What parameter can be changed to affect the I:E ratio on a ventilator?

• A. Flow
• B. I Time
• C. Tidal Volume
• D. Respiratory Rate

Answer: (B)

The key idea is that the I:E ratio describes how long the breath is spent INspiring compared with EXPIRing. The ventilator cycle has an inspiratory time (how long the inhalation lasts) and an expiratory time, with the total breath time set by the respiratory rate. Since the expiratory time is basically the remainder of the cycle (expiratory time = cycle time minus inspiratory time), changing the duration of inspiration directly changes the ratio. If you lengthen the inspiratory time, you spend more of the breath inhaling and the I:E ratio increases (more time inhaling relative to exhaling). Shortening the inspiratory time has the opposite effect.

Flow affects how quickly gas is delivered during the inhalation but not the duration of the inhalation itself. Tidal volume is the amount delivered per breath and depends on pressure/flow settings and timing, but it doesn’t set the ratio. Respiratory rate sets how long the overall cycle lasts, which can indirectly influence the expiratory time, but the direct control of the I:E ratio is the inspiratory time.