New Ventilator Modes: Do They Help?

New Ventilator Modes Do They Help? Dean Hess PhD RRT Assistant Director of Respiratory Care Massachusetts General Hospital Associate Professor of Anesthesia Harvard Medical School Editor in Chief Respiratory Care

1970s 1980s 1990s 2000 IMV PSV PCV Closed Loop

New Modes
Closed loop ventilation
Negative feedback
Adaptive control ventilation
Adaptive support ventilation
Positive feedback
Proportional assist ventilation
Tube compensation
Neurally adjusted ventilatory assist
Smartcare
Airway pressure release ventilation
High frequency ventilation

Closed Loop Ventilation
Clinician sets a target (e.g., tidal volume)
The ventilator microprocessor compares the target value to the actual value and determines a new output value (e.g., pressure)
Negative control : minimize difference between target and actual values; e.g., change pressure to minimize difference between actual and target tidal volume; adaptive control modes (PRVC)
Positive control : increase the difference between actual and target values; e.g., increase driving pressure with increased respiratory drive (PAV, NAVA)

Adaptive Control Ventilation: 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

volume from ventilator = set tidal volume calculate new pressure limit pressure limit based on V T Trigger patient or ventilator Time = set inspiratory time cycle off yes yes no no same pressure limit PRVC, VC+, autoflow, APV (pressure-controlled breath) (first breath problem)

volume from ventilator = set tidal volume calculate new pressure limit pressure limit based on V T Trigger Pressure or Flow flow = % of peak flow cycle off yes yes no no same pressure limit Volume Support (pressure support breath) (first breath problem)

Adaptive Control: PRVC, AutoFlow, VC+ Effect of compliance increase (or effort increase) Branson, 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.

Tidal Volume with PRVC, AutoFlow, VC+, and VS Branson, Respir Care 2005;50:187

Effect of Increased Effort Jaber, Anesthesiology 2009; 110:620 APC (PRVC)

AVAPS: Average Volume Assured Pressure Support
Estimates patient tidal volume over several breaths and compares it to target tidal volume
Gradually changes IPAP (0.5 – 1 cm H 2 O/min) to maintain tidal volume
Similar to PRVC, AutoFlow, and VS

Adaptive Support Ventilation: Negative Feedback Control
Target minute ventilation: 100 ml/min/kg (IBW)
% Min Volume: 20 – 200%
Rate based on Otis minimal work equation (1950)
All combinations of rate/V T 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 apnea Over-distention (pressure limit) auto-PEEP rapid-shallow breathing (4.4 mL/kg) Safety Box Determined by IBW -

Adaptive Support Ventilation ↓ P, ↑ rate ↓ P, ↓ rate ↑ P, ↑ rate ↑ P, ↓ rate Correct IBW setting important May overshoot tidal volume Role in complicated cases?

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

P AW = V E + V R . Support adjusted to normalize WoB . WoB = ∫ P × Vdt

Proportional Assist Ventilation Marantz, JAP 1996; 80:397

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
pressure (cm H 2 O Paw = PEEP + ΔPet flow (L/min)

Automatic Tube Compensation: Do We Need It?
Estaban, Am J Respir Crit Care Med 1997;156:459 PSV or T-piece acceptable for spontaneous breathing trials
Straus, Am J Respir Crit Care Med 1998;157:23 Spontaneous breathing through endotracheal tube mimics work of breathing after extubation
Haberthur, Acta Anaesthesiol Scand 2002;46:973
No difference in patient tolerance of SBT between patients randomized to tube compensation, PSV 5 cm H 2 O, or T-piece
Does not compensate for changes in resistance that occur in-vivo; e.g., kinking or secretions

Neurally Adjusted Ventilatory Assistance (NAVA): Positive Feedback Control Sinderby, Nature Medicine 1999;5:1433

Effort/Drive support Volume Control PSV/PCV PAV/TC/NAVA APC/ASV

SmartCare (Draeger Evita XL)
Ventilates the patient with conventional PSV
Clinician enters a “Zone of Respiratory Comfort” defined by breathing frequency, tidal volume and end-tidal PCO 2 ; SmartCare decreases or increases PSV
SmartCare actively reduces PSV to lowest level set by clinician (e.g., 0 cm H 2 O); if reached, performs a SBT
What was the control? “In the usual care arm, weaning was conducted according to usual local practice”
Weaning duration reduced from of 5 to 3 d. Lellouche, Am J Respir Crit Care Med 2006; 174: 894

Airway Pressure Release Ventilation (APRV) Improved oxygenation, but is mortality improved? Transpulmonary pressure with spontaneous breaths? Alveolar ventilation Oxygenation

Airway Pressure-Release Ventilation (APRV)
Several names for essentially the same mode: APRV, BiLevel BIPAP, BiVent, BiPhasic, PCV+, DuoPAP
Produces alveolar ventilation as an adjunct to CPAP
Allows spontaneous breathing at any time during the ventilator cycle
Minimizes hazards of high airway pressure??
Decreased need for sedation??
Improved ventilation of dependant lung zones?
Sydow, AJRCCM 1994;149:1550 Putensen, AJRCCM 1999;159:1241 Putensen, AJRCCM 2001;164:43

Spontaneous Breathing
During spontaneous breathing, the dependent part of the diaphragm has greatest displacement
Paralysis causes a cephalad shift of the end-expiratory position of the diaphragm, predominantly in the dependant region; reverses the pattern of diaphragmatic displacement
Froese, Anesthesiology 1974;41:242

Transpulmonary Pressure: APRV Neumann, Intensive Care Med 2002;28:1742

High Frequency Oscillation (3100B Ventilator)
Used more commonly in neonates that in adults
May improve PaO 2 in some patients because it provides higher mean airway pressure (PEEP)
Interest in its use in adults with ALI/ARDS, but evidence of better outcomes is lacking

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.

http://banhachest.blogspot.com	15
http://www.banhachest.blogspot.com	13
http://elterapistarespiratorio.webuda.com	8
http://www.elterapistarespiratorio.webuda.com	7
http://www.slideshare.net	6
http://bb9test.carilion.com	1

New Ventilator Modes: Do They Help?

by scribeofegypt on Feb 20, 2010

Accessibility

Tags

Upload Details

Usage Rights

6 Embeds 50

Statistics

New Ventilator Modes: Do They Help? — Presentation Transcript