Initiation of mechanical ventilation and weaning

INITIATION OF
MECHANICAL
VENTILATION AND
WEANING
MODERATOR: DR. AHSAN SIDDIQUI
BY: DR. PRIYAL GUPTA
DR. ABHISHEK PRAKASH
DR. SHIV SHANKAR
YADAV

• Mechanical Ventilation is ventilation of the
lungs by artificial means usually by a
ventilator.
PURPOSES
• To improve gas exchange
• To relieve respiratory distress
• To improve pulmonary mechanics
• To permit lung and airway healing
• To avoid complications by protecting lung and
airway

INDICATIONS
Mechanical ventilation is indicated when the paient cannot maintain
spontaneous ventilation to provide adequate oxygenation or carbon dioxide
removal
INDICATION EXAMPLES
1.Acute ventilatory failure Apnoea or bradypnoea
Acute lung injury (ALI), ARDS
pH<7.3, PaCO2>50mmHg
2.Severe hypoxemia PaO2<40mmHg, SaO2<75%
P/F ratio≤300mmHg for ALI, ≤200mmHg for
ARDS
3.Impending ventilatory failure Progressive acidosis and hypoventilation to
pH<7.3, PaCO2>50mmHg
Spontaneous frequency>30/min
4.Prophylactic ventilatory support Post anaesthesia recovery
Muscle fatigue
Neuromuscular disease

ACUTE VENTILATORY FAILURE
• Sudden increase in PaCO2 to greater than 50mmHg with an
accompanying respiratory acidosis (pH<7.30).
• In the COPD patient, mechanical ventilation is indicated by an acute
increase in PaCO2 above the patient’s normal baseline PaCO2
accompanied by a decompensating respiratory acidosis.
• Other helpful signs: apnoea, severe cyanosis
• If hypoxemic patient is able to maintain adequate ventilation as
documented by the PaCO2, then patient may be supported with
supplemental O2 or CPAP.
SEVERE HYPOXEMIA
• Hypoxemia can be assessed by measuring the PaO2 or the alveolar-
arterial oxygen pressure gradient [P(A-a)O2].
• Severe hypoxemia is present when PaO2<60mmHg on 50% or more
of oxygen or <40mmHg at any FiO2

ASSESSMENT OF IMPENDING VENTILATORY
FAILURE
PARAMETER LIMIT
Tidal volume <3 to 5mL/kg
Respiratory rate and pattern >30/min
Laboured or irregular respiratory pattern
Minute ventilation >10L/min
Vital capacity <15mL/kg
Max. inspiratory pressure <-20cm H2O
PaCO2 trend Increasing to over 50mmHg
Vital signs Increase in heart rate, blood pressure

INDICATIONS FOR PROPHYLACTIC
VENTILATORY SUPPORT
INDICATION EXAMPLES
Reduce risk of pulmonary
complications
Prolonged shock
Head injury
Smoke inhalation
Reduce hypoxia of major body
organs
Hypoxic brain
Hypoxia of heart muscles
Reduce cardiopulmonary stress Prolonged shock
Coronary artery bypass surgery
Other thoracic or abdominal
surgeries

CONTRAINDICATIONS
• ABSOLUTE:
Untreated tension pneumothorax: mechanical
ventilation at any positive pressure level must not be
done without a functional chest tube to relieve the
pleural pressure
• RELATIVE:
1. Patient’s informed request
2. Medical futility
3. Reduction or termination of patient pain and
suffering

TYPES OF MECHANICAL
VENTILATION

• NEGATIVE PRESSURE VENTILATION: creates a
transairway pressure gradient by decreasing the alveolar
pressures to a level below the airway opening pressure (i.e.
below atmoshperic pressure)
Classic devices: iron lung, chest cuirass
• POSITIVE PRESSURE VENTILATION
Deliver gas to the patient under positive-pressure,
during the inspiratory phase and classified according to how
the inspiratory phase ends.
The factor which terminates the inspiratory cycle reflects the
machine type.
Types: pressure-cycled ventilator
volume cycled ventilator
time-cycled ventilator
flow-cycled ventilator

• Volume-cycled ventilator:
The ventilator delivers a preset tidal volume (VT), and
inspiration stops when the preset tidal volume is achieved.
• Pressure-cycled ventilator:
The ventilator delivers a preset pressure; once this pressure is
achieved, expiration 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.

MODES OF MECHANICAL
VENTILATION
• A ventilator mode can be defined as a set of
operating characteristics that control how the
ventilator functions.
• An operating mode can be described by the way a
ventilator is triggered into inspiration and exhalation
and whether it allows mandatory breaths or
spontaneous breaths or both.

CONTROLLED MANDATORY
VENTILATION (CMV)
• Also known as continuous mandatory ventilation or control
mode.
• The ventilator delivers a preset tidal volume at a time-triggered
respiratory rate.
• The patient cannot change the ventilator respiratory rate or
breathe spontaneously.
• Should only be used when the patient is properly medicated
with a combination of sedatives, respiratory depressants and
neuromuscular blockers.
• Indicated when the patient ‘fights’ the ventilator in the initial
stages.
• Primary hazard is the potential for apnoea and hypoxia if the
patient becomes accidently disconnected or if the ventilator
fails to operate.

