1. VENTILATION MECHANICAL Phunsup Wongsurakiat, MD, FCCP
Division of Respiratory Disease and TB
Department of Medicine, Siriraj Hospital

3. Mechanical Ventilation
Invasive (intubation)
Non-invasive (other interface such as face mask):
- negative pressure
- positive pressure

12. DISTENDING PRESSURES
Plat P - Base P (PEEP) = pressure to distend resp system
(lung + chest wall)
Plat P = peak alveolar pressure
Transpulmonary pressure = Plat P – Pleural pressure

13. Influence of chest wall stiffness
35 cm H2O
35 cm H2O
5 cm H2O
10 cm H2O
30 cm H2O
25 cm H2O

14. FLOW Resistance (R)
Peak P - PlatP = pressure for flow
R = Flow/(PeakP - Plat P)

15. Physiology of Respiration
O2 consumption (VO2) ≈ 250 mL/ min
CO2 production (VCO2) ≈ mL/ min
Cardiac output (CO) ≈ 5 L/min
Minute ventilation = RR X VT ≈ L/min
VT ≈ mL / kg
RR ≈ bpm
PaCO2 = mmHg
pH =

16. Physiology of Respiration
PAO2 = PIO2 – PaCO2 / R
[PIO2 = FIO2 x (barometric pressure – 47)]
PaCO2 = k x VCO2 / VA

17. Mechanical Ventilation
Variables
Mode
Objectives
Clinical settings
Complications

19. Mechanical Ventilation Variables
Tidal volume
Rate
Total time (inversely related to rate):
- inspiratory time (adjustable)
- expiratory time (total time - inspiratory time)
Flow (tidal volume / inspiratory time)
Minute ventilation

21. Mechanical Ventilation Variables
Trigger sensitivity
FiO2
Pressure:
- peak pressure
- plateau pressure
Compliance

25. Mechanical Ventilation Modes
Limit
variables rise no higher than some preset value and increase to preset value before inspiration ends = limit variable
Cycle
Variable that terminate inspiration = cycle variable

26. Breath characteristics Gas Delivery

27. Mechanical Ventilation
Bird
Limit: pressure, flow
Cycle: pressure
Bennett 7200 (volume assist-control)
Limit: volume, flow
Cycle: volume
Pressure support
Limit: pressure
Cycle: flow

28. Mechanical Ventilation Modes
Volume-targeted: Pre-set tidal volume
Pressure-targeted: Pre-set inspiratory pressure
Mandatory breaths: Breaths that the ventilator delivers to the patient at a set frequency, volume/pressure, flow/time
Spontaneous breaths: Patient initiated breath

29. Mechanical Ventilation Modes
Volume-targeted
Controlled mechanical ventilation (CMV)
Assist/control (A/C) mechanical ventilation
Synchronized intermittent mandatory ventilation (SIMV)

30. Modes of Ventilation (CMV) Background:
Full preset tidal volume at a fixed preset rate
Rate and minute ventilation cannot  by patient effort
Trigger sensitivity is locked out, need sedated or paralyzed

31. Modes of Ventilation (CMV)
Advantages:
Near complete resting of ventilatory muscles
Respiratory muscle rest, secured minute ventilation
Disadvantages:
“Stack" breaths (air trapping) and develop barotrauma
“AutoPEEP" with barotrauma or hypotension
Need sedated or paralyzed
Respiratory muscle atrophy
Uses:
apnea, little breathing effort, unstable

32. Modes of Ventilation (Assist/Control)
Background:
Full preset tidal volume at a minimum preset rate
Additional full tidal volumes given if the patient initiates extra breaths

33. Modes of Ventilation (Assist/Control) Advantages:
Near complete resting of ventilatory muscles
Comfortable, respiratory muscle rest, secured minute ventilation
Effectively used in awake, sedated, or paralyzed patients
Disadvantages:
Hyperventilate and become alkalotic
“Stack" breaths (air trapping) and develop barotrauma
“AutoPEEP" with barotrauma or hypotension
Uses:
apnea, little breathing effort, unstable

