Mechanical Ventilation by ms preeti Singh

MECHANICAL VENTILATION 04/21/2022
KOMAL POONIA- MSC (CVTN) 1
Mechanical Ventilation
Mechanical Ventilation is ventilation of the lungs by artificial means usually
by a ventilator. Once a patient’s PaO2 cannot be maintained by the basic
methods of oxygen delivery systems, i.e. masks, cannula; endotracheal
intubation and mechanical ventilation are instituted.
A ventilatordelivers gas to the lungs with either negative or positive pressure.
It must be understood that no mode of mechanical ventilation can or will
cure a disease process but merely supports the patient until resolution of his/
her symptoms is accomplished.
Purposes:
Mechanical ventilation is instituted to:
1- Maintain or improve ventilation, i.e. for adequate tissue oxygenation.
2- Decrease the work of breathing and improve patient’s comfort.
Indications:
Acute respiratory failure due to:
• Mechanical failure, includes neuromuscular diseases as Myasthenia
Gravis, Guillain-Barré Syndrome, and Poliomyelitis (failure of the
normal respiratory neuromuscular system)
• Musculoskeletal abnormalities, such as chest wall trauma (flail chest)
• Infectious diseases of the lung such as pneumonia, tuberculosis.
Abnormalities of pulmonary gas exchange as in:
• Obstructive lung disease in the form of asthma, chronic bronchitis or
emphysema.
• Conditions such as pulmonary edema, atelectasis, pulmonary fibrosis.

**Patients who has received general anesthesia as well as post cardiacarrest
patients often require ventilatory support until they have recovered from
the effects of the anesthesia or the insult of an arrest.
Criteria for institution of ventilatory support:
Parameters Ventilation
indicated
Normal range
Pulmonary function studies:
• Respiratory rate (breaths/min).
• Tidal volume (ml/kg body wt)
• Vital capacity (ml/kg body wt)
• Maximum Inspiratory Force (cm
HO2)
> 35
< 5
< 15
<-20
10-20
5-7
65-75
75-100
Arterial blood Gases
• PH
• Pa2 (mmHg)
• PaCO2 (mmHg)
< 7.25
< 60
> 50
7.35-7.45
75-100
35-45
These parameters are used in making judgments about the adequacy of
respiratory function.
Types of Mechanical ventilators:
1- Negative-pressure ventilators
2- Positive-pressure ventilators.

Negative-Pressure Ventilators
- Early negative-pressure ventilators were known as ―iron lungs. The
patient’s body was encased in an iron cylinder and negative pressure was
generated by a large piston to enlarge the thoracic cage. This caused
alveolar pressures to fall, and a pressure gradient was formed so that air
flowed into the lungs.
- The use of negative-pressure ventilators is restricted in clinical practice,
however, because they limit positioning and movement and they lack
adaptability to large or small body torsos.
- Our focus will be on the positive-pressure ventilator.
Positive-pressure ventilators
Positive-pressure ventilators deliver gas to the patient under positive-
pressure, during the inspiratory phase.

Classification of positive-pressure ventilators:
- Ventilators are classified by their method of cycling from the inspiratory
phase to the expiratory phase (changeover from inspiratory to expiratory
phase), that is to say according to how the inspiratory phase ends. The
factor which terminates the inspiratory cycle reflects the machine type.
- They are classified as: pressure, volume or time cycled machines.
• Volume-cycled ventilator,
- In which inspiration is terminated after a preset volume has been delivered
by the ventilator. i.e. the ventilator delivers a preset tidal volume (VT), and
inspiration stops when the preset tidal volume is achieved.
• Pressure-cycled ventilator,
- In which inspiration is terminated when a specific airway pressure has been
reached. i.e. the ventilator delivers a preset pressure; once this pressure is
achieved, end inspiration occurs.
• Time-cycled ventilator,
- In which inspiration is terminated when a preset inspiratory time, has
elapsed. Time cycled machines are not used in adult critical care
settings.They are used in pediatric intensive care areas.

