critical care ventilation technology perspective fran hegarty
Post on 02-Jan-2016
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Atoms and Molecules are connected together.
The connections arethe attraction of molecules
to each other.
Atoms and Molecules are connected together.
The connections arethe attraction of molecules
to each other.
As molecules get more energy (temperature) they tend to become less bound by the attraction
between them, and the properties of the matter change.
Molecules have:
Low Energy
Low Temperature.
Molecules held in place byattraction to each other.
Solid.
Molecules have:
Some Energy
Higher Temperature.
Molecules held in place byattraction to each other
but have enough energy to moverelative to each other.
Liquid
Molecules have:
Lots of Energy
Higher Temperature.
Molecules no longer held in placeby attraction to each other
but move freelyrelative to each other.
Gas
Molecules have:
Lots of Energy
Higher Temperature.
Molecules no longer held in placeby attraction to each other
but move freelyrelative to each other.
Gas
Gases.
Volume = Defined Space i.e. 1 Litre.
If it is empty i.e. contains no matter of any kind its called a vacuum.
Gases.
The gas molecules are in constant motion, and sothey regularly hit the walls of the container.
Gases.
The force of the gas molecules hitting the walls of the container is called the Gas Pressure.
Gases.
The more gas molecules there are, the more often thewalls of the container are hit,
therefore the Gas Pressure is higher.
Gases.
If the temperature (energy) of the gas is increased the molecules move faster and so hit the walls harder
causing the Gas Pressure to rise also.
Gases.
The effect of the expected variations in room temperature have very little effect on
medical gas pressure (so we will ignore this effect).
Gases.
Volume = 1Pressure = 1
Volume = 1Pressure = 2
The amount of Gas Molecules in a volume is given by the Volume x Gas pressure.
Volume = 1Pressure = 2
What would happen if we suddenly doubledthe size of the container ?
Volume = 2Pressure = ?
Remember there are the same number of molecules in each.
Gas expands to fill the volume.Density of gas falls.
Force per unit ares due to gas hitting the walls falls.Pressure falls.
Volume = 2Pressure = 1
Volume = 1Pressure = 2
Volume = 0.5Pressure = 4
Volume = 2Pressure = 1
V x P = 2 V x P = 2 V x P = 2
Volume = 1Pressure = 2
How come we never talk about the pressure whendeciding how much gas is to be delivered to the patient ?
To answer that we need to know more about Atmospheric Pressure.
Atmospheric Pressure
Pressure of the Airmolecules hitting
the earth.(or any other surfacein the atmosphere).
14 lbs. per square inch
So, when we say we want to give a patient
“a tidal volume of half a litre of air”
…….we realy mean….
“ a tidal volume of half a litre of air at atmospheric pressure”.
Airway Pressure Waveform
Patmtime.
Volume of Air in Lungs
FRC
0.7 L
time.
Airway Flow Waveform
Into Lungs
Out of Lungs
time.
Modes of Ventilation.
Different ways of controlling gas flow into and out of the patients lungs.
Computer
User Interface
Display&
Alarms
Flow Pressure Volume Lung Response
Volume Controlled Ventilation.
Define Tidal Volume
Define Breath Waveshape (timing)
Ventilator works out the Gas Flowon inspiration (expiration is lungdependent).
Resultant Airway Pressure isa function of gas flow into and out oflung (lung condition important)
Pressure Controlled Ventilation.
Define Target Airway Pressure
Define Breath Waveshape (timing)
Ventilator works out the Gas Flowto achieve and maintain the Target Pressure.
Resultant Volume delivered isa function of gas flow into and out oflung (lung condition important)
All modes are just different ways of controlling the flow of gas into the patients lungs.
VentilatorControlled
Volume
Pressure
CMV
Bellows Lungs
Pressure Regulated Volume Controlled
Who is in charge ?How do you determine the waveshape?
Pressure Regulated Volume Controlled Ventilation.
Machine takes a guess at the pressureRequired to deliver this breath.
Define Breath Waveshape (timing)
Ventilator works out the Gas Flowto achieve and maintain the Target Pressure.
Define the target volume
Pressure Regulated Volume Controlled Ventilation.
Machine takes a guess at the pressureRequired to deliver this breath.
Define Breath Waveshape (timing)
Ventilator works out the Gas Flowto achieve and maintain the Target Pressure.
Define the target volume
Machine takes a guess at the pressureRequired to deliver this breath.
Define Breath Waveshape (timing)
Ventilator works out the Gas Flowto achieve and maintain the Target Pressure.
Define the target volume
Pressure Regulated Volume Controlled Ventilation.
