13. weaning
TRANSCRIPT
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WEANING FROM MECHANICAL VENTILATION
Dr MEGHA JAIN
University College of Medical Sciences & GTB
Hospital, Delhi
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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.
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Different stages in mech. Ventilated pts.
1. Treatment of ARF
2. Suspicion
3. Assessingreadiness to
wean
4. SBT
5. Extubation 6. Reintubation
Admit Discharge
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DEFINITIONS
Weaning is the gradual reduction in the level of ventilatory support.
Weaning success : effective spontaneous breathingwithout 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.
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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 nosocomialpneumonia
Precludes oral feeding
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The assessment of weaning proceeds in twophases:
Phase 1: To ensure that certain basic criteriaregarding initial reason for
mechanical ventilation are satisfied
Phase 2: Determine whether weaning is likelyto succeed on the basis of specifiedcriteria
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READINESS FOR VENTILATOR WEANING
Major determinants of ability to wean can be classifiedinto three categories:
oxygenation ventilatory pump function
neuropsychiatric status
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OXGYGENATION
Criteria of AdequacyPaO2 > 60 mmHg on FIO2 200
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 AdequacyPaCO2 < 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 productionwithout compensatory in alveolar Ve:
fever, hypermetabolism, carbohydrate overfeeding- dead space ventilationwithout 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 accidentSleep deprivation/ICU psychosisDrug therapyDepression
Psychological dependency on ventilatory support
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WEANING CRITERIA
Used to evaluate the readiness of a patient for weaningtrial.
Common weaning criteria :Ventilatory criteriaOxygenation criteriaPulmonary reservePulmonary measurementsOther factors
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VENTILATORY CRITERIA
PaCO2: < 50 mmhg with pH >/= 7.35. VC: > 10 to 15 ml/kg
Spontaneous VT: > 5 to 8 ml/kg Spontaneous RR: < 30/min Minute ventilation: < 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 > 60 mmhg @FiO2 upto 0.4 PaO2 with PEEP > 100 mmhg @ FiO2 upto 0.4
SaO2 > 90% @ FiO2 upto 0.4 Qs/Qt < 20% P(A-a)O2 < 350 mmhg PaO2/FiO2 > 200 mmhg
Qs/Qt estimate wasted pulmonary perfusionP(A-a)O2 is related to degree of hypoxemia/shunt
In pts with anemia or dysfunct Hb, PaO2 and SaO2 dont reflect true oxygenation statusSo arterial oxygen content should be measured
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PULMONARY RESERVE AND MEASUREMENTS
Pulmonary reserve:Max. voluntary ventilation 2min. vent@FiO2 upto 0.4
Max. Insp. Pressure < -20 to -30 cmH2O in 20 sec. Pulmonary measurements :
Static compliance > 30 ml/cm H2OVd/Vt < 60%
Pulmonary reserve requires active pt cooperationPulmonary 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 < 9/min.
CROP index: evaluates pulmonary gas exchange and balanceb/w respiratory demands and respiratory neuromuscular reserve.
= ( Cd MIP PaO2/PAO2)/f.Should be > 13 ml/breath/min.
RSBI:should be < 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 haveadequately abated and the pt. triggers 2 to 3 breaths/min aboveventilator 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 (> 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 < 72 hrs., hasgood spont RR, MV, MIP, f/Vt
SBT for 30 to 120 min.
EXTUBATEif no other limiting factor
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Spontaneous Breathing Trial
T-Tube trial:allows spont. breathing several times per dayinterspersed 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 ptsNo 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 adequatePaO2>/= 60mmhg on FiO2 7.35
Other indices : - f/VT < 105 - MIP < -20 cm H2O- f < 30 and > 6/min. - VC > 10 to 15 ml/kg
- TV > 5 ml/kg
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Weaning protocol for a SBT with a T-Tube
Prepare for T-Tube trial
3 min. screening trial
Measure TV,RR
Measure MIP thrice selecting the best
Adequate staff, equipment, no sedatives
Formal SBT of upto 2 hrs.
MIP < -20 cm H20TV spon. > 5 ml/kg
RR spon. < 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 > 30 to 35/min
SpO2 < 90% > 20% or in HR or HR > 120 to 140/min SBP > 180 or < 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 andclinical assessment.
Rate is generally adjusted in increments of 2 breaths/min.followed by pt assessment.
ADVANTAGESGradual transition
Easy to useMinimum MV guaranteed
Alarm system may be usedShould be used in comb. with PSV/CPAP
DISADVANTAGES
Pt. ventilator asynchronyProlonges weaningMay worsen fatigue
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Pressure Support Ventilation (PSV)
Patient determines RR, VE, inspiratory time a purely spontaneous mode Parameters
Triggered bypts own breath Limited by pressure Affects inspiration only
Uses Complement volume-cycled
modes (i.e., SIMV) Does not augment TV but
overcomes resistance createdby ventilator tubing PSV alone
Used alone for recoveringintubated 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 ventilatortubing, 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 twicedaily. 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
ADVANTAGESGradual transitionPrevents fatigue
Increased pt comfortWeans faster than SIMV alone
Every breath is supportedPt can control cycle length, rate
and inspiratory flow.Overcomes resistive WOB d/tET tube and circuit.
