Patient-Ventilator Synchrony & Successful Weaning 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” 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 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 EXTUBATION

Weaning Phase Weaning Phase Weaning Phase Facilitate spontaneous breathing Facilitate spontaneous breathing Promote P T -Vent synchrony Promote P T -Vent synchrony Appropriate WOB for the patient Appropriate WOB for the patient

Patient-Ventilator Synchrony Evaluate Inspiratory & Expiratory Synchrony Inspiratory Synchrony Inspiratory Synchrony Trigger Sensitivity ETT effect / leaks Ventilator Response Time Flow Patterns – Fixed vs Variable Appropriate tidal volume

Trigger Sensitivity Trigger Sensitivity = effort required to initiate a ventilator assisted breath Trigger Sensitivity = effort required to initiate a 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 triggering Pressure or Flow triggering Proximal vs distal sensing Proximal vs distal sensing ETT leaks / size ETT leaks / size

Pressure Trigger Paw (cm H2O) Time (secs) Pressure Trigger WOB

Flow Triggering Flow Triggering = Change in flow due to P T Flow Triggering = Change in flow due to P T effort initiates vent. Assisted breath effort initiates vent. Assisted breath Advantages of Flow Triggering Advantages of Flow Triggering More sensisitive to small efforts ( ↓WOB ) More sensisitive to small efforts ( ↓WOB ) Disadvantages of Flow Triggering Disadvantages of Flow Triggering Autocycling risk higher Autocycling risk higher Indications Indications Failure of a pressure trigger to initiate a Failure of a pressure trigger to initiate a ventilator assisted breath ventilator assisted breath

Pressure vs Flow Trigger Paw (cm H2O) Time (secs) Flow (ml/sec)

Proximal vs Distal Sensing Proximal sensing = measured at ETT Proximal sensing = measured at ETT Distal sensing = measured at exp. valve Distal sensing = measured at exp. valve Advantages of proximal sensing Advantages 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 ETT Requires a sensing device at ETT Can be effected by condensation Can be effected by condensation Indications for proximal sensing Indications for proximal sensing Neo / Peds to improve inspiratory synchrony Neo / Peds to improve inspiratory synchrony

Effects of ETT leaks on Triggering Problem Problem ETT leak = ↓ airway pressure ETT leak = ↓ airway pressure “Loss” of baseline PEEP “Loss” of baseline PEEP Sensed as a P T effort Sensed as a P T effort Result Result Initiates a ventilator assisted Initiates a ventilator assisted breath in the absence of a PT effort breath in the absence of a PT effort “ autocycling ” “ autocycling ”

Leak Compensation If baseline airway pressure ↓0.25cm H 2 O below set PEEP, flow added to maintain PEEP If baseline airway pressure ↓0.25cm H 2 O below set PEEP, flow added to maintain PEEP Adjustments Q 8 msec Adjustments Q 8 msec Max flow added Max flow added Sens = 1 cm H 2 O, flow = 0 – 5 LPM Sens = 1 cm H 2 O, flow = 0 – 5 LPM Sens = 2 – 5 cm H 2 O, flow = 0 – 10 LPM Sens = 2 – 5 cm H 2 O, flow = 0 – 10 LPM Solution

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

Effects of ETT on Vent WOB Flow (L/min) Work (Joules/min) 6.5 ETT 6.0 ETT 5.5 ETT 4.5 ETT 4.0 ETT

Inspiratory Synchrony Inspiratory Synchrony Trigger Sensitivity Trigger Sensitivity ETT effects / leaks Ventilator Response Time Ventilator Response Time Flow patterns – Fixed vs Variable Appropriate tidal volume Patient-Ventilator Synchrony Patient-Ventilator Synchrony Evaluate Inspiratory & Expiratory Synchrony

Ventilator 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 flow and the onset of inspiratory flow Ventilator response time is dependent on Ventilator response time is dependent on manufactures algorithms + technology manufactures algorithms + technology msec range for neonatal / peds 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 Time Paw (cm H 2 O) Time (secs) Trigger Set at -0.1ml/sec or -1cm H 2 0 Delayed Response Flow (ml/sec)

Inspiratory Synchrony Inspiratory Synchrony Trigger Sensitivity ETT effects / leaks ETT effects / leaks Ventilator Response Time Flow patterns – Fixed vs Variable Appropriate tidal volume Patient-Ventilator Synchrony Patient-Ventilator Synchrony Evaluate Inspiratory & Expiratory Synchrony

Decelerating Square Sine Ascending Flow Airway Pressure Time Flow and Airway Pressure Area =Mean Airway Pressure

Flow and Airway Pressure Decelerating Square Flow (l/sec) Airway Pressure (cmH 2 0) MAP = Area Under Curve PIP Gas Distribution

Fixed 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 mechanics Responsive 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 mode Usually not in volume limited mode Indications for variable flow Indications for variable flow Most P TS Most P TS

