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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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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


Weaning Parameters

  • Predictors of successful liberation from ventilatory support

  • Applied prior to attempted weaning


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


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


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


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


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)


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


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


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


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


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


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


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


Sipes Study: Practice

Weaning Parameters Measured

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


Sipes Study: Practice

Techniques Used

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

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


Sipes Study: Techniques Used Practice

Use CPAP and/or PSV?

Wait How Long?

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


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


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


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


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


Problems with Weaning Parameters Minutes?

  • Variable applicability with different diagnoses and patient populations

  • Varying definitions and techniques used in published studies

  • Variability of technique

    • Between institutions

    • Among individual clinicians


Efficacy Minutes?versusEffectiveness

  • 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: Minutes?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* Minutes?

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



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 Available Evidence:*

  • 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


Four Key Elements in Managing Patients with Acute Respiratory Failure

  • Oxygenation

  • Ventilation

  • Airway Protection

  • Secretion Clearance


Four Key Elements in Managing Patients with Acute Respiratory Failure

  • Oxygenation

  • Ventilation

  • Airway Protection

  • Secretion Clearance

Assessed by SBT


“Extubation Parameters” Respiratory Failure

(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


“Extubation Parameters” Respiratory Failure

(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


Weaning: 1960s-1970s Respiratory Failure

Full Ventilatory Support

Extubation


Extubation Respiratory Failure

Pass

Fail

Full Ventilatory Support

Weaning: 1980s-1990s

Weaning Parameters

Full Ventilatory Support

SBT


General Readiness Criteria Respiratory Failure

Weaning: 2000s

Extubation

Pass

Full Ventilatory Support

SBT

Fail

Full Ventilatory Support


Weaning: 2000s Respiratory Failure

General Readiness Criteria

Extubation

Pass

Full Ventilatory Support

SBT

Fail

Full Ventilatory Support

Weaning Parameters


Most Commonly Used Weaning Parameters: Respiratory Failure

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)


  • Weaning parameters are not dead. Respiratory Failure

  • 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.


W Respiratory Failure

  • P

  • P


W Respiratory Failure

  • 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


What is Weaning

  • Discontinuation of ventilatory support


What is Weaning

  • Extubation


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


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’s First Law of Weaning:

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




Oxygenation

Ventilation

Secretion Clearance

Elements Involved in Weaning

(SBTs Address Only the First Two)

Airway Protection


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