Mechanical Ventilation-101

1. Mechanical Ventilation-101 Carey Thomson, MD, MPH Critical Care Services Mount Auburn Hospital

2. Mechanical Ventilation Individualized approach Anatomy of mechanical ventilation Modes �the basics Modes --the sophisticated Waveforms and Mechanics Liberation from mechanical ventilation

3. Individualize your approach

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5. Goals When Setting The Ventilator Avoid alveolar over-distension Provide adequate alveolar ventilation Promote patient-ventilator synchrony Apply PEEP to maintain alveolar recruitment Provide adequate oxygenation Use the lowest possible FIO2 Avoid auto-PEEP

7. Anatomy of a Vent Triggering Flow pattern Cycling Modes Waveforms and Mechanics

8. Breath Types Delivered By Vents Assisted: either triggered by the patient or cycled by the ventilator Volume-controlled Pressure-controlled Mixed modes Spontaneous: triggered and cycled by the patient CPAP Pressure support

9. Triggering: start inspiration Triggered based on time, pressure, or flow Vent initiated= Time: The vent cycles based on a set rate (if pt does not initiate) Patient initiated (i.e. inspiratory effort maintained) Negative Pressure: Patient's effort sensed by a decrease in the baseline pressure Unnecessary work Replaced by Flow triggers Flow triggers (�flow by�): Inspiration deflects the flow of continuous gas traveling around the system

10. Triggering Pitfalls: If the trigger is too sensitive the patient �overtriggers� and hyperventilates If it is not sensitive enough, the patient becomes dysynchronous�air hunger Example: PCP/ARDS with PTX and 60/minute

11. Flow pattern Decelerating High initial flow Inspiration slows down as alveolar pressure increases results in a lower peak airway pressure than constant and accelerating flow better distribution characteristics Can be used in both pressure targeted and volume targeted ventilation Constant = constant rate until the set tidal volume is delivered Accelerating = flow increases progressively This should not be used in clinical practice. Sinusoidal = spontaneous breathing and CPAP

12. Peak inspiratory flow rate How quickly the breath is delivered Default 60L/min Ti (inspiration) = VT/Flow Rate Pitfalls: Flow rate is too high => rapid delivery to most compliant at higher peak pressures Peak flow is too low=> pt demands more? dysynchrony and Higher Ti = Lower Te = autopeep Pressure augmentation: automatic increased flow when the patient�s demands exceed the peak flow.

13. Setting the Ventilator:PEEP PEEP: Prevent alveolar collapse; improve oxygenation Alveolar recruitment may decrease the risk of VILI Evidence is lacking that higher levels of PEEP, compared to modest levels of PEEP, decrease mortality (N Engl J Med, 2004;351:327) Counter-balance auto-PEEP, thus improving the ability to trigger Improve cardiac performance by decreasing venous return and left ventricular afterload Pitfalls: reduced venous return, hypotension, interpretation of wedge readings inaccurate

14. Modes

15. Pressure Support Ventilation Spontaneous breathing mode Patient triggered Pressure limited (inspiration) Flow cycled Vent cycles to expiration when flow decreases by a preset amount (i.e. 25% of peak flow). Pitfall: Not guaranteed minute ventilation COPD patients with slow flow changes

16. Pressure Control Ventilation Flow occurs until a preset peak pressure is met over a fixed inspiratory period Set Ti: too short=too rapid breath; too long= autoPeep (short expir time) Longer Ti=higher mean airway pressures Flow waveform always decelerating (flow slows as it reaches the pressure limit) Good: Patient synchrony/comfort Noncompliant lung units are more likely to be inflated in PCV due to decelerating flow and maintenance of airway pressure over time. Pitfall: Change in compliance/mechanics = change in delivered tidal volume. Autopeep= decreased driving pressure

17. Volume Controlled Ventilation Fixed peak flow rate (60L/min) Specified flow pattern (constant or decelerating) Fixed Tidal Volume Fixed inspiratory time = VT/Flow rate Pressure varies with lung mechanics Pitfall: Respiratory alkalosis Airway pressures may be too high (ARDS)

18. SIMV Fixed volume delivered at a set rate Spontaneous breaths can be taken and/or supported Breaths synchronized to prevent "stacking� Good: set minute ventilation Pitfalls: Difficulty adapting to �intermittent� nature of assistance�..decrease wob less than desired

19. Work of Breathing and SIMV

20. SIMV

21. New and Salvage Modes Airway pressure release ventilation; bilevel Pressure-regulated volume control Proportional Assist Ventilation Automatic Tube compensation

