seminar on MV

1. MECHANICAL
VENTILATION
Dr Mohammed Hussein
(R1)
MICU,
October 6 2023
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2. Outline
• Introduction
• Types of Mechanical Ventilation
• Aims of Ventilatory Support
• Indications
• Modes of ventilation
• Ventilator settings
• Monitoring
• Complications of mechanical ventilation
• Weaning
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3. Introduction
• Mechanical Ventilator: A device which assists or replaces spontaneous breathing
,Support ventilatory function and improve oxygenation.
• Inspiratory trigger  predetermined air (O2 + other gases) forced into airways &
alveoli  lungs inflate  ↑ intraalveolar pressure  termination signal – vent
stops delivery  ↓airway pressure  expiration follows passively due to
pressure gradiant.
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4. Several models evolving over time
• Negative pressure ventilation – past
• Positive pressure ventilation – present
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5. Negative pressure ventilators
• Developed in 1929.
• Used widely in 1940 polio
epidemic.
• The patient’s body was
encased in an iron cylinder
and negative pressure was
generated
Emerson JH, Loynes JA. The evolution of iron lungs: respirators of the body-
encasing type. Cambridge:JH Emerson & Company; 1958. Google Scholar
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6. Positive-pressure
ventilators
A positive pressure is applied to the mouth or
mask providing a positive pressure gradient
from mouth to alveoli resulting in inspiration
Invasive ventilation first used at Massachusetts
General Hospital in 1955
This can be applied with a mask (non-invasive)
or with a tracheal tube or tracheostomy
(invasive).
Current ICU ventilators are primarily positive
pressure ventilators
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7. Noninvasive ventilation (NIV)
• Provided with tight fitting face mask or nasal mask
• Candidates for NIV trial: exacerbations of COPD and respiratory acidosis (pH
<7.35)
• Several RCTs – NIV is associated with low failure rate (15-20%) and good
outcome (intubation rate, length of stay in ICU, mortality) in patients with
ventilatory failure characterized by blood pH levels between 7.25 and 7.35
• For pH <7.25: As pH decreases, failure rate increases
• For pH >7.35: NIV is not better than conventional therapy (oxygen therapy &
pharmacotherapy like bronchodilator, steroid, antibiotics)
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8. Indication of NIPPV
Pulmonary edema
Asthma
COPD
Cardiogenic Pulmonary edema
Chest trauma
Assisting in early extubation
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9. 4/19/2024 9

10. Conventional Mechanical Ventilation
• Delivers conditioned gas (warmed, oxygenated, and humidified) via an
endotracheal tube or tracheostomy tube at pressures above atmospheric pressure
• Mechanical ventilators are comprised of four main elements:
1. A source of pressurised gas including a blender for air and O2.
2. An inspiratory valve, expiratory valve and ventilator circuit.
3. A control system, including control panel, monitoring and alarms.
4. A system to sense when the patient is trying to take breath.
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11. 4/19/2024 11

