Basic modes of mechanical ventilation

Mechanical Ventilation Basic ModesLOKESH TIWARIAIIMS PATNA

CME on Mechanical Ventilation: Bench to Bedside AIIMS RAIPUR: 22nd August 2015

What are ventilators ?

A machine that generates a controlled flow of gas into a patient’s airways

Supportive role to buy time

Mechanical ventilation

Several models have evolved over time- Negative pressure ventilation

Positive pressure ventilation Simple pneumatic system New generation microprocessor controlled systems.

The basic function and applications remain common.

Basic Ventilator Parameters

Tidal volume Frequency PIP Plateau Pressure PEEP Inspiratory Time Expiratory time I:E Ratio

Basic Ventilator Parameters

Mode Tidal volume Frequency PIP Plateau Pressure PEEP Inspiratory Time Expiratory time I:E Ratio

Starting a ventilator: Mode

Mode denotes interplay b/w patient and the ventilator

Describes the style of breath support based on relationship between the various possible types of breath and inspiratory – phase variables

Where to Start ? CPAP, IPAP, EPAP, NIV Pressure control, Volume control CMV, Assist Control, IMV, SIMV, PSV, ASV, MMV, APRV PCV, PRVC, PSV, VCIRV, Volume

Support, Auto Mode, BiLevel, BiPAP, HFJV, HFOV

Objective From

Objective To

Objectives

Understand how ventilators control breath delivery, phase and control variables.

Understand the basic modes of ventilation.

Combinations, tailor-making, mix and match…

The ventilator circuit

The ventilator circuit

50 psi air

50 psi O2

BlenderAir-O2 mixture of desired FiO2 at 50 psi

Stepped down pressure

Flow regulator

Pressure regulating valve

T-piece & ETT tube

Insp limb

Exp limb

Flow regulators / PEEP

Flow in ventilator circuit- constant

Flow in ET & patient airway-

keeps changing in magnitude & direction !!

T-connection

ETT

Baby’s airway

PEEP

PIP

Flow sensor

What does flow sensor do?

Flow in ventilator circuit- constant

T-connection

ETT

Flow sensor

Insp flow

RR

= tidal vol

Exp flow

- insp flow

= peri-tube leak

Ventilatory Phases

• Inspiration: Inspiratory valve opens and expiratory valve is closed

• Inspiratory pause: inspiratory valve and expiratory valve closed

• Expiration: Inspiratory valve closed and expiratory valve open

• Expiratory pause: Inspiratory valve and expiratory (or PEEP) valve closed at end of expiration

Ti Te

0

Phase Variables: Trigger, Limit and Cycling

Phase variables Trigger : ventilator (time)- triggered or patient (pressure or

flow) triggered Limit: flow-limited or pressure-limited Cycling: volume, time, flow or pressure cycled.

Phase variables: Trigger

What causes the breath to begin (signal to open the inspiratory valve) Machine (controlled): the ventilator will trigger regular

breaths at a frequency which will depend on the set respiratory rate, ie, they will be ventilator time triggered.

Patient (assisted): If the patient does make an effort to breathe and the ventilator can sense it (by either sensing a negative inspiratory pressure or an inspiratory flow) and deliver a breath, it will be called a patient-triggered breath.

Phase Variables: Trigger

Phase Variables: Trigger

Phase variables: LimitFactor which controls the inspiration inflow

Flow Limited: a fixed flow rate and pattern is set and maintained throughout inspiration. An adequate tidal volume (Ti dependent) Pressure will be variable (comp and resistance dependent)

Pressure limited: the pressure is not allowed to go above a preset limit. The tidal volume will be variable (comp and resistance dependent)

Phase variables: Cycling

Signal that stops the inspiration and starts the expiration. Without inspiratory pause: one signal With inspiratory pause: two cycling signals (one to close inspiratory

valve and the second to open the expiratory valve) Volume Time Flow Pressure : back-up form of cycling when the airway pressure

reaches the set high-pressure alarm level

The ventilatory cycle

Ti Te

PIP

PEEP

0.35 sec 0.65 sec

1 resp cycle= Ti + Te

Mechanical

Time (sec)

