ventilator modes: what’s new why new modes? and what’s worth keeping? · ventilator modes:...
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Hess, New Modes
Ventilator Modes: What’s New
and What’s Worth Keeping?
An Evidence-Based Approach
Dean Hess PhD RRT
Assistant Director of Respiratory Care
Massachusetts General Hospital
Associate Professor of Anesthesia
Harvard Medical School
Editor in Chief
Respiratory Care
Why New Modes?
� Address important clinical issues:
� poor trigger
� variable physiology
� refractory hypoxemia
� Satisfies our craving for adventure (engineers
and clinicians)
� We like better numbers (seduction by pulse oximetry)
Arguments Against New Modes
� Lack high-level evidence for better patient outcomes
� If we try a new mode and the patient has a good outcome,
we say it was due to the new mode.
� But if try a new mode and there is a bad outcome, we say the
patient was going to die anyway.
� Potential for harm (these are often not reported)
� Improved gas exchange does not necessarily improve
outcomes: high tidal volume, iNO, prone
� New is not necessarily better
� Solution to a problem or in search of a problem?
Mechanical Ventilation Strategies
With Level 1 Evidence For
Improved Outcomes
� Noninvasive ventilation (several meta-analyses)
� Volume/pressure limitation (ARDSnet, Gajic)
� Spontaneous awaking/spontaneous breathing trials (Ely, Kress)
New Modes (Some Not So New)
� Closed loop ventilation
� Negative feedback
� Adaptive pressure control
� Adaptive support ventilation
� Positive feedback
� Proportional assist ventilation
� Tube compensation
� Neurally adjusted ventilatory assist
� SmartCare
� Airway pressure release ventilation
Adaptive Pressure Control:
Negative Feedback Control
� PCV with volume guarantee: AutoFlow, pressure-regulated volume control (PRVC), VC+, adaptive pressure ventilation (APV), volume targeted pressure control, pressure controlled volume guaranteed
� PSV with volume guarantee: Volume Support (VS)
� Pressure adjusts to achieve the target tidal volume: pressure changes with changes in lung mechanics, patient effort, or both
Hess, New Modes
Adaptive Pressure Control:
PRVC, AutoFlow, VC+, APVEffect of compliance increase
(or effort increase)
Branson, Respir Care 2005;50:187Branson, Respir Care 2005;50:187
Effect of compliance decrease(or effort decrease)
The ventilator can take away support if patient effort increases!
Tidal volume limitation is not guaranteed.
1. PRVC: ventilator inspiratory pressure is reduced to the minimum necessary to maintain the airway pressure at 0 cm H2O.
2. AutoFlow and VC+: ventilator inspiratory pressure decreases, but never below a
minimum set by the ventilator algorithm.3. APV: a combination of patterns 1 and 2.
Respir Care 2009;54:1467
Adaptive Support Ventilation:
Negative Feedback Control
� Target minute ventilation: 100 mL/min/kg (IBW)
� % Min Volume: 25 – 350%
� Rate based on Otis minimal work equation (1950)
� All combinations of rate/VT calculated
� Te = 3 RC (I:E ratio)
� PRVC or VS depending upon whether or not the patient is actively breathing
� Available on Hamilton ventilator
Adaptive Support Ventilation
Correct IBW setting importantMay overshoot tidal volumeRole in complicated cases?
apne
a Over-distention (pressure limit)
auto
-PE
EP
rapid-shallow breathing (4.4 mL/kg)
Safety Box↓↓↓↓ P, ↑↑↑↑ rate ↓↓↓↓ P, ↓↓↓↓ rate
↑↑↑↑ P, ↑↑↑↑ rate ↑↑↑↑ P, ↓↓↓↓ rate
Effect of Increased Effort
Jabe
r, A
nest
hesi
olog
y 2
00
9;
11
0:6
20
APC (PRVC)Negative feedback
APC
Proportional Assist Ventilation:
Positive Feedback Control
P = V/C + V R.
(proportion of assist adjustable)
respiratory drive
end-inspiratory and expiratory pause maneuvers of 300 ms every 4 to 10 s to estimate of R and C
With neuromuscular disease, drive may not translate into flow
PAW = V/C + V R.
.WoB=∫P×Vdt
Support adjusted to normalize WoB
Hess, New Modes
Proportional Assist Ventilation
Mar
antz
, JA
P 1
99
6;
80
:39
7
Crit Care Med 2007;35:1048
Tube Compensation:
Positive Feedback Control� Pressure determined by inspiratory effort of the patient
and the resistance of the endotracheal tube
Paw = PEEP + ΔΔΔΔPet
Does not compensate for changes in resistance that occur in-vivo;
e.g., kinking or secretions
Res
pir
Car
e 2
01
0;5
5:5
49
Neurally Adjusted Ventilatory Assistance
(NAVA): Positive Feedback Control
Sinderby, Nature Medicine 1999;5:1433
SmartCare (Draeger Evita XL)� Clinician enters a “Zone of Respiratory Comfort” defined
by breathing frequency, tidal volume and end-tidal PCO2; SmartCare decreases or increases PSV
� SmartCare actively reduces PSV to lowest level set by clinician (e.g., 0 cm H2O); if reached, performs a SBT
Lellouche, AJRCM 2006; 174: 894 Rose, Intensive Care Med 2008;34:1788
Hess, New Modes
Airway Pressure Release
Ventilation (APRV)
Alveolar ventilationOxygenationImproved oxygenation, but is mortality improved?
Transpulmonary pressure with spontaneous breaths?
Airway Pressure-Release
Ventilation (APRV)
� Several names for essentially the same mode: APRV,
BiLevel BIPAP, BiVent, BiPhasic, PCV+, DuoPAP
� Minimizes hazards of high airway pressure??
� Decreased need for sedation??
� Improved ventilation of dependant lung zones?
Froese, Anesthesiology 1974;41:242
Act
a A
naes
thes
iol
Sca
nd 2
00
4;
48
: 7
22
Transpulmonary Pressure: APRV
Neu
man
n, I
nten
sive
Car
e M
ed 2
00
2;2
8:1
74
2
The Evidence for New Ventilator
Modes …
It’s not the ventilator mode that makes a difference …
… It’s the skills of the clinician that makes the difference.
Any ventilator mode has the potential to do harm!
High level evidence is lacking that any new ventilator
mode improves patient outcomes compared to existing
lung-protective ventilation strategies.