akella mvweaning

8/8/2019 Akella MVWeaning

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Weaning from Mechanical

Ventilation

Akella Chendrasekhar MD FACS FCCP


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Objectives

Discuss physiologic variables that are used to indicatereadiness to wean from mechanical ventilation

Contrast the approaches used to wean patients frommechanical ventilation

Discuss the use of protocols to wean patients fromventilatory support

Discuss the criteria used to indicate readiness forextubation

Describe the most common reasons why patients failto wean from mechanical ventilation


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A 55 year old COPD patient s/p complicated acute MI is on

the ventilator, weaning is being considered, what is the first

consideration?

1. Primary medical problem

2. COPD issues

3. Fluid status of the patient4. Not sure


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We use weaning protocols in our ICU

1. All of the time

2. Some of the time

3. No protocols exist in our ICU


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The weaning protocol once initiated, is

run by

1. Physician- intensivist

2. Respiratory therapist

3. Nursing


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Introduction

75% of mechanically ventilated patients areeasy to be weaned off the ventilator withsimple process

10-15% of patients require a use of a weaningprotocol over a 24-72 hours

5-10% require a gradual weaning over longer

time 1% of patients become chronically dependent

on MV


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Readiness To Wean

Improvement of respiratory failure

Absence of major organ system failure

Appropriate level of oxygenation Adequate ventilatory status

Intact airway protective mechanism (needed

for extubation)


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Oxygenation Status

PaO2 60 mm Hg

FiO2 0.40

PEEP 5 cm H2O


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Ventilation Status

Intact ventilatory drive: ability to control their

own level of ventilation

Respiratory rate < 30 Minute ventilation of < 12 L to maintain PaCO2

in normal range

VD/VT < 60% Functional respiratory muscles


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Intact Airway Protective Mechanism

Appropriate level of consciousness

Cooperation

Intact cough reflex

Intact gag reflex

Functional respiratory muscles with ability to

support a strong and effective cough


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Function ofOther Organ Systems

Optimized cardiovascular function

Arrhythmias

Fluid overload

Myocardial contractility

Body temperature 1 degree increases CO2 production and O2 consumption by 5%

Normal electrolytes

Potassium, magnesium, phosphate and calcium

Adequate nutritional status Under- or over-feeding

Optimized renal, Acid-base, liver and GI functions


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Predictors of Weaning Outcome

PredictorPredictor ValueValue

Evaluation of ventilatory drive:Evaluation of ventilatory drive:

P 0.1P 0.1 < 6 cm H2O< 6 cm H2O

Ventilatory muscle capability:Ventilatory muscle capability: Vital capacityVital capacity

Maximum inspiratory pressureMaximum inspiratory pressure

> 10 mL/kg> 10 mL/kg

3 times V> 3 times VEE

< 100< 100

< 30 /min< 30 /min


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Maximal Inspiratory Pressure

Pmax: Excellent negative predictive value if less than

20 (in one study 100% failure to wean at this value)

An acceptable Pmax however has a poor positive

predictive value (40% failure to wean in this study

with a Pmax more than 20)


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Frequency/Volume Ratio

Index of rapid and shallow breathing RR/Vt

Single study results:

RR/Vt>105 95% wean attempts unsuccessful RR/Vt


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Measurements Performed Either While Patient Was Receiving Ventilatory Support or During a

Brief

Period of Spontaneous Breathing That Have Been Shown to Have Statistically Significant LRs To

Predict the

Outcome of a Ventilator Discontinuation Effort in More Than One Study*


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Approaches To Weaning

Spontaneous breathing trials

Pressure support ventilation (PSV)

SIMV

New weaning modes


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Do Not WeanTo Exhaustion


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With regard to spontaneous breathing trials a

physician can reliably predict the result

1. True

2. False


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Spontaneous Breathing Trials

SBT to assess extubation readiness

T-piece or CPAP 5 cm H2O

30-120 minutes trials

If tolerated, patient can be extubated

SBT as a weaning method

Increasing length of SBT trials

Periods of rest between trials and at night


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Frequency of Tolerating an SBT in Selected Patients and Rate of

Permanent Ventilator Discontinuation

Following a Successful SBT*

*Values given as No. (%). Pts patients.30-min SBT.

