This document provides an overview of basic concepts and applications of mechanical ventilation. It discusses various ventilation modes including controlled, assisted, assist-control, IMV, and SIMV modes. It also covers settings such as tidal volume, respiratory rate, I:E ratio, and FIO2. Key aspects of setting up and monitoring mechanical ventilation are summarized, including how to initially set parameters based on patient size and desired minute ventilation. Factors that affect oxygenation and ventilation are outlined. Waveforms and pressure-volume loops are presented to illustrate lung mechanics under different conditions. The importance of monitoring airway pressures and compliance is emphasized to optimize ventilation.

1. Basic Concepts & Application of
Mechanical Ventilation
2012. 06. 04
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2. • Mode of ventilation
• Setting & Monitoring
Contents

3. Modes
• Control Modes:
– every breath is fully supported by the ventilator
– in classic control modes, patients were unable to
breathe except at the controlled set rate
– in newer control modes, machines may act in
assist-control, with a minimum set rate and all
triggered breaths above that rate also fully
supported.

4. Controlled Mode
(Volume-Targeted Ventilation)
Preset VT
Volume Cycling
Dependent on
CL & Raw
Time (sec)
Flow
(L/m)
Pressure
(cm H2O)
Volume
(mL)
Preset Peak Flow

5. Assisted Mode
(Volume-Targeted Ventilation)
Time (sec)
Flow
(L/m)
Pressure
(cm H2O)
Volume
(mL)
Preset VT
Volume Cycling

6. Assist-Control Mode
(Volume-Targeted Ventilation)

7. • IMV Modes: intermittent mandatory
ventilation modes - breaths “above” set
rate not supported
• SIMV: vent synchronizes IMV “breath”
with patient’s effort
Modes

8. IMV
(Volume-Targeted Ventilation)

9. SIMV
(Volume-Targeted Ventilation)
Spontaneous Breaths
Flow
(L/m)
Pressure
(cm H2O)
Volume
(mL)

10. Whenever a breath is supported by the
ventilator, regardless of the mode, the
limit of the support is determined by a
preset pressure OR volume.
– Volume Limited: preset tidal volume
– Pressure Limited: preset PIP or PAP
Modes

11. Pressure vs. Volume
• Pressure Limited
– tidal volume by change
suddenly as patient’s
compliance changes
– this can lead to
hypoventilation or
overexpansion of the
lung
– if ETT is obstructed
acutely, delivered tidal
volume will decrease
• Volume Limited
– no limit per se on PIP
(usually vent will have
upper pressure limit)
– square wave(constant)
flow pattern results in
higher PIP for same
tidal volume as
compared to Pressure
modes

12. Pressure Support Ventilation
• Pressure augmented breathing
• Allows patient to determine the inflation
volume and respiratory cycle duration
• Uses: augment inflation during spontaneous
breathing or overcome resistance of breathing
through ventilator circuits (during weaning)
• Popular an a non-invasive mode of ventilation
via nasal or face masks

13. PSV
Time (sec)
Flow
(L/m)
Pressure
(cm H2O)
Volume
(mL)
Flow Cycling
Set PS
level

14. Continuous Positive Airway Pressure
• Spontaneous breathing
• Patient does not need to generate negative
pressure to receive inhaled gas
• CPAP replaced spontaneous PEEP
• Use: Non-intubated patients (OSA, COPD)

15. Positive End-Expiratory Pressure
• Alveolar pressure at end-expiration is above
atmospheric pressure : PEEP
• Extrinsic PEEP
• Auto PEEP

16. Positive End-Expiratory Pressure
• CLINICAL USES:
– Reduce toxic levels of FiO2 (ARDS)
– Low-volume ventilation
– Obstructive lung disease (Extrinsic=Occult PEEP)

17. • Mode of ventilation
• Setting & Monitoring
Contents

18. Setting Up the Ventilator
• Mode
• Triggering sensitivity
• Tidal volume
• Respiratory rate
• Flow rate and I:E ratio
• FIO2

19. Initial Setting
• Pressure Limited
– FiO2
– Rate
– I-time or I:E ratio
– PEEP
– PIP or PAP
• Volume Limited
– FiO2
– Rate
– I-time or I:E ratio
– PEEP
– Tidal Volume

20. • Minute ventilation (VE)
– Men VE = 4 X BSA
– Women VE = 3.5 X BSA
• Tidal volume (VT)
– Min 4mL/kg IBW ~ Max 12mL/kg IBW
– Keep alveolar pressure < 30 ~ 35cmH2O
• Respiratory frequency (f)
– f = VE / VT
Initial Setting (Volume Ventilation)

21. • Pressure Control Ventilation (PCV)
– Set pressure to achieve a target VT
– Set frequency to achieve same VE (f = VE / VT)
• Pressure Support Ventilation (PSV)
– Set pressure at 5~10cmH2O to overcome Rsys
– Set pressure to achieve a target VT for ventilatory support
Initial Setting (Pressure Ventilation)

22. Trigger
• How does the vent know when to give a breath?
- “Trigger”
– patient effort
– elapsed time
• The patient’s effort can be “sensed” as a
change in pressure or a change in flow (in the
circuit)

23. Triggering Sensitivity
• Pressure
– -1 to -2 cm H2O
• Flow
– 1 to 10L/min below the base flow
– less WOB
– faster response time than pressure triggering

24. Pattern of Flow Waveform

25. Change of Flow Waveform during VCV
Constant  Descending Same Volume, Increased TI

26. • Flow is greatest at beginning of inspiration
• TI will be longer
• Mean Paw is higher
• Peak pressure is lower
• Consequences: increase oxygenation, reduce dead space,
improve the distribution of gas in the lungs
• Occurs naturally in pressure ventilation
Advantage of Descending Flow

