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Chapter 47 Discontinuing Ventilatory Support

Chapter 47 Discontinuing Ventilatory Support. Learning Objectives. Discuss the relationship between ventilatory demand and ventilatory capacity in the context of ventilator discontinuance. List factors associated with ventilator dependence.

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Chapter 47 Discontinuing Ventilatory Support

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  1. Chapter 47Discontinuing Ventilatory Support

  2. Learning Objectives • Discuss the relationship between ventilatory demand and ventilatory capacity in the context of ventilator discontinuance. • List factors associated with ventilator dependence. • Explain how to evaluate a patient before attempting ventilator discontinuation or weaning. • List acceptable values for specific weaning indices used to predict a patient’s readiness for discontinuation of ventilatory support. • Describe factors that should be optimized before an attempt is made at ventilator discontinuation or weaning.

  3. Learning Objectives (cont.) • Describe techniques used in ventilator weaning, including daily spontaneous breathing trials, synchronized intermittent mandatory ventilation, pressure support ventilation, and other newer methods. • Contrast the advantages and disadvantages associated with various weaning methods and techniques. • Describe how to assess a patient for extubation. • List the primary reasons why patients fail a ventilator discontinuance trial. • Explain why some patients cannot be successfully weaned from ventilatory support.

  4. Introduction • Ventilatory support sustains life but is not curative • Has many complications and hazards • Should be withdrawn expeditiously • All patients should be evaluated on a daily basis for their ability to wean from ventilatory support • Balance desire for early extubation with its exposure to the risks of reintubation.

  5. Ventilatory Capacity

  6. All of the following are TRUE about mechanical ventilation, except: • Ventilatory support sustains life but is not curative. • It has few complications and hazards. • It should be withdrawn expeditiously. • All patients should be evaluated on a daily basis for their ability to wean from ventilatory support

  7. Methods of Discontinuing Ventilation • Three main methods • Spontaneous breathing trials (SBT) • SIMV • PSV • Novel modes with no data to support • VSV = volume support ventilation, MMV= mandatory minute volume ventilation, ATC = automatic tube compensation, PAV = proportional assist ventilation **Systematic review: 1 SBT per day has shown best results

  8. Probability of Successful Weaning

  9. Discontinuing Ventilatory Support • In general, patients being considered for removal from ventilatory support fall into one of four categories: • removal is quick and routine, normally the vast majority of patients • need a more systematic approach, about 15 to 20% of ventilated patients • require days to weeks to wean, usually less than 5% of patients • ventilator-dependent or “unweanable” patients, less than 1% of patients

  10. Global Criteria for Discontinuing Ventilatory Support(cont.) • Success is tied to • Ventilatory work load versus capacity • Oxygenation status • Cardiovascular status • Psychological factors

  11. Most Important Criteria • Reversal of disease state that necessitated ventilatory support • Oxygenation status adequate on <0.5 FIO2 • Medically and hemodynamically stable • Patient can breathe spontaneously • If the above are all true, then perform a formal evaluation for extubation.

  12. 66 Measurements: 8 Most Consistently Predictive • Spontaneous rate 6 to 30 beats/min • Spontaneous VT >5 ml/kg • f/VT (RSBI) – most predictive <105 • Minute ventilation <10 L/min • MIP <20 to 30 mm Hg • P0.1 <6 cm H2O • P0.1/MIP <0.3 • CROP (CDyn, f, O2, PImax) >13 * No single index has high predictive power, so it is important to consider the total picture.

  13. Which of the following predictive value is consistent with a patient weaning successfully? • Spontaneous rate 40 beats/min • Spontaneous VT 4 mL/kg • f/VT (RSBI) 85 • MIP –18 mm Hg

  14. Preparing the Patient • Patient should be rested and stable • Maximize bronchodilator and anti-inflammatory medications as well as bronchial hygiene • Communicate well with patient so as to relieve/minimize anxiety • Optimize nutrition, acid/base status, fluid balance, and oxygenation • Minimize sedation

  15. Rapid Ventilator Discontinuance • Patients that are likely to wean rapidly • Presenting problem corrected in 72 hours • Good weaning parameters • Good results in SBT of 30 to 120 minutes • If the above criteria are met, most patients can be removed from ventilatory support • If the patient can protect his or her airway, then extubate at this time

  16. Progressive Weaning of Ventilatory Support • Patients likely to need longer weaning period • Ventilated longer then 72 hours • Marginal: oxygen, ventilatory, cardiovascular, or medical status • Most common methods of weaning: • SBT alternating with rest periods on • A/C, SIMV, or significant levels of PSV

  17. Progressive Weaning: SBT • T-tube trial • 5 to 30 minutes SBT • 1 to 4 hours of rest on A/C, SIMV, or high PSV • Gradually, SBT times increase while rest periods diminish • Patients rested at night • Alternate method is 1 SBT/day and then rest. • This can also be done on the ventilator in CPAP mode with PSV or ATC.

