Dr Priyanka

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Ventilatory Care of Critically ill Patient and
Weaning from Mechanical Ventilation

• Dr Priyanka

University College of Medical Sciences GTB
Hospital, Delhi
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CONTENTS

• Introduction
• Goals of mechanical ventilation
• Indications of mechanical ventilation
• Criteria for initiating mechanical ventilation
• Physiological effects of mechanical ventilation
• Basic Physics
• Modes of mechanical ventilation
• Management, monitoring and complications of
  mechanical ventilation
• Ventilatory Care bundles
• Weaning from mechanical ventilation

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Basic physics related to mechanical ventilation
(equation of motion)

• P aw Flow Resistance Volume / Compliance
  PEEP
• Paw resistive load elastic load
• Pressure at point B is equivalent to alveolar
  pressure and is determined by the volume
  inflating the alveoli divided by compliance of
  alveoli plus baseline pressure i.e. PEEP
• Pressure at point A is the sum of the product of
  flow and resistance due to the tube and pressure
  at point B

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Distending pressure of lungs
Resistance load
Distending pressure
Elastance load
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Mechanical Ventilation

• If volume is set, pressure varies..if pressure
  is set, volume varies..
• .according to the compliance...
• COMPLIANCE
• ? Volume / ? Pressure
• Is the change in volume per unit change in
  pressure

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Compliance
Burton SL Hubmayr RD Determinants of
Patient-Ventilator Interactions Bedside Waveform
Analysis, in Tobin MJ (ed) Principles Practice
of Intensive Care Monitoring
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Compliance

• Static compliance
• Measured when there is no air flow
• Reflects the elastic properties of the lung
  and the chest wall
• Static compliance Corrected tidal volume
• Plateau
  pressure-PEEP
• For critically ill patients, static compliance
  varies between 40 - 60 ml/cm H2O

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Compliance

• Dynamic compliance
• Measured when air flow is present
• Reflects the airway resistance (non elastic
  resistance) and elastic properties of lung and
  chest wall
• Dynamic complianceCorrected tidal volume
• Peak inspiratory
  pressure-PEEP
• For critically ill patients, dynamic
  compliance varies between 30 - 40 ml/cm H2O

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Conditions decreasing compliance

• Atelectasis
• ARDS
• Tension pneumothorax
• Obesity
• Retained secretions
• Bronchospasm
• Kinking of the tube
• Airway obstruction

Static compliance
Dynamic compliance
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High compliance

• Exhalation is often incomplete due to lack of
  elastic recoil by the lungs
• Seen in conditions that increase patients FRC
• Obstructive lung defect Airflow obstruction

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Inflation pressure

• Plateau pressure
• Pressure needed to maintain lung inflation in
  the absence of air flow
• Peak inspiratory pressure (PIP)
• Pressure used to deliver the tidal volume by
  overcoming non elastic (airways) and elastic
  (lung parenchyma) resistance

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Components of inflation pressure
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• ARTIFICIAL VENTILATION

Negative pressure ventilation
Positive pressure ventilation

• Creates a transairway Pres gradient by ? alveolar
  Pres to a level below airway opening Pres
• Creates ve Pres around thorax
• e.g. iron lung
• chest cuirass / shell

Achieved by applying ve Pres at airway opening
producing a transairway Pres gradient
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• Ventilatory support

FULL
PARTIAL
All energy provided by ventilator e.g. CMV / ACV
Pt provides a portion of energy needed for
effective ventilation e.g. SIMV (RR lt 10)
WOB total WOB ventilator (forces gas into
lungs) WOB patient (msls draw gas
into lungs)
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Ventilatory support
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• Guiding principle in choosing mode of ventilatory
  support
• To use the minimum amount of support necessary to
  provide adequate oxygenation of the tissues.
• Secondary considerations
• Maintenance of reasonable acid-base status
• Patient comfort

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Selecting Mode of ventilation
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Non invasive Ventilation

