All about basics of mechanical ventilation. Graphs ,scalars and loops discussed in detail.

3. Indications
 Acute ventilatory failure
 Impending ventilatory failure
 Severe hypoxemia
 Prophylactic ventilatory suppport

4. Goals of ventilation
 Improving gas exchange
 Relieve respiratory distress
 Improving pulmonary mechanics
 Permit airway healing
 Avoid complications

5. Initial mode
Ventilator mode
Full support
Full WOB done
by ventilator
Partial support
Mode that
performs less
than total WOB

6. Minute ventilation
 For men MV = 4 × BSA (IBW/Height in m2)
 For women MV = 3.5 × BSA
 Increase by 9% for every 10 C above 370 C
 20% for metabolic acidosis
 Decrease MV by 9% for every 10 C below 370 C

7. IBW
 For Female, IBW = 45.5 + 2.3 (Height in Inches-50)
 For Male, IBW = 50 + 2.3 (Height in Inches-50)

8. Tidal volume
 6 to 8 ml/kg of IBW.
 Required tidal volume increases linearly with body
weight upto the IBW.
 Pplateau should be maintained less than 30 cm-H2O.

9. Respiratory rate
 RR = MV/TV
 10 to 12/min.
 Target RR × Target PaCO2= current RR × current PaCO2
 Target RR = current RR × current PaCO2/Target PaCO2

10. Tidal volume & RR
• TV of 6 to 8ml/kg
• RR of 12 to 18/min
Normal
• TV of 8 to 10 ml/kg
• RR of 8 to 10/min
COPD
• TV of 4 to 6 ml/kg
• Higher RR
Restrictive

11. FiO2
 Least possible FiO2 to maintain SpO2 of > 94%
 FiO2 > 50% ---Free radicals production exceeds the
scavenging effects (superoxide dismutase by type II
epithelial cells).
 Increasing FiO2 will not have much improving
oxygenation in patients with shunt or diffusion defect.

12. Time constant
 Time constant = C × R
 One time constant = 63%
 Two time constant = 86%
 Three time constant = 95%
 Four time constant = 98%

13. Compliance & Airway Resistance
 Cdyn = VT /Ppeak- PEEP
 Normal 100 ml/cmH2O
 On PPV: 50 ml/cmH2O
 Cstat = VT/Pplateau- PEEP
 Raw= Pressure/flow
 Normal: 0.5-2 cmH2O/liter/Second

14. TI & TE
 I:E = 1:2 to 1:3
 TCT = TI + TE
 Example: RR 12/min & TI of 2 sec.
 TCT = 5 sec; TE of 3 sec.
 I:E = 2:3 = 1:1.5

15. Flow pattern

16. Flow
 Flow must be set to meet the patient’s demand.
 Flow should be higher at the beginning of inspiration.
 In COPD, keep higher flow thereby shorten the TI .

17. Flow
 Flow = VT/TI .
 If TV is 500 ml (0.5 l) & TI is 1 sec, then flow is 0.5
l/sec or 30 l/min
 In Galileo ventilator flow can not be set. We can set
only the TV & TI.
 Flow pattern can be set in VCV & in PCV it is
descending ramp pattern as default.

18. PEEP
 PEEP prevents collapse of the alveoli at the end of
expiration.
 Optimal PEEP should be set according to the patient’s
requirement.
 PEEP can not open up the alveoli rather it will maintain the
patency of the already opened alveoli.
 Recruitment should be done to open up the collapsed
alveoli.

19. PEEP
 PEEP increases FRC.
 PEEP decreases the required FiO2.
 High PEEP in a patient with normal lung compliance
can lead to deterioration in hemodynamics.

20. Pressure support
 PS is used to augment the patient’s breathing effort by
reducing the airflow resistance.
 Airflow resistance can be caused by artificial airway,
circuit, secretions.
 Initial PS = Ppeak - Pplateau
 Titrate PS to TV of 6 – 8 ml/kg.

21. Alarm settings
 High inspiratory pressure alarm
 Apnea alarm
 Low minute volume alarm
 Low tidal volume alarm
 High RR alarm
 Low & high FiO2 alarm

23. Flow waveforms

24. Pressure waveforms

25. Flow time scalar

26. Volume time scalar

27. Pressure time scalar

28. Flow time scalar

29. Pressure time scalar

30. VCV

31. Assisted VCV

32. SIMV

33. PSV

34. Leak

35. Active exhalation

36. Inadequate flow

37. Auto PEEP

38. Patient ventilator asynchrony

40. Ventilation mode
Ventilation mode is defined as specific combination of
breathing pattern, control type and operational
algorithms.
Chatburn, 2007

41. Chatburn’s Classification of modes
 Breathing pattern
 Control variable
 Volume
 Pressure
 Breath sequence
 CMV
 IMV
 CSV

42. Chatburn’s Classification of modes
…..continued
 Targeting scheme
 Set point
 Dual
 Servo
 Adaptive
 Optimal
 Intelligent

43. Phases of respiration
Change from
expiration to
inspiration
Inspiration
Change from
inspiration to
expiration
Expiration

44. Phase variables
 Triggering variable
 Control Variable
 Cycling
 Baseline variable

45. Trigger variable
Trigger
Time
Pressure
Flow

46. Trigger variable
 Time trigger: time is the trigger for mandatory breaths
 Pressure trigger: ventilator senses the generation of
negative pressure by the patient and support his
breath with set PS
 Flow trigger: Continuous & constant base flow during
later part of exhalation

47. Flow time scalar

48. Flow trigger

49. Control variable
 It is a variable with which ventilator achieves the
inspiration.
 Pressure, volume, time & flow.
 Common are pressure & volume.
 Pressure control:
 Pressure waveform & set pressure is constant. Volume & flow
change
 Volume control:
 volume waveform & set volume is constant. Pressure changes.

