Download MECHANICAL VENTILATION

MECHANICAL
VENTILATION
INDICATIONS FOR
MECHANICAL
VENTILATION
RULE 1. The indication for intubation
and mechanical ventilation is thinking of
it.
RULE 2. Intubation is not an act of
personal weakness.
RULE 3. Initiating mechanical
ventilation is not the "kiss of death
Indications
Relieve respiratory distress
Rest respiratory muscles
Decrease work of breathing
Improve oxygenation
Prevent or reverse atelectasis
Improve ventilation
Decrease O2 consumption
Permit sedation
Stabilize chest wall
Prevent complications
Ventilator indications:

hypoxic respiratory failure


O2sat<90%
Pao2<60(with Fio2.60%)



Hepercapnic respiratory failure



Example ARDS
Always should be treated even contiouss
Acute:Pco2>50, PH<7.3
Chronic:Loss of contiousness
Respiratory depression
Objectives of
Mechanical Ventilation
Improve pulmonary gas exchange
Reverse hypoxemia and Relieve acute respiratory acidosis
Relieve respiratory Distress
Decrease oxygen cost of breathing and reverse respiratory
muscle fatigue
Alter pressure-volume relations
Prevent and reverse atelectasis
Improve Compliance
Prevent further injury
Permit lung and airway healing
Avoid complications
CONTRAINDICATIONS











Intracranial pressure (ICP) > 15 mm Hg
Hemodynamic instability
Recent facial, oral, or skull surgery
Tracheoesophageal fistula
Recent esophageal surgery
Active hemoptysis
Nausea
Air swallowing
Active untreated tuberculosis
Radiographic evidence of bleb
Singulation (hiccups)
Mechanical Ventilation
Abbreviations:
VT: Tidal volume (ml)
RR: Respiratory Rate (bpm)
MV: Minute Volume = VT x RR (l/m))
FiO2: Fraction of inspired Oxygen
PEEP: Positive end expiratory pressure
(cmH20)
(I:E) Ratio : Ratio of inspiratory to
expiratory time.
Ti: Inspiratory time
Flowrate: Speed of gas flow in liters per
minute.
Ventilator settings
1.
2.
3.
4.
5.
6.
7.
8.
Ventilator mode
Respiratory rate
Tidal volume or pressure settings
Inspiratory flow
I:E ratio
PEEP
FiO2
Inspiratory trigger
Mode
FIO2
20% -100%
Rate
4-30
Tidal volume
4-9 cc/kg
Flow
20-100 Lit/min
PEEP/CPAP
0-22 mmH2O
Pressure
5-20 mmH2O
Just for PSV Mode
P ins
5-40mm H2o
Just for CMV Mode
Trigger
1cc/sec (flow trigger)
-1 Cm H2O(pressure
trigger)
Always on minimum
I/E ratio
1/4 1/3 1/2
1/1
2
Respiratory Rate
Tidal Volume or
Pressure setting
Maximum volume/pressure to achieve
good ventilation and oxygenation
without producing alveolar
overdistention
Max cc/kg = 10 cc/kg
Some clinical exceptions
Tidal Volume
Vt > TLC can result in over-distended
lung and lung injury
TLC reduced in lung disease
TLC  plateau pressure = 30 – 35
cmH2O
Tidal Volume
Airway Pressures
Tidal Volume
What Vt should be used?
Traditionally 10-12 ml/kg

“Kg” based on ideal body weight


PBW (male) = 50 + 2.3 [(Ht in inches) – 60]
PBW (female) = 45.5 + 2.3[(Ht in inches) – 60]

Theoretically prevents atelectasis

Most appropriate if normal lungs

Anesthesia, drug overdose
Tidal Volume
What Vt should be used?
Lung disease present

8 –10 ml/kg
Regardless of Vt

Pplateau < 30 – 35 cmH2O
Vt
Obstructive Lung Disease
How do you avoid/correct autoPEEP?

Use smaller tidal volumes

Vt = 6 – 8 ml/kg

 Respiratory rate

 Flow rate

(typical default flow rate ~ 60 L/min)
Vt
ARDS
What is the recommended Vt in ARDS?

Vt = 6 ml/kg

Vt < 6 ml/kg if Pplateau > 30 – 35 cmH2O
What are the complications of low Vt?

