Download SMA and Respiratory Care

SMA
Nanci Yuan, MD
LPCH/Stanford Medical Center
May 17, 2006
Spinal Muscular Atrophy (SMA)
Spinal muscular atrophy (SMA) is a genetic,
motor neuron disease caused by progressive
degeneration of motor neurons in the entire
spinal cord and in select brainstem motor nuclei
(nuclei of cranial nerves V, VII, IX, and XII).
The disorder causes weakness and wasting of
the voluntary muscles.
Weakness is often more severe in the legs than
in the arms.
SMA 5q: General Features
H&E stain
ATPase pH 9.4 stain
Large fibers: Hypertrophied & Type I
Small fibers: Type I or II
Grouped atrophy
Small muscle fibers are often rounded
Large muscle fibers hypertrophied.
SMA
SMA is the second most common autosomal
recessive disease in the US after cystic fibrosis.
Incidence:
– Type 1: 1 per 10,000 live births
– Types II and III: 1 per 24,000 births
– SMA types I and III each account for about one fourth
of cases, whereas SMA type II is the largest group
and accounts for one half of all cases
Worldwide 7.8-10 cases per 100,000 live births
? M:F predominance or M>F
No ethnic predominance.
SMA
The genetic defects associated with SMA
types I-III are localized on chromosome
5q11.2-13.3.
Mutations in the SMN gene result in a loss
of function of the SMN protein.
Many classification systems based on
inheritance, clinical, and genetic criteria.
International SMA Consortium (ISMAC,
1994) systems is the most common.
SMA Type 1
SMA type I, (Werdnig-Hoffmann acute infantile,
non-sitters), occur birth – 6 months (95% by 3
months)
Severe, progressive muscle weakness and
flaccid or reduced muscle tone (hypotonia).
Bulbar dysfunction includes poor suck ability,
reduced swallowing, and respiratory failure.
Patients have no involvement of the extraocular
muscles, and facial weakness is often minimal or
absent.
They have no evidence of cerebral involvement,
and infants appear alert.
SMA Type 1
Impaired fetal movements are observed in 30%
of cases
60% of infants with SMA type I are floppy babies
at birth. Prolonged cyanosis may be noted at
delivery.
In some instances, the disease can cause
fulminant weakness in the first few days of life.
Such severe weakness and early bulbar
dysfunction -> mean survival of 5.9 months.
Affected children never sit or stand.
In 95% of cases, infants die from complications
of the disease by 18 months.
SMA Type 2
SMA type II (chronic infantile, sitters) usually
begin between 6 - 18 months.
Most common form of SMA
Most common manifestation is developmental
motor delay. Infants with SMA type II often have
difficulties with sitting independently or failure to
stand by 1 year of age.
These children may learn to sit but will never be
able to stand or walk.
SMA Type 2
An unusual feature of the disease is a postural
tremor affecting the fingers. This is thought to be
related to fasciculations in the skeletal muscles
Pseudohypertrophy of the gastrocnemius
muscle, musculoskeletal deformities, and
respiratory failure can occur.
The lifespan of patients with SMA type II varies
from 2 years to the third decade of life.
Respiratory infections account for most deaths.
SMA Type 3
SMA type III (Kugelberg-Welander, chronic
juvenile, walkers) appear 18 months – adult.
Slowly progressive proximal weakness. Most
can stand and walk but have trouble with motor
skills, such as going up and down stairs.
Bulbar dysfunction occurs late in the disease.
Patients may show evidence of
pseudohypertrophy.
The disease progresses slowly, and the overall
course is mild. Many patients have normal life
expectancies.
SMA
Kennedy syndrome or progressive spinobulbar
muscular atrophy may occur between 15 and 60
years of age. Features of this type may include
weakness of muscles in the tongue and face,
difficulty swallowing, speech impairment, and
excessive development of the mammary glands
in males. The course of the disorder is usually
slowly progressive. Kennedy syndrome is an Xlinked recessive disorder, which means that
women carry the gene, but the disorder only
occurs in men.
Bulbo-Spinal Muscular Atrophy (BSMA; Kennedy's
Syndrome; X-linked)
SMA
Congenital SMA with arthrogryposis
(persistent contracture of joints with fixed
abnormal posture of the limb) is a rare
disorder. Manifestations include severe
contractures, curvature of the spine, chest
deformity, respiratory problems, an
unusually small jaw, and drooping upper
eyelids.