12. Indications
1. Acute Respiratory Failure
• Hypoxic/Hypercapnic
2. Air way protection
• To prevent Aspiration in deeply sedated & unconscious pt
• Maintain patency in obstruction (Asthma, Anaphylaxis, Tumor)
3. Pulmonary vascular disease:
 PTE, Amniotic fluid embolism, tumor emboli
4. Hyperventilation Therapy - raised ICP
5. Hypoventilation:
• Decreased central drive (General anesthesia, Drug overdose), PNS/respiratory muscle
dysfunction
6. Increased ventilatory demand
• E.g:- Severe sepsis, septic shock, severe metabolic acidosis
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13. Aims of Mechanical Ventilation
• Achieve and maintain adequate pulmonary gas exchange (ventilation and
oxygenation)
• Reduce or eliminate excessive work of breathing
• Optimize patient comfort
• Minimize the risk of complications
• Maintain and protect the airway and allow more effective clearance of secretions
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14. Modes
Mode refers to the manner in which ventilator breaths are triggered,
cycled, and limited
The trigger, either an inspiratory effort or a time based signal, defines
what the ventilator senses to initiate an assisted breath.
The limiting factors -are operator-specified values, such as airway
pressure
Cycle refers to the factors that determine the end of inspiration.
Other types of cycling include pressure cycling and time cycling.
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15. Modes of Ventilation
1. CMV
2. Assist control (AC)
3. Synchronized intermittent mandatory ventilation (SIMV)
4. Pressure support ventilation
5. CPAP
15
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16. Controlled mechanical ventilation (CMV)
• During CMV, the minute ventilation is determined entirely by the set
respiratory rate and tidal volume.
• This may be due to pharmacologic paralysis, heavy sedation, coma, or lack of
incentive to increase the minute ventilation because the set minute ventilation
meets or exceeds physiologic need.
16
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17. VCV
• Trigger – timed, limit – flow, termination – volume
• Set: TV, flow rate, RR, FiO2, PEEP, inspiratory time
• Monitor: Pplat, PIP,
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18. 700 ml
-70
70 l/min
50 cmH2O
Volume control
Pressure
Flow
Volume
T
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19. PRESSURE-CONTROL VENTILATION (PCV)
• Are ventilator-initiated breaths with a pressure limit.
• Limits inflation pressure
• Mandatory breath only
• Set: PIP, I:E ratio, RR, PEEP, FiO2
• Inspiration ends at delivery of set PIP.
• Tidal volume is variable, related to
• PIP, compliance, airway resistance, tubing resistance
• High VT: can be due to High PIP & low compliance
19
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20. …PCV
20
Time cycled(control)--inspiratory flow should return to normal
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21. PCV
Advantage
• Prevents excessive airway
pressures
• Avoid regional alveolar
over distention
• May lead to earlier
liberation from MV
Disadvantage
• Very uncomfortable and
requires deep sedation
+/- paralysis
• Unable to guarantee
minimum VE
21
Indications= patients who are at particularly
high risk from barotrauma and post thoracic
surgery.
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22. Assist-Control Ventilation
• ACMV is the most widely used mode of ventilation.
• In this mode, an inspiratory cycle is initiated either by the patient’s
inspiratory effort or, if none is detected within a specified time window, by
a timer signal within the ventilator.
• During AC, the clinician determines the minimal minute ventilation by
setting the respiratory rate and tidal volume.
• The patient can increase the minute ventilation by triggering additional
breaths.
22
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23. Cont…
• Each patient-initiated breath receives the set tidal volume from the
ventilator.
• Every breath delivered, whether patient- or timer-triggered, consists of the
operator-specified tidal volume.
• It is a mixed mode in which pts receive a mandatory breath with set tidal
volume (if volume AC) or pressure (pressure AC).
• In ACV, the mechanical breaths are limited by volume and/or flow and
cycled by volume or time.
23
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24. 24
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25. Volume pre-set assist control
• Advantages
• Relatively simple to
set
• Guaranteed minimum
minute ventilation
• Rests muscles of
respiration (if
properly set)
• Disadvantages
• Not synchronized
• Patient may “lead”
ventilator
• Inappropriate triggering
may result in excessive
minute ventilation
•  lung compliance  
alveolar pressure with
risk of barotrauma
• Often requires sedation to
achieve synchrony.
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26. Intermittent Mandatory
Ventilation
• IMV allows the patient to breathe spontaneously between machine-cycled
or mandatory breaths.
• In the most frequently used synchronized mode (SIMV), mandatory breaths
are delivered in synchrony with the patient’s inspiratory efforts at a
frequency determined by the operator.
• SIMV differs from ACMV in that only a preset number of breaths are
ventilator-assisted.
26
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27. Cont…
27
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28. Cont…
• IMV is similar to AC in two ways:
• The clinician determines the minimal minute ventilation (by setting the
respiratory rate and tidal volume) and
• The patient is able to increase the minute ventilation.
• However, IMV differs from AC in the way that the minute ventilation is
increased.
• SIMV allows patients with an intact respiratory drive to exercise
inspiratory muscles between assisted breaths; thus it is useful for both
supporting and weaning intubated patients.
28
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29. Pressure support (PSV)
• The ventilator applies a pre-determined amount of positive pressure to the
airways upon inspiration.
• This form of ventilation is patient-triggered, flow-cycled, and pressure-
limited.
• The patient breathes spontaneously.
• With PSV, patients receive ventilator assistance only when the ventilator
detects an inspiratory effort.
• PSV is well tolerated by most patients who are being weaned from MV.
• Comfortable mode for awake and conscious patient
• Can be combined with SIMV mode.
29
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30. Cont…
30
In flow cycled (supported) flow does not return to baseline
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31. Continuous positive airway pressure (CPAP)
• Is the way of delivering PEEP
but also maintains the set
pressure through out the
respiratory cycle.
• Allows spontaneous
breathing at elevated
baseline pressure.
• Set P = 5-15cmH2O
• CPAP is most commonly
used in the management of
sleep related breathing
disorders, cardiogenic
pulmonary edema, and 31
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32. 4/19/2024 32