22. Airway Pressure Release Ventilation The ventilator cycles between an upper and lower CPAP level SEVERE inverse I:E: Usually of 8-9:1: SHORT expir time is key (can�t allow full exhalation), and longer Ti=more oxygenation The pressure is intermittently �released� to a lower level, thus eliminating waste gas Time-triggered, pressure-limited, time-cycled mode The key element of APRV is that the baseline airway pressure is the upper CPAP level

23. APRV evidence? Improves aeration (Wrigge. Anesth. 2003;99:376) 24pts with ARDS and APRV vs PSV (Purensen, AJRCCM 1999:159 reduced shunt, dead space, VQmismatch 30 pts with ARDS after trauma (Putensen, AJRCCM 2001) Improved LOS (23 vs 30; p=0.032), Length of vent support (15 vs 21; p=0.032) Increased Crs, PaO2, CI, reduced shunt

24. BILEVEL Bilevel CPAP or BIPAP is APRV with spontaneous breathing. Can also be used with PCV A valve allows the patient to breath spontaneously at either CPAP/PEEP levels, and partial assistance (pressure support or automatic tube compensation) is used to assist breaths. Well tolerated

25. Pressure Regulated Volume Control Form of assist-control ventilation. Breaths can be: ventilator initiated (control breath) or patient initiated (assist breath) Constant pressure applied throughout inspiration (like pressure control) Ventilator adjusts pressure from breath to breath, as patient's airway resistance and respiratory system compliance changes, in order to deliver the set tidal volume If the delivered volume is too low it increases the inspiratory pressure on the next breath. If it is too high it decreases the pressure

26. Proportional Assist Ventilation Vent guarantees the % of work which it does in the face of changes in respiratory system (elastance, resistance, flow demand by patient) NO PRE-SET TV, flow, or pressure Flow Asssist (FA: cmH20/L/s) or Volume Assist (VA: cmH20/L) are delivered Varies from breath to breath based on patient effort and positive pressure at the airway opening based on the levels of set VA or FA This mode is interactive, as the ventilator varies its output to maintain its proportion of the workload

27. High Frequency Oscillation High Peep, TINY tidal volume (1-5ml/kg) at high RR (60-300) Avoid over-distention High rate clears CO2 Some Case series in adults have reported some efficacy in salvage cases Improved PaO2 and PaCO2 with lower FIO2 with apparent safety Multiple trials show no benefit over mechanical ventilation

28. Other�mainly in salvage ARDS Inverse ratio ventilation (I:E>1) Reduce cardiac output (high pressures, autopeep) NO improves PaO2 but not mortality in ARDS (Dellinger, CCM 1998;26:15) Higher PEEP increases PaO2/FIO2 and compliance but not mortality (NEJM 2004;351:327-336) Prone positioning improves PaO2 but not mortality (Gattinoni, NEJM 2001;345;568) ECMO: lung to rest while on �bypass� Heroic salvage European trial ongoing: CESAR

29. Trouble shooting

30. Monitoring Respiratory Mechanics Assessment of mechanics is useful in vented patients Insights into the pathophysiology Pressure, flow, and volume in ventilator circuit Derived measures Compliance Resistance Time-based graphics (waveforms) Pressure Flow Volume

31. Assessing Mechanics Typical Mechanics/Use of waveforms: PIP, Pplat, RAW auto-PEEP Compliance: CL, CCW, Crs

32. Case PC IP 20, TV 400ml, RR set 28 Gas: PaCO2 60, PaO2 60 Resident increases RR to 32 1hr later, you are called to a pt with an SpO2 88%, TV now 260ml ABG PaCO2 88, PaO2 55 What do you think? Compliance problem and needs increased IP?

33. Waveform analysis

34. Waveform analysis

36. Flow Waveform

37. Auto-peep Gas trapped at end expiration Insufficient E time Inability to trigger (multiple attempts leads to autoPeep and high elastic recoil) Raises the baseline pressure �decreased driving pressure Further adds to difficulty in triggering Problem: Poor ventilation (lower driving pressure) and oxygenation Increased work of breathing: Tachypnea, Dyssynchrony High airway pressures?pneumothorax; hemodynamic effects Solution: Reduce RR Bronchodilate, clear airway ?Other factors: agitation, pain, fever Applied PEEP Possibly: Increase inspiratory flow rate (to decrease I time and increase E time)�but may lead to tachypnea

38. Auto-PEEP and Triggering

39. Case You are called to assess a patient who has a RR of 45 and is described as �guppy� breathing. The nurse has tried sedation, suctioning, and the RR was increased to 35 by the resident, but the pattern continues.

