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BASICS OF MECHANICALVENTILATION
Muthiah P. Muthiah, MD, FCCP
Associate Professor of Medicine
Pulmonary & Critical Care & Sleep MedicineUniversity of Tennessee, Memphis
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MECHANISM OF BENEFIT
Improves gas exchange (positivepressure improves V/Q matching,decrease intrapulmonary shunting)
Decreases work of breathing
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Some Conditions Requiring MV
Pneumonia / ALI /ARDS
Acute Pulmonary Edema
Severe Sepsis / Shock Severe Exacerbations of Asthma / COPD
Neuro: Guillain–Barre/ Myasthenia /
Drug OD etc.
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MAIN INDICATION
Acute Respiratory Failure:
inability to oxygenate arterial blood
adequately and/or loss of capacity to sustain adequate
alveolar ventilation
Clinically manifested by presence of rapid,shallow breathing
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Suggested Criteria fro MV
RR > 35
VC < 10 ml/Kg
NIF < -25 CmH2O INC in PaCO2 (> 10)
PaO2 < 55 mmHg despite supplemental
O2 > 45%
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Some Modes of Ventilation
AC
SIMV
SIMV + PS PSV
PC
BiLevel / APRV VC Plus
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INDICATION
Ultimately,decision to initiate mechanicalventilation must take clinicalcircumstances into account as well as
physiologic derangements
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VENTILATOR CYCLINGMECHANISMS
Volume-cycled: inspiration terminated after delivery of a
preset tidal volume
Pressure-cycled: inspiration terminated when a preset maximum
pressure reached.
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VENTILATOR CYCLINGMECHANISMS
Flow-cycled: inspiration terminated when particular flow
rate reached. (e.g. Pressure supportventilation)
Time-cycled: inspiration terminated following a preset
inspiratory time. (e.g.Home ventilators)
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Basic Ventilator Modes “Control” modes
Volume control (Assist control): AC. Pressure control: PC.
Mixed Synchronized Intermittent Mandatory
Ventilation (SIMV) with support (controlled &s pontaneous)
“Spontaneous” Modes Pressure Support (PS) CPAP (NOT A MODE!!)
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Mode characteristics
What parameters do I have to set/order?
What initiates a breath?
What terminates a breath (i.e. how theventilator cycle )?
What are the flow characteristics?
What are the pressure characteristics?
What are the determinants of VT ?
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General Measures in Patientson Mechanical Ventilation
Use as low FiO2 as possible
Head of bed at 30o to decrease risk ofaspiration
GI bleed prophylaxis:H2 blockers, PPIs or Sucralfate
DVT prophylaxis on all patients:
TED hose plus pneumatic compression stocking orSQ heparin
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FAST HUG
Feeding
Analgesia
Sedation T hromboembolism Prophylaxis
Head of Bed Elevation
Ulcer Prophylaxis Glucose Control
FA
STH
UG
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Assist Control
Ventilator senses an inspiratory effort bythe patient and responds by delivering apreset TV.
Patient work required to trigger theventilator
A control mode back-up rate is set toprevent hypoventilation
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Assist control (AC)
Flow: constant
Pressure:
Increases as lungs distend untilinspiration terminates; pressurepotentially varies breath to breath
VT : Fixed
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Assist control (AC)
Orders: RR, VT , FIO2 +/- PEEP
Initiate: patient or controlled
Breaths beyond set rate get the set VT Termination: VT – “volume-cycled”
Example initial orders: AC / RR 14 / Vt 400 ml / PEEP 5 / FiO2 100
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AC/CMV
Airway
pressure
Time
Inspiration Expiration
Ventilator triggered
breath
Patient triggered breath
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Assist Control (AC) Advantages:
Reduced work of breathing Allows patient to increase minute ventilation;
can’t decrease below set VE
Minimal VE is ensured
Disadvantages potential adverse hemodynamic effects or
inappropriate hyperventilation airway pressures vary with changes in lung
compliance
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SIMV with PS
Degree of ventilatory support determined by theselected IMV rate.