33. Mechanical Ventilator Settings
Trigger
Tidal Volume
Respiratory Rate
PEEP
Flow rate
Fraction of Inspired oxygen(Fio2)
Flow Pattern
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34. Trigger
• Trigger sensitivity
•  sensitivity preferable
• Flow triggering generally more sensitive than pressure triggering
•  flow or less negative pressure   sensitivity
• Trigger types
• pressure triggering or
• A trigger sensitivity of -1 to -3 cmH2O is typically set.
• flow triggering
• initiated when the return flow is less than the delivered flow.
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35. Tidal volume
• Optimal tidal volume for mechanically ventilated patients:-
• without existing lung disease 6-8ml/kg of IBW.
• For ARDS-4-6 ml/kg of IBW
• Female PBW= 45.5 + 0.91 (Ht – 152.4)
• Male PBW = 50 + 0.91 (Ht – 152.4)
• As Tv inc., peak airway pressure also inc.(>45cmH20 barotrauma)
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36. Respiratory rate
• Initial respiratory rate between 12 and 16 breaths per minute is reasonable.
• RR adjustment-
• Modification according to mode
• Desired PH & paco2
• autoPEEP(if >5cmH20)
• For ALI/ARDS-up to 35’
• MV= TV X RR
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37. PEEP
• PEEP is used to mitigate end-expiratory alveolar collapse.
• An initial PEEP is 5 cmH2O.
• 20 cmH2O may be used in patients with ARDS.
• Elevated levels of PEEP-
• reduced preload(CO)
• increases risk of barotrauma and
• impaired cerebral venous outflow (increases ICP)
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38. Fraction of inspired oxygen(Fio2)
• % of oxygen in each breath.
• Titrated to meet patient needs.
• Goal-
• PaO2 above 60 mmHg and
• SpO2 above 90 percent.
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39. Inspiratory time
• Set as:
• % of respiratory cycle
• I:E ratio
• Indirectly, by setting flow
• Expiratory time not set
• Remaining time after inspiration before next breath
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40. Inspiratory Time
• Longer inspiratory time
• Improved oxygenation
• Higher mean airway pressure
• Re-distribution
• Lower peak airway pressure
• More time available to deliver set tidal volume
• Shorter inspiratory time
• Less risk of gas trapping and PEEPi
• Less effect on cardiovascular system
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41. Inspiratory to expiratory (I:E) ratio
• Inspiratory time is equal to tidal volume divided by flow rate.
• Normal I:E ratio: 1:2 to 1:3.
• Can be reduced to 1:4 or 1:5 in COPD (longer expiratory time)
• inverse I:E ratio may be necessary in states of low compliance, such as ARDS.