50. Cycling variable
Time
Mandatory
Flow
Spontaneous

51. Cycling variable

52. Baseline variable
 TE starts from beginning of expiration to start of
inspiration.
 Variable that is controlled during expiration.
 PEEP

53. Modes of ventilation
Mode Pressure
control
Volume
control
Time
trigger
Flow/
Pressure
trigger
Time
cycled
Flow
cycled
CMV × × ×
CMV
(A/C)
× × × ×
P-CMV × × ×
P-CMV
(A/C)
× × × ×

54. Modes of ventilation
Mode Pressure
control
Volume
control
Time
trigger
Flow/
Pressure
trigger
Time
cycled
Flow
cycled
SIMV (PS) × × × × ×
P-SIMV × × × × ×
SPONT (PS) × ×
APV
cmv
× × × × ×
APV
simv
× × × × × ×

55. Control settings
Pcontrol
• Pressure to be applied above PEEP
during inspiration (mandatory)
Psupport
• Pressure to be applied above PEEP
during inspiration (spontaneous)
Flow
pattern
• Flow pattern for gas delivery

56. Control settings
Flow trigger
• Continuous & constant base flow
during later part of exhalation
Pressure
trigger
• Pressure drop below PEEP to begin a
patient-initiated breath
Pramp
• Time required for the inspiratory
pressure to reach the target

57. Control settings
ETS
• The % of peak inspiratory flow at
which ventilator cycles for
Spontaneous breaths
Pause
• % of total breath cycle time

58. SIMV
 Partial ventilatory support mode.
 Each SIMV interval includes mandatory time (Tmand)
and spontaneous time (Tspont) portions.
 During Tmand ventilator waits for the patient to trigger
a breath and if so it delivers a mandatory breath.

59. SIMV
 If patient does not trigger a breath, then ventilator
delivers a mandatory breath.
 During Tspont, patient can take any number of
spontaneous breaths.

60. Pressure support mode (SPONT)
 PS is used to augment the patient’s breathing effort by
reducing the airflow resistance.
 Airflow resistance can be caused by artificial airway,
circuit, secretions.
 Apnea backup should be enabled when using this
mode.
 It is a patient triggered, pressure targeted, flow cycled
breath.

61. Adaptive pressure modes
 Vtarget will be achieved with lowest possible pressure
depending upon the lung characteristics.
 During short term post-operative ventilation, the
delivered volume remains constant despite rapid
changes in breathing activity.
 Ventilator assesses the V/P response.
 It uses V/P to calculate the lowest inspiratory pressure
to achieve the Vtarget.

62. Adaptive pressure modes
 The minimal pressure delivered is 5 cm-H2O above the
PEEP.
 Adaptive controller compares the measured VT &
Vtarget.
 If measured VT = Vtarget then ventilator maintains the
inspiratory pressure.
 If not so, inspiratory pressure gradually adjusted by
upto 2 cmH2O per breath to attain the target level.

63. Adaptive pressure modes
 High pressure alarm limit setting should be atleast 10
cmH2O above the Ppeak.
 Blue band 10 cmH2O below the high-pressure limit.
 Inspiratory pressure range = (PEEP + 5 cmH2O) to
(High pressure alarm limit – 10 cmH2O)
 APV-CMV & APV-SIMV modes.

64. Adaptive support ventilation
 ASV maintains an operator preset, minimum minute
ventilation independent of patient’s activity.
 Target breathing is calculated based on Otis’ equation.
 With least work of breathing & with least possible
ventilator applied pressure.

65. Adaptive support ventilation
 Advantages:
 Guide the patient using favorable breathing pattern
 Avoid rapid shallow breathing
 Avoids excessive dead space ventilation
 Avoids breath stacking
 Maintains a preset minimum minute ventilation
 Fully ventilate the patient in apnea or low respiratory drive
 Without exceeding Pplateau of 10 cmH2O below the upper
pressure limit

66. Adaptive support ventilation
 User should set three important parameters:
 High pressure limit
 IBW
 % of minute ventilation

67. ASV
 Dead space = 2.2ml/kg of IBW
 Add 10% of body weight if using HME
 Longer than conventional catheter mount requires
compensation
 Shorter ETT, TT have minor effects.

68. ASV – lung protective rules strategy
 High VT limit:
 High pressure limit
 IBW ( 22ml/kg)
 Low VT limit:
 Atleast twice the dead space
 4.4 ml/Kg
 High rate limit:
 fmax = target MV/minimum VT
 Minimum TI = 1 × RCexp
 Minimum TE = 2 × RCexp

69. ASV – optimal breathing pattern
 Optimal breathing pattern is identical to the one a
totally unsupported patient would choose naturally.
 ASV calculates the optimal RR based on %MV, IBW,
RCexp.
 Once optimal RR is determined then optimal VT will
be determined.

70. ASV
 Initial breaths:
 ASV employs SIMV mode initially.
 Three initial breaths are delivered.
 ASV compares actual & target VT and actual & target RR
 Mandatory breaths are pressure preset, time cycled;
spontaneous breaths are pressure supported & flow
cycled.

71. Dynamic adjustment of breath
pattern
 Optimal breath pattern is revised with each breath
according to the measurement of RCexp.
 Otis’ equation is applied & new target breathing
pattern is calculated when respiratory system
mechanics change.

72. Thank you