are weaning parameters dead? david j pierson md harborview medical center university of washington...
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Are Weaning Parameters Dead?
David J Pierson MD
Harborview Medical CenterUniversity of Washington
Seattle
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What is Weaning?
• The gradual reduction of ventilatory support and its replacement with spontaneous ventilation
• Discontinuation of ventilatory support
• Extubation
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Weaning Parameters
• Predictors of successful liberation from ventilatory support
• Applied prior to attempted weaning
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Weaning Parameters Studied and/or Advocated, 1970-2000
• Measures of Oxygenation and Gas ExchangePaO2/FIO2 PaO2/PAO2 P(A-a)O2
Oxygenation Index VD/VT pH RQ
• Simple Measures of Capacity and LoadVital capacity (mL/kg) Tidal volume (mL; mL/kg)
Respiratory rate (breaths/min)
Minute ventilation (L/min)
Maximum voluntary ventilation (L/min)
Maximal inspiratory pressure (NIF; PImax; cm H2O)
Epstein SK. Respir Care Clin North Am 2000;6(2):253-301
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Weaning Parameters Studied and/or Advocated, 1970-2000
• Simple Measures of Capacity and LoadStatic compliance Dynamic compliance
Maximal expiratory pressure
• Complex Measures of Capacity and LoadAirway occlusion pressure (P0.1)
P0.1/PImax CO2-stimulated P0.1
Effective inspiratory impedance (P0.1/VT/TI)
Work of breathing (several techniques)
Pdi/Pdimax PI/PImax Intrinsic PEEP
Epstein SK. Respir Care Clin North Am 2000;6(2):253-301
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Weaning Parameters Studied and/or Advocated, 1970-2000
• Integrative IndicesRapid shallow breathing index (RSBI; f/VT)
CROP index (compliance, rate, oxygenation, pressure)
Weaning index Inspiratory effort quotient
Adverse factor score/ventilator score
• Clinical SignsClinical gestalt Nurses’ opinion Cough
Mental status Respiratory muscle activity
Numerous others
Epstein SK. Respir Care Clin North Am 2000;6(2):253-301
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Most Commonly Used Weaning Parameters
• VC, minute ventilation, MIPSahn & Lakshminarayan Chest 1973;63:1002-5
• f/VT (Rapid shallow breathing index; RSBI)
Yang & Tobin NEJM 1991;324:1445-50
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Most Commonly Used Weaning Parameters:
Implications of “Failure”
• Low VC and MIP: muscle weakness
• Low RSBI: insufficient ventilatory drive
• High RSBI, or inability to generate required minute ventilation: excessive work of breathing for patient’s capabilities
• High minute ventilation, normal PaCO2:
– Excessive CO2 production
– High dead space (VD/VT)
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Measuring Weaning Parameters: Does Technique Matter?
• In the original studies:*
– Full ventilatory support (volume A/C)
– Disconnection for measurements
– FIO2 0.40 or 0.21
– No CPAP; no pressure support
– Patient allowed to stabilized for fixed period
– Direct measurement of respiratory rate and minute ventilation for 1 full minute
*Sahn & Lakshmi 1973; Yang & Tobin 1991
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Measuring Weaning Parameters: Does Technique Matter?
• In everyday practice in 2008:
– Patient remains connected to ventilator circuit
– CPAP and/or pressure support commonly used
– Data often collected immediately
– Respiratory rate, tidal volume, and minute ventilation are read directly from ventilator’s digital display
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Measuring Weaning Parameters: Does Technique Matter?
• Why this might lead to different results:
– Lung volumes (and compliance) may change
• CPAP higher FRC
• Pressure support higher peak inspiratory volume
– Work of breathing may change
• Ventilator circuit vs T-piece
• Pressure support
• ?effect of automatic tube compensation
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Measuring Weaning Parameters: Does Technique Matter?