• Advantages

• Disadvantages

• Cooperation
• Mask discomfort
• Air leaks
• Facial ulcers, eye irritation, dry nose
• Limited Pressure support e.g. BiPAP, CPAP

• Avoid intubation
• Preserve natural airway defences
• Comfort
• Speech/ swallowing
• Less sedation needed
• Intermittent use

TECHNIQUE OF PROVIDING ventilation without the
use of an artificial airway It is used
successfully in patients with OSA, acute
ventilatory failure or impending ventilatory
failure
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Mechanical Ventilation

• Ventilators deliver gas to the lungs using
  positive pressure at a certain rate.
• The amount of gas delivered can be limited by
  time, pressure or volume.
• The duration can be cycled by time, pressure or
  flow.

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Breath characteristics

A what initiates a breath - TRIGGER B what
controls / limits it LIMIT C What ends a
breath - CYCLING
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Trigger

• How does the ventilator know when to give a
  breath? Pressure
• Patient effort
• Flow
• Pressure triggering 1 to 2 cmH2O
• Flow triggering 1to 3 l/min
• Machine effort - Elapsed time

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Limit /control variables

• Pressure control /limit
• Pressure targeted
• Volume variable
• Flow variable
• Volume control/limit
• Volume targeted
• Flow targeted
• Pressure variable

compliance
resistance
compliance
resistance
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Limit /control variables

• Flow control/limit
• Flow targeted
• Volume targeted
• Pressure varies
• Time control /limit
• Inspiratory and expiratory time targeted
• Pressure variable
• volume variable
• Flow variable

compliance
resistance
compliance
resistance
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Cycling Variable

• Determines the end of inspiration and the switch
  to expiration
• Machine cycling
• Time
• Pressure
• Volume
• Patient cycling
• Flow
• pressure

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Criteria for determining phase variables during a
ventilator assisted breath
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Modes

• Relationship between various possible breath
  types and inspiratory phase variables
• Whenever a breath is supported by the ventilator,
  regardless of the mode, the limit of the support
  is determined by a preset pressure OR volume.
• Volume controlled preset tidal volume
• Pressure controlled preset PIP or PAP

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Pressure controlled
Volume controlled

• FiO2
• Rate
• I-time
• PEEP
• PIP

• FiO2
• Rate
• Tidal Volume
• PEEP
• Peak flow

• Tidal Volume peak flow ( MV) Varies

PIP( MAP) IE ratio Varies
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Volume controlled Pressure controlled
Advantages Guaranteed TV Less atelectasis Advantages Limits excessive airway P ? MAP by constant insp P better oxygenation Better gas distribution high insp flow ?Ti ?Te ,thereby, preventing airtrapping Lower WOB high initial flow rates meet high initial flow demands Lower PIP as flow rates higher when lung compliance high i.e early insp. phase
Disadvantages Limited flow may not meet patients desired insp flow rate- flow hunger May cause high Paw ( barotrauma) Disadvantages Variable TV ?TV as compliance ? ?TV as resistance ?
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Commonly used modes of mechanical ventilation

• Controlled mandatory ventilation (CMV)
• Assist control ventilation (ACV)
• Synchronized intermittent mandatory ventilation
  (SIMV)
• Pressure support ventilation (PSV)
• Positive end expiratory pressure (PEEP)
• Continuous positive airway pressure (CPAP)
• Bilevel positive airway pressure (BIPAP)
• Intermittent mandatory ventilation (IMV)
• Pressure control ventilation (PCV)

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Other / newer modes

• Adaptive support ventilation(ASV)
• Proportional assist ventilation(PAV)
• Volume assured pressure support(VAPS)
• Pressure regulated volume control(PRVC)
• Volume ventilation plus(VV)
• Airway pressure release ventilation(APRV)
• Inverse ratio ventilation(IRV)
• Automatic tube compensation(ATC)