Ventilator Modes
- Several different modes of ventilatory control are available on ventilators.
- There is no one best mode for managing patients in respiratory failure,
although each mode has its advantages and disadvantages.
Modes of mechanical ventilation
- The term ―ventilator mode‖ refers to the way the machine ventilates the
patient.i.e. how much the patient will participate in his own ventilatory
pattern. Each mode is different in determining how much work of
breathing the patient has to do.
A- Volume Modes
1- Assist-control (A/C) mode
2- Synchronized intermittent mandatory ventilation (SIMV) mode.
1- Assist Control Mode A/C
- The ventilator provides the patient with a pre-set tidal volume at a pre-set
rate and the patient may initiate a breath on his own, but the ventilator
assists by delivering a specified tidal volume to the patient.
- Client can initiate breaths that are delivered at the preset tidal volume.
- Client can breathe at a higher rate than the minimum number of
breaths/minute that has been set.
- The total respiratory rate is determined by the number of spontaneous
inspiration initiated by the patient plus the number of breaths set on the
ventilator.
- In A/C mode, a mandatory (or ―control‖) rate is selected.
- If the patient wishes to breathe faster, he or she can trigger the ventilator
and receive a full-volume breath.
- Often used as initial mode of ventilation
-This mode of ventilation is often used fully to support a patient,
such as when the patient is first intubated

- When the patient is too weak to perform the work of breathing(e.g., when emerging
from anesthesia).
Advantages:
- Ensures ventilator support during every breath
- Each breath has the same tidal volume
Disadvantages:
- Hyperventilation,
- Air trapping
2- Synchronized Intermittent Mandatory Ventilation SIMV
- The ventilator provides the patient with a pre-set number of breaths/minute
at a specified tidal volume and fio2. In between the ventilator-delivered
breaths, the patient is able to breathe spontaneously. The ventilator does not
assist the spontaneous breaths i.e. the patient determines the respiratoryrate
and tidal volume.
- Between machine breaths, the client can breathe spontaneously at his own
tidal volume and rate with no assistance from the ventilator.
- In SIMV mode, the rate and tidal volume are preset.
- If the patient wants to breathe above this rate, he or she may.
- However, unlike the A/C mode, any breaths taken above the set rate are
spontaneous breaths taken through the ventilator circuit.
- The tidal volume of these breaths can vary drastically from the tidal volume
set on the ventilator, because the tidal volume is determined solelyby the
patient’s spontaneous effort.
- Adding pressure support during spontaneous breaths can minimize the risk
of increased work of breathing. In the past, SIMV has been used as a popular
weaning mode.
- Same as intermittent mandatory ventilation except stacking is avoided i.e.
ventilators breaths are synchronized with the patient spontaneous breathe.
- Used to wean the patient from the mechanical ventilator.
- To wean the patient, the mandatory breaths were gradually decreased,
thereby allowing the patient to assume more and more of the work of
breathing.

- Often used as initial mode of ventilation and for weaning
Advantages:
- Allows spontaneous breaths (tidal volume determined by patient) between
ventilator breaths;
- Weaning is accomplished by gradually lowering the set rate and allowing
the patient to assume more work
Disadvantages:
- Patient–ventilator asynchrony possible
B- Pressure Modes
- Pressure modes include :-
1- Pressure-controlled ventilation (PCV) mode,
2- Pressure-support ventilation (PSV) mode,
3- Continuous positive airway pressure (CPAP)/PEEP mode,
5- Noninvasive bilevel positive airway pressure ventilation (BiPAP) mode.
1- Control Mode CM
Continuous Mandatory Ventilation( CMV)
•Ventilation is completely provided by the mechanical ventilator with a
preset tidal volume, respiratory rate and oxygen concentration prescribed
by the physician.
•Ventilator totally controls the patient’s ventilation i.e. the ventilator
initiatesand controls both the volume delivered and the frequency of
breath.
•Client does not breathe spontaneously.
•Client cannot initiate breathe
2-Pressure-Controlled Ventilation Mode( PCV)
The PCV mode is used
- to control plateau pressures in conditions such as ARDS where
compliance is decreased and the risk of barotrauma is high.