Inspiratory Synchrony Inspiratory Synchrony Trigger Sensitivity ETT effects / leaks ETT effects / leaks Ventilator Response Time Flow patterns – Fixed vs Variable Appropriate tidal volume Patient-Ventilator Synchrony Patient-Ventilator Synchrony Evaluate Inspiratory & Expiratory Synchrony

Pulmonary Injury Sequence There are two injury zones during mechanical ventilation There are two injury zones during mechanical ventilation –Low Lung Volume Ventilation tears adhesive surfaces –High Lung Volume Ventilation over-distends, resulting in “Volutrauma” The difficulty is finding the “Sweet Spot ” The difficulty is finding the “Sweet Spot ” Froese AB, Crit Care Med 1997; 25:906

Determination of effective tidal volume Can you calculate the tidal volume “lost” due to the distensibility of the ventilator circuit and compensate for it? calculated effective Vt = Vt at exp valve ﹣ [circuit compliance  (PIP-PEEP)]

Tidal Volume Determination Cannon, AJRCCM,  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 Circuit Vt(ml) p Vt(ml) p Exp valve Vt 70.4 ± 31.1 Calcuated Vt 59.2 ± 28.8 < Pneumotach Vt 39.4 ± 21.5 < The Vt as measured at the ETT was on average only 56% of that measured at the expiratory valve of the ventilator.

Circuit Compliance Calculations Calculating effective tidal volumes are not sufficient because of multiple uncontrolled variables: -in-line suction catheters -condensation -secretions -EtCO2 adapters -humidifiers / heaters -etc.

Vt(ml) p Vt(ml) p Exp valve Vt ± 96.6 Calcuated Vt ± Pneumotach Vt ± Results: Pediatric Circuit The Vt as measured at the ETT was on average 73% of that measured at the exp. valve of the ventilator.

Optimal Inspiratory Synchrony Optimal inspiratory PT – ventilator synchrony Optimal inspiratory PT – ventilator synchrony is a function of : is a function of : Trigger ( pressure / flow ) Trigger sensitivity Ventilator response time Flow pattern Appropriate tidal volume

Expiratory Synchrony Expiratory Synchrony End Expiratory Lung Volume End Expiratory Lung Volume Premature Termination of Exhalation Premature Termination of Exhalation Intrinsic PEEP Intrinsic PEEP Expiratory Resistance Expiratory Resistance Patient-Ventilator Synchrony Patient-Ventilator Synchrony Evaluate Inspiratory & Expiratory Synchrony

End Expiratory Lung Volume End expiratory lung volume ( EELV ) = volume of gas in lung prior to inspiratory ( FRC ) End expiratory lung volume ( EELV ) = volume of gas in lung prior to inspiratory ( FRC ) EELV is function of total PEEP and lung compliance, Estimate by loops, CXR EELV is function of total PEEP and lung compliance, Estimate by loops, CXR If EELV too low : If EELV too low : ↓ Lung compliance, ↓ V T or ↑PIP, ↑RR ↓ Lung compliance, ↓ V T or ↑PIP, ↑RR IF EELV too high : IF EELV too high : Pulmonary overdistention develops Pulmonary overdistention develops

Effects of EELV on Exp. Synchrony EELV too low : EELV too low : ↓ Lung compliance, ↓ V T or ↑PIP, ↑RR ↓ Lung compliance, ↓ V T or ↑PIP, ↑RR ↑RR may cause premature termination of ↑RR may cause premature termination of exhalation and intrinsic PEEP exhalation and intrinsic PEEP ↑RR perceived as weaning failure ↑RR perceived as weaning failure Inappropriate vent strategies employed Inappropriate vent strategies employed

Mechanical graphics Airway Pressure(cmH2O) Volume(ml) Vt=145ml PEEP PIP=42 2Y ARDS Low compliance Dynamic compliance=Vt/(PIP-PEEP)=3.9 Ins Exp

Expiratory Synchrony Expiratory Synchrony End Expiratory Lung Volume End Expiratory Lung Volume Premature Termination of Exhalation Premature Termination of Exhalation Intrinsic PEEP Intrinsic PEEP Expiratory Resistance (estimate loops, Expiratory Resistance (estimate loops, scalars ) scalars ) Patient-Ventilator Synchrony Patient-Ventilator Synchrony Evaluate Inspiratory & Expiratory Synchrony

Premature Termination of Exhalation Failure of airway pressure, volume, and flow to return to baseline prior to the next mechanical breath Failure of airway pressure, volume, and flow to return to baseline prior to the next mechanical breath “ Gas trapping “ causes intrinsic PEEP “ Gas 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 breaths ↓VT in PL breaths, ↑PIP in VL breaths Treatment strategies : Increase T E Treatment strategies : Increase T E

Gas-trapping or intrinsic PEEP Time inspirationexspiration 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-trapping Time inspirationexspiration Flow (L/sec) 0 Pressure (cmH2O) 0 Exhalation complete Intrinsic PEEP=0, set PEEP=5, total=5 I:E=1:1.5