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1. Control mode ventilation (CMV)

• Breath - MANDATORY
• Trigger TIME
• Limit - VOLUME
• Cycle VOL / TIME

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CMV
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2.) Assist Control Mode Ventilation (ACMV)

• Breath MANDATORY
• ASSISTED
• Trigger PATIENT
• TIME
• Limit - VOLUME
• Cycle VOLUME / TIME

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Assist Control Mode Ventilation (ACMV)

• Patient has partial control over his respiration
  Better Pt ventilator synchrony
• Ventilator rate determined by patient or backup
  rate (whichever is higher) risk of respiratory
  alkalosis if tachypnoea
• PASSIVE Pt acts like CMV
• ACTIVE pt ALL spontaneous breaths assisted to
  preset volume
• Once patient initiates the breath the ventilator
  takes over the WOB
• If he fails to initiate, then the ventilator
  does the entire WOB

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3. Intermittent mandatory ventilation (IMV)

• Breath MANDATORY
• SPONTANEOUS
• Trigger PATIENT
• VENTILATOR
• Limit - VOLUME
• Cycle - VOLUME

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Intermittent mandatory ventilation (IMV)

• Basically CMV which allows spontaneous breaths in
  between
• Disadvantage - In tachypnea can lead to breath
  stacking
• Not used now has been replaced by SIMV
• Breath stacking - Spontaneous breath immediately
  after a controlled breath without allowing time
  for expiration ( SUPERIMPOSED BREATHS) - leading
  to dynamic hyperinflation

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4.Synchronized Intermittent Mandatory
Ventilation (SIMV)

• Breath SPONTANEOUS
• ASSISTED
• MANDATORY
• Trigger PATIENT
• TIME
• Limit - VOLUME
• Cycle VOLUME/ TIME

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• Synchronisation window Time interval from the
  previous mandatory breath to just prior to the
  next time triggering, during which ventilator is
  responsive to patients spontaneous inspiratory
  effort

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Synchronized Intermittent Mandatory
Ventilation (SIMV)
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5.Pressure controlled ventilation (PCV)
Ventilator delivers pressure limited breaths at
preset inspiratory pressure and inspiratory times

• Time taken for airway pressure to rise from
  baseline to maximum
• Breath MANDATORY
• Trigger TIME
• Limit - PRESSURE
• Cycle TIME/ FLOW

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Pressure controlled ventilation (PCV)
Disadvantages
Advantages

• Reduction of peak pressure and barotrauma
• Ensures better ventilation and gas exchange

• Does not guarantee minute ventilation
• Requires more intensive monitoring

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6.Pressure support ventilation (PSV)

• After the trigger, ventilator generates a flow
  sufficient to raise and then maintain airway
  pressure at a preset level for the duration of
  the patients spontaneous respiratory effort
• Breath SPONTANEOUS
• Trigger PATIENT
• Limit - PRESSURE
• Cycle FLOW
• ( 5-25 OF PIFR

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Pressure support ventilation (PSV)
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7)Positive end expiratory pressure (PEEP)

• Increases the end expiratory or baseline airway
  pressure to a value greater than atmospheric
  (0cmH2O) on ventilator manometer
• Keeps alveoli partially inflated
• Provides protection against the development of
  shear forces during mechanical inflation
• Not a stand alone mode, applied in conjunction
  with other modes

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Positive end expiratory pressure (PEEP)

• Indications
• Intrapulmonary shunt
• Refractory hypoxemia
• Decreased FRC
• Decreased lung compliance
• Maintaining pulmonary function in non-cardiogenic
  pulmonary edema, especially ARDS

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Positive end expiratory pressure (PEEP)

• BENEFITS
• Restore FRC/ Alveolar recruitment
• ? shunt fraction
• ?Lung compliance
• ?PaO2 for given FiO2

• DETRIMENTAL EFFECTS
• Barotrauma
• ? VR/ CO
• ? PVR
• ? MAP
• ? Renal / portal bld flow

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How much PEEP to apply???

