icu intro resp
TRANSCRIPT
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Absolute Basics of Mechanical Ventilation
Dr David Howell
Consultant in Intensive Care, Respiratory and Acute Medicine
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Aims and Objectives
• Define Positive Pressure Mechanical Ventilation
• Explain Continuous Mandatory Ventilation (CMV)
• Explain Synchronised Mandatory Ventilation (SIMV)
• Explain Pressure Support Ventilation (PSV)
• Explain Basic Ventilator Settings
• Not a Talk on Physiology of Mechanical Ventilation
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What you Encounter
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Positive Pressure Mechanical Ventilator
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Lots of Monitors and Knobs to Turn
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Some are More Complicated than Others
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Wake, Warm & Wean
Weaning Screen/standard
protocol
Long Term Weaning/Individual
planWeaning
Non-Invasive Ventilation
Oxygen Therapy
Mask CPAP
Non-invasive support
Tracheostomy
Intubation
ExtubationDecannulation
Standard Ventilation
AdvancedVentilation
Invasive support
Optimising the Pt for weaning
Prone Position
Nitric Oxide
Suctioning
Humidification
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• NIV is defined as ventilatory support provided via a tight fitting mask or similar interface as opposed to invasive support, which is provided via a laryngeal mask, endotracheal tube or tracheostomy tube.
• Tight fitting masks deliver can CPAP, BIPAP or NIV via the mechanical ventilator.
NIV vs. Invasive Mechanical Ventilation
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• The work of breathing usually accounts for 5% of oxygen consumption (V02).
• In the critically ill patient this may rise to 30%.
• Invasive mechanical ventilation eliminates the metabolic cost of breathing.
Indications for Mechanical Ventilation
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• Inadequate oxygenation (not corrected by supplemental O2 by mask).
• Inadequate ventilation (increased PaCO2).
• Retention of pulmonary secretions (bronchial toilet).
• Airway protection (obtunded patient, depressed gag reflex).
Indications for Mechanical Ventilation
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Intubation
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1 Airway: oral Guedel airway to lift tongue off posterior pharynx to facilitate mask ventilation during pre-intubation phase.
2 Liquids: stop feed and aspirate ng tube.
3 Suction: extremely important to avoid pulmonary aspiration.
4 Oxygen: preoxygenate patient and ensure a source of O2 with a delivery mechanism (ambu-bag and mask) is available.
Bare Essentials for IntubationALSOBLEED
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5 Bougie: to facilitate tube insertion in more difficult airway.
6 Laryngoscope: have a long and short blade available.
7 Endotracheal tube: for average adult, cuffed oral endotracheal tube 7.0 for women and 8.0 for men.
8 End tidal CO2: to confirm correct position of tube.
9 Drugs: an induction agent, muscle relaxant, sedative are usually required.
Bare Essentials for IntubationALSOBLEED
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Principles of Mechanical Ventilation
ET tubeVentilator Tubing
Major Airways
Alveoli
PEEP
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• Positive pressure ventilation involves delivering a mechanically generated ‘breath’ to get O2 in and CO2 out.
• Gas is pumped in during inspiration (Ti) and the patient passively expires during expiration (Te).
• The sum of Ti and Te is the respiratory cycle or ‘breath’.
Principles of Mechanical Ventilation
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Flo
wP
ress
ure
Principles of Mechanical Ventilation
Ti TeTiTe
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• In the fully ventilated patient, positive pressure breaths are delivered either as preset volume or pressure continuous mandatory breaths (CMV) breaths.
• The mechanical ventilator triggers the breath and switches from inspiration to expiration when the preset volume, pressure (or time) is achieved/delivered.
• During CMV the patient takes no spontaneous breaths.
• CMV is usually used in theatre and in very unwell ICU patients.
Principles of Mechanical Ventilation
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Principles of Mechanical Ventilation
Volume control
• Tidal volume is preset
• Usually 500 mls
• Airway Pressure is Variable
Pressure control
• Inspiratory Pressure is preset
• Usually 15-20 cm H20
• Tidal Volume is Variable
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• Mandatory breaths are delivered during inspiration, to generate a tidal volume (Vt), at a set rate (f), the quotient of which is the minute volume (MV).
• Minute Volume = Tidal Volume x frequency
• In volume control ventilation, an inspiratory flow rate is also set.
• The ratio of the time spent in inspiration:expiration (I:E ratio) is usually 1:2.
Principles of Mechanical Ventilation
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Flo
wP
ress
ure
Ti TeTiTe
Principles of Mechanical Ventilation
Volume Control Breath Pressure Control Breath
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• Mechanically ventilated patients usually receive positive end-expiratory pressure (PEEP), to overcome the loss of physiological PEEP provided by the larynx and vocal cords.