SpontaneousPaw (cm H2O)

Inspiration

ExpirationExpiration

Inspiration

Breath type: Spontaneous vs Mechanical vs assisted

Assisted

Control variables

Pressure: Pressure signal is the feedback signal (Pressure Preset) Volume: Volume signal is the feedback signal. usually measure

the flow and turn it into volume signal electronically. (volume preset)

Time Flow

Combinations

Volume Control Ventilation

Pressure

Volume

FlowPreset Peak Flow

Preset Vt

Dependent onCl & Raw

Time (sec)

Pressure Control Ventilation

Flow

Pressure

VolumeClCl

Set PC level

Time (sec)

Basic Modes of Ventilation

Controlled Mechanical Ventilation Assist Control Ventilation Intermittent Mandatory Ventilation Synchronized Intermittent Mandatory Ventilation

Pressure Support Combinations

Controlled mandatory ventilation (CMV)

The ventilator delivers Preset tidal volume (or pressure) at a time triggered (preset)

respiratory rate. As the ventilator controls both tidal volume (pressure) and

respiratory rate, the ventilator “controls” the patients minute volume.

Pres

sure


Volume controlled Pressure controlled

Preset VT

Volume Cycling

Dependent onCL & Raw

Time (sec)

Flow(L/m)

Pressure(cm H2O)

Volume(mL)

Preset Peak Flow Time triggered, Flow limited, Volume cycled Ventilation

Controlled mandatory ventilation (Volume-Targeted)

Pressure

Flow

Volume

(L/min)

(cm H2O)

(ml)Time (sec)

Time-Cycled

Set PC level

Time Triggered, Pressure Limited, Time Cycled Ventilation

Controlled mandatory ventilation (Pressure-Targeted)


Patient can not breath spontaneously Patient can not change the ventilator respiratory rate

Suitable only when patient has no breathing efforts Disease or Under heavy sedation and muscle relaxants


Asynchrony and increased work of breathing.

Not suitable for patient who is awake or has own respiratory efforts

Can not be used during weaning

Assist Control Ventilation

Time (sec)

Control ventilation (CMV) Assist / control ventilation

Pres

sure

Control Control Assisted



Pres

sure


A set tidal volume (volume control) or a set pressure and time (pressure control) is delivered at a minimum rate

Additional ventilator breaths are given if triggered by the patient Mandatory breaths: Ventilator delivers preset volume and preset

flow rate at a set back-up rate Spontaneous breaths: Additional cycles can be triggered by the

patient but otherwise are identical to the mandatory breath.


Tidal volume (VT) of each delivered breath is the same, whether it is assisted breath or controlled breath

Minimum breath rate is guaranteed (controlled breaths with set VT)


Pres

sure

Assist Control Ventilation(volume) Assist Control Ventilation

(Pressure) Assist Control Ventilation

Time (sec)

Patient / TimeTriggered, Pressure Limited, Time Cycled Ventilation

Pressure

Flow

Volume

Set PC level

Time-Cycled

Pt triggered

Time triggered

Assist Control Ventilation (Pressure)

Patient / Time triggered, Flow limited, Volume cycled Ventilation

Assist Control Ventilation (Volume)

Time (sec)

Flow

Pressure

VolumePreset VT

Volume Cycling

Assist Control Ventilation Asynchrony taken care of to some

extent Low work of breathing, as every breath

is supported and tidal volume is guaranteed.

Hyperventilation Respiratory alkalosis.

Natural breaths are not allowed Breath stacking High volumes and pressures


Pres

sure


Hyperventilation and breath stacking can usually be overcome by choosing optimal ventilator settings and appropriate sedation.


Pres

sure

Intermittent Mandatory Ventilation (IMV)

Pres

sure

Machine breaths are delivered at a set rate (volume or pressure limit)

Time (sec)


Pres

sure

Machine breaths are delivered at a set rate (volume or pressure limit)

Patient is allowed to breath spontaneously from either a demand valve or a continuous flow of gases but not offering any inspiratory assistance.

