Patient-Ventilator Synchrony & Successful Weaning Shao-Hsuan Hsia, MD Pediatric Critical Care and...

Patient-Ventilator Patient-Ventilator Synchrony & Successful Synchrony & Successful WeaningWeaning

Shao-Hsuan Hsia, MD

Pediatric Critical Care and Emergency Medicine

Chang Gung Children’s Hospital

What is your interpretation?

Does these two patients “synchronize” ventilator?

Can we “wean” these patients smoothly?

Definition of “Weaning”Definition of “Weaning”

The decrease of ventilatory support in preparation for imminent extubation

Weaning should be initiated as soon as a patient is intubated

It is necessary to gradually wean the patient from mechanical ventilation implemented because of respiratory failure, to retrain their respiratory muscles

Liberation from mechanical ventilation:– many patients who have been traditionally weaned over

the course of days can be rapidly extubated without complication

The Goal of WeaningThe Goal of Weaning

Minimize the duration of ventilation for every patient

Prolonged mechanical ventilation is associated with prolonged ICU stay, prolonged hospital stay, higher costs, higher risk of nosocomial pneumonia, progressive ventilator-induced lung injury, airway injury, excessive pharmacologic sedation, and possibly higher mortality

The optimal weaning process can be a clinically difficult balance between minimizing the duration of mechanical ventilation and decreasing the risk of reintubation.

WEANING AND EXTUBATIONWEANING AND EXTUBATION

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Weaning Weaning Weaning Extubation

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Ventilator support

Spontaneous breathing

Weaning PhaseWeaning Phase

Weaning PhaseWeaning Phase

Facilitate spontaneous breathingFacilitate spontaneous breathing

Promote PPromote PTT-Vent synchrony-Vent synchrony

Appropriate WOB for the patientAppropriate WOB for the patient

Patient-Ventilator SynchronyPatient-Ventilator SynchronyEvaluate Inspiratory & Expiratory Synchrony

Inspiratory SynchronyInspiratory Synchrony

Trigger SensitivityTrigger Sensitivity

ETT effect / leaksETT effect / leaks

Ventilator Response TimeVentilator Response Time

Flow Patterns – Fixed vs Flow Patterns – Fixed vs VariableVariable

Appropriate tidal volumeAppropriate tidal volume

Trigger SensitivityTrigger Sensitivity

Trigger Sensitivity Trigger Sensitivity = effort required to initiate = effort required to initiate a ventilator assisted breatha ventilator assisted breath

A determinate of effort required (WOB)A determinate of effort required (WOB) What effects trigger sensitivity ?What effects trigger sensitivity ? Pressure or Flow triggeringPressure or Flow triggering Proximal vs distal sensingProximal vs distal sensing ETT leaks / sizeETT leaks / size

Pressure TriggerPressure Trigger4

2

0

-2

Paw(cm H2O)

Time (secs)

0.25 0.50

Pressure Trigger

WOB

Flow TriggeringFlow Triggering Flow Triggering Flow Triggering = Change in flow due to P= Change in flow due to PTT effort initiates vent. Assisted breatheffort initiates vent. Assisted breath Advantages of Flow Triggering Advantages of Flow Triggering More sensisitive to small efforts (More sensisitive to small efforts (↓WOB↓WOB)) Disadvantages of Flow TriggeringDisadvantages of Flow Triggering Autocycling risk higherAutocycling risk higher IndicationsIndications Failure of a pressure trigger to initiate aFailure of a pressure trigger to initiate a ventilator assisted breathventilator assisted breath

PressurePressure vs Flow Trigger vs Flow Trigger4

2

0

-2

Paw(cm H2O)

Time (secs)

0.25 0.50

0.4 0.3 0.2 0.1 0-0.1-0.2

Flow(ml/sec)

