Mechanical ventilation (MV) works by applying a positive pressure breath and is dependent on the compliance and resistance of the airway system

1. Dr Roshana Mallawaarachchi
25th March 2023

2. Explore the indications and contra-indications
Overview of the modes of ventilation
Be familiar with normal parameters of ventilation
Discuss the indications for weaning and extubation
VAP care bundle

3. Respiratory Failure
Cardiopulmonary arrest
Trauma Events
Cardiovascular impairment
Neurological impairment
Pulmonary impairment
Procedures requiring sedation/paralysis
For recovery after prolonged major surgery or trauma

4. Inadequate gas exchange
 Pneumonia, pulmonary oedema, acute respiratory distress syndrome (ARDS)
Inadequate breathing
 Chest wall problems eg fractured ribs, flail chest
 Pleural wall problems eg pneumothorax, haemothorax
 Respiratory muscle failure eg myasthenia gravis, poliomyelitis, tetanus
 Central nervous system depression eg drugs, brain stem compression
Obstructed breathing
 Upper airway obstruction eg epiglottitis, croup, oedema, tumour
 Lower airway obstruction eg bronchospasm

5.  Respiratory rate >35 or <5 breaths/ minute
 Exhaustion, with laboured pattern of breathing
 Hypoxia - central cyanosis, SaO2 <90% on oxygen or PaO2 < 8kPa
(60mmHg)
 Hypercarbia - PaCO2 > 8kPa (60mmHg)
 Decreasing conscious level - (GCS) of 8 or less
 Significant chest trauma (Flail segment/ Rib Fracture)
 Tidal volume < 5ml/kg or Vital capacity <15ml/kg

6. Treat hypoxemia/hypercapnia
Relieve respiratory distress/reverse fatigue
Decrease Myocardial O2 demand
Prevention or reversal of atelectasis
Breath for the sedated/paralysed patient
Stabilise the chest wall

7. Risks outweigh benefits, for example Neutropenia
Non-invasive deemed preferable to invasive ventilation
Invasive ventilation considered medically futile
Contrary to the expressed wishes of the patient

9. A machine that generates a
controlled flow of blended air and
oxygen into a patient’s airway.

10. Two categories Volume or Pressure
This refers to the mode of breath
delivery rather than the mode itself

11. In volume category modes of ventilation the
machine generates flow to achieve a set volume
known as
TIDAL VOLUME

12. VT
Definition –
‘the volume of air
that is inspired or
expired in a single
breath during
regular breathing’

13. Advantages
Guaranteed Minute
Ventilation (Mv).
Disadvantages
Increased monitoring
of airway pressures.
Airway pressures will
increase if lung
compliance decreases.
Risk of barotrauma.

14. MV
Definition –
‘the total volume of
gas in litres expelled
from the lungs per
minute’
RR X TV

15. In pressure modes of ventilation a pressure limit
is set, the machine generates flow until the peak
pressure limit is achieved-
PAP or PIP
Peak Airway
(inspiratory) Pressures

16. Pip
Pap
Ppeak
Definition –
‘is the highest level of
pressure applied to
the lungs during
inhalation expressed
in cmH2o’

17. Advantages
Greater control of
airway pressure.
Less risk of
barotrauma.
Disadvantages
No guaranteed minute
ventilation.
Increased monitoring of
VT required.
Rapid changes in the
compliance can cause
hypoventilation/hypoxia.

18. FLOW TRIGGER - a breath is generated when the patient’s
respiratory effort causes flow to reach a set level.
PRESSURE TRIGGER - a breath is generated by measuring
pressure and starting assisted ventilation when pressure reaches a
given level.
TIME TRIGGER - a breath is generated by measuring frequency
of respirations and starting ventilation when respirations
frequency is at a given.

19.  TIME CYCLED - such in in pressure controlled ventilation
 FLOW CYCLED - such as in pressure support
 VOLUME CYCLED - the ventilator cycles to expiration once a set
tidal volume has been delivered: this occurs in volume controlled
ventilation.

20. MANDATORY
MODES OF
VENTILATION

21. IPPV

22. Set: TV, rate, Fi02, PEEP,
No capacity for the patient to
trigger a breath
Uncomfortable if patient not
fully sedated &/ paralysed
Suitable only for patients who
have no ability to breathe
spontaneously

23. MANDATORY
ASSIST MODES
OF
VENTILATION

24. Synchronized Intermittent
Mandatory Ventilation

25.  Provides a set TIDAL VOLUME at a set RATE (F)
 Patient can breathe in-between mandatory
ventilation
 Spontaneous breaths are supported with pressure
support
 Ventilator synchronises mandatory breaths and
spontaneous breaths for increased patient comfort
NB
Usually volume targeted but some machines offer SIMV (pc)

27. Advantages
Guaranteed Minute
Ventilation
Disadvantages
Increased monitoring
of airway pressures.
Airway pressures will
increase if lung
compliance decreases.
Risk of barotrauma.