Elevated PaCO2


Permissive hypercapnea
Alveolar de-recruitment

Hypoxemia
Double-checking the
selected tidal volume
Once a tidal volume is selected, the peak
airway pressure necessary to deliver a single
breath should be recorded. As tidal volume
increases, the pressure required to force that
volume into the lung also increases. During
mechanical ventilation, a persistent breath-tobreath peak pressure higher than 45 cm
water is a risk factor for barotrauma.
Sighs
Because a spontaneously breathing individual
typically sighs 6-8 times per hour to avoid
microatelectasis, giving periodic machine breaths of
1.5-2 times the preset tidal volume 6-8 times per hour
was once recommended. Often, the peak pressure
needed to deliver such a volume would predispose
the patient to barotrauma.
Today, sighs are usually not used if the patient is
receiving tidal volumes of 10-12 mL/kg or requires
the use of positive end-expiratory pressure (PEEP).
I:E Ratio
1:2
Prolonged at 1:3, 1:4, …
Inverse ratio
FIO2
The usual goal is to use the minimum
Fio2 required to have a PaO2 >
60mmhg or a sat >90%
Start at 100%
Oxygen toxicity normally with Fio2
>60%
Inspiratory flow
Varies with the Vt, I:E and RR
Normally about 40-60 l/min
Can be majored to 100- 120 l/min
Definitions:
Mechanical Ventilation
Volume Ventilation: Pre-set Tidal volume will be
delivered to the patient.
Pressure Ventilation: Pre-set Inspiratory pressure will
be delivered to the patient.
Mandatory breaths: Breaths that the ventilator
delivers to the patient at a set frequency, volume,
flow.
Spontaneous breaths: Patient initiated breath.
Definitions: (Cont’d)
Triggering: The sensitivity of the ventilator to the
patient’s respiratory effort.
Either flow or pressure setting that allows the
ventilator to detect the patient’s inspiratory effort.
Allows the ventilator to be in synchronization with the
patient’s spontaneous respiratory efforts improving
patient comfort during mechanical ventilation.
Ventilators are programmed with
a trigger, which opens the inspiratory
valve and initiates gas flow
a limit, the factor that regulates the
rate/amount of gas flow
cycling, the parameter that ends gas
flow and opens the expiratory valve.
Positive end-expiratory
pressure
PEEP is a mode of therapy used in
conjunction with mechanical ventilation. At
the end of exhalation (either mechanical or
spontaneous), patient airway pressure is
maintained above atmospheric pressure by
exerting a pressure that opposes complete
passive emptying of the lung. This pressure is
typically achieved by maintaining a positive
pressure flow at the end of exhalation.
Positive end-expiratory
pressure
PEEP therapy can be effective when used in patients
with a diffuse lung disease that results in an acute
decrease in functional residual capacity (FRC). In
many pulmonary diseases, FRC is reduced because
of the collapse of the unstable alveoli. This reduction
in lung volume decreases the surface area available
for gas exchange and results in intrapulmonary
shunting. If the FRC is not restored, a high
concentration of inspired oxygen may be required to
maintain the arterial oxygen content of the blood at
an acceptable range.
Positive end-expiratory
pressure
Applying continuous positive pressure at the
end of exhalation (eg, PEEP, continuous
positive airway pressure [CPAP]) causes an
increase in alveolar pressure and an increase
in alveolar volume. This increase in lung
volume increases the surface area by
reopening or stabilizing collapsed or unstable
alveoli. This “splinting” or “propping open” of
the alveoli with positive pressure may provide
a better matching of ventilation to perfusion,
thereby reducing the shunt effect.
Positive end-expiratory
pressure
Once
a
true
shunt
is
changed
to
a
ventilation/perfusion mismatch, lower concentrations
of oxygen can be used to maintain an adequate
PaO2. PEEP therapy has also been effective for
improving lung compliance. When the FRC and lung
compliance are decreased, more energy and volume
are needed to inflate the lung. By applying PEEP, the
lung volume at the end of exhalation is increased,
which decreases the work of breathing because the
lung is already partially inflated; therefore, less
volume and energy are needed to inflate the lung.
Positive end-expiratory
pressure
In summary, when used to treat patients with
a diffuse lung disease, PEEP should improve
compliance, decrease dead space, and
decrease the intrapulmonary shunt effect.
The most significant benefit of PEEP is that
the patient can maintain an adequate PaO2
at a lower and safer concentration of oxygen
(<60%), thereby reducing the risk of oxygen
toxicity.
Positive End-Expiratory
Pressure
PEEP maintains positive airway and
alveolar pressure throughout expiration.
Airway
Pressure
Time
PEEP/CPAP
Indications
Refractory hypoxemia
PaO2/FIO2 < 150
 Prototypic disease = ARDS

COPD with air-trapping
“Physiologic” PEEP
PEEP/CPAP
Where do you start?

