Transcript tums.ac.ir

1
Terminology
– f: rate of breathing
– Vt: Tidal volume
– VA: Alveolar ventilation
– VD: dead space = 2.2 ml/ kg
– FiO2: fraction of inspired O2
– PEEP: Positive End Expiratory Pressure
– PASB : Pressure Above Spontaneous Breathing
– ASB : Assisted Spontaneous Breathing
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Basic pulmonary physiology
 Air that moves in and out of a patient's lungs per
minute that is 7-10 L/min  Minute volume (MV)
MV =Vt x f
 Alveolar ventilation (VA)  in contact with the
alveolar-capillary gas exchange interface
 VA = (Vt - VD ) x f
Volume-pressure relation: P = V/C
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Plateau pressure (static pressure)
• … is the pressure at the end of inspiration
with a short breath hold
• It should not be exceed 30 cmH2O
• P plateau ~ 1/compliance (P = V/C)
•
volume =
P plateau
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Pressure-time diagram for
volume controlled constant
flow ventilation
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Peak Airway Pressure
(dynamic pressure)
• …. is pressure during inspiration
• So related to both airway resistance and compliance
•
compliance and/or
resistance 
P peak
• P peak – P plateau < 4 cm H2O (normal gradient)
• P peak is a vital sign for mechanically ventilated
patients.
• P peak < 35 cmH2O
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Changes in inspiratory airway resistance
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Paw-peak increased but Plateau
pressure unchanged:
1. Tracheal tube obstruction
and kinking
2. Airway obstruction from
secretions
3. Acute bronchospasm
Rx: Suctioning and
Bronchodilators
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Changes in compliance
In this situation P-P gradient is fixid.
increasing compliance → plateau and peak pressures fall
decreasing compliance → plateau and peak pressures rise
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Paw-peak and Plateau pressure
are both increased:
1. Pneumothorax
2. Lobar atelectasis
3. Acute pulmonary edema
4. Worsening pneumonia
5. ARDS
6. COPD with tachypnea and Auto-PEEP
7. Increased abdominal pressure
8. Asynchronous breathing
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Decreased Paw-peak:
1.Inadequate gas supply, inadvertent change in
setting, system air leak, Tubing disconnection,
cuff leak, unintended extubation and failure of
the ventilator
Rx: Manual inflation, listen for leak
2. Hyperventilation: Enough negative intrathoracic
pressure to pull air into lungs may drop PawPeak
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Measurements
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Measurements
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P –T curve
At the start of inflation, the airway pressure immediately rises
because of the resistance to gas flow (A), and at the end of
inspiratory gas flow the airway pressure immediately falls by the
same pressure (A) to an inflexion point.
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P/T F/T V/T curves in
VCV
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Increase in Ppeak–Pplat gradient
• Increased airway resistance caused
by heat and moisture exchanger (HME)
• Patient biting endotracheal tube
• Kinked or twisted endotracheal tube
• Obstruction of endotracheal tube by
secretions, mucus, blood
• Bronchospasm
• Obstruction of lower airways
Schematic of two superimposed pressure-time curves
showing a small increase in peak inspiratory pressures
(Ppeak) with a greater increase in plateau pressures
(Pplat).
This is characteristic of decreased lung compliance
Unchanged or decreased
Ppeak–Pplat gradient
•
•
•
•
•
•
Pneumonia
Atelectasis
Mucus plugging of one lung
Unilateral intubation
Pneumothorax
Pulmonary edema (noncardiogenic and
cardiogenic)
• Abdominal distention/pressure
Spontaneous Breathing
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Positive End Expiratory Pressure
• … is the pressure at the end of expiration
• Serial Elevated PEEP 
P plateau and FRC
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1- Extrinsic PEEP
(applied PEEP by MV)
•
•
•
•
3 - 20 cm H2O and be started on 5 cm H2O
It improves the oxygenation not CO2 removal
It may be increased 3-5 cmH2O Q 10-15 min
It has some side effects: biotraumas and
hemodynamic compromise
• What is the optimal PEEP?
1- increasing PEEP until a complication occurs
2- assessing P plateau
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Optimal PEEP
1. P-V curve monitoring
2. Cardiac Output monitoring and Venous Oxygen
Saturation
If SmvO2 decreases after PEEP application  Drop
C.O.
