1. Are Weaning Parameters Dead?
David J Pierson MD
Harborview Medical Center
University of Washington
Seattle

2. What is Weaning?
The gradual reduction of ventilatory support and its replacement with spontaneous ventilation
Discontinuation of ventilatory support
Extubation

3. Weaning Parameters
Predictors of successful liberation from ventilatory support
Applied prior to attempted weaning

4. Weaning Parameters Studied and/or Advocated, 1970-2000
Measures of Oxygenation and Gas Exchange
PaO2/FIO PaO2/PAO 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):

5. 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):

6. 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):

7. 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:

8. Implications of “Failure”
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)

9. Measuring Weaning Parameters: Does Technique Matter?
In the original studies:*
Full ventilatory support (volume A/C)
Disconnection for measurements
FIO 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. Measurement of Weaning Parameters: Survey of Current Practice
48/72 departments (67%) completed the questionnaire and provided complete data
Hospitals: beds (mean 491)
ICUs: beds (mean 59)
33/48 departments (67%) used therapist- driven protocols
Sipes MW et al, Respir Care 1999;44(10):1218

16. Weaning Parameters Measured
Sipes Study:
Weaning Parameters Measured
Sipes MW et al, Respir Care 1999;44(10):1218

17. 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

18. Sipes Study: Techniques Used
Use CPAP and/or PSV?
Wait How Long?
Sipes MW et al, Respir Care 1999;44(10):1218

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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):

26. 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;
Meade MO et al, Respir Care 2001;46(12):

27. *Brochard L et al, AJRCCM 1994;150:896-903
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:
Esteban A et al, NEJM 1995;332:345-50

28. Brochard L et al, AJRCCM 1994;150:896-903
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:
Esteban A et al, NEJM 1995;332:345-50

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

30. Recent Evolution of Approach to Weaning, Based on Best Available Evidence
Predicting
Checking

31. Criteria for Performing a Spontaneous Breathing Trial:*
Evidence for some reversal of underlying cause of ARF;
Adequate gas exchange: PaO2/FIO2 > on PEEP  5-8, on FIO2  , 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

32. Four Key Elements in Managing Patients with Acute Respiratory Failure
Oxygenation
Ventilation
Airway Protection
Secretion Clearance

33. Four Key Elements in Managing Patients with Acute Respiratory Failure
Oxygenation
Ventilation
Airway Protection
Secretion Clearance
Assessed by SBT

34. “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

35. “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

36. Full Ventilatory Support
Weaning: 1960s-1970s
Full Ventilatory Support
Extubation

37. Weaning: 1980s-1990s SBT Weaning Parameters Extubation
Full Ventilatory Support
Pass
Fail
Full Ventilatory Support
SBT

38. Weaning: 2000s SBT General Readiness Criteria Extubation
Pass
Full Ventilatory Support
SBT
Fail
Full Ventilatory Support

39. Weaning: 2000s SBT General Readiness Criteria Extubation
Pass
Full Ventilatory Support
SBT
Fail
Full Ventilatory Support
Weaning Parameters

40. Implications of “Failure”
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)

41. 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.

46. W P

47. W P

48. 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

49. 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

50. Summary ROC Curve for RSBI Predicting Successful Extubation*
Text
*Meade M et al. Chest 2001;120 (6 suppl):400s-424s

51. 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 > );
Hemodynamic stability; and,
Capability to initiate an inspiratory effort

52. 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)

53. 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

54. What is Weaning
The gradual reduction of ventilatory support and its replacement with spontaneous ventilation

55. What is Weaning
Discontinuation of ventilatory support

56. What is Weaning
Extubation

57. 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

58. Clinical Settings for Weaning
Short-term ventilation in acute illness
Prolonged ventilation in acute illness
Long-term mechanical ventilation

59. 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

60. 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:

61. 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

62. Robertson’s First Law of Weaning:
When the patient gets well, the patient will get off the ventilator.

63. Ventilatory Support
Intubation

64. Ventilatory Support
Intubation

65. Elements Involved in Weaning (SBTs Address Only the First Two)
Ventilation
Secretion Clearance
Oxygenation
Airway Protection