Using SIMV and Pressure Support

Although a very popular method of ventilatory support internationally, SIMV plus Pressure Support (SIMV with CPAP alone is not indicated) really should be viewed as a "halfway house" between anesthesia and rapid weaning. If the patient is breathing spontaneously then assist (+/-control (pressure or volume)) is more effective in patients who are not ready to control the depth and duration of their breaths. Otherwise pressure support alone is more consistent. SIMV is a poor weaning mode, and there is little utility in the patient receiving, during each minute, three types of breath: controlled, synchronized or pressure supported.


Set PEEP as  in protocol (click here)
Set initial rate at 12-14 breaths/minute
Set tidal volume at 6ml/kg
Set the peak flow at 50l/minute
Set flow triggering
Use a decelerating flow pattern
Start with pressure support 20cmH20
Calculate the driving pressure from
Plateau pressure-PEEP (volume control breaths)
Reset the PS at the driving pressure
Check a blood gas after 30-60 minutes
If CO2 is elevated increase the respiratory rate
but be careful of auto-PEEP.
Consider reducing tidal volumes to 4-5ml/kg
Is the patient breathing spontaneously?
Ensure that the peak flow is adequate
If respiratory drive intact, and lung injury is
not advancing, switch off controlled breaths
and place the patient on pressure support alone
Look at pressure waveform, adjust inspiratory
flow (slope) to optimal setting.
Watch lung compliance: increase PS if
compliance reduces (decreased tidal volumes)
decrease PS if compliance improves
(tidal volumes >6ml/kg).
Address patient sedation (tachypnea in PSV
is often from inadequate sedation)