WEANING FROM MECHANICAL VENTILATION

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WEANING FROM MECHANICAL VENTILATION

• Dr MEGHA JAIN

University College of Medical Sciences GTB
Hospital, Delhi
2
HEADINGS

• Purpose of weaning and extubation.
• Rationale of predictive indices in weaning.
• Application of weaning parameters.
• Methods of weaning.
• Impediments to weaning.
• Extubation and terminal weaning.

3
Different stages in mech. Ventilated pts.
1. Treatment of ARF
3. Assessing readiness to wean
5. Extubation
6. Reintubation
2. Suspicion
4. SBT
Admit
Discharge
4
DEFINITIONS

• Weaning is the gradual reduction in the level of
  ventilatory support.
• Weaning success effective spontaneous breathing
  without any mechanical assisstance for 24 hrs or
  more.
• Weaning failure when pt is returned to
  mechanical ventilation after any length of
  weaning trial.
• Signs of weaning failure abnormal blood gases,
  diaphoresis, tachycardia, tachypnea, arrythmias,
  hypotension.

5
Morbidity Associated With Prolonged Intubation
and Mechanical Ventilation

• Vocal cord granulomas
• Ulceration of the true vocal cords
• Circumferential fibrous stenosis of trachea
• Epithelial damage, loss of cilia, and impairment
  of tracheal mucus clearance
• Risk factor for nosocomial pneumonia
• Precludes oral feeding

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The assessment of weaning proceeds in two phases

• Phase 1 To ensure that certain basic criteria
• regarding initial reason for
• mechanical ventilation are satisfied
• Phase 2 Determine whether weaning is likely
• to succeed on the basis of specified
• criteria

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READINESS FOR VENTILATOR WEANING

• Major determinants of ability to wean can be
  classified into three categories
• oxygenation
• ventilatory pump function
• neuropsychiatric status

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OXGYGENATION

• Criteria of Adequacy
• PaO2 gt 60 mmHg on FIO2 lt0.4 at minimal PEEP,
• PaO2/FIO2gt200
• Selected causes of failure
• Hypoventilation neurologic injury or drugs
• V/Q mismatch severe CHF
• Anatomic (R-to-L) shunt (e.g. intracardiac,
  pulmonary
• A-V malformation).

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VENTILATION

• Criterion of Adequacy
• PaCO2 lt 50 mmHg or within 8 mmHg of baseline
• Selected causes of failure
• respiratory drive sedation, drug overdose.
• resp bellows function diaph weakness, N-m
  disease
• CO2 production without compensatory ? in alveolar
  Ve
• fever, hypermetabolism, carbohydrate overfeeding
• - dead space ventilation without compensatory ?
  alveolar Ve
• PE, bullous emphysema

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NEUROPSYCHIATRIC INTEGRITY

• Criteria of adequacy
• Awake, alert, cooperative, with intact gag
  and swallowing
• Selected causes of failure
• Cerebrovascular accident
• Sleep deprivation/ICU psychosis
• Drug therapy
• Depression
• Psychological dependency on ventilatory
  support

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WEANING CRITERIA

• Used to evaluate the readiness of a patient for
  weaning trial.
• Common weaning criteria Ventilatory
  criteria Oxygenation criteria Pulmonary
  reserve Pulmonary measurements Other
  factors

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VENTILATORY CRITERIA

• PaCO2 lt 50 mmhg with pH gt/
  7.35.
• VC gt 10 to 15 ml/kg
• Spontaneous VT gt 5 to 8 ml/kg
• Spontaneous RR lt 30/min
• Minute ventilation lt 10 lts

PaCO2 most reliable indicator VC and spon VT
indicate mechanical cond of lungs A high spon RR
and MV indicate ? WOB
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OXYGENATION CRITERIA

• PaO2 without PEEP gt 60 mmhg _at_FiO2 upto 0.4
• PaO2 with PEEP gt 100 mmhg _at_ FiO2 upto
  0.4
• SaO2 gt 90 _at_ FiO2 upto
  0.4
• Qs/Qt lt 20
• P(A-a)O2 lt 350 mmhg
• PaO2/FiO2 gt 200 mmhg

Qs/Qt estimate wasted pulmonary
perfusion P(A-a)O2 is related to degree of
hypoxemia/shunt In pts with anemia or dysfunct
Hb, PaO2 and SaO2 dont reflect true oxygenation
status So arterial oxygen content should be
measured
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PULMONARY RESERVE AND MEASUREMENTS

