Which of the following explains the monitor reading seen here?

More than one of the above

The capnograph portion of the monitor shows that this patients CO2 is above 0 mmHg even after expiration. The easiest way this can happen is when the CO2 absorbent is exhausted because exhaled CO2 will be able to return to the inspiratory limb of the breathing circuit. This can be corrected by replacing the soda lime or increasing the gas flow. CO2 is also elevated when there is an incompetent expiratory valve. The expiratory valve is supposed to prevent expired air from passing back to the patient, so if it is broken, the patients own previously exhaled CO2 will cause the reading seen on the monitor here. Miller RD, Pardo MC, Basics of Anesthesia: pg 210. 6th edition, Elsevier, Philadelphia, 2011.