A patient is receiving pressure support ventilation at 10 cm H2O. If the therapist places the patient in a lateral decubitus position, where in the lungs can the therapist expect this patient ventilation to preferentially be distributed?

A. to the lung bases
B. to the apical region of the lung
C. to the dependent region of the lung
D. to the nondependent portion of the lung

?ANS: C
A. Incorrect response: See explanation C.
B. Incorrect response: See explanation C.
C. Correct response: For spontaneously breathing persons, regardless of body position, ventilation is preferentially distributed to the dependent lung for the following two reasons: (1) Regional lung inflation and alveolar ventilation are greater on the nondependent portions of the lung. These alveoli are already distended, placing them on the flat portion of the compliance. The flat portion of the compliance demonstrates small volume changes for any corresponding pressure change. In other words, the nondependent alveoli are less compliant than those in the dependent lung regions. (2) Research has demonstrated that the greater displacement of the dependent hemidiaphragm shifted ventilation to the dependent lung.
D. Incorrect response: See explanation C.