MODES OF MECHANICAL VENTILATION
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Transcript MODES OF MECHANICAL VENTILATION
Educational Resources
PICU
resident handbook with relevant
PICU topics is available at
http://peds.stanford.edu/Rotations/picu/pic
u.html
Hard copy is available in the resident call
room.
PICU chapters at
http://peds.stanford.edu/Rotations/picu/picu.html
Monitors in ICU
Vascular Access
Codes
ICP management
Status Epilepticus
Sedation
Pediatric Airway
Airway Management
Mechanical
Ventilation
ARDS
Status Asthmaticus
Inotropes
Shock
Sepsis
Meningococcus
PICU chapters at
http://peds.stanford.edu/Rotations/picu/picu.html
Cardiomyopathy
Liver Failure
Acute Renal Falilure
Fluids, Electrolytes,
Nutrition
Oncology
Transfusions
DKA
Submersion Injuries
Brain Death
End of life issues
PICU Tables at
peds.stanford.edu
Sedation
Inotropes
Shock
MECHANICAL VENTILATION
SARASWATI KACHE, M.D.
Clinical Assistant Professor
Spontaneous respiration vs.
Mechanical ventilation
Natural
Breathing
Negative
inspiratory force
Air pulled into lungs
Mechanical
Positive
Ventilation
inspiratory pressure
Air pushed into lungs
Initiate Mechanical Ventilation
Hypoxia
Hypercarbia
Airway
protection
(Decrease demand in cases of poor
cardiac output)
Ventilators: a Schematic
IMPORTANT TERMS
TIME
Volume
Amount of tidal volume that a patient receives
Pressure
I - Time: amount of time spent in inspiration
E - Time: amount of time spent in expiration
Measure of impedance to gas flow rate
Flow
Measure of rate at which gas is delivered
A Few More Terms
PEEP = positive end expiratory pressure
Pressure maintained in the airways at the end of
exhalation
Keeps Alveoli from collapsing
PIP = peak inspiratory pressure
Point of maximal airway pressure
Delta P = the difference between PIP – PEEP
MAP = mean airway pressure
ICU Ventilator: Evita 4
ICU Ventilator: Evita 4
Types of Ventilation ….
Compliance = Volume
Pressure
Volume Ventilation
Preset
Volume
PEEP
Rate
I-time
FiO2
Ventilator
Determines
Pressure required
Advantages
Guaranteed minute
ventilation
More comfortable for
patient
Draw-backs
Large ETT leak
Not optimal for poorly
compliant lungs
Pressure Ventilation
Preset
PIP
PEEP
Rate
I-time
FiO2
Vent determines
Tidal volume given
Advantages
Provides more
support at lower PIP
for poorly compliant
lungs
Draw back
Minute ventilation not
guaranteed
Volume vs. Pressure
Amount of support to
give…
MODES OF VENTILATION
Controlled Mechanical Ventilation (CMV)
Assist Control (AC)
Continuous Positive Airway Pressure (CPAP)
Intermittent Mandatory Ventilation (IMV)
Synchronized Intermittent Mandatory Ventilation
(SIMV)
Pressure Support
Volume Support
Pressure Regulated Volume Control (PRVC)
Assist Control
Volume
or Pressure control mode
Parameters to set:
Volume
Rate
– time
FiO2
I
or pressure
Assist Control
Machine
breaths:
Delivers
Patient’s
the set volume or pressure
spontaneous breath:
Ventilator
delivers full set volume or
pressure & I-time
Mode
of ventilation provides the most
support
SIMV
Synchronized intermittent mandatory ventilation
Volume or Pressure mode
Parameters set:
Volume or pressure
Respiratory rate
I – time
FiO2
Pressure support
SIMV
Synchronized intermittent mandatory ventilation
Machine breaths: d
Patient’s spontaneous breath:
Delivers the set volume or pressure
Set pressure support delivered
Mode of ventilation provides moderate amount
of support
Works well as weaning mode
Pressure Support
Parameters
Pressure
set:
support,
FiO2
Machine
breaths: none *****
Patient’s spontaneous breaths: set
pressure support delivered
Purposes:
Final
step prior to extubation
Re-train muscle strength
Continuous Positive Airway
Pressure (CPAP)
Positive
airway pressure maintained
throughout respiratory cycle: during
inspiratory and expiratory phases
Can be administered via ETT or nasal
prongs
Managing the Patient…
Pulmonary Compliance
Compliance
= Volume
Pressure
Monitor patient’s clinical changes
i.e. as compliance improves
Volume
mode: required pressure decreases
Pressure mode: generated volume
