Critical Care Ventilation Technology Perspective Fran Hegarty

Atoms and Molecules are connected together. The connections are the attraction of molecules to each other.

Atoms and Molecules are connected together. The connections are the 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 by attraction to each other. Solid.

Molecules have: Some Energy Higher Temperature. Molecules held in place by attraction to each other but have enough energy to move relative to each other. Liquid

Molecules have: Lots of Energy Higher Temperature. Molecules no longer held in place by attraction to each other but move freely relative to each other. Gas

Molecules have: Lots of Energy Higher Temperature. Molecules no longer held in place by attraction to each other but move freely relative 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 a one litre volume ?

To answer that we need to know more about Gas Pressure.

Gases. The gas molecules are in constant motion, and so they 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 the walls 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 = 1 Pressure = 1 Volume = 1 Pressure = 2 The amount of Gas Molecules in a volume is given by the Volume x Gas pressure.

Volume = 1 Pressure = 2 What would happen if we suddenly doubled the size of the container ?

Volume = 1 Pressure = 2 What would happen if we suddenly doubled the size of the container ? Volume = 2 Pressure = ? 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 = 2 Pressure = 1 Volume = 1 Pressure = 2

Volume = 0.5 Pressure = 4 Volume = 2 Pressure = 1 V x P = 2 Volume = 1 Pressure = 2

How come we never talk about the pressure when deciding how much gas is to be delivered to the patient ? To answer that we need to know more about Atmospheric Pressure.

Space is a vacuum. Atmosphere is a gas (Air). Air molecules hit the surface of the earth.

Atmospheric Pressure Pressure of the Air molecules hitting the earth. (or any other surface in 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 do with the Siemens 300 ?

Lungs P atm

Lungs P atm

Lungs P atm

Lungs P atm

Lungs P atm

How we Breath. P atm = P L

How we Breath. P atm > P L

How we Breath. P atm < P L Boyles Law in action !

P atm

Volume of Air in Lungs FRC 0.7 L Airway Pressure P Spontaneous Breathing.

Bellows Lungs P atm Mechanical Ventilation.

Bellows Lungs P atm

Bellows Lungs P atm

Bellows Lungs P atm

Ventilator Patient Bellows Lungs

Ventilator Patient Bellows Lungs

Ventilator Patient P atm Bellows Lungs

Ventilator Patient P atm Bellows Lungs Inspiration

Ventilator Patient P atm Bellows Lungs Inspiration

Ventilator Patient P atm Bellows Lungs Inspiration

Ventilator Patient P atm Bellows Lungs Inspiration

Ventilator Patient P atm Bellows Lungs Pause

P atm Bellows Lungs Pause

P atm Lungs Expiration

P atm Lungs Expiration

P atm Lungs Expiration

Airway Pressure Waveform P atm time. Inspiration

Airway Pressure Waveform P atm time. Inspiration Gas flows into patients lungs.

Airway Pressure Waveform P atm time. End of Inspiration As lung expands the pressure falls

Airway Pressure Waveform P atm time. Pause

Airway Pressure Waveform P atm time. Start of Expiration.

Airway Pressure Waveform P atm time. End of Expiration. Gas flows out of patients lungs.

Airway Pressure Waveform P atm time. Volume of Air in Lungs FRC 0.7 L

Airway Pressure Waveform P atm time. Volume of Air in Lungs FRC 0.7 L

Airway Pressure Waveform P atm time. Volume of Air in Lungs FRC 0.7 L time. Airway Flow Waveform Into Lungs Out of Lungs time.

Airway Pressure Waveform P atm 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 Flow on inspiration (expiration is lung dependent). Resultant Airway Pressure is a function of gas flow into and out of lung (lung condition important)

Time. Respiration Waveform (Volume v Time). V InspirationPauseExpirationGap I E

Bellows Lungs Pressure Controlled Who is in charge ? How do you determine the waveshape?

Pressure Controlled Ventilation. Define Target Airway Pressure Define Breath Waveshape (timing) Ventilator works out the Gas Flow to achieve and maintain the Target Pressure. Resultant Volume delivered is a function of gas flow into and out of lung (lung condition important)

All modes are just different ways of controlling the flow of gas into the patients lungs. Ventilator Controlled Volume Pressure CMV

Bellows Lungs Pressure Regulated Volume Controlled Who is in charge ? How do you determine the waveshape?