Pulmonary Needs
Is NOT Duchenne’s Muscular Dystophy
Diaphragm NOT involved and IS the
primary muscle of breathing
Diaphragm function better when flat or in
Trendelenburg
Intercostals are weak/ineffective
Chest wall compliance is increased ->
chest wall shape changes (pulled down
chest appearance) -> then decreases
Pulmonary Needs
Pulmonary compliance increases then
decreases
Hypoventilation
Oxygen therapy does not address
hypoventilation
Non-invasive positive pressure ventilation
(NIPPV) – BiPAP NOT CPAP or noninvasive volume ventilator
NIPPV Goals
From Mehta and Hill
Short – term
– Relieve symptoms
– Reduce WOB
– Improve/stabilize blood gas
– Optimize patient comfort
– Good patient-ventilator synchrony
– Minimize risk
– Avoid intubation
NIPPV Goals
From Mehta and Hill
Long – term
– Improve sleep duration and quality
– Maximize quality of life
– Enhance functional status
– Prolong survival
NIPPV
More effective in decreasing work of
breathing than CPAP or negative pressure
Increasing tidal volume -> decreases
respiratory rate
More effective gas exchange
Reduces daytime PCO2
– ?resets PCO2 set point, improves
microatelectasis, rests fatigued muscles
BiPAP
High IPAP (PIP) -> goal is ventilation NOT to
overcome obstruction
– Want to rest muscles/decrease WOB
Low EPAP (PEEP) -> LOW 3-6 cm H20 ->
compromise ability to exhale
Spontaneous – Timed mode -> want high
respiratory rate that will capture their respiratory
effort and rest patient (goal patient synchrony
and rest) – ex. 30
– May also overdrive them if problems with synchrony
and then decrease
BiPAP
I – time based on patient age and
respiratory rate
Rise time (speed of breath delivery)
usually medium setting and on room air (at
home)
NIPPV
Respironics Synchrony
ResMed VPAP III
Puritan Bennett
Need appropriate interface
Heated or pass-over cool mist
humidification
Non-invasive Ventilator
Pressure versus volume NO difference on
outcomes
Volume – breaths on demand during day
– Usually tidal volume 13-20 ml/kg/on nasal
mask
Intubated
Extubate to BiPAP settings
Do NOT wean to low rates or T-piece
Extubate when already on room air so not
to mask atelectasis with supplemental
oxygen
Respiratory Aids
Cough Assist
Chest physiotherapy
IPV
Home suction
Pulse oximeter
Ambubag
Nebulizer
– ?bronchodilators, mucolytics, anticholinergics
Gtube and Nissen fundoplication
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Feature Story
A Matter of Life and Breath
Dr. John Bach "Inspires" Patients to Survive and Thrive
Sidebar Stories
Moving Beyond the Iron Lung
The Hazards of Oxygen
A Recent Study
Reprinted from UMDNJ HealthState
Summer 2002, used by permission.
Conventional
[Top]
1. Oxygen administrated arbitrarily in concentrations that maintain SaO2 well above
95%.
2. Frequent airway suctioning via the tube.
3. Supplemental oxygen increased when desaturations occur.
4. Ventilator weaning attempted at the expense of hypercapnia.
5. Extubation not attempted unless the patient appears to be ventilator weaned.
6. Extubation to CPAP or low span bi-level positive airway pressure and continued
oxygen therapy.
7. Deep airway suctioning by catheterizing the upper airway along with postural
drainage and chest physical therapy.
8. With increasing CO2 retention or hypoxia supplemental oxygen is increased and
ultimately the patient is reintubated.
9. Following re-intubation tracheostomy is thought to be the only long-term option
...or following successful extubation bronchodilators and ongoing routine chest
physical therapy are used.
10. Eventually discharged home with a tracheostomy, often following a rehabilitation
stay for family training.
Protocol
[Top]
1. Oxygen administration limited only to approach 95% SaO2.
2. Mechanical insufflation-exsufflation used via the tube at 25 to 40
cm H2O to -25 to -40 cm H2O pressures up to every 10 minutes as
needed to reverse oxyhemoglobin desaturations due to airway
mucus accumulation and when there is auscultatory evidence of
secretion accumulation. Abdominal thrusts are applied during
exsufflation. Tube and upper airway are suctioned following use of
expiratory aids as needed.
3. Expiratory aids used when desaturations occur.
4. Ventilator weaning attempted without permitting hypercapnia.
5. Extubation attempted whether or not the patient is ventilator
weaned when meeting the following:
A. Afebrile
B. No supplemental oxygen requirement to maintain SaO2 >94%
C. Chest radiograph abnormalities cleared or clearing
D. Any respiratory depressants discontinued
E. Airway suctioning required less than 1-2x/eight hours
F. Coryza diminished sufficiently so that suctioning of the nasal orifices is
required less than once every 6 hours (important to facilitate use of nasal
prongs/mask for post-extubation nasal ventilation)
6. Extubation to continuous nasal ventilation and no supplemental oxygen.
7. Oximetry feedback used to guide the use of expiratory aids, postural
drainage, and chest physical therapy to reverse any desaturations due to
airway mucus accumulation.
8. With CO2 retention or ventilator synchronization difficulties nasal interface
leaks were eliminated, pressure support and ventilator rate increased or the
patient switched from BiPAP-ST™ to using a volume cycled ventilator.
Persistent oxyhemoglobin desaturation despite eucapnia and aggressive use
of expiratory aids indicated impending respiratory distress and need to reintubate.
9. Following re-intubation the protocol was used for a second trial of
extubation to nasal ventilation
...or following successful extubation bronchodilators and chest physical
therapy were discontinued and the patient weaned to nocturnal nasal
ventilation.
10. Discharge home after the SaO2 remained within normal limits for 2 days
and when assisted coughing was needed for less than 4 times per day.
Mary Schroth, MD
Associate Professor
UW Hospital - Clinical Science Center
Office Suite K4/942
Office: (608) 263-8555
Email: [email protected]
View Dr. Mary Schroth's Full CV