The I:E ratio describes how each ventilator breath is split between time spent breathing in (inspiration) and breathing out (expiration).
Typical range; longer expiration suits obstructive disease.
Short expiratory time — watch for air trapping.
Inverse ratio — deliberate in severe ARDS, higher auto-PEEP risk.
Long expiratory time — common when airways are very obstructed.
Given: Ti 1.0 s, Te 2.0 s.
A normal breath spends about twice as long exhaling as inhaling.
About 1:2 during normal breathing — expiration takes roughly twice as long as inspiration. In obstructive disease a longer expiratory time (1:3 or 1:4) helps avoid air trapping.
When inspiration is set longer than expiration (I:E greater than 1:1). It can improve oxygenation in severe ARDS but raises the risk of auto-PEEP and air trapping, so it's used cautiously.
Narrowed airways slow exhalation, so a longer expiratory time gives the lungs time to empty and prevents breath-stacking (auto-PEEP).
Rate sets the total cycle time (60 ÷ rate). The I:E ratio then divides that time between inspiration and expiration, so a faster rate shortens both phases.