Time (sec)


Pres

sure

Patient’s capability determines Tidal volume of spontaneously breaths

Some freedom to breath naturally even on mechanical ventilator

Time (sec)


Pres

sure

Random chance of breath stacking and asynchrony: Increased WOB

Uncomfortable feeling

Time (sec)


Pressure controlled IMV Volume controlled IMV


Pros: Freedom for natural spontaneous

breaths even on machine Lesser chances of

hyperventilation

Cons: Asynchrony Random chance of breath

stacking. Increase work of breathing Random high airway pressure

(barotrauma) and lung volume (volutrauma)

Setting appropriate pressure limit is important to reduce the risk of barotrauma

Can we synchronize it?

Synchronized Intermittent Mandatory Ventilation

Ventilator delivers either patient triggered assisted breaths or time triggered mandatory breath in a synchronized fashion so as to avoid breath stacking

If the patient breathes between mandatory breaths, the ventilator will allow the patient to breathe a normal breath by opening the demand (inspiratory) valve but not offering any inspiratory assistance.

Synchronization windowPr

essu

re

Time interval just prior to time triggering in which the ventilator is responsive to the patient’s inspiratory effort.

Time (sec)

Time trigerring

SIMV Pr

essu

re

Patient trigerred synchronized breath

If the patient makes a spontaneous inspiratory effort that falls in sync window, the ventilator is patient triggered to deliver an assisted breath and will count it as mandatory breath

Time trigerred mandatory breath

SIMV Pr

essu

re


if patient does not make an inspiratory effort then ventilator will deliver a time triggered mandatory breath.


SIMV Pr

essu

re


if patient does not make an inspiratory effort then ventilator will deliver a time triggered mandatory breath.


If the pt triggers outside this window, vent will allow this spontaneous breath to occur by opening the demand (inspiratory) valve but does not offer any inspiratory assistance.


Pres

sure

3 types of breathing:

1. Patient initiated assisted ventilation, 2. Ventilator generated controlled ventilation,3. Unassisted spontaneous breath.


P-SIMV V-SIMV

Synchronized Intermittent Mandatory Ventilation (SIMV)

It allows patients to assume a portion of their ventilatory drive: Weaning is possible

Greater work of breathing than AC ventilation and therefore some may not consider it as the initial ventilator mode

Friendly cardiopulmonary interaction: Negative inspiratory pressure generated by spontaneous breathing leads to increased venous return, which theoretically may help cardiac output and function

Pressure Support Ventilation

Pressure (or Pressure above PEEP) is the setting variable No mandatory breaths Applicable on Spontaneous breaths: a preset pressure

assist, Flow cycling: terminates when flow drops to a specified

fraction (typically 25%) of its maximum. Patient effort determines size of breath and flow rate.


Pressure (or Pressure above PEEP) is the setting variable No mandatory breaths Applicable on Spontaneous breaths: a preset pressure assist, Flow cycling: terminates when flow drops to a specified fraction

(typically 25%) of its maximum. Patient effort determines size of breath and flow rate


Pressure (or Pressure above PEEP) is the setting variable No mandatory breaths Applicable on Spontaneous breaths: a preset pressure assist, Flow cycling: terminates when flow drops to a specified fraction

(typically 25%) of its maximum. Patient effort determines size of breath and flow rate.


It augments spontaneous VT decreases spontaneous rates and WOB

Used in conjunction with spontaneous breaths in any mode of ventilation.

No guarantee of tidal volume with changing respiratory mechanics,

No back up ventilation in the event of apnea.


Provides pressure support to overcome the increased work of breathing imposed by the disease process, the endotracheal tube, the inspiratory valves and other mechanical aspects of ventilatory support

Allows for titration of patient effort during weaning. Helpful in assessing extubation readiness

SIMV + PS VentilationPr

essu

re

Spontaneous breath with PS

Summary

Time (sec)

Control ventilation (CMV) Assist / control ventilationPr

essu

re Control Control Assisted

Pre

ssur

e P

ress

ure

Thank you!! You have done it!!!

Health & Medicine

Basic modes of mechanical ventilation