Respiratory Care in Neuromuscular
Disease
Cori Daines, MD
Pediatric Pulmonary Medicine
University of Arizona
Neuromuscular Disease
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Duchenne’s muscular dystrophy
Becker’s muscular dystrophy
Limb-Girdle muscular dystrophy
Spinal muscular atrophy
Myotonic dystrophy
Neuromuscular Disease
• Genetically inherited
• Muscle weakness
– Extremities
– Trunk/spine
– Respiratory
– Swallowing
– Cardiac
Neuromuscular disease
• Controller failure
• Chest wall compromise
• Muscle weakness
– Hypotonia
– Hypertonia
Respiratory Control
• Maintain homeostasis
– Oxygen
– Carbon dioxide
– Hydrogen ion concentration (pH)
• Optimize mechanical efficiency
• Complex functions
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Vocalization
Cough
Exercise
Adaptation to disease
Respiratory Muscles
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Diaphragm
Intercostals
Accessory muscles (shoulder girdle)
Pharynx
Larynx
Abdominal wall
Perineum
Physiologic impact
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Ventilatory impairment
Oxygenation impairment [(A-a)DO2 ]
Sleep disordered breathing
Maintenance of lung volume
Growth of the lung in children
Lung clearance impairment
Lung inflammation from aspiration
Nocturnal vs diurnal dysfunction varies
Prevention
• Assuming that there is no primary lung
disease most NMD patients can have normal
lungs
• “An ounce of prevention is worth a pound of
cure”
• 4 E’s = “Expansion, Evacuation, Evasion and
Evaluation”
– i.e. expand the lungs, clear the airways, and avoid
aspiration and infection
– Evaluate how the patient progresses acutely and
over the long term
Minimize work of breathing
• Normally 15% of energy = WOB
• In NMD this can be exceeded
– Decreased use of energy in movement
– Increased work of breathing due to
inefficient system and/or stiff/obstructed
lungs
• Increased WOB will lead to chronic
hypercapnea and compensatory
alkalosis
Expansion
• Weakness leads to
– Poor inspiration
– Atelectasis and decreased compliance due to fluid
accumulation and microatelectasis
– Chest wall/Shoulder girdle contracture
– Kyphoscoliosis (except DMD)
• Loss of MIP correlates with loss of lung
volume and MIP < 30 are predictive of
increases in CO2
Duchenne MD: FVC vs Age
Bach et al. Arch Phys Med Rehabil 1981; 62:328
Expansion
• Reduced: TLC, VC, FRC, ERV
• Balance between chest wall and
diaphragm
– Affects optimal position (Upright better with
weak diaphragm)
– Rate of loss of function affects degree of
breathing intolerance: Rapid is worse
Evacuation
• Optimal humidity and warmth to maintain ciliary
function
• Cough
– Sense
– Close glottis
– Pressurize pulmonary gas by tensing abdomen and
perineum (200 cm H2O)
– Explosively open airway
– Continue cough to lower lung volume
• Cough peak flow transients are 6 to 12 liters per
second; i.e. 360 to 720 L/min
Pulmonary clearance failure
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Disrupted cilia due to drying and inflammation
Low tidal volume (< 20 ml/kg)
Poor glottic closure
Poor abdominal compression
– CPF < 2.7 L/sec = 160L/min predict failure of
extubation in adults (i.e. < 2 L/min/kg)
• Poor coordination
• Inablility to continue to low lung volume
Evacuation
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Chest physiotherapy
Stacking with voluntary cough
Stacking with augmented cough
Mechanical insufflation-exsufflation
Tracheostomy
EVASION: Avoid pulmonary damage
• Growth failure
– Poor expansion
– Poor nutrition
• Aspiration
• Foreign body (tracheostomy)
• Poor clearance with inflammatory
processes
Evasion: Aspiration
• A tension exists between natural, pleasure giving aspects
of feeding and danger of aspiration and inadequate
nutrition
• Often this leads to an illogical approach; i.e. pt has to fail
oral feeds to go to alternative as opposed to succeed with
oral feedings to move off of supportive modalities (NG,GT
etc)
• Progresses early in SMA/Brainstem dysfunction and later
in DMD
• Oral hygiene important even if NPO
Evaluation
