Principles of Mechanical Ventilation

1. Principles of Mechanical Ventilation RET 2284 Module 3.0 Modes of Ventilation

2. Modes of Ventilation • Mode • Description of a breath type and the timing of breath delivery • Terms or acronyms used to describe the way a ventilator performs in a particular situation; often invented by physicians, therapists, or manufacturers • Basically there are three breath delivery techniques used with invasive positive pressure ventilation • CMV – controlled mode ventilation • SIMV – synchronized • Spontaneous modes

3. Modes of Ventilation • CMV • Continuous Mandatory Ventilation • All breaths are mandatory and can be volume or pressure targeted • Controlled Ventilation – when mandatory breaths are time triggered • Assist/Control Ventilation – when mandatory breaths are either time triggered or patient triggered

4. Modes of Ventilation • CMV • Continuous Mandatory Ventilation • Controlled Ventilation – when mandatory breaths are time triggered • Mandatory breath – ventilator determines the start time (time triggered) and/or the volume or pressure target

5. Modes of Ventilation • CMV • Controlled Ventilation • Appropriate when a patient can make no effort to breathe or when ventilation must be completely controlled • Drugs • Cerebral malfunctions • Spinal cord injury • Phrenic nerve injury • Motor nerve paralysis

6. Modes of Ventilation • CMV • Controlled Ventilation • In other types of patients, controlled ventilation is difficult to use unless the patient is sedated or paralyzed with medications • Seizure activity • Tetanic contractions • Inverses I:E ratio ventilation • Patient is fighting (bucking) the ventilator • Crushed chest injury – stabilizes the chest • Complete rest for the patient

7. Modes of Ventilation • CMV • Controlled Ventilation • Adequate alarms must be set to safeguard the patient • E.g., disconnection • Sensitivity should be set so that when the patient begins to respond, they can receive gas flow from the patient Do not lock the patient out of the ventilator!

8. Modes of Ventilation • CMV • Assist/Control Ventilation • A time or patient triggered CMV mode in which the operator sets a minimum rate, sensitivity level, type of breath (volume or pressure) • The patient can trigger breaths at a faster rate than the set minimum, but only the set volume or pressure is delivered with each breath

9. Modes of Ventilation • CMV • Assist/Control Ventilation • Indications • Patients requiring full ventilatory support • Patients with stable respiratory drive • Advantages • Decreases the work of breathing (WOB) • Allows patients to regulate respiratory rate • Helps maintain a normal PaCO2 • Complications • Alveolar hyperventilation

10. Modes of Ventilation • CMV • Volume Controlled – CMV • Time or patient triggered, volume targeted, volume cycled ventilation • Graphic (VC-CMV) • Time-triggered, constant flow, volume-targeted ventilation

11. Modes of Ventilation • CMV • Volume Controlled – CMV • Time or patient triggered, volume targeted, volume cycled ventilation • Graphic (VC-CMV) • Time-triggered, descending-flow, volume-targeted ventilation

12. Modes of Ventilation • CMV • Pressure Controlled – CMV • PC – CMV (AKA – Pressure control ventilation - PCV) • Time or patient triggered, pressure targeted (limited), time cycled ventilation • The operator sets the length of inspiration (Ti), the pressure level, and the backup rate of ventilation • VT is based on the compliance and resistance of the patient’s lungs, patient effort, and the set pressure

13. Modes of Ventilation • CMV • Pressure Controlled – CMV • Note inspiratory pause

14. Modes of Ventilation • CMV • Pressure Controlled – CMV • Note shorter Ti

15. Modes of Ventilation • CMV • Pressure Controlled – CMV • Airway pressure is limited, which may help guard against barotrauma or volume-associated lung injury • Maximum inspiratory pressure set at 30 – 35 cm H2O • Especially helpful in patients with ALI and ARDS • Allows application of extended inspiratory time, which may benefit patients with severe oxygenation problems • Usually reserved for patient who have poor results with a conventional ventilation strategy of volume ventilation

16. Modes of Ventilation • CMV • Pressure Controlled – CMV • Occasionally, Ti is set longer than TE during PC-CMV; known as Pressure Control Inverse Ratio Ventilation • Longer Ti provides better oxygenation to some patients by increasing mean airway pressure • Requires sedation, and in some cases paralysis

17. Modes of Ventilation • IMV and SIMV • Intermittent Mandatory Ventilation – IMV • Periodic volume or pressure targeted breaths occur at set interval (time triggering) • Between mandatory breaths, the patient breathes spontaneously at any desired baseline pressure without receiving a mandatory breath • Patient can breathe either from a continuous flow or gas or from a demand valve