• Why this might lead to different results:
– Values on digital display are rolling averages determined from much shorter intervals than 1 minute (eg, 12 seconds)
– Patient’s breathing pattern may change over time when ventilatory support is discontinued
– Unclear how values obtained would correlate with those from use of original studies’ techniques
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Two Studies by Mike Sipes to Address These Issues,
1998-1999
• Survey of University Health System Consortium RC departments to find out how weaning parameters were actually being done in everyday practice
• Serial assessment of breathing pattern and values obtained over the 1st 5 minutes after discontinuation of ventilatory support
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Measurement of Weaning Parameters: Survey of Current Practice
• All 72 hospitals in UHSC
• Written (mailed) 12-item questionnaire sent to RC department managers
• Telephone follow-up
• Demographics, weaning techniques used, and how weaning parameters were measured in each institution
Sipes MW et al, Respir Care 1999;44(10):1218
Poster Presented at AARC Convention, December 1999
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Measurement of Weaning Parameters: Survey of Current Practice
• 48/72 departments (67%) completed the questionnaire and provided complete data
• Hospitals: 110-1100 beds (mean 491)
• ICUs: 11-120 beds (mean 59)
• 33/48 departments (67%) used therapist-driven protocols
Sipes MW et al, Respir Care 1999;44(10):1218
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Sipes Study:Weaning Parameters Measured
Sipes MW et al, Respir Care 1999;44(10):1218
0102030405060708090
100
VT f MIP VC VE f/VT P0.1 MVV
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Sipes Study:Techniques Used
Sipes MW et al, Respir Care 1999;44(10):1218
25%
44%
29%
2%AlwaysDisconnectfrom Ventilator
Always UseVentilatorDisplay
Use EitherMethod
Don't MeasureParameters
73% Use Ventilator’s
Digital Display at
Least Some of the Time
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Sipes Study: Techniques Used
Sipes MW et al, Respir Care 1999;44(10):1218
0
5
10
15
20
25
30
35
40
45
50
CPAP PSV0
10
20
30
40
50
60
70
80
90
No Set Time Preset Interval
Use CPAP and/or PSV? Wait How Long?
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Measurement of Weaning Parameters: Survey of Current Practice
• Most hospitals use very different techniques for measuring weaning parameters from those used in the original studies that established their predictive value.
• Effects of CPAP and PSV on the predictive value of the traditional weaning parameters are unknown
• The clinical value of the data collected may be much less than we think.
Sipes MW et al, Respir Care 1999;44(10):1218
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Do Weaning Parameter Variables Change over the First 5 Minutes?*
Poster Presented at ATS Meeting,
May 1999
*Izumi T et al, AJRCCM 1999; 159(3 pt 2):A371
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Do Weaning Parameter Variables Change over the First 5 Minutes?
Izumi T et al, AJRCCM 1999; 159(3 pt 2):A371
• Clinical study in 28 HMC patients being assessed for weaning after acute respiratory failure
• All patients initially on volume assist-control
• Randomized, cross-over design:
– Separate T-piece circuit
– CPAP mode through ventilator circuit
• Continuous measurement of f, VT, and VE for 5 minutes
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Do Weaning Parameter Variables Change over the First 5 Minutes?
Izumi T et al, AJRCCM 1999; 159(3 pt 2):A371
• CPAP values were different from T-piece values in most patients
• Tidal volumes were higher on CPAP
• Minute ventilation evolved over time
– On CPAP (20 pts): from 8.5 L in 1st minute to 11.6 L in 5th minute
• Changes in rate and tidal volume highly variable among the different patients
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Problems with Weaning Parameters
• Variable applicability with different diagnoses and patient populations
• Varying definitions and techniques used in published studies
• Variability of technique
– Between institutions
– Among individual clinicians
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Efficacy versus Effectiveness
• Results under the conditions of a clinical trial
• Carefully selected patients
• No comorbidities or other interfering problems
• Rigidly controlled protocol for management and monitoring
• Overseen by investigators
• Results obtained with real-world, everyday clinical practice
• Unselected patients
• Techniques and protocol may or may not match what was done in the clinical trial
• No special oversight in terms of the intervention
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Weaning from Ventilatory Support:Quality of the Evidence*
• Comprehensive literature review using 5 computerized databases and duplicate independent review protocol
• Included RCTs on any weaning intervention and nonrandomized trials of weaning predictors
• Used in developing new ACCP-AARC-SCCM weaning guidelines (Chest 2001;120[6 suppl]:375-95s)
*Meade MO et al, Respir Care 2001;46(12):1408-15
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Weaning From Mechanical Ventilation: The Evidence Base*
• No “weaning parameter” can consistently predict successful weaning and extubation.