  18. Initial Screening SBT • Perform 2–3 minute SBT. If 2 out of 3 of the criteria below are met, start formal wean • VT >5 ml/kg • RR <30–35 beats/min • MIP-a.k.a (NIF) <20 cm H2O • Alternate: adequate cough, no vasopressors • P/F ratio >200 • PEEP 5 • f/VT <105

  19. SBT Termination • Termination occurs if any of these criteria met • Agitation, anxiety, diaphoresis, altered mental state • Respiratory rate > 30 or 35 beats/min • SpO2 <90% • 20% change in HR or HR > 120 to 140 beats/min • Systolic BP > 180 mm Hg or < 90 mm Hg

  20. Weaning With SIMV • Faster weans claimed but contrary to evidence • Ease of use is primary reason for use • Evidence that at 50% of full ventilatory support, patient WOB approximates that on CPAP • In addition, demand flow SIMV imposes considerable WOB • Modern ventilators minimize this effect.

  21. Weaning With SIMV (cont.) • Support set below required level; patient makes up the difference. • Once precipitating event corrects, support is rapidly reduced. • Support is typically reduced in increments of 2 breaths per minute until spontaneous ventilation is achieved

  22. All of the following are TRUE about SIMV weaning except: • Faster weans claims are supported by evidence • Ease of use is primary reason for use • Evidence that at 50% of full ventilatory support, patient WOB approximates that on CPAP • Demand flow SIMV imposes considerable WOB

  23. PSV Weaning • Level is set to PSVmax 6 to 10 ml/kg. • On resolution of precipitating event • PSV reduced increments 2 to 4 cm H2O, usually 1 to 2 times per day • Rested at nights • 2 strategies for discontinuance of PSV: • Patient tolerates PSV of 5 – 8 cm H2O with no distress • Patient tolerates CPAP with no PSV without distress

  24. Monitoring During Weaning • PaCO2 best index of adequacy of ventilation but only tied to clinical data • PaCO2 40 mm Hg with f/VT of 250 shows impending ventilatory failure. • PaCO2 40 mm Hg with f/VT of 40 shows ability to breathe spontaneously. • SpO2 monitor continuously • Cardiovascular status

  25. Extubation • Weaning and extubation separate decisions • Extubation requires • Ability to protect airway • Gag • Effective cough • Airway patency • Minimal edema • Positive “cuff-leak” > 12% volume loss • Adequate pulmonary hygiene

  26. All of the following are required for extubation, except: • Maximal edema • Patients ability to protect airway • Airway patency • Adequate pulmonary hygiene

  27. Postextubation Stridor • Occurs in 2% to 16% of ICU patients • Can result in complete airway obstruction • Management includes • Cool aerosol mist with oxygen via mask • Nebulized racemic epinephrine (0.5 ml 2.25%) • Nebulized 1 mg in 4 ml NS dexamethasone • HeliOx 60%/40%

  28. Failure of Extubation • Up to 25% of patients require MV again • Half of patients with distress following MV discontinuance develop marked hypercapnia • Myocardial ischemia associated with failed weaning attempts • Failed weans may be undiagnosed NMD or psychological dependence • Most common reason: inadequate ventilatory capability which cannot meet ventilatory demand

  29. Chronically Ventilator-Dependent Patients • Prolonged MV occurs in 3% to 7% of ventilated patients, while <1% become dependent • Definition: ventilator dependency remains following 3 months of weaning attempts • Special long-term acute care facilities specialize in weaning these patients • Once dependency established, goal is to restore highest level of independence

  30. Terminal Weaning • Refers to weaning in the face of catastrophic and irreversible illness • Weaning occurs despite likely result of patient death • Decision made by patient and/or family in consultation with physician. • Must meet ethical and legal guidelines • May be due to advanced directives, current patient decision, or very poor prognosis

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