42. Flow rate
• The peak flow rate is the maximum flow delivered by the ventilator during
inspiration.
• Peak flow rates of 60 L per minute may be sufficient, although higher rates are
frequently necessary.
• Increased peak flow rates –
increase the peak airway pressure.
decreased inspiratory time lowers the mean airway pressure, which can
decrease oxygenation.
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43. Inspiratory flow Pattern
• Different flow rates are associated with different airflow
waveforms.
1. Square waveforms
flow accelerates very quickly and then reaches a set rate,
which is maintained throughout inspiration. Flow rate is
constant
This waveform allows for an adequate I:E ratio with a normal
flow rate.
Inspiratory
arm

44. Inspiratory flow Pattern
2. Ramp waveforms
flow rate rapidly accelerates but is followed by a
gentle tapering.
This waveform may require much higher flow
rates to obtain an adequate I:E ratio.
This waveform can be used if abnormally high
PIP is encountered.
Inspiratory
arm
Expiratory
arm

45. Pressures
• Peak inspiratory pressure- the pressure required to administer a set tidal volume
• As the tidal volume increases, the pressure required to administer that volume also
increases..
• Pawp above 45 cmH2O -the risk of barotrauma is increased.
• plateau pressure - is the pressure after the delivery of the tidal volume but before
the patient is allowed to exhale.
• is maintained < 30 cmH2O.
• Mean airway pressure- refers to the mean across the entire respiratory cycle,
both inspiration and expiration
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46. Mean airway pressure
Mean airway pressure
Mean airway pressure
Time
Pressure
Time
Pressure
 Tidal volume
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47. Mean airway pressure
Mean airway pressure
Mean airway pressure
Time
Pressure
Time
Pressure
 Inspiratory time
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48. Dyssynchrony

49. 4/19/2024 49

50. Waveform showing increased airways resistance
Ppeak
Pplat
Pres
‘Square
wave’ flow
pattern

51. Recognizing secretion in the ETT
51
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52. Waveform showing decreased lung compliance
Ppeak
Pplat
Pres
‘Square
wave’ flow
pattern

53. • Incomplete expiration leading
to air trapping
• Causes include
• High minute ventilation
• Expiratory flow limitation
• Expiratory resistance
Auto PEEP

55. Patient-ventilator dys-synchrony
• State when the respiratory cycle of the patient does not match
that of the ventilator.
• It can happen during triggering process, flow delivery or breath
cycling.
• Clinical features: ↑HR, RR; ↓SO2; ↑expiratory mm activity,
coughing, anxiety, visible inspiratory effort without triggering the
ventilator; Ventilator waveforms
• Consequences include: ↑Work Of Breath, prolongation of MV,
perceived need for deeper sedation

56. Vent triggers to start inspiration does not always correlate with the patient attempt to start inspiration
Airflow what the patient is demanding does not match what the vent is providing
Vent and patient went transitions from inspiration to expiration at different times

