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