ASSIST CONTROL VENTILATION
(ACV)
• The mandatory mechanical breaths may be either:
-patient triggered by the patient’s spontaneous inspiratory
efforts (assist)
-time triggered by a preset respiratory rate (control)
• Typically used for patients who have a stable respiratory
drive (spontaneous efforts of at least 10 to 12 BPM).
• Patient’s work of breathing requirement is very small when
the triggering sensitivity(pressure or flow) is set
appropriately.
• This mode allows the patient to control the respiratory rate
and therefore the minute volume required to normalize the
patient’s PaCO2
• Potential hazard associated is alveolar hyperventilation
(respiratory alkalosis).

INTERMITTENT MANDATORY
VENTILATION (IMV)
• The ventilator delivers control breaths and allows the
patient to breathe spontaneously at any tidal volume the
pt is capable of in between mandatory breaths.
• Primary complication is the random chance for ‘breath
stacking’ causing increased lung volume and airway
pressure.
• This occurs when pt takes a spontaneous breath and the
ventilator delivers a time-triggered mandatory breath at
the same time.
• No new adult ventilators offer IMV mode but are
designed to provide synchronised IMV.

SYNCHRONIZED INTERMITTENT
MANDATORY VENTILATION
(SIMV)
• The ventilator delivers either assisted breaths to a
patient at the beginning of a spontaneous breath or a
time triggered mandatory breath.
• Synchronization window: the time interval just prior to
time triggering in which the ventilator is responsive to the
patient’s spontaneous inspiratory effort.
• It is approximately 0.5sec, though may differ with
different manufacturer.
• In between mandatory breaths, SIMV permits the pt to
breathe spontaneously to any tidal volume the pt
desires.
• Mandatory breaths are volume cycled and the patient
controls spontaneous rate and volume.

• The primary indication is to provide partial ventilatory
support so that the pt provides a part of the minute
ventilation.
• Advantages:
1. Maintains respiratory muscle strength/avoids muscle
atrophy
2. Reduces ventilation to perfusion mismatch
3. Decreases mean airway pressure
4. Facilatates weaning
• Main disadvantage is the desire to wean the patient too
rapidly, leading first to high work of spontaneous breathing
and ultimately to muscle fatigue and weaning failure.

PRESSURE CONTROL VENTILATION
(PCV)
• The pressure controlled breaths are time trigggered by a
preset respiratory rate.
• Once inspiration begins, a pressure plateau is created and
maintained for a preset inspiratory time.
• Pressure controlled breaths are therefore time triggered,
pressure limited and time cycled.
• It is usually indicated for patients with severe ARDS who
have extremely high peak inspiratory pressures during
mechanical ventilation in a volume-cycled mode.
• Using this mode would reduce the peak inspiratory
pressure while still maintaining adequate
oxygenation(PaO2) and ventilation(PaCO2) therefore
reducing the risk of barotrauma in such patients.

PRESSURE SUPPORT
VENTILATION (PSV)
• PSV is used to lower the work of spontaneous breathing and augment
a patient’s spontaneous tidal volume.
• These breaths are spontaneous because:
1. They are patient triggered
2. Tidal volume varies with the patient’s inspiratory flow demand
3. Inspiration lasts only for as long as the patient actively inspires
• Inspiration is terminated when the patient’s inspiratory flow rate falls
to 25% of the peak level.
• Low levels of PSV (5-10cm H2O): used during weaning to overcome
the resistance to flow in artificial airways and ventilator tubing.
• High levels of PSV(15-30 cm H2O): to augment tidal volume as a form
of noninvasive ventilation.
• Pressure supported breaths are technically flow-cycled by a minimum
spontaneous inspiratory flow threshold.

SPONTANEOUS MODE
• Not an actual mode since the rate and tidal volume
during spontaneous breathing are determined by the
patient.
• Role is to provide:
1. Inspiratory flow to the patient in a timely manner
2. Flow adequate to fulfil a patient’s inspiratory demand
3. Provide adjunctive modes such as PEEP to compliment
a patient’s effort.
• Apnoea ventilation: a safety feature which in the event of
apnoea or an extremely slow respiratory rate, invokes
backup ventilation to give a predetermined tidal volume,
FiO2 etc.

INVERSE RATIO VENTILATION (IRV)
• This mode reverses the I:E ratio so that inspiratory time is
equal to, or longer than, expiratory time (1:1 to 4:1).
• IRV improves oxygenation by:
1. Reduction of intrapulmonary shunting
2. Improvement of V/Q matching
3. Decrease of deadspace ventilation
• These can also be achieved by use of conventional
modes with PEEP.
• 2 notable changes in IRV:
1. Increase of mean airway pressure
2. Presence of auto-PEEP
• Adverse effects: increase of mean alveolar pressure and
volume, incidence of barotrauma
• Used in conjunction with pressure control (PC-IRV)

PRESSURE REGULATED VOLUME
CONTROL VENTILATION (PRVC)
• Also known as adaptive pressure ventilation.
• Used primarily to achieve volume support while keeping
the peak inspiratory pressure at lowest possible level.
• Alters the peak flow and inspiratory time in response to
changing airway compliance characteristics.
• Automode: provides time-triggered, PRVC breaths when
prolonged apnoea is detected.