increases
Hypoxia
Hypoventilation: decreased alveolar
ventilation, i.e. CNS depression
Diffusion impairment: abnormality at
pulmonary capillary bed
Shunt: blood flow without gas exchange
Intra-pulmonary
Intra-cardiac
Ventilation-perfusion mismatch: Both dead
space and shunt abnormalities
Treating Hypoxia
Increase
FiO2: >60% toxic to lung
parenchyma
Increase mean airway pressure
PEEP
PIP
I-time
: not too much, not too little
Hypercarbia
Decreased
minute ventilation
Respiratory
rate
Tidal volume
Treatment:
Increase
respiratory rate: assure I-time not
too short as rate increased
Increase tidal volume
Allow permissive hypercarbia
Pulmonary Disease: Obstructive
Airway obstruction causing increase resistance to
airflow: e.g. asthma
Optimize expiratory time by minimizing minute
ventilation
Bag slowly after intubation
Don’t increase ventilator rate for increased CO2
Pulmonary Disease: Restrictive
Compromised lung volume:
Intrinsic
lung disease
External compression of lung
Recruit
alveolia, optimize V/Q matching
Lung protective strategies
High
PEEP
Pressure limiting PIP: 30-35 cmH2O
Low tidal volume: 4-8 ml/kg
FiO2 <60%
Permissive hypercarbia
Permissive hypoxia
High Frequency Oscillatory
Ventilation
HIFI - Theory
Resonant
frequency phenomena:
Lungs
have a natural resonant frequency
Outside force used to overcome airway
resistance
Use
of high velocity inspiratory gas flow:
reduction of effective dead space
Increased bulk flow: secondary to active
expiration
HIFI - Gas Transport
Conventional bulk flow
Coaxial flow: different
flow directions in central
and peripheral air
columns
Taylor dispersion: gas
molecules disperse
beyond the bulk flow
front
HIFI - Gas Transport
Molecular diffusion:
gas mixing within
alveoli
Pendelluft
phenomenon: interalveolar gas mixing
due to impedance
differences
HIFI - Advantages
Advantages:
Decreased barotrauma / volutrauma: reduced
swings in pressure and volume
Improve V/Q matching: secondary to different flow
delivery characteristics
Disadvantages:
Greater potential of air trapping
Hemodynamic compromise
Physical airway damage: necrotizing
tracheobronchitis
Difficult to suction
Often require paralysis
HIFI – Clinical Application
Adjustable
Mean
Parameters
Airway Pressure: usually set 2-4
higher than MAP on conventional ventilator
Amplitude: monitor chest rise
Hertz: number of cycles per second
FiO2
I-time: usually set at 33%
HIFI - Applications
Oxygenation
Mean airway
pressure
FiO2
Ventilation
Amplitude
Hertz
I-Time
Scenario #1
The following blood gas is presented to you for a 4yr
patient that is now 3hours post-op from an OLT.
7.52 / 24 / 250 / 20 / -4
The ventilator settings are SIMV PC/PS PEEP – 4,
Delta P-28, FiO2 – 50%, RR – 12.
Scenario #2
A 8yr female with ALL s/p chemo presents to the
PICU with fever and neutropenia 1day prior. She is
found with positive blood cultures this AM and got
intubated secondary to respiratory failure. It is now
4am and the morning labs show the following ABG:
7.23 / 60 / 58 / 22 / -2
The ventilator settings are SIMV TV - 10cc/Kg,
PEEP – 5, PIP – 38, PS – 14, FiO2 – 70%, RR – 20,
I-time – 0.7
You go to examine the patient and she is agitated,
hypertensive, and with a respiratory rate of 40.
Scenario #3
There is a 6 month old patient that presents with RSV
bronchiolitis that progresses to severe disease and the
patient is now on a HIFI ventilator. The patient’s ABG is
as follows:
7.24 / 58 / 75 / 21 / -3
The ventilator settings are as follows: HIFI with MAP –
20, Amp – 28, Hz – 8, FiO2 – 40%.
As you are looking at the chest X-ray, the nurse
mentions the patient looks more edematous this evening
compared to last night.
References
http://www.ccmtutorials.com/rs/mv/
Editors: Rogers MC & Nichols DG. Textbook
of Pediatric Intensive Care. Baltimore,
Willimams & Wilkins, 1996.
Cairo JM & Pilbeam SP. Mosby’s Respiratory
Care Equipment. St. Louis, Mosby, 1999.
Evita 4 Intensive Care ventilator, Operating
instructions, 2001.
West JB. Pulmonary Pathophysiology.
Baltimore, Willims & Wilkins, 1992.