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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

Are Weaning Parameters Dead?

David J Pierson MD

Harborview Medical Center

University of Washington

Seattle


Are weaning parameters dead

What is Weaning?

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

  • Discontinuation of ventilatory support

  • Extubation


Are weaning parameters dead

Weaning Parameters

  • Predictors of successful liberation from ventilatory support

  • Applied prior to attempted weaning


Are weaning parameters dead

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


Are weaning parameters dead

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


Are weaning parameters dead

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


Are weaning parameters dead

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


Are weaning parameters dead

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)


Are weaning parameters dead

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


Are weaning parameters dead

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


Are weaning parameters dead

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


Are weaning parameters dead

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


Are weaning parameters dead

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


Are weaning parameters dead

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


Are weaning parameters dead

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


Are weaning parameters dead

Sipes Study: Practice

Weaning Parameters Measured

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


Are weaning parameters dead

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


Are weaning parameters dead

Sipes Study: Techniques Used Practice

Use CPAP and/or PSV?

Wait How Long?

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


Are weaning parameters dead

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


Are weaning parameters dead

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


Are weaning parameters dead

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


Are weaning parameters dead

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


Are weaning parameters dead

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


Are weaning parameters dead

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



Are weaning parameters dead

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


Are weaning parameters dead

Four Key Elements in Managing Patients with Acute Respiratory Failure

  • Oxygenation

  • Ventilation

  • Airway Protection

  • Secretion Clearance


Are weaning parameters dead

Four Key Elements in Managing Patients with Acute Respiratory Failure

  • Oxygenation

  • Ventilation

  • Airway Protection

  • Secretion Clearance

Assessed by SBT


Are weaning parameters dead

“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


Are weaning parameters dead

“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


Are weaning parameters dead

Weaning: 1960s-1970s Respiratory Failure

Full Ventilatory Support

Extubation


Are weaning parameters dead

Extubation Respiratory Failure

Pass

Fail

Full Ventilatory Support

Weaning: 1980s-1990s

Weaning Parameters

Full Ventilatory Support

SBT


Are weaning parameters dead

General Readiness Criteria Respiratory Failure

Weaning: 2000s

Extubation

Pass

Full Ventilatory Support

SBT

Fail

Full Ventilatory Support


Are weaning parameters dead

Weaning: 2000s Respiratory Failure

General Readiness Criteria

Extubation

Pass

Full Ventilatory Support

SBT

Fail

Full Ventilatory Support

Weaning Parameters


Are weaning parameters dead

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)


Are weaning parameters dead

  • 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.


Are weaning parameters dead

W Respiratory Failure

  • P

  • P


Are weaning parameters dead

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


Are weaning parameters dead

What is Weaning

  • Discontinuation of ventilatory support


Are weaning parameters dead

What is Weaning

  • Extubation


Are weaning parameters dead

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


Are weaning parameters dead

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.




Are weaning parameters dead

Oxygenation

Ventilation

Secretion Clearance

Elements Involved in Weaning

(SBTs Address Only the First Two)

Airway Protection