Volume triggering occurs when the ventilator detects a small drop in volume in the patient circuit during exhalation. The machine interpretes this drop as a patient effort and begins inspiration.

 

Manual triggering is another option. A button or touch pad may be labeled "Manual" breath or "Start" breath. When this control is activated, the ventilator delivers a breath according to the set variables. Even though some patients begin to breathe spontaneously and patient triggering can be used, occasionally the patient stops breathing. For this reason, a respiratory rate is set with the rate control to guarantee a minimum number of breaths per minute.

 

Each breath is either patient triggered or time triggered, depending on which occurs first. The rate control determines the minimum rate, but the patient has the option of breathing at a faster rate. This is often referred to as the assist/control mode.