Ventilator Discontinuation: The evidence base and best practice

Ventilator dependency reflects an imbalance in loads/capacities

Ventilator dependency can also be iatrogenic
Failure to recognize discontinuation potential
Imposed loading:
insufficient support
insensitive/unresponsive triggers
flow dys-synchrony
cycle dys-synchrony
Inefficient weaning “rules”
Unnecessary sedation:
Kollef et al (1999) demonstrated sedation protocols reduce ventilator time

The Ventilator Discontinuation Process - EBM Projects
AHCPR - McMaster comprehensive evidence based review
5000 papers screened
Over 150 quality trials systematically analyzed
Published Nov 1999

The Ventilator Discontinuation Process - EBM Projects
ACCP/SCCM/AARC Task Force
Organized May 1999
Used McMaster report + own research + consensus to “fill in the gaps”
Developed 12 evidence based guidelines published in Chest Supplement December 2001

McMaster EBM Review - significant LRs
Although statistically significant, LRs not high enough to drive decisions in isolation

No strategy has been shown to be faster than daily SBTs with an “integrated “ assessment

ACCP/SCCM/AARC EBM Guidelines
Criteria for considering vent discontinuation:
stability/reversal of respiratory failure
P/F > 150-200, PEEP < 5-8, FiO2 < 0.4-0.5, pH > 7.25
hemodynamic stability (no pressors/inotropes)
capable of reliable insp efforts

ACCP/SCCM/AARC EBM Guidelines
SBT is most effective way of assessing d/c potential:
5 cm H2O PS, 5 cm H2O CPAP, ATC, T-piece
T-piece closest to mimicking extubation
“Integrated assessment”
Vent pattern – especially change
Gas exchange – especially change
Hemodynamics – especially change
“Comfort”
30-120 min - 1st 1-5 minutes needs close monitoring

ET tube removal requires ability to protect airway
Cough is essential
Cough velocity (>1 l/sec)
White card test
Suctioning frequency
Less important:
Gag reflex present
Cuff leak
Alertness – GCS 8 adequate
Expected extubation failures: 10-15%

Routine daily SBTs shortens weaning
NEJM 1996;335:1864

ACCP/SCCM/AARC EBM Guidelines
For patients who fail the SBT:
Search for reversible causes

In between the daily SBT:
Address the reversible aspects of load/capabilities imbalance:
Loads:
improve mechanics (edema, airways)
metabolic demands
Capabilities
nutrients/electrolytes
provide adequate DO2 to vent muscles (CO*,Hb)
adrenal function
SEDATION STRATEGIES – SAT vs targeted protocols?
*removal of intrathoracic pressure may precipitate heart failure

ACCP/SCCM/AARC EBM Guidelines
For patients who fail the SBT:
Search for reversible causes
Repeat SBTs q 24 hrs in those maintaining clinical stability
In between, provide stable and comfortable assisted ventilation
Little data demonstrating gradual support reduction reduces VLOS – likely wastes resources and risks fatigue

In between daily SBTs
Properly load the muscles:
“Normalize” amount of load
avoid atrophy, avoid fatigue
“Optimize” comfort with synchronous flow delivery throughout the breath
sensitive/responsive triggering
responsive (variable) flow with EVERY breath
proper breath termination (cycling)
Maintain this level without change until next SBT
“Weaning” this level has never been shown to improve outcomes

Practical aspects of “normalized”, comfortable loading
Triggering - max sensitivity, “balance” PEEPi with applied PEEP
Pressure/flow targets
Variable flow easier to synchronize with effort - therefore pressure targeted modes (PS, PA) best
Operational pressure range 10-25 cm H2O - start at 15 and titrate to breathing pattern, comfort
Cycling - PS uses flow, PA uses time - adjust to comfortable I:E

Newer approaches to improving synchrony
Proportional assist ventilation
Pressure and flow driven by sensed pt flow
Neurally adjusted ventilator assistance
Pressure and flow driven by diaphragm EMG
All have theoretical appeal and have
been shown to support patient effort –
However, no meaningful outcome data

ACCP/SCCM/AARC EBM Guidelines
For patients who fail the SBT:
Search for reversible causes
Repeat SBTs q 24 hrs in those maintaining clinical stability
Stable comfortable support – no need to “wean”

ACCP/SCCM/AARC EBM Guidelines
For patients who fail the SBT:
Search for reversible causes
Repeat SBTs q 24 hrs in those maintaining clinical stability
Stable comfortable support – no need to “wean”
Is this what is happening?

2174 Successfully Discontinued
(> 12 hrs support)
55% simple
82% SBTs only, “wean”* 18%
39% complex (3 SBT)
47% SBTs, “wean”* 53% at first
then “wean”* 71%/SBTs 29%
6% prolonged (> 7)
38% SBTs, 62% “wean”* at first
then “wean”* 80%/SBTs 20%
*62-71% PSV, 26-29% SIMV
AJRCCM 2011; 184:430

Can weaning be automated?
Assumes that gradual support reductions help – evidence supporting this is weak
Pressure support reductions based on various feedback algorithms
VS – target VT
Smart Care – target VT, MV, ETCO2

Volume Support (VS, ASV)
Adjusts pressure to targeted tidal volume
In theory:
As patient recovers, bigger VT, VS drops PS
In practice:
Too high a VT selected – no PS reductions
Too low a VT selected – patient overloaded
Transient increased efforts from pain/anxiety leads to inappropriate PS reduction
NO outcome data

Lellouche, AJRCCM 2006; 174: 894
SmartCare I

Lellouche, AJRCCM 2006; 174: 894
Control group
used SBTs but
may have been
done only 50%
SmartCare I

Int Care Med 2008;34:1788
SmartCare II

So is there a role for automatic PS reductions?
No evidence that says this facilitates muscle recovery
Patient tolerance to decreasing PS could signal clinicians to initiate SBTs (weaning and weaning success diagnostic, not therapeutic):
Rapidly recovering patient (overdose, post op)
Slowly recovering after many failed SBTs (PMV population)

NIV and Vent Discontinuation:
Two Scenarios
The failed/borderline SBT but good airway protection
Supportive evidence, especially in COPD
The failed extubation:
Supportive evidence in COPD
May delay life saving intubation in other forms of ARF