CBET Ventilators and Respiratory Therapy Equipment

Question 1

A ventilator is set to Volume-Controlled Ventilation (VCV) at 500 mL tidal volume. The high peak pressure alarm activates with every breath. Plateau pressure measured during an inspiratory hold is normal. What is the most likely cause?

Accepted Answer

Increased airway resistance (e.g., bronchospasm or secretions)

Answer

In VCV, peak pressure reflects both airway resistance and lung compliance, while plateau pressure (measured during no-flow inspiratory hold) reflects compliance only. A high peak pressure with a NORMAL plateau pressure indicates increased airway resistance — the lungs can accept the volume, but the airway is obstructed. If compliance were decreased, both peak AND plateau would be elevated.

Question 2

What is the primary physiological purpose of Positive End-Expiratory Pressure (PEEP) in a mechanically ventilated patient?

Accepted Answer

To prevent alveolar collapse (atelectasis) at end-expiration and improve oxygenation

Answer

PEEP maintains positive airway pressure throughout the expiratory phase, keeping alveoli open and preventing end-expiratory collapse. This recruits more alveolar surface area for gas exchange, improving oxygenation (PaO₂). It does not change minute ventilation directly, reduce peak pressure, or affect FiO₂ delivery.

Question 3

During annual PM on a mechanical ventilator, which test is MOST critical for patient safety regarding oxygen delivery?

Accepted Answer

Calibration and accuracy check of the oxygen sensor/analyzer

Answer

The oxygen sensor (typically a galvanic fuel cell) degrades over time and can drift, causing the ventilator to deliver incorrect FiO₂. Delivering too little O₂ causes hypoxia; too much causes oxygen toxicity. Calibrating and verifying oxygen sensor accuracy is a mandatory safety check. While exhalation valve and humidifier checks are important, an FiO₂ error can be immediately life-threatening.

Question 4

In Pressure-Controlled Ventilation (PCV), what variable is directly set by the clinician and remains constant despite changes in the patient's lung mechanics?

Accepted Answer

Inspiratory pressure above PEEP

Answer

In PCV, the ventilator delivers gas until the set inspiratory pressure is reached and then maintains that pressure for the set inspiratory time. The pressure is constant regardless of lung compliance or resistance. Tidal volume, however, will vary — if lungs become stiffer, less volume is delivered at the same pressure. This is the fundamental difference from VCV.

Question 5

A ventilator's continuous high-pressure alarm is sounding. The patient is stable on manual (bag) ventilation. After checking for obvious circuit kinks and confirming the ETT is not kinked, what should the BMET check next on the ventilator itself?

Accepted Answer

The exhalation valve for sticking or obstruction

Answer

If the exhalation valve sticks closed or becomes obstructed, exhaled gas cannot escape and pressure builds continuously in the circuit during exhalation, triggering the high-pressure alarm persistently. The inspiratory filter causing high pressure would be more intermittent (only during inspiration), and flow trigger/PEEP settings affect baseline parameters rather than causing sustained pressure spikes.

CBET - Certified Biomedical Equipment Technician Practice Test

CBET - Certified Biomedical Equipment Technician Practice Test

CBET Ventilators and Respiratory Therapy Equipment