POSITIVE END-EXPIRATORY PRESSURE
(PEEP)
• PEEP increases the end-expiratory or baseline airway pressure to a
value greater than atmospheric pressure(0cmH2O).
• Applied in adjunction with other ventilator modes.
• 2 major indications:
1. Intrapulmonary shunt and refractory hypoxemia
2. Decreased FRC and lung compliance
• PEEP reinflates the collapsed alveoli and maintains alveolar inflation
during exhalation.
• Once ‘recruitment’ of the alveoli has occurred, PEEP lowers the
alveolar distending pressure and facilitates gas diffusion and
oxygenation.
• Complications:
. 1. Decreased venous return and cardiac output
2. Barotrauma
3. increased intracranial pressure

AIRWAY PRESSURE RELEASE
VENTILATION (APRV)
• APRV employs prolonged periods of spontaneous
breathing at high end-expiratory pressures, which are
interrupted by brief periods of pressure release to
atmospheric pressure.
• It is a variant of CPAP.
• The CPAP in APRV improves arterial oxygenation by
opening collapsed alveoli (alveolar recruitment) and
preventing further alveolar collapse.
• The pressure release is designed to facilitate CO2
removal.

• Ventilator settings:
1. High airway pressure- this should be equal to end-
inspiratory alveolar pressure (plateau pressure) but
should not exceed 30cm H2O
2. Low airway pressure- set to zero (atmospheric pressure)
to maximize the driving pressure for rapid pressure
release
3. Timimg- time spent at high airway pressure is usually
85-95% of the total cycle time
• Disadvantage: contraindicated in severe asthma and
COPD, cardiac output is often decreased due to high
mean airway pressures.

HIGH FREQUENCY OSCILLATORY
VENTILATION (HFOV)
• HFOV uses high-frequency, low volume oscillations to
create a high mean airway pressure.
• Improves gas exchange in the lungs by opening collapsed
alveoli (alveolar recruitment) and preventing further alveolar
collapse. It is used in paediatric cases.
• The small tidal volumes (typically 1-2mL) limit the risk of
alveolar overdistension and volutrauma.
• Ventilator setting: specialized ventilator required
frequency and amplitude of oscillations (4-7Hz)
mean airway pressure
bias inspiratory flow rate
inspiratory time
• Cardiac output is often decreased during HFOV and
requires augmentation of intravascular volume.

ADAPTIVE SUPPORT VENTILATION
(ASV)
• Also known as intelligent ventilation.
• The ventilator measures the dynamic compliance and expiratory
time constant to adjust the mechanical tidal volume and
frequency for a target minute ventilation.
• The therapist inputs the patient’s body weight and the percent
minute volume.
• Predetermined setting of 100mL/min/kg for adults and
200mL/min/kg for children is used.
• The percent minute volume from 20% to 200% of the
predetermined adult or child setting can be selected.
• Test breaths are used by the ventilator to measure to measure
the system compliance, airway resistance and any intrinsic PEEP.
• With increasing triggering efforts, the number of mandatory
breaths decreases and the pressure support level increases until
tidal volume=alveolar volume+2.2mL/kg of deadspace volume.

CONTINUOUS POSITIVE AIRWAY
PRESSURE (CPAP)
• CPAP is spontaneous breathing at a positive end-
expiratory pressure.
• Requires only a source of oxygen and a face mask with
an expiratory valve that maintains a PEEP.
• Usually set at 5-10cm H2O.
• Patient must have adequate lung functions that can
sustain eucapnic ventilation documented by PaCO2.
• In neonates, nasal CPAP is the method of choice.
• It is a limited form of ventilatory support as it does not
augment the tidal volume and thus limits its use in acute
respiratory failure.

BILEVEL POSITIVE AIRWAY
PRESSURE (BiPAP)
• BiPAP is CPAP that alternates between two pressure levels.
• It is actually a variant of APRV.
• High pressure level is inspiratory positive airway pressure
(IPAP) and low pressure level is expiratory positive airway
pressure (EPAP).
• More time is spent at the low pressure level.
• Requires a specialized ventilator.
• Indications: COPD patients, chronic ventilatory failure,
restrictive chest wall disease, neuromuscular disease etc.
• Initial settings of IPAP as 5cm H2O and EPAP as 10cm H2O
with inspiratory time of 3sec.
• Further adjustments in pressure are determined by the
resultant changes in gas exchange (P/F ratio, PaCO2) and
signs of respiratory distress.

PARAMETERS
• Mode of ventilation
• Respiratory rate
• Tidal volume
• PEEP level
• Fraction of inspired O2 conc.(FiO2)
• I:E ratio
• Peak flow/ flow rate
• Minute volume

MODE
• Full ventilatory support vs partial ventilatory support.
• Pressure vs volume control or dual control mode (volume
targeted, pressure limited and time cycled)
RESPIRATORY RATE
• If the patient has no spontaneous respirations, the RR is set
to achieve the estimated minute volume (4×BSA in males
and 3.5×BSA in females) but not more than 35 breaths/min.
• If the pt is triggering each ventilator breath, rate is set at just
below the pt’s spontaneous RR.
• The arterial PCO2 is checked after 30 minutes and RR is
adjusted to achieve the desired PCO2.
• Patients who are breathing rapidly and have an acute
respiratory alkalosis or evidence of occult PEEP, consider
switching over to SIMV.

