New Modes in
Mechanical Ventilation
Manish Tandon
Hartford Hospital
July 10, 2013
SIMV (VC) + PS
Understanding differences in vent
modes
• What initiates the breath
• What controls the amount of airflow during
inspiration
• What controls the duration of inspiration
• Philosophy of the mode
Standard Modes
•
•
•
•
•
Volume Control
Pressure Control
Pressure Control Inverse Ratio Ventilation
Pressure Support
CPAP
Traditional Volume Control
Flow
Pressure
Volume
Current Volume Control
Flow
Pressure
Volume
Pressure Control
Flow
Pressure
Volume
Pressure = __Volume__
Compliance
+
Flow * Resistance
Initially, high pressure on vent >> low volume of lung (therefore low pressure in lung) => high flow
Later, high pressure on vent = higher lung volume (therefore higher pressure in lung) => low or zero flow
Pressure Control Inverse Ratio
Flow
Pressure
Volume
Philosophy of mode = control and increase mean airway pressure,
by increasing ratio of time spent at higher pressure
FiO2
PEEP
pO2
MAP
I/E ratio
Rate
Minute volume
pCO2
Tidal Volume
Dead space
Pressure Support
Flow
Pressure
Volume
CPAP
Flow
Pressure
Volume
Newer Modes
•
•
•
•
PRVC/VC/VS
APRV
PAV
NAVA
Pressure Regulated Volume Control,
Volume Control, Volume Support
• Breath is initiated by patient or elapsed time
• PC used for ventilator initiated breath, to target goal
tidal volume
• PS used for patient initiated breath, to target goal tidal
volume
• “Set like VC, flows like PC”
• Philosophy – allow more natural decelerating flow
• Fallacy – uses lower pressure to achieve the same
volume
Flow
Pressure
Volume
APRV
• Sustained CPAP to ventilate the lung while
recruited
• Short, infrequent releases of pressure to
augment the minute volume for CO2
clearance
• Fallacy – inverse ratio ventilation
Proportional Assist Ventilation
• Ventilator provides support in proportion to
patient’s effort
Neurally Adjusted Ventilator Assist
• Measures diaphragmattic activity as a proxy of
phrenic nerve activity
• Breath initiated and ended based on
diaphragmattic activity
• Flow proportional to amount of activity and
based on ratio set by provider
• Philosophy – better synchrony with patient’s
efforts
Why all of the new modes?
For the company
For the providers
• Latest hardware, latest
• Greatest/latest toy
software
• Easier to achieve goals
• Modalities requested by
of ventilation
providers
• Product differentiation
• Increased switching
costs
• Sell more vents
Goals of mechanical ventilation
• Provide support
– Not necessarily a perfect ABG
• Do no harm
– Ventilator Induced Lung Injury
• Shortest required duration on ventilator
• Improve long term lung function in survivors
Too Much of a Good Thing
Tremblay L, et al. J Clin Invest 1997; 99(5): 944.
Current best practice
• Limit airway pressures
• Limit tidal volumes
Limitation of current practice
• How to minimize shear injuries from
collapse/re-opening
Heterogeneous Lung =
Heterogeneous Opening &Closing Pressures
• Shear forces are
increased in
heterogeneous lung
• These abnormal
stresses can also affect
the pulmonary
capillaries
Marini JJ (ed). Phys Basis of Vent Support (1998): p. 1226.
Mead J, et al. JAP 1970; 28: 596.
West JB, et al. JAP 1991; 70: 1731.
Recruiting with time – HFO and APRV
Marini JJ (ed). Acute Lung Injury (1997): p. 240.
Recruiting with Spontaneous Breaths
Froese AB, Bryan AC. Anesthesiology 1974; 41: 242.
Evidence for APRV
• Improves oxygenation
• Improves distribution of ventilation
• Improves renal blood flow
• Improves mesenteric perfusion
• Decreases development of ARDS
Limitation – unknown if decrease in mortality or
less time on vent
Putensen C, et al. AJRCCM 1999; 159: 1241.
Putensen C, et al. AJRCCM 2001; 164: 43.
As promising as HFO?
Hering R, et al. ICM 2002; 28: 1426.
Hering, R, et al. Anesthesiology 2003; 99(5): 1137.
Roy, S, et al. Shock 2013; 39(1): 28.
Liberating from ventilator
Current best practice
• Fix underlying problem
• Daily assessment of need for ventilator
• Correct underlying reason for needing support
Additional goals
• Use vent mode which allows lower sedation
– Decrease dysynchrony
• Allow the patient to do some, but not too much,
work of breathing
Studies of PAV and NAVA
• Evidence of better synchrony with patient
• More natural variation in tidal volumes
– Better oxygenation
• No proven benefit so far of shorter duration
on ventilator
Fastest way to liberate off vent
• Daily spontaneous breathing trial
– Remove the ventilator to eliminate dysynchrony
• Limit/avoid sedation
• Fix underlying problem each day the patient
needs the vent
– e.g. Infection, Fluids, Debilitation
• Automated Weaning Trials
– Eliminate our variability in removing support
Potential value of PAV and NAVA
• NIV
• May allow more patients to be supported
without intubation
The Future of the Ventilator?
Conclusion
• Keep it simple
• Don’t intubate the patient if you don’t have to
– Use NIV in appropriate settings
• Provide support, but not so much that it will
harm the patient
• Look each day to see if the patient still needs the
vent
• Determine why it is needed, and fix the
underlying issue
• Future – avoiding the ventilator altogether?
– NIV, ECMO