• Pulmonary reserve
• Max. voluntary ventilation 2min.
  vent_at_FiO2 upto 0.4
• Max. Insp. Pressure lt -20
  to -30 cmH2O in 20 sec.
• Pulmonary measurements
• Static compliance gt 30
  ml/cm H2O
• Vd/Vt
  lt 60

Pulmonary reserve requires active pt
cooperation Pulmonary measurements indicate
workload needed to support spont. ventilation
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COMBINED WEANING INDICES

• Simplified weaning index evaluates efficiency of
  gas exchange. ( fmv (PIP PEEP)/MIP)
  PaCO2/40. should be lt 9/min.
• CROP index evaluates pulmonary gas exchange and
  balance b/w respiratory demands and respiratory
  neuromuscular reserve. ( Cd MIP
  PaO2/PAO2)/f. Should be gt 13 ml/breath/min.
• RSBI should be lt 105 cycles/min/lt.
  f/Vt. Most accurate test to predict
  weaning success.

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RSBI

• First described by Yang and Tobin in 1991.
• Its a one min. trial of unassisted breathing
  measured during the T piece trial.
• Main defect excessive false ves
• Should not be measured until sedative and
  narcotic effects have adequately abated and the
  pt. triggers 2 to 3 breaths/min above ventilator
  set rate.
• Measure RR and MV for 1 min. during unassisted
  breathing( 0 PEEP/5 cmH2O PSV).
• At end of 1 min. divide MV by RR to calculate
  avg. tidal vol.
• Divide RR by TV to obtain RSBI.

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OTHER FACTORS

• Metabolic factors Inadequate nutrition
  protein catabolism Overfeeding - ? CO2
  production Phosphate, ? Magnesium deficiency
  - ?respi pump functn Impaired O2 delivery -
  ?respi pump functn.
• Renal function Patient should have adeq
  renal output (gt 1000 ml/day) Monitor
  electolytes to ensure adequate respi msl functn
• Cardiovascular function Ensures sufficient
  O2 delivery to tissues Cardiac rate, rhythm,
  BP, CO and CI should be optimal with
  minimal pressure support
• CNS assessment Assess for LOC, anxiety,
  dyspnea, motivation CNS should be intact for
  protection of airway.

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Weaning methods

• Spontaneous breathing trial
• SIMV with pressure support.
• PSV
• Rapid ventilator discontinuation pt.on vent for
  lt 72 hrs., has good spont RR, MV, MIP, f/Vt
  SBT for 30 to 120
  min. EXTUBATE if no other limiting
  factor

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Spontaneous Breathing Trial

• T-Tube trial allows spont. breathing several
  times per day interspersed with periods of
  ventilatory support.
• Initial SBTs may last only 5 to 30 min.
• Resume mechanical ventilation at night or if
  distress occurs.

ADVANTAGES Tests pts spon breathing
ability Allows periods of work and rest Weans
faster than SIMV
DISADVANTAGES Abrupt transition difficult for sm
pts No alarms, unless attached to vent. Requires
careful observn.
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Weaning protocol for a SBT with a T-Tube
Verify that pt is a candidate for vent.
discontinuation
Primary cause reversed
Pt is afebrile, awake, alert and free of seizures
HD stable with adeq. Hb, S.E.
Oxygenation and ventilation adequate PaO2gt/
60mmhg on FiO2 lt/ 0.4 with PEEP/CPAP lt/ 5 to 8
cmH2O PaO2/FiO2 gt 150 to 200 mmhg PaCO2 lt 50 pH
gt 7.35
Other indices - f/VT lt 105
- MIP lt -20 cm H2O -
f lt 30 and gt 6/min. - VC gt 10 to 15
ml/kg - TV gt 5 ml/kg

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Weaning protocol for a SBT with a T-Tube
Prepare for T-Tube trial
Adequate staff, equipment, no sedatives
3 min. screening trial
Measure TV,RR Measure MIP thrice selecting the
best
Formal SBT of upto 2 hrs.
MIP lt -20 cm H20 TV spon. gt 5 ml/kg RR spon. lt
35/min.
Continue trial for 30 120 min.
Extubate if no signs of intolerance
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Signs of intolerance of SBT

• Agitation, anxiety, diaphoresis or change in
  mental status
• RR gt 30 to 35/min
• SpO2 lt 90
• gt 20 ? or ? in HR or HR gt 120 to 140/min
• SBP gt 180 or lt 90 mmhg.
• Such pts are returned to full ventilatory
  support for 24 hrs. to allow the ventilatory
  msls. to recover.

