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Are Weaning Parameters Dead?. David J Pierson MD Harborview Medical Center University of Washington Seattle. What is Weaning?. The gradual reduction of ventilatory support and its replacement with spontaneous ventilation Discontinuation of ventilatory support Extubation.

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slide1

Are Weaning Parameters Dead?

David J Pierson MD

Harborview Medical Center

University of Washington

Seattle

slide2

What is Weaning?

  • The gradual reduction of ventilatory support and its replacement with spontaneous ventilation
  • Discontinuation of ventilatory support
  • Extubation
slide3

Weaning Parameters

  • Predictors of successful liberation from ventilatory support
  • Applied prior to attempted weaning
slide4

Weaning Parameters Studied and/or Advocated, 1970-2000

  • Measures of Oxygenation and Gas Exchange

PaO2/FIO2 PaO2/PAO2 P(A-a)O2

Oxygenation Index VD/VT pH RQ

  • Simple Measures of Capacity and Load

Vital 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

slide5

Weaning Parameters Studied and/or Advocated, 1970-2000

  • Simple Measures of Capacity and Load

Static compliance Dynamic compliance

Maximal expiratory pressure

  • Complex Measures of Capacity and Load

Airway 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

slide6

Weaning Parameters Studied and/or Advocated, 1970-2000

  • Integrative Indices

Rapid shallow breathing index (RSBI; f/VT)

CROP index (compliance, rate, oxygenation, pressure)

Weaning index Inspiratory effort quotient

Adverse factor score/ventilator score

  • Clinical Signs

Clinical gestalt Nurses’ opinion Cough

Mental status Respiratory muscle activity

Numerous others

Epstein SK. Respir Care Clin North Am 2000;6(2):253-301

slide7

Most Commonly Used Weaning Parameters

  • VC, minute ventilation, MIP

Sahn & Lakshminarayan Chest 1973;63:1002-5

  • f/VT (Rapid shallow breathing index; RSBI)

Yang & Tobin NEJM 1991;324:1445-50

slide8

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)
slide9

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

slide10

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
slide11

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
slide12

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
slide13

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
slide14

Measurement of Weaning Parameters: Survey of Current Practice

Poster Presented at AARC Convention, December 1999

  • 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

slide15

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

slide16

Sipes Study:

Weaning Parameters Measured

Sipes MW et al, Respir Care 1999;44(10):1218

slide17

Sipes Study:

Techniques Used

73% Use Ventilator’s Digital Display at Least Some of the Time

Sipes MW et al, Respir Care 1999;44(10):1218

slide18

Sipes Study: Techniques Used

Use CPAP and/or PSV?

Wait How Long?

Sipes MW et al, Respir Care 1999;44(10):1218

slide19

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

slide20

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

slide21

Do Weaning Parameter Variables Change over the First 5 Minutes?

  • 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

Izumi T et al, AJRCCM 1999; 159(3 pt 2):A371

slide22

Do Weaning Parameter Variables Change over the First 5 Minutes?

  • 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

Izumi T et al, AJRCCM 1999; 159(3 pt 2):A371

slide23

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
slide24

EfficacyversusEffectiveness

  • 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
weaning from ventilatory support quality of the evidence

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

weaning from mechanical ventilation the evidence base

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

importance of doing a spontaneous breathing trial in hard to wean patients

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;150:896-903

Esteban A et al, NEJM 1995;332:345-50

importance of doing a spontaneous breathing trial in hard to wean patients1

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;150:896-903

Esteban A et al, NEJM 1995;332:345-50

slide30

Recent Evolution of Approach to Weaning, Based on Best Available Evidence

Predicting

Checking

criteria for performing a spontaneous breathing trial

Criteria for Performing a Spontaneous Breathing Trial:*

  • 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.

*Chest 2001;120(6 suppl):375s-848s;

Respir Care 2002(Jan);47(1):69-90

slide32

Four Key Elements in Managing Patients with Acute Respiratory Failure

  • Oxygenation
  • Ventilation
  • Airway Protection
  • Secretion Clearance
slide33

Four Key Elements in Managing Patients with Acute Respiratory Failure

  • Oxygenation
  • Ventilation
  • Airway Protection
  • Secretion Clearance

Assessed by SBT

slide34

“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
slide35

“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

slide36

Weaning: 1960s-1970s

Full Ventilatory Support

Extubation

slide37

Extubation

Pass

Fail

Full Ventilatory Support

Weaning: 1980s-1990s

Weaning Parameters

Full Ventilatory Support

SBT

slide38

General Readiness Criteria

Weaning: 2000s

Extubation

Pass

Full Ventilatory Support

SBT

Fail

Full Ventilatory Support

slide39

Weaning: 2000s

General Readiness Criteria

Extubation

Pass

Full Ventilatory Support

SBT

Fail

Full Ventilatory Support

Weaning Parameters

slide40

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)
slide41

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.
slide46

W

  • P
  • P
slide47

W

  • P
  • P
accp aarc sccm evidence based guidelines for ventilator weaning

ACCP-AARC-SCCM Evidence-Based Guidelines for Ventilator Weaning*

  • Assessment for extubation should consider the ability to protect the airway and clear secretions in addition to the results of the SBT.

*Chest 2001(Dec);120(6 suppl):375s-848s;

Respir Care 2002(Jan);47(1):69-90

accp aarc sccm evidence based guidelines for ventilator weaning1

ACCP-AARC-SCCM Evidence-Based Guidelines for Ventilator Weaning*

  • 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.

*Chest 2001(Dec);120(6 suppl):375s-848s;

Respir Care 2002(Jan);47(1):69-90

summary roc curve for rsbi predicting successful extubation

Summary ROC Curve for RSBI Predicting Successful Extubation*

Text

*Meade M et al. Chest 2001;120 (6 suppl):400s-424s

weaning recommendation 2
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
weaning recommendation 3
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)
weaning recommendation 5
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
what is weaning
What is Weaning
  • The gradual reduction of ventilatory support and its replacement with spontaneous ventilation
slide55

What is Weaning

  • Discontinuation of ventilatory support
slide56

What is Weaning

  • Extubation
slide57

Weaning: Why All the Confusion?

Published studies vary with respect to:

  • 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
clinical settings for weaning
Clinical Settings for Weaning
  • Short-term ventilation in acute illness
  • Prolonged ventilation in acute illness
  • Long-term mechanical ventilation
traditional weaning criteria
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

slide60

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

traditional weaning protocol
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
robertson s first law of weaning

Robertson’sFirst Law of Weaning:

When the patient gets well, the patient will get off the ventilator.

slide65

Oxygenation

Ventilation

Secretion Clearance

Elements Involved in Weaning

(SBTs Address Only the First Two)

Airway Protection

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