Principles of Mechanical Ventilation

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Principles of Mechanical Ventilation

• RET 2284
• Module 6.0
• Discontinuation From Mechanical Ventilation

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Discontinuation From Mechanical Ventilation

• Discontinuation (ACCP/SCCM/AARC)
• The process of withdrawing mechanical ventilatory
  support and transferring the work of breathing
  from the ventilator to the patient
• AKA
• Weaning (used to describe the gradual reduction
  of ventilatory support)
• Gradual reduction
• Liberation
• Can be accomplished
• Abruptly
• Gradually

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Discontinuation From Mechanical Ventilation

• Discontinuation
• Once the need for mechanical ventilation has
  been resolved, ventilation can be discontinued
• About 80 of patients requiring temporary
  mechanical ventilation do not require a slow
  withdrawal process and can be disconnected within
  a few hours or day of initial support
• Postoperative recovery from anesthesia
• Uncomplicated drug overdose
• Exacerbations of asthma

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Discontinuation From Mechanical Ventilation

• Discontinuation
• The ventilator and airway should be discontinued
  as soon as possible to avoid the risks associated
  with mechanical ventilation
• Ventilator induced lung injury (VILI)
• Nosocomial pneumonia
• Airway trauma form ET
• Unnecessary sedation
• Premature discontinuation also is associated with
  a higher mortality rate

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Discontinuation From Mechanical Ventilation

• Evaluation of Clinical Criteria for Weaning
• Criteria for Weaning Three Key Points
• The problem that caused the patient to require
  ventilation has been resolved
• Certain measurable criteria should be assessed to
  help establish a patients readiness for
  discontinuation of ventilation
• A spontaneous breathing trial should be performed
  to establish readiness for weaning

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Discontinuation From Mechanical Ventilation

• Evaluation of Clinical Criteria for Weaning
• Pathology of Ventilator Dependence
• Primary pathology that led to ventilatory support
  must be corrected
• In patients who require mechanical ventilation
  for gt24 hours, a formal search should be made for
  all causes that may be contributing to ventilator
  dependence

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Discontinuation From Mechanical Ventilation

• Evaluation of Clinical Criteria for Weaning
• Weaning Criteria
• When a patients condition is stable, alert, and
  cooperative, clinicians commonly evaluate certain
  ventilatory mechanic and gas exchange values to
  help assess readiness for weaning

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Discontinuation From Mechanical Ventilation

• Evaluation of Clinical Criteria for Weaning
• Ventilatory Performance and Muscle Strength
• Vital Capacity
• Adequate VC is essential for airway clearance
  (cough)
• gt15 ml/kg (IBW)
• Requires active patient effort and cooperation
• Tidal Volume
• Adequate VT is essential for effective
  ventilation
• 4 6 ml/kg (IBW)

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Discontinuation From Mechanical Ventilation

• Evaluation of Clinical Criteria for Weaning
• Ventilatory Performance and Muscle Strength
• Spontaneous Respiratory Rate
• lt35 breaths per minute
• Rate gt35/min associated with
• Increased work of breathing
• Weaning failure

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Discontinuation From Mechanical Ventilation

• Evaluation of Clinical Criteria for Weaning
• Ventilatory Performance and Muscle Strength
• Minute Ventilation VE
• Should be lt10 15 L/min (with normal PaCO2)
• VE gt10 15 L/min required to normalize PaCO2
  implies that the work of spontaneous breathing
  will be excessive
• Increased CaO2 Production
• - Extensive burns
• - Elevated body temperature
• - Overfeeding (carbohydrates)
• Increased Alveolar Deadspace
• - Pulmonary emboli
• - Decreased cardiac output

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Discontinuation From Mechanical Ventilation

• Evaluation of Clinical Criteria for Weaning
• Ventilatory Performance and Muscle Strength
• Respiratory Frequency/Tidal Volume Ratio (f/VT)
• Failure to wean may be related to spontaneous
  breathing that is rapid (high respiratory rate)
  and shallow (low tidal volume)
• Procedure
• Disconnect the spontaneous breathing patient from
  the ventilator and oxygen for 1 minute
• VE, respiratory frequency, VT are measured
• Calculate f/VT
• RSBI lt 105 associated with successful weaning

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Discontinuation From Mechanical Ventilation

• Ventilatory Performance and Muscle Strength
• VC, VTSP, RRSP, VESP

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Discontinuation From Mechanical Ventilation