TIDAL VOLUME
• Initial volume of 8mL/kg using predicted body weight.
• Reduce tidal volume to 6mL/kg over the next 2 hours if
possible.
• Monitor the peak alveolar pressure and keep it <30cm
H2O to limit risk of volutrauma.
• In voulme control mode the peak alveolar pressure is the
end-inspiratory occlusion pressure, also called the
plateau pressure.
• In the pressure control mode, the peak alveolar pressure
is the end-inspiratory airway pressure

PROTOCOL FOR LUNG PROTECTIVE
VENTILATION IN ARDS
I. Tidal volume goal: Vt=6mL/kg (predicted body weight-PBW)
1. Calculate patient’s PBW
males: PBW=50+[2.3*(height in inches-60)]
females: PBW=45.5+[2.3*(height in inches-60)]
2. Use volume controlled ventilation and initial Vt set at 8mL/kg
3. RR set to match baseline minute ventilation but not>35/min
4. PEEP at 5cm H2O
5. Reduce Vt by 1mL/kg every 1-2hrs until Vt=6mL/kg
6. Adjust PEEP and FiO2 to maintain SpO2 of 88-95%
II. Plateau pressure goal: Ppl<=30cm H2O
If Ppl>30cm H2O and Vt at 6mL/kg, decrease Vt in 1mL/kg increments until Ppl falls
to <=30cmH2O or Vt reaches a min. of 4mL/kg.
III. pH goal: pH=7.30-7.45
1. if pH=7.15-7.30, increase RR until pH>7.30, PaCO2<25mmHg or RR=35bpm
2. if pH<7.15, increase RR to 35bpm. If pH remains<7.15, increase in Vt in
1mL/kg increments until pH>7.15 (Ppl target maybe exceeded)
3. if pH>7.45, decrease RR, if possible

INSPIRATORY FLOW RATE
• Select an inspiratory flow rate of 60L/min if pt is breathing
quietly or has no spontaneous respiration.
• Use higher inspiratory flow rates (eg. 80L/min) for patients
with respiratory distress or a high minute ventilation
(>10mL/min).
I:E RATIO
• The I:E ratio should be >=1:2
• If the I:E ratio is <1:2, options for increasing I:E ratio include
a. increasing inspiratory flow rate
b. decreasing the tidal volume
c. decreasing the respiratory rate
• Inverse I:E ratio is used to correct refractory hypoxemia in
ARDS patients with very low compliance

PEEP
• Set the initial PEEP to 5cm H2O to prevent the collapse of
diatal airspaces at end-expiration.
• Further increases may be required in:
1. a toxic level of inhaled oxygen (>60%) is required to
maintain adequate oxygenation (saO2>=90%)
2. hypoxemia is refractory to oxygen therapy
OCCULT PEEP
• Check the flow rate at the end of expiration to detect
presence of auto PEEP.
• If present, prolong the expiratory time by increasing I:E ratio
• If this is not possible or not successful, measure the level of
occult PEEP with end-inspiratory occlusion method and add
extrinsic PEEP at a level just below the occult PEEP.

FiO2
• For patients with severe hypoxemia or abnormal
cardiopulmonary functions (post resuscitation, smoke
inhalation, ARDS) initial FiO2 maybe set at 100%.
• FiO2 is evaluated by means of arterial blood gas analyses
after stablization of the patient.
• Should be adjusted accordingly to maintain a PaO2 between
80 and 100mm Hg.
• After patient stablization, the FiO2 is best kept below 50% to
avoid oxygen-induced lung injuries.
• For patients with mild hypoxemia and normal
cardiopulmonary functions, the initial FiO2 may be set at
40% and changed accordingly by subsequent ABG
analyses.

TRIGGER SENSITIVITY
• The sensitivity function controls the amount of patient
effort needed to initiate an inspiration
• Increasing the sensitivity (requiring less negative force)
decreases the amount of work the patient must do to
initiate a ventilator breath.
• Decreasing the sensitivity increases the amount of
negative pressure that the patient needs to initiate
inspiration and increases the work of breathing.
• The most common setting for pressure sensitivity are -1
to -2 cm H2O

FLOW PATTERN
Principal flow patterns are:
1. Square/constant flow pattern- used initially when setting up a
ventilator, initial peak flow overcomes airway resistance and the peak
flow throughout the inspiratory phase enhances gas distribution in lungs.
2. Accelerating/ ascending flow pattern- increasing flow throughout
respiratory cycle, it may improve ventilation distribution in partial airway
obstruction.
3. Decelerating/ descending flow pattern- high initial inspiratory pressure
and decrease in flow improves gas exchange and distribution of tidal
volume.
4. Sine wave flow pattern- more physiologic, similar to normal
spontaneous breathing.

VENTILATOR ALARM SETTINGS
• Basic ventilator alarms:
1. Low exhaled volume alarm: 100mL lower than expired
Vt, used to detect system leak or circuit disconnection.
2. Low inspiratory pressure alarm: 10-15cm H2O below the
observed PIP.
3. High inspiratory pressure alarm: 10-15cm H2O above
the PIP, can be triggered due to water in circuit, kinking or
biting of ET tube, airway secretions, bronchospasm,
tension pneumothorax, decreased lung compliance,
coughing, increased airway resistance.
4. Apnoea alarm: 15-20 sec time delay
5. High respiratory rate alarm: 10-15bpm over the observed
RR, sign of respiratory distress.
6. High and low FiO2 alarms: 5-10% over and below the
analysed FiO2.

