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.