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

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)

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

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

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

Sipes Study: Techniques Used 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 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

*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;150:896-903 Esteban A et al, NEJM 1995;332:345-50

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;150:896-903 Esteban 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:* 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” (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 Support Weaning: 1960s-1970s Full Ventilatory Support Extubation

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

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

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

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)

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.

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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 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* 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

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

Ventilatory Support Intubation

Ventilatory Support Intubation

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