18. Modes of Ventilation • IMV and SIMV • Intermittent Mandatory Ventilation – IMV • Indications • Facilitate transition from full ventilatory support to partial support • Advantages • Maintains respiratory muscle strength by avoiding muscle atrophy • Decreases mean airway pressure • Facilitates ventilator discontinuation – “weaning”

19. Modes of Ventilation • IMV and SIMV • Intermittent Mandatory Ventilation – IMV • Complications • When used for weaning, may be done too quickly and cause muscle fatigue • Mechanical rate and spontaneous rate may asynchronous causing “stacking” • May cause barotrauma or volutrauma

20. Modes of Ventilation • IMV and SIMV • Synchronized IMV • Operates in the same way as IMV except that mandatory breaths are normally patient triggered rather than time triggered (operator set the volume or pressure target) • As in IMV, the patient can breathe spontaneously through the ventilator circuit between mandatory breaths

21. Modes of Ventilation • IMV and SIMV • Synchronized IMV • At a predetermined interval (respiratory rate), which is set by the operator, the ventilator waits for the patient’s next inspiratory effort • When the ventilator senses the effort, the ventilator assists the patient by synchronously delivering a mandatory breath

22. Modes of Ventilation • IMV and SIMV • Synchronized IMV • If the patient fails to initiate ventilation within a predetermined interval, the ventilator provides a mandatory breath at the end of the time period

23. Modes of Ventilation • IMV and SIMV • Synchronized IMV • Indications • Facilitate transition from full ventilatory support to partial support • Advantages • Maintains respiratory muscle strength by avoiding muscle atrophy • Decreases mean airway pressure • Facilitates ventilator discontinuation – “weaning”

24. Modes of Ventilation • IMV and SIMV • Synchronized IMV • Complications • When used for weaning, may be done too quickly and cause muscle fatigue

25. Modes of Ventilation • Spontaneous Modes • Three basic means of providing support for continuous spontaneous breathing during mechanical ventilation • Spontaneous breathing • CPAP • PSV – Pressure Support Ventilation

26. Modes of Ventilation • Spontaneous Modes • Spontaneous breathing • Patients can breathe spontaneously through a ventilator circuit; sometimes called T-Piece Method because it mimics having the patient ET tube connected to a Briggs adapter (T-piece) • Advantage • Ventilator can monitor the patient’s breathing and activate an alarm if something undesirable occurs • Disadvantage • May increase patient’s WOB with older ventilators

27. Modes of Ventilation • Spontaneous Modes • CPAP • Ventilators can provide CPAP for spontaneously breathing patients • Helpful for improving oxygenation in patients with refractory hypoxemia and a low FRC • CPAP setting is adjusted to provide the best oxygenation with the lowest positive pressure and the lowest FiO2

28. Modes of Ventilation • Spontaneous Modes • CPAP • Advantages • Ventilator can monitor the patient’s breathing and activate an alarm if something undesirable occurs

29. Modes of Ventilation • Spontaneous Modes • PEEP (Positive End Expiratory Pressure) “According to its purest definition, the term PEEP is defined as positive pressure at the end of exhalation during either spontaneous breathing or mechanical ventilation. However, use of the term commonly implies that the patient is also receiving mandatory breaths from a ventilator.” (Pilbeam) • PEEP becomes the baseline variable during mechanical ventilation

30. Modes of Ventilation • Spontaneous Modes • PEEP • Helps prevent early airway closure and alveolar collapse and the end of expiration by increasing (and normalizing) the functional residual capacity (FRC) of the lungs • Facilitates better oxygenation NOTE: PEEP is intended to improve oxygenation, not to provide ventilation, which is the movement of air into the lungs followed by exhalation

31. Modes of Ventilation • Spontaneous Modes • Pressure Support Ventilation – PSV • Patient triggered, pressure targeted, flow cycled mode of ventilation • Requires a patient with a consistent spontaneous respiratory pattern • The ventilator provides a constant pressure during inspiration once it senses that the patient has made an inspiratory effort

32. Modes of Ventilation • Spontaneous Modes • PSV

33. Modes of Ventilation • Spontaneous Modes • PSV • Indications • Spontaneously breathing patients who require additional ventilatory support to help overcome • WOB, CL, Raw • Respiratory muscle weakness • Weaning (either by itself or in combination with SIMV)