DISADVANTAGESLarge changes in MV can occur
ed MAP versus T-TubeTV not guaranteed
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Mandatory minute ventilation
Also called minimum minute ventilation, provides predeterminedminute ventilation when pts spon. breathing effort becomesinadequate.
Prevents hypoventilation and respi. acidosis in final stages of weaning.
Trigger is in mandatory RR when actual MV < 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
ADVANTAGESBackup ventilation ensured,Potential to speed weaning
compared with SIMV.
DISADVANTAGESMay 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) (L / r 4 ) flow WOB
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Static condition single P support level can eliminate ETTresistance
Dynamic condition variable flow e.g. tachypnoea & indiff phases of resp.
- P support needs to be continously alteredto eliminate dynamically changing WOB d/t ETT
1. Feed resistive coef of ETT2. Feed % compensation
desired3. Measures
instantaneous flow
Calculates P supportproportional to resistancethroughout respiratorycycle
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 patientswork duringspontaneous breaths
Automatically adjusts flow, volume and pressure neededeach breath
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WOB
Ventilator measures elastance & resistanceClinician 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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ventilation without artificialairway
-Nasal , face maskadv.1.Avoid intubation / c/c2.Preserve natural airwaydefences3.Comfort4.Speech/ swallowing +5.Less sedation needed6.Intermittent use
Disadv1.Cooperation
2.Mask discomfort3.Air leaks4.Facial ulcers, eye irritation, drynose5.Aerophagia
6.Limited P supporte.g. BiPAP, CPAP
Noninvasive
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Role of tracheostomy in weaning
Performed in ventilator dependent pts., timing iscontroversial.
Beneficial in: ed sedationrequirement, 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 spaceLess 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 anylength of weaning trial or is reintubated within 48 hrs followingextubation.
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 ( >50 mmhg)ing pH < 7.30 ing PaO2 (
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Indicators of weaning failure
Respiratory parameters: ing TV ( < 250 ml) ing RR ( > 30/min) ing f/TV ratio ( > 105 cycles/L) ing MIP ( 60%)
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Pathophysiology of weaning failure
NONRESPIRATORY PARAMETERS AFFECTING ABILITY TOWEAN
Nutritional statusFluid balanceMetabolic and acid-base derangementsCardiac FunctionRenal functionNeuropsychiatric 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 CO2Produced 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
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Sleep Deprivation and Psychological Issues
Twilight awareness -> nap during the day -> 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
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Ventilator induced diaphragmatic dysfunction
VIDD loss of diaphragmatic force generating capacity related touse 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.
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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( < 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 mthsof weaning attempts have failed.
Often transferred to regional weaning centers/long term carefacilities.
Goal is to restore pt to highest level of independent functionpossible.
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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 patencyCuff leak test
Qualitative Quantitativeaudible air leak< 110 mlair leak
Parameters for airway protectionEffective cough
Secretion volumeMental status
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Extubation failure
Defined as need for reinstitution of vent. Support within 24 72hrs. 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 indeath 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
1. Egans fundamentals of respiratory care 9th ed.2. International Anaesthesiology Clinics Update on respiratory
critical care , vol 37, no 3, 1999.3. Anaesthesia newsletter ,Indore city ,June 2009, vol 10, no 24. David W Chang, Clinical application of mechanical ventilation 2nd
ed5. Paul L Marino, The ICU Book, 3rd ed.6. Weaning from mech. Ventilation, Eur. Respi. J 2007; 29: 1033
1056.
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THANK YOU
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Ventilator management algorithimInitial intubation FiO2 = 50% PEEP = 5
RR = 12 15 VT = 8 10 ml/kg
S a O2 < 90% S a O2 > 90%
S a O2 > 90% Adjust RR to maintain PaCO 2 = 40 Reduce FiO 2 < 50% as tolerated Reduce PEEP < 8 as tolerated Assess criteria for SBT daily
S a O2 < 90% Increase FiO 2 (keep S aO2>90%) Increase PEEP to max 20 Identify possible acute lung injury Identify respiratory failure causes
Acute lung injury
No injury
Fail SBT
Acute lung injury Low T V (lung-protective) settings
Reduce T V to 6 ml/kg Increase RR up to 35 to keep
pH > 7.2, P aCO2 < 50 Adjust PEEP to keep FiO 2 < 60%
Sa O2 < 90% S a O2 > 90%
S a O2 < 90% Dx/Tx associated conditions
(PTX, hemothorax, hydrothorax) Consider adjunct measures
S a O2 > 90% Continue lung-protective
ventilation until: PaO2 /FiO 2 > 300
Persistently fail SBT Consider tracheostomy Resume daily SBTs with CPAP or
tracheostomy collar
Pass SBT
Airway stableExtubate
Intubated > 2 wks
Consider PSV wean (gradualreduction of pressure support)
Consider gradual increases in SBT
Prolonged ventilatordependence
Pass SBT
Pass SBT
Airway stable