Ghamartaj Khanbabaee,MD

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Weaning from Mechanical Ventilation

• Ghamartaj Khanbabaee,MD
• Pediatric Pulmonologist
• Mofid Childrens Hospital
• SBMU

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Definition of Weaning

• The transition process from
• total ventilatory support
• to spontaneous breathing.
• This period may take many forms ranging from
  abrupt withdrawal to gradual withdrawal from
  ventilatory support.

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Weaning and Extubation

• Mechanical ventilation is a life-saving
  intervention
• Risk of complications increases with duration
• Short periods of mechanical ventilation, weaning
  and extubation can often be accomplished 2and 4
  of the total duration of mechanical ventilation
• Longterm MV 60 to 70 of total duration

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Weaning

• Discontinuation of IPPV is achieved in most
  patients without difficulty
• Up to 20 of patients experience difficulty
• requires more gradual process so that they can
  progressively assume spontaneous respiration

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weaning

• Is the cause of respiratory failure gone or
  getting better ?
• Is the patient well oxygenated and ventilated ?
• Can the heart tolerate the increased work of
  breathing ?

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Extubation

• Extubation
• Control of airway reflexes
• Patent upper airway (air leak around tube?)
• Minimal oxygen requirement
• Minimal rate
• Minimize pressure support (0-10)
• Awake patient

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• Clinical criteria used to determine readiness for
  trials of spontaneous breathing
• Required criteria
• 1. The cause of the respiratory failure has
  improved
• 2. PaO2/FiO2150 or SpO290 percent on FiO2o.4
  percent and positive end-expiratory pressure
  (PEEP) 5 cmH2O
• 3. pH gt7.25
• 4. Hemodynamic stability (no or low dose
  vasopressor medications)
• 5. Able to initiate an inspiratory effort

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• Clinical criteria used to determine readiness for
  trials of spontaneous breathing
• Additional criteria (optional criteria)
• 1. Hemoglobin 8 to 10 mg/dL
• 2. Core temperature 38 to 38.5 degrees
  Centigrade
• 3. Mental status awake and alert or easily
  arousable
• A threshold of PaO2/FiO2120 can be used for
  patients with chronic hypoxemia. Some patients
  require higher levels of PEEP to avoid
  atelectasis during mechanical ventilation.

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• (1) The resolution of the etiology of
  respiratory failure and attainment of stable
  respiratory status (decreased FIO2 and PEEP
  level) absence of tachypnea with a respiratory
  rate lt60 for infants younger than 12 months, lt40
  for the preschool and school-aged child, and lt30
  for adolescents absence of acidosis pH lt7.35
  or hypercapnia PCO2 gt60 mm Hg the parameters
  to indirectly assess oxygenation and compliance
  include PaO2FIO2 ratio gt267 PaO2 gt80 mm Hg on
  an FIO2 of 0.3 and oxygen saturation SpO2 gt94
  on an FIO2 lt 0.5, PIP lt20 cm H2O, and PEEP lt 5 cm
  H2O) and adequate respiratory muscle function

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• (2) Hemodynamic stability, including no
  evidence of shock this criterion includes good
  perfusion
• (capillary refill lt3 seconds), age-appropriate
  blood pressure, and good cardiac function
• (3) Neurologic stability Pediatric Glasgow
  Coma Score gt 11
• (4) Metabolic factors serum potassium,
  magnesium, and phosphorus
• RCP blood gas analyses, pulse oximetry,
  end-tidal CO2 measurements, and airway function
  screenings

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• Adjuncts to Weaning
• Pharmacologic Agents corticosteroid
• Heliox Helium-oxygen (HeO2) mixture has a low
  density and a high kinematic viscosity, allowing
  for a reduction in airway resistance
• Epinephrin
• Noninvasive Mechanical Ventilatory Support

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Weaning

• The best approach for all patients is to question
  (perhaps several times) every day
• Why are they receiving mechanical ventilation?
• Do they require the current levels of support?
• Do they actually still need to be ventilated?

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Methods of Weaning

• 1- T tube trials
• - 30 minute T tube trial is sufficient
• -Attention to increased effort ( nasal
  flaring, accessory muscle recruitment,
  suprasternal and intercostal retraction, or
  paradoxic motion of the rib cage and abdomen).
• - New wheezing or crackles
• - Dyspnea and changes of mental status,
  blood pressure, heart rate, or cardiac
  rhythm
• Failing a T tube trial is a significant stress on
  the respiratory muscles

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•  

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Methods of Weaning

• 2-Intermittent Mandatory Ventilation(IMV)
• Gradual reduction in the amount of support
• Progressive increase in the amount of
  respiratory work  
•  The IMV rate is reduced, usually in steps of one
  to three breaths per minute
•   An arterial blood gas is measured approximately
  30 minutes after the IMV rate was reduced
•  The IMV rate is further reduced as long as the
  pH remains above 7.30 or 7.35
• IMV may contribute to the development of
  respiratory muscle fatigue or prevent recovery
  from it, which could delay weaning

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Methods of Weaning

• 3-Pressure Support Ventilation (PSV)
•     PSV is an attractive weaning method
• Patient has control over the respiratory
  frequency and the depth, length, and flow of each
  breath
• PSV can compensate for the increased work
  imposed by the resistance of the endotracheal
  tube and the ventilator circuit
• Dyspnea is the same in PSV or IMV
• Resistance posed by an endotracheal tube varies
  as a result of diameter, flow rates, tube
  deformation, and adherent secretions, which makes
  it difficult to determine the level of PSV that
  overcomes the resistance of the endotracheal tube
  and ventilator circuit without assisting
  ventilation
• The gradual withdrawal of PSV is a poor predictor
  of a patient's ability to sustain ventilation
  after extubation (asynchrony in COPD)

