Normal Crs on a ventilator is ...

Normal Crs on a ventilator is ...

• A. 10-20
• B. 30-40
• C. 50-100
• D. 120-150

Answer: (C)

Respiratory system compliance (Crs) reflects how easily the lungs and chest wall expand when ventilated. It is calculated as the tidal volume divided by the transpulmonary driving pressure, typically Crs = Vt / (Pplat − PEEP). Normal Crs falls roughly in the 50 to 100 mL per cm H2O range, indicating normal distensibility of the respiratory system. If Crs drops below this, the system is stiffer—lung pathology like edema, fibrosis, ARDS, or chest wall restrictions raise the pressure needed to achieve the same volume. If Crs is higher than normal, the system is more compliant, which can occur with loss of elastic recoil such as emphysema. For example, with a tidal volume of 500 mL, a plateau pressure of 15 cmH2O and PEEP of 5, Crs = 500/(15−5) = 50 mL/cmH2O, which is within the normal range.

Respiratory system compliance (Crs) reflects how easily the lungs and chest wall expand when ventilated. It is calculated as the tidal volume divided by the transpulmonary driving pressure, typically Crs = Vt / (Pplat − PEEP). Normal Crs falls roughly in the 50 to 100 mL per cm H2O range, indicating normal distensibility of the respiratory system. If Crs drops below this, the system is stiffer—lung pathology like edema, fibrosis, ARDS, or chest wall restrictions raise the pressure needed to achieve the same volume. If Crs is higher than normal, the system is more compliant, which can occur with loss of elastic recoil such as emphysema. For example, with a tidal volume of 500 mL, a plateau pressure of 15 cmH2O and PEEP of 5, Crs = 500/(15−5) = 50 mL/cmH2O, which is within the normal range.