PEEP = 5 –7 cmH2O

Increase in increments of 2-3 cmH2O
Where do you stop?

Goals:
Adequate oxygenation
 FIO2 reduced to acceptable level


No upper limit exists
Positive End-Expiratory
Pressure
Physiologic Effects
Increases end-expiratory volume
 Prevents alveolar collapse
Reduces shunt fraction
 Improves PaO2


May over-distend alveoli

Ventilator-induced lung injury
Positive End-Expiratory
Pressure
Physiologic Effects
Increases pleural (intra-thoracic) pressure

Reduces venous return
 Reduces cardiac output and DO2
PEEP
What are the secondary effects of
PEEP?
Barotrauma
 Diminish cardiac output
 Regional hypoperfusion
 NaCl retention
 Augmentation of ICP?
 Paradoxal hypoxemia

PEEP
Relative Contraindications:
Barotrauma
 Airway trauma
 Unilateral lung disease
 Hemodynamic instability
 Hypovolemia
 ICP?
 Bronchopleural fistula

PEEP/CPAP
Why might PEEP worsen hypoxemia in
unilateral lung disease?

Effects of PEEP go to normal alveoli and
not diseased alveoli
PEEP/CPAP
PEEP/CPAP
Complications
What is the most feared complication?

Barotrauma
What is the most common?

Reductions in cardiac output
Loss of venous return to right atrium
 Paradoxical movement of intraventricular
septum
 Pulmonary vessel compression

Ventilator Settings
Changing Initial Settings
Base changes in FIO2 on:
ABG’s
 Pulse oximetry

Base changes in Vt and/or RR on:
Normalizing pH, NOT PaCO2 or HCO3 Avoid “routine” ABG’s