In this situation 
PEEP and/or tidal volume
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P-V curve
Adequate PEEP
Inadequate PEEP
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PEEP
PEEP Disadvantages:
• 1. Decrease BP & CPP
2. Increase PCO2
3. because alveolar injury is often heterogeneous,
appropriate PEEP in one region may be
suboptimal in another and excessive in another
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2- Intrinsic PEEP
• …is incomplete alveolar emptying during expiration
due to air trapping
• Ventilator Factors: High inflation volumes, rapid
rate, low exhalation time
• Disease factors: Asthma, COPD (collapsed airway)
• And has some effects:
– Decreased C.O.
– Alveolar rupture
– increased work of breathing
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Int. PEEP
• Int. PEEP may be detected in two ways:
(1) evaluating the flow-time trace (exp. Flow not
returned to zero before next breath)
(2) disconnecting the patient from the ventilator and
listening for additional exhaled gas after an
exhalation has occurred.
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 Pressure cycled
• Volume
cycled
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 No absolute contraindications
 Loss of airway anatomy
Loss airway protection
 Respiratory and cardiac Failure





Apnea / Respiratory Arrest
Inadequate ventilation (acute vs. chronic)
Inadequate oxygenation
Eliminate work of breathing
Reduce oxygen consumption
 Neurologic dysfunction
 Central hypoventilation/ frequent apnea
 Comatose patient, GCS < 8
 Inability to protect airway
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Control mechanisms
1. Spontaneous breathing (PSV)
2. Pressure targeted ventilation
3. Volume targeted ventilation
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• Setting: FiO2 and PEEP
• Flow and f is dictated by patient
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Alters gas flow and volume  fixed preset airway
pressure (Paw) for the duration of a preset
inspiratory time (Ti )
 Advantage: fixed pressure  limit or eliminate
alveolar over-distention and barotraumas
 One problem: changes in compliance or resistance
with fixed Paw  variable received volume
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
Deliver a preset volume of gas ( VT)  Paw is
variable
Advantage: delivery a constant VT
changes in compliance or resistance with fixed
volume  changes airway pressure
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• There are no clinical outcome studies showing benefit
of one breath-targeting strategy over the other.
• Pressure-targeting provide a variable flow tends to
synchronize better with patient effort.
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Control Mode Ventilation
Continuous mandatory ventilation
Continuous mechanical ventilation
Controlled mandatory ventilation
 Intermittent Positive Pressure Ventilation (Dräger)
 …is a full support mode (machine breaths)
 All breaths are supported regardless of initiation of
breathing and can be set to VCV and PCV
 Used for: apneic patients, respiratory muscle
weakness and LV dysfunction
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(CMV/AC )
Sensitivity pressure  0.5 to 2 cm H2O (1-3
cm H2O Tintinalli)
The higher sensitivity  the greater work of
breathing
After spontaneous breath  the ventilator`s
timer resets from this time
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(CMV /AC)
CMV  preferred and most commonly used
initial mode for acute phase of respiratory failure
in ED
 but CMV :
1. Poor toleration in awake patients
2. Worsening of volume retention in COPD /
asthma
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A/C mode
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SIMV (Dräger, Hamilton)
SIMV (VC) + PS (Maquet)
 VCV-SIMV (Puritan-Bennett, Respironics)
Volume SIMV (Viasys)
Intermittent demand ventilation
 IMV  combination of spontaneous vent. and AC
 IMV  is a partial support mode
 This ventilator mode provides breaths at a preset rate
(machine breath) similar to the AC mode
 Can be set to PCV and VCV
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(IMV / SIMV )
 But in spontaneous breath  only receive a spontaneous VT
with no support from the ventilator and has a high work of
breathing
 The synchronized version of IMV
spontaneous and machine breaths

coordination
 SIMV:
1. To prevent excess VT delivered (stacking)  decreased
hyperinflation, barotrauma
2.