1. Related to positive pressure ventilation:
barotrauma (pneumothorax, mediastinal air leak,
subcutaneous air leak)
hypotension, decrease in cardiac output
oxygen toxicity
bronchopleural fistula
upper GI hemorrhage
2. Related to patient condition:
infection (due to reduced immunity)
physical and physiological trauma
multiple organ failure (may be pre-existing)

3. Related to equipment (ventilator and artificial airway):
ventilator and alarm malfunction
circuit disconnection
accidental extubation
endobronchial intubation
ET tube blockage
tissue damage
atelectasis
4. Related to medical professionals:
nosocomial pneumonia
inappropriate ventilator settings
misadventures (lapses of understanding and communication)

WEANING FROM
MECHANICAL
VENTILATION

• Weaning is the process of withdrawing
mechanical ventilatory support and transferring
the work of breathing from the ventilator to the
patient.
• Weaning success: effective spontaneous
breathing without any mechanical assistance for
48hrs or more.
• Weaning failure: when pt is returned to
mechanical ventilation after any length of weaning
trial.

EVALUATING A PATIENT FOR
WEANING
A daily routine follow up should be done in every
patient receiving mechanical ventilation and
exploring the following condition
 Resolution/improvement of the underlying disease
 Stop sedation
 Core temperature below 38 ºC
 Stable haemodynamics
 Adequate haemoglobin ( Hb > 8 g/dL)
 Adequate mentation ( arousable, GCS > 13)
 No major metabolic and/or electrolyte disturbances

WEANING CRITERIA
CLINICAL CRITERIA
• Adequate cough
• Absence of excessive
tracheobronchial
secretions
• Resolution of the
disease acute phase
for which the patient
was intubated
• Cardiovascular and
hemodynamic stability
OBJECTIVE CRITERIA
• Ventilatory criteria
• Oxygenation criteria
• Pulmonary reserve
• Pulmonary
measurements

VENTILATORY CRITERIA
 Spontaneous breathing trial tolerates 20 to 30 mins
 PaCO2 < 50 mmHg with normal pH
 Vital Capacity > 10 ml/kg
 Spontaneous VT > 5 ml/kg
 Spontaneous RR < 35/min
 f/Vt <105 breaths/min/L
 Minute ventilation < 10 l/min with satisfactory ABG

OXYGENATION CRITERIA
 PaO2 without PEEP > 60 mmHg at FiO2 < 0.4
 PaO2 with PEEP >100mmHg at FiO2 upto 0.4
(<8cm H2O)
 SaO2 > 90% at FiO2 < 0.4
 PaO2/FiO2 ≥ 150 mmHg
 Qs/Qt <20%
(physiologic shunt to total perfusion)
 P(A-a)O2 < 350 mmHg at FiO2 of 1.0
(corresponds to 14% shunt)

PULMONARY RESERVE
• Vital capacity >10mL/kg
• Max. Insp. Pressure (MIP) > -30 cmH2O in 20 sec
Pulmonary reserve can be assessed by measuring the
vital capacity (VC) and maximum inspiratory pressure
(MIP) which require active patient co-operation.
For successful weaning patient should have a vital
capacity of greater than10mL/kg.

PULMONARY MEASUREMENTS
• Static compliance > 30 ml/cm H2O
• Airway resistance stable or improving
• Vd/Vt
(deadspace to tidal volume) < 60% while intubated
Not dependent on patient’s co-operation or effort.
Used to indicate the amount of pulmonary workload that
is needed to support spontaneous ventilation.

• Weaning is more likely to succeed if a
patient meets most of the criteria.
• If a patient can meet only one or two of the
weaning criteria, the success rate is likely
to be low.
• Though not fool proof, all patients who fit
most of the criteria can undergo a formal
spontaneous breathing trial (SBT).

COMBINED WEANING INDICES
• Since respiratory failure is multifactorial, individual
parameters are unreliable predictors of weaning
outcome
• Indices integrating several physiological variables may
be more effective predictors of weaning outcome
1. RSBI (Rapid shallow breathing index)
2. CROP Index
3. SWI Index

RAPID SHALLOW BREATHING
INDEX (RSBI)
• Respiratory frequency to tidal volume (f/Vt) ratio.
• Rapid (high RR) and shallow (low Vt) breathing pattern
induces inefficient, deadspace ventilation.
• >105 suggests potential weaning failure.
• Patient is taken off the ventilator and allowed to breath
spontaneously for 3 min or until a stable breathing
pattern is established.
• More accurate predictor of weaning success than any
other parameter studied
• Disadvantage: excessive false +ve

COMPLIANCE RATE OXYGENATION
AND PRESSURE (CROP) INDEX
• Evaluates pulmonary gas exchange and balance b/w
respiratory demands and respiratory neuromuscular reserve
CROP Index= ( Cd × MIP × PaO2/PAO2)/f
 Where: Cd = dynamic compliance
MIP= maximum inspiratory pressure
PaO2 = Arterial oxygen tension
PAO2 = Alveolar oxygen tension
f = spontaneous respiratory rate per minute
 Should be > 13 ml/breath/min for successful weaning
 Widespread application limited by complicated calculation &
no. of variables involved

SIMPLIFIED WEANING INDEX (SWI)
• Evaluates efficiency of gas exchange and ventilatory
endurance
SWI = ( fmv (PIP – PEEP)/MIP) × PaCO2/40
PIP = peak inspiratory pressure
PEEP = Peak end expiratory pressure
MIP = Maximal inspiratory pressure
fmv = ventilatory frequency
PaCO2 = Arterial CO2 tension while on ventilator
• When SWI< 9/min, it is highly predictive (93%) of weaning
success.
• SWI> 11/min there is a 95% probability of weaning failure.