• Daily checks for readiness for spontaneous breathing will identify patients not clinically considered ready for weaning.
*AHRQ Publication #00-E028, 2000;www.ahrq.gov/clinic/mechsumm.htm;
Meade MO et al, Respir Care 2001;46(12):1408-15
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Importance of Doing a Spontaneous Breathing Trial in Hard-To-Wean Patients
• 2 large multicenter trials* comparing T-piece, pressure support, and IMV as weaning strategies in difficult-to-wean patients.
• For entry, each patient’s managing physician had to designate them as:
– A “difficult-to-wean” patient, and
– Not yet ready to come off the ventilator
*Brochard L et al, AJRCCM 1994;150:896-903Esteban A et al, NEJM 1995;332:345-50
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Importance of Doing a Spontaneous Breathing Trial in Hard-To-Wean Patients
In the Brochard and Esteban studies, 70-75% of potentially eligible patients could not be enrolled because they passed a 2-hr spontaneous breathing trial and were successfully extubated.
Brochard L et al, AJRCCM 1994;150:896-903Esteban A et al, NEJM 1995;332:345-50
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Recent Evolution of Approach to Weaning, Based on Best
Available Evidence
Predicting
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Recent Evolution of Approach to Weaning, Based on Best
Available Evidence
Predicting Checking
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Criteria for Performing a Spontaneous Breathing Trial:*
*Chest 2001;120(6 suppl):375s-848s;Respir Care 2002(Jan);47(1):69-90
• Evidence for some reversal of underlying cause of ARF;
• Adequate gas exchange: PaO2/FIO2 >150-200 on PEEP 5-8, on FIO2 0.4-0.5, with pH 7.25;
• Hemodynamic stability; and
• Capability to initiate an inspiratory effort.
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Four Key Elements in Managing Patients with
Acute Respiratory Failure
• Oxygenation
• Ventilation
• Airway Protection
• Secretion Clearance
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Four Key Elements in Managing Patients with
Acute Respiratory Failure
• Oxygenation
• Ventilation
• Airway Protection
• Secretion Clearance
Assessed by SBT
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“Extubation Parameters”(Much Less Studied Than “Weaning Parameters”)
• Level of alertness
• Absence of upper airway structural abnormalities
• Cuff leak test
– Several studies, using various techniques
– Poorly predictive of extubation failure
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“Extubation Parameters”(Much Less Studied Than “Weaning Parameters”)
• Respiratory secretions– Quantity– Appearance– Viscositiy
• Gag• Spontaneous cough*• Frequency of suctioning*
*Only variables among these 6 that correlated with need for re-intubation in cohort of brain-
injured patients.Coplin WM et al, AJRCCM 2000;161:1530-6
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Full Ventilatory
SupportExtubation
Weaning: 1960s-1970s
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Full Ventilatory
Support
Weaning Parameters
SBT
Weaning: 1980s-1990s
Extubation
Full Ventilatory
Support
Pass
Fail
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Full Ventilatory
Support
Extubation
SBT
Weaning: 2000s
Full Ventilatory
Support
Pass
Fail
General Readiness
Criteria
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Full Ventilatory
Support
Extubation
Weaning Parameters
SBT
Weaning: 2000s
Full Ventilatory
Support
Pass
Fail
General Readiness
Criteria
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Most Commonly Used Weaning Parameters:
Implications of “Failure”
• Low VC and MIP: muscle weakness
• Low RSBI: insufficient ventilatory drive
• High RSBI, or inability to generate required minute ventilation: excessive work of breathing for patient’s capabilities
• High minute ventilation, normal PaCO2:
– Excessive CO2 production
– High dead space (VD/VT)
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• Weaning parameters are not dead.
