Peak inspiratory pressure (P<sub>IP</sub>) is the highest level of pressure applied to the lungs during inhalation. In mechanical ventilation the number reflects a positive pressure in centimeters of water pressure (cm H<sub>2</sub>O). In normal breathing, it may sometimes be referred to as the maximal inspiratory pressure (M<sub>IPO</sub>), which is a negative value.
Peak inspiratory pressure increases with any airway resistance. Factors that may increase P<sub>IP</sub> include increased secretions, bronchospasm, biting down on ventilation tubing, and decreased lung compliance. P<sub>IP</sub> should never be chronically higher than 40 cm H<sub>2</sub>O unless the patient has acute respiratory distress syndrome.