The capnograph is reading zero on the patient and on the tech who tests the cannula. The most likely cause of the equipment failure is:

The capnograph is reading zero on the patient and on the tech who tests the cannula. The most likely cause of the equipment failure is:

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

Answer: (C)

Capnography relies on infrared absorption by CO2 to detect exhaled gas. If something blocks the infrared path, such as secretions reaching the infrared portion of the tubing, the CO2 signal can’t reach the sensor and the reader will show zero for both measurements. That blockage directly explains a flat, zero trace even when you test the cannula. Other possibilities are less likely here: if the power were off, the monitor would typically be nonfunctional or show an error rather than simply reading zero. If the cannula were defective, you’d expect an abnormal or absent signal in one test, but not necessarily a clean zero on both patient and cannula testing. Mouth-breathing wouldn’t produce a true zero, since CO2 is still present in exhaled breath and would be detected if the sampling path is intact.

Capnography relies on infrared absorption by CO2 to detect exhaled gas. If something blocks the infrared path, such as secretions reaching the infrared portion of the tubing, the CO2 signal can’t reach the sensor and the reader will show zero for both measurements. That blockage directly explains a flat, zero trace even when you test the cannula.

Other possibilities are less likely here: if the power were off, the monitor would typically be nonfunctional or show an error rather than simply reading zero. If the cannula were defective, you’d expect an abnormal or absent signal in one test, but not necessarily a clean zero on both patient and cannula testing. Mouth-breathing wouldn’t produce a true zero, since CO2 is still present in exhaled breath and would be detected if the sampling path is intact.