34. (SIMV + Pressure support)
Modes of Ventilation
(SIMV + Pressure support)
Background:
Preset tidal volume at a fixed preset rate
Ventilator waits a predetermined trigger period
Patient can take additional breaths but tidal volume of these extra breaths is dependent on the patient's inspiratory effort

35. (SIMV + Pressure support)
Modes of Ventilation
(SIMV + Pressure support)
Advantages:
Improved venous return: intermittent negative pressure (spontaneous) breaths
More comfortable: more control over their ventilatory pattern and minute ventilation
Disadvantages:
Can result in chronic respiratory fatigue if set rate is too low;
Uses:
Weaning, bronchopleural fistula

38. Mechanical Ventilation Modes
Pressure-targeted
Pressure support ventilation (PSV)
Pressure-control ventilation (PCV)
Pressure-targeted assist-control (A/C-PC)
Pressure-targeted SIMV (SIMV-PC)

39. Pressure support Ventilation
Background:
Patient triggers, a preset pressure support is delivered
Terminate inspiration by flow rate
Tidal volume and minute ventilation are dependent on the preset pressure
and patient’s lung-thorax compliance

40. Pressure support Ventilation
Advantages:
Avoids patient-ventilator asynchrony
More comfortable: full control over ventilatory pattern and minute ventilation
Avoids breath stacking and autoPEEP (especially in patients with COPD)
Disadvantages:
Required patient’s triggering, cannot be used in heavily sedated, paralyzed, or comatose patients
Respiratory muscle fatigue if pressure support is set too low

42. Pressure Control Ventilation
Background:
Ventilator control predetermined pressure in a
fixed predetermined time and rate

43. Pressure Control Ventilation
Advantages:
Pressure and time are controlled
High flow rate
Disadvantages:
Tidal volume variable
Produced autoPEEP if inspiratory time too long
Uncomfortable mode for most patients

44. Pressure-targeted assist-control (A/C-PC)
All breaths machine-delivered at a preset inflation pressure
Patients can  rate by triggering additional machine breaths if desired
Same as assist/control volume targeted mode

45. Pressure-targeted SIMV (SIMV-PC)
Fixed rate of machine-delivered breaths at a preset inflation pressure
Patients can breathe spontaneously between machine-delivered breaths if desired
Same as SIMV volume targeted mode

46. Mechanical Ventilation
Objectives:
Physiology
Comfortable
Least complications

47. Mechanical Ventilation
Usual settings
Minute Ventilation = RR X VT ( L/min)
VT = mL / kg
RR = bpm
PaCO2 = mmHg
pH =

48. Mechanical Ventilation
Triggering: sensitivity of ventilator to patient’s respiratory effort.
Flow or pressure setting that allows ventilator to detect patient’s inspiratory effort
Allows ventilator synchronize with patient’s spontaneous respiratory efforts
Improving patient’s comfort during mechanical ventilation.
Setting: lowest but not self cycling
Less work in flow triggering

49. Mechanical Ventilation
Flow rate:
adjust to patient’s comfort
Usually > 60 L/min
Pressure:
Plateau pressure < 30 cmH2O

50. Positive End Expiratory Pressure (PEEP)
 Functional residual capacity
Move fluid from alveoli into interstitial space
Improve oxygenation

51. PEEP In COPD : To offset auto-PEEP
To improve oxygenation in acute lung injury
To improve oxygenation, preload, afterload in cardiogenic pulmonary edema

52. PEEP Titration Goal : -  PaO2 -  FiO2 (< 0.5)
PEEP Titration
Goal : -  PaO2
-  FiO2 (< 0.5)
- No adverse effect:
cardiac output
lung compliance from overdistension
( plateau pressure)
Obtained baseline respiratory & hemodynamic
Change (PEEP) only , keep other parameter constant
 PEEP 5 cmH2O q 15 – 20 min
Repeat respiratory and hemodynamic data at each new PEEP level

