2. CHRIS CROPSEY, MD VENTILATION – THE BASICS AND BEYOND

3. OVERVIEW Modes of Ventilation VC, PC, PRVC, BiVent Control of ventilation (SIMV PS vs. A/C) Cases Please feel free to ask questions any time!!

4. WHY DO WE CARE? Ventilators save lives! But… Ventilators are bad! Barotrauma Volutrauma Atelectrauma

5. Pressure Dynamic pressure OR Peak pressure Static pressure OR Plateau pressure What pressures are we interested in?

6. Normally P plat = P peak – 5to10 cm H2O – In what situations isn’t that the case? Why are we more interested clinically in Pplat? Ppeak Pplat Puts a pause in the Inspiratory Cycle – no flow – measures pressure Estimates alveolar pressure at end- inspiration Indirect indicator of alveolar distension Goal is PIP <40, Pplat <30

7. BASIC VENTILATOR SETTINGS Ventilation (Clear CO2) TIDAL VOLUME RESPIRATORY RATE MINUTE VENTILATION Oxygenation (O2 sats) FiO2 PEEP MEAN AIRWAY PRESSURE

8. SCHEMATIC OF BASIC MODES PCVC PRVC BiVent

9. VOLUME CONTROL Volume Controlled You set: Tidal volume Peak flow (or I:E) Rate

10. BASIC VC SETTINGS Tidal volume (Vt) – volume to be given with each breath (usually in mL) Peak flow (VMAX) – rate at which volume is delivered (in L/min) – controls the I:E Alternately, set I:E directly Rate - Breaths/minute

11. VC BASIC PROPERTIES Preset rate and tidal volume at the set interval Full mechanical breath delivered. Uses: weak respiratory effort, allows synchrony with the patient. Not a weaning mode

12. ADVANTAGES Consistent TV changing impedance Auto-PEEP Minimum minute ventilation guaranteed (R x TV) Variety of flow waves But usually square wave

13. DISADVANTAGES Variable pressures airway alveolar Fixed flow pattern Compressible volume Circuit leaks = volume loss Tachypnea leads to excess MV

14. FLOW/PRESSURE TRACINGS - VC Pressure Flow Note that pressure is variable (and has plateau); flow is constant

15. You set: Pressure limit Time spent in inspiration Rate Pressure Controlled PRESSURE CONTROL

16. PRESSURE CONTROL BASIC SETTINGS Inspiratory pressure is the target – tells ventilator max pressure each breath (note that PIP = Pinspiratory + Ppeep) Inspiratory time (I-time) is set and constant Note that I:E ratio is affected by I-time Rate in breaths/min

17. ADVANTAGES - PC For given PIP, the TV will be higher in PC than VC Put another way, the “cost” of TV is lower in PC More physiologic – decelerating flow

18. DISADVANTAGES - PC No guaranteed tidal volume/minute ventilation Can lead to extreme under- or over- ventilation

19. FLOW/PRESSURE TRACINGS - PC Note that flow is variable; pressure is constant

20. COMPARISON – VC VS. PC Volume Control Pressure Control

21. PRESSURE REGULATED VOLUME CONTROL PRVC You set: TARGET TV Regulation Pressure Rate

22. PRESSURE REGULATED VOLUME CONTROL Combines positives from VC and PC Set TV is “targeted” Ventilator estimates vol./press. relationship each breath Ventilator adjusts level of pressure control breath by breath

23. PRVC First breath = Volume Control V/P relationship measured Next Breath = PC at Pplateau Then up to +/- 3 cm H2O changes per breath Time ends inspiration (like PC) If PIP reaches regulation minus 5, breath stops and ventilator alarms

24. PRESSURE REGULATED VOLUME CONTROL - CONSIDERATIONS Constant pressure during each breath - variable pressure from breath to breath Time cycled Delivered TV can vary from set TV breath to breath

25. FLOW/PRESSURE WAVEFORM - PRVC Note 1 st breath is VC; 2 nd breath is “PC” with Pplat as PIP

26. ADVANTAGES Decelerating flow pattern Pressure automatically adjusted for changes in compliance and resistance within a set range – Tidal volume “guaranteed” – Limits volutrauma/barotrauma – Prevents hypoventilation

27. DISADVANTAGES Pressure delivered is dependent on tidal volume achieved on last breath Intermittent patient effort → variable tidal volumes Asynchrony with variable patient effort Richard et al. Resp Care 2005 Dec Less suitable for patients with asthma or COPD