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Weaning with SIMV

• Involves gradual reduction in machine rate based
  on ABG and clinical assessment.
• Rate is generally adjusted in increments of 2
  breaths/min. followed by pt assessment.

ADVANTAGES Gradual transition Easy to use Minimum
MV guaranteed Alarm system may be used Should be
used in comb. with PSV/CPAP
DISADVANTAGES Pt. ventilator asynchrony Prolonge
s weaning May worsen fatigue
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Pressure Support Ventilation (PSV)
Patient determines RR, VE, inspiratory time a
purely spontaneous mode

• Parameters
• Triggered by pts own breath
• Limited by pressure
• Affects inspiration only
• Uses
• Complement volume-cycled modes (i.e., SIMV)
• Does not augment TV but overcomes resistance
  created by ventilator tubing
• PSV alone
• Used alone for recovering intubated pts who are
  not quite ready for extubation
• Augments inflation volumes.

PSV is most often used together with other
volume-cycled modes. PSV provides sufficient
pressure to overcome the resistance of the
ventilator tubing, and acts during inspiration
only.
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Pressure support ventilation

• Begin with PSV that achieves a RR of 20 to 25/min
  or less.
• Adjust pressure to achieve a TV of 8 to 10 ml/kg.
• Reduce PSV 2 to 4 cm H2O as tolerated, ideally at
  least twice daily.
• Consider extubation when pt. tolerates PSV of 5
  to 8 cm H2O for 2 hrs with no apparent distress.

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Pressure support ventilation
ADVANTAGES Gradual transition Prevents
fatigue Increased pt comfort Weans faster than
SIMV alone Every breath is supported Pt can
control cycle length, rate and inspiratory
flow. Overcomes resistive WOB d/t ET tube and
circuit.
DISADVANTAGES Large changes in MV can occur ?ed
MAP versus T-Tube TV not guaranteed
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Mandatory minute ventilation

• Also called minimum minute ventilation, provides
  predetermined minute ventilation when pts spon.
  breathing effort becomes inadequate.
• Prevents hypoventilation and respi. acidosis in
  final stages of weaning.
• Trigger is ? in mandatory RR when actual MV lt
  preset MV.
• All mandatory breaths are volume cycled.
• Desired min. minute vol. is preset on the vent.
  Slightly lesser than that required to normalize
  PaCO2.
• If distress pt tends to ? RR at expense of ? TV
  , leads to significant dead space ventilation

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Mandatory minute ventilation
ADVANTAGES Backup ventilation ensured, Potential
to speed weaning compared with SIMV.
DISADVANTAGES May not ensure efficient pattern
of breathing, Rapid shallow breathing possible
with MMV.
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Automatic Tube Compensation

• Compensates for the resistance of ETT
• Facilitates electronic weaning i.e pt during
  ATC mimic their breathing pattern as if extubated
  ( provided upper airway contorl provided)
• OPERATION
• As the flow ? / ETT dia ?, the P support needs to
  be ?to ?WOB

?P (P support) a (L / r4 ) a flow a WOB
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• Static condition single P support level can
  eliminate ETT resistance
• Dynamic condition variable flow e.g. tachypnoea
  in diff phases of resp.
• - P support needs
  to be continously altered
  to eliminate dynamically changing WOB d/t ETT

• Feed resistive coef of ETT
• Feed compensation desired
• Measures
• instantaneous flow

Calculates P support proportional to
resistance throughout respiratory cycle
Limitation resistive coef changes in vivo (
kinks, temp molding, secretions) Under/
overcompensation may result.
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Proportional Assist Ventilation

• Targets fixed portion of patients work during
  spontaneous breaths
• Automatically adjusts flow, volume and pressure
  needed each breath

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• WOB
• Ventilator measures elastance resistance
• Clinician sets -Vol. assist reduces work of
  elastance
• Flow assist reduces
  work of resistance's
• Increased patient effort (WOB) causes increased
  applied pressure (and flow volume)

ELASTANCE (TV)
RESISTANCE (Flow)
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• Limitations
• 1. Elastance (E) resistance (R) cannot be
  measured accurately.
• 2. E R vary frequently esp in ICU patients.
• 3. Curves to measure E ( PV curve) R(P-F curve
  ) are not linear as assumed by ventilator.