Machine takes a guess at the pressureRequired to deliver this breath.
Define Breath Waveshape (timing)
Ventilator works out the Gas Flowto achieve and maintain the Target Pressure.
Define the target volume
Pressure Regulated Volume Controlled Ventilation.
Time.
V
P
Patient is completely paralysed - makes no effort
Mode 2. Volume Controlled (Flow-Time Regulated) Ventilation.
Time.
V
P
Patient is completely paralysed - makes no effort
Volume Controlled (Pressure Regulated) CMV.
Insp. Time.
Time.
Vti
AirwayPressure
Pressure Regulated Volume Controlled.
1st Breath – Test Breath (Volume Controlled)
2nd Breath – PRVC Breath
Plateaux Pressure from VolumeControlled breath used as thestarting point for the PRVC breaths.
Time.
© F. Hegarty 2009
Time.
Vti
AirwayPressure
Pressure Regulated Volume Controlled.
Time.
© F. Hegarty 2009
Set / RequiredTidal Volume
Breath A.Inspiratory Pressure insufficientto deliver the required Vti.
Computer detects the volumeIs short and increases the inspiratory
Pressure on the next breath by 3 cmH20
Breath B.Inspiratory Pressure now sufficientto deliver the required Vti.
Time.
Vti
AirwayPressure
Pressure Regulated Volume Controlled.
Time.
© F. Hegarty 2009
Set / RequiredTidal Volume
Breath B.Inspiratory Pressure now sufficientto deliver the required Vti.
Set UpperInspiratory
Pressure Alarm Limit
Breath C.If something goes wrong and venttries to deliver a high pressure breath theAirway alarm will sound.
Patient is completely paralysed - makes no effortVolume Controlled (Pressure Regulated) CMV.
Time.
V
P
All modes are just different ways of controlling the flow of gas into the patients lungs.
VentilatorControlled
Volume
Pressure
PRVC
VentilatorControlled
Volume
Pressure
AssistedVentilation
All modes are just different ways of controlling the flow of gas into the patients lungs.
CMV
P
Trigger
Pressure Support above PEEP
Patient effort controls the rate (need to set the Trigger Sensitivity).
Ventilator does not deliver a volume…………….
It delivers a flow of gas until the patient airway reaches adefined pressure (need to define this new pressure level).
Pressure Support.
VentilatorControlled
Volume
Pressure
AssistedVentilation
Mix
All modes are just different ways of controlling the flow of gas into the patients lungs.
CMV SIMV
V
CMV Volume Controlled (Revision)
CMV Rate Insp. Time %Pause Time %Insp. Rise Time %.
Breath Period = 60/CMV Rate
2 Sec
Waveform determined by flow controls
Volume set by tidal volume
V
CMV Volume Controlled (Revision)
CMV Rate Insp. Time %Pause Time %Insp. Rise Time %.
Breath Period = 60/CMV Rate
2 Sec
Waveform determined by flow controls
Volume set by tidal volume
VC
V
SIMV Volume Controlled
CMV Rate Insp. Time %Pause Time %Insp. Rise Time %.
N.B. The repetition rate is set by a newcontrol the SIMV Rate.
SIMV Rate
V
SIMV Volume Controlled
CMV Rate Insp. Time %Pause Time %Insp. Rise Time %.
SIMV Rate = 6 Time = 60/6 = 10Therefore the next VC breath is in ten seconds.
SIMV Rate
VentilatorControlled
Volume
Pressure
AssistedVentilation
Mix
VC
PCPS
SIMV(VC&PS)
SIMV(PC&PS)
All modes are just different ways of controlling the flow of gas into the patients lungs.
VS
PRVC
Auto Mode
CMV
SIMV
PredominantlyMandatorywith someAssisted
AssistModes
SIMV
PredominantlyAssisted
with someMandatory
Control Mode
Assist Mode
CMV
SIMV
PredominantlyMandatorywith someAssisted
AssistModes
SIMV
PredominantlyAssisted
with someMandatory
Control Mode
Assist Mode
Perfusion Side.
Arterial Blood Gas
Venous Blood Gas
O2 CO2 Bicarb pH
HB
Invivo Oximetry
RSO2 SvO2 SpO2
Pulmonary Arterial Pressure
Pulmonary Venous Pressure
Cardiac Output
Ventilation Side
Volumes and Timing
How the Volume changes with Pressure
Airway Pressures
Gas Composition
SwannGantz
CatheterisationThermodilution
Manometry
Spirometry
RespiratoryMechanics
Real Time Gas Monitoring
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