27. Flow Rate & I:E Ratio
• Conventional situation
– I:E ratio= 1:2
– Flow rate; 60 L/min
• Airway obstruction
– I:E ratio = 1:3
– Increase flow rate
• Hypoxemia
– Increase inspiratory time

28. Too short Te will not allow
to deliver max. possible
Vt at given P
 will induce PEEPi
 increases the risk for
hemodynamic instability
Too short Ti will
reduce delivered Vt
 unneccessary high
PIP will be applied
 unnecessary high
intrathoracic pressures

29. Change in Termination of Flow during PSV
Cycle off

30. Adjustment of Rising Time

31. Effect of Rise Time during PSV
Faster Rise Time Slow Rise Time
▪ Too fast
 pressure overshoot
 dyssynchrony

32. Respiratory Rate
• Btw 10 to 20 breath/min
• A/C mode
– 4 breaths lower than spontaneous
rate
• SIMV mode
– At least 80% of pt’s MV

33. FiO2 and O2 toxicity
• FiO2
– As low as possible without hypoxia
• O2 toxicity
– tracheobronchitis - exposure of up to 12-24hours with 100%
oxygen
– increased alveolar permeability - 48hr
– ARDS - 60hr
– No one knows for sure what the threshold level for FIO2 or
duration
• HYPOXIA is more dangerous than oxygen toxicity

34. Desired FiO2
Desired FiO2 =
PaO2 (known)
PaO2 (desired) X FiO2(known)
• Baseline ABGA is available
• Baseline ABGA is not available
– Start with high initial FiO2 setting (0.50 to 1.0)
– Reduce this as quickly as possible

35. 100% Oxygen
• Continuous use of 100% O2 is not recommended
– Result in absorption atelectasis
– May cause oxygen toxicity
– 100% O2 should not be withheld if the patient is seriously ill
• Brief use of 100% O2
– Before and after suctioning
– During bronchoscopy
– During any procedure that might be risky for the patient

36. • To affect
oxygenation,
adjust:
– FiO2
– PEEP
– I time
– PIP
• To affect
ventilation,
adjust:
– Respiratory Rate
– Tidal Volume
MAP MV
Adjustments

37. • To affect
oxygenation,
adjust:
– FiO2
– PEEP
– I time
– PIP
MAP
Adjustments

38. Factors that affect on PaCO2 during MV

39. Factors that affect on PaCO2 during MV
Inspiratory Time ↑

40. Factors that affect on PaCO2 during MV
Pressure-controlled ventilation
TI ↑  VT ↑till plateau

41. Airway Pressure during VCV
• End-inspiratory breath hold
: Pplateau
• End-expiratory breath hold
: Auto-PEEP

42. Waveforms
A : Normal
B : ↓ compliance
C : ↑ compliance
Volume-controlled ventilation

43. A: Normal
B: Compliance halved
C: Resistance doubled
A B C
Waveforms
Pressure-controlled ventilation

44. Pressure-Volume (P-V) loop

45. P-V loop according to Compliance
Pressure-controlled ventilation

46. P-V loop according to Compliance
Volume-controlled ventilation

47. Normal Flow-Volume (F-V) loop
Volume-controlled ventilation

48. Abnormal F-V loop
Airflow limitation
ex) COPD

49. Abnormal F-V loop
Air leaking

50. Proximal Airway Pressures
1. Peak Pressure (Pk)
Function of Inflation volume, recoil force of lungs and chest
wall, airway resistance
2. Plateau Pressure (Pl)
Occlude expiratory tubing at end-inspiration
Function of elastance alone
Monitoring Lung Mechanics

51. Proximal Airway Pressure

52. Pk increased Pl unchanged:
Tracheal tube obstruction
Airway obstruction from secretions
Acute bronchospasm
Rx: Suctioning and Bronchodilators
Use of Airway Pressure

53. Pk and Pl are both increased:
Pneumothorax
Lobar atelectasis
Acute pulmonary edema
Worsening pneumonia
ARDS
COPD with tachypnea and Auto-PEEP
Increased abdominal pressure
Asynchronous breathing
Use of Airway Pressure

54. Decreased Pk:
System air leak: Tubing disconnection, cuff leak
Rx: Manual inflation, listen for leak
Use of Airway Pressure

55. Volume
Pressure
D V
D P
C =
D V
D P
Compliance
C stat =
Pplat - PEEP
tidal volume

56. Static Compliance (Cstat):
Distensibility of Lungs and Chest wall
Cstat = Vt/Pl
Normal C stat: 50-80 ml/cm of water
Provides objective measure of severity of illness in a
pulmonary disorder
Dynamic Compliance:
Cdyn: Vt/Pk
*Subtract PEEP from Pl or Pk for compliance
measurement
Use Exhaled tidal volume for calculations
Compliance

57. 1. Increased
Ppk-Pplat
2. Low and
prolonged
expiratory
flow
1. Elevated
Pplat-PEEP
2. Normal
expiratory
flow
Resistance ↑vs Compliance ↓

58. Take Home Message
1. Mode :
- pressure-limited vs volume-limited
- phase variables ; trigger, limit, cycle
2. Setting :
- to improve oxygenation ; mean airway pressure
- to improve ventilation ; minute ventilation
3. Monitoring :
- plateau pressure / static compliance / elastance
- peak pressure / dynamic compliance / + resistance

59. Thank you for your attention !