WEANING PROCEDURE
• Rapid ventilator discontinuation
• Spontaneous breathing trials
• Pressure support ventilation (PSV)
• SIMV
• Other Modes used for weaning

RAPID VENTILATOR
DISCONTINUATION
• Considered in patients with no underlying cardiovascular,
pulmonary, neurologic, or neuromuscular disorders and
patients receiving ventilatory support for short periods e.g.
post-op patients.
• SBTs are superior to both SIMV and PS in both duration of
weaning and the likelihood of success after weaning.
Patient on ventilator
for < 72 hrs
SBT for 20 to 30 min.
EXTUBATE if no
other limiting factor
Good spont RR,
MV, MIP, f/Vt

SPONTANEOUS BREATHING
TRIAL
• SBT can be in the form of T – tube trial or PSV of 5-10 cm
H2O or CPAP 5-7 cmH2O
• T-Tube trial: allows spontaneous breathing interspersed
with periods of full ventilatory support
ADVANTAGES
• Tests pt’s spontaneous
breathing ability
• Allows periods of work and
rest
• Weans faster than SIMV
DISADVANTAGES
• Abrupt transition difficult for
some pts
• No alarms, unless attached
to ventilator
• Requires careful observation.

SIGNS OF INTOLERANCE OF SBT
• Agitation, anxiety, diaphoresis or change in mental status
• RR > 30 to 35/min
• SpO2 < 90%
• > 20% ↑ or ↓ in HR or HR > 120 to 140/min
• SBP > 180 or < 90 mmhg.
Such patients are returned to full ventilatory support for
24 hrs. to allow the respiratory muscles to recover.

T-TUBE ADAPTER
A T-piece (or trach-collar) trial involves
the patient breathing through a T-
piece (essentially the endotracheal
tube (ett) plus a flow of oxygen-air and
no ventilatory assistance) for a set
period of time. The work of breathing
is higher than through a normal airway
(although this simulates laryngeal
edema/airway narrowing). If tolerated,
the chances of successful extubation
are high. If not reattachment to a
ventilator is simple.
Gas flow to inspiratory limb should
be at least twice that of the patient’s
spontaneous minute ventilation in
order to meet the patient’s peak
inspiratory flow rate. An extension
piece of about 12 inches should be
added to the expiratory limb to prevent
entrainment of room air

WEANING PROTOCOL FOR SBT WITH A
T-TUBE
Prepare for T-Tube trial
3 min. screening trial
Measure TV,RR
Measure MIP thrice
selecting the best
. Formal SBT for 20 to 30 min
MIP < -20 cm H20
TV spon. > 5 ml/kg
RR spon. < 35/min.
no signs of intolerance
If signs of
intolerance are
present
Put the patient
back on previous
ventilator
settings
Repeat next trial
after 24 hrs
extubate
Optimize the
patient’s medical
condition
suction,
adequate
humidification,
bronchodilator
therapy, good
nutrition, optimal
position,
psychological
counseling,
adequate staff,
equipment, no
sedatives

SBT WITH CPAP
• CPAP circuit overcomes
some of the work of
breathing through the
tracheal tube and prevents
airway collapse.
• CPAP may improve lung
mechanics and reduce the
effort required by
mechanically ventilated
patients with air flow
obstruction and may
enhance breath triggering in
patients
with significant auto-PEEP.

WEANING WITH SIMV
• Breaths are either spontaneous or mandatory
• Mandatory breaths are synchronized with patient’s own
efforts
ADVANTAGES
•Gradual transition
•Easy to use
•Minimum MV guaranteed
•Alarm system may be used
•Should be used in comb.
with PSV/CPAP
DISADVANTAGES
•Prolongs weaning
•May worsen fatigue

PROTOCOL OF SIMV
WEANING
Start with SIMV rate
at 80% of full support
f is then decreased by
2 – 4 breaths twice daily
If the patient tolerates an
SIMV rate of 2-4 breaths
for> 2 hrs
Consider extubation
Monitor
patient’s
appearance,
respiratory
rate, SpO2,
BP, obtain
ABG sample
If
deterioration
→ ↑ SIMV
rate
Allow pt’s
resp msls to
rest at night
by ↑ing SIMV
rate

WEANING WITH PSV
• Pressure support is given with each spontaneous breath to ensure an
adequate TV.
• Trachea can be extubated directly from PS as PS overcomes the
tube resistance
• 7cmH2O of pressure support is required to overcome the resistance
through a size 7.5mm (internal diameter) endotracheal tube
• 3cmH2O PS is required through a tracheostomy
• If a smaller tube is in place, pressure support of 10 cmH2O is
required. ADVANTAGES
•Gradual transition
•Prevents fatigue
•Increased pt comfort
•Weans faster than SIMV alone
•Pt can control cycle length, rate
and inspiratory flow.
•Overcomes resistive WOB d/t
ET tube and circuit.
DISADVANTAGES
•↑ed MAP versus T-Tube
•TV not guaranteed

PROTOCOL OF PSV WEANING
PSV is adjusted to deliver
TV 10-12 ml/kg, (PSVmax)
PSV level is decreased by
2-4 cm H2O twice daily to
maintain TV
If patient tolerates PSV level of
5-8 cm H2O for greater than 2 hrs
Consider
extubation
Monitor
patient’s
appearance,
respiratory
rate, SpO2,
BP, obtain
ABG sample

ROLE OF TRACHEOSTOMY IN WEANING
• Early tracheostomy ( in 2 days of admission ) reduces
mortality, risk of pneumonia, accidental extubation, ICU
length of stay.
Reduces dead space
Less airway resistance
↓ed WOB
Better suctioning
Improved pt comfort
Facilitates weaning