During exhalation from a spontaneous breath
exhalation compromised
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Assisted Spontaneous Breathing(Dräger)
Spontaneous mode(Hamilton, Puritan-Bennett)
Pressure support (Maquet)
CPAP (Respironic)
Pressure Support Ventilation (Viasys)
continuous positive-pressure breathing (CPPB )
EPAP
 Is a partial support mode
 Breathing control by the patient (spontaneous mode ) ,
and peak Paw control by machine (pressure targeted)
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PSV
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PSV / ASB / CPAP
 Help the patient overcome the resistance of the
circuit  decreased work of breathing
 This is not useful in apnea
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CPAP / PSV / ASB
 CPAP  the least amount of support and used with IPPV
or NIPPV
Most commonly used in (COPD) , CHF and
obstructive sleep apnea with NIPPV ( via a tightfitting nasal or full face-mask)
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CPAP / PSV / ASB
 With IPPV  CPAP is typically used as a weaning
mode
 The CPAP level when transitioning from IMV/PSV or AC
mode should be the PEEP level that was being used
 Reducing the CPAP below the previous PEEP :
1.
2.
3.
4.
Loss of alveolar recruitment
Atelectasis
Hypoxia
Increased work of breathing
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CPAP / PSV
In partial support:
 CPAP range is from 0 up to 35 cm H20 pressure
 Some ventilators may deliver PSV that achieves a
greater range.
 The average starting point is:
10 cm H20
 Use PSV for approximation of spontaneous Vt and
the set Vt for mandatory breaths
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(CPAP) benefits
Eliminate the work of breathing
To aid in weaning from IMV-base ventilation
and is frequently part of a transition strategy
from IMV to CPAP
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Breath type & examples
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DRÄGER Evita 2
CMV
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DRÄGER Evita 4
CMV
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DRÄGER Evita 2
SIMV
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DRÄGER Evita 4
SIMV
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DRÄGER Evita 2 CPAP
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DRÄGER Evita 4
CPAP
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DRÄGER Evita 2
PCV
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DRÄGER Evita 4 PCV
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DRÄGER Evita XL SIMV
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1. Oxygen
 The fraction of inspired O2 (FiO2) is set in a range
from 21% (room air; not generally indicated) to
100%
 In the ED it is common to start at 100% FiO2 to
ensure adequate oxygenation and titrate the FiO2
down to nontoxic levels (FiO2< 60%) following the
SaO2 via the pulse oximeter (SaO2> 90%) during
first 72 h.
 some practitioners recommend using 95% O2 as the
upper limit of FiO2
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2. Inspiration : Expiration
(I:E) Ratio
• The normal I:E ratio in a spontaneously breathing,
non intubated patient is 1:4
• Intubated patients commonly achieve I:E ratios of
1:2
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3. Flow rate (Q )
• This is the rate of gas delivery (L/min).
• The range of flows that can be achieved by
current ventilation is from 10 to 160 L/min.
• Common flow settings are from 40 to 75 L/min.
• The higher the flow rate, the faster the ventilator
will reach its set volume or pressure.
• Start at Q=60 L/ min
• A faster flow rate  decreased ins. time
• A slower flow rate  decreased exp. time
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Flow-time diagram
VCV
PCV
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Initial ventilator setting
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Pressure triggering
• The sensitivity of the trigger can be adjusted by
changing the pressure drop required for
inspiratory cycling to be triggered, and this can
be set to a value between −1 cm H2O (very
sensitive) and −20 cm H2O (very insensitive)
• If the setting is too sensitive, minor fluctuations
in breathing circuit pressure (e.g. from cardiac
pulsations) can trigger the ventilator
inappropriately.
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Flow triggering
• The reduction in return flow that has to be
detected for triggering to occur can be
adjusted between 1 (very sensitive) and 10
(insensitive) L/min
• Flow triggering is considered to require less
work from the patient to initiate a breath and
therefore may enhance patient comfort and
reduce the work of breathing.