Proximal vs Distal SensingProximal vs Distal Sensing Proximal sensing Proximal sensing = measured at ETT= measured at ETT Distal sensing Distal sensing = measured at exp. valve= measured at exp. valve Advantages of proximal sensingAdvantages of proximal sensing Faster response time & removes effects of Faster response time & removes effects of circuit and expiratory valve = ↓WOB circuit and expiratory valve = ↓WOB Disadvantages of proximal sensing Disadvantages of proximal sensing Requires a sensing device at ETTRequires a sensing device at ETT Can be effected by condensationCan be effected by condensation Indications for proximal sensingIndications for proximal sensing Neo / Peds to improve inspiratory synchronyNeo / Peds to improve inspiratory synchrony

Effects of ETT leaks on TriggeringEffects of ETT leaks on Triggering

Problem Problem ETT leak = ↓ airway pressureETT leak = ↓ airway pressure “ “Loss” of baseline PEEP Loss” of baseline PEEP Sensed as a PSensed as a PTT effort effort ResultResult Initiates a ventilator assistedInitiates a ventilator assisted breath in the absence of a PT effortbreath in the absence of a PT effort “ “ autocycling ”autocycling ”

Leak CompensationLeak Compensation

If baseline airway pressure ↓0.25cm HIf baseline airway pressure ↓0.25cm H22O O below set PEEP, flow added to maintain PEEPbelow set PEEP, flow added to maintain PEEP

Adjustments Q 8 msecAdjustments Q 8 msec Max flow addedMax flow added

Sens = 1 cm HSens = 1 cm H22O, flow = 0 – 5 LPMO, flow = 0 – 5 LPM

Sens = 2 – 5 cm HSens = 2 – 5 cm H22O, flow = 0 – 10 LPMO, flow = 0 – 10 LPM

Solution

Leak CompensationLeak Compensation Advantages Advantages Maintain set PEEP Maintain set PEEP ↓ ↓AutocyclingAutocycling Disadvantages Disadvantages May not allow triggering with weak or May not allow triggering with weak or marginal effort ( small prematures) marginal effort ( small prematures) IndicationsIndications PT with a significant leak where loss ofPT with a significant leak where loss of PEEP or “ autocycling” are presentPEEP or “ autocycling” are present

Effects of ETT on Vent WOBEffects of ETT on Vent WOB

Flow (L/min)

Work

(Joules/m

in)

6.5 ETT

6.0 ETT

5.5 ETT

4.5 ETT

4.0 ETT

Inspiratory SynchronyInspiratory Synchrony Trigger Sensitivity Trigger Sensitivity

ETT effects / leaksETT effects / leaks Ventilator Response TimeVentilator Response Time

Flow patterns – Fixed vs VariableFlow patterns – Fixed vs VariableAppropriate tidal volumeAppropriate tidal volume


Ventilator Response TimeVentilator Response Time Ventilator Response Time :Ventilator Response Time : Post trigger phase Post trigger phase Time between initiation of inspiratory effort Time between initiation of inspiratory effort and the onset of inspiratory flowand the onset of inspiratory flow Ventilator response time is dependent on Ventilator response time is dependent on manufactures algorithms + technologymanufactures algorithms + technology 25-50 msec range for neonatal / peds25-50 msec range for neonatal / peds Graphics are essential to determine problems Graphics are essential to determine problems with ventilator response time with ventilator response time

Ventilator Response TimeVentilator Response Time4

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Paw(cm H2O)

Time (secs)

0.25 0.50

Trigger Set at -0.1ml/sec or -1cm H20 Delayed

Response

0.4 0.3 0.2 0.1 0-0.1

Flow(ml/sec)

Inspiratory SynchronyInspiratory SynchronyTrigger Sensitivity Trigger Sensitivity

ETT effects / leaksETT effects / leaksVentilator Response TimeVentilator Response TimeFlow patterns – Fixed vs VariableFlow patterns – Fixed vs VariableAppropriate tidal volumeAppropriate tidal volume


Decelerating Square Sine Ascending

Flow

AirwayPressure

Time

Flow and Airway PressureFlow and Airway Pressure

Area =Mean Airway Pressure

Flow and Airway PressureFlow and Airway Pressure

Decelerating Square

Flow(l/sec)