• Lower inflection point transition from flat
  to steep part
• - ?compliance
• - recruitment begins (pt. above closing
  vol)
• Upper inflection point transition from steep
  to flat part
• - ?compliance
• - over distension

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How much PEEP to apply??
Set PEEP above LIP Prevent end expiratory
airway collapse Set TV so that total P lt UIP
prevent overdistention Limitation lung is
inhomogenous - LIP / UIP differ for different
lung units
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Selection of degree of PEEP

• Lowest level of PEEP which maintains PaO2 gt 60
  mmHg on a FIO2 lt 0.6
• Ensures optimal oxygenation
• Ensures maximal oxygen transport
• Best compliance
• Lowest Qs/Qt ratio
• Lowest Vd/Vt ratio
• Lowest PaCO2 PetCO2 gradient

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8) Continuous positive airway pressure (CPAP)
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Continuous positive airway pressure (CPAP)

• CPAP is actually PEEP applied to spontaneously
  breathing patients.
• But CPAP is described a mode of ventilation
  without additional inspiratory support while PEEP
  is not regarded as a stand-alone mode

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9)Biphasic positive airway pressure (BiPAP)

• Single ventilation mode which covers entire
  spectrum from mechanical ventilation to
  spontaneous breathing
• Permits spontaneous breathing
• Two pressure levels are set P high P low
• Two time intervals are set T high T low
• Spontaneous breathing possible at both levels
• Changeover between 2 pressure levels is
  synchronized with exp insp

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• .
• Can provide total / partial ventilatory support
• BiPAP CMV if pt not breathing
• BiPAP SIMV- spontaneous breathing at lower
  pressure level only mandatory breaths by
  switching between 2 pressure levels
• CPAP both pressure levels are identical in
  spontaneously breathing patient
• Genuine BiPAP _Spontaneous breathing at both the
  pressure levels

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• Advantages
• Allows unrestricted spontaneous breathing
• Continuous weaning without need to change
  ventilatory mode universal ventilatory mode
• Reduced atelactasis
• Less sedation needed

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Management of a patient on mechanical ventilation
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Management of mechanical ventilation

• Tidal volume 8-10 ml/kg BW

Atelectasis Hypoventilation Hypoxemia
Low tidal volume
Respiratory alkalosis Decrease cardiac
output Ventilator induced lung injury
High tidal volume
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Management

• Respiratory rate 10-14 breaths /min
• Minute Ventilation 5-10 l/min

Hypoventilation Hypoxemia
Low respiratory rate
Respiratory alkalosis Ventilator induced lung
injury
High respiratory rate
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Management

• I E ratio 12 1 3
• FIO2 should be 1 ( to start with )
• After 15 20 min , gradually reached to a
  level which allows PaO2 gt60 mmHg and O2
  saturation gt 90
• Inspiratory flow rate 40 60 l/ min
• PEEP used if O2 saturation lt 90 on FIO2 of 0.6

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Guidelines in practical management of patients on
ventilatory support
Maintain flow chart of vital signs ,PaO2, PaCO2 and pH of arterial blood Chart ventilator settings---VT, MV, RR, Peak and plateau pressure, compliance( static and dynamic) Maintain normal oxygenation( in most patients PaO2 of 60-70 mmHg suffices) maintain PaCO2 between 35-40 mmHg permissive hypercapnia in selected cases Monitor alveolar arterial oxygen gradient on 100 oxygen and PaO2/FIO2 ratio Monitor VD/ VT and shunt fraction ( QS/QT) in selected patients