• History and physical including QOL and sleep
questionnaire
• Chest film
• Lung volumes
• MIP/MEP
• Sniff MIP
• Inspiratory flow reserve
• Maximum insufflation capacity
• Cough peak flows
Patient status changes with
viral respiratory infections
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Increased secretions
Decreased muscle strength
Surfactant dysfunction in LRI
Transient increase in need for support
We commonly evaluate patients when
they have recovered from an illness or
are stable
Dr. Bach: Outpatient Protocol
• Patients at risk
– During chest colds w/ assisted PCF below 270 LPM
• Patients prescribed
– Oximeter and MIE device
• Patients trained in
– Air stacking insufflated volumes via mouth and nasal
interfaces
– Manually assisted coughing
– Mechanical in-exsufflation at [+35 to +50] to [-35 to -50] cm
H2O
Outpatient Protocol
• Patients given 1-hour access to
– Portable volume ventilator
– Cough Assist MIE (J. H. Emerson Co., Cambridge, MA)
– Various mouthpieces and nasal interfaces
• Patients and care providers are instructed
– SaO2 <95% indicates hypoventilation or airway mucus
accumulation that must be cleared to prevent atelectasis and
pneumonia
– Use SaO2 monitoring whenever fatigued, short of breath, or
ill
– Use noninvasive IPPV and manually and mechanically
assisted coughing as needed to maintain normal SaO2 at all
times
Outpatient Protocol
• Patients with elevated EtCO2 or daytime SaO2 <95%
– Undergo nocturnal SaO2 monitoring
• When symptomatic or nocturnal SaO2 mean <94%
– A trial of nocturnal nasal IPPV is provided
• People continue to use nocturnal nasal IPPV when
they felt less fatigue and nocturnal mean SaO2
increases.
• Most young patients use noninvasive IPPV for the
first time to assist lung ventilation during chest
infections.
Respiratory muscle aids: Indications
• Failure to maintain a healthy lung with
growth and optimal ventilatory function
– i.e. failing the 3 E’s
• Prevention is key
• Optimize support in relation to the
needs of the patient
Using what the patient has
• Daytime spontaneous respiration with
nocturnal support for control, airway
obstruction, recruitment of lung volume
• Glossopharyngeal breathing during the
daytime with nocturnal ventilation
• Optimizing cough and lung volume with
stacking maneuvers
Glossopharyngeal breathing
Maximal insufflation capacity
• Breath stacking
• Measured unassisted with spontaneous
breathes or GPB breaths
• Commonly 1.5x the VC
• Can be augmented with interface and manual
resuscitator bag
• Maintain lung volume and compliance and
chest wall compliance
Inspiratory muscle aids
• Rocking bed and abdominal belt
– Disadvantage is no expansion of lung; i.e.
frc to less than frc
• Negative pressure ventilators
– Disadvantages are OSAS and aspiration
• Non-invasive IPPV
• Tracheostomy and IPPV
Nocturnal support
• Used prior to need for 24/7 support
• Improves daytime PaO2, PaCO2
• Reduces respiratory muscle work at
night and rests the muscles
• Reverses cor pulmonale perhaps in
addition to O2 by improving lung volume
Nocturnal support
• Increases MIP and lung volume
• Improves compliance and FRC during the
daytime
• Can be used even in patients with severe
breathing intolerance
– CCHS or Quadraparesis with daytime
diaphragmatic pacing
– GPB during daytime
• Can be transitioned to 24/7 with illnesses
NIPPV: Interfaces
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Full face mask
Nasal mask
Custom mask
Mouthpiece / Lipseal
– Leakage and dental issues
• Sipper mouthpiece
NIPPV: Nasal mask / Prongs
• 2-3 x preferred compared
to mouthpiece
• Problems:
– Leak, esp mouth
– Nasal bridge pressure with
mask
– Gum erosion or compression
with mask
– Nasal erosion with prongs
• Chin strap may be needed
NIPPV: Full face mask
• Decreased leak
• Decreased
– Cough
– Talking
– Eating
• Nocturnal use with
daytime nasal mask
NIPPV: Sipper / Mouthpiece
• Daytime use
• Allows facial freedom
• Flexed mouthpiece +/- custom
orthodontics
• Intermittently used to augment
breathing
• Continuously used
NIPPV: Sipper / Mouthpiece