AirwayPressure(cmH20)

MAP = Area Under Curve

PIP PIP

Gas Distribution

Fixed vs Variable FlowFixed vs Variable Flow Advantages of variable flow Advantages of variable flow Matches flow to spontaneous demand Matches flow to spontaneous demand Responsive to changes in lung mechanicsResponsive to changes in lung mechanics Disadvantages of variable flow Disadvantages of variable flow Not available for all breath types Not available for all breath types Usually not in volume limited modeUsually not in volume limited mode Indications for variable flow Indications for variable flow Most PMost PTSTS

1 40 1 / 9 7 , m t - i - p m , e 2 d l o n g e . p p t

E v i t a 2 d u r a

B I P A P a n d t h e S y n c h r o n i s a t i o n o f S p o n t a n e o u sB r e a t h i n g

P

t

E x p .T r i g g e r

I n s p .T r i g g e r

T r i g .W i n d ow

T r i g .W i n d ow

T h e s e t B I P A P p h a s e s y n c h r o n i s e s w i t hS p o n t a n e o u s B r e a t h

S m o o t h s y n c h r o n i s a t i o n o f t h e m a n d a t o r ys t r o k e s w i t h a p p r o p r i a t e t i m e w i n d o w

F l o w - t r i g g e r i n I n s p i r a t i o n a n d E x p i r a t i o n

Inspiratory SynchronyInspiratory SynchronyTrigger Sensitivity Trigger Sensitivity

ETT effects / leaksETT effects / leaksVentilator Response TimeVentilator Response TimeFlow patterns – Fixed vs VariableFlow patterns – Fixed vs VariableAppropriate tidal volumeAppropriate tidal volume


Pulmonary Injury SequencePulmonary Injury Sequence

There are two injury There are two injury zones during zones during mechanical ventilationmechanical ventilation– Low Lung Volume Low Lung Volume

Ventilation tears Ventilation tears adhesive surfacesadhesive surfaces

– High Lung Volume High Lung Volume Ventilation over-distends, Ventilation over-distends, resulting in “Volutrauma”resulting in “Volutrauma”

The difficulty is finding The difficulty is finding

the “Sweet Spotthe “Sweet Spot””Froese AB, Crit Care Med 1997; 25:906Froese AB, Crit Care Med 1997; 25:906

Determination of effective tidal volumeDetermination of effective tidal volume

Can you calculate the tidal volume “lost”due to the distensibility of the ventilatorcircuit and compensate for it?

calculated effective Vt = Vt at exp valve [circuit compliance ﹣ (PIP-PEEP)]

Tidal Volume DeterminationTidal Volume DeterminationCannon , AJRCCM , 2000.

Population: PICU pts<16yrs old(n=98) Ventilator circuit: -infant: n=70 ; 2.8± 2.3mos -pediatric: n=28 ; 7.3± 5.6 yrs Ventilator:SV300(Siemens) Pneumotach -placed between ETT & vent circuit -Ventrak or CO2SMP Plus Monitor (Novametrix Medical Systems)

Results: Infant CircuitResults: Infant Circuit

Vt(ml) pVt(ml) p

Exp valve Vt 70.4 Exp valve Vt 70.4 ±± 31.1 31.1

Calcuated Vt 59.2 Calcuated Vt 59.2 ±± 28.8 <0.0001 28.8 <0.0001

Pneumotach Vt 39.4 Pneumotach Vt 39.4 ±± 21.5 <0.0001 21.5 <0.0001

The Vt as measured at the ETT was onaverage only 56% of that measured at theexpiratory valve of the ventilator.

Circuit Compliance CalculationsCircuit Compliance Calculations

Calculating effective tidal volumesare not sufficient because ofmultiple uncontrolled variables:-in-line suction catheters-condensation-secretions-EtCO2 adapters-humidifiers / heaters-etc.

