Maintain medical mechanical ventilators

1. SILVESTER WABWIRE
DEPARTMENT OF APPLIED SCIENCES
JFC MUNENE COLLEGE OF HEALTH SCIENCES

2. Overview of topics
1. Anatomy and Physiology Of Respiratory
System.
2. Introduction About Mechanical Ventilation
3. History
4. Meaning of Mechanical Ventilation
5. Indications for use
6. Types or Forms Of Mechanical Ventilation

3. 8. Settings
9. Modes.
10. Advantages and disadvantages between
modes.
11. Guidelines in the initiation of mechanical
ventilation.
12. Common trouble shooting examples with
mechanical ventilation

4. Introduction
 Ventilation is the movement of air into and out
of the alveoli.

5. Introduction
 Mechanics of Ventilation:
 Elasticity
 Compliance
 Resistance
 Pressure
 Gravity

6. Anatomy and Physiology
 Respiratory Structures
 Respiratory Zones
 Partitioning of Respiratory Pressures
 Boyles Law
 Respiratory Volumes and Capacity
 Ventilation and Perfusion

7. Anatomy and Physiology of Respiratory System

9. Increase V = Decreased P
Decreased V = Increased
P

10. Boyles Law
 Air flows from a region of higher pressure to a
region of lower pressure.
 To initiate a breath, airflow into the lungs must
be precipitated by a drop in alveolar pressures.

11. Respiratory Volumes and Capacit

13. Introduction about Mechanical
Ventilation
 Mechanical ventilation is typically used after an
invasive intubation, a procedure wherein an
endotracheal or tracheostomy tube is inserted into
the airway.
 It is used in acute settings such as in the ICU for a
short period of time during a serious illness. It may
be used at home or in a nursing or rehabilitation
institution if patients have chronic illnesses that
require long-term ventilation assistance.

14. Objective of Ventilation
 Support though illness
 Reversal of hypoxemia
 Reversal of acute respiratory acidosis
 Relief of respiratory distress
 Resting of the ventilatory muscles
 Decrease in oxygen consumption
 Reduction in intracranial pressures
 Stabilisation of the chest wall

15. History
 Andreas Vesalius (1555)
 Vesalius is credited with the first description of
positive pressure ventilation, but it took 400
years to apply his concept to patient care. The
occasion was the polio epidemic of 1955, when
the demand for assisted ventilation outgrew the
supply of negative-pressure tank ventilators
(known as iron lungs).

16. History
 The roman physician Galen may have been the
first to describe mechanical ventilation: "If you
take a dead animal and blow air through its
larynx [through a reed], you will fill its bronchi
and watch its lungs attain the greatest
distention.”
 Vesalius too describes ventilation by inserting a
reed or cane into the trachea of animals.
 In 1908 George Poe demonstrated his mechanical
respirator by asphyxiating dogs and seemingly
bringing them back to life.

17.  In Sweden, all medical schools shut down and
medical students worked in 8-hour shifts as
human ventilators, manually inflating the lungs
of afflicted patients.
Invasive ventilation first used at Massachusetts
General Hospital in 1955.
 Thus began the era of positive-pressure
mechanical
 ventilation (and the era of intensive care
medicine).

19. Meaning of Mechanical
Ventilation
In medicine, mechanical ventilation is a method
to mechanically assist or replace spontaneous
breathing.

20. Types or Forms Of Mechanical
Ventilation
The two major types of
Mechanical Ventilation are
Negative pressure and
positive Pressure ventilation
The main form of
mechanical ventilation is
positive pressure
ventilation, which works by
increasing the pressure in
the patient's airway and thus
forcing air into the lungs.

21. Less common today are negative pressure
ventilators (for example, the "iron lung") that
create a negative pressure environment around
the patient's chest, thus sucking air into the
lungs.

22. The iron lung, often referred
to in the early days as the
"Drinker respirator", was
invented by Phillip
Drinker(1894 – 1972)
and Louis Agassiz Shaw
Junior, professors of
industrial
hygiene at the Harvard
School
of Public Health .
The machine was powered by
an electric motor with air
pumps from two vacuum
cleaners. The air pumps
changed the pressure inside a
rectangular, airtight metal

23. Positive pressure ventilators
 Inflate the lungs by exerting positive pressure
on the airway, similar to a bellows
mechanism, forcing the alveoli to expand
during inspiration
 Expiration occurs passively.
 modern ventilators are mainly PPV s and are
classified based on related features,
principles and engineering.

