Respiratory Failure

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Respiratory Failure

• Esam H. Alhamad, M.D
• Assistant Professor of Medicine
• Consultant Pulmonary and Critical Care Medicine.

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Definitions

• acute respiratory failure occurs when
• pulmonary system is no longer able to meet the
  metabolic demands of the body
• hypoxaemic respiratory failure
• PaO2 ? 50 mm Hg when breathing room air
• hypercapnic respiratory failure
• PaCO2 ? 50 mm Hg.

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Basic respiratory physiology
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O2
CO2
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Oxygen in

• Depends on
• PAO2
• Diffusing capacity
• Perfusion
• Ventilation-perfusion matching

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Oxygen
Carbon dioxide
Water vapour
Nitrogen
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Oxygen in

• Depends on
• PAO2
• FIO2
• PACO2
• Alveolar pressure
• Ventilation
• Diffusing capacity
• Perfusion
• Ventilation-perfusion matching

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Carbon dioxide out

• Largely dependent on alveolar ventilation
• Anatomical deadspace constant but physiological
  deadspace depends on ventilation-perfusion
  matching

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Carbon dioxide out

• Respiratory rate
• Tidal volume
• Ventilation-perfusion matching

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Pathophysiology
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?FIO2
Ventilation without perfusion (deadspace
ventilation)
Hypoventilation
Diffusion abnormality
Normal
Perfusion without ventilation (shunting)
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?FIO2
Ventilation without perfusion (deadspace
ventilation)
Hypoventilation
Diffusion abnormality
Normal
Perfusion without ventilation (shunting)
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75
75
100
75
87.5
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Perfusion without ventilation (Shunting)

• Intra-cardiac
• Any cause of right to left shunt
• eg Fallots, Eisenmenger
• Intra-pulmonary
• Pneumonia
• Pulmonary oedema
• Atelectasis
• Collapse
• Pulmonary haemorrhage or contusion

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Perfusion without ventilation (shunting)

• Intra-pulmonary
• Small airways occluded ( e.g asthma, chronic
  bronchitis)
• Alveoli are filled with fluid ( e.g pulm edema,
  pneumonia)
• Alveolar collapse ( e.g atelectasis)

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?FIO2
Ventilation without perfusion (deadspace
ventilation)
Hypoventilation
Diffusion abnormality
Normal
Perfusion without ventilation (shunting)
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V/Q mismatch

• Dead space ventilation
• Alveoli that are normally ventilated but poorly
  perfused
• Anatomic dead space
• Gas in the large conducting airways that does not
  come in contact with the capillaries e.g pharynx

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V/Q mismatch

• Dead space ventilation
• Physiologic dead space
• Alveolar gas that does not equilibrate fully with
• capillary blood

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Dead space vantilation

• DSV increase
• Alveolar-capillary interface destroyed e.g
  emphysema
• Blood flow is reduced e.g CHF, PE
• Overdistended alveoli e.g positive- pressure
  ventilation

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?FIO2
Ventilation without perfusion (deadspace
ventilation)
Hypoventilation
Diffusion abnormality
Normal
Perfusion without ventilation (shunting)
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Diffusion abnormality

• Less common
• Abnormality of the alveolar membrane or a
  reduction in the number of capillaries resulting
  in a reduction in alveolar surface area
• Causes include
• Acute Respiratory Distress Syndrome
• Fibrotic lung disease

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?FIO2
Ventilation without perfusion (deadspace
ventilation)
Hypoventilation
Diffusion abnormality
Normal
Perfusion without ventilation (shunting)
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Brainstem
Spinal cord
Nerve root
Airway
Nerve
Lung
Pleura
Neuromuscular junction
Chest wall
Respiratory muscle
Sites at which disease may cause ventilatory
disturbance
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Brainstem
Spinal cord
Nerve root
Airway
Nerve
Lung
Pleura
Neuromuscular junction
Chest wall
Respiratory muscle
Sites at which disease may cause ventilatory
disturbance
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Brainstem
Spinal cord
Nerve root
Airway
Nerve
Lung
Pleura
Neuromuscular junction
Chest wall
Respiratory muscle
Sites at which disease may cause ventilatory
disturbance
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Brainstem
Spinal cord
Nerve root
Airway
Nerve
Lung
Pleura
Neuromuscular junction
Chest wall
Respiratory muscle
Sites at which disease may cause ventilatory
disturbance
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Brainstem
Spinal cord
Nerve root
Airway
Nerve
Lung
Pleura
Neuromuscular junction
Chest wall
Respiratory muscle
Sites at which disease may cause ventilatory
disturbance
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Brainstem
Spinal cord
Nerve root
Airway
Nerve
Lung
Pleura
Neuromuscular junction
Chest wall
Respiratory muscle
Sites at which disease may cause ventilatory
disturbance
29
Brainstem
Spinal cord
Nerve root
Airway
Nerve
Lung
Pleura
Neuromuscular junction
Chest wall
Respiratory muscle
Sites at which disease may cause ventilatory
disturbance
30
Brainstem
Spinal cord
Nerve root
Airway
Nerve
Lung
Pleura
Neuromuscular junction
Chest wall
Respiratory muscle
Sites at which disease may cause ventilatory
disturbance
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Respiratory FailureSymptoms

