Mechanical ventilation is a therapeutic method that uses physical devices to assist or replace spontaneous breathing. There are two main types: negative pressure ventilation which applies pressure lower than atmospheric to the chest, and positive pressure ventilation which applies pressure higher than atmospheric to the lungs. Positive pressure ventilation is more commonly used today. It is important to carefully monitor patients on mechanical ventilation to optimize ventilation and prevent lung injury, through monitoring pressures, volumes, oxygen levels and CO2 levels. The goals are to provide adequate gas exchange while applying the lowest possible pressures and volumes to the lungs.

1. MECHANICAL VENTILATION
Dr ANVESH NARIMETI
UNIT 1
INTERNAL MEDICINE

2. • Mechanical ventilation is a therapeutic
method that is used to assist or replace
spontaneous breathing
• Objectives- understand the concept of
negative pressure and positive pressure
ventilation
• Mechanical ventilation is any means in which
physical devices or machines are used to
either assist or replace spotaneous respiration

3. Indications
• Four major indications
a)Need for high levels of inspired oxygen(hypoxic
respiratory failure)
b)Need for assisted ventilation (hypercapnic respiratory
failure or surgical procedures)
c)Protection of airways against aspiration
d)Relief from upper airway obstruction
TYPES
2 types of ventilation
a)Negative pressure ventilation
b)Positive pressure ventilation

4. • a)Negative pressure ventilation-Pressure
lower than atmospheric pressures is applied
to extra thoracic space during the inspiration
• b)Positive pressure ventilation-pressure
higher than atmospheric pressures is applied
to the intra alveolar space during inspiration

6. Negative pressure ventilation
• These are called IRON LUNGS
• Only historic imporatance
• Helped a lot during polio outbreak in 1952

10. Positive pressure ventilation

13. NORMAL LUNG MECHANICS
• VOLUMES –TV,IRV,ERV,RV
• CAPACITIES-IC,FRC(ERV+RV)
• VC=IRV+TV+ERV
• RV+VC=TLC
• DEAD SPACE VOLUME-volume of air in the airways and
lungs that do not participate in gas exchange
a)Anatomic dead space-air in conducting airways not
lined by diffusing membranes
b)Physiologic dead space-sum of anotomic dead space
and volume of air in alveoli which are ventilated and not
perfused

14. Compliance-how volume of a space changes
with pressure changes
MOST IMPORTANT THING IS TO UNDERSTAND
INSPIRATORY AIRWAY PRESSURE P peak and P
plateau
AND TO UNDERSTAND HOW TO USE P peak and
P plateau to monitor AIRWAY RESISTANCE AND
LUNG COMPLIANCE

15. • Measuring airway pressure is an most direct way
to continously monitor lung mechanics
• Ventilation pressure=pressure delivered to
proximal airway
=resistive pressure+elastic pressure
• P peak pressure-maximum pressure in the
proximal airway at the end of inspiration
• P plateue=equlibrium pressure reached if the
expiratory tubing is occluded at the end of
inspiration-it is a surrogate of intra alveolar
pressure

18. • Increase in P peak pressure in absence of an
increase in P plateus= indicates increase in
AIRWAY RESISTANCE
1. Brochospasm
2. Extrinsic airway compression
3. Mucous plugs
4. Excessive aspiration
5. Foreign body aspiration

19. Monitoring compliance
• Compliance = change in volume/change in
pressure
• So increase in plateue pressure indicates
compliance is decreasing
1. Pulmonary edema
2. Pleural effusion
3. Pneumo thorax
4. Et tube in rt main stem bronchus
5. Abdominal distension

21. Normal gas exchange
• Most important is to calculate (A-a)gradient
• It measure how effectively oxygen moves
from the alveoli into pulmonary vasculature
• Normal (A-a)gradient=[age/4]+4
• When there is increase in(A-a)gradient the
possible causes

23. HOW TO MONITOR GAS EXCHANGE
• Pulse oximetry
• Arterial blood gas analysis
• Capnography

24. Pulse oximetry
• It provides a real time measurement of the
percentage of the haemoglobin that is bound
to oxygen in arterial blood

27. Capnography
• Continous measurement of carbondioxide
tension in expired air which can serve as a real
time surrogate marker of carbondioxide
tension in arterial blood

30. • If Paco2-Pet co2= if more than 5
1. Low cardiac output
2. Copd
3. Pulmonary embolism
4. Advanced age

32. NON INVASIVE POSITIVE PRESSURE VENTILATION
NPPV- means to support the failing respiratory function by delivering oxygen
enriched gas under pressure without requiring endotracheal intubation
• It is best used as short term strategy to buy time
• Noninvasive ventilation usually is provided by using a tight-fitting face mask or
nasal mask similar to the masks traditionally used for treatment of sleep apnea.
• Noninvasive ventilation has proved highly effective in patients with respiratory
failure from acute exacerbations of chronic obstructive pulmonary disease and is
most frequently implemented by using bilevel positive airway pressure
ventilation or pressure support ventilation.