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Advanced modes
• BREATH TO BREATH
–
–
–
–
–
Pressure-regulated volume control (PRVC)
Auto flow
Volume control plus (VC+)
Adaptive pressure ventilation (APV)
Variable-pressure control (VPC)
• WITHIN A BREATH
– Volume-assured pressure support ventilation (VAPSV)
– Pressure augmentation
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Other modes
• High Frequency
Ventilation
• Proportional assist
ventilation
• Airway Pressure Release
Ventilation (Bi-level
ventilation)  PCV
• T high : 4 – 6 s
T low : 0.2 – 1.5 s
• P high : up to 40 cmH2O
P low : 10 cmH2O
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TUMS
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TUMS
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Noninvasive Ventilation
•
For prevention of invasive MV in selected patients
•
No need to definitive airway control
•
Candidates :
COPD, CHF, Asthma, hypoxia, DNR patients
and Immunocompromised patients
1. the airway must be patent,
2. the respiratory drive must be intact,
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3. the patient must be cooperative
(i.e., awake and alert).81
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• Serial assessment and close monitoring Q 30
min
• ABG Q 1-2 h
• Contraindications:
–
–
–
–
–
–
Near arrest
Severe GIB
Anatomic defect of face
Up airway obstruction
AMS
Risk of aspiration and defect in secretion clearance
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Nasal mask
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Advantages of NIV
The potential benefits of NIV over MV are:
1.
2.
3.
4.
a decrease in potential airway injury
decrease in VAP
probably a shorter length of stay
Eating and speech reserved
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Disadvantages of NIV
1. Pulmonary baro-trauma (volu-trauma)
2. pressure necrosis of the facial skin, subcutaneous tissue
and musculature and patient discomfort
3. aerophgia  gastric dilation  vomiting and aspiration
4. hemodynamic compromise
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TUMS
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Bi-level
ventilation
Bi-level ventilation.
A: Baseline pressure cycles between Plow and Phigh with spontaneous, unsupported,
patient breaths during high and low phases.
Transition from low to high phase is synchronized to the patient’s inspiration, and
transition from high to low phase is synchronized to patient’s expiration.
B: As in A, but now inspiratory efforts during the Plow phase trigger support (Psupp).
Bi-level
ventilation
Bi-level ventilation.
C: As in A, but now inspiratory effort during both Plow and Phigh phase trigger support which is targeted to the
same absolute support pressure (Psupp).
If Phigh is greater than Psupp, patient effort during Phigh becomes unsupported.
D: As in A, but now inspiratory effort during both Plow and Phigh phase trigger support which is set specifically for
each phase,relative to the baseline pressure of the phase.
Approach to NIPPV
• In hypoxemia:
EPAP + 2 cmH₂O
and fix interval IPAP
• In hypercapnia:
IPAP + 2 cmH₂O
and
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EPAP= 40% IPAP
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High flow nasal cannula
• … can deliver warm
and humidified air up
to 40 L/min
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1. Severe Acute Lung Injury and ARDS
• Preferred PCV
• consider permissive hypercapnia.
If able to achieve P02> 60 mm Hg on FiO2<60%, the
PCO2 may be allowed to be >40 mm Hg if pH> 7.25.
if needed, use NaHCO3
•
•
•
•
Tv  6 – 8 ml / kg
F  20 – 25 / min
PEEP  8
Monitor P plateau: if > 30 cm H2O  Tv : 4 ml/kg
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2. Severe Asthma and COPD
• The defect is decreased gas flow.
• In conventional ventilation use higher flow rate and
lower respiratory rate to allow more time for
exhalation.
• Tv  5 -8 ml / kg
• F  8 – 10 / min
• Q 80 l/min
• PEEP  5 (50 - 80% intrinsic PEEP)
• Detection of intrinsic PEEP with wean and chest
compression
• Optimal P plateau < 30 cmH2O
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Monitoring of treatment in asthma
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3. Pulmonary edema
• NIPPV is preferred
• If the patient is intubated  PEEP is useful
• But in hypotensive patients  min. PEEP
with continuous evaluation
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5. Traumatic brain injury
• Do not lower PC02 < 35 mm Hg, as it may induce
severe cerebral vasoconstriction and lead to cerebral
ischemia.
• The goal is PC02: 35-40 mm Hg.
• Acceptable to hyperventilate for a patient with an
acute herniation syndrome as a bridging maneuver
for definitive therapy.