Oxygenation decisions
With the target PaO2 identified, the
FIO2 can be adjusted using the
following formula:
New FIO2 = (old FIO2 X desired
PaO2)/measured PaO2
Ventilation Decisions
New rate = (old rate X measured
PCO2)/desired PCO2
Assist-control,
volume
Ingento EP & Drazen J: Mechanical Ventilators, in Hall JB,
Scmidt GA, & Wood LDH(eds.): Principles of Critical Care
IMV,
volume-limited
Ingento EP & Drazen J: Mechanical Ventilators, in Hall JB, Scmidt
GA, & Wood LDH(eds.): Principles of Critical Care
SIMV, volumelimited
Ingento EP & Drazen J: Mechanical Ventilators, in Hall JB,
Scmidt GA, & Wood LDH(eds.): Principles of Critical Care
MODE
TRIGGER
CYCLING
Clinical situation
PCV
TIME
PRESSU
RE
PNEUMOTHPRAX,THORAX
SURGERY,FLAIL CHEST
CMV
TIME
VOLUME
COMPLETE APNEA,FULL
SUPPORT
ACMV
TIME/PATIE
NT
VOLUME
CHF,EDEMA ,ARDS
SIMV
TIME/PATIE
NT
VOLUME
APNEA,ARDS,ASTHMA,COP
D,ILD,…
PSV(spo
nt)
PATIENT
FLOW
WEANING
PCV: pressure controled Ventilation
CMV: controled mode ventilation
ACMV: Assist controled mode
ventilation
SIMV: spontanous intermittent
mandatory ventilation
PSV:pressure support ventilation
ASV:asssist spontanous ventilation
‫همیشه دم اکتیواست و باز دم پسیو‬
‫‪PCV‬‬
‫‪‬‬
‫‪‬‬
‫‪‬‬
‫مثال هر ‪ 5‬ثانیه دستگاه یک دم میدهد‪.‬‬
‫بیمار اپنه کامل باشد‬
‫حجم متغیر خواهد بود‪.‬‬
‫‪CMV‬‬
‫‪ACMV‬‬
‫‪‬‬
‫‪‬‬
‫همه تنفس های بیمار را ساپورت می کند حتی اگر ‪30‬تنفس در دقیقه‬
‫خطر بارو تروما‬
‫‪SIMV‬‬
‫‪‬‬
‫تنفس های بیمار را بیشتر از ریت دستگاه ساپورت نمی کند‬
‫‪PSV‬‬
‫فشار اعمال شده هنگام دم باعث افزایش حجم جاری می شود‪.‬‬
‫‪Trigger:‬‬
‫‪ ‬به ونتیالتور می فهماند که تنفس بیمار شروع شده است‪.‬‬
A NEW STRATEGY FOR
MECHANICAL
VENTILATION
In the early
days , large inflation volumes
were recommended to prevent alveolar
collaps.
tidal volume during is normally 5 to 7 mL/kg
(ideal body weight), the standard inflation
volumes during volume-cycled ventilation
have been twice as large, or 10 to 15 mL/kg.
The large inflation volumes can damage the
lungs , and promote injury in distant organs
through the release of inflammatory cytokines
. ( velltilator-induced lungg injury)
Ventilator-Induced Lung
Because inflation volumes
are distributed preferentially to
Injury
regions of normal lung function overdistend the normal
regions of diseased lungs. The hyperinflation of normal
lung regions can produce stress fractures at the
alveolar-capillary interface
These fractures may be the result of excessive alveolar
pressures (barotrallma) or excessive alveolar volumes
(voilltrallma) .
Alveolar rupture can have three adverse consequences:
first is accumulation of alveolar gas in the pulmonary
parenchyma (pulmonary interstitial emphysema),
mediastinum
(pneumomediastinum), or pleural cavity (pneumothorax).
second : inflammatory lung injury that is indistinguishable
from ARDS
third and possibly worst consequence is multiorgan injury
from release of inflammatory mediators into the
bloodstream (biotrallma)
Lung-Protective
Ventilation
Low volume or lung protective ventilation is now
recommended for all patients with ARDS, but there
is evidence that ventilator-induced lung
injury also occurs in conditions other than ARDS .
Therefore, lung protective ventilation with low tidal
volumes is considered a beneficial strategy for all
patients with acute respiratory failure.
Using tidal volume of 6cc/kg is recommended
Positive End-Expiratory
Pressure
Low tidal volumes can result in airway
collapse, Repeated opening and
closing of airways at the end of
expiration can become a source of lung
injury
Airways collapse can be mitigated by
adding positive end-expiratory pressure
(PEEP)
Permissive Hypercapnia
Another consequence of low volume
ventilation is a reduction in CO2
elimination via the lungs, which can lead
to hypercapnia and respiratory acidosis.
Allowing hypercapnia to persist in favor
of maintaining low volume ventilation is
known as permissive hypercapnia
MONITORING LUNG
MECHANICS
Proximal Airway Pressures
Positive-pressure mechanical
ventilators have a pressure gauge that
monitors the proximal airway pressure
during each respiratory cycle.
End-Inspiratory Peak
Pressure
The peak pressure at the end of inspiration (P peak)is a
function of the inflation volume, the flow resistance in the
airways, and the elastic recoil force of the lungs and chest
wall
P peak= (Resistance + Elastance)
when the inflation volume is constant, an increase in peak
inspiratory pressure indicates an increase in airway
resistance or an increase in the elastic recoil force of the
lungs (or both).
'End-Inspiratory Plateau
Pressure
When the inflation volume is held in the lungs, the
proximal airway pressure decreases initially and then
reaches a steady level, which is called the end-inspiratory
plateau pressure.
the Plateau Pressure is directly related to the elastic
recoil force (elastance) of the lungs and chest wall.
PpIateau=:Elastance
the difference between end-inspiratory peak and plateau
pressures is proportional to the flow resistance in the
airways.
(P k - P I t) =:Airways Resistance
Practical Applications
A common scenario in any ICU is a
ventilator-dependent patient who
develops a sudden deterioration in
cardiopulmonary status (this could
include hypotension, hypoxemia, or
respiratory distress).
If the peak pressure is increased but the plateau
pressure is unchanged, the problem is an
increase in airways resistance.
In this situation, the major concerns are
obstruction of the tracheal tube, airway
obstruction from secretions, and acute
bronchospasm.Therefore, airways suctioning is
indicated to clear secretions,followed by an
aerosolized bronchodilator treatment if
necessary.
If the peak and plateau pressures are both increased,the
problem is a decrease in distensibility of the lungs and
chest wall.
the major concerns are pneumothorax, lobar atelectasis,
acute pulmonary edema, and worsening pneumonia or
ARDS.
Active contraction of the chest wall and increased abdominal
pressure.
Finally,a patient with obstructive lung disease who becomes
tachypneic an develop auto-PEEP