WEANING : SELECTING AN
APPROACH!!!
• Many studies have compared the different
methods of weaning.
• Common conclusions are:
 No clear superiority exists between T-tube
weaning and pressure support based
weaning
SIMV is the least efficient technique of
weaning

OTHER MODES USED FOR
WEANING
• Non invasive ventilation (NIV)
• Biphasic positive airway pressure (BiPAP)
• Automatic tube compensation (ATC)
• Volume support (VS)
• Volume assured pressure support (VAPS)
• Mandatory minute ventilation (MMV)
• Servo controlled ventilation ( Automatic
Ventilatory Support)

WEANING PROTOCOLS
• Weaning protocols provide structured guidance
regarding weaning of patients on mechanical ventilation.
• Protocols are usually presented as written guides or
algorithms, and ventilator settings are manually adjusted
by healthcare professionals.
3 components
• A list of objective criteria (often referred to as “readiness
to wean” criteria)
• Structured guidelines for reducing ventilatory support
e.g. abrupt/gradual using different weaning modes
• A list of criteria for deciding if the patient is ready for
extubation

WEANING FAILURE
Weaning failure is defined as either the
failure of SBT or the need for
reintubation within 48 h following
extubation.

INDICATORS OF WEANING
FAILURE
Inadequate gas exchange
• Arterial oxygenation saturation (SaO2) <85% - 90%
• PaO2 <50 – 60 mmHg
• pH < 7.32
• Increase in PaCO2 >10 mmHg
Unstable ventilatory/respiratory pattern
• Respiratory rate >30 – 35 breaths/minute
• Respiratory rate change over 50%
Hemodynamic instability
• Heart rate change greater than 20%
• Systolic blood pressure >180 mmHg or <90 mmHg
• Blood pressure change greater than 20%
• Vasopressors required

Change in mental status
 Coma
 Agitation
 Anxiety
 Somnolence
Signs of increased work of breathing
 Nasal flaring
 Paradoxical breathing movements
 Use of accessory respiratory muscles

FACTORS WHICH MAY INCREASE
VENTILATORY WORKLOAD
Increased ventilatory demand
 Increased CNS drive : hypoxia, acidosis, pain, fear,
anxiety and stimulation of J receptors ( pulmonary
edema)
 Increased metabolic rate : increased CO2 production,
fever, shivering, agitation, trauma, infection, and sepsis
 Increased dead space :COPD, pulmonary embolus
Decreased compliance
 Decreased lung compliance: atelectasis, pneumonia,
fibrosis, pulmonary edema, and ARDS
 Decreased thoracic compliance : obesity, ascites,
abdominal distension, pregnancy

Increased resistance
• Increased airway resistance : bronchospasm, mucosal
edema, and secretions
• Artificial airways: endotracheal, tracheostomy tube
• Other mechanical factors : ventilator circuits, demand flow
systems, and inappropriate ventilator flow and/or sensitivity
settings
Cardiac load
• Increased cardiac workload leading to myocardial
dysfunction; dynamic hyperinflation; increased metabolic
demand; unresolved sepsis
Neuromuscular
• Depressed central drive: metabolic alkalosis;
sedative/hypnotic medications
• Peripheral dysfunction: primary causes of neuromuscular
weakness; critical illness neuromuscular abnormalities
(CINMA )

Metabolic
• Metabolic disturbances -hypokalemia,
hypomagnesemia, hypophosphatemia,
hypothyroidism, hypoadrenalism
• Role of corticosteroids
• Hyperglycaemia
Nutrition
• Overweight
• Malnutrition
• Ventilator-induced diaphragm dysfunction
Neuropsychological
• Delirium
• Anxiety, depression

1. PEEP is indicated in patients who have a
decreased:
a) Tidal volume, chronic hypercapnia
b) FRC, refractory hypoxemia
c) Vital capacity, acute hypercapnia
d) Tidal volume, refractory hypoxemia

• Ans: b
• PEEP increases the FRC and is useful to treat
refractory hypoxemia (low PaO2 not responding
to high FiO2).
• Initial PEEP is set at 5cm H2O
• Subsequent changes of PEEP should be based
on the patient’s blood gas results, FiO2
requirement, tolerance of PEEP and
cardiovascular responses.
REF: clinical application of mechanical ventilation,
David W. Chang, 4rd edition, Page no. 225

2. The primary purpose of prophylactic
mechanical ventilation include all of the following
except:
a) To minimize risk of pulmonary
complications
b) To reduce prolonged hypoxia of major
body organs
c) To reduce the work of cardiopulmonary
system
d) To monitor arterial blood gases and vital
signs

• Ans: d
• Prophylactic ventilatory support is provided in
clinical settings in which risk of pulmonary
complications, ventilatory failure or oxygenation
failure is high.
• This will reduce the work of breathing and
oxygen consumption and preserve
cardiopulmonary system and promote patient
recovery.

3. The application of CPAP or PEEP leads
to all except:
a) Increased FRC
b) Reduction in preload in patients with acute
cardiogenic pulmonary oedema
c) Increased intracranial pressure
d) Increased cardiac output

• Ans: d
• PEEP increases alveolar distending pressure
and increases FRC by alveolar recruitment.
• Since PEEP increases both peak inspiratory
pressures and mean airway pressures, it has the
potential to decrease venous return and cardiac
output.
• Due to impedance of venous return from the
head, PEEP may increase the ICP in patients
with normal lung compliance.

