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Are Weaning Parameters Dead?

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  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/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

  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):253-301

  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):253-301

  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;324:1445-50

  8. 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 • 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

  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: 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

  16. 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. 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

  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):1408-15

  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; www.ahrq.gov/clinic/mechsumm.htm; Meade MO et al, Respir Care 2001;46(12):1408-15

  27. 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

  28. 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

  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 >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

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

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

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

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

  40. 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.

  42. W • P • P

  43. W • P • P

  44. 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

  45. 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

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