28. If in assisted breaths the Pt's demand ↑ pressure level ↓ at a time when support is most necessary mean airway pressure will ↓ hypoxemia

29. BIVENT (BILEVEL, APRV) BiVent You set: Phigh Plow (i.e. PEEP) Thigh Tlow Pressure support

30. BIVENT BASICS Think of it as glorified BiPAP Ventilator cycles between high pressure and low pressure based on set time intervals Thigh is usually [much] longer than Tlow Tlow allows time for release Patient can (and should!) breath spontaneously throughout pressure cycle This differentiates between inverse ratio PC

32. BIVENT - ADVANTAGES Allows for high mean airway pressure relative to peak airway pressure Sustained recruitment of alveoli over time Possibly more comfortable – patient can breathe whenever s/he wants

33. BIVENT - DISADVANTAGES High intrathoracic pressures can lead to decreased venous return and blood pressure Often leads to hypercapnia In practice – anecdotally seems to be uncomfortable Really requires spontaneous ventilation (so shouldn’t paralyze)

34. WHAT ABOUT PATIENT EFFORT? When patient does nothing, things are pretty simple When patient wants to breathe, ventilator has to figure out what to do Patient “triggers” vent: Flow – easier, more sensitive in general Pressure – tougher to trigger but less accidental breaths

35. PRESSURE SUPPORT We set: Pressure support PEEP Flow % cutoff When patient triggers a breath ventilator bumps up inspiratory pressure to PS level Pressure support continues until flow drops to set percent of maximum

36. PRESSURE/VOLUME WAVEFORM - PS Note that every breath has pink “trigger” marking on upslope

37. ASSIST CONTROL Not a mode on its own, but a way to describe patient-ventilator interaction In A/C, every patient trigger results in full tidal volume breath Advantages: Reliable TV Decreases patient work Disadvantages: Can lead to severe hyperventilation Possibility of breath stacking / auto-PEEP

38. Patient efforts recognized by ventilator – notice breath time reset every cycle ASSIST CONTROL (A/C)

39. WHAT IS “AUTO-PEEP”? FLOW INSP EXP Expiratory flow ends before next breath Next breath begins before exhalation ends Obstructive lung disease Rapid breathing Forced exhalation

40. SIMV SIMV is like a hybrid of A/C and PS Like A/C, not a mode itself but way of patient- vent interaction SIMV divides Tb into Mandatory periods (Tm) and Spontaneous periods (Ts)

41. SIMV If patient tries to breathe during Tm, the ventilator gives a FULLY ASSISTED BREATH – the SAME TIDAL VOLUME IS ACHIEVED

42. SIMV If patient tries to breathe during Ts, the ventilator allows the patient to take the breath. Assistance provided with PRESSURE (PRESSURE SUPPORT) TIDAL VOLUME depends on patients effort and pressure support

43. PRESSURE/FLOW WAVEFORM – SIMV VC Notice that first breath is VC, next two are PS

44. CASE 1 52 y/o F, 70 kg with aspiration pneumonia, gets intubated on floor and sent to unit Initial settings: VC A/C, Rate 12, TV 700, FiO2 100%, PEEP 6 Sats 88% Ventilator alarm going off for high Peak Pressures (50 cm H2O) What do you do?

45. CASE 1 (CONT’D) Consider hand bagging patient (but be careful!) Drop TV – goal 6-8 ml/kg Increase PEEP Change modes – PC or PRVC (or BiVent)

46. CASE 2 62 y/o F, 52 kg, intubated for exacerbation of severe COPD Initial vent settings: SIMV VC, R 12, TV 400, FiO2 50%, PEEP 5 Total respiratory rate: 16, Sats 100% ABG: pH 7.35, PCO2 65, PO2 180 Vent is alarming because of high PIP – what do you do?

47. CASE 2 – CONT’D Disconnect and hand bag – allow for expiration Decrease I:E ratio – allow more time to exhale Treat underlying problem (bronchodilators) Take into account pt’s chronic compensation

48. SUMMARY Major modes of ventilation: VC, PC, PRVC, BiVent, PS VC, PC, PRVC can be either A/C or SIMV Pressure controlled breaths offer smaller PIP for same TV but no guarantee of TV VC breaths guarantee TV but at expense of PIP The sooner you can extubate, the better!