24. Settings of Mechanical
Ventilation
Mechanical Ventilator Settings
regulates the rate, depth and other
characteristics of ventilation.
Settings are based on the patient’s
status (ABGs, Body weight, level of
consciousness and muscle strength)

26. Settings
1. Trigger mode and sensitivity
2. Respiratory rate
3. Tidal Volume
4. Positive end-expiratory pressure (PEEP)
5. Flow rate
6. Inspiratory time
7. Fraction of inspired oxygen

27. Trigger
 There are two ways to initiate a ventilator-delivered breath:
pressure triggering or flow-by triggering
 When pressure triggering is used, a ventilator-delivered
breath is initiated if the demand valve senses a negative
airway pressure deflection (generated by the patient trying
to initiate a breath) greater than the trigger sensitivity.
 When flow-by triggering is used, a continuous flow of gas
through the ventilator circuit is monitored. A ventilator-
delivered breath is initiated when the return flow is less
than the delivered flow, a consequence of the patient's
effort to initiate a breath

28. Tidal Volume
 The tidal volume is the amount of air delivered
with each breath. The appropriate initial tidal
volume depends on numerous factors, most
notably the disease for which the patient
requires mechanical ventilation.

29. Respiratory Rate
 An optimal method for setting the respiratory
rate has not been established. For most patients,
an initial respiratory rate between 12 and 16
breaths per minute is reasonable

30. Positive End-Expiratory Pressure
(PEEP)
 Applied PEEP is generally added to mitigate end-
expiratory alveolar collapse. A typical initial
applied PEEP is 5 cmH2O. However, up to 20
cmH2O may be used in patients undergoing low
tidal volume ventilation for acute respiratory
distress syndrome (ARDS)

31. 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. An insufficient peak flow rate is
characterized by dyspnea, spuriously low peak
inspiratory pressures, and scalloping of the
inspiratory pressure tracing

32. Inspiratory Time: Expiratory Time
Relationship (I:E Ratio)
 During spontaneous breathing, the normal I:E
ratio is 1:2, indicating that for normal patients
the exhalation time is about twice as long as
inhalation time.
 If exhalation time is too short “breath stacking”
occurs resulting in an increase in end-expiratory
pressure also called auto-PEEP.
 Depending on the disease process, such as in
ARDS, the I:E ratio can be changed to improve
ventilation

33. Fraction of Inspired Oxygen
 The lowest possible fraction of inspired oxygen
(FiO2) necessary to meet oxygenation goals
should be used. This will decrease the likelihood
that adverse consequences of supplemental
oxygen will develop, such as absorption
atelectasis, accentuation of hypercapnia, airway
injury, and parenchymal injury

35. Modes of Mechanical
Ventilation
 Controlled Mandatory Ventilation (CMV)
 Asst-Control Mandatory Ventilation (ACV)
 Synchronized Intermittent Mandatory
Ventilation(SIMV)
 Continuous Positive Airway Pressure (CPAP)
 Positive Expiratory End Pressure(PEEP)
 Pressure Support Ventilation (PSV)

36. Controlled Mandatory
Ventilation (CMV)
Controlled Mechanical Ventilation (CMV).
In this mode the ventilator provides a
mechanical breath on a preset timing. Patient
respiratory efforts are ignored.
This is generally uncomfortable for children and
adults who are conscious and is usually only used
in an unconscious patient. It may also be used in
infants who often quickly adapt their breathing
pattern to the ventilator timing

37. Asst-Control Mandatory
Ventilation (ACV)
 Assist Control (AC). In this mode the ventilator
provides a mechanical breath with either a pre-
set tidal volume or peak pressure every time the
patient initiates a breath.
 Traditional assist control used only a pre-set tidal
volume--when a preset peak pressure is used this is
also sometimes termed Intermittent Positive
Pressure Ventilation or IPPV.
 However, the initiation timing is the same--both
provide a ventilator breath with every patient
effort.

