In APRV, the ratio between T-high and T-low is commonly set to what?

• A. 1:1
• B. 2:1
• C. 10:1
• D. 3:1

Answer: (C)

In APRV the aim is to keep alveoli recruited by spending most of the cycle at a high airway pressure, then briefly releasing to a lower pressure to ventilate. Because you want to maintain opening of the lung airways, the duration of the high-pressure phase is made much longer than the low-pressure phase. This long high-time with a short low-time keeps the lungs open for the majority of the cycle while still allowing a quick swing down to clear CO2 during the release. Ratios that allocate substantial time to the low phase would permit derecruitment and lessen the recruitment benefit, whereas an extended high-phase reliably supports oxygenation and alveolar stability. In practice, clinicians favor this pattern—a long high-time relative to a brief low-time—to balance recruitment with ventilation.