The capnograph reading zero on both patient and tester is most likely caused by:

The capnograph reading zero on both patient and tester is most likely caused by:

• A. The power is off
• B. The patient is a mouth-breather
• C. The cannula is faulty
• D. The patient's secretions have reached the infrared portion of the tubing

Answer: (D)

Capnography detects CO2 by sending infrared light through the sampled gas. If secretions have reached the infrared portion of the tubing, they can block or absorb the IR beam, preventing CO2 from reaching the sensor. The result is no CO2 signal and a flat zero trace, which matches a reading of zero on both the patient side and the monitor. This scenario points to an obstruction in the sampling path rather than a true absence of CO2 in exhaled air. If the issue were a power problem, you’d expect no display or an error rather than a clean zero trace; a mouth-breather or a faulty cannula could reduce the signal but would not typically produce a perfect zero unless the sampling path were blocked.

Capnography detects CO2 by sending infrared light through the sampled gas. If secretions have reached the infrared portion of the tubing, they can block or absorb the IR beam, preventing CO2 from reaching the sensor. The result is no CO2 signal and a flat zero trace, which matches a reading of zero on both the patient side and the monitor. This scenario points to an obstruction in the sampling path rather than a true absence of CO2 in exhaled air. If the issue were a power problem, you’d expect no display or an error rather than a clean zero trace; a mouth-breather or a faulty cannula could reduce the signal but would not typically produce a perfect zero unless the sampling path were blocked.