Static Crs calculation uses tidal volume divided by which pressure difference?

Static Crs calculation uses tidal volume divided by which pressure difference?

• A. Pplat - PEEP
• B. Pplat + PEEP
• C. PEEP - Pplat
• D. Palv - Ppl

Answer: (A)

Static compliance reflects how easily the respiratory system can be stretched when there’s no air flow. To measure it, you perform an inspiratory hold so airway resistance doesn’t affect the reading; the pressure then present is plateau pressure, which mostly represents the elastic recoil of the lungs and chest wall. The pressure actually used to distend the alveoli during that hold is the difference between plateau pressure and the PEEP, because PEEP adds a baseline pressure that the system must overcome to further inflate. Thus, static compliance equals tidal volume divided by (plateau pressure minus PEEP). Using any other combination would mix in resistive pressure or PEEP improperly, or even give a negative value, which isn’t meaningful for this measurement.

Static compliance reflects how easily the respiratory system can be stretched when there’s no air flow. To measure it, you perform an inspiratory hold so airway resistance doesn’t affect the reading; the pressure then present is plateau pressure, which mostly represents the elastic recoil of the lungs and chest wall. The pressure actually used to distend the alveoli during that hold is the difference between plateau pressure and the PEEP, because PEEP adds a baseline pressure that the system must overcome to further inflate. Thus, static compliance equals tidal volume divided by (plateau pressure minus PEEP). Using any other combination would mix in resistive pressure or PEEP improperly, or even give a negative value, which isn’t meaningful for this measurement.