Introduction to Mechanical Ventilation

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Introduction to Mechanical Ventilation

• Craig A. Hawkins BS RRT RCP
• Respiratory Therapy Supervisor
• Presbyterian Hospital

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Indications for Mechanical Ventilation

• Impending Respiratory Failure
• Acute Respiratory Failure/Arrest
• Post-Operatively

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Indications for Mechanical Ventilation

• Impending Respiratory Failure
• Progressively worsening clinical appearance.
• Worsening CXR.
• Hypoxemic Respiratory Failure.
• Hypercapnic Respiratory Failure.

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Indications for Mechanical Ventilation

• Acute Respiratory Failure/Arrest
• Acute change in ABG results
• Respiratory Arrest/Status Post CPR
• Acute epiglottitis/anaphylaxis

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Indications for Mechanical Ventilation

• Postoperatively
• Oversedation/paralytics
• Pain Control
• Proper Immobilization

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Key Terms in Mechanical Ventilation

• Tidal Volume (Vt)
• The volume of air inhaled and exhaled from the
  lungs.
• Breaths per Minute (RR, f)
• Also known as frequency.
• Positive End Expiratory Pressure (PEEP)
• Maintenance of above atmospheric pressure at the
  airway throughout exp. phase.

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Key Terms in Mechanical Ventilation

• Minute Ventilation (VE)
• The total amount of volume moving in and out of
  the lung in one minute.
• Fractional Inspired Oxygen (FiO2)
• Correctly written with decimal place (21-0.21
  100-1.0)
• InspiratoryExpiratory Ratio (IE ratio)
• Normal IE ratio 12-3

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Negative Pressure Ventilation

• Rarely Used Currently used for patients with
  neuromuscular diseases.
• Thoracic cage is encased where negative pressure
  is applied across the chest wall.
• Generates subatmospheric pressures creating a
  difference in pressure gradients.
• During exhalation, negative pressure is replace
  by atmospheric pressure allowing the lungs to
  deflate.

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Negative Pressure Ventilation

• Types of Negative Pressure Ventilators

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Iron Lung circa 1950s
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Modern(ized) Iron Lung
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Chest Cuirass
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Complications with Negative Pressure Ventilation

• Limited access for patient care.
• Inability to properly monitor pulmonary
  mechanics.
• Patient discomfort.

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Positive Pressure Ventilation

• Defined as the application of pressure to the
  lungs in order to improve gas exchange.
• The Lungs are physically filled/ventilated with
  air using machinery.
• Multiple modes, methods, and theory.

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Positive Pressure Ventilation

• Basically broken into two categories
• Control Modes.
• Supportive Modes.

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Control Modes of Ventilation

• Assist/Control (usually abbreviated A/C also
  known as Volume Control VC).
• Tidal Volume is set and remains constant.
• Respiratory Rate is set.
• Airway Pressure will vary according to lung
  compliance.
• Ventilator will deliver set volume whether
  patient triggers a breath or mandatory breath is
  being delivered.

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Control Modes of Ventilation

• Pressure Control Ventilation (usually abbreviated
  PCV or sometimes PCIRV).
• Upper Airway Pressure Level is set and remains
  constant.
• Respiratory Rate is set.
• Tidal volumes will vary according to lung
  compliance.
• Ventilator will deliver set pressure level
  whether patient triggers a breath or mandatory
  breath is being delivered.

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Control Modes of Ventilation

• Pressure Regulated Volume Control (usually
  abbreviated PRVC).
• Tidal Volume is set, however may or may not
  remain constant.
• Respiratory Rate is set.
• Ventilator will deliver volume however volume may
  decrease according to patients lung compliance.
• A lung protective mode.

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Supportive Modes of Ventilation

• Synchronized Intermittent Mandatory Ventilation
  (usually abbreviated SIMV).
• Tidal Volume is set and delivered on each
  mandatory breath.
• Respiratory Rate is set.
• When a patient triggers the ventilator
  spontaneously , the patient receives a Pressure
  Supported breath.

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Supportive Modes of Ventilation

• Pressure Support Ventilation (PSV)
• Is a strictly patient dependant mode patient
  must be breathing spontaneously.
• An upper (inspiratory) pressure level is adjusted
  to provide adequate tidal volumes for each
  patient triggered breath.
• PEEP is also adjusted as an independent pressure
  from the upper pressure level and is active
  during expiration.
• PSV is a weaning mode.

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Supportive Modes of Ventilation

• Volume Support (VS)
• Is a strictly patient dependant mode patient
  must be breathing spontaneously.
• Tidal Volume is set.
• Each spontaneous breath is supported with dialed
  volume.

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Supportive Modes of Ventilation

• Continuous (Constant) Positive Airway Pressure
  (CPAP)
• Is a strictly patient dependant mode patient
  must be breathing spontaneously.
• Closely resembles Pressure Support, however CPAP
  is a constant set pressure that does not change
  during inspiration or expiration.
• CPAP is a weaning mode.

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Drager Evita II
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Puritan Bennett 840
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Servo 900c
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Servo 300a
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Servo i
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One of the Most Famous Ventilators
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Complications to Mechanical Ventilation

• Ventilator Induced Lung Injury (VILI)
• Induced by excessive pressure (barotrauma)
• Induced by excessive Volume (volutrauma)
• Ventilator Associated Pneumonia (VAP)
• Most commonly Pseudomonas, Gram Negative Bacilli,
  and staphylococci.

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Ventilatory Discontinuance

• Weaning
• Process of discontinuing ventilatory support,
  regardless of the time frame involved.
• Categories
• Quick removal routine
• More gradual reduction in support (trach collar
  trials)
• Ventilator dependent patients

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Ventilatory Discontinuance

• Success in discontinuing ventilatory support is
  related to the patients conditions in four main
  areas
• Ventilatory workload
• Oxygenation status
• Cardiovascular function
• Psychological factors.

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Ventilatory Discontinuance

• Common indices in successful weaning

FiO2 lt 0.4-0.5 PaO2 gt 60 PaO2/FiO2 ratio gt
200 PaCO2 lt 50 pH gt 7.35 RSBI lt 100
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Questions?