What is the typical I:E time ratio on ventilation?

• A. 1:1
• B. 2:1
• C. 1:2
• D. 3:1

Answer: (C)

In ventilation, the I:E ratio shows how long the machine spends delivering breath (inspiration) compared with letting air out (expiration). The typical default is 1:2, meaning the inspiratory phase is half as long as the expiratory phase. This balance gives enough time for exhalation to prevent air trapping and high airway pressures while still delivering the required tidal volume. Ratios with longer inspiration (like 2:1 or 3:1) shorten expiration, which can lead to air trapping and increased intrathoracic pressure. A 1:1 ratio shortens expiration as well, which can also raise the risk of airflow limitation in some patients. So, 1:2 is the standard, practical baseline for most ventilation scenarios.