 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

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

Breath Type ControlTriggerLimitCycle MandatoryPressure Or Volume Time Or Patient Time or Volume SpontaneousPatientPressureFlow

(L/m) Pressure (cm H 2 O) Volume (mL) M T supp T synch Set PS Level Flow-cycled Time (sec)

Flow (L/m) Pressure (cm H 2 O) Volume (mL) Spontaneous Breaths Time (sec) T synch

Flow (L/m) Pressure (cm H 2 O) Volume (mL) T supp T synch Time Cycled Flow-cycled T synch Set PC Level Set PS Level Time (sec)

SIMV

 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

 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

 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 H 2 O) Cycles Triggered window for supported breaths Triggered window for synchronized breaths Mandatory Cycle Time M T supp T synch M T supp

SIMV

 Facilitate transition from full ventilatory support to partial support

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

 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