Mechanical ventilation is a life-supporting intervention used in intensive care units to assist breathing when a patient’s lungs can no longer function adequately. This technology works by delivering controlled breaths to the patient, but the pressure used to inflate the lungs must be carefully managed to ensure safety. Plateau pressure, specifically, serves as a significant safety metric, providing insight into the mechanical strain placed on the delicate lung tissue during each breath.
Defining Plateau Pressure and Its Measurement
Plateau pressure, often abbreviated as Pplat, represents the static pressure exerted on the small airways and air sacs, known as alveoli, after a breath has been delivered. It is the pressure that remains after all airflow has stopped, eliminating the component of pressure needed to overcome friction through the airways. This measurement reflects the pressure that is actually distending the alveoli and the lung tissue itself.
To obtain the Pplat reading, a clinician must instruct the ventilator to perform an “inspiratory pause” maneuver. This involves the ventilator temporarily halting the flow of air for a brief period, typically between 0.5 and 2 seconds, immediately following the delivery of the set breath. During this pause, the pressure within the entire system, including the alveoli, equalizes, and the ventilator displays the static pressure value.
The distinction between Pplat and Peak Inspiratory Pressure (PIP) is fundamental to interpreting ventilator data. PIP is the highest pressure reached during the delivery of a breath, reflecting the force needed to overcome both the resistance of the airways and the elasticity of the lung tissue. Pplat, measured during the no-flow pause, eliminates the resistance component and thus is always lower than PIP under normal volume-controlled ventilation. A large difference between PIP and Pplat often points to an issue with airway resistance, such as a kinked tube or bronchospasm, whereas an elevated Pplat indicates a problem with the stiffness or compliance of the lung itself.
The Normal and Target Range
The primary target for plateau pressure management is to keep the reading at or below 30 centimeters of water (\(\text{cmH}_2\text{O}\)). This threshold is the widely accepted upper boundary for safe mechanical ventilation in most patient populations and is a central tenet of a lung-protective strategy. For patients with severely diseased lungs, such as those with Acute Respiratory Distress Syndrome (ARDS), \(30\ \text{cmH}_2\text{O}\) is the absolute maximum, and clinicians often aim for even lower values.
Some evidence suggests that targeting a Pplat of \(25\ \text{cmH}_2\text{O}\) or less may be associated with improved patient outcomes. For patients with otherwise healthy lungs undergoing surgery, the target is often much stricter, with values of \(16\ \text{cmH}_2\text{O}\) or less associated with the lowest risk of postoperative respiratory complications.
The definition of a “normal” Pplat is relative and depends heavily on the patient’s underlying lung condition and chest wall mechanics. Lungs that are stiff or have reduced compliance, as seen in conditions like pulmonary fibrosis or ARDS, will naturally require higher pressures to achieve the same volume, resulting in an increased Pplat. Conversely, a patient with highly compliant lungs, such as those with emphysema, may have a lower Pplat for the same delivered volume.
Clinical Significance of Elevated Pressure
When the plateau pressure exceeds \(30\ \text{cmH}_2\text{O}\), it signals that the lungs are being subjected to excessive stress, which significantly increases the risk of Ventilator-Induced Lung Injury (VILI). High Pplat values directly correlate with the danger of over-distending the delicate alveolar sacs. This over-distension, or stretching of the alveoli, is known as Volutrauma.
Volutrauma causes mechanical damage to the alveolar cell walls, triggering an inflammatory response that can worsen the patient’s lung condition. The resulting cellular damage and inflammation release chemical mediators that can injure other parts of the body. High Pplat also raises the risk of Barotrauma, which is damage caused by high pressure leading to air leaks within the chest cavity, such as a pneumothorax.
The magnitude of the pressure required to expand the lungs, known as the driving pressure, is a related metric that is often more closely linked to patient mortality than Pplat alone. Driving pressure is calculated by subtracting the Positive End-Expiratory Pressure (PEEP) from the Pplat. An elevated Pplat means a high driving pressure, which reflects the strain placed on the lungs during each breath and is a strong indicator of poor outcomes in patients with stiff lungs.
Strategies for Pressure Management
The most effective and primary strategy for reducing a high plateau pressure is to implement “lung protective ventilation” by lowering the Tidal Volume (TV). TV is the volume of air delivered with each breath, and reducing it directly reduces the pressure required to inflate the lungs. This often involves setting the TV to a range as low as 4 to 8 milliliters per kilogram of the patient’s predicted body weight.
If the Pplat remains above the target despite using a lower TV, clinicians may make further adjustments to the ventilator settings. This includes strategically optimizing the Positive End-Expiratory Pressure (PEEP), which is the pressure maintained in the lungs at the end of exhalation to prevent the alveoli from collapsing. Adjusting PEEP must be done carefully, as increasing it can sometimes improve lung mechanics but can also increase Pplat.
Other clinical interventions focus on improving the mechanics of the lung and chest wall to lower pressure requirements.
Additional Interventions
Turning a patient into the prone position can sometimes redistribute lung fluids and mass, which may improve lung expansion and pressure distribution. In cases where the patient’s own breathing efforts are fighting the ventilator and causing high pressures, deep sedation or the use of neuromuscular blocking agents may be employed. These measures ensure the ventilator is solely controlling the breathing mechanics.