Pressures on the Ventilator

The ventilator mode refers to the way the ventilator interacts with a patient. Assist control (AC) is one of the most used ventilation modes, set to target either a desired pressure or volume for each breath at a set rate per minute. Pressure support (PS) ventilation is a pressure-controlled mode of ventilation with no set respiratory rate or tidal volume that supports spontaneous respirations. There are also many pressure-driven advanced ventilator modes, such as airway pressure release ventilation (APRV), that utilize high mean airway pressures to promote oxygenation. Regardless of the mode of ventilation, the system will have measurable pressures that can be used to guide care. Understanding these pressures on a ventilator starts with comprehending the relationship between ventilator modes, settings, calculated values, and how they interact with the patient’s anatomy and physiology. The most common pressure value is the peak inspiratory pressure (PIP), representing the maximal pressure produced in inspiration in the entire airway system. It is a measure of both resistance and compliance. Another common value is the plateau pressure (Pplat), measured during an inspiratory hold and reflects the pressure delivered to the alveoli and reflects the respiratory system’s compliance. When air is trapped in the alveoli at the end of exhalation, it exerts pressure beyond the set PEEP. This pressure can be quantified on the ventilator by pressing the expiratory pause button. This pressure is known as autoPEEP. Many new ventilators display PIP, Pplat, and autoPEEP without performing an inspiratory or expiratory hold during a patient’s ventilation cycle. The modern ventilator provides a plethora of information to understand the patient’s ventilatory course and to guide ventilator strategies to prevent lung injury during their care. Driving pressure and the mean airway pressure (MAP or Paw) are two less discussed measurements that can assist with ventilator decision-making. By understanding the described measured values on the ventilator, sound clinical decisions can be made to guide safe ventilator management for the patient.