Bellows Lungs Pressure Regulated Volume Controlled

Bellows Lungs Pressure Regulated Volume Controlled

Pressure Regulated Volume Controlled Ventilation. Machine takes a guess at the pressure Required to deliver this breath. Define Breath Waveshape (timing) Ventilator works out the Gas Flow to achieve and maintain the Target Pressure. Define the target volume

Pressure Regulated Volume Controlled Ventilation. Machine takes a guess at the pressure Required to deliver this breath. Define Breath Waveshape (timing) Ventilator works out the Gas Flow to achieve and maintain the Target Pressure. Define the target volume

Machine takes a guess at the pressure Required to deliver this breath. Define Breath Waveshape (timing) Ventilator works out the Gas Flow to achieve and maintain the Target Pressure. Define the target volume Pressure Regulated Volume Controlled Ventilation.

Machine takes a guess at the pressure Required to deliver this breath. Define Breath Waveshape (timing) Ventilator works out the Gas Flow to 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 Pressure Controlled Ventilation.

Time. V P Patient is completely paralysed - makes no effort Volume Controlled (Pressure Regulated) CMV. Insp. Time.

Time. Vti Airway Pressure Pressure Regulated Volume Controlled. 1 st Breath – Test Breath (Volume Controlled) 2 nd Breath – PRVC Breath Plateaux Pressure from Volume Controlled breath used as the starting point for the PRVC breaths. Time. © F. Hegarty 2009

Time. Vti Airway Pressure Pressure Regulated Volume Controlled. Time. © F. Hegarty 2009 Set / Required Tidal Volume Breath A. Inspiratory Pressure insufficient to deliver the required Vti. Computer detects the volume Is short and increases the inspiratory Pressure on the next breath by 3 cmH20 Breath B. Inspiratory Pressure now sufficient to deliver the required Vti.

Time. Vti Airway Pressure Pressure Regulated Volume Controlled. Time. © F. Hegarty 2009 Set / Required Tidal Volume Breath B. Inspiratory Pressure now sufficient to deliver the required Vti. Set Upper Inspiratory Pressure Alarm Limit Breath C. If something goes wrong and vent tries to deliver a high pressure breath the Airway alarm will sound.

Patient is completely paralysed - makes no effort Volume Controlled (Pressure Regulated) CMV. Time. V P

All modes are just different ways of controlling the flow of gas into the patients lungs. Ventilator Controlled Volume Pressure PRVC

Ventilator Controlled Volume Pressure Assisted Ventilation All modes are just different ways of controlling the flow of gas into the patients lungs. CMV

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

P 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 a defined pressure (need to define this new pressure level). Pressure Support.

V P Trigger Pressure Support above PEEP F

Volume Support. P Pressure Support above PEEP V

Volume Support. P Pressure Support above PEEP V

Ventilator Controlled Volume Pressure Assisted Ventilation Mix All modes are just different ways of controlling the flow of gas into the patients lungs. CMVSIMV

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 new control the SIMV Rate. SIMV Rate

V SIMV Volume Controlled CMV Rate Insp. Time % Pause Time % Insp. Rise Time %. SIMV Rate = 6 Time = 60/6 = 10 Therefore the next VC breath is in ten seconds. SIMV Rate

V SIMV Volume Controlled - Pressure Support

V

V

V

V

V

V

Ventilator Controlled Volume Pressure Assisted Ventilation Mix VC PC PS 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

CMVSIMV Assist Modes Control Mode Assist Mode

CMV SIMV Predominantly Mandatory with some Assisted Assist Modes SIMV Predominantly Assisted with some Mandatory Control Mode Assist Mode

CMV SIMV Predominantly Mandatory with some Assisted Assist Modes SIMV Predominantly Assisted with some Mandatory Control Mode Assist Mode

Perfusion Side. Arterial Blood Gas Venous Blood Gas O 2 CO 2 Bicarb pH HB Invivo Oximetry RSO 2 S v O 2 S p O 2 Pulmonary Arterial Pressure Pulmonary Venous Pressure Cardiac Output Ventilation Side Volumes and Timing How the Volume changes with Pressure Airway Pressures Gas Composition Swann Gantz Catheterisation Thermodilution ManometrySpirometry Respiratory Mechanics Real Time Gas Monitoring