57. Principles of monitoring
• Follow the patient clinical condition
• Assess ventilation and oxygenation – ABGs
• Follow vent parameters
• Flow and pressure time curves
• Pressure and volume alarms
• Always evaluate for weaning readiness
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58. Alarms
• Never ignore an alarm
• Common causes of alarms
• Dislodgement: check ETT length of insertion (av. 22) at incisor
• Obstruction: secretion, blood clot, fighting patient biting the ETT
• Suction, sedation
• Pneumothorax: barotrauma
• Equipment failure: air leak, disconnected corrugator tube, ↓ humidifier
water, uninflated ETT cuff
58
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59. Complications of MV
• During Act of intubation
• Artificial air way related complication
• Pulmonary complications
• Non pulmonary complications
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60. During Act of intubation
• Dental trauma
• Aspiration – bag ventilation for preoxygenation can cause gastric distension +
irritation during ETT insertion  vomiting
• Laryngeal trauma – hoarseness, URTO
• Laryngeal edema, ulceration, granuloma, vocal cord paralysis
• Bronchospasm – mechanical irritation
• Esophageal intubation
• Right main bronchus intubation – it goes too far
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61. Artificial air way related complication
• Failure of alarms or ventilator, Alarm “turned off”
• Disconnection, circuit leaks
• Obstruction by secretions
• Inadequate nebulization or humidification
• Overheated inspired air, resulting in hyperthermia
• Dyssynchronous breathing pattern
• Tube kinked, plugged
• Cuff failure
• Migration – ETT migrates with suctioning, coughing, movement
• Tracheal stenosis – pressure necrosis  ulceration, scarring
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62. Pulmonary complications
Ventilator Induced Lung Injury
• Barotrauma, volutrauma
• Alveolar overdistension  rupture  extra-alveolar air 
Pneumothorax/emphysema, Pneumomediastinum, pneumopericardium, SC
emphysema, air embolism
• Atelectrauma (Cyclic atelectasis) – repeatitive opening and collapse of alveoli during
ventilator cycle  shear stress injures them
• Biotrauma – proinflammatory cytokines released from over distended lung 
inflammatory injury
• Risk factors: asthma, chronic lung disease, ARDS
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63. VILI – management
• Protective lung ventilation principle
• The plateau airway pressure be immediately lowered to ≤35 cm H 2 O
• lowering the tidal volume, positive end-expiratory pressure, or inspiratory flow
• increasing sedation, administering neuromuscular blockade,
• advancing treatment of the underlying medical condition (eg, bronchodilators
for asthma)
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64. Oxygen toxicity
• Inappropriate O2 supplementation is deleterious
• Hyperoxia  ↑reactive oxygen species (superoxide anion, hydroxyl radical,
H2O2) [+depleted antioxidant system]  cellular injury
• There is no single threshold of FiO2 defining a safe upper limit for prevention of
oxygen toxicity.
• Reducing FiO2 to lowest tolerable limit is a good principle for all patients
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65. Infectious Complications
Risk factors
• ETT bypasses the glottis closure protective mechanism allowing
seepage of oropharyngeal content into airways.
• ETT impairs cough reflex
• Airway and parenchymal injury (primary illness + positive
pressure ventilation)
• ICU environment itself – heavy antibiotics use, sick patients in
close proximity
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66. Non pulmonary complications
• Hemodynamics
 Decreased venous return
 Reduced right ventricular output
 Reduced left ventricular output
• Gastrointestinal
 Erosive esophagitis, stress ulceration, diarrhea, acalculous cholecystitis, and
hypomotility
• Renal – acute renal failure ( decrease CO, release of inflammatory Mediators), acid
base disturbance.
• MSS- bed sore, contracture
• CNS: Critical illness polyneuropathy, myopathy,
• ICU psychosis etc.
66
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67. Weaning from mechanical ventilation
• The process of decreasing ventilator support & Discontinuation
of mechanical ventilation or liberation from the mechanical
ventilator
• three step process that consists of Readiness Testing ,Weaning &
extubation
67
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68. Readiness testing
• Readiness Testing – 2 goals
• Identify patients who are ready to wean
• Protect against premature weaning
• Objective clinical criteria and weaning predictors used
68
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69. Patients with uncertainty
• For patients in whom uncertainty exists as to whether the readiness criteria will predict a
successful weaning trial, we sometimes use a weaning predictor to identify potential
candidates suitable for weaning or to confirm lack of readiness to wean (eg, patients with
