In conditions where the lung compliance is decreased (e.g. atelectasis), the Pplat pressure and PIP are both increased (think AB=Atelectasis is Both increased). On the other hand, in conditions where the airflow resistance is increased (e.g bronchospasm), the peak inspiratory pressure (PIP) is increased while the plateau pressure (Pplat) stays UNCHANGED. In regards to vent leaks, rule of thumb is "leaks prevent pressure buildup, & obstruction cause pressure buildup".
Overview of Mechanical Ventilation - PEEP = positive end-expiratory pressure. Bi-PAP can be used for chronic ventilation in patients w/ neuromuscular or chest wall diseases. Ventilator settings: Too high a setting causes weak patients to be unable to trigger a breath. Too low a setting may lead to over ventilation by causing the machine to auto-cycle. merckmanuals.com