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General Guidelines for Initial Invasive Ventilator Settings in Various
Clinical Settings / Rosen`s EM
Mode
FIO2 (%)
VT (mL/kg)
F / min
I/E
PEEP (cm
H2O)
Overdose in
healthy patient
CMV, A/C, IMV,
SIMV
95
8–10
10–12
1:2
0–5
Status
asthmaticus
CMV, A/C, IMV,
SIMV
95
5–10
8–12
1:4
2.5–10
COPD
exacerbation
pulmonary
edema
CMV, A/C, IMV,
SIMV
95
5–10
10–12 1:3–1:4 2.5–10
CMV, A/C, IMV,
SIMV
95
8-10
10–12
1:2
2.5–15
ARDS
CMV, A/C, IMV,
SIMV
95
6-8
20-25
1:2
2.5-10
Hypovolemic
shock
CMV, A/C, IMV,
SIMV
95
8-10
-
1:2
0-5
complications
•
•
•
•
•
•
•
•
•
Pneumothorax
Ventilator induced lung injury
Hemodynamic instability
Difficult trigger ventilation
Auto-cycling (seizure, shivering)
Outstripping and double cycling (demand over Vt)
Straining over the ventilator (demand over Q)
Coughing
Failure to MV
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Approach to res. distress
100
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Indications for extubation
No weaning parameter completely accurate when used alone
• Clinical parameters
• Resolution/Stabilization of disease
process
• Hemodynamically stable
• Intact cough/gag reflex
• Spontaneous respirations
• Acceptable vent settings
• FiO2< 40%, PEEP < 8, PaO2 > 75, pH
> 7.25
Numerical Parameters
Normal
Range
Weaning
Threshold
P/F
> 400
> 200
Tidal volume
5 - 7 ml/kg
5 ml/kg
Respiratory rate
14 - 18 breaths/min
< 40 breaths/min
Vital capacity
65 - 75 ml/kg
10 ml/kg
Minute volume
5 - 7 L/min
< 10 L/min
Greater Predictive
Value
Normal
Range
Weaning
Threshold
NIF (Negative
Inspiratory Force)
> - 90 cm H2O
> - 25 cm H2O
RSBI (Rapid Shallow
Breathing Index)
(RR/TV)
< 50
< 100
Marino P, The ICU Book (2/e). 1998.
Criteria :
• The cause of respiratory failure is
improving or has been eliminated,
• FiO2 < 0.40
• PEEP < 8cm H2O
• No pressors other than
dopamine at <5 μg/kg / min or
Epinephrine or NorEpi. at < 0.05 µg /kg /
min.
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weaning
Parameter
Normal Adult
range
Threshold for
weaning
PaO2/FiO2
>400
200
Tidal Volume 5-7 ml/kg
5 ml/kg
RR
<40 /min
14-18 /min
Minute Vent. 5-7
L/min
Vital
capacity
65-75 ml/kg
Peak
Inspiratory
Pressure
>90 cmH2O (F)
>120 cmH2O (M)
RSBI (f/Vt)
<50
/L
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<10 L/min
10 ml/kg
25 cmH2O
<105
/L
The Problem Wean
• RAPID BREATHING  1
• 1. Check Vt
Low Vt  Resume vent. support
Vt not low  2
• 2. Check PaCO2
PaCO2 decreased  sedate (anxiety)
PaCO2 not decreased  Resume vent.
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• ABDOMINAL PARADOX :
Inward displacement of the diaphragm during
inspiration is a sign of diaphragmatic muscle
fatigue
• HYPOXEMIA : May be due to low C.O.
• HYPERCAPNEA:
– Increase in PaCO2-PetCO2
= increase dead space ventilation
– Unchanged gradient: Respiratory muscle fatigue or
enhanced CO2 production
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Weaning
108
Tracheal Decannulation
• Successful weaning is not synonymous with tracheal
decannulation
• If weaned and not fully awake or unable to clear
secretions, leave ETT in place
• Tracheal decannulation increases the work of
breathing due to laryngeal edema and secretions
• Do not perform tracheal decannulation to reduce
work of breathing
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Inspiratory Stridor
• Post extubation inspiratory stridor is a sign of severe
obstruction and should prompt re-intubation
• Laryngeal edema (post-ext) may respond to aerosolized
epinephrine in children
• Steroids have no role
• Most need reintubation followed by tracheostomy
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Case 1
• An l8-year-old otherwise healthy 60-kg female
presents with an overdose of benzodiazepines.
• She requires intubation for airway protection and
ventilatory support.
• There is no evidence of aspiration or an intrinsic
lung problem.
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With VCV setting
Target Vm = 7.2 L / min
It is reasonable to assume a normal need for
Vm since she has no evidence of
hypoperfusion or infection, and she has not
ingested an medications known to cause a
metabolic acidosis that would require a
higher Vm to buffer by induced hypocarbia.