borderline readiness criteria or suspected respiratory muscle weakness).
• Use of weaning predictors is most pertinent among patients in whom the risk associated
with a failed spontaneous trial is significantly elevated (eg, patients with prolonged
mechanical ventilation, patients with critical care neuromyopathy).
• Among the predictors, the rapid shallow breathing index (RSBI) is our preferred
weaning predictor because it is well studied, easy to measure, and no alternative
predictor has been shown to be superior.
• For patients who have an RSBI <105 breaths/minute/L (measured without ventilatory
support), we initiate a weaning trial.
• For patients who have an RSBI ≥105 breaths/minute/L (measured without ventilatory
support), we maintain full ventilatory support.
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70. Choosing a weaning method
• For patients who have been intubated for more than 24 hours and have been
deemed as ready to wean ,we suggest a weaning trial.
• Daily spontaneous breathing trials (SBTs) with inspiratory pressure support is our
preferred method of weaning based upon randomized trials that have shown it is
efficient, safe, and effective
• Approximately 50 to 75 percent of patients pass the initial SBT and are
able to be successfully extubated
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71. • Spontaneous breathing Trial
• with minimal ventilator
support a low level of
pressure support(5-8mmH2O),
or CPAP (5mmH2O)
• Breathing through the ETT
without any ventilator support
(T-piece using 1–5 cmH2O
• Duration of a weaning trial
• 30 min to 120 min
71
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72. Extubation
• Extubation refers to removal of the endotracheal tube. It is the final step in
liberating a patient from mechanical ventilation.
• Extubation should not be performed until it has been determined that the patient's
medical condition is stable, a weaning trial has been successful, the airway is
patent, and any potential difficulties in reintubation have been identified. Most
patients are extubated during daytime hours
• Prior to Extubation Evaluate for Airway protection and Airway patency
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73. Airway protection
• Is the ability to guard against aspiration during spontaneous breathing It requires sufficient
cough strength and an adequate level of consciousness
• Universally accepted threshold levels of cough strength, level of consciousness, and suctioning
frequency that prohibit extubation have not been established. For many patients, it is reasonable
to delay extubation if the cough strength is weak, the GCS is <8 , or suctioning is required more
frequently than every two to three hours.
1. Cough strength (peak expiratory flow rate (PEF) >60 L/min)
2. Secretions (< 2.5 ml/hr) no more suctioning than once 2-3 hrs
3. Level of consciousness (able to obey command) 73
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74. Airway patency
• Cuff leak test: (assessing the presence of air movement around a deflated endotracheal
tube cuff)
• To identify pts at risk to develop post extubation laryngeal edema.
• A "cuff leak" refers to normal airflow around the ETT after the cuff of the ETT is
deflated. Its absence suggests there is reduced space between the ETT and the larynx.
• The cuff leak predicts post-extubation stridor with a sensitivity of 15 to 85 % and a
specificity of 70 to 99 %.
74
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75. Cont’d
 The cuff leak can be detected qualitatively or quantitatively:
• Qualitative assessment by deflating the cuff and then listening for air movement
around the ETT using a stethoscope.
• Quantitatively is by deflating the ETT cuff and measuring the difference
between the inspired and expired TV of ventilator-delivered breaths during
volume-cycled MV (<110 ml or 12-24% of the delivered tidal volume) =
diminished patency
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76. How do we prevent post-extubation complications?
• Post extubation complications
Post-extubation laryngeal edema
Hypoxia and re-intubation
• Short course of glucocorticoid therapy before extubation.
Methylprednisolone (20 mg) administered every four hours for a total of four
doses.
Alternatively, a single dose of methylprednisolone 40 mg four hours prior to
extubation may be used 76
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77. Extubation procedure
• The patient is placed into an upright position and both the oral cavity and the
endotracheal tube (ETT) are suctioned.
• Instructions are given for the patient to take a deep breath and then exhale.
• During exhalation, the cuff is deflated and the ETT is removed in a single, smooth
motion. Orogastric tubes are typically removed simultaneously.
77
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78. References
• Up-to-date, online
• Hand book of Mechanical Ventilation, User’s guide
• Practical Guide for Mechanical Ventilation,4th edition
• Harrison’s 21st edition
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