Critical Care Ventilation Technology Perspective Fran Hegarty

Critical Care Ventilation

Technology Perspective

Fran Hegarty

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

Properties of Gases.

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.

A gas will expand to fill the volume which contains it.

Gases.

A gas will expand to fill the volume which contains it.As it does so it becomes less dense.

Gases.

1 Litre of Oxygen(low density)

1 Litre of Oxygen(high density)

So how do you know how much gas is in aone litre volume ?

To answer that we need to know more

about

Gas Pressure.

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


The amount of Gas Molecules in a volume is given by the Volume x Gas pressure.


What would happen if we suddenly doubledthe size of the container ?


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 = 0.5Pressure = 4


V x P = 2 V x P = 2 V x P = 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.

Spaceis a vacuum.

Atmosphere isa gas (Air).

Air moleculeshit the surface ofthe earth.

Atmospheric Pressure

Pressure of the Airmolecules hitting

the earth.(or any other surfacein the atmosphere).

14 lbs. per square inch

We are so use to Atmospheric Pressure that we forget its there.

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”.

How do you make a gas move or flow.

Gases flow from areas of high pressure,to areas of low pressure.

What does it all have to dowith the Siemens 300 ?

Lungs

Patm

Lungs

Patm

Lungs

Patm

Lungs

Patm

Lungs

Patm

How we Breath.

Patm = PL

How we Breath.

Patm > PL

How we Breath.

Patm < PL

Boyles Law in action !

Patm

Patm

Volume of Air in LungsFRC

0.7 L

Airway Pressure

P

Spontaneous Breathing.

Bellows Lungs

Patm

Mechanical Ventilation.

Bellows Lungs

Patm

Bellows Lungs

Patm

Bellows Lungs

Patm

Patm

Patm

Patm

Patm

Patm

Ventilator Patient

Bellows Lungs

Ventilator Patient

Bellows Lungs

Ventilator Patient

Patm

Bellows Lungs

Ventilator Patient

Patm

Bellows LungsInspiration

Ventilator Patient

Patm


Ventilator Patient

Patm


Ventilator Patient

Patm


Ventilator Patient

Patm

Bellows LungsPause

Patm

Bellows LungsPause

Patm

LungsExpiration

Patm

LungsExpiration

Patm

LungsExpiration

Airway Pressure Waveform

Patmtime.

Inspiration


Patmtime.

Inspiration

Gas flows intopatients lungs.


Patmtime.

End ofInspiration

As lung expandsthe pressure falls


Patmtime.

Pause


Patmtime.

Start ofExpiration.


Patmtime.

End ofExpiration.

Gas flows out ofpatients lungs.


Patmtime.

Volume of Air in Lungs

FRC

0.7 L


Patmtime.


FRC

0.7 L


Patmtime.


FRC

0.7 L

time.

Airway Flow Waveform

Into Lungs

Out of Lungs

time.


Patm

time.

Airway Flow Waveform

Into Lungs

Out of Lungs

What is a Ventilator ?

Lets make one from scratch.

What is a Ventilator ?

Bellows Lungs

Key Components: Inspiration and Expiration Limbs and Expiration Valve.

Bellows Lungs

Bellows Lungs

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

Gas Volume

Gas Pressure

Gas Flow

Timing

Gas Volume

Gas Pressure

Gas Flow

Timing

Bellows Lungs

Volume Controlled

Who is in charge ?How do you determine the waveshape?

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)

Time.

Respiration Waveform (Volume v Time).

VIn

spir

ati

on

Pau

se

Exp

irati

on

Gap

I

E

Bellows Lungs

Pressure Controlled


Pressure Controlled Ventilation.

Define Target Airway Pressure


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


Bellows Lungs


Bellows Lungs


Pressure Regulated Volume Controlled Ventilation.

Machine takes a guess at the pressureRequired to deliver this breath.



Define the target volume
















Time.

V

P

Patient is completely paralysed - makes no effort

Mode 2. Volume Controlled (Flow-Time Regulated) Ventilation.

Time.

V

P


Pressure Controlled Ventilation.

Time.

V

P


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


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


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



Volume

Pressure

PRVC


Volume

Pressure

AssistedVentilation


CMV

Patient effort controls the rate (need to set the Trigger Sensitivity).

Pressure Support.

P

Trigger

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.

Pressure Support.

V

P

Trigger

Pressure Support above PEEP

F

Volume Support.

PPressure Support above PEEP

V

Volume Support.

PPressure Support above PEEP

V


Volume

Pressure

AssistedVentilation

Mix


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)


Breath Period = 60/CMV Rate

2 Sec

Waveform determined by flow controls

Volume set by tidal volume

VC

V

SIMV Volume Controlled


N.B. The repetition rate is set by a newcontrol the SIMV Rate.

SIMV Rate

V

SIMV Volume Controlled


SIMV Rate = 6 Time = 60/6 = 10Therefore the next VC breath is in ten seconds.

SIMV Rate

V

SIMV Volume Controlled - Pressure Support

V


V


V


V


V


V



Volume

Pressure

AssistedVentilation

Mix

VC

PCPS

SIMV(VC&PS)

SIMV(PC&PS)


VS

PRVC

Auto Mode

CMV SIMVAssistModes

Control Mode

Assist 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

Documents

Critical Care Ventilation Technology Perspective Fran Hegarty