A very large proportion of Intensive Care Patients. Discussed in detail about causes diagnosis and management pearls of neuromuscular respiratory failure. Intensive Care Physicians will find this presentation very useful and informative.
2. Introduction
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Respiratory Failure… definition
Types…. I & II
Why this distinction is important?
Causes & Classification
– Pulmonary
– Non pulmonary
• Nonpulmonary causes of respiratory failure
include diverse group of disorders….
• Pathophysiologic hallmark….. Hypoventilation
• Approx 20% cases of respiratory failure
3. Introduction
• Hypoventilation
• Theoretical definition:
– Deviation from the usual state of ventilatory
control resulting in decreased minute ventilation
relative to metabolic requirements
• Operational definition:
– Hypoventilation exists when alveolar or arterial
PaCO2 exceeds normal upper limit (44 mmHg)
4. Single compartment lung model
PaCO2= VCO2/VE (1-VD/VT)
PAO2= FiO2(Patm-P H2O)-1.2(PaCO2)
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VCO2= CO2 elimination rate
VE= minute ventilation
VD= dead space
VT= tidal volume
5. EtiologicalClassification
Plum & Leigh & Phillipson
Nonpulmonary causes of respiratory failure
Ventilatory control
Neuromuscular Disorders
↓Peripheral
Chemosensitivity
Anterior horn cells
Brain stem neurons
Phrenic neuropathies
Spinal Cord pathways
NMJ disorders
Respiratory muscles
In all these conditions the lungs are normal !!!!
Chest wall & Other
disorders
Obesity-hypovent
Syndrome
Kyphoscoliosis
Fibrothorax
Thoracoplasty
Ankylosing
spondylitis
Flail chest
Metabolic alkalosis
6. Primary disorders of ventilatory control
↓Peripheral
Chemosensitivity
Carotid body
surgery
Prolonged hypoxia
Metabolik alkalosis
Brain stem neurons
Bulbar polio
Syringobulbia
Encephalitis
Infarction
Neoplasm
Demyelinating
disorders
Drugs
Neoplasms
Spinal Cord pathways
Trauma
Bilateral high
cervical cordotomy
Anterior spinal
cord surgery
Transverse myelitis
Encephalomyelitis
9. Neurogenic Respiratory Failure
• Definition
– Respiratory failure due to difficulties with
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Cortical, Brainstem respiratory centers
Motor neurons (Cell bodies)
Axons
Neuromuscular junction
– Pre synaptic
– Post synaptic
• Muscle
– Not due to primary pulmonary problems
10. Clinical Recognition
Signs and Symptoms
• The initial manifestation of respiratory failure & the
age at presentation can vary….
• Primary disorders of ventilatory control
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Excessive day time somnolence
Pulmonary HTN
Corpulmonale
Severe respiratory failure following sedatives
• Neuromuscular disorders
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Unexplained hypercapnia
Dyspnea
Sleep disruption
Recurrent pneumonia
11. Manifestation of Respiratory Muscles Involvement
• Tachypnea …. (expression of muscle fatigue)
• Signs of diaphragmatic weakness
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Orthopnea
Paradoxical abdominal wall movement
Respiratory alternans
REM associated hypoventilation
• Signs of abdominal muscle weakness
– Decreased cough effort
• Signs of bulbar muscle weakness
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Dysarthria
Dysphonia
Dysphagia
Aspiration
Obstructive sleep apnea
12. Functional Assessment
Disorders of ventilatory control
Chronic neuromuscular disorders
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• Lung mechanics & muscles
Lung mechanics
Respiratory muscle strength
Gas exchange
Arterial PaCO2
Central apneas
Response to exogenous
hypoxia
• Polycythemia & ↑ HCO3
• Voluntary breath-holding
• Response to elastic & resistive
load..(Borg scale of dyspnea)
– Restricted lung volumes
– Decline in vital capacity
– PI max & PE max (
– Electromyography
• Gas exchange
– Mild hypoxemia
– Normal diffusion capacity
• Contribution of additional
factors
– Microatelactasis
– Alteration in surfactant
– Progressive deformity of thorax
13. Laboratory Values in Monitoring
Acute Neuromuscular Failure
Normal
value
Measurement
Procedure
Vital capacity
Max exhalation
45-70 mL/kg
Maximal Inspiratory
pressure (PI max)
Max inhalation
M >-100 cm H2O
F >-70 cm H2O
Maximal expiratory pressure
(PE max)
Max blowing out
M >200 cm H2
F >140 cm H2O
15. Respiratory weakness
• Arterial blood gases
– Initial changes
• Subtle drop in oxygen levels with the development of
atelectasis
– Later changes
• Mild hypercapnia with normal ph
• Rapid deterioration with apnea
16. Respiratory weakness
• Respiratory parameters
– Forced vital capacity
• Generally intubate if <10 ml/kg
• May be underestimated by respiratory technician
• Similar flow volume loops as COPD
– Prolonged tail due to extended exhalation time
• Count to 30 on one breath
– Cheap but effective way to estimate VC
– Approximately 2 Liters
• Neck flexors and proximal muscle strength correlate
best with respiratory strength
17. Guillain-Barre Disease
(Acute Inflammatory demyelinating polyneuropathy)
• Autoimmune process
– Effects myelin sheath of
peripheral nerves
– Humoral attack may be
induced by viruses,
