SIMV vs. PSV

in a nut shell...

IMV will deliver a set number of ventilations per minute...though the patient can still breath at his/her own rate/tidal volume/etc on top of these pre-determined breaths

PS only adds some extra 'pressure' to facilitate the patients own breathing...it does not provide any ventilations.

In pressure support, the patient triggers the ventilator and a pressure-limited breath is delivered: the patient determines the rate, the duration of inspiration and the tidal volume. We can determine how much work the ventilator can take from the patient, by altering the pressure limit. When SIMV is used, the patient receives three different types of breath:

In pressure support, the patient triggers the ventilator and a pressure-limited breath is delivered: the patient determines the rate, the duration of inspiration and the tidal volume. We can determine how much work the ventilator can take from the patient, by altering the pressure limit. When SIMV is used, the patient receives three different types of breath:

1. The controlled (Mandatory) breath.

2. Assisted (synchronized) breaths.

3. Spontaneous breaths, which can be pressure supported

Pressure support is a method of assisting spontaneous breathing in a ventilated patient. It can be used as a partial or full support mode. The patient controls all parts of the breath except the pressure limit. The patient triggers the ventilator - the ventilator delivers a flow up to a preset pressure limit (for example 10cmH2O) depending on the desired minute volume, the patient continues the breath for as long as they wish, and flow cycles off when a certain percentage of peak inspiratory flow (usually 25%) has been reached. Tidal volumes may vary, just as they do in normal breathing

umm...yeah all of that.

The important difference that you should remember , though, is that IMV will initiate/deliver breaths (as an adjunct(sp?) to the patients own respiratory rate/drive), whereas PS will not. If your patient isnt breathing, PS wont help.

PS 'helps' the patient by 'supporting' her own respirations(thus the name 'pressure support')...IMV will DELIVER breaths (at a pre-set rate, TV, etc) regardless of the patients respiratory drive.

(And to mix things up a bit, you can combine these settings and have them both functioning at the same time...)