The therapist enters the ICU, and hears the high-pressure alarm sounding on a mechanical ventilator. Which of the following considerations need to be taken into account as possible causes of this alarm situation? I. Auto-PEEP may have developed. II. The cuff on the patient's endotracheal tube has deflated. III. The patient may be experiencing increased lung secretions. IV. The flow waveform has

converted from a square configuration to that of a descending ramp.

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

?ANS: A?I. Correct response: Auto-PEEP is the inadvertent retention of air in the lungs at the end of exhalation. Dynamic hyperinflation (air trapping develops because of incomplete emptying of the lungs. Patients (COPD and status asthmaticus) whose lungs are characterized by long time constants are susceptible to this problem. Other causes include:
• ? High minute ventilation (<10 to 20 L/min)
• ? Small ID endotracheal tube
• ? Bronchospasm
• ? Increased lung secretions
• ? Mucosal edema
• ? Short expiratory time
• ? Inverse ratio ventilation
II. Incorrect response: A deflated endotracheal tube cuff would not activate the low-pressure alarm. It would stimulate a low-pressure alarm, a low-volume alarm, low minute ventilation alarm, or an apnea alarm.
III. Correct response: Any condition that increases airway resistance and interferes with lung emptying can cause auto-PEEP.
IV. Incorrect response: Changing the flow waveform configuration from square (rectangular) to a descending ramp pattern does not influence lung emptying or cause auto-PEEP.