Vt(ml) pVt(ml) p

Exp valve Vt 185.4 Exp valve Vt 185.4 ±± 96.6 96.6

Calcuated Vt 167.8Calcuated Vt 167.8±± 94.6 0.16 94.6 0.16

Pneumotach Vt 135.3Pneumotach Vt 135.3±± 75.8 0.03 75.8 0.03

Results: Pediatric CircuitResults: Pediatric Circuit

The Vt as measured at the ETT was onaverage 73% of that measured at the exp.valve of the ventilator.

Optimal Inspiratory SynchronyOptimal Inspiratory Synchrony

Optimal inspiratory PT – ventilator synchronyOptimal inspiratory PT – ventilator synchrony is a function of :is a function of :

Trigger ( pressure / flow )Trigger ( pressure / flow )Trigger sensitivityTrigger sensitivityVentilator response timeVentilator response timeFlow patternFlow patternAppropriate tidal volumeAppropriate tidal volume

Expiratory SynchronyExpiratory Synchrony

End Expiratory Lung VolumeEnd Expiratory Lung Volume

Premature Termination of ExhalationPremature Termination of Exhalation

Intrinsic PEEPIntrinsic PEEP

Expiratory ResistanceExpiratory Resistance


End Expiratory Lung VolumeEnd Expiratory Lung Volume End expiratory lung volume ( EELV ) = volume End expiratory lung volume ( EELV ) = volume

of gas in lung prior to inspiratory ( FRC )of gas in lung prior to inspiratory ( FRC ) EELV is function of total PEEP and lung EELV is function of total PEEP and lung

compliance, Estimate by loops, CXRcompliance, Estimate by loops, CXR If EELV too lowIf EELV too low : : ↓ ↓ Lung compliance, ↓ VLung compliance, ↓ VTT or ↑PIP, ↑RR or ↑PIP, ↑RR IF EELV too highIF EELV too high : : Pulmonary overdistention developsPulmonary overdistention develops

Effects of EELV on Exp. SynchronyEffects of EELV on Exp. Synchrony

EELV too low : EELV too low :

↓ ↓ Lung compliance, ↓ VLung compliance, ↓ VTT or ↑PIP, ↑RR or ↑PIP, ↑RR

↑ ↑RR may cause premature termination of RR may cause premature termination of

exhalation and intrinsic PEEPexhalation and intrinsic PEEP ↑↑RR perceived as weaning failure RR perceived as weaning failure

Inappropriate vent strategies employedInappropriate vent strategies employed

Mechanical graphicsMechanical graphics

0 15 30 45

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250

Airway Pressure(cmH2O)

Volu

me(m

l)

Vt=145ml

PEEP

PIP=42

2Y ARDS

Low compliance

Dynamic compliance=Vt/(PIP-PEEP)=3.9

Ins

Exp





Expiratory Resistance (estimate loops,Expiratory Resistance (estimate loops,

scalars )scalars )


Premature Termination of ExhalationPremature Termination of Exhalation Failure of airway pressure, volume, and flow to Failure of airway pressure, volume, and flow to

return to baseline prior to the next mechanical breathreturn to baseline prior to the next mechanical breath “ “ Gas trapping “ causes intrinsic PEEPGas trapping “ causes intrinsic PEEP Intrinsic PEEP ( may be good, may be bad ) Intrinsic PEEP ( may be good, may be bad ) May ↑WOB, ↑mean intrathoracic pressure May ↑WOB, ↑mean intrathoracic pressure ↓ ↓C.O. C.O. ↓ ↓Trigger sensitivity Trigger sensitivity ↓ ↓VT in PL breaths, ↑PIP in VL breathsVT in PL breaths, ↑PIP in VL breaths Treatment strategies : Increase TTreatment strategies : Increase TEE

Gas-trapping or intrinsic PEEPGas-trapping or intrinsic PEEP

Time

inspiration exspiration

Flow (L/sec) 0

Pressure (cmH2O) 0

Incomplete exhalation (gas trapping)