• Ventilatory Performance and Muscle Strength
• VC, VTSP, RRSP, VESP

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Discontinuation From Mechanical Ventilation

• Ventilatory Performance and Muscle Strength
• VC, VTSP, RRSP, VESP

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Discontinuation From Mechanical Ventilation

• Ventilatory Performance and Muscle Strength
• VC, VTSP, RRSP, VESP

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Discontinuation From Mechanical Ventilation

• Evaluation of Clinical Criteria for Weaning
• Ventilatory Performance and Muscle Strength
• Maximum Inspiratory Pressure (MIP)
• Sometimes referred to Negative Inspiratory Force
  (NIF)
• The maximum amount of negative force a patient
  can generate in 20 seconds
• lt-25 cm H20 is associated with weaning success

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Discontinuation From Mechanical Ventilation

• Evaluation of Clinical Criteria for Weaning
• Ventilatory Performance and Muscle Strength
• MIP

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Discontinuation From Mechanical Ventilation

• MIP

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Discontinuation From Mechanical Ventilation

• MIP

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Discontinuation From Mechanical Ventilation

• MIP

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Discontinuation From Mechanical Ventilation

• MIP

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Discontinuation From Mechanical Ventilation

• MIP

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Discontinuation From Mechanical Ventilation

• Evaluation of Clinical Criteria for Weaning
• Measurement of Drive to Breathe
• P0.1 gt-6

The airway is occluded after patient inspiration.
Pressure at the mouth is measured at 100 msec,
and the airway then is opened. The upper airway
pressure at 100 msec is the P0.1 value, reported
as an absolute number.
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Discontinuation From Mechanical Ventilation

• Evaluation of Clinical Criteria for Weaning
• Measurement and Estimation of WOB
• WOB lt0.8 J/L
• CD gt25 mL/cm H2O
• VD/VT lt0.60
• CROP Index gt13 mL/breaths/min

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Discontinuation From Mechanical Ventilation

• Evaluation of Clinical Criteria for Weaning
• Measurement and Estimation of WOB
• Compliance Rate Oxygenation and Pressure Index
  (CROP)
• Evaluates a patients pulmonary gas exchange and
  the balance between respiratory demands and
  respiratory neuromuscular reserve
• CROP CD x MIP x PaO2
• PAO2
• _________________________________
  ________
• f
• CROP 13 ml/breaths/min is predictive of weaning
  success

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Discontinuation From Mechanical Ventilation

• Evaluation of Clinical Criteria for Weaning
• Measurement of Adequacy of Oxygenation
• PaO2 ?60 mm Hg (FiO2 lt0.40)
• PEEP ?5 8 cm H2O
• PaO2/FiO2 gt250 mm Hg (consider at 150 200 mm
  Hg)
• P(A-a)O2 lt350 mm Hg (FiO2 1)
• OS/QT lt20 - 30

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Discontinuation From Mechanical Ventilation

• Evaluation of Clinical Criteria for Weaning
• Measurement of Adequacy of Oxygenation
• PA-aO2 (A-a Gradient)
• Used to estimate
• Degree of hypoxemia
• Degree of physiologic shunt
• The larger the gradient the more severe the
  hypoxemia or the larger the shunt
• Room air
• lt4 mm Hg per 10 years of age
• 100 O2
• lt350 mm Hg for weaning success
• gt350 mm Hg associated with weaning failure

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Discontinuation From Mechanical Ventilation

• Evaluation of Clinical Criteria for Weaning
• Measurement of Adequacy of Oxygenation
• QS/QT (The portion of cardiac output that is
  shunted)
• Shunted pulmonary perfusion cannot take part in
  gas exchange due to lack of ventilation (e.g.
  atelectasis)
• Normal value is 3-5
• QS/QT in the clinical setting
• 10 Normal
• lt20 Weaning success
• gt20 Weaning failure

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Discontinuation From Mechanical Ventilation

• Evaluation of Clinical Criteria for Weaning
• Measurement of Adequacy of Oxygenation
• QS/QT Equation
• Requires
• Arterial blood gas
• Mixed venous blood sample (PA Line)
• (PA-a O2)(.003)
• (PA-a O2)(.003) Ca-vO2
• Normal value is 3-5

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Weaning From Mechanical Ventilation

