All of the following will cause the pop-off alarm on a bubble humidifier to sound EXCEPT:

• A. Kinked connecting tubing
• B. Leak in the water reservoir
• C. Clogged nasal cannula
• D. Flowmeter set too high

Answer: (B)

The main idea is that the pop-off alarm sounds when there is excess pressure in the bubble humidifier circuit, triggering the safety relief valve to prevent the patient from experiencing high airway pressures. Anything that raises circuit pressure tends to make the pop-off operate.

Kinked connecting tubing increases resistance in the path of flow, boosting upstream pressure and causing the bubble chamber to vent more often, which sets off the alarm. A clogged nasal cannula also adds resistance, raising the pressure the patient receives and triggering the pop-off. If the flowmeter is set too high, more gas is pushed into the circuit, increasing flow-related pressure and again activating the pop-off.

A leak in the water reservoir, on the other hand, reduces the available water for bubbling and tends to lower or fail to raise circuit pressure, so it does not provoke the pop-off valve to vent. That’s why it’s the exception.