What is the typical I:E ratio in controlled ventilation, and how can it be adjusted?

• A. Often 1:2 but adjustable; increasing I time increases inspiration duration affecting ventilation
• B. Always 1:1 and fixed; can't be changed
• C. Typically 2:1 and reduces inspiration time
• D. Often 1:3 and can't be adjusted.

Answer: (A)

In controlled ventilation, the timing of breaths is described by the inspiratory-to-expiratory (I:E) ratio. Because the ventilator delivers breaths at set intervals, this ratio is adjustable to balance ventilation and airway pressures. A common starting point is about 1:2, meaning the expiratory phase is longer than the inspiratory phase.

You adjust the ratio by changing the inspiratory time (I time). Lengthening the I time increases the duration of inspiration, making the ratio closer to 1:1 (or higher, depending on settings). This can improve alveolar recruitment and oxygenation through a longer inflation, but it also reduces the time available for exhalation, which can impact CO2 clearance and peak pressures. So the I:E ratio is adjustable by altering the inspiratory time while monitoring the resulting gas exchange and pressures.