120-min SBT.


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Criteria Used in Several Large Trials To Define

Tolerance of an SBT*

*HR heart rate; Spo2 hemoglobin oxygen saturation. See Table 4 for

abbreviations not used in the text.


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Which modality of ventilation do you use when

weaning the patient from a ventilator?

1. PSV

2. CPAP

3. SIMV4. T-PIECE


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Pressure Support

Gradual reduction in the level of PSV

PSV that prevents activation of accessory

muscles Gradual decrease on regular basis (hours or

days) to minimum level of 5-8 cm H2O

Once the patient is capable of maintaining thetarget ventilatory pattern and gas exchange at

this level, MV is discontinued


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SIMV

Gradual decrease in mandatory breaths

It may be applied with PSV

Has the worst weaning outcomes in clinicaltrials

Its use is not recommended


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Protocols

Developed by multidisciplinary team

Implemented by respiratory therapists and

nurses to make clinical decisions Results in shorter weaning times and shorter

length of mechanical ventilation than

physician-directed weaning


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Daily SBT

35/minSpo2 < 90%

HR > 140/minSustained 20% increase in HRSBP > 180 mm Hg, DBP > 90 mm HgAnxietyDiaphoresis

30-120 min

PaO2/FiO2 200 mm Hg

PEEP 5 cm H2O

Intact airway reflexesNo need for continuous infusions of vasopressors or inotrops

RSBI

ExtubationNo

> 100

Rest 24 hrs

Yes

Stable Support Strategy

Assisted/PSV

24 hours

Low level CPAP (5 cm H2O),Low levels of pressure support (5 to 7 cm H2O)T-piece breathing


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Failure to Wean

Weaning to exhaustion

Auto-PEEP

Excessive work ofbreathing

Poor nutritional status Overfeeding

Left heart failure

Decreased magnesium and phosphate leves

Infection/fever

Major organ failure

Technical limitation


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Weaning to Exhaustion

RR > 35/min

Spo2 < 90%

HR > 140/min Sustained 20% increase in HR

SBP > 180 mm Hg, DBP > 90 mm Hg

Anxiety Diaphoresis


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Work-of-Breathing

Pressure= Volume/compliance+ flow X resistance

High airway resistance

Low compliance

Aerosolized bronchodilators, bronchial

hygiene and normalized fluid balance assist in

normalizing compliance, resistance and work-

of-breathing


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Auto-PEEP

Increases the pressure gradient needed toinspire

Use of CPAP is needed to balance alveolar

pressure with the ventilator circuit pressure

Start at 5 cm H2O, adjust to decrease patientstress

Inspiratory changes in esophageal pressurecan be used to titrate CPAP


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0

-5

Gradient

0

-5


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0

Auto PEEP +10-5

Gradient

-15


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PEEP

10

Auto PEEP +105

Gradient

-5


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Left Heart Failure

Increased metabolic demands that are associatedwith the transition from mechanical ventilation tospontaneous breathing

Increases in venous return as that is associated withthe negative pressure ventilation and the contractingdiaphragm which results into an increase in PCWPand pulmonary edema

Appropriate management of cardiovascular status isnecessary before weaning will be successful


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Nutritional/Electrolytes

Imbalance of electrolytes causes muscular

weakness

Nutritional support improves outcome Overfeeding elevates CO2 production due to

excessive carbohydrate ingestion


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Infection/Fever/Organ Failure

Organ failure precipitate weaning failure

Infection and fever increase O2 consumption

and CO2 production resulting in an increaseventilatory drive


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Points to Remember

The primary prerequisite for weaning is reversal of the indication ofmechanical ventilation

Adequate gas exchange should be present with minimal oxygenation andventilatory support before weaning is attempted

The function of all organ systems should be optimized, electrolytes should

be normal, and nutrition should be adequate before weaning is attempted The most successful predictor of weaning is RSBI < 100

Maximum inspiratory pressure is the best predictor of weaning failure

Ventilatory discontinuation should be done if patient tolerates SBT for 30-120 minutes

Patients who fail an SBT should receive a stable, non-fatiguing,

comfortable form of ventilatory support Use of liberation and weaning protocol facilitates the process and

decreases the ventilator length of stay

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