What is controlled by the settings 'Thigh' and 'Tlow' in APRV?

• A. Mean airway pressure
• B. Inspiratory to expiratory ratio
• C. Tidal volume
• D. Respiratory rate

Answer: (B)

In Adaptive Pressure Release Ventilation (APRV), the settings 'Thigh' and 'Tlow' specifically determine the duration of the high-pressure phase (Thigh) and the duration of the low-pressure phase (Tlow). These settings directly influence the inspiratory to expiratory ratio.

By adjusting 'Thigh', clinicians can alter how long the patient receives positive pressure for inspiration, while 'Tlow' controls how long the patient is allowed to exhale or experience lower pressures. This ratio between 'Thigh' and 'Tlow' can affect the overall breathing pattern and the distribution of ventilation in the lungs, optimizing oxygenation and reducing the risk of ventilator-induced lung injury.

Therefore, the correct answer reflects the relationship between these settings and the inspiratory to expiratory ratio, which is crucial in managing ventilation and gas exchange effectively in patients requiring mechanical support.