Andrea Vianello Fisiopatologia Respiratoria Ospedale-Università di Padova

1. CONOSCERE I VENTILATORI Andrea Vianello Fisiopatologia Respiratoria Ospedale-Università di Padova

2. RESPIRATORY FAILURE LUNG FAILURE PUMP FAILURE GAS EXCHANGE FAILURE VENTILATORY FAILURE HYPERCAPNIA HYPOXEMIA

3. What’s the point of ventilation? • Deliver O2 to alveoli • Hb binds O2 (small amount dissolved) • CVS transports to tissues to make ATP - do work • Remove CO2 from pulmonary vessels • from tissues - metabolism

4. Why ventilate?- purposes • To maintain or improve ventilation, & tissue oxygenation. • To decrease the work of breathing & improve patient’s comfort.

5. When ventilate?- indications • Failure of pulmonary gas exchange • Hypoxaemia: low blood O2 • “Mechanical” failure • Hypercarbia: high blood CO2 • Respiratory muscle fatigue • Need to intubate eg patient unconscious • Others eg • need neuro-muscular paralysis to allow surgery • cardiovascular reasons

6. Definition: What is it? • Mechanical Ventilation =Machine to ventilate lungs = move air in (+ out) • Several ways to..move air in (IPPV vs others) Intermittent Positive Pressure Ventilation

8. Definition: What is it? • Mechanical Ventilation =Machine to ventilate lungs = move air in (+ out) • Several ways to..move air in (IPPV vs others) Intermittent Positive Pressure Ventilation • Several ways to connect the ventilator to the patient

9. Several ways to connect the machine to patient • Oro-tracheal Intubation • Tracheostomy • Non-Invasive Ventilation

10. Normal breath Normal breath inspiration, awake Lung @ FRC= balance Diaphragm contracts -2cm H20 Chest volume Pleural pressure -7cm H20 Alveolar pressure falls Air moves down pressure gradient to fill lungs

11. La pompa diaframmatica genera Pgarantendo la ventilazione polmonare, regolata da: • Equazione di moto del Sistema Respiratorio: Pmusc = V / C + V’ x R

12. Normal breath Normal breath expiration, awake -7cm H20 Diaphragm relaxes Pleural / Chest volume  Pleural pressure rises -2cm H20 Alveolar pressure rises Air moves down pressure gradient out of lungs

13. Ventilator breath Portableventilator ICU ventilator ICU ventilator

14. Ventilator breath Ventilator breath inspiration Air blown in 0 cm H20  lung pressure Air moves down pressure gradient to fill lungs +5 to+10 cm H20  Pleural pressure

15. Il ventilatore sostituisce totalmente o parzialmente la pompa muscolare: • Equazione di moto del Sistema Respiratorio: Pappl (+ Pmusc) = V / C + V’ x R

16. Ventilator breath Ventilator breath expiration Similar to spontaneous…ie passive Ventilator stops blowing air in Pressure gradient Alveolus-trachea Air moves out Down gradient  Lung volume

17. Practicalities • Ventilator settings: • Pressure vs volume • ‘Assist’ vs ‘Control’ • PEEP?

18. Practicalities Ventilator settings: Pressure vs volume ‘Assist’ vs ‘Control’ PEEP?

19. Details: Inspiration Pressure or Volume? • Do you push in.. • A gas at a set pressure? = ‘pressure…..’ • A set volume of gas? = ‘volume….’

20. Pressure Ventilators • The use of pressure ventilators is increasing in critical care units. • A typical pressure mode delivers a selected gas pressure to the patient early in inspiration, and sustains the pressure throughout the inspiratory phase. • By meeting the patient’s inspiratory flow demand throughout inspiration, patient effort is reduced and comfort increased.

21. Details: Inspiration Pressure or Volume? Pressure cm H20 Time Pressure cm H20 Time

22. Although pressure is consistent with these modes, volume is not. • Volume will change with changes in resistance or compliance • Therefore, exhaled tidal volume is the variable to monitor closely. • With pressure modes, the pressure level to be delivered is selected, and with some mode options, rate and inspiratory time are preset as well.

