for better aeration of the lower lobes of the lungs—thus reducing the risk for pulmonary infection.
Self-Assessment Questions
1.Which of the following is an indication for ventilatory support in a patient with neuromuscular disease?
a.Awake PaCO2 ≥45 mm Hg
b.MIP <60 cm H2O
c.Sleeping oxygen saturation ≤88% for ≥5 minutes with a minimum of 2 hours recording time
d.FVC <50% predicted
e.All of the above
2.Spinal cord injuries involving the upper thoracic area affect breathing in which of the following ways?
a.Impairment in diaphragm function
b.Altering respiratory drive
c.Impairment of the intercostal muscles, abdominal muscles, and scalenes.
d.Increased airway resistance
e.All of the above
3.What is the most common cause of death in patients with ALS?
a.Respiratory failure
b.Cardiovascular disease
c.Traumatic injury
d.Cerebrovascular disease (e.g., stroke)
4.Which of the following is not a finding typically seen in muscular dystrophy?
a.Calf pseudohypertrophy
b.Gower sign
c.Tongue fasciculations
d.Limb contractures
5.You are caring for a patient with ALS who was recently started on noninvasive ventilation to treat chronic hypoventilation. You choose Pressure Control, Average Volume-Assured Pressure Support (AVAPS) as your initial ventilatory mode. The settings are RR 10, targeted tidal volume 500 mL, IPAP min 10 cm H2O, IPAP max 15 cm
H2O, EPAP 5 cm H2O, inspiratory time 0.8 s, rise time 3. The patient states the settings are comfortable, but she
is not taking as large of a breath as she would want. You check the ventilator and note that the patient is only achieving exhaled tidal volumes of 300 mL with those settings. The maximum pressure of each breath is at 15 cm H2O. Which of the following adjustments will increase the patient's exhaled tidal volume?
a.Increase IPAP max to 25 cm H2O
b.Increase set tidal volume to 800 mL
c.Increase the inspiratory time to 1.2 s
d.Decrease the respiratory rate to 8 breaths/min
e.b and d
f.a and c
1The MetaNeb System consists of the following three modes: (1) continuous positive expiratory pressure (CPEP), (2) continuous high-frequency chest wall oscillation, and (3) aerosol mode.
changes associated with acute ventilatory failure.
values will be lower than expected for a particular PaCO
changes associated with chronic ventilatory failure.
25, PaO2 58 mm Hg, and SaO2 68%, which was immediately assessed by
24, PaO
24, PaO
28, PaO
28, PaO
25, PaO