New Modes in Mechanical Ventilation
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New Modes in Mechanical Ventilation
Manish TandonHartford Hospital
July 10, 2013
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PRVC
VC +
VS
APRV
HFO
Bi-LevelPAV
PAV +
NAVAATC
ASV
PC-IRV
AC (VC)
AC (PC)
SIMV (VC) + PS
SIMV (PC) + PS
PSV
CPAP
Variable PS
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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
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Standard Modes
• Volume Control• Pressure Control• Pressure Control Inverse Ratio Ventilation• Pressure Support• CPAP
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Traditional Volume Control
Flow
Pressure
Volume
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Current Volume Control
Flow
Pressure
Volume
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Pressure Control
Pressure = __Volume__ + Flow * Resistance Compliance
Initially, high pressure on vent >> low volume of lung (therefore low pressure in lung) => high flowLater, high pressure on vent = higher lung volume (therefore higher pressure in lung) => low or zero flow
Flow
Pressure
Volume
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Pressure Control Inverse Ratio
Philosophy of mode = control and increase mean airway pressure, by increasing ratio of time spent at higher pressure
Flow
Pressure
Volume
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pO2
FiO2
MAP
PEEP
I/E ratio
pCO2
Minute volume
Rate
Tidal Volume
Dead space
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Pressure Support
Flow
Pressure
Volume
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CPAP
Flow
Pressure
Volume
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Newer Modes
• PRVC/VC/VS• APRV• PAV• NAVA
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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
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Flow
Pressure
Volume
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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
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Proportional Assist Ventilation
• Ventilator provides support in proportion to patient’s effort
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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
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Why all of the new modes?
For the company• Latest hardware, latest
software• Modalities requested by
providers• Product differentiation• Increased switching
costs• Sell more vents
For the providers• Greatest/latest toy• Easier to achieve goals
of ventilation
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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
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Too Much of a Good Thing
Tremblay L, et al. J Clin Invest 1997; 99(5): 944.
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Current best practice
• Limit airway pressures• Limit tidal volumes
Limitation of current practice• How to minimize shear injuries from
collapse/re-opening
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• Shear forces are increased in heterogeneous lung
• These abnormal stresses can also affect the pulmonary capillaries
Mead J, et al. JAP 1970; 28: 596.West JB, et al. JAP 1991; 70: 1731.Marini JJ (ed). Phys Basis of Vent Support (1998): p. 1226.
Heterogeneous Lung = Heterogeneous Opening &Closing Pressures
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Marini JJ (ed). Acute Lung Injury (1997): p. 240.
Recruiting with time – HFO and APRV
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Froese AB, Bryan AC. Anesthesiology 1974; 41: 242.
Recruiting with Spontaneous Breaths
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Evidence for APRV• Improves oxygenation• Improves distribution of ventilation• Improves renal blood flow• Improves mesenteric perfusion• Decreases development of ARDSLimitation – unknown if decrease in mortality or
less time on ventPutensen C, et al. AJRCCM 1999; 159: 1241.
Putensen C, et al. AJRCCM 2001; 164: 43.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.
As promising as HFO?
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Liberating from ventilator
Current best practice• Fix underlying problem• Daily assessment of need for ventilator• Correct underlying reason for needing supportAdditional goals• Use vent mode which allows lower sedation– Decrease dysynchrony
• Allow the patient to do some, but not too much, work of breathing
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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
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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
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Potential value of PAV and NAVA
• NIV• May allow more patients to be supported
without intubation
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The Future of the Ventilator?
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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