In APRV, the ratio of T-high to T-low is often set to which value?

• A. 1:1
• B. 10:1
• C. 5:1
• D. 2:1

Answer: (B)

In APRV the aim is to keep the lungs recruited by spending most of the cycle at a high airway pressure, with only a brief release to allow CO2 elimination. The ratio of T-high to T-low defines how long the ventilator stays at the high pressure versus the low pressure. A long T-high with a very short T-low means the lungs stay opened longer, maintaining alveolar recruitment and improving oxygenation, while the brief low-pressure phase provides a quick vent to remove CO2 without giving the alveoli time to collapse. This combination reduces derecruitment and supports spontaneous breathing during the cycle. Other ratios shorten the high-pressure phase or lengthen the low-pressure phase, which can lead to more time at lower pressures and greater risk of alveolar collapse, making them less optimal for maintaining recruitment. Therefore, a ratio around 10:1 is commonly used because it emphasizes prolonged high-pressure support with only a brief release.