What is the formula for static compliance?

• A. Vt/PEEP
• B. Vt/Plat-PEEP
• C. Vt/PIP-PEEP
• D. PIP/Plat

Answer: (B)

Static compliance is an important parameter in mechanical ventilation that reflects the distensibility of the lungs and thorax. It is calculated using the formula where tidal volume (Vt) is divided by the difference between the plateau pressure (Plat) and the positive end-expiratory pressure (PEEP).

This method evaluates how well the lungs can expand with each breath, taking into account the pressure exerted by the airway at the end of inspiration, which is represented by the plateau pressure. The subtraction of PEEP ensures that the compliance measurement accounts only for the change in volume above the baseline pressure maintained by PEEP. Therefore, the formula effectively demonstrates how much volume is delivered to the lungs for each unit of pressure change, giving clinicians insight into lung mechanics.

Other options do not accurately reflect the definition of static compliance with respect to how pressure influences lung volume and would not yield the correct insights into the lung's behavior during mechanical ventilation.