• Oxygenation Criteria
• PA-aO2 (A-a Gradient)
• Used to estimate
• Degree of hypoxemia
• Degree of physiologic shunt
• The larger the gradient the more severe the
  hypoxemia or the larger the shunt
• Room air
• lt4 mm Hg per 10 years of age
• 100 O2
• lt350 mm Hg for weaning success
• gt350 mm Hg associated with weaning failure

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Discontinuation From Mechanical Ventilation

• Weaning Techniques
• Methods of Titrating Ventilator Support
• Ventilator support can be reduced as patients
  become increasingly able to resume part of the
  work of breathing
• Three Common Approaches
• Synchronized Intermittent Mandatory Ventilation
  (SIMV)
• PSV Pressure Support Ventilation (PSV)
• Spontaneous Breathing Trial (SBT)

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Discontinuation From Mechanical Ventilation

• Weaning Techniques
• Methods of Titrating Ventilator Support
• SIMV Synchronized Intermittent Mandatory
  Ventilation
• Common practice is to reduce the mandatory rate
  progressively (1 2 breaths/min) at a pace that
  matches the patients improvement
• Pressure support can be added to unload
  spontaneous breaths through circuit and ET (helps
  prevent fatigue)
• PEEP of 3 5 cm H2O is also used to help
  compensate for changes in FRC
• Studies done clearly show that weaning took
  longer with SIMV when compared to PSV and T-piece
  methods

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Discontinuation From Mechanical Ventilation

• Weaning Techniques
• Methods of titrating Ventilator Support
• SIMV Synchronized Intermittent Mandatory
  Ventilation

Measurements of flow, volume, airway pressure,
and esophageal pressure in a patient ventilated
with SIMV. The esophageal pressure swings reflect
the changes in pleural pressure and are the
result of respiratory muscle contraction. These
pressure swings are nearly as large during a
mandatory breath as during spontaneous breaths.
(From Hess DR Respir Care 471007, 2002.)
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Discontinuation From Mechanical Ventilation

• Weaning Techniques
• Methods of Titrating Ventilator Support
• PSV Pressure Support Ventilation
• Patient triggered, pressure limited, flow cycled
• Patient controls the rate, timing and depth of
  each breath
• Theoretically, PSV allows the clinician to adjust
  the ventilatory workload for each spontaneous
  breath to enhance endurance conditioning of the
  respiratory muscles without causing fatigue

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Discontinuation From Mechanical Ventilation

• Weaning Techniques
• Methods of Titrating Ventilator Support
• PSV Establishing PS level
• Set PS level to 5 15 cm H2O until a reasonable
  ventilatory pattern for the patient is
  accomplished
• Or
• Reestablish patients baseline respiratory rate
• (15 25 breaths/min)
• VT (300 600 mL/min)
• Inappropriate PS level will produce tachycardia,
  hypertension, tachypnea, diaphoresis, excessive
  use of accessory muscles, paradoxical breathing,
  respiratory alternans

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Discontinuation From Mechanical Ventilation

• Weaning Techniques
• Methods of Titrating Ventilator Support
• PSV Weaning
• Gradually reduce PS level as long as an
  appropriate spontaneous respiratory rate and VT
  are maintained and no distress is evident
• When PS is reduced to 5 cm H2O it is not high
  enough to contribute to ventilatory support, but
  will help overcome the work imposed by the
  ventilator system and ET

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Discontinuation From Mechanical Ventilation

• Weaning Techniques
• Methods of Titrating Ventilator Support
• Spontaneous Breathing Trial (SBT) - Abrupt Method
• Patient is removed from full ventilatory support
  and placed one of the following for a few minutes
  to assess their ability to perform a more
  extended spontaneous breathing trial
• T-Piece
• Low level of CPAP (e.g., 5 cm H2O) and/or low
  level of PS (e.g., 5 8 cm H2O) on ventilator
• Automatic Tube Compensation (ATC) on ventilator
• Considered a screening phase

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Discontinuation From Mechanical Ventilation

• Weaning Techniques
• Methods of Titrating Ventilator Support
• Spontaneous Breathing Trial (SBT) - Abrupt Method
• During the SBT the patients ability to tolerate
  unsupported ventilation is determined
• Respiratory pattern
• Adequacy of gas exchange
• Hemodynamic stability
• Subjective comfort
• A patient is considered ready for ventilator
  discontinuation when they can tolerate an SBT of
  30 120 minutes