38. Assist Control Ventilation
 A set tidal volume (if set to volume control) or a
set pressure and time (if set to pressure control)
is delivered at a minimum rate
 Additional ventilator breaths are given if
triggered by the patient

39.  In most ventilators a back-up minimum breath
rate can be set in the event that the patient
becomes apnoeic. Although a maximum rate is
not usually set, an alarm can be set if the
ventilator cycles too frequently.
 This can alert that the patient is tachypneic or
that the ventilator may be auto-cycling (a
problem that results when the ventilator
interprets fluctuations in the circuit due to the
last breath termination as a new breath
initiation attempt)

40. Synchronized Intermittent
Mandatory Ventilation(SIMV)
Synchronized Intermittent Mandatory
Ventilation (SIMV). In this mode the ventilator
provides a pre-set mechanical breath (pressure
or volume limited) every specified number of
seconds (determined by dividing the respiratory
rate into 60 - thus a respiratory rate of 12 results in
a 5 second cycle time).

41.  Within that cycle time the ventilator waits for
the patient to initiate a breath using either a
pressure or flow sensor. When the ventilator
senses the first patient breathing attempt within
the cycle, it delivers the preset ventilator breath

42.  If the patient fails to initiate a breath, the
ventilator delivers a mechanical breath at the
end of the breath cycle. Additional spontaneous
breaths after the first one within the breath cycle
do not trigger another SIMV breath.
 However, SIMV may be combined with pressure
support. SIMV is frequently employed as a
method of decreasing ventilatory support
(weaning) by turning down the rate, which
requires the patient to take additional breaths
beyond the SIMV triggered breath.

43. Synchronized Intermittent
Mandatory Ventilation
 Breaths are given are given at a set minimal rate,
however if the patient chooses to breath over the set rate
no additional support is given
 One advantage of SIMV is that it allows patients to
assume a portion of their ventilatory drive
 SIMV is usually associated with greater work of
breathing than AC ventilation and therefore is less
frequently used as the initial ventilator mode
 Like AC, SIMV can deliver set tidal volumes (volume
control) or a set pressure and time (pressure control)
 Negative inspiratory pressure generated by spontaneous
breathing leads to increased venous return, which
theoretically may help cardiac output and function

44. Continuous Positive Airway
Pressure (CPAP)
(CPAP). A continuous level of elevated pressure is
provided through the patient circuit to maintain adequate
oxygenation, decrease the work of breathing, and
decrease the work of the heart (such as in left-sided heart
failure — CHF).
Note that no cycling of ventilator pressures occurs and the
patient must initiate all breaths. In addition, no additional
pressure above the CPAP pressure is provided during
those breaths. CPAP may be used invasively through an
endotracheal tube or tracheostomy or noninvasively with
a face mask or nasal prongs

45. Positive End Expiratory
Pressure(PEEP)
(PEEP) is functionally the same as CPAP, but refers
to the use of an elevated pressure during the
expiratory phase of the ventilatory cycle.
After delivery of the set amount of breath by the
ventilator, the patient then exhales passively. The
volume of gas remaining in the lung after a
normal expiration is termed the functional residual
capacity (FRC).

46.  The FRC is primarily determined by the elastic
qualities of the lung and the chest wall. In many
lung diseases, the FRC is reduced due to collapse
of the unstable alveoli, leading to a decreased
surface area for gas exchange and
intrapulmonary shunting , with wasted oxygen
inspired.
 Adding PEEP can reduce the work of breathing
(at low levels) and help preserve FRC.

47. Pressure Support Ventilation
Pressure Support Ventilation (PSV). When a
patient attempts to breath spontaneously through
an endotracheal tube, the narrowed diameter of
the airway results in higher resistance to airflow,
and thus a higher work of breathing.
PSV was developed as a method to decrease the
work of breathing in-between ventilator
mandated breaths by providing an elevated
pressure triggered by spontaneous breathing
that "supports" ventilation during inspiration

48. Pressure Support Ventilation
 The patient controls the respiratory rate and
exerts a major influence on the duration of
inspiration, inspiratory flow rate and tidal
volume
 The model provides pressure support to
overcome the increased work of breathing
imposed by the disease process, the endotracheal
tube, the inspiratory valves and other
mechanical aspects of ventilatory support.