Intrinsic PEEP=5, set PEEP=5, total=10

I:E=1:0.8

Reduction of Gas-trappingReduction of Gas-trapping

Time

inspiration exspiration

Flow (L/sec) 0

Pressure (cmH2O) 0

Exhalation complete

Intrinsic PEEP=0, set PEEP=5, total=5

I:E=1:1.5

Termination SensitivityTermination Sensitivity Premature termination of exhalation Premature termination of exhalation Inadequate I:E ratio, RR induced Inadequate I:E ratio, RR induced Inspiration is time cycle and responsive Inspiration is time cycle and responsive to change in flowto change in flow Goal : Shortest TGoal : Shortest TII to obtain desired V to obtain desired VTT Termination SensitivityTermination Sensitivity Terminates PL breath via flow versus timeTerminates PL breath via flow versus time Clinician select % of peak flow at whichClinician select % of peak flow at which inspiration terminates ( 0 - 25 % ) inspiration terminates ( 0 - 25 % )

Termination SensitivityTermination Sensitivity Advantages Advantages Matches the TMatches the TII with P with PTT pathophysiology pathophysiology Improves expiratory synchrony , ↑TImproves expiratory synchrony , ↑TEE

Disadvantages Disadvantages If termination sen. set too high, loss VIf termination sen. set too high, loss VTT If termination sen. Set too low, premature If termination sen. Set too low, premature termination of exhalation continuestermination of exhalation continues IndicationIndication Pt with short TPt with short TII ( flow = zero prior to end of T ( flow = zero prior to end of TII ) )

Termination sensitivity





Expiratory ResistanceExpiratory Resistance


Elevated Expiratory ResistanceElevated Expiratory Resistance

Prolonged expiratory phase cause “Gas Prolonged expiratory phase cause “Gas trapping”, ↑WOB, ↓Trigger sensitivity trapping”, ↑WOB, ↓Trigger sensitivity

Obstruction to exhalation caused by :Obstruction to exhalation caused by :

Airway obstruction : ETT occlusionAirway obstruction : ETT occlusion

Bronchospasm : Aerosol therapy Bronchospasm : Aerosol therapy

Expiratory valve performance : Expiratory valve performance :

Ventilator evaluationVentilator evaluation

Expiratory SynchronyExpiratory Synchrony Optimal expiratory synchrony results in Optimal expiratory synchrony results in

complete exhalation at the lowest expiratory complete exhalation at the lowest expiratory resistanceresistance

To achieve this : To achieve this : Optimize end expiratory lung volume Optimize end expiratory lung volume Eliminate premature termination of Eliminate premature termination of exhalation & intrinsic PEEP exhalation & intrinsic PEEP Minimize expiratory resistance Minimize expiratory resistance

Pressure SupportPressure Support Spontaneous BreathSpontaneous Breath

Pressure triggered, Flow cycled, pressure Pressure triggered, Flow cycled, pressure

limited, decelerating flow limited, decelerating flow

Time cycled ( VIP )Time cycled ( VIP ) Each “ sensed” PEach “ sensed” PTT effort supported with effort supported with

Pressure limited breathPressure limited breath ↓↓WOB ( ETT effects ) & WOB ( ETT effects ) & ↑↑VVTT of P of PTT breath breath

WOB During Pressure SupportWOB During Pressure Support

PS = 15 cmH2O

PS = 5-10 cmH2O

PS = 0 cmH2O

Volume

Pressure

Pressure SupportPressure Support Advantages Advantages Improves PImproves PTT/vent synchrony and ↓WOB /vent synchrony and ↓WOB since each Psince each PTT effort supported effort supported Disadvantages Disadvantages Inadequate triggering may limit useInadequate triggering may limit use ETT leaks may prolong inspiratory phase ETT leaks may prolong inspiratory phase IndicationIndication PPTT with active spontaneous breathing with active spontaneous breathing WeaningWeaning