23. Volume Ventilators • The volume ventilator has been historically used in critical care settings • A respiratory rate, inspiratory time, and tidal volume are selected for the mechanical breaths. • The basic principle of this ventilator is that a designated volume of air is delivered with each breath. • Theamount of pressure required to deliver the set volume depends on : - Patient’s lung compliance - Patient–ventilator resistance factors

24. Details: Inspiration Pressure or Volume?

25. Peak Inspiratory Pressure (PIP ) must be monitored in volume modes because it varies from breath to breath 30 Peak Inspiratory Pressure P aw Time (s) cmH2O 1 2 3 -10

26. Details: Pressure vs Volume in the Acute Setting Secretions hypoventilation Vt preserved partial compensation hypoventilation sensitive insensitive Schönhofer ERS Monograph 2001; 16: 259-73, mod

27. small leak huge leak Details: leak compensation without leakage with leakage Pressure Vol Pressure Vol Pre-set Mehta et al. Eur Respir J 2001; 17: 259-267

28. Hybrid modes combine the advantages of pressure pre-set and volume pre-set VAPS Volume Assured Pressure Support • Automatic adjustment of inspiratory pressure (range setting) • Target volume set • Measurement of inspiratory pressure and expiratory volume • Calculation of missing inspiratory volume • Increase of inspiratory pressure Assurance of tidal volume + comfort of pressure pre-set

29. VAPS Volume Assured Pressure Support

30. VAPS Volume Assured Pressure Support

31. Storre et al. Chest 2006;130: 815-821

32. Efficacy and comfort of Volume-Guaranteed Pressure Support (PSV-VTG) in patients with chronic ventilatory failure of neuromuscular origin

33. Efficacy and comfort of Volume-Guaranteed Pressure Support (PSV-VTG) in patients with chronic ventilatory failure of neuromuscular origin

34. Four types of asynchronies: • Ineffective inspiratory effort (IE): thoraco-abdominal displacements not assisted by the ventilator positive pressure boost; • Inspiratory trigger delay: a time lag between the initiation of the patent’s IE and the onset of inspiratory support; • Prolonged inspiration or late expiratory cycling (hang-up): prolongation of mechanical insufflation beyond the end of patient inspiration; • Autotriggering: rapid succession of at least three pressurizations at a RR of >40 br/min. Efficacy and comfort of Volume-Guaranteed Pressure Support (PSV-VTG) in patients with chronic ventilatory failure of neuromuscular origin

35. Efficacy and comfort of Volume-Guaranteed Pressure Support (PSV-VTG) in patients with chronic ventilatory failure of neuromuscular origin

36. Practicalities Ventilator settings: Pressure vs volume ‘Assist’ vs ‘Control’ PEEP?

37. Interaction Ventilator Respiratory muscle pump

38. . . Ventilator Respiratory muscle pump work of breathing spontaneous assisted controlled

40. Noninvasive mechanical ventilation in acute exacerbation of restrictive thoracic disease Eur Respir Mon 2001; 6:70-73

42. Practicalities Ventilator settings: Pressure vs volume ‘Assist’ vs ‘Control’ PEEP?

43. RESPIRATORY FAILURE LUNG FAILURE PUMP FAILURE GAS EXCHANGE FAILURE VENTILATORY FAILURE HYPERCAPNIA HYPOXEMIA

44. Compliance of the Respiratory System ‘over-distended’ alveoli Compliance= Volume  Pressure Volume • energy needed to open alveoli • damaged during open/closing? • - abnormal forces Pressure

45. Regional ventilation Spontaneous, standing Compliance= Volume  Pressure Volume Pressure

46. Abnormalities of CRS Compliance= Volume  Pressure Volume Pressure

48. V/Q mismatching (shunt effect)

49. CPAP/PEEP to improve oxygenation

50. What is PEEP? A constant positive pressure applied to the RS throughout the respiratory cycle Constant pressure → does not generate flow, does not increase volume !! Cannot be considered a form of ventilation in a strict sense!!however: It exerts important effects on RS mechanics: it may increase lung volume in order to correct acute lung restriction contributing to hypoxemia Pressure cm H20 PEEP Time Positive End Expiratory Pressure