The diagram shown below represents the same lung unit (alveoli) under three different conditions. Which of the three conditions characterizes the optimum level of PEEP?

Question

A. A
B. B
C. C
D. The optimum PEEP level cannot be determined.

Answer 1

ANS: B

?
A. Incorrect response: Curve A represents the lung unit (alveoli) with no PEEP and 1L of volume. Note that at end-expiration this unit is gasless and that 8 cm H2O of positive pressure is required to open this lung unit. Note also that the end-inspiratory pressure is 45 cm H2O.
B. Correct response: Curve B refers to the lung unit (alveoli) exposed to 10 cm H2O PEEP. This lung unit is no longer gasless at end-expiration, and its ventilation–perfusion ratio has improved. Its end-inspiratory pressure following inflation of 1L of air is reduced to 40 cm H2O (reflecting improved pulmonary compliance).
C. Incorrect response: Curve C depicts the lung unit (alveoli) with 15 cm H2O PEEP. This PEEP level is higher than that needed to maintain recruitment, and when coupled with 1 L of inflation, the lung unit contains excessive inspiratory pressure and volume, exposing this lung unit to barotrauma or volutrauma.
D. Incorrect response: The optimum PEEP level can be ascertained from the figure presented.?