49. Advantages of Each Mode
Mode Advantages
Assist Control Ventilation (AC) Reduced work of breathing
compared to spontaneous
breathing
AC Volume Ventilation Guarantees delivery of set tidal
volume
AC Pressure Control Ventilation Allows limitation of peak
inspiratory pressures
Pressure Support Ventilation (PSV) Patient comfort, improved patient
ventilator interaction
Synchronized Intermittent
Mandatory Ventilation (SIMV)
Less interference with normal
cardiovascular function

50. Disadvantages of Each Mode
Mode Disadvantages
Assist Control Ventilation (AC) Potential adverse hemodynamic
effects, may lead to inappropriate
hyperventilation
AC Volume Ventilation May lead to excessive inspiratory
pressures
AC Pressure Control Ventilation Potential hyper- or hypoventilation
with lung resistance/compliance
changes
Pressure Support Ventilation (PSV) Apnea alarm is only back-up,
variable patient tolerance
Synchronized Intermittent
Mandatory Ventilation (SIMV)
Increased work of breathing
compared to AC

51. Guidelines in the Initiation of
Mechanical Ventilation
 Primary goals of mechanical ventilation are
adequate oxygenation/ventilation, reduced work
of breathing, synchrony of vent and patient, and
avoidance of high peak pressures
 Set initial FIO2 on the high side, you can always
titrate down
 Initial tidal volumes should be 8-10ml/kg,
depending on patient’s body habitus. If patient is
in ARDS consider tidal volumes between
5-8ml/kg with increase in PEEP

52. Guidelines in the Initiation of
Mechanical Ventilation
 Use PEEP in diffuse lung injury and ARDS to
support oxygenation and reduce FIO2
 Avoid choosing ventilator settings that limit
expiratory time and cause or worsen auto PEEP
 When facing poor oxygenation, inadequate
ventilation, or high peak pressures due to
intolerance of ventilator settings consider
sedation, analgesia or neuromuscular blockage

53. Trouble Shooting the Vent
 Common problems
 High peak pressures
 Patient with COPD
 Ventilator synchrony
 ARDS

54. Trouble Shooting the Vent
 If peak pressures are increasing:
 Check plateau pressures by allowing for an
inspiratory pause (this gives you the pressure in
the lung itself without the addition of resistance)
 If peak pressures are high and plateau pressures
are low then you have an obstruction
 If both peak pressures and plateau pressures are
high then you have a lung compliance issue

55. Trouble Shooting the Vent
 High peak pressure differential:
High Peak Pressures
Low Plateau Pressures
High Peak Pressures
High Plateau Pressures
Mucus Plug ARDS
Bronchospasm Pulmonary Edema
ET tube blockage Pneumothorax
Biting ET tube migration to a
single bronchus
Effusion

56. Trouble Shooting the Vent
 If you have a patient with history of
COPD/asthma with worsening oxygen saturation
and increasing hypercapnia differential includes:
 Given the nature of the disease process, patients have
difficultly with expiration (blowing off all the tidal volume)
 Must be concern with breath stacking or auto- PEEP
 Management options include:
Decrease respiratory rate Decrease tidal volume
Adjust flow rate for
quicker inspiratory rate
Increase sedation
Adjust I:E ratio

57. Trouble Shooting the Vent
 Increase in patient agitation and dis-synchrony
on the ventilator:
 Could be secondary to overall discomfort
 Increase sedation
 Could be secondary to feelings of air hunger
 Options include increasing tidal volume, increasing
flow rate, adjusting I:E ratio, increasing sedation

58. Trouble shooting the vent
 If you are concern for acute respiratory distress
syndrome (ARDS)
 Correlate clinically with HPI and radiologic
findings of diffuse patchy infiltrate on CXR
 Obtain a PaO2/FiO2 ratio (if < 200 likely ARDS)
 Begin ARDSnet protocol:
 Low tidal volumes
 Increase PEEP rather than FiO2
 Consider increasing sedation to promote synchrony
with ventilator