Are Weaning Parameters Dead?

Are Weaning Parameters Dead?

David J Pierson MD

Harborview Medical CenterUniversity 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 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


• 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



• 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


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

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


• 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


• 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


• 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

• 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


• 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 Study:Weaning Parameters Measured


0102030405060708090

100

VT f MIP VC VE f/VT P0.1 MVV

Sipes Study:Techniques Used


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

Sipes Study: Techniques Used


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?


• 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.


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?

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

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

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

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

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*

• 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

http://www.ahrq.gov/clinic/mechsumm.htm

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

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

Recent Evolution of Approach to Weaning, Based on Best

Available Evidence

Predicting

Recent Evolution of Approach to Weaning, Based on Best

Available Evidence

Predicting Checking

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.

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”(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”(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

Full Ventilatory

SupportExtubation

Weaning: 1960s-1970s

Full Ventilatory

Support

Weaning Parameters

SBT

Weaning: 1980s-1990s

Extubation

Full Ventilatory

Support

Pass

Fail

Full Ventilatory

Support

Extubation

SBT

Weaning: 2000s

Full Ventilatory

Support

Pass

Fail

General Readiness

Criteria

Full Ventilatory

Support

Extubation

Weaning Parameters

SBT

Weaning: 2000s

Full Ventilatory

Support

Pass

Fail

General Readiness

Criteria

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)

• 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.

W

• P

• P

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.

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.

Summary ROC Curve for RSBI Predicting Successful Extubation*

•Text

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

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


• 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)


• 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

• 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?

• 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:

Clinical Settings for Weaning

• Short-term ventilation in acute illness

• Prolonged ventilation in acute illness

• Long-term mechanical ventilation

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

• 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’sFirst Law of Weaning:

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

ventilator.

Ventilatory Support

Intubation

Airway Protection

Ventilation

Secretion Clearance

Oxygenation

Elements Involved in Weaning(SBTs Address Only the First Two)

Are Weaning Parameters Dead?

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