Plateau pressure is a measurement taken during mechanical ventilation that reflects the pressure within the small airways and air sacs (alveoli) of the lungs when airflow has momentarily stopped. This measurement is distinct from peak inspiratory pressure, which includes the resistance of the larger airways during active airflow. Monitoring plateau pressure is important for assessing the mechanical stress on a patient’s lungs and preventing ventilator-induced lung injury.
Understanding Plateau Pressure
Plateau pressure provides insight into the static pressure exerted on the lung tissue, offering a more accurate gauge of lung stress compared to peak inspiratory pressure. Peak inspiratory pressure, or PIP, measures the maximum pressure during inhalation and accounts for both airway resistance and the pressure required to expand the lungs. In contrast, plateau pressure specifically measures the pressure after airflow ceases, allowing the pressure within the lungs to equalize. This distinction is important because while high peak pressure can indicate issues with airway resistance, high plateau pressure directly points to problems with lung stiffness or compliance.
Lung compliance refers to the ability of the lungs to expand and contract, essentially how “stiff” or “elastic” they are. A lung with high compliance is easily stretched, while a lung with low compliance is stiff and requires more pressure to inflate. Plateau pressure is a direct indicator of static lung compliance. Therefore, a higher plateau pressure for a given volume of air indicates lower lung compliance. This static measurement helps clinicians understand the actual pressure being delivered to the fragile alveolar structures.
The Measurement Process
Measuring plateau pressure involves a specific maneuver performed on the mechanical ventilator, known as an inspiratory hold or end-inspiratory pause. The ventilator delivers a breath, and at the end of the inspiratory phase, before exhalation begins, the airflow is momentarily stopped.
During this brief pause, usually lasting between 0.5 to 2 seconds, the pressure within the airways and alveoli equilibrates. The ventilator then displays the plateau pressure on its screen. This value represents the static pressure within the lungs, as airway resistance is eliminated. Modern ventilators are equipped with controls to perform this inspiratory hold maneuver, making it a standard part of assessing lung mechanics. Obtaining an accurate measurement may sometimes require the patient to be sufficiently sedated to ensure passive breathing and prevent spontaneous respiratory efforts from affecting the reading.
Interpreting the Results
A commonly accepted upper limit for plateau pressure to minimize the risk of ventilator-induced lung injury (VILI) is typically below 30 cm H₂O. Maintaining plateau pressure within safe limits helps prevent overdistension of the alveoli, which can lead to lung damage.
Elevated plateau pressures, exceeding the safe threshold, often indicate reduced lung compliance. This can be a sign of various conditions such as Acute Respiratory Distress Syndrome (ARDS), pulmonary fibrosis, or pulmonary edema. High plateau pressures are associated with increased lung injury and mortality. Conversely, a plateau pressure within the normal range, especially when accompanied by a high peak pressure, suggests that any pressure issues are more related to airway resistance rather than lung compliance. While low plateau pressures generally indicate good lung compliance, clinicians assess this value in conjunction with other parameters to ensure adequate ventilation.
Factors Influencing Plateau Pressure
Several variables can affect a patient’s plateau pressure reading, reflecting changes in lung mechanics. Tidal volume, the amount of air delivered with each breath, has a direct relationship with plateau pressure; larger tidal volumes generally result in higher plateau pressures. Therefore, reducing tidal volume is a primary method to lower plateau pressure, particularly in strategies aimed at lung protection.
Positive End-Expiratory Pressure (PEEP), which is the pressure maintained in the lungs at the end of exhalation to keep alveoli open, also influences plateau pressure. Higher PEEP levels contribute to higher plateau pressures because they increase the baseline pressure within the lungs. Patient-specific factors, such as underlying lung conditions, also play a significant role. Conditions that stiffen the lungs, like ARDS or pulmonary fibrosis, decrease lung compliance and lead to higher plateau pressures. While airway resistance primarily affects peak inspiratory pressure, it does not directly impact plateau pressure.