Transcript Absolute Basics of Mechanical Ventilation Dr David Howell

Absolute Basics of
Mechanical Ventilation
Dr David Howell
Consultant in Intensive Care, Respiratory
and Acute Medicine
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
What you Encounter
Positive Pressure Mechanical Ventilator
Lots of Monitors and Knobs to Turn
Some are More Complicated than Others
Invasive support
Advanced
Ventilation
Tracheostomy
Prone Position
Nitric Oxide
Weaning
Standard
Ventilation
Optimising the
Pt for weaning
Suctioning
Long Term
Weaning/Individual
plan
Weaning
Screen/standard
protocol
Intubation
Humidification
Wake, Warm
& Wean
Non-Invasive
Ventilation
Oxygen
Therapy
Mask CPAP
Non-invasive support
Extubation
Decannulation
NIV vs. Invasive Mechanical Ventilation
• 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.
Indications for Mechanical Ventilation
• 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
• 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).
Intubation
Bare Essentials for Intubation
ALSOBLEED
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 Intubation
ALSOBLEED
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.
Principles of Mechanical Ventilation
PEEP
ET tube
Ventilator Tubing
Major Airways
Alveoli
Principles of Mechanical Ventilation
• 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’.
Flow
Pressure
Principles of Mechanical Ventilation
Ti
Te
Ti
Te
Principles of Mechanical Ventilation
• 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
Volume control
Pressure control
• Tidal volume is preset
• Inspiratory Pressure is preset
• Usually 500 mls
• Usually 15-20 cm H20
• Airway Pressure is Variable
• Tidal Volume is Variable
Principles of Mechanical Ventilation
• 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
Pressure Control Breath
Flow
Pressure
Volume Control Breath
Ti
Te
Ti
Te
Principles of Mechanical Ventilation
• 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.
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)
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.
Principles of Mechanical Ventilation
Volume Breath
Pressure Breath
Flow
Pressure
35 cm H20
Ti
Te
Ti
Te
Pneumothorax
Principles of Mechanical Ventilation
Don’t forget that the peak airway pressure
will also include the PEEP that is added
Principles of Mechanical Ventilation
• 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
• 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
• 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
SIMV and Pressure Support Ventilation
Ventilator
Patient
Principles of Mechanical Ventilation
• 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
Pressure Support Ventilation
Patient
Patient
Successful Weaning and Extubation
• 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
• 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.
Basic Ventilatory Modes: Summary
• Continuous Mandatory Ventilation (CMV)
Pressure control
Volume control
No spontaneous breathing
Ventilator 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
• Pressure Support Ventilation (PSV)
Spontaneous breathing with inspiratory support
All patient triggered breaths
• PEEP/CPAP (5 cm H20)
Entirely spontaneous breathing
Consider extubation
Basic Ventilatory Modes: Summary
CMV
PSV
PEEP
SIMV
PSV
Mandatory
Overlap
Spontaneous
Standard Ventilator Settings
MORITE
Mode
O2
Respiratory Rate
Inspiratory Action
Inspiratory Time
Expiratory Action
Standard Ventilator Settings
MORITE
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
Spontaneously Ventilating Patient Failing Conventional Therapy
Consider
CPAP on Ward
Optimise
NIV
BIPAP
on ICU
Patient Position
Humidification
BIPAP on Ward
Patient Requiring Basic Invasive Mechanical Ventilation
CMV (VCV or PCV)
Escalation
IMV (VCV or PCV)
PSV
PEEP/CPAP
De-escalation