Mechanical Ventilation: Advanced Ventilator Modes

Mechanical Ventilation:
Advanced Ventilator Modes
AATS/STS Cardiothoracic Critical Care Symposium
AATS Annual Meeting
Toronto, Canada
April 27th 2014
No Disclosures
Aaron M Cheng, MD FACS
University of Washington
Division of Cardiothoracic Surgery
Co‐Director, UWMC Cardiothoracic ICU
Seattle, Washington
Mechanical Ventilation:
SUPPORTIVE NOT THERAPEUTIC • Airway protection
• Support gas exchange
• Reduce work of breathing
Different Vent Modes:
ALL Use Positive Pressure Ventilation
• Vent MODES: Differences in how PPV is applied
• PPV  LUNG INJURY
• ALL VENT MODES CAN CAUSE LUNG INJURY
Mechanical Ventilator Support
DIFFERENT VENT MODES
PSV
NAVA
PAV
Volume‐AC Pressure‐AC PRVC
APRV
HFOV
HFPV
Ventilator Basics
4 Phases during Ventilator Cycle
Breath Initiation
Flow delivery phase
Breath termination
Expiratory phase
Control Variables (Target)
• Pressure, Volume/Flow
Phase Variables
• Trigger—Initiation of inspiratory phase: Pressure, Flow, or Time
• Limit– Sustains inspiratory cycle eg. Limit flow 50 L/min
• Cycle– Ends inspiratory cycle eg. Cycle at TV 500 ml
• Baseline– Usually passive‐‐depends on airway resistance & lung elastance
Conditional Variables
IfThen programming eg. Switching to patient trigger from machine trigger
Assist‐Control (AC): Most common ICU vent mode
• Control: Pressure or Volume
• Trigger: (Patient effort & sensitivity)Pressure, Flow, or (Machine)Time • Limit: Pressure, Flow, or Volume • Cycle: (Machine) Flow, Volume, Pressure, Time
Pressure or Volume:
Is there a difference?
Assist Control‐‐VOLUME
Advantages
Disadvantages
Constant Tidal Volume (Vt)
Peak alveolar pressure are variable‐‐Over distension risk
PaCO2 constant
Cannot respond to changes in ventilator demand‐‐flow limited
Changes in Peak Inspiratory pressure easy to detect
Assist Control‐‐PRESSURE
Advantages
Disadvantages
Peak alveolar pressure is limited
Vt is variable
Flow responds to patient
PaCO2 can vary
Better vent synchrony
Decelerating flow waveform
• Decelerating flow waveform
– Increased mPaw
– Decreased PIP
– Improved oxygenation
Dual Modes: Combines features of pressure & volume target to achieve goals of ventilation
• Known by different names
– Volume Assured Pressure Support
• Pressure Augmentation
– Pressure Regulated Volume Control
• Auto‐flow
• Variable Pressure Control
Dual Modes: Pressure regulated volume control (PRVC)
• Pressure control waveform but “guaranteed tidal volume”
• Ventilator (Machine) adjusts Pressure target to least value needed to maintain minimum Tidal Volume target
Pressure control compared to PRVC
PCV: Pressure remains constant
and volume changes (decreases)
due to changes in lung
compliance
PRVC: Pressure target is adjusted
to changes in compliance to meet
volume target
Rescue Ventilator Modes:
APRV
Hi Frequency Oscillation
Airway Pressure Release Ventilation
• “Inverse‐ratio” Bi‐
Level Mode
• Maintains Lung Volume throughout cycle
– CO2 clearance occurs • Settings
– PHigh & PLow
with pressure release & spontaneous – THigh & TLow
breathing
APRV: Spontaneous Breathing
Reported benefits of APRV
• Decreases VILI
– Reduces peak airway pressures
• Promotes improved aeration at lung bases—
where atelectasis commonly occurs
• Allows patient to breathe while providing “OPEN” lung ventilation
– Less sedation needed
• Improves oxygenation
– Higher mean airway pressure (mPaw)
The role of APRV
• Frequently used in awake patients with moderate‐severe ARDS
– Decreased sedation requirement less vasoactive requirements
• Improved aeration & cardiovascular stability lost when patient unable to breathe spontaneously
– Can be detrimental in patient with high ventilatory
requirements & severe obstructive lung disease
• Hyperinflation High alveolar pressure Barotrauma
High Frequency Oscillation: OSCILLATE & OSCAR
Multi‐center randomized controlled trials comparing Adult patients with ARDS to treatment with Conventional mechanical ventilation versus HFOV
OSCILLATE trial terminated early due to increased in‐hospital mortality in the HFOV arm (47% versus 35%)
OSCAR trial demonstrated no difference in 30‐day mortality between groups: HFOV was not superior
Adaptive Ventilator Modes:
Adapting the ventilator to the patient
(Better synchrony through technology)
Increasing Ventilator Assistance
PAV
NAVA
Pressure
Support
Increasing Patient Effort
Proportional Assist Ventilation (PAV)
• Adaptive mode: Delivers ventilator “breath” proportional to patient’s instantaneous effort
– Airway pressure delivered is NOT CONSTANT 
Differs from Pressure Support
– “Breath” delivered depends on Patient’s respiratory mechanics & set level of assistance (0‐
100%) to respiratory muscles
• Referred to as “POWER STEERING” Vent Mode
Proportional Assist Ventilation
Drawback: difficult to learn to use
Neurally Adjusted Ventilator Assist (NAVA)
• Partial vent support mode
• Pressure controlled
• Pressure delivered proportional to diaphragm electrical activity
• Trigger and cycle set to electrical activity of diaphragm
• Can be applied with non‐invasive ventilation
Neural Adjusted Synchrony
Improvement in Patient‐Vent Synchrony
NAVA
PSV
PCV
Pediatric Research (2012) 72, 194–20
Summary: Take Home Points
• All mechanical ventilator modes can cause lung injury (VILI)
• No conclusive evidence that “advanced ventilator modes” are superior to Assist Control in ARDS mortality
• New vent technologies try to adapt the ventilator to the patient • The BEST VENT MODE is the one you and your team is most comfortable using