At regular intervals, ventilator delivers a breathbased upon a preset TV and rate.
Pt allowed to breathe spontaneously at TV and
rate determined according to need and capacity
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SIMV
Airway
pressure
Time
Inspiration Expiration
Ventilator triggered
breath
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SIMV
Airway
pressure
Time
Inspiration
Expiration
Ventilator triggered
breathPatient triggered breath
Inspiration
Expiration
Ventilator triggered
breath
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SIMV with PS
Potential advantages More comfortable for some patients
Less hemodynamic effects
Potential disadvantages Increased work of breathing, especially when
weaning
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PS ventilation
Flow-cycled: preset pressure sustained until inspiratory
flow tapers to 25 % of max
Comfortable ventilatory modality Patient with greater control over ventilator
cycling and flow rates
Close monitoring because neither TV nor MVguaranteed
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Pressure Support (PS)
Orders: Pinsp above PEEP, FIO2 +/- PEEP Initiate: Patient only Termination:
Flow 25% of max (flow cycled) Flow:
decelerating rate; patient can increase Pressure: constant
Volume: varies with pressure, effort, and compliance of
lung and chest wall
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Pressure Support (PS)
Potential advantages Patient comfort Decreased work of breathing
May enhance patient-ventilator synchrony
Potential disadvantages
Variable VT if pulmonaryresistance/compliance changes rapidly
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CPAP
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T-piece (T-tube)
Orders: FIO2
Initiate: Patient Termination: Patient Flow: Patient Pressure: negative with inspiration Volume: varies with effort and compliance
Spontaneous breathing through an ETT
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T-piece
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Managing the ventilatedpatient
Initial orders
Normal lungs Obstructive lung disease
Acute Lung Injury/ARDS
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Suggested guidelines formechanical ventilation
Maintain Plateau Pressure < 30 cm H2O
PS during spontaneous breaths
Use lowest FIO2 to maintain acceptablearterial PaO2
Keep patient comfortable
Anxiety, pain, WOB (RR < 20-30)
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Short-Term: Normal Lungs
Post-op, procedures, drug overdose:
AC or SIMV/PS
VT : 6 - 8 cc/kg (IBW) RR: 10 - 14 I:E – 1:2 (default) PEEP: 5 cm H2O FIO2 to keep SpO2 > 92% HOB up >30 (ALL pts)
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Elevated ICP: Normal lungs
Closed head injury
Same guidelines as normal lungs Avoid PEEP unless need for hypoxemia
Hyperventilate? PaCO2 30-35 (controversial)
Sedation
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Obstructive Lung Disease
COPD, Asthma
AC, SIMV/PS
VT : 8 cc/kg
RR:8 - 12
I:E – shorter I time
Good sedation for first 24h (rest) Bronchodilators
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Acute Lung Injury/ARDS
AC, PC , BiLevel / APRV
VT : 6 cc/kg
I:E- 1:2
RR: 15-25
PEEP: > 8-10
Sedation
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MV –Adjustment phase
Target Spo2 : > 94%, paO2 > 60 mmHg
Target pco2: based on pH
To adjust ventilation (co2): change eitherRR (and /or TV)
To adjust oxygenation: change either FIO2or PEEP
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MV –Adjustment phase
Monitor Peak and Plateau pressures
Peak Pressure-Plateau Pressure= Airwayresistance
Peak airway pressure should be < 45-50 cm
H2O (decrease barotrauma)
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MV –Adjustment phase
Provide appropriate I:E ratio Normal ratio of 1:2 COPD/asthma require much longer expiratory
time to avoid air trapping
Attempt to shorten inspiratory time, leaving restof cycle for exhalation : Decrease tidal volume Decrease respiratory rate Increase peak flow
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WEANING / Liberation from MV
Process used safely remove patient fromMechanical Ventilation
First condition before starting the
liberation process: Satisfactory control of the condition
that initially caused the need forassisted breathing
Weaning actually starts soon afterPlacing on MV: Eg. : Decreasing Oxygen
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TRIALS OF SPONTANEOUSBREATHING
Decision to extubate based upon clinicalassessment during course of the trial,
usually (not always) supplemented by ABG
Trial of spontaneous breathing once a day
shown to be as effective as multiple trials
R id Sh ll B thi I d
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Rapid Shallow Breathing IndexRSBI, or Tobin Index
Measured as respiratory frequency (f)divided by tidal volume (TV) in liters
Eg.: RR 18, Vt 500 ml: 18 ÷ 0.5 = 36 <105:
80 % chance of weaning success >105:
95% chance of weaning failure
Q i k V t Ti A f
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Quick Vent Tips: A few caseScenarios
Initial Settings
Appropriate Vt in ARDS
Low pressure High pressure
High pr with Pk – Pl diff >10
High pr with Pk – Pl diff <10 Difficult to Oxygenate patient
Which mode of ventilation is usually selected wheniniti tin m ch nic l ntil ti n in p ti nt h just
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initiating mechanical ventilation in a patient who justgot intubated for respiratory failure followingCommunity Acquired Pneumonia?