- It is used when the patient has persistent oxygenation problems
despite a high FIO2 and high levels of PEEP.
- The inspiratory pressure level, respiratory rate, and
inspiratory–expiratory(I:E) ratio must be selected.
- Tidal volume varies with compliance and airway resistance
and must beclosely monitored.
•Sedation and the use of neuromuscular blocking agents are frequently
indicated, because any patient–ventilator asynchrony usually results in
profound drops in the SaO2.
•This is especially true when inverse ratios are used. The ―unnatural‖
feeling of this mode often requires muscle relaxants to ensure patient–
ventilator synchrony.
•Most ventilators operate with a short inspiratory time and a long expiratory
time (1:2 or 1:3 ratio). This promotes venous return and allows time for air
to exit the lungs passively.
•When the PCV mode is used, the mean airway and intrathoracic pressures
rise, potentially resulting in a decrease in cardiac output and oxygen
delivery. Therefore, the patient’s hemodynamic status must be monitored
closely.
•Used to limit plateau pressures that can cause barotrauma
•Severe ARDS
Disadvantages:
Patient–ventilator asynchrony possible, necessitating sedation/paralysis
Monitor
a- Tidal volume at least hourly.
b- Barotraumas
c- Hemodynamic instability

2- Pressure Support Ventilation ( PSV)
•The patient breathes spontaneously while the ventilator applies a pre-
determined amount of positive pressure to the airways upon inspiration.
•Helps to overcome airway resistance and reducing the work of breathing.
•Patient must initiate all pressure support breaths.
•Pressure support ventilation may be combined with other modes such as
SIMV or used alone for a spontaneously breathing patient.
•Indicated for patients with small spontaneous tidal volume and difficult to
wean patients.
•The patient’s effort determines the rate, inspiratory flow, and tidal volume.
•Because the level of pressure support can be gradually decreased,
endurance conditioning is enhanced.
2- Continuous Positive Airway Pressure CPAP (a variation of PEEP)
•Positive pressure applied at the end of expiration during spontaneous
breaths i.e. for patients breathing spontaneously.
•No mandatory breaths (ventilator-initiated are delivered in this mode)
•All ventilation is spontaneously initiated by the patient.
•PEEP & CPAP are used in patients with hypoxemia refractory to oxygen
therapy. They improve oxygenation by opening collapsed alveoli &
preventing them from collapsing at the end of expiration.
•CPAP allows the nurse to observe the ability of the patient to breathe
spontaneously while still on the ventilator.
•CPAP can be used for intubated and non-intubated patients.
•It may be used as a weaning mode and for nocturnal ventilation (nasal or
mask CPAP) to splint open the upper airway, preventing upper airway
obstruction in patients with obstructive sleep apnea.
4- Noninvasive Bilateral Positive Airway Pressure Ventilation (BiPAP)
•BiPAP is a noninvasive form of mechanical ventilation provided by means
of a nasal mask or nasal prongs, or a full-face mask.
•It is used in the treatment of :-
a- Patients with chronic respiratory insufficiency to manage acute or
chronic respiratory failure without intubations and conventional
mechanical ventilation.
b- Used as a bridge to weaning patients from mechanical ventilation,

c- As an alternative to conventional mechanical ventilation

Common Ventilator Settings
● Fraction of inspired oxygen (FIO2)
- The percent of oxygen concentration that the patient is receiving from the
ventilator. (Between 21% & 100%) (room air has 21% oxygen content).
•Initially a patient is placed on a high level of FIO2 (60% or higher).
Subsequent changes in FIO2 are based on ABGs and the SaO2.
•In adult patients who can tolerate higher levels of oxygen for a period of
time, the initial FiO2 may be set at 100% until arterial blood gases can
document adequate oxygenation.
•An FiO2 of 100% for an extended period of time can be dangerous
(oxygen toxicity) but it can protect against hypoxemia from
unexpected intubation problems.
•For infants, and especially in premature infants, high levels of FiO2
(>60%) should be avoided.
-Usually the FIO2 is adjusted to maintain an SaO2 of greater than 90%
(roughly equivalent to a PaO2 >60 mm Hg). Oxygen toxicity is a concern
when an FIO2 of greater than 60% is required for more than 25 hours;
therefore, most clinicians attempt to use strategies to allow for maintenance
of an FIO2 of 60% or less.
• Signs and symptoms of oxygen toxicity :-
1- Flushed face
2- Dry cough
3- Dyspnea
4- Chest pain
5- Tightness of chest
6- Sore throat