SIMV with Pressure SupportSIMV with Pressure SupportFlow

Pressure

Volume control

Pressure support

Successful WeaningSuccessful Weaning Successful weaning involves : Successful weaning involves : Optimal POptimal PTT – Ventilator inspiratory & – Ventilator inspiratory & expiratory synchrony expiratory synchrony Appropriate WOBAppropriate WOB Inspiratory synchrony depends on proper Inspiratory synchrony depends on proper selection of trigger sensitivity, response time, selection of trigger sensitivity, response time, flow pattern and appropriate tidal volumeflow pattern and appropriate tidal volume Expiratory synchrony depends on selection of Expiratory synchrony depends on selection of the appropriate EELV, absence of intrinsic the appropriate EELV, absence of intrinsic PEEP & minimal expiratory resistance PEEP & minimal expiratory resistance

Extubation CriteriaExtubation Criteria CXR, Guide onlyCXR, Guide only Respiratory mechanics Respiratory mechanics CCDYNDYN, Raw, Spontaneous effort, Raw, Spontaneous effort Weight gain ( post – op )Weight gain ( post – op ) Pulmonary toilet ??Pulmonary toilet ?? HemodynamicsHemodynamics Level of consciousness / sedationLevel of consciousness / sedation Air – leak ( upper airway disease )Air – leak ( upper airway disease ) Predicting methodsPredicting methods: RR/Vt, CROP index, T-piece : RR/Vt, CROP index, T-piece

trial, negative inspiratory measurements, Vd/Vttrial, negative inspiratory measurements, Vd/Vt

Assess

Extubation Criteria: AdultsExtubation Criteria: AdultsSuccessful extubation predictors:

Respiratory frequency to tidal volume ratio .Yang , NEJM , 1991 .Tahvanainen , CCM , 1983 T-piece trials .Sahn , Chest , 1973 Negative insp effort measurements . Sahn , Chest , 1973CROP index (compliance , rate , oxygenation , pressure) .Yang , NEJM ,1991

Extubation Criteria: AdultsSuccessful extubation predictors:

Respiratory frequency to tidal volume ratio .Yang , NEJM , 1991 .Tahvanainen , CCM , 1983 T-piece trials .Sahn , Chest , 1973 Negative insp effort measurements . Sahn , Chest , 1973CROP index (compliance , rate , oxygenation , pressure) .Yang , NEJM ,1991

Extubation Criteria in Peds Extubation Criteria in Peds Khan , CCM ,1996

Successful extubation predictors:

Variable Low-risk value High risk valueVtspont 6.5cc/kg 3.5 cc/kgFiO2 0.30 >0.40Paw <5 cm H2O >8.5 cm H2OOI 1.4 4.5FrVe 20% 30%PIP 25 cm H2O 30 cm H2OCdyn 0.9 cc/kg/cm H2O <0.4 cc/kg/cm H2O

Vd/Vt: Clinical Prediction for ExtubationVd/Vt: Clinical Prediction for Extubation Hubble , CCM , 2000. Extubation determined by the clinical team using standard clinical assessment. Minimal vent settings for extubation: -FiO2 0.40 -PEEP 7cm H2O -PIP 30cm H2OPrior to extubation , Vd/Vt was calculated from a single breath CO2 waveform. (CO2SMO Plus Monitor , Novametrix Medical Systems)

End-tidal CO2End-tidal CO2

Area p=q

X=alveolar ventilation, Y=alveolar dead space, Z=airway dead space,

Y+Z

X+Y+Z Vd/Vt=

Results: Individual OutcomesResults: Individual Outcomes

Vd/VtVd/Vt SuccessfulSuccessful

ExtubationExtubation

FailedFailed

ExtubationExtubation

0.10-0.500.10-0.50 24/25(96%)24/25(96%) NIV(1)NIV(1)

0.51-0.640.51-0.64 6/9(67%)6/9(67%) NIV(3)NIV(3)

0.65-0.950.65-0.95 2/10(20%)2/10(20%) NIV(6),PPV(2NIV(6),PPV(2))

P<0.001

Patient-Ventilator Synchrony & Successful Weaning Shao-Hsuan Hsia, MD Pediatric Critical Care and...

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