Termination 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 flow to change in flow Goal : Shortest T I to obtain desired V T Goal : Shortest T I to obtain desired V T Termination Sensitivity Termination Sensitivity Terminates PL breath via flow versus time Terminates PL breath via flow versus time Clinician select % of peak flow at which Clinician select % of peak flow at which inspiration terminates ( % ) inspiration terminates ( % )

Termination Sensitivity Advantages Advantages Matches the T I with P T pathophysiology Matches the T I with P T pathophysiology Improves expiratory synchrony, ↑T E Improves expiratory synchrony, ↑T E Disadvantages Disadvantages If termination sen. set too high, loss V T If termination sen. set too high, loss V T If termination sen. Set too low, premature If termination sen. Set too low, premature termination of exhalation continues termination of exhalation continues Indication Indication Pt with short T I ( flow = zero prior to end of T I ) Pt with short T I ( flow = zero prior to end of T I )

Termination sensitivity

Expiratory Synchrony Expiratory Synchrony End Expiratory Lung Volume End Expiratory Lung Volume Premature Termination of Exhalation Premature Termination of Exhalation Intrinsic PEEP Intrinsic PEEP Expiratory Resistance Expiratory Resistance Patient-Ventilator Synchrony Patient-Ventilator Synchrony Evaluate Inspiratory & Expiratory Synchrony

Elevated Expiratory Resistance Prolonged expiratory phase cause “Gas trapping”, ↑WOB, ↓Trigger sensitivity Prolonged expiratory phase cause “Gas trapping”, ↑WOB, ↓Trigger sensitivity Obstruction to exhalation caused by : Obstruction to exhalation caused by : Airway obstruction : ETT occlusion Airway obstruction : ETT occlusion Bronchospasm : Aerosol therapy Bronchospasm : Aerosol therapy Expiratory valve performance : Expiratory valve performance : Ventilator evaluation Ventilator evaluation

Expiratory Synchrony Optimal expiratory synchrony results in complete exhalation at the lowest expiratory resistance Optimal expiratory synchrony results in complete exhalation at the lowest expiratory resistance 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 Support Spontaneous Breath Spontaneous 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” P T effort supported with Each “ sensed” P T effort supported with Pressure limited breath Pressure limited breath ↓ WOB ( ETT effects ) & ↑ V T of P T breath ↓ WOB ( ETT effects ) & ↑ V T of P T breath

WOB During Pressure Support PS = 15 cmH2O PS = 5-10 cmH2O PS = 0 cmH2O Volume Pressure

Pressure Support Advantages Advantages Improves P T /vent synchrony and ↓WOB Improves P T /vent synchrony and ↓WOB since each P T effort supported since each P T effort supported Disadvantages Disadvantages Inadequate triggering may limit use Inadequate triggering may limit use ETT leaks may prolong inspiratory phase ETT leaks may prolong inspiratory phase Indication Indication P T with active spontaneous breathing P T with active spontaneous breathing Weaning Weaning

SIMV with Pressure Support Flow Pressure Volume control Pressure support

Successful Weaning Successful weaning involves : Successful weaning involves : Optimal P T – Ventilator inspiratory & Optimal P T – Ventilator inspiratory & expiratory synchrony expiratory synchrony Appropriate WOB Appropriate 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 volume flow 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 Criteria CXR, Guide only CXR, Guide only Respiratory mechanics Respiratory mechanics C DYN, Raw, Spontaneous effort C DYN, Raw, Spontaneous effort Weight gain ( post – op ) Weight gain ( post – op ) Pulmonary toilet ?? Pulmonary toilet ?? Hemodynamics Hemodynamics Level of consciousness / sedation Level of consciousness / sedation Air – leak ( upper airway disease ) Air – leak ( upper airway disease ) Predicting methods: RR/Vt, CROP index, T-piece trial, negative inspiratory measurements, Vd/Vt Predicting methods: RR/Vt, CROP index, T-piece trial, negative inspiratory measurements, Vd/Vt Assess

Extubation Criteria: Adults Successful 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, 1973  CROP index (compliance, rate, oxygenation, pressure).Yang, NEJM,1991

Extubation Criteria: Adults Successful 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, 1973  CROP index (compliance, rate, oxygenation, pressure).Yang, NEJM,1991

Extubation Criteria in Peds Khan, CCM,1996 Successful extubation predictors: Variable Low-risk value High risk value Vtspont 6.5cc/kg 3.5 cc/kg FiO >0.40 Paw 8.5 cm H2O OI FrVe 20% 30% PIP 25 cm H2O 30 cm H2O Cdyn 0.9 cc/kg/cm H2O <0.4 cc/kg/cm H2O

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

End-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 Outcomes Results: Individual Outcomes Vd/VtSuccessfulExtubationFailedExtubation /25(96%)NIV(1) /9(67%)NIV(3) /10(20%)NIV(6),PPV(2) P<0.001