• Tidal Volume (VT)
•The volume of air delivered to a patient during a ventilator breath.
•The amount of air inspired and expired with each breath. (Usual
volume selected is between 5 to 15 ml/ kg body weight)
•Research has identified a phenomenon of iatrogenic lung injury
(volutrauma) in which forces produced in the lungs by the large tidal
volumes may aggravate the damage inflicted on the lungs by the
pathological process that necessitated mechanical ventilation.
•For this reason, lower tidal volume targets (6 to 8 mL/kg) are now
recommended.
Respiratory Rate/ Breath Rate / Frequency ( F)
•The number of breaths the ventilator will deliver/minute (10-16 b/m).
I:E Ratio (Inspiration to Expiration Ratio):-
•The ratio of inspiratory time to expiratory time during a breath
(Usually = 1:2)
Sign:-
•A deep breath.
•A breath that has a greater volume than the tidal volume.
•It provides hyperinflation and prevents atelectasis.
Positive End-Expiratory Pressure (PEEP)
•Positive pressure applied at the end of expiration during ventilator breaths.
•The PEEP control adjusts the pressure that is maintained in the lungs at the
end of expiration.
•PEEP is usually USED IN low levels increased in increments of 2 to 5 cm
H2O in the intubated patient.

Ensuring humidification and thermoregulation
•All air delivered by the ventilator passes through
the water in the humidifier, where it is warmed
and saturated. Because of this, insensiblewater loss
is decreased.
•Humidifier temperatures should be kept close to
body temperature 35 ºC-37ºC.
•In some rare instances (severe hypothermia), the air
temperatures can beincreased. Caution is advised
because prolonged inhalation of air at high
temperatures can cause tracheal burns.
•The humidifier should be checked for adequate water levels
•An empty humidifier contributes to drying the
airway, often with resultantdried secretions, mucus
plugging and less ability to suction out secretions.
•Humidifier should not be overfilled as this may
increase circuit resistance and interfere with
spontaneous breathing.
•As air passes through the ventilator to the patient,
water condenses in the corrugated tubing. This
moisture is considered contaminated and must be
drained into a receptacle and not back into the sterile
humidifier.
•If the water is allowed to build up, resistance is
developed in the circuit and PEEP is generated. In
addition, if moisture accumulates near the
endotracheal tube, the patient can aspirate the water.
Ventilator alarms:-
•Mechanical ventilators comprise audible and visual
alarm systems, whichact as immediate warning

signals to altered ventilation.
•High-pressure alarms warn of rising pressures.
Electrical failure alarms arenecessary for all
ventilators.
•Low-pressure alarms warn of disconnection
of the patient from theventilator or circuit
leaks.
Complications of Mechanical Ventilation:-
I- Airway Complications,
a. Aspiration
b. Decreased clearance of secretions
c. Nosocomial or ventilator-acquired pneumonia
II- Mechanical complications,
a. Hypoventilation with atelectasis with
respiratory acidosis or hypoxemia.
b. Hyperventilation with hypocapnia and
respiratory alkalosis
c. Barotrauma
d. Alarm - Failure of alarms or ventilator
III- Physiological Complications,
a. Fluid overload with humidified air and
sodium chloride (NaCl) retention
b. Depressed cardiac function and
hypotension
c. Stress ulcer
d. Gastric distension
e. Starvation
f. Dyssynchronous breathing pattern

Mechanical Ventilation by ms preeti Singh

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