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Dräger evAita 2
Patient data
Ventilator setting
Alarm setting
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Vt and f
• F= 12 /min
• Vt = 600 mL (7-10 mL/kg)
• This setting will guarantee the desired Vm even
if the patient continues to develop respiratory
depression from the benzodiazepine ingestion.
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Pressure Support Ventilation.
• Initiate PSV at 10 cm H20 pressure, and then
titrate up or down to achieve a spontaneous
breath Vt approximately equal to that of the set
Vt.
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• Gas Delivery Waveform:
Begin with a decelerating waveform.
• Maximal Inspiratory Flow :
Set the initial Q at 60 L/min.
lower Q(Q = 50 L/min) in hypoxemia
higher flow (Q = 70 L/min) in exhalation
obstruction (e.g. COPD), then evaluate the
resultant Paw-peak.
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• If the Vt is appropriate, reduce the flow rate by
L/min and re-evaluate; repeat if necessary.
5
• If the Q is reduced to 40 L/min and the Paw-peak
remains high, :
1) the Vt is, in fact, too large for the available lung
mass,
2) there is a tube obstruction (partial)
3) the patient has a pleural space occupying
disorder (pneumo-, hemo-, hemopneumo-, or
hydro-thorax),
4) the patient requires a different mode
5) there is a ventilator dysfunction
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1
Order writing
2
SIMV
f : 12/ min
FiO2 : 95%
PEEP : 5 cm H2O
ASB / CPAP / PSV : 10 cm
H2O
Flow : 60 L/min Ramp
wave
Then titrate PSV to achieve Vt
spont. 600 ml
• ABG 20 min later
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120
The same patient with PCV setting
 Vm = 7.2 L/min
 Mode = ( in E4 , 2 )
PCV+ SIMV, .PCV.
PSV. ASB
 Q = 160 L/min
( devise adjust the Q in
response to the
patient`s breath.)
 Wave = ramp
 F = 12/ min
 FiO2= 95%
 PSV =10 cm H2O
 PEEP=5 cm H2O
 PC
=[(Paw peak) – PEEP] ×2/3
= (35 – 5)× 2/3
=20 cm H2O
 (Paw Peak )
=PC+ PEEP
=25
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Order writing
1
SIMV
f : 12/ min
PC : 20 cm H2O
Ti : 1 s
FiO2 : 95 %
2
PEEP :5 cm H2O
PSV : 10 cm H2O
Q : max (160) L/min
Wave : ramp
ABG 20 min later
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Case 2
• A 45-year-old, 70-kg male presents with high fevers,
cough, and shortness of breath.
• The ED portable chest film demonstrates bilateral
infiltrates as well as lower lobe air bronchograms.
• While awaiting admission to the hospital for presumed
community-acquired pneumonia, the patient develops
hypoxia, suffers respiratory failure, and requires urgent
intubation.
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• Mode : SIMV-As before, allow the patient to breathe
spontaneously when the short acting neuromuscular
blockers or heavy sedative (e.g., etomidate, fentanyl,
midazolam) used to facilitate intubation wears off.
• Target Vm :Given the likely acidosis, this patient's Vm
needs to exceed the lower limit of normal value.
• Thus, a target of 9.8 L/minute is a 40% increase above the
baseline .
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• initial f= 14 / min
• Vt = 700 ml
• One must evaluate the resultant Paw-peak after starting
at this setting.
• One may also need to reduce the tidal volume and
increase the rate if the Paw-peak is high and no other
mode of ventilation is available.
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• Fi02 : Begin with FiO2 :95% then titrate.
• PEEP : ≥5 (to maintain FRC and alveolar
recruitment with V/S consideration )
• Flow:
• A longer Ti is ideal for alveolar recruitment
and a slow flow rate will complement the
decelerating waveform and further prolong
the Ti.
• Then start with a Q of 50 L/min
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• Start with a higher PSV because the pulmonary compliance
is less than the normal lungs.
• Initiate PSV at 15 cm H20 and titrate to achieve similar Vt
with the machine and spontaneous breaths.
• In PCV : the same MODE & Vm …
• Only set the Ti & PC (longer Ti)
• Then reevaluate the patient`s condition
TUMS
127
TUMS
128