34. • The major limitation to its widespread application
has been patient intolerance because the tight-fitting
mask required for NIV can cause both
physical and emotional discomfort
• Benefits of NPPV
1. Avoids trauma secondary to intubation
2. Avoids the need of sedation
3. Ability to communicate
4. Aloows intermittent drinking eating if aspiration
risk is felt low
5. Avoids ventilator associated pneumonia

35. Contraindications to NPPV
1. Cardio pulmonary arrest
2. Haemodynamic instability
3. Fascial trauma and deformity
4. Severe upper gastrointestinal bleed
5. Severe encephalopathy
6. Inability to cooperate and protect airway
7. Inability to clear secretions
8. Upper airway obstructions
9. High risk for aspiration

36. • NPPV has two options
CPAP- Continous Positive Airway Pressure
BPAP- Bilevel Positive Airway Pressure
• In both of these modes, a preset positive
pressure is applied during inspiration and a
lower pressure is applied during expiration at
the mask

41. Other indications of NPPV
• Obstructive sleep apnoea
• Neuro muscular disease
• Fascilitating weaning from ventilator
• In immunocompramised states

42. VENTILATOR MODES
• We should know three variables that
determine and define a ventilator
mode
• We should know most commonly
used ventilator modes

43. 3 Variables
1. Trigger variable
2. Control variable
3. Cycling variable

44. Trigger variable
• It defines how the ventilator determines when to intiate a
machine driven breath
• Common options
1. Time triggered(no spontaneous breathing)
2. Pressure triggered(spontaneous breathing)
3. Flow triggered
•. un common options
1. Volume,chest wall electrical impedence and motion

45. Control variable
• It defines what aspect of inspiration is the
primary variable controlled by the ventilator
during inspiration
• Options
1. Presssure controlled
2. Flow controlled

46. Cycling variable
• It defines what signals the ventilator to
terminate inspiration
• Options
1. Volume cycled
2. Flow cycle(when 25%of peak flow decreases)
3. Time cycle

48. • Compliance=change in volume/change in
pressure
• Volume targetted ventilation
high compliance=low airway pressures
low compliance=high airway pressures
• Pressure targetted ventilation
high compliance=increase volume
low compliance = low volume

50. BASIC VENTILATOR MODES
• ASSIST CONTROL(AC)
• SYNCHRONISED INTERMITTENT MANDATORY
VENTILATION(SIMV)
• PRESSURE CONTROL VENTILATION(PCV)
• PRESSURE SUPPORT VENTILATION(PSV)

51. ASSIST CONTROL(AC)

54. SYNCHRONISED INTERMITTENT MANDATORY VENTILATION(SIMV)

58. PRESSURE CONTROL VENTILATION

61. PRESSURE SUPPORT VENTILATION(PSV

64. DUAL CONTROLLED MODES
• Uses instantaneous feed back to control the
aspects of lung volume and airway pressure
simultaneously
• PRVC-Pressure Regulated Volume Control
• Volume support
• Volume Assured Pressure Support

65. VENTILATOR OPTIONS
• We should understand basic options used during
mechanical ventilation
• OPTIONS
1. MODE
2. FiO2
3. TIDAL VOLUME
4. RESPIRATORY RATE
5. PEEP
6. PRESSURE SUPPORT
7. FLOW SHAPE/CONTOUR
8. I:E RATIO

66. FiO2
• Applicable to all modes
• Should be titrated to lowest possible level at the same
time maintaining adequate oxygenatiom
• First set at 100% and then titrate down over several
hours indicated by pulse oximeter or serial ABG
• FiO2 >60% is toxic to lungs
• If adequate oxygenation requires FiO2 >60% then
additional strategies like
1. Increasing PEEP
2. Recruitment manuever
3. Trial of another mode

67. TIDAL VOLUME
• Mostly applicable to volume cycled
modes(SIMV,AC)
• WEIGHT BASED
1. Healthy lungs-10ml/kg
2. COPD -8ml/kg
3. ARDS -6ml/kg
•. High tidal volume-lower Paco2,high ph,high
Pplateue
•. Low tidal volume-high Paco2,low ph,low P
plateue

68. RESPIRATORY RATE
• For time triggered mode and SIMV
• TYPICAL-10-20 breaths/min
• High respiratory rate- low paco2,high ph,high
risk of auto peep
• Low respiratory rate- high paco2,low ph,low
risk of auto peep

69. POSITIVE END EXPIRATORY PRESSURE(PEEP)
• Continous positive pressure present through out all phase of
ventilation
• Used in almost all pateints
• Physiological effects-
1. Increase alveolar recruitment,and alveolar surface area– so
improves oxygenation
2. Decrease preload and LV after load-increase cardiac out put
in congestive cardiac failure
3. Increase right ventricular load- increase right to left shunt
•. SET PEEP TO LOWEST POSSIBLE VALUE TO ALLOW FiO2 <60%
WITH MINIMUM OF 5 CM OF H2O

71. Pressure support
• Amount of additional positive pressure
beyond PEEP that is provided during the
inspiration
• An integral parameter used in pressure
support ventilation and BPAP, SIMV

72. FLOW SHAPE/CONTOUR
• It describes the pattern of air flow during
inspiration
• Set by clinician in volume targetted mode and
always decelerating shape in pressure
targetted as a consequence of lung mechanics

73. I:E RATIO
• Ratio between amount of time spent in
inspiration and amount of time spent in
expiration

76. VENTILATOR ASSOCIATED LUNG INJURY
• It can occur in any lungs but most commonly in
ARDS/ALI
• FOUR TYPES
1. BARO TRAUMA
2. VOLUM TRAUMA
3. BIO TRAUMA
4. CYCLIC ATELECTASIS

77. PROTECTIVE LUNG VENTILATION
• Target tidal volume close to 6 mL/kg of ideal
body weight.
• Prevent plateau pressure over 30 cmH2O.
• Lowest possible fraction of inspired oxygen
(FIO2) to keep SaO2 90%.
• Adjust the PEEP to maintain alveolar patency
while preventing overdistention and
closure/reopening

78. General support during mechanical ventilation
• Sedation and analgesia
• DVT propylaxis
• Bed sores prevention
• Ulcer prophylaxis
• Nutrition
• Delayed gastric emptying is common responds
to promotility agents such as metoclopramide

79. Tracheostomy
• It is generally agreed that if a
patient is in need of MV for more
than 10–14 days, a tracheostomy is
indicated and should be planned
under optimal conditions

80. THANK YOU