Synchronized Intermittent Mandatory Ventilation: SIMV

Objectives Understand the different breath types with

SIMV Know the Phase variables of the different

breath types: trigger/limit/cycle Know the breath sequence with SIMV Controlled variables: PC-CMV vs VC-CMV Understand the synchronization mechanism Initial settings of SIMV Adjustment of SIMV Indications, advantages and disadvantages

Phase VariableSIMV

Patient or Time Triggered

Time Cycled

Breath Sequence and ModeSIMV

IMV and SIMV Periodic volume or pressure targeted breaths

occur at set interval (time triggering) Between mandatory breaths, the patient

breathes spontaneously at any desired baseline pressure without receiving a mandatory breath Patient can breathe either from a continuous flow or

gas or from a demand valve

SIMV/PS: Phase and Control Variables

Breath Type

Control Trigger Limit Cycle

Mandatory PressureOr

Volume

Time Or

Patient

Time or

VolumeSpontaneou

sPatient Pressure Flow

Flow(L/m)

Pressure(cm H2O)

Volume(mL)

MTsuppTsynch

Set PS Level

Flow-cycled

Time (sec)

SIMV+PS(Volume Targeted Ventilation)

Flow(L/m)

Pressure(cm H2O)

Volume(mL)

Spontaneous Breaths

Time (sec)

SIMV(Volume Targeted Ventilation)

Tsynch Tsynch Tsynch

Flow(L/m)

Pressure(cm H2O)

Volume(mL)

Tsupp

Tsynch

Time Cycled Flow-cycled

Tsynch

Set PC Level Set PS

Level

Time (sec)

SIMV + PS (Pressure-Targeted Ventilation)

VC-SIMV: +Efforts:

VC-SIMV/Psupp:

PC-SIMV: Spontaneous Efforts, 0 PSV

PC-SIMV+ PSupp

SIMV: No Efforts

SynchronizationSIMV

Synchronized IMV

Operates in the same way as IMV except that mandatory breaths are normally patient triggered rather than time triggered (operator set the volume or pressure target)

As in IMV, the patient can breathe spontaneously through the ventilator circuit between mandatory breaths

Synchronized IMV

At a predetermined interval (respiratory rate), which is set by the operator, the ventilator waits for the patient’s next inspiratory effort

When the ventilator senses the effort, the ventilator assists the patient by synchronously delivering a mandatory breath

Synchronized IMV

If the patient fails to initiate ventilation within a predetermined interval, the ventilator provides a mandatory breath at the end of the time period

Time (sec)

Flow(L/m)

Pressure(cm H2O)

Cycles

Triggered window for supported breaths

Triggered window for synchronized breaths

Mandatory Cycle Time

M Tsupp Tsynch M Tsynch Tsupp

Synchronization (SIMV+PSV)

Advantages and DisadvantagesSIMV

Indications

Facilitate transition from full ventilatory support to partial support

SIMV

ADVANTAGES

Maintains respiratory muscle strength by avoiding muscle atrophy

Decreases mean airway pressure

Facilitates ventilator discontinuation – “weaning”!

DISADVANTAGES

When used for weaning, may be done too quickly and cause muscle fatigue

Mechanical rate and spontaneous rate may asynchronous causing “stacking” May cause barotrauma

or volutrauma

IMV: Stacking When used for weaning, may be

done too quickly and cause muscle fatigue

Mechanical rate and spontaneous rate may asynchronous causing “stacking” May cause barotrauma or volutrauma

Thank You