Chapter 29

Neuromuscular and Other Diseases of the Chest Wall

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Learning Objectives

List the potential respiratory complications associated with neuromuscular disease.

Identify the clinical signs and symptoms associated with respiratory muscle weakness.

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Learning Objectives (cont.)

Describe techniques for monitoring the patient with respiratory muscle weakness.

Describe the general respiratory care management of patients with respiratory muscle weakness.

Learning Objectives (cont.)

Describe the clinical findings and treatment for each of the following neuromuscular disorders: Duchennes muscular dystrophy, Myotonic dystrophy, Polymyositis , Myasthenia gravis, Lambert-Eaton syndrome, Guillain-Barre syndrome, Unilateral diaphragmatic paralysis, Amyotrophic lateral sclerosis, Critical illness myopathy and polyneuropathy, Spinal cord injury, Stroke, Traumatic brain injury, Kyphoscoliosis, Flail chest

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Introduction

Pulmonary consequences of NMD may include: Hyperventilation Central apnea Atelectasis leading to hypoxemia Hypertension

Introduction (cont.)

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All of the following are consequences of Neuromuscular disorder, except:

A. Atelactasis leading to hypoxemia

B. Hypertension

C. Central Apnea

D. Stroke

Principles of Neuromuscular Weakness of Ventilatory Muscles

Pathophysiology & pulmonary function testing Monitoring & assessing patients for

respiratory insufficiency Management of respiratory muscle weakness

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Pathophysiology & PFTs

NMD normal lung parenchyma reveals restrictive defect Decreased VC, FEV1, TLC

Normal or increased RV & diffusing capacity corrected for VA

Positional changes suggest diaphragmatic weakness Seated to supine: >20% decline in FEV1 & VC

Decreased PImax & Pemax

ABG: PaO⇓ 2, PaCO⇓ 2, but deterioration leads to PaCO⇑ 2

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. .

Pathophysiology & PFTs (cont.)

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All of the following reveal a restrictive lung defect, except:

A. Increased RV

B. Decreased FVC

C. Decreased FEV1

D. Decreased TLC

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Monitoring & Assessing Patients for Respiratory Insufficiency

Respiratory muscle weakness leads to fatigue & respiratory failure May necessitate MV, so monitor carefully to

determine when to initiate Monitoring involves serial measurements of

PImax, VC, & ABG values May monitor maximal nasal sniff inspiratory

force & nocturnal oximetry Close monitoring of all respiratory function is

important

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Management of Respiratory Muscle Weakness

Weakness leads to respiratory insufficiency & retained secretions

Consider NIV or MV via tracheostomy Augmentation of secretion clearance & assist with

cough NIV increasingly used for short-term & intermittent

ventilatory support i.e., Pneumonia or surgical event

Diaphragmatic pacing for spinal injuries FDA approved May be useful to treat NMD as well

Specific Neuromuscular Diseases

Disorders of muscle: Duchenne Muscular Dystrophy Myotinic Dystrophy Polymyositis

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Duchenne Muscular Dystrohpy

Genetic muscle-wasting disorder Manifests early by waddling gait, lordosis,

frequent falls Most affected children are wheelchair dependent

by age 12 Point of significant respiratory function decline Adapt rapid shallow breathing pattern Progression leads to PPV, initially only nocturnal

Death occurs by age 20, usually result of declining respiratory muscle strength & subsequent infection

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Myotonic Dystrophy

Most common MD in adults Respiratory dysfunction is common

Respiratory muscle weakness OSA & CSA , very common even at early age Bulbar muscle dysfunction Aspiration

Tend to be sensitive to anesthesia & respiratory depressants so prolonged postoperative monitoring is required

Nocturnal NIV for oxygen & ventilation issues, while central hypoventilation requires tracheostomy & MV

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Polymyositis

Inflammatory myopathy of unknown cause Ventilatory insufficiency & failure are usual

If occurs, parallel progression of limb weakness Corticosteroids are mainstay of initial

management 10–30% develop interstitial lung disease, with

diffuse infiltrates predominantly in bases

Disorders of the Neuromuscular Junction

Myasthenia gravis (MG) Lambert-Eaton syndrome (LES)

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Disorders of the Neuromuscular Junction

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Myasthenia Gravis

Characterized by intermittent muscle weakness Worsens with repetition Improves with anticholinesterase medications

Caused by antibodies that inactivate ACh-R, blocking electrical impulse transmission

Neoplastic growth within the thymus gland is common

Typically occurs earlier in life in women & later in men

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Myasthenia Gravis (cont.)

Characterized by progressive loss of muscle function often starting with eye muscles Vary through day or progress, especially with

repetitive use Diagnosis is by presence of anti–ACh-R

antibodies & improvement with use of edrophonium

Treatment includes Thymectomy & anticholinesterase drugs Plasmapheresis to remove anti–ACh-R antibodies

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Myasthenia Gravis (cont.)