34. Modes of Ventilation • Spontaneous Modes • PSV • Advantages • Full to partial ventilatory support • Augments the patients spontaneous VT • Decreases the patient’s spontaneous respiratory rate • Decreases patient WOB by overcoming the resistance of the artificial airway, vent circuit and demand valves • Allows patient control of TI, I, f and VT

35. Modes of Ventilation • Spontaneous Modes • PSV • Advantages • Set peak pressure • Prevents respiratory muscle atrophy • Facilitates weaning • Improves patient comfort and reduces need for sedation • May be applied in any mode that allows spontaneous breathing, e.g., VC-SIMV, PC-SIMV

36. Modes of Ventilation • Spontaneous Modes • PSV • Disadvantages • Requires consistent spontaneous ventilation • Patients in stand-alone mode should have back-up ventilation • VT variable and dependant on lung characteristics and synchrony • Low exhaled E • Fatigue and tachypnea if PS level is set too low

37. Modes of Ventilation • Spontaneous Modes • Flow Cycling During PSV • Flow cycling occurs when the ventilator detects a decreasing flow, which represents the end of inspiration • This point is a percentage of peak flow measured during inspiration • PB 7200 – 5 L/min • Bear 1000 – 25% of peak flow • Servo 300 – 5% of peak flow • No single flow-cycle percent is right for all patients

38. Modes of Ventilation • Spontaneous Modes • Flow Cycling During PSV • Effect of changes in termination flow • A: Low percentage (17%) • B: High percentage (57%) • Newer ventilators have an adjustable flow cycle criterion, which can range from 1% - 80%, depending on the ventilator

39. Modes of Ventilation • Spontaneous Modes • PSV during SIMV • Spontaneous breaths during SIMV can be supported with PSV (reduces the WOB) PCV – SIMV with PSV

40. Modes of Ventilation • Spontaneous Modes • PSV during SIMV • Spontaneous breaths during SIMV can be supported with PSV VC – SIMV with PSV

41. Modes of Ventilation • Spontaneous Modes • PSV NOTE: During pressure support ventilation (PSV), inspiration ends if the inspiratory time (TI) exceeds a certain value. This most often occurs with a leak in the circuit. For example, a deflated cuff causes a large leak. The flow through the circuit might never drop to the flow cycle criterion required by the ventilator. Therefore, inspiratory flow, if not stopped would continue indefinitely. For this reason, all ventilators that provide pressure support also have a maximum inspiratory time.

42. Modes of Ventilation • Spontaneous Modes • PSV • Setting the Level of Pressure Support • Goal: To provide ventilatory support • Spontaneous tidal volume is 10 – 12 mL/Kg of ideal body weight • Maintain spontaneous respiratory rate <25/min • Goal: To overcome system resistance (ET Tube, circuit, etc.) in the spontaneous or IMV/SIMV mode • Set pressure at (PIP – Pplateau) achieved in a volume breath or at 5 – 10 cm H2O

43. Modes of Ventilation • Spontaneous Modes • PSV Exercise: Using the PIP and thePPlateaufrom the pressure waveform below, recommend a pressure support setting for this patient (patient is in VC-SIMV mode) 35 25 Answer: 10 cm H2O

44. Modes of Ventilation • Spontaneous Modes • PSV - The results of your work 35 cm H2O 10 cm H2O

45. Modes of Ventilation • Spontaneous Modes • Bilevel Positive Airway Pressure (BiPAP) • An offshoot of PEEP/CPAP therapy • Most often used in NPPV • AKA • Bilevel CPAP • Bilevel PEEP • Bilevel Pressure Support • Bilevel Pressure Assist • Bilevel Positive Pressure • Bilevel Airway Pressure

46. Modes of Ventilation • Spontaneous Modes • Bilevel Positive Airway Pressure (BiPAP) • Commonly patient triggered but can be time triggered, pressure targeted, flow or time cycled • The operator sets two pressure levels • IPAP (Inspiratory Positive Airway Pressure) • IPAP is always set higher than EPAP • Augments VT and improves ventilation • EPAP (Expiratory Positive Airway Pressure) • Prevents early airway closure and alveolar collapse at the end of expiration by increasing (and normalizing) the functional residual capacity (FRC) of the lungs • Facilitates better oxygenation

47. Modes of Ventilation • Spontaneous Modes • Bilevel Positive Airway Pressure (BiPAP) • The operator sets two pressure levels • IPAP • EPAP NOTE: The pressure difference between IPAP and EPAP is pressure support

48. Modes of Ventilation • Questions?