Chapter 47

Discontinuing Ventilatory Support

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Objectives 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.

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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.

Explain why some patients cannot be successfully weaned from ventilatory support.

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Introduction

Ventilatory support sustains life but is not curative.

It has many complications and hazards.

It should be withdrawn expeditiously.

Balance desire for early extubation with its exposure to the risks of reintubation.

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Methods of Discontinuing Ventilation

Three main methods Spontaneous breathing trials (SBT) SIMV PSV

Novel modes with no data to support MMV = mandatory minute volume, VSV = volume support

ventilation, ATC = automatic tube compensation, PAV = proportional assist ventilation

**Systematic review: 1 SBT per day has shown best results

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Discontinuing Ventilatory Support

Success is tied to Ventilatory work load versus capacity Oxygenation status Cardiovascular status Psychological factors

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Most Important Criteria

1. Reversal of disease state that necessitated ventilatory support

2. Oxygenation status adequate on <0.5 FIO2

3. Medically and hemodynamically stable

4. Patient can breathe spontaneously

If the above are all true, then perform a formal evaluation for extubation.

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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.

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Preparing the Patient Patient should be rested and stable.

Maximize bronchodilator and antiinflammatory 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.

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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.

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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

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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 are 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.

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Initial Screening SBT Perform 2–3 minute SBT. If 2 out of 3 of the criteria below are

met, start a formal wean VT >5 ml/kg RR <30–35 beats/min MIP <20 cm H2O

Alternate: adequate cough, no vasopressors P/F ratio >200 PEEP 5 f/VT <105

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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

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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.

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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.

Weaning With SIMV (cont.)

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PSV Weaning

Level is set to PSVmax 8 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

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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

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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

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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%

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Failure of Extubation

Up to 25% of patients require MV again. Half of patients with distress following MV discontinuance

develop marked hypercapnia. Myocardial ischemia is 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

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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.

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Terminal Weaning Refers to weaning in the face of catastrophic and irreversible

illness

Weaning occurs despite the likely result of patient death

Decision is 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