Patient-Ventilator Synchrony & Successful Weaning

1. Patient-Ventilator Synchrony & Successful Weaning Shao-Hsuan Hsia, MD Pediatric Critical Care and Emergency Medicine Chang Gung Children’s Hospital

2. What is your interpretation? Does these two patients “synchronize” ventilator? Can we “wean” these patients smoothly?

3. 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

4. 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.

5. WEANING AND EXTUBATION

6. Weaning Phase • Weaning Phase Facilitate spontaneous breathing Promote PT-Vent synchrony Appropriate WOB for the patient

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

8. Trigger Sensitivity • Trigger Sensitivity = effort required to initiate a ventilator assisted breath • A determinate of effort required (WOB) • What effects trigger sensitivity ? Pressure or Flow triggering Proximal vs distal sensing ETT leaks / size

9. Pressure Trigger 4 2 0 -2 Paw (cm H2O) WOB 0.25 0.50 Time (secs) Pressure Trigger

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

11. 4 2 0 -2 0.4 0.3 0.2 0.1 0 -0.1 -0.2 Paw (cm H2O) Flow (ml/sec) 0.25 0.50 Time (secs) Pressure vs Flow Trigger

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

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

17. Leak Compensation Solution • If baseline airway pressure ↓0.25cm H2O below set PEEP, flow added to maintain PEEP • Adjustments Q 8 msec • Max flow added Sens = 1 cm H2O, flow = 0 – 5 LPM Sens = 2 – 5 cm H2O, flow = 0 – 10 LPM

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

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

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

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

22. Ventilator Response Time 4 2 0 -2 0.4 0.3 0.2 0.1 0 -0.1 Paw (cm H2O) Flow (ml/sec) Trigger Set at -0.1ml/sec or -1cm H20 Delayed Response 0.25 0.50 Time (secs)

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

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

25. Flow and Airway Pressure DeceleratingSquare Flow (l/sec) MAP = Area Under Curve PIP PIP Airway Pressure (cmH20) Gas Distribution

26. Fixed vs Variable Flow • Advantages of variable flow Matches flow to spontaneous demand Responsive to changes in lung mechanics • Disadvantages of variable flow Not available for all breath types Usually not in volume limited mode • Indications for variable flow Most PTS

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

29. Pulmonary Injury Sequence • 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” Froese AB, Crit Care Med 1997; 25:906

30. 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)]

31. Tidal Volume Determination Cannon , 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)

33. Results: Infant Circuit The Vt as measured at the ETT was on average only 56% of that measured at the expiratory valve of the ventilator.

35. 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.

36. Results: Pediatric Circuit The Vt as measured at the ETT was on average 73% of that measured at the exp. valve of the ventilator.

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

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

40. End Expiratory Lung Volume • 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 • If EELV too low : ↓ Lung compliance, ↓ VT or ↑PIP, ↑RR • IF EELV too high : Pulmonary overdistention develops

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

42. Mechanical graphics Dynamic compliance=Vt/(PIP-PEEP)=3.9 2Y ARDS 250 Volume(ml) 150 Exp Vt=145ml Ins PIP=42 75 Low compliance 0 PEEP 15 30 45 Airway Pressure(cmH2O)

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

44. Premature Termination of Exhalation • Failure of airway pressure, volume, and flow to return to baseline prior to the next mechanical breath • “ Gas trapping “ causes intrinsic PEEP • Intrinsic PEEP ( may be good, may be bad ) May ↑WOB, ↑mean intrathoracic pressure ↓C.O. ↓Trigger sensitivity ↓VT in PL breaths, ↑PIP in VL breaths • Treatment strategies : Increase TE

45. Gas-trapping or intrinsic PEEP I:E=1:0.8 Flow (L/sec) 0 Incomplete exhalation (gas trapping) Pressure (cmH2O) 0 Intrinsic PEEP=5, set PEEP=5, total=10 inspiration exspiration Time

46. Reduction of Gas-trapping I:E=1:1.5 Flow (L/sec) 0 Exhalation complete Pressure (cmH2O) 0 inspiration exspiration Intrinsic PEEP=0, set PEEP=5, total=5 Time

47. Termination Sensitivity • Premature termination of exhalation Inadequate I:E ratio, RR induced Inspiration is time cycle and responsive to change in flow • Goal : Shortest TI to obtain desired VT • Termination Sensitivity Terminates PL breath via flow versus time • Clinician select % of peak flow at which inspiration terminates ( 0 - 25 % )

48. Termination Sensitivity • Advantages Matches the TI with PT pathophysiology Improves expiratory synchrony , ↑TE • Disadvantages If termination sen. set too high, loss VT If termination sen. Set too low, premature termination of exhalation continues • Indication Pt with short TI ( flow = zero prior to end of TI )

49. Termination sensitivity

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