Spontaneous breaths by a patient on synchronized intermittent mandatory ventilation (SIMV) should be supported by sufficient pressure to overcome the work of breathing (WOB).



(1) tidal volume delivered by the ventilator in mL

(2) inspiratory flow rate on the ventilator in L per minute

(3) peak inspiratory pressure in cm H2O

(4) plateau pressure following an inspiratory pause in cm H2O

(5) spontaneous inspiratory flow rate in L per minute by the patient


pressure support in cm H2O =

= ((peak inspiratory pressure) - (plateau pressure)) * ((spontaneous inspiratory flow rate) / 60)) / ((ventilator inspiratory flow rate) / 60)



• The ventilator is set to have a square inspiratory flow waveform.

• The calculations using inspiratory flow rates in L per second.


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