29. BILEVEL
POSITIVE
AIRWAY
PRESSURE
BiPAP

30.  Provides a set P-insp at a set RATE (F)
 Patient can breathe in-between mandatory ventilation
 Spontaneous breaths are supported with pressure support
 Pt can breathe at any point of respiratory cycle, not just between
breaths
 Breathing takes between two levels Pinsp and PEEP

33. Advantages
Increased patient comfort
Can limit high airway
pressures
Reduce risk of barotrauma
Disadvantages
No guaranteed Minute
Ventilation
Increased monitoring of
Tidal Volumes
Patient may hypo-
ventilate and become
hypoxic if lung compliance
changes suddenly

34. SPONTANEOUS
MODES OF
VENTILATION

35. The patient triggers the ventilator and
receives a supported breath at a pre-set
pressure.
This helps overcome the increased work of
breathing or resistance of breathing
through an endotracheal tube.

37. POSITIVE END-EXPIRATORY
PRESSURE
 Maintains pressure within the
breathing circuit at a pre-set level at
the end of expiration
 When used during spontaneous
respiration it is called CPAP
 A degree of PEEP should be applied
on all ventilation modes to minimise
risk of atelectasis
 PEEP causes a rise in intrathoracic
pressure and can reduce venous
return and so precipitate hypotension

38. Same as PEEP, but in spontaneously breathing patients.

40.  I:E ratio is 1:2
 Can be reversed – 1:1 or less: 2:1
 Some machines automatically
alter I:E ratios when the set resp
rate is altered.

41. Disadvantages
Air trapping from
increased
intrathoracic pressure
Hypercarbia ( Î C02)
Breath stacking
Extreme discomfort
for the pt
Reduction in cardiac
return
Advantages
Alveolar recruitment
Reduced alveolar
collapse due to shorter
expiratory times
Increased mean airway
pressure without
increasing PAP

43. Increase FiO2
Increase PEEP
Increase inspiratory time (I:E ratio)
Prone position

45. Underlying illness is treated and improving
Respiratory function:
 - Respiratory rate < 35 breaths/minute
 - FiO2 < 0.5, SaO2 > 90%, PEEP <10 cmH2O
 - Tidal volume > 5ml/kg
 - Vital capacity > 10 ml/kg
 - Minute volume < 10 l/min
Absence of infection or fever
Cardiovascular stability

46. Airway:
 Aspiration pneumonia
 Trauma to trachea during
intubation
 Hypoxia prior to / during
intubation
 Laryngeal oedema
 Occlusion of blood supply
to trachea (if cuff pressures
to high)
 Sinus infection

47. Mechanical:
 Ventilator malfunction.
 Ventilator circuit:
occlusion, kinks,
bronchospasm,
disconnection & biting.
 Barotrauma / Volutrauma
can rupture alveoli,
causing pneumothorax.

48. Decreased cardiac output:
 Induction agents
 Changes intrathoracic pressure &
reduces venous return
 Cardiac output falls, BP drops
 CVP and LV preload rise
 This has implications for the
perfusion of all vital organs: brain,
kidneys, GI tract

50. VAP CARE
BUNDLE

51. VAP is a type of hospital-acquired
pneumonia that occurs more than 48 hours
after endotracheal intubation.
Average time take – 5-7 days
This can be further classified into early onset (within the first 96 hours of MV)
and late onset (more than 96 hours after the initiation of MV), which is more
commonly attributable to multidrug–resistant pathogens.

52. Overall rate of VAP is 13.6 per 1000
ventilator days.
Mortality rate quoted as between 24% and 76%

53.  Increasing age (55 years)
 Chronic lung disease
 Aspiration/ microaspiration from being nursed in a supine position
 Chest or upper abdominal surgery
 Previous broad spectrum antibiotic therapy
 Reintubation after unsuccessful extubation, or prolonged intubation
 Acute respiratory distress syndrome
 Frequent ventilator circuit changes
 Polytrauma patient
 Prolonged paralysis
 Premorbid conditions such as malnutrition, renal failure, and anaemia

54. 1. Head-of-bed elevation: 300 to 450
2. Adequate endotracheal tube cuff pressure (>20-25
cmH2O)
3. Oral care with 0.5% chlorhexidine solution every 8h
4. Daily “sedation vacation” and daily assessment of
readiness for extubation
5. Peptic ulcer prophylaxis
6. Subglottic suction
7. DVT Prophylaxis