• CNS
• Headache
• Visual Disturbances
• Anxiety
• Confusion
• Memory Loss
• Weakness
• Decreased Functional Performance

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Respiratory FailureSymptoms

• Pulmonary
• Cough
• Chest pains
• Sputum production
• Stridor
• Dyspnea

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Respiratory FailureSymptoms

• Cardiac
• Orthopnea
• Peripheral edema
• Chest pain
• Other
• Fever, Abdominal pain, Anemia, Bleeding

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Clinical

• Respiratory compensation
• Sympathetic stimulation
• Tissue hypoxia
• Haemoglobin desaturation

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Clinical

• Respiratory compensation
• Tachypnoea RR gt 35 Breath /min
• Accessory muscles
• Recesssion
• Nasal flaring
• Sympathetic stimulation
• Tissue hypoxia
• Haemoglobin desaturation

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Clinical

• Respiratory compensation
• Sympathetic stimulation
• ?HR
• ?BP
• sweating
• Tissue hypoxia
• Haemoglobin desaturation

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Clinical

• Respiratory compensation
• Sympathetic stimulation
• Tissue hypoxia
• Altered mental state
• ?HR and ?BP (late)
• Haemoglobin desaturation

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Clinical

• Altered mental state
• ?PaO2 ?PaCO2 ? acidosis ? dilatation of cerebral
  resistance vesseles ? ?ICP
• Disorientation Headache
• coma asterixis
• personality changes

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Clinical

• Respiratory compensation
• Sympathetic stimulation
• Tissue hypoxia
• Haemoglobin desaturation
• cyanosis

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Respiratory FailureLaboratory Testing

• Arterial blood gas
• PaO2
• PaCO2
• PH
• Chest imaging
• Chest x-ray
• CT sacn
• Ultrasound
• Ventilationperfusion scan

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Respiratory FailureLaboratory Testing

• Respiratory mechanics
• Spirometry (FVC, FEV1, Peak flow)
• Respiratory muscle pressures
• MIP ( maximum inspiratory pressure)
• MEP ( maximum expiratory pressure)

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Respiratory FailureLaboratory Testing

• Other tests
• Hemoglobin
• Electrolytes, blood urea nitrogen, creatinine
• Creatinine phosphokinase, aldolase
• EKG, echocardiogram
• Electromyography (EMG)
• Nerve conduction study

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True or False

• Diffusion abnormality is considered the most
  common cause of hypoxia.

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True or False

• Dead space ventilation decreases when blood flow
  is reduced

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True or False

• Shunt occurs when areas of lung are perfused but
  not ventilated

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True or False

• In myasthenia gravis mechanism of hypoxia may be
  due to alveoli being perfused but not ventilated

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True or False

• Arterial hypoxemia may be caused by alveolar
  hypoventilation alone

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True or False

• The distinction between ventilation/perfusion
  mismatch and intrapulmonary shunting can be made
  by measuring the response to the administration
  of 100 oxygen

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True or False

• There is a good relationship between dyspnea and
  arterial hypoxemia but a poor relationship
  between dyspnea and arterial carbon dioxide
  retention

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Which of the following statements regarding the
physical examination for patients with acute
respiratory failure are true or false?

• Central nervous examination is important
• Breath sounds are commonly diminished
• Supraclavicular and intercostal space muscle
  retractions do not correlate with increased work
  of breathing

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Pulse oximetry
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Sources of error

• Poor peripheral perfusion
• Dark skin
• False nails or nail varnish
• Lipaemia
• Bright ambient light
• Poorly adherent probe
• Excessive motion
• Carboxyhaemoglobin or methaemoglobin

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Sources of error

• Poor peripheral perfusion
• Dark skin
• False nails or nail varnish
• Lipaemia
• Bright ambient light
• Poorly adherent probe
• Excessive motion
• Carboxyhaemoglobin or methaemoglobin

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Sources of error

• Poor peripheral perfusion
• Dark skin
• False nails or nail varnish
• Lipaemia
• Bright ambient light
• Poorly adherent probe
• Excessive motion
• Carboxyhaemoglobin or methaemoglobin

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Sources of error

• Poor peripheral perfusion
• Dark skin
• False nails or nail varnish
• Lipaemia
• Bright ambient light
• Poorly adherent probe
• Excessive motion
• Carboxyhaemoglobin or methaemoglobin

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Sources of error

• Poor peripheral perfusion
• Dark skin
• False nails or nail varnish
• Lipaemia
• Bright ambient light
• Poorly adherent probe
• Excessive motion
• Carboxyhaemoglobin or methaemoglobin

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Sources of error

• Poor peripheral perfusion
• Dark skin
• False nails or nail varnish
• Lipaemia
• Bright ambient light
• Poorly adherent probe
• Excessive motion
• Carboxyhaemoglobin or methaemoglobin

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Sources of error

• Poor peripheral perfusion
• Dark skin
• False nails or nail varnish
• Lipaemia
• Bright ambient light
• Poorly adherent probe
• Excessive motion
• Carboxyhaemoglobin or methaemoglobin

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Sources of error

• Poor peripheral perfusion
• Dark skin
• False nails or nail varnish
• Lipaemia
• Bright ambient light
• Poorly adherent probe
• Excessive motion
• Carboxyhaemoglobin or methaemoglobin

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Arterial blood gases

• See Arterial blood gases lecture