Chapter 47 Discontinuing Ventilatory Support

Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc.

Chapter 47

Discontinuing Ventilatory Support

Copyright © 2013, 2009, 2003, 1999, 1995, 1990, 1982, 1977, 1973, 1969 by Mosby, an imprint of Elsevier Inc. 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.


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.


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Has many complications and hazards Should be withdrawn expeditiously All patients should be evaluated on a daily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.


Ventilatory Capacity

5


All of the following are TRUE about mechanical ventilation, except:

A.Ventilatory support sustains life but is not curative.

B.It has few complications and hazards.

C.It should be withdrawn expeditiously.

D.All patients should be evaluated on a daily basis for their ability to wean from ventilatory support


Methods of Discontinuing Ventilation

Three main methods1. Spontaneous breathing trials (SBT)

2. SIMV

3. 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


Probability of Successful Weaning

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Discontinuing Ventilatory Support

In general, patients being considered for removal from ventilatory support fall into one of four categories: 1. removal is quick and routine, normally the vast

majority of patients

2. need a more systematic approach, about 15 to 20% of ventilated patients

3. require days to weeks to wean, usually less than 5% of patients

4. ventilator-dependent or “unweanable” patients, less than 1% of patients


Global Criteria for Discontinuing Ventilatory Support

(cont.) Success is tied to

Ventilatory work load versus capacity Oxygenation status Cardiovascular status Psychological factors


Most Important Criteria

1. Reversal of disease state that necessitated ventilatory support

2. Oxygenation status adequate on <0.5 FIO2

3. Medically and hemodynamically stable4. Patient can breathe spontaneously

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


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.


Which of the following predictive value is consistent with a patient weaning successfully?

A.Spontaneous rate 40 beats/min

B.Spontaneous VT 4 mL/kg

C.f/VT (RSBI) 85

D.MIP –18 mm Hg


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


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


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


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.


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


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


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.


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.)


All of the following are TRUE about SIMV weaning except:

A.Faster weans claims are supported by evidence

B.Ease of use is primary reason for use

C.Evidence that at 50% of full ventilatory support, patient WOB approximates that on CPAP

D.Demand flow SIMV imposes considerable WOB


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


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


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


All of the following are required for extubation, except:

A.Maximal edema

B.Patients ability to protect airway

C.Airway patency

D.Adequate pulmonary hygiene


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%


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


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


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

Chapter 47 Discontinuing Ventilatory Support

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