The therapist notices that the tidal volume of a mechanically ventilated patient is greater during inspiration than during exhalation. Which of the following conditions is likely the cause of this situation? I. The patient has a bronchopleural fistula. II. The patient has developed retained secretions. III. The ventilator's in-line nebulizer has been turned on. IV. The ventilator's humidifier has

been overfilled with sterile water.

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

?ANS: A
A. Correct response: A bronchopleural fistula is a communication between the pleural space and the tracheobronchial tree. This condition can cause the disparity between the inspired and expired tidal volume to be of the magnitude of 100 ml or more, depending on the size of the fistula.
B. Incorrect response: Retained secretion will cause increased airway resistance. During VC ventilation, the tidal volume will be constant, and the PIP will increase. During PC ventilation, the tidal volume will vary and the PIP will remain constant.
C. Incorrect response: If the ventilator's in-line nebulizer is operating, a separate gas source often drives the device. That additional gas combines with the delivered tidal volume and causes the tidal volume to increase.
D. Incorrect response: Overfilling the humidifier of a mechanical ventilator will not cause a disparity between the delivered tidal volume and the exhaled tidal volume.