4. A 45 yr male in ICU with acute pancreatitis, is
having severe ARDS and refractory hypoxia.
PEEP and FiO2 have been increased over the
day. Now, SpO2 is 85% on FiO2 0.65 with PEEP
at 15cm H2O and plateau pressure of 29cm H2O.
I:E is 1:1 and pt is sedated and paralysed. Most
effective next step?
a) Commencing inhaled NO
b) Adjusting PEEP to 20cm H2O
c) Placing the pt in prone position
d) Inverting the I:E ratio.

• Ans: c
• Switching from supine to prone position can improve
pulmonary gas exchange by diverting blood away from poorly
aerated lung regions in the posterior thorax and increasing
blood flow in aerated lung regions in anterior thorax.
• A recent study combining lung protective ventilation with
prone positioning showed lower than expected mortality rate
in patients with severe ARDS.
• Inhaled NO is a selective pulmonary vasodilator that can
improve arterial oxygenation in ARDS but this is temporary
and no effective survival benefit with associated side effects of
NO.
REF: The ICU book, Paul Marino, 4th edition, page 459-460

5. Out of the following the only parameter
that suggests successful weaning is:
a) Spontaneous frequency (f)= 40/min
b) Spontaneous Vt= 7mL/kg
c) Minute ventilation= 16L
d) PaCO2= 55mmHg

6. In assist-control ventilation (ACV):
a) Breaths triggered by the ventilator result in the
full preset tidal volume being delivered,while
breaths triggered by the patient are
unsupported by the ventilator
b) All breaths result in the full preset tidal volume
being delivered, regardless of whether they are
initiated by the ventilator or by the patient
c) All breaths must be initiated by the patient
d) The patient is incapable of triggering breaths

• Ans: b
• The essence of ACV is that all breaths receive the
full preset tidal volume regardless of whether the
breaths are initiated by the ventilator or by the
patient. With ACV if the ventilator is set at Vt = 500
mL, the frequency is set at 10 breaths/min, and the
patient exhibits no respiratory effort, the ventilator
will deliver 500 mL breaths 10 times per minute.
• If that same patient makes 8 respiratory efforts in
addition to the 10 mandatory breaths, the ventilator
will deliver 500 mL breaths 18 times per minute.
David W. Chang, 4rd edition, Page no. 94-96

7. In pressure-support ventilation (PSV),
inspiration ends (and expiration begins) when:
a) A preset tidal volume has been achieved
b) A preset airway pressure has been achieved
c) Flow decreases to a preset level
d) A preset amount of time has passed

• Ans: c
• In PSV, inspiration is triggered by a patient’s respiratory effort.
• A continuous airway pressure is maintained by gas flow that
decreases throughout inspiration.
• When flow decreases to a preset fraction of the peak flow
(usually 25% of peak flow), gas flow into the inspiratory limb
ends and expiration begins.
• Choice A describes volume-preset ventilation, often called
“volume control.”
• Choice B is incorrect because in PSV, a preset airway pressure
is maintained throughout inspiration.
• Choice D is incorrect because in PSV, decrease in flow(not a
preset time) determines the length of inspiration.
REF: clinical application of mechanical ventilation, David W.
Chang, 4rd edition, Page no. 102

8. A patient is at greatest risk for requiring
endotracheal intubation and mechanical
ventilation if the SpO2 is 91% while breathing
a) Room air
b) 4 L/min of oxygen via nasal cannula
c) 15 L/min of oxygen via a non-rebreathing mask
with reservoir bag
d) Noninvasive positive-pressure ventilation with an
FIO2 of 35%

• Ans: c
• The non-rebreathing mask with reservoir bag can deliver
an FIO2 of nearly 100% when oxygen flow is 15 L/min or
greater.
• An SpO2 of 91% on an FIO2 of 100% should alert the
clinician to the likely need for endotracheal intubation and
mechanical ventilation.
• Choice D is incorrect assuming that other variables are
safe and stable (PaCO2, mental status, ability to protect
airway).
• Many chronic obstructive pulmonary disease patients in
the ICU benefit from short-term support from noninvasive
positive-pressure ventilation and do quite well with SpO2
readings in the low 90s
REF: clinical application of mechanical ventilation, David W.
Chang, 4rd edition, Page no. 218

9. According to the weaning protocol for
mechanical ventilation, the time limit for a
spontaneous breathing trial should be upto ------
unless terminated earlier:
a) 5min
b) 30min
c) 120mins
d) 4hours

10. A mechanically ventilated, 70-kg patient has an
arterial blood gas of pH = 7.06, PCO2 = 83 mmHg,
and PO2 = 140 mm Hg on volume control ventilation
(tidal volume = 450 mL, respiratory rate = 8, FIO2 =
50%, and positive end-expiratory pressure [PEEP] =
8 cm H2O). The most appropriate next step in the
management is:
a) Increase PEEP
b) Increase FIO2
c) Increase the respiratory rate
d) Administer sodium bicarbonate

• Ans: c
• This is a case of nearly pure respiratory acidosis. The pH
is very low as a result of a significantly elevated PCO2.
• The management of a respiratory acidosis consists of
increasing the minute ventilation by increasing either
respiratory rate (choice C) or tidal volume (not given as
an answer choice).
• Choices A and B are incorrect because neither would
result in an increased minute ventilation.
• Choice D is incorrect because giving bicarbonate will
temporarily increase the pH, but will not address the
underlying problem of inadequate elimination of CO2.

Initiation of mechanical ventilation and weaning

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