Pulmonary complications depend on affected muscles Upper airway obstruction Exertional dyspnea Ventilatory failure

Typically display Decreased TLC, VC, PImax, PEmax

• Sensitive markers of early respiratory muscle weakness Myasthenic crisis is acute respiratory

insufficiency caused by infection, surgery or excess anticholinesterase inhibitors

Myasthenia Gravis (cont.)

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Myasthenia Gravis (cont.)

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Lambert-Eaton Syndrome

More than fifty percent of cases associated with cancer, most of those with small cell carcinoma of lung

Autoantibodies interfere with release of ACh Presence is supported by nerve conduction

studies Increasing strength with repetition differentiates LES

from MG Respiratory failure is rare

Disorders of the Nerves

Guillain-Barre Syndrome (GBS) Phrenic Nerve & Diaphragmatic Paralysis

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Disorders of the Nerves (cont.)

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Guillain-Barre Syndrome

Most common peripheral neuropathy Characterized by paralysis & hyporeflexia, self-

limiting Thought to be caused by antimyelin antibodies Diagnosis: High CSF protein levels & slow

impulse transmission

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Patient has a sigh mechanism compromised with Atelactasis ,mild hypoxemia and VC of 30 mL/kg. Which would be most appropriate?

A. Chest physical therapy

B. Incentive Spirometry

C. Positive pressure ventilation

D. Full ventilation

Phrenic Nerve Damage & Diaphragmatic Paralysis

Phrenic nerve arises from C3 to C5 Damage to one phrenic nerve affects one

hemidiaphragm Bilateral interruption in high cervical injuries

results in complete diaphragmatic paralysis Reversible unilateral paralysis can occur due

to pneumonia Typically asymptomatic, diagnosed by radiography

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Phrenic Nerve Damage & Diaphragmatic Paralysis

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Which of the following does the phrenic nerve arise from?:

A. C1 to C3

B. C3 to C5

C. T1 to T3

D. T3 to T5

Disorders of the Spinal Cord

Amytrophic Lateral Sclerosis (ALS): Lou Gehrig Disease

Spinal Cord Trauma

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Amyotrophic Lateral Sclerosis (ALS): Lou Gehrig Disease

Characterized by progressive deterioration of upper & lower motor neurons

Male-to-female ratio for ALS is approximately 1.2:1

80% of patients have died by 5 years Medical treatment is essentially ineffective

Riluzole: trials shown extended life 4.2 months

Amyotrophic Lateral Sclerosis (ALS): Lou Gehrig Disease (cont.)

Supportive therapy central theme in managing ALS Key strategies: Prevent respiratory complications

& assess need for MV If PEmax <40 cm H2O patient has ineffective

cough• Treat with assisted cough, postural drainage

Consider instituting MV if:• PImax <60 cm H2O, PaCO2 >45 mm Hg, VC <20 ml/kg,

or NSIF >–40 cm H2O• Many patients opt not to prolong life with MV

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All of the following would lead to initiation mechanical ventilation in ALS patients, except:

A. VC >20 ml/kg

B. PaCO2 >45 mm Hg

C. PImax <60 cm H2O

D. NSIF >–40 cm H2O

Spinal Cord Trauma

Respiratory impact of spinal injury depends on level of injury & if complete or partial

High cervical injuries (C1-2) result in complete paralysis & death unless immediate MV is instituted

Middle-low cervical injury (C3-C8): though diaphragm is impacted at C3-C5, many can come off MV Adapt rapid shallow breathing pattern by use of

accessory muscles

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Disorders of the Brain

Trauma, stroke, hemorrhage, & infection can all impact respiration by: Abnormalities in lungs themselves, such as

neurogenic pulmonary edema

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Stroke

Interruption of blood flow to portion of brain, which results in persistent dysfunction

Could be thrombotic, embolic or hemorrhagic Impairment related to which structures were

damaged Treatment

Early (3–4.5 hours) use of thrombolytic agents after thrombotic event improves survival & function

Physical & occupational therapy Speech therapy if indicated

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Stroke (cont.)

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Traumatic Brain Injury

Blunt or penetrating injury resulting in brain lesions May cause direct trauma to respiratory centers Cause neurogenic pulmonary edema,

hypersecretion of mucus, leading to respiratory failure

Disorders of the Thoracic Cage

Kyphoscoliosis Flail chest

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Kyphoscoliosis

Posterior angulation of thorax (kyphosis) & lateral curature of spine (scoliosis) occur together

Kyphoscoliosis may result in hypoventilation, hypercapnia, & pulmonary HTN Decreased compliance seen with these patients

• Result in TLC & VC & restrictive disorder⇓• May have impaired diaphragmatic function

Spinal fixation may improve compliance, prevent further pulmonary dysfunction, preexisting conditions will not be reversed

Kyphoscoliosis (cont.)

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Kyphoscoliosis (cont.)

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Flail Chest

Multiple rib fractures result in portion of chest wall becoming free-floating, moving in paradoxic motion during respiratory cycle Bows out during expiration, in during inspiration

Often accompanied by pneumothorax, pulmonary contusion, hemothorax, which require emergent care