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Noninvasive

• ventilation without artificial airway
• Nasal , face mask
• adv.
• Avoid intubation / c/c
• Preserve natural airway defences
• Comfort
• Speech/ swallowing
• Less sedation needed
• Intermittent use
• Disadv
• Cooperation
• Mask discomfort
• Air leaks
• Facial ulcers, eye irritation, dry nose
• Aerophagia

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Role of tracheostomy in weaning

• Performed in ventilator dependent pts., timing is
  controversial.
• Beneficial in ?ed sedation requirement,
  articulated speech, allowed orally, enhanced
  mobility.

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Role of tracheostomy in weaning

• Early tracheostomy ( in 2 days of admission )
  reduces mortality, risk of pneumonia, accidental
  extubation, ICU length of stay.

Reduces dead space Less airway resistance ?ed
WOB Better suctioning Improved pt comfort
Facilitates weaning
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Complications

• Misplacement
• Hemorrhage
• Obstruction
• Displacement
• Impairment of swallowing reflexes
• Late tracheal stenosis.

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Weaning failure

• Defined as when pt is returned to mech.
  Ventilation after any length of weaning trial or
  is reintubated within 48 hrs following
  extubation.
• Causes 1. ?ed air flow resistance- ET
  tube, abdominal distention, tracheal
  obstruction. 2. ?ed compliance-
  atelectasis, ARDS, tension pneumothorax,
  obesity, retained secretions, bronchospasm,
  kinking of ETtube. 3. Electrolyte imbalance,
  inadequate nutrition.

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Indicators of weaning failure

• Blood gases- ?ing PaCO2 ( gt50 mmhg) ?ing
  pH lt 7.30 ?ing PaO2 (lt60 mmhg)
  ?ing SpO2 (lt90) ?ing PaO2/FiO2
  (lt150 mmhg)
• Vital signs- ?ing HR ( by gt 20/min. or gt
  110/min.) abnormal ECG changing BP ( 20
  mmhg SBP or 10 mmhg DBP)

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Indicators of weaning failure

• Respiratory parameters ?ing TV ( lt 250 ml)
  ?ing RR ( gt 30/min) ?ing f/TV
  ratio ( gt 105 cycles/L) ?ing MIP ( lt
  -20 cm H2O) ?ing static compliance ( lt 30
  ml/cm H2O) ?ing VD/VT ( gt 60)

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Pathophysiology of weaning failure

• NONRESPIRATORY PARAMETERS AFFECTING ABILITY TO
  WEAN

Nutritional status Fluid balance Metabolic and
acid-base derangements Cardiac Function Renal
function Neuropsychiatric factors
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Nutritional status

• Malnutrition has adverse effects on the
  respiratory system
• ?respiratory muscle strength and function
• ?diaphragmatic mass and contractility
• ?endurance

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Nutritional status

• Overnutrition may impede weaning
• High CO2
• Produced by excessive CHO loading
• Other causes of increased CO2 production fever,
  sepsis, shivering, seizures, and inefficient
  ventilation due to ? dead space, PE

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Metabolic abnormalities

• Hypophosphatemia
• Hypocalcemia
• Hypothyroidism

45
Sleep Deprivation and Psychological Issues

• Twilight awareness -gt nap during the day -gt
  shift day-night cycle
• Give sedative-hypnotic at bedtime to restore
  normal daily cycle
• Depression in the long-term ICU patient
• TCA at bedtime for sedative effect and to
  forestall depression.
• Anxiety
• Adequate sedation only to minimize detrimental
  WOB
• Very slow changes in PS level to prevent
  anxiety induced by sudden changes to the response
  of the lung stretch receptors

46
Ventilator induced diaphragmatic dysfunction

• VIDD loss of diaphragmatic force generating
  capacity related to use of mech. Ventilation
  can ocurr as early as 12 hrs. and reduction
  in max force production is of the order of 30
  50 after 1 3 days of CMV.
• Causes of VIDD msl. atrophy, oxidative stress,
  structural injury, msl fiber remodelling.
• Management - Minimise use of NM blockers,
  steroids Optimize PO4, Mg, nutrition.
  Cervical magnetic stimulation of phrenic
  nerve Antioxidant supplementation.

