Liberation from Mechanical Ventilation Weaning

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Liberation fromMechanical Ventilation(Weaning)

• Dr. George John,
• Division of Critical Care,
• Christian Medical College,
• Vellore

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WEANING

• In the intensive care, weaning from the following
  5 modalities has to be independently assessed
• Supplemental Oxygen
• PEEP
• Mechanical Ventilation
• Artifical Airway (endotracheal tube/tracheostomy)
• Inotropes

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Weaning

• Weaning should be based on accurate concepts
  the capacity to breathe spontaneously occurs when
  the underlying condition improves. This has more
  to do with accurate diagnosis and effective
  treatment of the underlying condition and less to
  do with manipulation of ventilator settings.

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Weaning

• Delayed extubation is associated with increased
  risk for ventilator associated pneumonia,
  increased ICU and hospital length of stay and
  increased mortality. Failed extubation may occur
  in 20 of patients - hence there is a need for
  improving the prediction of extubation outcome.

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WEANING versus LIBERATION

• Weaning
• graded removel of a therapeutic modality on which
  the patient has become dependent (and hence
  sudden withdrawal will not be tolerated). The
  term
• gradual removal of a benevolent process.
• In actual fact, weaning from many of the life
  support interventions instituted in the intensive
  care is not removal of a benevolent life
  sustaining process but the removal of a necessary
  (in the short term) but potentially damaging
  (when prolonged) intervention as early as
  feasible.
• In this context it is appropriate to name this
  process as liberation from mechanical
  ventilatory and other life support measures.

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Domains of Criteria

• Respiratory
• Cardiovascular
• Neuromuscular
• There are two types of criteria used to determine
  whether a patient passes or fails a spontaneous
  breathing trial objective criteria (abnormal
  arterial blood gas measurements) and subjective
  criteria (diaphoresis, evidence of increasing
  effort, tachycardia, agitation, anxiety).

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RESPIRATORY

• CLINICAL SIGNS of increased work of breathing
• intercostal retraction
• accessory muscle use
• nasal flaring, sternomastoid / trapezius use
• paradoxical or asynchronous rib
  cage- abdominal breathing movements
• VENTILATION / OXGENATION
• - respiratory frequency gt 35 breaths/min
• - arterial oxygen saturation below 90
• - f / VT ratio (Tobin Index) less than 100
  predicts successful weaning. f is respiratory
  rate in breaths per minute and VT is tidal
  volume in litres.

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CARDIOVASCULAR

• Heart rate
• gt 140 beats/minute or
• sustained increase or decrease in the heart
  rate of more than 20
• Systolic blood pressure
• gt180 mmHg or
• lt 90 mmHg

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NEUROLOGICAL

• Glasgow Coma Score gt 8
• If lt 8, consider tracheostomy
• Diaphoresis / anxiety / agitation

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Weaning - Preconditions

• - off sedation for a sufficient length of time
  (depending on the half life of the sedative
  given)
• - propped up (to allow easier diaphragmatic
  movement)the airway is to be cleared by
  suctioning secretions
• - FiO2 should be increased by 0.1 (if not COPD)
• - baseline values for pulse, respiratory rate,
  blood pressure, SaO2 and PaCO2 should be obtained.

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Modes of Weaning

• 1. T-tube
• 2. CPAP
• 3. SIMV
• Pressure Support
• Because the endotracheal tube imposes a
  resistive load on the respiratory muscles that
  is inversely related to its cross-sectional
  diameter, some clinicians advocate use of 5-8
  cmH2O pressure support to offset this imposed
  load.
• 5. SIMV PS

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Weaning which mode?

• T-piece weaning is more efficient than pressure
  support based weaning which in turn is better
  than one based on SIMV.
• protocol based weaning is more efficient than one
  based on subjective evaluation because subjective
  judgment is not sensitive enough to detect the
  fact that a patient is ready for extubation.
• successful extubation was achieved equally
  effectively with trials targeted to last 30 and
  120 min.

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Failure of Weaning

• Indicators of deterioration are
• 1. respiratory rate gt35/mt.
• 2. falling tidal volume lt5ml/kg
• 3. PaO2 lt55mm Hg Rising PaCO2
• 4. fall in blood pressure
• 5. tachycardia, cardiac arrythmias, sweating
  -increased sympathetic activity
• 6. altered mental status - restlessness,
  anxiety, confusion

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FAILURE TO WEAN OFF VENTILATOR CAUSES - 1

• Respiratory
• - Use wider bore artificial airway
• ET tube / tracheostomy
• - Treat bronchospasm adequately
• - Improve lung compliance by removing excess
  fluid (wet lungs) by using
  diuretics if volume overloaded / congestive
  cardiac failure is the cause. - Improve
  diaphragmatic function by using xanthines.
• Cardiovascular
• left ventricular dysfunction
• - pulmonary oedema (backward failure)
• - inability of the cardiovascular system to
  provide the increase in
  delivery of oxygen needed
  by the respiratory muscles during weaning
• (forward failure)
• Appropriate therapy (diuretics / vasodilators
  / inotropes)
• Wean the inotropes only after successful
  weaning from mechanical ventilatory support.
• Haemoglobin must also be optimized
• gt 8g
• gt 10g with myocardial ischemia / cerebral
  ischemia

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FAILURE TO WEAN OFF VENTILATOR CAUSES - 2

• Neurological
• -brain stem dysfunction due to trauma, hypoxia
  or infection, critical illness polyneuropathy
• -intermediate syndrome due to organophosphorus
  insecticides
• Fluid Balance
• Positive cumulative fluid balance is associated
  with failure to wean and a negative fluid
  balance was predictive of a successful weaning
  in a recent study.
• Infection
• any sepsis and/or respiratory infection should
  have resolved

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FAILURE TO WEAN OFF VENTILATOR CAUSES - 3

• Drugs
• - stop sedatives and drugs likely to impair
  neuromuscular function.
• - give antidotes ( flumazenil, nalorphine,
  neostigmine) as indicated
• Electrolytes - maintain normal serum potassium
  and phosphorous
• Alkalosis
• - respiratory dont chase the PaCO2
• - metabolic reduce base excess
  (?acetazolamide)
• PaO2
• Endocrine - hypothyroidism

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Post Extubation Stridor

• The Cuff leak test
• The ventilator is used in Assist Control mode
  with a tidal volume of 10-12ml/kg. The expired
  tidal volume is measured with the cuff inflated.
  The cuff is then deflated and after elimination
  of artefacts due to cough, four to six
  consecutive breaths are used to compute the
  average value for the expiratory tidal volume.
  The difference in the tidal volumes with the cuff
  inflated and deflated is the leak. A value of
  130ml (12 of inspiratory tidal volume) gave a
  sensitivity of 85 and a specificity of 95 to
  identify patients with an increased risk of post
  extubation stridor.
• Cough / Leak test In spontaneously breathing
  patients
• the tracheal cuff is deflated and monitored for
  the first 30 seconds for cough. Only cough
  associated with respiratory gurgling (heard
  without a stethoscope and related to secretions)
  is taken into account.
• The tube is then obstructed with a finger while
  the patient continues to breath. The ability to
  breathe around the tube is assessed by the
  auscultation of a respiratory flow.

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THANK YOU