• Large VT set on ventilator or High insp
flow if pressure controlled
• Allows stacking maneuvers
• Head/neck control for intermittent use
• Use of flexed mouthpiece with a back
pressure of 2-3 cmH2O can reduce low
pressure/disconnect alarms
Complications of NIPPV
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Facial and orthodontic changes
Aerophagia (PIP > 25 cmH2O)
Nasal drying/congestion = humidify
Volutrauma - air leak
Tracheostomy
• Controversial
• Current view in rehab circles is that with
proper care a tracheostomy is never needed
• Our experience is that tracheostomy may
have a role
– Patient preference
– Upper airway dysfunction
– Severe central airway obstruction by secretions
Ventilators
Ventilators
• Pressure cycled vs Volume cycled
• Pressure cycled are often triggered by flow
sensing reducing work of breathing
• Flow sensing is also important in pts with
high respiratory rates = infants/toddlers
Ventilators
• Leak can vary with sleep, position, and
effort which is problematic with volume
cycled ventilators
• Variable airway resistance and/or
pulmonary or chest wall compliance better
with volume settings
• Pressure cycling limits ability to stack
Ventilator triggering and rate
• Small/weak or brainstem/CNS pts may
not trigger well
• Spontaneous-timed modes are useful
with a backup rate higher than
spontaneous when initiating ventilation
in infants/young children
• Back-up rates lower than spontaneous
once comfortable
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Ventilation goals
Healthy lungs with good volumes and no atelectasis
Rate on the low side and Vt or PIP on the high side
PaCO2 = 35 ± 5 mmHg
Room air
Patient comfort
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Ability to trigger vent
Ability to deliver needed volume/flow in time
No auto-PEEP
No auto-cycling / Ventilator-Patient dysynchrony
• Primary lung disease may change this approach
BiPAP settings
• S/T mode / High span IPAP/EPAP
– If OSAS is main issue low span is appropriate
• IPAP range 15-18
– May need higher with high UA resistance, noncompliant lungs, obesity/non-compliant chest wall
– May need to be lower with high spont rates
• EPAP range 2-4
– Depending upon circuit may need 4 cmH2O to
avoid rebreathing
– High EPAP is rarely needed
Other issues
• Inspiratory time
– I:E of 1:2
– Ti of 0.5 min (infant) and 1.0 (>infant)
• Insp flow rate necessary to achieve pressure
comfortably
• Trigger sensitivity set to reduce WOB, but not
autocycle
• Pressure support may improve comfort with
spontaneous breaths
– Ultimately creates an S/T mode depending upon settings
LTV system - Pulmonetics
LTV system - Pulmonetics
LTV system
LTV: Features
Control mode ventilation
Limited respiratory control / Inability to trigger breaths
Assist Control Mode
Can trigger breaths, but needs support with each breath
SIMV Mode
Most patients, improved comfort, stable CO2s
Bilevel Mode
Mimic BiPAP / No Backup Rate
Rise Time
• Pressure
control
• Pressure
support
• Flow in
volume
control is set
by Ti and Vt
Rise Time
• Slow rise time
– Small ET
– Bronchospasm / AOD
– Pressure overshoot on PIP
• Fast rise time
– Short Ti / High respiratory rate
• Vary with age; i.e. larger VT = faster rise time
Home ventilation reality
• Every patient is unique
• These are “more guidelines rather than
rules”
• Vary settings, interfaces, strategies to
achieve goals of good health and
optimized quality of life
Discharge home: Medical Issues
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Presence of a stable airway
FiO2 less than 40%
PCO2 safely maintained
Nutritional intake optimal
Other medical conditions well controlled
Above may vary if palliative care
Jardine E, Wallis C. Thorax 1998; 53:762
Discharge Home: Support
• Goals and plans clarified with family and
caregivers
• Family and respite caregivers trained in the 4
E’s and all equipment
• Nursing support arranged for nighttime
• Equipment lists developed and implemented
with re-supply and funding addressed
• Funding and insurance issues addressed