Ventilator modes classification

JEEVANLAL RESPIRATORY THERAPIST

AIMS

KEY POINTS

1. CONTROL

To describe how the ventilator manages p v and flow delivery within a breath

Sequence of mandatory and spontns brth to create specific breathing patterns

Equation of motion for respiratory system

equation of

motion

Pvent

+Pmus

= P E+ PR

Pvent =

pressure

generated by

the vent @

Airway

opening

Pmus

=

presur

e generated by

the vent mus

PE = the

elastic load

PR =

the resistive load

Two main functions in mech .vent

1. To calculate the lung mechanic parameters of R, C given information about p, v and flow.

2. To predict p, v, flow given values for R & C

“For any mode only one variable can be controlled at a time” ( p v &flow)

Flow is the derivative of volume as a function of tme, and volume is the integral of flow

MODE

Continue….

Thus a mode description reduces a

specification of how the ventilator controls

P, V, flow within a breath .

Along with a description of how

the breaths are sequenced.

3 componentsA description of the breathing sequence & control

variables within brths.

A description of control

type used within & between brths.

A detailed description of adjunctive contr

ol algorithms.

CLASSIFICATION

1. Breathing pattern

a. Primary breath-control variable Volume Pressure Dual b. Breath sequence Continuous mandatory ventilation (CMV) Intermittent mandatory ventilation (IMV) Continuous spontaneous ventilation (CSV)

2. CONTROLL TYPE

a. Tactical control (within breaths) Set point Auto-set-point Servo b. Strategic control (between breaths) Adaptive Optimal C. Intelligent control (between patients) Knowledge-based Artificial neural network

3. operational algorithms

a. Phase variables Trigger Limit Cycle Baseline b. Conditional variables c. Computational logic

BREATHING PATTERN

a). Primary Breath Control Variable

V, P & Dual Control

b). Breath Sequence

CMV, IMV and CSV

1.Breathing pattern

1a. Control variable.

The control variable is the variable that the ventilator uses as a feedback signal to control inspiration

(ie, pressure, volume, or flow).

Continue….

The control variable can be identified as follows: If the peak inspiratory pressure remains constant

as the load experienced by the ventilator changes,

then the control variable is pressure.

If the peak pressure changes as the load changes but VT remains constant, then the control variable is volume.

Volume control implies flow control and vice versa,

Dual control

‘’ Inspiration starts out as VCV and then switches to PCV before the end of breath

or vice versa ”

BREATH SEQUENCE

CMV

IMV

CSV

8 breathing patterns…

Volume Continuous mandato

ry ventilation

VC-CMV

Intermittent

mandato

ry ventilation VC-IMV

Pressur

e Continuous mandato

ry ventilation

PC-CMV

Intermittent

mandato

ry ventilation

PC-IMV

Continuous spontaneou

s ventilation

PC-CSV

Dual

Continuous mandato

ry ventilation

DC-CMV

Intermittent

mandato

ry ventilation

DC-IMV

Continuous spontaneou

s ventilation

DC-CSV

Why not VC-CSV

Volume control implies that the ventilator determines the

tidal volume [VT], whereas in a spontaneous breath the

patient determines the VT.

CMV VS IMV

The key difference now between CMV and IMV is that

with CMV the clinical intent is to make every inspiration a mandatory breath,

Whereas with IMV the clinical intent is to partition ventilatory support between mandatory and spontaneous breaths.

Continue..

CMV is normally considered a method of full ventilatory support,

whereas IMV is usually viewed as a method of partial ventilatory support (eg, for weaning).

“Thus for classification purposes, if spontaneous breaths are not allowed between mandatory breaths, the breath sequence is CMV; otherwise the sequence is IMV ”

CONTROL TYPE

Control type is a categorization of the ventilators feedback control function .

At the most basic level control is focused on what happens within a breath

Tactical Control – within breath (set point, auto set point , servo )

Strategic Control – between breaths ( adaptive , optimal ) Intelligent Control – between patients ( knowledge based , artificial neural network)

Basic types of control used

Set point The output of the ventilator matches a

constant operator preset input value . Mandatory breaths are pressure limited and

time cycled, according to the operator set values for peak inspiratory pressure and frequency

Eg : PC-IMV

Auto set point

The ventilator Selects which operator adjusted set points are enforced at the moment

Inspiration starts in PCV and switches to VCV

Eg ; volume assured pressure support

Servo

The ventilator output automatically follows a varying input

The instantaneous value of pressure is proportional to the instantaneous volume or flow generated by the patient .

Eg; PAV & ATC

Adaptive

One ventilator set point is automatically adjusted to achieve another set point as the patient condition changes .

Mandatory breaths are pressure limited , and the pressure limit is automatically adjusted between breaths to achieve the preset tidal volume

Eg ; PRVC

OPTIMAL

One ventilator set point is automatically adjusted to optimize another set point according to some model of system behavior, whose output can be maximized or minimized dynamically.