47
Critical care illness neuromyopathy

• Causes sepsis, malnutrition, paralysing agents,
  sedatives, narcotics, steroids.
• Affects all msls. Including diaphragm and
  intercostals.
• B/L proximal msl weakness.
• Diagnosis using Medical Research Council Score( lt
  48), electrophysiological testing and msl biopsy
  if appropriate.
• Transdiaphragmatic pressure in response to B/L
  phrenic nerve stimulation.
• Treatment options Good nutrition
  Withdrawal of offending drugs
  Inspiratory msl exercises

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Prolonged mechanical ventilation

• Required in 3 to 7 of ventilated pts.
• Unless cause is irreversible ( high spinal cord
  injury) pt should not be considered permanently
  ventilator dependent until 3 mths of weaning
  attempts have failed.
• Often transferred to regional weaning
  centers/long term care facilities.
• Goal is to restore pt to highest level of
  independent function possible.

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Complications of PMV

• Infection
• Bacterial Pneumonia
• Line sepsis
• Volume Overload
• Laryngeal Edema
• Pneumothorax
• Tracheal Bleeding
• Ileus
• DVT
• Additional Complications if Tracheostomy is
  necessary

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Extubation

• Discontinuation of invasive PPV involves 2 steps
  separation of pt. from vent. based on
  assessment of removal of artificial airway.
  airway patency protection

Parameters for airway patency Cuff leak
test Qualitative Quantitative audible
air leaklt 110 ml air leak

Parameters for airway protection Effective
cough Secretion volume Mental status
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Extubation failure

• Defined as need for reinstitution of vent.
  Support within 24 72 hrs. of ETT removal.
• Occurs in 2 25 of pts.
• Predisposing factors advanced age
  duration of mech. Vent. anemia use
  of cont. IV sedation semirecumbent
  positioning after extubation.
• Find manage the cause.

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Terminal weaning

• Defined as withdrawal of mechanical ventilation
  that results in death of the pt.
• 3 concerns must be evaluated and discussed
  pts informed consent medical futility
  reduction of pain and suffering
• Carries many ethical and legal implications.

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References

• Egans fundamentals of respiratory care 9th ed.
• International Anaesthesiology Clinics Update on
  respiratory critical care , vol 37, no 3, 1999.
• Anaesthesia newsletter ,Indore city ,June 2009,
  vol 10, no 2
• David W Chang, Clinical application of mechanical
  ventilation 2nd ed
• Paul L Marino, The ICU Book, 3rd ed.
• Weaning from mech. Ventilation, Eur. Respi. J
  2007 29 1033 1056.

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THANK YOU
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Ventilator management algorithim

• Initial intubation
• FiO2 50
• PEEP 5

• RR 12 15
• VT 8 10 ml/kg

SaO2 lt 90
SaO2 gt 90

• SaO2 gt 90
• Adjust RR to maintain PaCO2 40
• Reduce FiO2 lt 50 as tolerated
• Reduce PEEP lt 8 as tolerated
• Assess criteria for SBT daily

• SaO2 lt 90
• Increase FiO2 (keep SaO2gt90)
• Increase PEEP to max 20
• Identify possible acute lung injury
• Identify respiratory failure causes

No injury
Pass SBT
Extubate
Airway stable
Acute lung injury
Fail SBT
Airway stable

• Persistently fail SBT
• Consider tracheostomy
• Resume daily SBTs with CPAP or tracheostomy collar

• Acute lung injury
• Low TV (lung-protective) settings
• Reduce TV to 6 ml/kg
• Increase RR up to 35 to keep pH gt 7.2, PaCO2 lt 50
• Adjust PEEP to keep FiO2 lt 60

Pass SBT
Intubated gt 2 wks
SaO2 lt 90
SaO2 gt 90
Prolonged ventilator dependence

• SaO2 lt 90
• Dx/Tx associated conditions (PTX, hemothorax,
  hydrothorax)
• Consider adjunct measures (prone positioning,
  HFOV, IRV)

• SaO2 gt 90
• Continue lung-protective ventilation until
• PaO2/FiO2 gt 300
• Criteria met for SBT

• Consider PSV wean (gradual reduction of pressure
  support)
• Consider gradual increases in SBT duration until
  endurance improves

Pass SBT