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Methods of Weaning

•  4-Noninvasive ventilation 
• Noninvasive positive pressure ventilation (NPPV)
  has been investigated as weaning method for
  patients with COPD and acute hypercapnic
  respiratory failure
• NIPPV was well tolerated
• Nasal abrasions and gastric distension.
• Exclusion postoperative, altered
  neurologic status, hemodynamic instability,
  severe concomitant diseases

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• Recognition of Weaning Failure
• 1-Increased respiratory load increased elastic
  load (unresolved lung disease, secondary
  pneumonia,abdominal distension, and hyperinflated
  lungs), increased resistive load (thickened
  airway secretions, partially occluded
  endotracheal tube, and upper airway obstruction),
  or increased minute ventilation (pain and
  irritability, sepsis /hyperthermia, and metabolic
  acidosis)
• 2- Decreased respiratory capacity is
  represented by decreased respiratory drive
  (sedation, CNS infection, traumatic brain injury,
  and hypocapnia/alkalosis), muscular dysfunction
  (muscular catabolism and weakness ,malnutrition,
  and severe electrolyte disturbances), and
  neuromuscular disorder (diaphragmatic
  dysfunction, prolonged neuromuscular blockade,
  and cervical spinal injury)

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Weaning

• A trial of spontaneous breathing with assessment
  of the gas exchange and pattern of breathing with
  minimal pressure support(10 cm H2O) or T-tube
  without pressure support appears to be equally
  useful approaches in order to evaluate readiness
  for extubation
• Levels of PaO2 lt60 mm Hg, where FiO2 gt0.4
  constitutes
• a relative contraindication to extubation
• Increased respiratory rate or reduction in tidal
  volume(or particularly a combination of both)
  during spontaneous breathing strongly suggests
  that the patient is not ready for extubation.

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• Difficult to wean
• chronic pulmonary disease, neurologic disease,
  malnutrition
• Causes of extubation failure
• upper airway obstruction
• poor airway protection
• excess secretions
• pulmonary atelectasis
• young age (i.e., lt3 years),
• duration of ventilation, severity of underline
  lung disease
• oxygenation impairment (i.e., oxygenation index
  gt5)
• intravenous sedation.

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Extubation

• Prerequisites to extubation include
  1) A good cough/gag (to allow the child to
  protect their airway). 2) NPO about 4
  hours prior to extubation (in case the trial of
  extubation fails and reintubation is required).
  3) Minimize sedation. 4)
  Adequate oxygenation on 40 FiO2 with CPAP (or
  PEEP) 4. 5) The availability of
  someone who can reintubate the patient, if
  necessary. 6) Equipment available to
  reintubate the patient, if necessary.

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• Extubation failure
• decreasing tidal volume indexed to body weight
  of a spontaneous breath
• increasing FiO2
• increasing MAP
• increasing oxygenation index
• increasing fraction of total minute ventilation
  provided by the ventilator
• increasing peak ventilatory inspiratory
  pressure
• decreasing mean inspiratory flow

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Weaning Protocol

• Is patient is a candidate for weaning?
• PaO2 gt 60mmHg
• FiO2 lt0.5
• PEEP lt 8 cm H2O
• Screen for readinessRSB Trial
• SBT for one minute to calculate RSBI
• Ensure intact airway reflexes
• Coughing during suctioning
• Patient can now be subject to SBTs
• PS, CPAP, or T-piece
• Up to 120 minutes
• SBT can be terminated if patient
• Successfully tolerates the SBT from 30-120
  minutes
• Shows s/sx of failure

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RSBI

• First described by Yang and Tobin in 1991
• Rapid Shallow Breathing Index (RSBI) is the ratio
  of respiratory frequency to tidal volume (f/VT)
• A patient who has a RR of 25 breaths/min and
  a VT of 250 mL/breath has an RSBI of (25
  breaths/min)/(.25 L) 100 breaths/min/L.
• Patients who cannot tolerate independent
  breathing tend to breathe rapidly (high
  frequency) and shallowly (low tidal volume), they
  generally have a high RSBI.
• RSBI, the respiratory frequency (f) and tidal
  volume (VT) were measured using a hand-held
  spirometer attached to the endotracheal tube
  while a patient breathed room air for one minute
  without any ventilator assistance
• Causes of increased RSBI
• narrow endotracheal tube, female gender,
  sepsis, fever, supine position, anxiety,
  suctioning, and chronic restrictive lung disease.

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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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Dependence/Failure to Wean

• Additional Features
• Cardiovascular Function
• Ischemia
• Heart Failure
• Metabolic Derangements
• Hypophosphatemia
• Hypocalcemia
• Hypomagnesemia
• Hypothyroidism (severe)
• Nutrition
• Poorprotein catabolism
• Overfeedingexcess CO2
• Deconditioning

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Predictions of the outcome of weaning

• Variables used to predict weaning success Gas
  exchange
• PaO2 of gt 60 mmHg with FiO2 of lt 0.35
• A-a PaO2 gradient of lt 350 mmHg
• PaO2/FiO2 ratio of gt 200

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Initiate Weaning

• When there is
• Adequate Oxygenation
• PaO2/FiO2 gt150-200
• Vent Settings PEEP lt8 and FiO2 lt0.5
• pH gt7.25
• Hemodynamic stablility
• Ability to Initiate an Inspiratory Effort
• Sedation (esp. with resp-depressing drugs) has
  itself been weaned

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THANK YOU
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Conclusion