Each breath is pressure limited , and the pressure limit is automatically adjusted between breaths ( using ventilator mechanics measurements ) to minimize WOB

Eg ; adaptive support ventilation

KNOWLEDGE BASED

Set points are automatically adjusted according to a rule based expert system.

pressure support level for spontaneous breath is automatically adjusted to maintain appropriate breathing frequency, TV, ETCO2, depending on the type of patient .

Eg : smart care

Artificial neural network

Auto adjusted set points by artificial neural network. The relation b/w inputs & outputs determined by

weighting factors at neural nodes that change with learning.

The network inputs are the current ventilator settings and partial pressure of ABG and PH

Network outputs are the most appropriate ventilator settings projected to maintain blood gases within an acceptable range

Eg ; experimental

Scheme

VentilatorOperator Patient

Tactical Control

Stategic Control

VentilatorModelOperator Patient

Intelligent Control

ModelVentilator

Patient

Operating algorithm

PHASE VARIABLES

a. Phase variables Trigger Limit Cycle Baselineb. Conditional variablesc. Computational logic

T - Trigger

L - Limit

C - Cycle

B - Baseline

Time

Pre

ssu

re

Phase variable

The phase variable begins, sustains, and ends each of the four phases of a breath .

The four phases are ;

1. Change from exhalation to inhalation

2. inspiration

3. Change from inspiration to expiration

4. Exhalation

Triggering

The mechanism the ventilator uses to end exhalation and begin inspiration is the triggering mechanism .

Time trigger ; the ventilator can trigger itself, the rate of breathing is controlled by the

ventilator . So this mode sometimes is called controlled

ventilation

PRESSURE TRIGGERVentilator initiates a breath according to a predetermined time interval

•Patient trigger ;#. when the ventilator detects changes in P, F or V pt triggered breath occurs .#. P & flow are common patient triggering mechanisms. #. The operator must set the sensitivity level to fit the patients needs. (auto trigger,WOB)

PRESSURE TRIGGER

Flow trigger $. flow triggering occurs the ventilator detects a drop in flow through the patient circuit during exhalation Volume trigger $. Volume triggering occurs when the ventilator detects a small drop in volume in the pt circuit during exhalation

FLOW TRIGGER

Limit variable

A limit variable is the maximum value a variable ( p, v, v; t) can attain .

1. Pressure limiting; allows pressure to rise to a certain value but not exceed it .

To prevent excessive pressure from entering the patients lungs , the operator set a control sometimes labeled a high pressure limit.

when the vent reaches the high p limit excess pressure will vented through a spring loaded pressure release or valve.

2.Volume limiting

A volume limited breath is controlled by an electronically operated valve that measures the flow passing through during a specific interval .

The volume may be set by the operator, or the ventilator may have a bag, or piston cylinder that contains a fixed volume .

3. Flow limiting

If ventilator flow to the patient reaches but does not exceed a maximum value before the end of inspiration , the ventilator is flow limited .

Cycle variable

The variable a ventilator measures to determine the end of inspiration is called the cycling mechanism .

Volume cycling ; the inspiratory phase of a volume cycled breath is terminated when the set volume has been delivered .

Time cycling ; a breath is considered time cycled if the inspiratory phase ends when a predetermined time has elapsed (PCV)

Flow cycling ; the ventilator cycles into the expiratory phase once the flow has decreased to a pre determined value during inspiration (ps)

pressure cycling ; when a preset pressure threshold is reached@ the mouth or upper airway , a ventilator set to pressure cycle ends to inspiration .

Baseline variable

Baseline variable is the parameter that generally controlled during exhalation .

Although either V or flow could serve as a baseline variable , P is the most practical choice and is used by all modern ventilators.

The pressure level from which a ventilator breath begins is called the baseline pressure

It can be zero , which is also called (ZEEP) or (PEEP).

PEEP WITH MANDATORY BREATHS

5

P A

0 Time

Conditional Variables

Any unique combination of breathing pattern, control type, and operational

algorithms is technically a mode.

It can be described in terms of “if then” statements

Eg ; if spontaneous minute ventilation falls below a preset threshold , then deliver enough mandatory breaths to raise MV above the threshold .

Computational Logic

Description of the relationship between the inputs, feedback signals, and outputs, adding detail about how the mode operates that does not given in the

other components of mode specification.

Eg ; ASV mode of Hamilton Galileo uses WOB as the performance function , and it is related to lung

mechanics, alveolar ventilation , dead space volume

And breathing frequency. As lung mechanics change, the ventilator finds the optimum frequency ( to

minimize wob) and then sets the VT to meet the MV

requirement .(Smartcare mode on dragger)

Model delivery

Pt-triggered

No inspiratory effortSmall inspiratory effort

Large Insp effort

Machine Triggered

Reduced pressure indicates patient effort during inspirations

Set Tidal Volume

No inspiratory effort

Large Insp effort

Machine Triggered

Reduced pressure

Set Tidal VolumeVolume

Target

Volume overshoot

A machine that produces breathing patterns that mimic the humans normally breathe at rates and tidal volumes our bodies produces during the normal activities.

”I am caring and guarding your breaths…..”

THANK YOU