• When we should use them, and their role in assessing patients during the weaning process, have changed.
• Mike Sipes played an significant role in documenting the problems in their measurement, and in expanding our knowledge base in this important area of respiratory care.
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W
• P
• P
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W
• P
• P
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ACCP-AARC-SCCM Evidence-Based Guidelines for Ventilator Weaning*
*Chest 2001(Dec);120(6 suppl):375s-848s;Respir Care 2002(Jan);47(1):69-90
• Assessment for extubation should consider the ability to protect the airway and clear secretions in addition to the results of the SBT.
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ACCP-AARC-SCCM Evidence-Based Guidelines for Ventilator Weaning*
*Chest 2001(Dec);120(6 suppl):375s-848s;Respir Care 2002(Jan);47(1):69-90
• Patients who fail the initial SBT should be investigated for the cause, and have the SBT repeated daily.
• Patients who fail an SBT should receive a stable, nonfatiguing, comfortable form of ventilatory support.
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Summary ROC Curve for RSBI Predicting Successful Extubation*
•Text
*Meade M et al. Chest 2001;120 (6 suppl):400s-424s
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Weaning Recommendation #2
• Patients receiving mechanical ventilation for respiratory failure should undergo a formal assessment of discontinuation potential if there is:– Evidence for some reversal of underlying cause for
respiratory failure;
– Adequate oxygenation (eg, PaO2/FIO2 > 150-200);
– Hemodynamic stability; and,– Capability to initiate an inspiratory effort
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Weaning Recommendation #3
• These formal discontinuation assessments should be done during spontaneous breathing rather than while still receiving substantial ventilatory support
• These assessments should take the form of a spontaneous breathing trial (SBT)
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Weaning Recommendation #5
• Patients who fail a spontaneous breathing trial should have the cause determined
• Once reversible causes are corrected and the patient still meets criteria for spontaneous breathing trials, these should be performed every 24 hours
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What is Weaning
• The gradual reduction of ventilatory support and its replacement with spontaneous ventilation
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What is Weaning
• Discontinuation of ventilatory support
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What is Weaning
• Extubation
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Weaning: Why All the Confusion?
• Clinical setting/reason for ventilatory support
• Patient population studied
• Protocols and timing used in weaning regimens
• Definition of weaning success/failure
• Separation of weaning and extubation
Published studies vary with respect to:
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Clinical Settings for Weaning
• Short-term ventilation in acute illness
• Prolonged ventilation in acute illness
• Long-term mechanical ventilation
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Traditional Weaning Criteria*
• Vital capacity > 10 mL/kg
• Minute ventilation < 10 L/min
• Maximum voluntary ventilation > 2x VE
• Maximum inspiratory force > 30 cm H2O
* Sahn and Lakshminarayan, Chest 1973; 63:1002
•
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Rapid Shallow Breathing Index*
• f/VT > 105 breaths/min/liter predicts failure to wean
• Example:– f = 24 breaths/min, VT = 480 mL/breath– f/VT = 24 0.48 = 50 breaths/min/liter
* Yang KL, Tobin MH. NEJM 1991; 324:1445-50
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Traditional Weaning Protocol
• Fulfill predetermined objective criteria general status; gas exchange; mechanics
• Choose appropriate time and setting
• Eliminate respiratory depressants
• Position patient and clear airway
• T-piece trial assessment
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Robertson’sFirst Law of Weaning:
When the patient gets well, the patient will get off the
ventilator.
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Ventilatory Support
Intubation
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Ventilatory Support
Intubation
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Airway Protection
Ventilation
Secretion Clearance
Oxygenation
Elements Involved in Weaning(SBTs Address Only the First Two)