While monitoring a mechanically ventilated patient, the therapist performs an expiratory hold maneuver to ascertain the presence of auto-PEEP. During that maneuver, the therapist notes that the pressure indicates 0 cm H2O. How should the therapist interpret this finding? I. The patient has no auto-PEEP. II. Airway pressure at this time equals alveolar pressure. III. The patient's static

compliance has increased. IV. The patient's lungs have not completely emptied.

A. I only
B. IV only
C. I, II only
D. II, III only

?ANS: C
A. Incorrect response: See explanation C.
B. Incorrect response: See explanation C.
C. Correct response: During an expiratory hold maneuver, the flow during the expiratory phase is held at zero. When no gas flows at this time, alveolar pressure equilibrates with airway pressure. Therefore, if the reading during an expiratory hold is 0 cm H2O, the conclusion is that auto-PEEP is absent. Similarly, if this pressure measurement indicates some level of positive pressure, then auto-PEEP is present, assuming that the measured pressure exceeds any applied PEEP. In other words, if applied PEEP is 5 cm H2O, and the measured pressure during an expiratory hold is 10 cm H2O, 5 cm H2O of auto-PEEP is present.
D. Incorrect response: See explanation C.