Kishore P.

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Invasive Mechanical Ventilation
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• Ventilate is derived from
• Latin word ventus meaning wind

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Mask based device
Negative pressure ventilators The Iron Lung
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Why ventilate?

• Improve oxygenation
• Increase/maintain minute ventilation and help CO2
  clearance
• Decrease work of breathing
• Protect airway

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Common indications for ventilation

• Hypoxemic respiratory failure 66
• Acute exacerbation of COPD 13
• Neuromuscular disorders - 10
• Coma - 10

Data from Americas and Europe
Am. J. Respir. Crit. Care Med., Volume 161,
Number 5, May 2000, 1450-1458
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Key concepts

• Determinants of Oxygenation
• - Ventilator factors
• FiO2 ( fraction of oxygen in inspired air)
• Mean airway pressure
• PEEP ( positive end expiratory pressure)
• - Patient factors
• V/Q (ventilation/ perfusion) mismatch
• Shunt
• Diffusion defect
• Reduced mixed venous oxygen

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Key concepts

• Determinants of CO2 clearance
• - Ventilator factors
• Rate
• Tidal volume
• Anatomical dead space
• - Patient factors
• Physiological dead space
• CO2 production

Alveolar minute ventilation
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• Adjust FiO2 and PEEP according to PaO2 and SpO2
• Adjust TV and rate according to PCO2 and pH

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Modes of ventilationVolume controlled

• Machine delivers a set volume irrespective of the
  pressure generated within the system
• Adv.
• - predefined minute volume is guaranteed
• Disadv.
• - changes in mechanical properties of lungs
  (resistance or compliance) can lead to high
  pressures
• - Patient is unable to adjust breathing pattern
  to changes in ventilatory demand

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Modes of ventilationPressure controlled

• Ventilator applies a predefined target pressure
  to the airway during inspiration
• Adv.
• - decreased risk of barotrauma
• Disadv.
• - with decreasing compliance or increasing
  resistance, tidal volume and minute ventilation
  fall

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Volume control
Pressure control

• TV, inspiratory flow, IE ratio
• Tidal volume
• Airway pressure

• Peak inspiratory pressure, inspiratory time,
• Maximum inspiratory pressure
• Tidal volume

Settings
Constant
Variable
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Patient system interaction
CPAP
PEEP
Spontaneous
SIMV
IMV
Assist control
Assisted-pressure support
Controlled MV
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Continuous mandatory ventilation (CMV)

• Also known as controlled mechanical ventilation
• Rate, IE ratio, volume determined entirely by
  machine and cannot be altered by patient effort
• Used in paralyzed patients only

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Intermittent mandatory ventilation (IMV)

• Patient is allowed to take spontaneous breaths in
  between preset timed ventilator breaths
• The ventilator does not offer any assistance to
  the spontaneous breaths
• Stacking of breaths may occur

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Assist control (A/C)

• In addition to a preset number of mandatory
  breaths, the ventilator delivers additional full
  breaths whenever the patient has a spontaneous
  respiratory effort
• Sensitivity of trigger important

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Synchronized intermittent mandatory ventilation
(SIMV)

• The ventilator attempts to synchronize the set
  number of mandatory breaths with the patients
  respiratory efforts
• The ventilator waits for a patient effort during
  a sensitive peroid before every breath. In its
  absence, it gives a controlled breath
• Spontaneous breaths outside of this sensitive
  period are unsupported
• Commonly used mode

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Pressure support

• Delivers a breath to a preset airway pressure
  when the patient makes an inspiratory effort
• Cycles into expiration when inspiratory flow
  falls toward end of inspiration
• Used along with SIMV
• Useful for weaning

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Newer modes

• Hype
• Add to cost
• No reliable evidence for better outcomes in terms
  of mortality, duration of ventilation

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Adaptive support ventilation (ASV)

• A weight based minimum minute ventilation is set.
• the machine decides how to achieve that MV with
  the least work of breathing-fixes an appropriate
  TV and rate
• Decreases the need for frequent reassessment and
  changes in ventilator settings
• No outcome difference

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Proportional assist ventilation (PAV)

• Useful weaning mode
• The proportion of work of breathing to be
  contributed by the ventilator is set
• Each breath gets a different degree of support
  from the ventilator depending on patient effort.
• Theoretically smooth offloading

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Others

• Airway pressure release ventilation (APRV)
• Pressure controlled inverse ratio ventilation

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Patient system interaction
CPAP
PEEP
Spontaneous
SIMV
IMV
Assist control
Assisted-pressure support
Controlled MV
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• One of the key goals of mechanical ventilation is
  to decrease work of breathing
• Improper ventilator settings can however increase
  work of breathing, increasing patient distress
  and worsening hemodynamics and metabolic
  parameters

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Remember

• Ventilation is not an end in itself, it is only a
  form of organ support
• The nuances of ventilation should not take away
  from the primary goal of treating the underlying
  condition

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Whos Watching the Patient?
Pierson, IN Tobin, Principles and Practice of
Critical Care Monitoring
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Default settings

• TV-6-8ml/kg
• Rate 15/min
• FiO2 100
• PEEP 5cmH2O
• Pressure support 15cmH2O
• Ti 1.0 sec
• Pramp 50msec

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Monitor and re-adjust

• FiO2-
• based on PaO2 and SpO2. maintain PaO2 60-90mmHg
• Aim to reduce FiO2 below 60
• PEEP-
• based on PaO2 and SpO2.
• Aim to reduce FiO2 below 60.
• Can increase rapidly but can be reduced very
  gradually

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Monitor and re-adjust

• Rate
• To keep CO2 in normal range-30 to 50 mmHg
• Exceptions ?ICP, acute phase of MACD
• Pressure support
• Spontaneous breaths should have at least 80 of
  set TV
• Tidal volume
• Adjust so that peak pressure lt 30cm H2O
• Ti
• clinical and graphical synchrony
• Pramp
• increase only in obstructed airways

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Adjuncts

• Tracheobronchial hygiene
• Sedation and analgesia
• Stress ulcer prophylaxis
• DVT prophylaxis
• Eye care

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Considerations while buying a new ventilator

• Advanced modes are expensive-do you really need
  them
• Must have NIV
• Cost must include humidifier, nebulizer,
  compressor
• Find out cost of replacables-flow sensors
• Service back up
• Try out for a week in the ICU-hands on
• Bargain, bargain, bargain..