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Discontinuation From Mechanical Ventilation

• Weaning Techniques
• Methods of Titrating Ventilator Support
• Spontaneous Breathing Trial (SBT) - Gradual
  Method
• Patient is removed from full ventilatory support
  and placed on T-Tube, ATC, CPAP and/or PS for 5
  and minutes and returned to full support for the
  remainder of the hour
• Repeat process with progressively more time on
  T-Tube, ATC, CPAP and/or PS, working up to 20
  30 minutes, and less time on full support
• Full ventilatory support at night to rest patient
• A patient is considered ready for ventilator
  discontinuation when they can tolerate an SBT of
  30 120 minutes

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Discontinuation From Mechanical Ventilation

• Weaning Techniques
• SBT
• Clinical Signs and Symptoms Indicating Problems
• RR gt30 35 bpm
• Increases in RR gt10 bpm, or RR lt8 bpm
• Use of accessory muscles
• VT ? below 250 300 mL
• Blood Pressure
• ? 20 mm Hg systolic
• ? 30 mm Hg systolic
• Systolic values gt180 mm Hg
• Diastolic values change 10 mm Hg

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Discontinuation From Mechanical Ventilation

• Weaning Techniques
• SBT
• Clinical Signs and Symptoms Indicating Problems
• Heart Rate
• ? gt20 from baseline
• gt140 bpm
• PVCs sudden onset (gt4 6/hr)
• Diaphoresis, pallor, cyanosis
• Deterioration of ABG or SpO2
• Agitation, anxiety, drowsiness

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Discontinuation From Mechanical Ventilation

• Weaning Techniques
• SBT
• Clinical Signs and Symptoms Indicating Problems
• Patients should not be allowed to experience
  extreme exhaustion during the SBT
• Unnecessary prolongation of a failed SBT can
  result in muscle fatigue, hemodynamic
  instability, discomfort and worsening gas
  exchange

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Discontinuation From Mechanical Ventilation

• Weaning Techniques
• SBT
• If the patient fails an SBT, the causes of the
  failure must be determined and corrected when
  possible
• When the reversible causes of SBT failure have
  been corrected, and if the patient still meets
  the criteria for discontinuation of ventilation,
  an SBT should be performed every 24 hours

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Discontinuation From Mechanical Ventilation

• Weaning Techniques
• SBT
• The clinical focus for the 24 hours after a
  failed SBT should be on maintaining adequate
  muscle unloading, optimizing comfort (and thus
  sedation needs), and preventing complications,
  rather than on aggressive ventilatory support
  reduction
• When a patient fails an SBT, repeated testing the
  same day is of no benefit

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Discontinuation From Mechanical Ventilation

• Weaning Techniques
• SBT
• To date no studies offer any evidence that a
  gradual support reduction strategy is better than
  providing full, stable support between once daily
  SBTs

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Discontinuation From Mechanical Ventilation

• Weaning Techniques
• Nonrespiratory Causes That May Complicate Weaning
• Cardiac Factors
• Acute CHF
• Acid-Base Factors
• Patients with chronic hypercapnia fail to wean in
  the presence of relative hyperventilation,
  respiratory alkalosis and subsequent renal
  compensation, leading to a decrease in bicarbonate

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Discontinuation From Mechanical Ventilation

• Weaning Techniques
• Nonrespiratory Causes That May Complicate Weaning
• Metabolic Factors
• Hypophosphtemia muscle weakness
• Hypomagnesemia muscle weakness
• Hyopthyroidism blunts the central response to
  hypercarbia and hypoxemia
• Pharmacological Agents
• Opioids, tranquilizers, hypnotic agents
• Depress central ventilatory drive
• Must be minimized for weaning to be successful

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Discontinuation From Mechanical Ventilation

• Weaning Techniques
• Nonrespiratory Causes That May Complicate Weaning
• Nutritional
• Underfeeding
• Muscle wasting
• Overfeeding
• Carbohydrates Increased O2 concumption, CO2
  production, and VE

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Discontinuation From Mechanical Ventilation

• Weaning Techniques
• Nonrespiratory Causes That May Complicate Weaning
• Psychological Factors
• Psychological ventilator dependence
• Anxiety, fear, delirium
• Agitation and/or panic during attempt to reduce
  or D/C ventilatory support
• Lack of Motivation
• Depression
• Effects of drugs
• Organic brain dysfunction
• Preexisting personality factors