vaccinations
– Demyelination slows
conduction along nerves
• Leads to progressive
weakness
– Axonal variant
18. MGH Series
Retrospective Series
n=169
Upper
respiratory
tract infection
36%
No prior
illness
38%
Prospective Series
n=120
Upper respiratory
tract infection
49%
No prior
illness
27%
Diarrhea
10%
Diarrhea
8%
Malaise
6%
Surgery
6%
Ropper, Wijdicks, Truax, 1991
EBV
5%
Pregnancy
1%
Hodgkin’s
disease,
surgery, SLE,
vaccination
3%
CMV
Malaise 3%
3%
EBV
3%
Pneumonia
2%
CP1142597-8
19. Diagnostic Criteria for GBS
• Strongly supportive features
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Progression of symptoms over 4 weeks
Symmetric legs greater than arms weakness
Mild sensory symptoms
Cranial nerve involvement especially bilateral facial
weakness
– High protein content in the CSF with < 10 cells
– EMG/ NCV: Conduction block, increased F waves and distal
latencies
20. Treatment for GBS
• Supportive
– Respiratory
• Intubate Early
• No role for BiPap in GBS
– Treat dysautonomia
• Deafferented cardiac and baroreceptors
• Pseudoobstruction
• DVT prophylaxis
• Plasma Exchange
• IVIG
• Steroids not helpful
– Evaluate for CIDP
21. Plasma Exchange Trials in GBS
North American study
Plasma
exchange
n=122
Conventional
n=123
Days to reach grade 2 (median)
53
85
Patient improved at least 1 grade at 6 months (%)
97
87
Patients walking independently at 6 months (%)
82
71
French study
Days to onset motor recovery (median)
n=111
n=109
6
13
Days weaning (median)
18
31
Days to recover walking without
assistance (median)
70
111
CP1142597-47
22. Prognosis GBS
• Depends upon degree and extent of Axonal
damage
– Demyelination alone will recover within days to
weeks
– Axonal damage with intact myelin sheaths will
recover within months
– Most patients will make a complete recovery
• Psychological support
• GBS Support groups
24. Respiratory weakness
• Clinical findings
(Not all patients will have)
– Dyspnea
• VC is half of predicted
– Brow sweating
– Accessory muscle use
• INTUBATION SHOULD NOT BE BASED
UPON THE CLINICAL PRESENTATION
ALONE BUT ON THE RATE OF
RESPIRATORY DECLINE, AND
PULMONARY FUNCTION TESTS
25. Acute Respiratory Failure
• Inspiratory and expiratory muscles
involvement is variable
• Inspiratory muscle fatigue occurs because….
• Work of breathing is increased because….
• Blood flow to respiratory muscles is
compromised because….
• Inspiratory muscles weakness → atelactasis
26. Acute Respiratory Failure
• Risk of respiratory failure increases when VC falls
below 15 mL/kg
• Watch the trend….. Serial measurements
• The question of when to start ventilatory
support….
• An anticipatory approach avoids risks associated
with emergent intubation and minimizes
complications
• The mode of ventilation..
• Supportive care is important
27. Chronic Respiratory Failure
• Prolonged mechanical ventilation is defined by
the Centers for Medicare and Medicaid Services
in the United States as greater than 21 days of
mechanical ventilation for at least 6 hours per
day.
• Most patients requiring prolonged mechanical
ventilation will have a tracheostomy placed to
facilitate comfort, communication, and chronic
ventilator facility or home ventilation placement.
28. Chronic Respiratory Failure
• Common problems among patients undergoing
prolonged mechanical ventilation
– Infections (e.g., pneumonia,line sepsis, Clostridium difficile
colitis
– Ileus
– Renal failure
– Pneumothorax
– Seizures
– Tracheal bleeding
– Laryngeal edema
– Development of tracheal granulation tissue
– Tracheoesophageal fistula formation
– Loss of airway patency because of unplanned extubation
or decannulation
35. Conclusions
• A normal P(A - a)O2 difference should not be
required as a diagnostic criterion for
nonpulmonary causes of respiratory failure.
• The etiologic classification of nonpulmonary
disorders causing respiratory failure consists
of the following broad categories:
– disorders of ventilatory control,
– neuromuscular disorders
– disorders of the chest wall, and upper airway
obstruction.
36. Conclusions
• Clinical recognition of these disorders depends on
familiarity with the physiologic consequences of
chronic hypoxia and hypercapnia, the signs and
symptoms of respiratory muscle weakness, and their
effects on pulmonary function tests.
• The approach to the management of acute
respiratory failure does not differ in principle from
the approach used in lung diseases.
• Noninvasive nocturnal ventilatory support has gained
acceptance as a means of controlling diurnal
hypercapnia and providing respiratory muscle rest.
Resp failure def from 3rd ed. Introductory line from 2nd ed. First paragraph.
Any given patient may have more than one process leading to respiratory failure. Example hypothyroidism… poliomyelitis… muscular dystrophies…A series of responsis is elicited by chronic hypoxemia and hypercapnia….
Now as a physician you should have a wide index of suspicion, awareness of the possible involvement of muscles of respiration in particular the diaphragm and the ability to recognize its clinical expression areoften the most important elements in the diagnosis.