Critical Care Medicine-Neurologic Disorders>>>>>Mechanical Ventilation
Question 3#

A 68-year-old man with community-acquired pneumonia is intubated in the ICU with respiratory failure. Following induction of anesthesia, while paralyzed, his ventilator is set on:

• volume assistcontrol
• TV 450 mL
• respiratory rate 14 breaths per minute
• FiO₂ 0.8
• PEEP 5 cm H₂O

An inspiratory hold maneuver is performed and his peak inspiratory pressure is 25 cm H₂O and plateau pressure is 15 cm H₂O.

Which of the following is true regarding this patient’s respiratory mechanics?

A. The patient’s lung compliance is 45 mL/cm H₂O
B. The patient’s chest wall compliance is 30 mL/cm H₂O
C. The patient’s lung compliance is 10 mL/cm H₂O
D. The patient’s respiratory system compliance is 45 mL/cm H₂O

Correct Answer is D

Comment:

Correct Answer: D

The respiratory system compliance is equal to the change in volume divided by the change in pressure. In this case, the change in volume is the TV (450 mL) and the change in pressure is the plateau pressure minus the PEEP (15 cm H₂O − 5 cm H₂O = 10 cm H₂O) (answer D is correct). Without a measure of a pleural pressure, it is not possible to separately calculate lung and chest wall compliance (answers A, B and C are incorrect).