Normal static Crs for a normal, passively ventilated adult is typically between which values?

Normal static Crs for a normal, passively ventilated adult is typically between which values?

• A. 10-20 mL/cm H2O
• B. 20-40 mL/cm H2O
• C. 50-100 mL/cm H2O
• D. 150-200 mL/cm H2O

Answer: (C)

Static compliance reflects how much the lung and chest wall can expand for a given distending pressure when there is no flow. It is calculated as Crs = Vt / (plateau pressure - PEEP). In a normal adult receiving passive ventilation, tidal volume is typically about 0.5 L, and plateau pressure is roughly 10–15 cm H2O with a PEEP around 5 cm H2O. That makes the driving pressure about 5–10 cm H2O. Dividing 0.5 L by 5–10 cm H2O gives roughly 0.05–0.1 L per cm H2O, i.e., 50–100 mL/cm H2O. So the normal static Crs for a healthy, passively ventilated adult sits in the 50–100 mL/cm H2O range. Values well below this (e.g., 10–40 mL/cm H2O) would indicate a stiffer system, such as chest wall or lung pathology reducing compliance. Values above this (e.g., 150–200 mL/cm H2O) would imply unusually high compliance, which is not typical for a normal adult.

Static compliance reflects how much the lung and chest wall can expand for a given distending pressure when there is no flow. It is calculated as Crs = Vt / (plateau pressure - PEEP). In a normal adult receiving passive ventilation, tidal volume is typically about 0.5 L, and plateau pressure is roughly 10–15 cm H2O with a PEEP around 5 cm H2O. That makes the driving pressure about 5–10 cm H2O. Dividing 0.5 L by 5–10 cm H2O gives roughly 0.05–0.1 L per cm H2O, i.e., 50–100 mL/cm H2O. So the normal static Crs for a healthy, passively ventilated adult sits in the 50–100 mL/cm H2O range.

Values well below this (e.g., 10–40 mL/cm H2O) would indicate a stiffer system, such as chest wall or lung pathology reducing compliance. Values above this (e.g., 150–200 mL/cm H2O) would imply unusually high compliance, which is not typical for a normal adult.