53. PEEP to previous level
 O2 delivery
O2 delivery
SaO2 BP or co
SaO2
No adverse effect
SaO2
Compliance
SaO2
Volume + vasopressor
Adequate
Tidal volume
Indequate
PEEP to previous level
Use current PEEP
 FiO2
PEEP more

54. Contraindication Absolute: none
Relative: unilateral lung disease, bronchopleural fistulae, intracranial pressure, high plateau pressure, pulmonary embolism

55. Ventilator Alarms Setting
High minute ventilation
10-15% > set or target minute volume
Low minute ventilation
10-15% < set or target minute volume
High Vt
10-15% > set or target Vt
Low Vt
10-15% < set or target Vt
High-system pressure
10 cmH20 > average peak airway pressure
Low-system pressure
5-10 cmH20 < average peak airway pressure
Loss of PEEP
3-5 cmH2O < PEEP
O2 analyzer
0.05 </> Fio2

56. Alarms & Troubleshooting
High Peak Inspiratory Pressure:
Secretions
Patient biting ETT
Patient coughing
Changing patient’s clinical status
Low Pressure Alarm or low PEEP alarm:
Disconnect (check all connections)
Apnea

57. Mechanical Ventilation Complications
Disconnection
Malfunction
Patient-ventilator asynchrony
hemodynamic effects:
Barotrauma
Ventilator-induced lung injury
Oxygen toxicity
Infection
- ventilator-associated pneumonia
- sinusitis

58. Mechanical Ventilation Complications
Hemodynamic effects:
Impaired venous return, increased pulmonary vascular resistance   cardiac output
AutoPEEP
Mean lung volume or mean alveolar pressure correlate best with hemodynamic effects

59. AutoPEEP
Exhalation is not complete by the time the next breath is given:
- expiratory airflow obstruction
- high minute ventilation (> l/min)
Alveolar pressure & volume remain increased at end-expiration

63. AutoPEEP Adverse Effect Same effect as externally applied PEEP:
- Hyperinflation
-  cardiac output
Difficult to trigger ventilator → ↑ work of breathing

65. AUTOPEEP
Auscultation: persistent exhalation (specific but not sensitive)
Untriggering
Flow-time graphs
End-expiratory hold

69. Steps for Reducing Dynamic Hyperinflation & AutoPEEP
Eliminate unnecessary ventilation:
Weaning
Minute ventilation
Permissive hypercapnia
Expiratory airflow obstruction:
Rx bronchospasm
Keep airways free of secretions
Maximize expiratory time:
peak inspiratory flow rate to 70 – 100 l/min

71. Mechanical Ventilation Complications
Oxygen toxicity
High FiO2 is potentially injurious
Tissue injury depends on FiO2 and duration of exposure and some diseases/conditions
No evidence that sustained exposure to FiO2 < 0.5 causes tissue injury
Lowest FiO2 with adequate tissue oxygenation
Measurements to keep FiO2 < 0.5

72. Hemoglobin and 02 Transport
280 million hemoglobin/RBC.
Each hemoglobin has 4 polypeptide chains and 4 hemes.
In the center of each heme group is 1 atom of iron that can combine with 1 molecule 02.
Insert fig

73. Oxyhemoglobin Dissociation Curve
Insert fig.16.34

74. Mechanical Ventilation Respiratory Distress
Patient
Ventilator (malfunction)
Patient-ventilator asynchrony
- flow rate
- trigger
- autoPEEP

75. Ventilator-Induced Lung Injury (VILI)
Barotrauma : extraalveolar air, pneumothorax
Diffuse alveolar damage, pulmonary edema

78. Overdistention

79. Overdistention may be regional Even a “normal” VT can create regional overdistention

80. Ventilator Management of ARDS
INITIAL VENTILATOR TIDAL VOLUME AND RATE ADJUSTMENTS
Calculate predicted body weight (PBW)
Male= [height (inches) - 60]
Female= [height (inches) - 60]
Mode: Volume Assist-Control