40. Waveform analysis

41. Waveform analysis Inspiratory flow not high enough: scooped inward Patient attempting to trigger more and unable too (wants more breath)

42. Increasing peak flow Peak flow should be roughly four times that of the minute ventilation (MV 15L requires PF>60L) If the patient is breathing spontaneously, adjust to match their efforts In panel 1 the peak flow (PF) is 40 l/min and the patient is slightly dysynchronous. In the middle panel the PF is 50 l/min and the patient remains dysynchronous. In the last panel the PF is 100 l/min, but the peak airway pressure is too high.

43. Respiratory System Compliance mainstem intubation congestive heart failure ARDS atelectasis consolidation fibrosis hyperinflation tension pneumothorax pleural effusion abdominal distension chest wall edema thoracic deformity

46. Pplat = Palv; Pplat = Transpulmonary Pressure?

47. Pplat = Palv; Pplat = Transpulmonary Pressure?

48. Pplat = Palv; Pplat = Transpulmonary Pressure?

49. ?Peso � ?Ppl

50. Transpulmonary Pressure

51. Full Ventilator Support

53. Inspiratory Resistance Secretions Bronchospasm Small endotracheal tube

54. Goals When Setting The Ventilator Avoid alveolar over-distension Provide adequate alveolar ventilation Promote patient-ventilator synchrony Apply PEEP to maintain alveolar recruitment Provide adequate oxygenation Use the lowest possible FIO2 Avoid auto-PEEP

55. WEANING

56. Approach to Weaning

57. Most Patients Don�t Need Weaning Normal Crs Normal Raw Awake They need to be liberated!

58. �Weaning� Approaches Spontaneous breathing trial with T-piece Spontaneous breathing trial on ventilator Pressure support ventilation (PSV) Synchronized intermittent mandatory ventilation SIMV + PSV AC modes titrated down (ACVC, PC)

59. Work of Breathing and SIMV

60. Comparison of Weaning Methods Prior Trials with IMV Schacter et al:IMV vs other no difference Retrospective, nonuniform gps,poor protocol Hastings: SBT vs IMV at rate 4 Post-op cardiac; little difficulty expected Linson: IMV=SBT Weighted toward short term support 2/3 weaned in 2hrs and had vent support <72hrs Others with poor protocols/retrospective, etc

61. Comparison of Weaning Methods Brochard, Am J Respir Crit Care Med 1994; 150:896 456 Patients screened via Tpiece: 75% extubated SBT via Tpiece could be done up to 8x/day and potentially not extubated until 3 trials of 2hrs had been achieved !!!! increased demand/wob�fatigue

62. Comparison of Weaning Methods Esteban et al, N Engl J Med 1995; 332; 345 546 Patients (7.5+/-6days) screened via T-piece: ?75% extubated Greatest Success with SBT IMV was favored with least days (6.5) on vent vs 10.8 PSV, 11.5 SBT x 2hrs vs 8.4 SBT x 30min

63. Evidence Based Recommendation Patients receiving mechanical ventilation for respiratory failure should undergo a formal assessment of discontinuation potential if the following criteria are met: Evidence for some reversal of the underlying cause for respiratory failure Adequate oxygenation and pH Hemodynamic stability (absence of active myocardial ischemia, absence of significant hypotension) Capabile of initiating inspiratory efforts

64. Evidence Based Recommendation Patients should be assessed with a daily spontaneous breathing trial (SBT) An initial brief period of spontaneous breathing can be used to assess the capability of continuing on to a formal SBT Consider ventilator discontinuation after a well-tolerated SBT of 30-120min

65. Evidence Based Recommendation Criteria for tolerance: Respiratory pattern Subjective comfort Hemodynamic stability Adequacy of gas exchange Weaning Parameters are not predictive! Minute ventilation, RR, TV, MIP all have sensitivity from 0.76-1.0 but POOR specificities (0.11-0.54) Yang and Tobin. NEJM 1991;324:1447 RSBI best (sens 0.97; spec 0.64)-<105 on 0/0

66. Approach to Weaning

67. Weaning Summary Weaning parameters are of limited usefulness SBT is the best means of determining when a patient is able to sustain spontaneous breathing Weaning success is lower with SIMV than trials of spontaneous breathing or PSV The need for a ventilator should be separated from the need for an airway