• PEEP is delivered throughout the respiratory cycle and is synonymous to CPAP, but in the intubated patient.
• Standard PEEP setting is 5 cm H20.
• Sedation is often required to prevent ventilator-patient asynchrony.
Principles of Mechanical Ventilation
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Basic Settings on the Ventilator
• Tidal Volume
Pressure controlled breath (15-20 cm H20)Volume controlled breath (500 mls)
• Rate (frequency) (10-12 breaths/minute)
• Positive end expiratory pressure (PEEP) (5 cm H20)
• FiO2 (0.21-1)
• Peak airway pressure (PAP)
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Principles of Mechanical Ventilation
• Why is the peak airway pressure (PAP) important?
• Ventilator Induced Lung Injury (VILI).
• Mechanical ventilation is injurious to the lung.
• Aim PAP< 35 cm H20.
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Flo
wP
ress
ure
Ti TeTiTe
Principles of Mechanical VentilationVolume Breath Pressure Breath
35 cm H20
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Principles of Mechanical Ventilation
Don’t forget that the peak airway pressure will also include the PEEP that is added
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• Once stabilised on CMV, the level of ventilatory support may be reduced (weaning).
• This can be done by providing a mixture of synchronised intermittent mandatory breaths (SIMV) and spontaneously triggered pressure supported breaths (PSV).
Principles of Mechanical Ventilation
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• Ventilator assisted breaths are synchronized with the patient’s breathing to prevent the possibility of a mechanical breath on top of a spontaneous breath.
• However, the patient’s attempt at a breath would not be enough to generate an adequate tidal volume on its own, hence the term ‘pressure support’.
Principles of Mechanical Ventilation
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• Pressure support is only delivered during inspiration and the patient’s attempt at breathing triggers the breath rather than the ventilator.
• A standard level of pressure support delivered in inspiration is 20 cm H20
Principles of Mechanical Ventilation
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SIMV and Pressure Support Ventilation
Ventilator Patient
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• As patients improve, mandatory breaths are withdrawn and receive pressure-supported breaths alone.
• Finally, as tidal volumes improve, the level of pressure support is reduced and then withdrawn so patients breathe spontaneously with PEEP alone.
• Extubation can now be contemplated.
• Spontaneous modes of breathing should always be encouraged as respiratory muscle function is maintained
Principles of Mechanical Ventilation
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Pressure Support Ventilation
Patient Patient
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• To succeed, the initiating cause of respiratory failure, sepsis, fluid and electrolyte imbalance and nutritional status should all be treated or optimised.
• Failure to wean is associated with:
• Ongoing high V02.
• Muscle fatigue.
• Inadequate drive.
• Inadequate cardiac reserve.
Successful Weaning and Extubation
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• Weaning screens exist to help select patients for extubation.
• In the unsupported patient, if f/Vt is >100, extubation is likely to be unsuccessful.
• There is some evidence to support extubation to NIV, particularly in patients with COPD.
Successful Weaning and Extubation
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• Continuous Mandatory Ventilation (CMV)Pressure control Volume controlNo spontaneous breathingVentilator triggers breath
• Synchronised intermittent mandatory ventilation (SIMV)/Pressure Support Ventilation (PSV) Pressure control (SIMV)
Volume control (SIMV)Some spontaneous breathing is allowed (PSV)Mixture of ventilator and patient triggered
breaths
Basic Ventilatory Modes: Summary
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• Pressure Support Ventilation (PSV)Spontaneous breathing with inspiratory support All patient triggered breaths
• PEEP/CPAP (5 cm H20)Entirely spontaneous breathingConsider extubation
Basic Ventilatory Modes: Summary
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PSVPEEP
SIMVPSV
CMV
Mandatory SpontaneousOverlap
PSVPEEP
SIMVPSV
CMV PSVPEEP
SIMVPSV
CMV
Mandatory SpontaneousOverlap
Basic Ventilatory Modes: Summary
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Mode
O2
Respiratory Rate
Inspiratory Action
Inspiratory Time
Expiratory Action
Standard Ventilator SettingsMORITE
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Mode CMV, Volume Control
O2 0.5 (50% 02)
Respiratory Rate 12/minute
Inspiratory Action Set Vt at 500 mls
Inspiratory Time Set I:E ratio 1:2
Expiratory Action Set PEEP at 5 cm H20
Be Aware PAP ≤35 cm H2O
Standard Ventilator SettingsMORITE
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Patient Requiring Basic Invasive Mechanical Ventilation
Spontaneously Ventilating Patient Failing Conventional Therapy
Escalation
BIPAP
OptimiseConsider
Patient Position Humidification
CMV (VCV or PCV) PSV PEEP/CPAP
NIV on ICU
BIPAP on Ward
IMV (VCV or PCV)
De-escalation
CPAP on Ward