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Guidelines in practical management of patients on
ventilatory support
Prevent gross alveolar hyperventilation ( PaCO2 lt 25 mmHg) Avoid oxygen toxicity by using least FIO2 that allows adequate PaO2 ( 60-70 mmHg ) use PEEP only when indicated Maintain normal circulatory volume, good pump function, normal BP and adequate Hb concentration Humidification of inspired gases, frequent aseptic suction of tracheobronchial secretions, and frequent good physiotherapy necessary Support other organ systems
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Use of proximal airway pressures to evaluate a
patient with acute respiratory deterioration
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MONITORING OF THE PATIENT IN ICU
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monitoring
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Care of vascular lines and tubes
analgesia
Nutrition
Care of a patient on respiratory support
Sedation
Care of lungs
Care of unconscious patient
Muscle relaxation
Preventing complications Chest infections Venous
thrombosis Pulmonary embolism GI bleed
Psychological care
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Care of lungs

• Regular side to side turning of patient
• Chest physiotherapy
• Regular sessions of manual hyperinflation with
  external chest vibration and compression
• Regular aseptic suctioning - no touch technique
  with disposable sealed units
• Postural drainage

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Ventilatory care bundles

• A series of interventions related to ventilatory
  care that, when implemented together, will
  achieve significantly better outcomes than when
  implemented individually
• Goal to prevent ventilator associated pneumonia
  (VAP) and other complications in patients on
  ventilator

It is important that all key components are
implemented to achieve maximum outcome.
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Ventilatory care bundles

• Head of bed elevated to 30 degrees
• Peptic ulcer disease prophylaxis (PU)
• Deep vein thrombosis prophylaxis (DVT)
• Daily sedation hold

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Head end elevation

• Integral part of ventilatory care bundles
• Correlated with reduction in the rate of
  ventilator-associated pneumonia
• Recommended elevation is 30 to 45 degrees
•  

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Head end elevation

• Decreases the risk of aspiration of
  gastrointestinal contents or oropharyngeal and
  nasopharyngeal secretions
• Provides better respiratory mechanics and
  improves spontaneous tidal volumes
• Aids ventilatory efforts and minimize atelectasis

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Gastric ulcer prophylaxis

• Most common cause of GI bleed in ICU
• H2 receptor antagonists are the preferred agents
• Proton pump inhibitors have not been assessed in
  a direct comparison with H2 receptor antagonists

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DVT Prophylaxis

• Sequential compression devices (a.k.a.
  "venodynes" or "pneumoboots )
• Anticoagulation

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Daily sedation hold

• Results in a marked and highly significant
  reduction in time on mechanical ventilation
• Facilitates weaning
• Reduces VAP

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Pulmonary Pulmonary barotrauma Chest
infection Venous thrombosis Pulmonary
embolism Lung fibrosis (late) Alveolar
hyperventilation Atelactasis
Gastrointestinal Pneumoperitoneum Decreased GI
motility Gastrointestinal haemorrhage
Nutritional Malnutrition Excess CO2 production
Complications of mechanical ventilation
Others Bacteremia Multiorgan failure Psychological
consequences Endocrine dysfunction Pressure sores
Cardivascular Decreased cardiac
output Dysrhythmias Pulmonary artery catheter
complications
Renal Fluid retention Renal failure
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EFFECTIVE VENTILATION REQUIRES A BLEND
OF SCIENCE AND ART !!!
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References

• Egans Fundamentals of Respiratory Care 9th ed.
• International Anaesthesiology Clinics Update on
  respiratory critical care, vol 37, no 3, 1999.
• David W Chang, Clinical application of mechanical
  ventilation 3nd ed
• Paul L Marino, The ICU Book, 3rd ed.
• Farokh Erach Udwadia-Principles of Critical Care,
  2nd ed.
• Joseph M Civetta,Critical care, 3rd ed.
• Keith Sykes,JDYoung Respiratory Support in
  Intensive Care BMJ Publishers,2000
• PKVerma Mechanical Ventilation and nutrtion in
  Critically Ill Patients ,1999
• Curves and loops in mechanical ventilation
  Manual by Drager Medical
• BiPAP - Manual by Drager Medical