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)