A. Assist Control
B. SIMV
C. Pressure SupportD. CPAP
E. APRV
What is optimal tidal volume for a patient who
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p pweighs 70 Kgs, and is now getting intubated forrespiratory failure after he developed ARDS?
A. 420 ml
B. 700 ml
C. 840 mlD. 1 L
E. 1230 ml
Which are usual appropriate initial settings
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Which are usual appropriate initial settingsfor a patient who weighs 70 Kgs, and is nowgetting intubated for respiratory failure
after he developed ARDS?
A. SIMV/ RR 28/ VT 840 ml/ PEEP 5/ O2 50%
B. AC / RR 14 / 420 ml / PEEP 5 / O2 100%
C. PSV / PS 10/ PEEP 5
D. CPAP 10 / O2 100%
A patient is on the ventilator, and thel l i i ff Wh t
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low pressure alarm is going off. Whatare the possible reasons for this to
happen?A. Tube disconnect
B. Thick secretions
C. Excess fluid in the tubing
D. Pneumothorax
E. Right main stem intubation
A patient is on the ventilator, and thehigh pressure alarm is going off What
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high pressure alarm is going off. Whatare the possible reasons for this to
happen?A. Tube disconnect
B. Auto PEEP
C. Bronchopleural fistula
D. Hypoxemia
E. Hypoventilation
A patient is on the vent, and the High pralarm is going off Peak pr: 55 Plateau Pr
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alarm is going off. Peak pr: 55, Plateau Pr32. What should be considered in the diff
diagnosis in this patient?A. Worsening ARDS
B. Worsening bronchospasm
C. Right main stem intubationD. Pneumothorax
E. Tube disconnect
A patient is on the vent, and the Highl i i ff P k 55
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pressure alarm is going off. Peak pr: 55,Plateau Pr 50. What should be considered in
the diff diagnosis in this patient? A. Worsening ARDS
B. Worsening bronchospasm
C. Thick secretions
D. Patient is biting the tube
E. ET Tube is blocked
A patient who weighs 70 Kgs is on the
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p g gventilator, and you are called to evaluate thepatient for low SPO2 of 78%. Patient is on
A/C mode, RR 14, PEEP 5, Vt 450, O2 100%.Peak pr 35, Plateau Pr 28, minute ventilaton14 LPM.
He has bilateral breath sounds, and a statCXR shows bilateral diffuse infiltrates.ABG: pH 7.37 / paCO2 46 / paO2 51 / SaO2 81%.
What should be the initial intervention toimprove the patient’s oxygenation status?
What should be the initial interventiont impr ve the patient’s x enati n
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to improve the patient s oxygenationstatus?
A. Increase the tidal volume to 600 ml and callthe fellow
B. Increase the RR 22 and call the fellow
C. Change the mode to PSV and call the fellowD. Increase the PEEP to 10 and call the fellow
E. Administer Neuromuscular blockade with
Norcuron and call the fellow
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Q?