Neuromuscular Respiratory Failure


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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.

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  • 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.
  • Neuromuscular Respiratory Failure

    1. 1. Neuromuscular Respiratory Failure Dr. Muhammad Asim Rana MBBS, MRCP, EDIC, SF-CCM, FCCP Department of Critical Care Medicine
    2. 2. Introduction • • • • 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. 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. 4. Single compartment lung model PaCO2= VCO2/VE (1-VD/VT) PAO2= FiO2(Patm-P H2O)-1.2(PaCO2) – – – – VCO2= CO2 elimination rate VE= minute ventilation VD= dead space VT= tidal volume
    5. 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. 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
    7. 7. Neuromuscular disorders Anterior horn cells Amyotrophic lateral sclerosis Spinal muscular atrophies Poliomyelitis Phrenic neuropathies GBS Porphyria Neuralgic amyotrophy Surgical (cardiac hypothermia) Paraneoplastic Critical illness polyneuropathies Respiratory muscles NMJ disorders Myasthenia gravis Eaton-lambert Muscular dystrophies Drugs Myotonic Toxins dystrophies Tetanus Mitochondrial Electrolyte abnormalities myopathies Rhabdomyolysis Prolonged neuromuscular Scleroderma blockade
    8. 8. Recognizing Neuromuscular Respiratory Failure When to Suspect
    9. 9. Neurogenic Respiratory Failure • Definition – Respiratory failure due to difficulties with • • • • Cortical, Brainstem respiratory centers Motor neurons (Cell bodies) Axons Neuromuscular junction – Pre synaptic – Post synaptic • Muscle – Not due to primary pulmonary problems
    10. 10. Clinical Recognition Signs and Symptoms • The initial manifestation of respiratory failure & the age at presentation can vary…. • Primary disorders of ventilatory control – – – – Excessive day time somnolence Pulmonary HTN Corpulmonale Severe respiratory failure following sedatives • Neuromuscular disorders – – – – Unexplained hypercapnia Dyspnea Sleep disruption Recurrent pneumonia
    11. 11. Manifestation of Respiratory Muscles Involvement • Tachypnea …. (expression of muscle fatigue) • Signs of diaphragmatic weakness – – – – Orthopnea Paradoxical abdominal wall movement Respiratory alternans REM associated hypoventilation • Signs of abdominal muscle weakness – Decreased cough effort • Signs of bulbar muscle weakness – – – – – Dysarthria Dysphonia Dysphagia Aspiration Obstructive sleep apnea
    12. 12. Functional Assessment Disorders of ventilatory control Chronic neuromuscular disorders • • • • • • • 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. 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
    14. 14. Respiratory weakness • • • • • • Normal – 45--70 ml/kg Weak cough – 30 ml/kg Atelectasis – 20--25 ml/kg Sigh lost, atelectasis and shunting 15 ml/kg Hypoventilation – 10 ml/kg Hypercapnia – 5-10 ml/kg
    15. 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. 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. 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. 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. 19. Diagnostic Criteria for GBS • Strongly supportive features – – – – 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. 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. 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. 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
    23. 23. Patient Management Acute Respiratory Failure Chronic Respiratory Failure
    24. 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. 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. 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. 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. 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
    29. 29. Chronic Respiratory Assist Devices (Mode of Ventilation) • Abdominal displacement – Pneumobelt – Rocking Bed • Negative Pressure Ventilation – Pneumosuit – Chest Cuirass – Iron lung • Positive Pressure Ventilation – Volume Cycled – Pressure Cycled
    30. 30. Chronic Respiratory Assist Devices Pneumobelt
    31. 31. Chronic Respiratory Assist Devices Rocking Bed
    32. 32. Chronic Respiratory Assist Devices Pneumosuit and Iron Lung
    33. 33. Chronic Respiratory Assist Devices Iron Lung
    34. 34. Chronic Respiratory Assist Devices Diaphargm Pacing
    35. 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. 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.
    37. 37. Questions and Remarks If NO Thank you very much